JP7141019B2 - Ink set and inkjet recording method - Google Patents

Description

The present invention relates to an ink set and an inkjet recording method.

The inkjet recording method is a method of recording by ejecting droplets of ink from fine nozzles and depositing them on a recording medium. This method is characterized in that high-resolution, high-quality images can be recorded at high speed with a relatively inexpensive device.

2. Description of the Related Art In recent years, direct recording (printing) of a product label or the like on a flexible packaging film such as a PET film by an inkjet recording method has been studied. In addition, flexible packaging films are used for packaging foods and the like, and in such uses, a high level of safety is required, so it is desirable to use a water-based ink for the above-mentioned printing. When water-based ink is used, a heat drying process may be further performed after printing.

Moreover, since the recording surface of the flexible packaging film is made of plastic material such as polyolefin, nylon, polyester, etc., it is often transparent or translucent. Therefore, when performing inkjet recording, a predetermined image is sometimes formed with color inks on a layer formed with white ink called a base layer that hides the background (see, for example, Patent Document 1). When white ink and color ink are used, the white ink may contain more white pigment and the color ink may contain less pigment than white.

JP 2012-193280 A

When recording is performed on a heated recording medium using an ink with a high solids content and an ink with a low solids content, a problem of image misalignment occurs.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems. It is an object of the present invention to provide an ink set and a recording method capable of suppressing misalignment.

The present inventors have made intensive studies to solve the above problems. As a result, the content of the organic solvent in the ink composition with a lower solid content (second ink composition) was reduced to that of the ink composition with a higher solid content (first ink composition). It was found that misregistration of images caused by the two ink compositions can be suppressed by using a composition having a higher organic solvent content.

One aspect of the present invention is as follows.
[1]
comprising a first ink composition and a second ink composition;
The first ink composition and the second ink composition are water-based inkjet ink compositions containing a solid content containing a coloring material and an organic solvent,
The solid content of the first ink composition is greater than that of the second ink composition by 5% by mass or more,
the organic solvent content of the second ink composition is greater than that of the first ink composition by 7% by mass or more;
An ink set for use in an inkjet recording method in which ink is applied to a heated recording medium.
[2]
used for recording together with a treatment liquid containing an aggregating agent for aggregating components of the water-based inkjet ink composition,
The first ink composition has a solid content higher than that of the treatment liquid by 5% by mass or more,
The treatment liquid has an organic solvent content higher than that of the first ink composition by 7% by mass or more.
The ink set described in [1].
[3]
The difference in water content between the first ink composition and the second ink composition is within 8% by mass.
The ink set according to [1] or [2].
[4]
The difference in viscosity at 20° C. between the first ink composition and the second ink composition is within 1.5 mPa·s.
The ink set according to any one of [1] to [3].
[5]
Each of the first ink composition and the second ink composition has a water content of 50% by mass or more,
The ink set according to any one of [1] to [4].
[6]
The first ink composition has a solid content higher than that of the second ink composition by 5 to 13% by mass, and the second ink composition has an organic solvent content of 7 higher than that of the first ink composition. ~17 mass% more,
The ink set according to any one of [1] to [5].
[7]
The first ink composition contains 10 to 22% by mass of solids and 15 to 27% by mass of organic solvent, and the second ink composition contains 5 to 12% by mass of solids and 23 to 38% by mass of organic solvent. %contains,
The ink set according to any one of [1] to [6].
[8]
The first ink composition is a white ink composition containing a white colorant as a solid content, and the second ink composition is a non-white ink composition containing a non-white colorant as a solid content,
The ink set according to any one of [1] to [7].
[9]
The organic solvent content of the second ink composition is greater than that of the first ink composition by 9% by mass or more,
The ink set according to any one of [1] to [8].
[10]
It is carried out using the ink set according to any one of [1] to [9],
An inkjet recording method, comprising an ink applying step of applying the first ink composition and the second ink composition to a heated recording medium.
[11]
The surface temperature of the recording medium when attached is 30 to 50 ° C.
[10] The ink jet recording method described.
[12]
A step of applying a treatment liquid containing an aggregating agent for aggregating components of the water-based inkjet ink composition to the recording medium;
The inkjet recording method according to [10] or [11].
[13]
The ink application step is performed by performing a plurality of main scans in which the ink composition is ejected while changing the relative position between the inkjet head provided with the ink set and the recording medium in the main scan direction, and one main scan is performed. a maximum time of 0.8 seconds or more;
[10] The inkjet recording method according to any one of [12].

1 is a schematic diagram of an inkjet apparatus used in the inkjet recording method of the present embodiment; FIG. 1 is a block diagram of an inkjet device used in the inkjet recording method of the present embodiment; FIG. FIG. 2 is a schematic diagram around a carriage of an inkjet device used in the inkjet recording method of the present embodiment; FIG. 2 is a diagram showing an example of arrangement of heads (inkjet heads) mounted on a carriage of an inkjet device used in the inkjet recording method of the present embodiment;

Hereinafter, embodiments of the present invention (hereinafter referred to as "present embodiments") will be described in detail with reference to the drawings as necessary, but the present invention is not limited thereto and the gist thereof. Various modifications are possible without departing from the above. In the drawings, the same elements are denoted by the same reference numerals, and overlapping descriptions are omitted. In addition, unless otherwise specified, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of the drawings are not limited to the illustrated ratios.

[Ink set]
The ink set according to this embodiment comprises a first ink composition and a second ink composition. Each of the first ink composition and the second ink composition is a water-based inkjet ink composition containing a solid content containing a coloring material and an organic solvent. The solid content of the first ink composition is greater than that of the second ink composition by 5% by mass or more. The organic solvent content of the second ink composition is greater than that of the first ink composition by 7% by mass or more. It is used in an ink jet recording method in which ink is adhered to a heated recording medium.

A water-based composition is a composition containing water as one of the main solvent components of the composition, and the content of water in the composition is preferably 40% by mass or more. An inkjet ink composition is an ink composition used in a recording method by an inkjet method. The components and characteristics of the first ink composition and the second ink composition can be independently described below. Components contained in each ink according to the present embodiment will be described in detail below. In the following description, when there is no need to distinguish between the first ink composition and the second ink composition, they are simply referred to as ink compositions. When simply referring to the first ink composition (also referred to as the first ink) or the second ink composition (also referred to as the second ink), these inks are meant to be distinguished from each other. It is not meant to limit the components, characteristics, and the like.

The first ink composition and the second ink composition contain a solid content containing a coloring material and an organic solvent. Preferably, the first ink composition is a white ink composition containing a white colorant as a solid content, and the second ink composition is a non-white ink composition containing a non-white colorant as a solid content. A non-white colorant refers to a colorant other than a white colorant.
The first ink composition and the second ink composition may be other than the first ink composition being a white ink composition and the second ink composition being a non-white ink composition. For example, the first ink may be a colored ink capable of recording a certain color, and the second ink may be a colored ink capable of recording a certain color. Also in this case, it is possible to suppress misalignment between the image printed with the first ink and the image printed with the second ink. Preferably, the first ink is a colored ink capable of recording a certain color, and the second ink is a colored ink capable of recording another certain color.
Also in these cases, the first ink composition has a solid content of 5% by mass or more than the second ink composition, and the second ink composition has a higher organic solvent content than the first ink composition. By increasing the amount by 7% by mass or more, the first ink and the second ink can be different in solid content and organic solvent content, and the first ink and the second ink can be used according to their respective functions. can be of different compositions. Further, in such a first ink and a second ink, it is possible to suppress positional deviation between an image recorded with the first ink and an image recorded with the second ink. A colored ink composition is an ink composition used for coloring a recording medium.
Among them, it is preferable that the first ink composition is a white ink composition and the second ink composition is a non-white ink composition. In this case, it is possible to use a white ink having excellent whiteness as the first ink, and it is possible to suppress the positional deviation of an image when a white image and a non-white image are superimposed and recorded.

A white ink composition is an ink (ink) capable of recording a color commonly referred to as "white", and includes a slightly colored ink. Moreover, ink (ink) includes ink (ink) that is called and sold under names such as “white (color) ink (ink), white ink (ink)”. Furthermore, for example, when ink (ink) is recorded in an amount sufficient to cover the surface of a recording medium made of a transparent film, the lightness (L*) and chromaticity (a*, b*) is in the range of 60 ≤ L* ≤ 100, -4.5 ≤ a* ≤ 2, -10 ≤ b* ≤ 2.5 when measured using a CIELAB-compliant spectrophotometer Ink (ink) shown. Examples of transparent film recording media include LAG Jet E-1000ZC (manufactured by Lintec). As a spectrophotometer, for example, a spectrophotometer Spectrolino (trade name, manufactured by GretagMacbeth) can be mentioned, and the measurement conditions are a D50 light source, an observation field of view of 2°, a concentration of DIN NB, a white standard of Abs, a filter of No, and a measurement mode. is set as Reflectance.

A non-white ink composition is a colored ink that is not a white ink composition, and is an ink (ink) that can record a color that is not “white” in general terms. The non-white ink composition preferably contains a non-white colorant.
Specific materials of the coloring material are described below.

(colorant)
Pigments or dyes can be used as colorants, but pigments are preferably used. Examples of pigments include, but are not limited to, the following.

(white colorant)
White dyes and white pigments (white pigments) can be used as the white colorant, and the latter is preferred. Examples of white pigments include, but are not limited to, C.I. I. Pigment White 6, 18, 21, titanium oxide, zinc oxide, zinc sulfide, antimony oxide, magnesium oxide, and zirconium oxide. Metal compound pigments are preferred, and metal oxide pigments are more preferred. Besides the white inorganic pigment, white organic pigments such as white hollow resin particles and polymer particles can also be used.

(non-white colorant)
Examples of the non-white colorant include those other than the above white colorant. Non-white dyes and non-white pigments are mentioned, and the latter is preferred. There are various colors listed below, but the present invention is not limited to these. A chromatic coloring material can be mentioned.

Examples of black pigments include, but are not limited to, No. 2300, No. 900, MCF88, no. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100, No. 2200B, etc. (manufactured by Mitsubishi Chemical Corporation), Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700, etc. (manufactured by Carbon Columbia, R1), 400Rega Regal 330R, Regal 660R, Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc. (manufactured by Cabot Corporation (CABOT JAPAN), Wcolcol K.K.) 、Ｃｏｌｏｒ Ｂｌａｃｋ ＦＷ２、Ｃｏｌｏｒ Ｂｌａｃｋ ＦＷ２Ｖ、Ｃｏｌｏｒ Ｂｌａｃｋ ＦＷ１８、Ｃｏｌｏｒ Ｂｌａｃｋ ＦＷ２００、Ｃｏｌｏｒ Ｂ１ａｃｋ Ｓ１５０、Ｃｏｌｏｒ Ｂｌａｃｋ Ｓ１６０、Ｃｏｌｏｒ Ｂｌａｃｋ Ｓ１７０、Ｐｒｉｎｔｅｘ ３５、Ｐｒｉｎｔｅｘ Ｕ、Ｐｒｉｎｔｅｘ Ｖ、Ｐｒｉｎｔｅｘ １４０Ｕ、Ｓｐｅｃｉａｌ Ｂｌａｃｋ ６、Ｓｐｅｃｉａｌ Ｂｌａｃｋ ５、Ｓｐｅｃｉａｌ Black 4A, Special Black 4 (manufactured by Degussa).

Pigments used in the yellow ink are not particularly limited, but examples include C.I. I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 167, 172, 180.

Examples of magenta pigments include, but are not limited to, C.I. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 40, 41, 42, 48(Ca), 48(Mn), 57(Ca), 57:1, 88, 112, 114, 122, 123, 144, 146, 149, 150, 166, 168 , 170, 171, 175, 176, 177, 178, 179, 184, 185, 187, 202, 209, 219, 224, 245, or C.I. I. Pigment Violet 19, 23, 32, 33, 36, 38, 43, 50.

Examples of cyan pigments include, but are not limited to, C.I. I. Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, 66, C.I. I. bat blue 4,60.

Pigments used in color inks other than magenta, cyan, and yellow are not particularly limited, but include, for example, C.I. I. Pigment Green 7, 10, C.I. I. Pigment Brown 3, 5, 25, 26, C.I. I. Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 63.

Examples of pearl pigments include, but are not particularly limited to, pigments having pearl luster or interference luster such as titanium dioxide-coated mica, fish scale foil, and bismuth oxide.

Examples of metallic pigments include, but are not limited to, particles made of a single substance or an alloy of aluminum, silver, gold, platinum, nickel, chromium, tin, zinc, indium, titanium, copper, and the like.

The pigment content is preferably 0.1 to 20% by mass, more preferably 0.3 to 15% by mass, and even more preferably 0.4 to 12% by mass, based on 100% by mass of the ink composition. % by mass, more preferably 1 to 8% by mass, and even more preferably 2 to 5% by mass.
The content of the coloring material in the first ink is preferably 2 to 20% by mass, more preferably 4 to 15% by mass, still more preferably 7 to 13% by mass. The content of the coloring material in the second ink is preferably 0.1 to 7 mass %, more preferably 0.5 to 6 mass %, still more preferably 1 to 5 mass %. The content of the colorant in the first ink is preferably higher than that in the second ink, more preferably 2 to 15% by mass, and even more preferably 3 to 12% by mass.

(resin)
The first ink composition and the second ink composition may contain a resin as a solid content. Thereby, the fixability and abrasion resistance of the image can be improved. More preferably, it may contain resin particles. Resin particles can be used in the form of a resin emulsion or the like.

Although the type of resin is not particularly limited, for example, (meth)acrylic acid, (meth)acrylic acid ester, acrylonitrile, cyanoacrylate, acrylamide (the above are acrylic monomers), olefin, styrene, vinyl acetate, and vinyl chloride. , vinyl alcohol, vinyl ether, vinylpyrrolidone, vinylpyridine, vinylcarbazole, vinylimidazole, homopolymers or copolymers of vinylidene chloride, fluororesins, natural resins, urethane resins, polyester resins, and the like.
An acrylic resin is one in which at least an acrylic monomer is used as a component constituting the resin (a monomer component used for polymerizing the resin). The acrylic resin may be a copolymer of an acrylic monomer and a monomer other than the acrylic monomer. It is a homopolymer or copolymer using at least an acrylic monomer. Among these, vinyl-acrylic copolymers using acrylic monomers and vinyl-based monomers are preferable, and among vinyl-based monomers, styrene-acrylic copolymers using styrene are more preferable, and styrene and (meth)acrylic acid A copolymer resin using at least is more preferable.
Among the resins, acrylic resins, urethane resins and polyester resins are preferred, and acrylic resins are more preferred.
The above copolymer may be in any form of random copolymer, block copolymer, alternating copolymer and graft copolymer.

Although the above resin is not particularly limited, it can be obtained, for example, by the preparation methods shown below, and multiple methods may be combined as necessary. As the preparation method, a method of mixing a polymerization catalyst (polymerization initiator) and a dispersant in the monomer of the component constituting the desired resin and polymerizing (emulsion polymerization), a method in which a solution obtained by dissolving a resin in a water-soluble organic solvent is mixed with water and then the water-soluble organic solvent is removed by distillation or the like; A method of mixing can be mentioned.

The resin content is preferably 1% by mass or more and 15% by mass or less, more preferably 2% by mass or more and 10% by mass or less, and even more preferably 3% by mass or more and 7% by mass or less. By setting the content of the resin within the above range, it is possible to stably dissolve the resin while improving the abrasion resistance, thereby improving the ejection stability.

(wax)
The first ink composition and the second ink composition may contain wax as a solid content. When the recording head is heated, resin particles aggregate and adhere as water evaporates, which may cause clogging of the nozzles of the recording head and hinder stable ejection. On the other hand, when wax is used in combination, aggregation of polymer particles during water evaporation is suppressed. As a result, ejection failure and clogging due to sticking of the resin particles to the nozzles of the recording head can be suppressed, and an ink composition having excellent recording stability can be obtained. Also, during high-temperature recording, the wax prevents the film formed by the resin particles from becoming too brittle. Therefore, even if high-temperature recording is performed, the ink composition is less likely to deteriorate in abrasion resistance.

The wax has a melting point of 70° C. or higher and lower than 110° C., more preferably 80° C. or higher and 110° C. or lower. When the melting point is within the above range, it is possible to obtain a recorded matter which is excellent in recording stability and whose abrasion resistance is less likely to deteriorate even during high-temperature recording. The melting point can be measured with a differential scanning calorimeter (DSC). Further, the melting point of wax can be controlled, for example, by adjusting the ratio of a plurality of structural units that constitute the wax.

The wax preferably contains polyethylene wax. The polyethylene wax having a melting point of 70° C. or more and less than 110° C. is not particularly limited. (manufactured by Mitsui Chemicals, Inc.) Chemipearl W4005 (manufactured by Mitsui Chemicals, Inc.). The polyethylene wax having a melting point of 70° C. or more and less than 110° C. may be synthesized by a conventional method.

Waxes may be used singly or in combination of two or more.

The amount of wax added to the ink composition is preferably 0.1 to 5.0% by mass, more preferably 0.3 to 3.5% by mass, based on the total mass of the ink composition. 0 to 2.0% by weight is even more preferred. When the amount added is within the above range, the recording stability is excellent and the abrasion resistance is less likely to deteriorate even during high-temperature recording.

(Organic solvent)
The first ink composition and the second ink composition contain an organic solvent, preferably an organic solvent having a normal boiling point of 180 to 250°C. As a result, volatilization of the organic solvent contained in the ink composition in the head can be prevented, and clogging of the nozzles can be prevented. In addition, when mixed with the ink composition on the recording medium, the organic solvent can be rapidly volatilized, and sufficient image quality can be obtained on the recording medium.

A nitrogen-containing solvent may be included as the organic solvent. This makes it possible to stably dissolve the resin in the ink composition. In addition, the nitrogen-containing solvent has the effect of promoting the softening of the resin particles contained in the ink composition, and tends to improve adhesion even when the heating temperature is low.

Nitrogen-containing solvents include, but are not particularly limited to, pyrrolidone-based, imidazolidinone-based, amide ether-based, pyridine-based, pyrazine-based, and pyridone-based solvents. Pyrrolidones are preferred, such as 2-pyrrolidone, N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone. A nitrogen-containing solvent may be used individually by 1 type, and may use 2 or more types together. Among nitrogen-containing solvents, amide solvents are preferred. Examples of amide solvents include cyclic amides and non-cyclic amides. Examples of cyclic amides include pyrrolidones. Examples of non-cyclic amides include amide ether systems having non-cyclic structures.
Amide ethers include those also called alkoxyalkylamides, such as 3-methoxy-N,N-dimethylpropionamide, 3-methoxy-N,N-diethylpropionamide, 3-methoxy-N,N- methylethylpropionamide, 3-ethoxy-N,N-dimethylpropionamide, 3-ethoxy-N,N-diethylpropionamide, 3-ethoxy-N,N-methylethylpropionamide, 3-n-butoxy-N, N-dimethylpropionamide, 3-n-butoxy-N,N-diethylpropionamide, 3-n-butoxy-N,N-methylethylpropionamide, 3-n-propoxy-N,N-dimethylpropionamide, 3 -n-propoxy-N,N-diethylpropionamide, 3-n-propoxy-N,N-methylethylpropionamide, 3-iso-propoxy-N,N-dimethylpropionamide, 3-iso-propoxy-N, N-diethylpropionamide, 3-iso-propoxy-N,N-methylethylpropionamide, 3-tert-butoxy-N,N-dimethylpropionamide, 3-tert-butoxy-N,N-diethylpropionamide and the like can give.

The organic solvent may further contain an organic solvent other than the nitrogen-containing solvent. Such organic solvents preferably include polyol compounds, alkanediol compounds, and glycol ether compounds. Examples of the polyol compound include polyols of alkanes having 4 or less carbon atoms and intermolecular condensates of hydroxyl groups of polyols of alkanes having 4 or less carbon atoms. The number of carbon atoms is preferably 3 or less. The number of condensed molecules of the intermolecular condensate is preferably 2-4. The number of hydroxyl groups in the molecule of the polyol is 2 or more, preferably 2-4.
Examples of alkanediol compounds include diol compounds of alkanes having 5 or more carbon atoms. The number of carbon atoms is preferably 5 or more, preferably 10 or less, more preferably 7 or less.
Glycol ether compounds include those obtained by etherification of one or two hydroxyl groups of alkanediol, and ethers include alkyl ethers and aryl ethers, the former being preferred.
Examples of the above organic solvents or other organic solvents are not particularly limited, but specific examples include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 1,2 -butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl 1 , 3-hexanediol, diethylene glycol mono-n-propyl ether, ethylene glycol mono-iso-propyl ether, diethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono- n-butyl ether, triethylene glycol monobutyl ether, diethylene glycol mono-t-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-iso - propyl ether, propylene glycol mono-n-butyl ether, dipropylene glycol mono-n-butyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono-iso-propyl ether, methanol, ethanol, n-propyl alcohol, iso-propyl alcohol, n-butanol, 2-butanol, tert-butanol, iso-butanol, n-pentanol, 2-pentanol, 3-pentanol, and tert-pentanol, 2-methyl-1,3- Alcohols such as propanediol or glycols may be mentioned. Other solvents may be used singly or in combination of two or more.

The content of the organic solvent is preferably 3.0% by mass or more, more preferably 5.0% by mass or more and 37% by mass or less, and still more preferably 10% by mass or more, relative to the total amount of the ink composition. It is 35% by mass or less, more preferably 15% by mass or more and 30% by mass or less. As a result, the organic solvent can be rapidly volatilized on the recording medium, and sufficient image quality can be obtained on the recording medium.
Among the organic solvents, the content of the nitrogen-containing solvent is preferably 3% by mass or more, more preferably 5.0% by mass or more and 27% by mass or less, and still more preferably 10% by mass, relative to the total amount of the ink composition. % by mass or more and 25% by mass or less, more preferably 15% by mass or more and 20% by mass or less. This is preferable in terms of more excellent abrasion resistance and the like.

The content of the organic solvent of the polyol compound having a normal boiling point of more than 280° C. in the ink composition is preferably 2% by mass or less, more preferably 1% by mass or less, and 0.5% by mass, based on the total mass of the ink composition. The following are more preferable, 0.1% by mass or less is particularly preferable, and 0.05% by mass or less is even more preferable. The lower limit of the content is 0% by mass. When the content is within the above range, the abrasion resistance of recorded matter using the ink composition is suppressed from being lowered by an organic solvent having a normal boiling point of more than 280° C., and a recorded matter having more excellent abrasion resistance is produced. Obtainable.

Furthermore, in the first ink composition and the second ink composition, the content of an organic solvent (not limited to a polyol compound) with a normal boiling point exceeding 280° C. is preferably 5% by mass or less, and is within the above range. is more preferred. The organic solvent having a normal boiling point of over 280° C. is, for example, a polyol compound, but is not limited thereto. When the content of the organic solvent in the ink composition is within the above range, the drying property of the ink on the recording medium does not decrease significantly, and as a result, various recording media, particularly non-ink-absorbing or low-absorbing ink, can be used. In an absorptive recording medium, unevenness in image density can be reduced, and ink fixability is excellent.

(Surfactant)
The first ink composition and the second ink composition preferably contain a surfactant. Examples of surfactants include, but are not particularly limited to, acetylene glycol-based surfactants, fluorine-based surfactants, and silicone-based surfactants. Among these, acetylene glycol-based surfactants and silicone-based surfactants are preferred.

The content of the surfactant is preferably 0.1 to 2.0% by mass, more preferably 0.1 to 1.7% by mass, and even more preferably It is 0.1 to 1.5% by mass. When the surfactant content is 2.0% by mass or less, the abrasion resistance tends to be further improved. In addition, when the content of the surfactant is 0.1% by mass or more, there is a tendency that the embedding property of the obtained recorded matter is further improved and the ejection stability is further improved.

(water)
The first ink composition and the second ink composition contain water. Examples of water include pure water such as ion-exchanged water, ultrafiltrated water, reverse osmosis water, and distilled water, and water from which ionic impurities are removed as much as possible, such as ultrapure water. In addition, the use of water that has been sterilized by ultraviolet irradiation or the addition of hydrogen peroxide can prevent the formation of mold and bacteria during long-term storage of the pigment dispersion and the ink using the same.

The content of water is not particularly limited, but in the present invention, the content of water is preferably higher than that of the organic solvent. Also, it is a so-called "water-based ink", which contains at least water as a main component as a solvent component contained in the ink. The water content is preferably 40 to 95% by mass, more preferably 45 to 90% by mass, still more preferably 50 to 80% by mass, based on 100% by mass of the water-based ink composition. It is preferably 52 to 66% by mass.

(other ingredients)
The ink used in the present embodiment contains a dissolution aid, a viscosity modifier, a pH Various additives such as modifiers, antioxidants, preservatives, anti-mold agents, corrosion inhibitors, and chelating agents to trap metal ions that affect dispersion may also be added as appropriate.

The components that can be contained in the first ink composition and the second ink composition have been described above. Components that can be contained in the first ink composition and the second ink composition are defined as follows in order to suppress misregistration of the image due to the second ink composition.

In the present embodiment, the solid content of the first ink composition is 5% by mass or more, preferably 5 to 20% by mass, more preferably 5 to 13% by mass, and further more than the second ink composition. Preferably 6 to 10 mass % more. On the other hand, an increase of 5 to 6.5% by mass is also preferable from the viewpoint of ease of ink design.
The solid content of the first ink is preferably 7 to 25% by mass, more preferably 10 to 22% by mass, still more preferably 10 to 20% by mass, relative to the total mass of the ink composition. Yes, more preferably 12 to 18% by mass, particularly preferably 14 to 18% by mass. Furthermore, 15 to 18% by mass is preferable.
The solid content of the second ink is preferably 1 to 15% by mass, more preferably 2 to 13% by mass, still more preferably 2 to 12% by mass, relative to the total mass of the ink composition. , more preferably 5 to 11% by mass, and particularly preferably 8 to 11% by mass. Furthermore, 9 to 11% by mass is preferable. The above range is preferable from the viewpoint of better abrasion resistance, clogging resistance, and the like.

The content of solids in the ink composition is the content of components that do not evaporate in the secondary drying process as a post-drying process. The solid content of this ink composition includes at least a coloring material, and may further include resin particles, wax, and the like.

The content of the organic solvent in the ink composition is the content of the organic solvent such as the nitrogen-containing solvent described above, but does not include the content of the surfactant.
In addition, the organic solvent content of the second ink composition is 7% by mass or more, preferably 7 to 20% by mass, more preferably 8 to 17% by mass, and still more preferably 9% by mass, more preferably than the first ink composition. ~14% by mass more. Also, it is particularly preferably 9% by mass or more, more preferably 10% by mass or more, even more preferably 12% by mass or more, and even more preferably 12 to 14% by mass.
The content of the organic solvent in the first ink is preferably 5 to 27% by mass, more preferably 5 to 26% by mass, even more preferably 12 to 25% by mass, still more preferably 10 to 24% by mass. %, particularly preferably 15 to 23% by mass.
The content of the organic solvent in the second ink is preferably 10 to 40% by mass, more preferably 20 to 38% by mass, even more preferably 23 to 35% by mass, and particularly preferably 25 to 33% by mass. and more preferably 28 to 33% by mass.

Thus, the content of the organic solvent in the second ink composition is made larger than the content of the organic solvent in the first ink composition, and the solid content of the first ink composition and the solid content of the second ink composition By balancing the amount of the organic solvent, it is possible to suppress the occurrence of misregistration between images, as shown in Examples described later. In particular, it is possible to suppress an increase in misalignment between the image of the first ink composition and the image of the second ink composition during the pass. With such a composition, it was found that the degree of positional deviation between the image of the first ink composition and the image of the second ink composition is the same even if the drying of the ink progresses in the nozzles during the pass.

Although it is a guess as a principle, it guesses as follows. It is presumed that the ink dries and thickens in the nozzles, changes the ejection speed and ejection timing, and shifts the ink landing position, resulting in image positional deviation. It is presumed that the difference in the total content of the solid content and the organic solvent in the ink between the first ink and the second ink causes the degree of deviation of the landing position when the ink dries in the nozzle to become close. Among the main components of the water-based composition, the solid content and the organic solvent have common characteristics such as higher viscosity than water, and it is assumed that the total content of these is close to each other. In addition, when the main components of the ink are the solid content, the organic solvent, and water, if the total content of the solid content and the organic solvent is balanced between the first ink and the second ink, the water content will be the second highest. The difference is relatively small between the first ink and the second ink. When the ink dries in the nozzle, water dries quickly, but organic solvents and solids do not dry or dry relatively slowly. Therefore, when the ink dries in the nozzles, the drying of the ink temporarily stops when the water is almost dry, and the thickening of the ink also temporarily stops. If the water content is similar between the first and second inks, the drying rate of the inks in this state will be similar. This is because it dries as much as the water content. It is presumed that once the drying stops in this state, the degree of thickening also approaches. However, the above is a guess and is not limited to this.

The difference in water content between the first ink composition and the second ink composition (large-low) is preferably within 8% by mass, more preferably within 5.5% by mass, and more preferably It is within 3% by mass. The lower limit of the difference in water content is 0% by mass or more. On the other hand, the difference is preferably 2% by mass or more, more preferably 5% by mass or more, from the viewpoint of ease of ink design.
Although not limited, it is preferable that the first ink has a higher water content than the second ink within the above range. By making the water content uniform in this manner, the degree of drying of the ink can be made uniform, and the degree of increase in viscosity due to drying can be made uniform, thereby suppressing misregistration of the image.

The difference in viscosity (large-small) at 20° C. between the first ink composition and the second ink composition is preferably within 2 mPa·s, more preferably within 1.5 mPa·s, and further It is preferably within 1 mPa·s, and particularly preferably within 0.5 mPa·s. A lower limit is 0 mPa*s or more. It is also preferable that the viscosity of the first ink composition is lower than the viscosity of the second ink composition within the range of the viscosity difference. As described above, since the initial viscosity difference between the first ink composition and the second ink composition is small, the viscosity difference tends to be small when the ink is dried and thickened. Even if the initial viscosities of the first ink composition and the second ink composition are not the same, the initial viscosity can be improved by changing the head driving waveform for each ink composition or by adjusting the image recording start position. It is possible to align the positions of the images. Therefore, it is not always necessary for the initial viscosity difference to be small, but as described above, the first ink composition has a solids content of 5% by mass or more than the second ink composition. Since the organic solvent content of the second ink composition is 7% by mass or more larger than that of the first ink composition, an increase in misregistration between images during passes can be suppressed. For example, it is possible to prevent the ink from drying and thickening in the nozzles during printing, thereby preventing the misregistration of the image from gradually increasing. The viscosity of the ink can be measured using a rotary viscometer. For example, an MCR rheometer (manufactured by Anton Paar) can be used. It can be measured by keeping the temperature of the ink at 20°C.

It is preferable that the water content of each of the first ink composition and the second ink composition is 50% by mass or more. This embodiment is particularly effective when the water content in the ink composition is as high as 50% by mass or more.

The first ink composition preferably contains 10 to 22% by mass of solids and 10 to 27% by mass of organic solvent. It further preferably contains 12 to 20% by mass of solids and 12 to 26% by mass of organic solvent, and more preferably 14 to 20% by mass of solids and 15 to 24% by mass of organic solvent.
The second ink composition preferably contains 5 to 15% by mass of solids and 23 to 38% by mass of organic solvent, and preferably contains 5 to 11% by mass of solids and 25 to 37% by mass of organic solvent. More preferably, it contains 8 to 11% by mass of solids and 25 to 35% by mass of organic solvent.
Thus, since the first ink composition has a higher solid content than the second ink composition, the content of the organic solvent in the second ink composition is made higher than that in the first ink composition, and the first ink composition By balancing the solid content amount and the organic solvent amount of the ink composition and the second ink composition, misregistration between the image of the first ink composition and the image of the second ink composition during inkjet recording can be suppressed. can.

[Treatment liquid]
The ink set according to this embodiment is preferably used for recording together with a treatment liquid containing an aggregating agent for aggregating the components of the water-based inkjet ink composition. The treatment liquid is preferably an aqueous composition containing water as one of the main solvent components of the composition, and the content of water in the composition is preferably 40% by mass or more. The treatment liquid may further contain an organic solvent. By using the treatment liquid, the image quality of the ink composition can be improved. On the other hand, the abrasion resistance of the image may deteriorate. It is presumed that the reason for this is that the components of the ink agglomerate due to the treatment liquid, making it difficult to smooth the ink film. The treatment liquid is preferably applied to the recording medium before the ink composition is applied. By applying the treatment liquid to the recording medium in advance, the image quality can be improved as compared with the case where the ink composition is directly adhered to the recording medium. The treatment liquid is independent of the ink composition, with the content of ingredients that may be contained other than the flocculant, the content and characteristics of the ingredients, the physical properties of the composition, etc. can be done as In particular, they can be similar to those of the second ink. The treatment liquid is preferably not used for coloring the recording medium. In this case, the content of the coloring material in the treatment liquid is preferably 0.1% by mass or less, more preferably 0.05%. % by mass or less, and the lower limit is 0% by mass or more. Components in the treatment liquid are described below, but are not limited to the following as described above.

(coagulant)
The aggregating agent reacts with any of the components contained in the ink composition, preferably with either the coloring material or the resin, to cause aggregation and thickening, thereby allowing the resin or coloring material contained in the ink composition to quickly spread on the recording medium. It has the function of fixing to and suppressing the flow. As a result, the ink droplets can be fixed after they have landed, and interference between the ink droplets can be suppressed, so that an image with no density unevenness can be formed.

As the flocculant, any of polyvalent metal salts, organic acids and cationic polymers is preferred, with polyvalent metal salts and cationic polymers being more preferred, the former one being more preferred. The content of the flocculant contained in the treatment liquid is preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass, and even more preferably 2 to 10% by mass. This makes it possible to aggregate the components of the colored ink composition and improve the image quality.

A polyvalent metal compound is a compound composed of a polyvalent metal ion having a valence of two or more and an anion. Examples of polyvalent metal ions having a valence of 2 or more include Ca ²⁺ , Mg ²⁺ , Cu ²⁺ , Ni ²⁺ , Zn ²⁺ , Ba ²⁺ and the like. Examples of anions include Cl ⁻ , NO ₃ ⁻ , CH ₃ COO ⁻ , I ⁻ , Br ⁻ , ClO ₃ ⁻ , SO ₄ ^{− and} the like. Among these, magnesium salts, calcium salts and aluminum salts can be preferably used from the viewpoint that the above-mentioned aggregation effect is further enhanced.

Organic acids include, but are not limited to, succinic acid, acetic acid, propionic acid, and lactic acid.

Examples of cationic polymers include, but are not limited to, amine-based polymers and the like. As the amine-based polymer, any polymer having an amino group in its structure may be used, and examples thereof include resins produced from epihalohydrin and amine compounds, polyallylamine, quaternary salts of polyallylamine, and the like. Cationic polymers that are soluble in water and positively charged in water are included.

The content of the flocculant in the treatment liquid is preferably 0.5 to 15% by mass. It is more preferably 1 to 10% by mass, still more preferably 2 to 8% by mass. The content of the flocculant in the treatment liquid is preferably 0.1 to 1.5 mol/kg in terms of molar concentration. The lower limit of the coagulant content in the treatment liquid is more preferably 0.2 mol/kg or more. The upper limit of the content of the flocculant in the treatment liquid is more preferably 1.0 mol/kg or less, and still more preferably 0.6 mol/kg or less. As a result, it is possible to achieve a balance with other properties such as abrasion resistance while improving the image quality.

(Organic solvent)
The treatment liquid preferably contains an organic solvent, more preferably an organic solvent having a normal boiling point of 180 to 250°C. As a result, volatilization of the organic solvent contained in the processing liquid in the head can be prevented, and clogging of the nozzles can be prevented. In addition, when mixed with the ink composition on the recording medium, the organic solvent can be rapidly volatilized, and sufficient image quality can be obtained on the recording medium.

A nitrogen-containing solvent may be included as the organic solvent. This allows the resin in the ink composition to be stably dissolved and mixed with the ink composition. In addition, the nitrogen-containing solvent has the effect of promoting the softening of the resin particles contained in the ink composition, and tends to improve adhesion even when the heating temperature is low. As the nitrogen-containing solvent and other organic solvents, the same ones as those described in the ink composition can be used.

The content of the organic solvent is preferably 3.0% by mass or more, more preferably 5.0% by mass or more and 35% by mass or less, and still more preferably 10% by mass or more and 35% by mass or more, relative to the total amount of the treatment liquid. % by mass or less, more preferably 15% by mass or more and 30% by mass or less. As a result, the degree of aggregation of the components of the ink composition becomes appropriate when the ink composition and the treatment liquid are mixed. In addition, when mixed with the ink composition on the recording medium, the organic solvent can be rapidly volatilized, and sufficient image quality can be obtained on the recording medium having non-ink absorption or low absorption.

The treatment liquid preferably contains 2% by mass or less of an organic solvent having a normal boiling point of over 280°C. Examples of organic solvents having a normal boiling point of over 280° C. include polyol compounds. When the content of the organic solvent in the treatment liquid is within the above range, the drying property of the treatment liquid on the recording medium is not significantly deteriorated, which is preferable. As a result, it is preferable for various recording media, particularly non-ink-absorbing or low-ink-absorbing recording media, from the viewpoint of reducing image bleeding and being excellent in abrasion resistance.

The content of the organic solvent having a normal boiling point of more than 280° C. in the treatment liquid is more preferably 1% by mass or less, even more preferably 0.5% by mass or less, and 0.1% by mass or less relative to the total mass of the ink composition. is particularly preferred, and 0.05% by mass or less is more preferred. The lower limit of the content is 0% by mass. When the content is within the above range, deterioration of the abrasion resistance of the recorded matter due to an organic solvent having a normal boiling point of more than 280° C. can be suppressed, and a recorded matter having more excellent abrasion resistance can be obtained.

The treatment liquid also contains surfactants, resins, pastes (e.g., starch substances, cellulosic substances, polysaccharides, proteins, water-soluble polymers, etc.), pH adjusters, preservatives, antifungal agents, etc. may contain.

The components of the treatment liquid have been described above. It is preferable to define it within the same range as the difference in the content of solids and organic solvent. Specifically, the first ink composition has a solid content higher than that of the treatment liquid by 5 mass % or more, and the organic solvent content of the treatment liquid is higher than that of the first ink composition by 7 mass % or more. preferable. Accordingly, for the same reason as described for the first ink composition and the second ink composition, between the liquids having different solid content, such as the treatment liquid and the first ink composition, during ink jet recording, Image misalignment can be suppressed. In particular, it is possible to suppress misalignment between the image formed by the first ink and the treatment liquid layer formed by the treatment liquid, and the first ink can be sufficiently contacted with the treatment liquid, which is preferable in that the image quality is improved. .
The content of solids in the treatment liquid is the content of components that do not evaporate in the secondary drying process as the post-drying process, and the solids content of the treatment liquid includes a flocculant. When the treatment liquid contains a solid component among the components contained in the ink composition and the component that may be contained, these components are also considered as solid components.

In addition, the difference in water content and/or the difference in viscosity between the first ink composition and the treatment liquid is defined within the same range as described for the first ink composition and the second ink composition. is preferred.

[Recording device]
The recording apparatus according to this embodiment is a recording apparatus that performs recording by the recording method of this embodiment. The printing apparatus may be an inkjet printing apparatus, a serial inkjet printing apparatus, or a line inkjet printing apparatus.
An example of the configuration of the printing apparatus according to this embodiment will be described below.

FIG. 1 shows a schematic cross-sectional view of an example of a recording apparatus (inkjet apparatus) used in the inkjet recording method according to the present embodiment. As shown in FIG. 1, the inkjet device 100 includes a carriage 2, an inkjet head 3, a platen 4, a platen heater 4a, an after heater 5, a cooling fan 5a, a preheater 7, an IR heater 8, A ventilation fan 8a is provided. The cooling fan 5a, the preheater 7, the IR heater 8, and the ventilation fan 8a are used as necessary and can be omitted.

The inkjet head 3 is mounted on the carriage 2 and has a plurality of nozzle rows for ejecting the ink composition. Each nozzle row is formed by arranging a plurality of nozzle holes. The inkjet recording apparatus 1 is a so-called serial type inkjet recording apparatus. In a serial type inkjet recording apparatus, an inkjet head 3 is mounted on a carriage 2 that moves in a predetermined direction. It refers to a device that ejects liquid droplets. The carriage 2 moves in the main scanning direction, which is the front-to-back direction in the figure, and performs main scanning in which ink is ejected from an inkjet head 3 mounted on the carriage 2 and adhered to the recording medium. The inkjet head 3 may include a head that ejects the first ink composition, and a head that is arranged downstream of the first head and ejects the second ink composition. Alternatively, the inkjet head 3 may be one head provided with a nozzle row for ejecting the first ink composition and a nozzle row for ejecting the second ink composition.

Moreover, it is preferable that the inkjet head 3 is configured to eject the treatment liquid as well. In this case, the inkjet head 3 may be provided with a head for ejecting the treatment liquid upstream of the head for ejecting the first ink composition. Alternatively, the inkjet head 3 may include nozzles for ejecting the treatment liquid on the upstream side of the nozzle row for ejecting the first ink composition.

The platen heater 4a is used when heating the recording medium in the step of applying the ink composition. By using the platen heater 4a, the recording medium can be heated from the side opposite to the ink jet head 3 side. This makes the inkjet head 3 relatively difficult to heat.

The after-heater 5 serves to secondary dry and solidify the ink composition recorded on the recording medium 1 . The after-heater 5 heats the recording medium 1 on which an image has been recorded, so that the water contained in the ink composition evaporates and scatters more quickly, and the polymer particles contained in the ink composition form a film. be done. In this way, the dried ink product is firmly fixed (adhered) on the recording medium, and a high-quality image with excellent abrasion resistance can be obtained in a short period of time.

The cooling fan 5a is used to cool the ink composition on the recording medium after drying the recording medium by the afterheater 5, thereby forming a coating on the recording medium with good adhesion.

The preheater 7 preheats (preheats) the recording medium before the ink composition is discharged onto the recording medium.

The IR heater 8 is used as necessary, and is used to heat the recording medium from the inkjet head 3 side in the step of applying the ink composition. As a result, the inkjet head 3 is likely to be heated at the same time, but the temperature can be raised without being affected by the thickness of the recording medium, as compared with the case where the platen heater 4a or the like is heated from the back surface of the recording medium. The ventilation fan 8a is used to dry the ink composition adhering to the recording medium 1 more efficiently.

FIG. 2 is a functional block diagram of the inkjet recording apparatus 100. As shown in FIG.
The controller 10 is a control unit for controlling the inkjet recording apparatus 100 . The interface unit 11 (I/F) is for sending and receiving data between the computer 90 and the inkjet recording apparatus 100 . The CPU 12 is an arithmetic processing unit for controlling the entire inkjet recording apparatus 100 . The memory 13 is for securing an area for storing programs of the CPU 12, a work area, and the like. The CPU 12 controls each unit through the unit control circuit 14 . The detector group 60 monitors the conditions inside the inkjet recording apparatus, and the controller 10 controls each unit based on the detection results.

The conveying unit 20 controls sub-scanning (conveyance) of inkjet recording, and specifically controls the conveying direction and conveying speed of the recording medium 1 . Specifically, the conveying direction and conveying speed of the recording medium 1 are controlled by controlling the rotating direction and rotating speed of a conveying roller driven by a motor.

The carriage unit 30 controls the main scanning (pass) of inkjet recording, and specifically, reciprocates the inkjet head 3 in the main scanning direction. The carriage unit 30 includes a carriage 2 on which the inkjet head 3 is mounted, and a carriage movement mechanism for reciprocating the carriage.

The head unit 40 controls the ejection amount of the treatment liquid or ink composition from the nozzles of the inkjet head. For example, when the nozzles of the inkjet head are driven by piezoelectric elements, the operation of the piezoelectric elements in each nozzle is controlled. The head unit 40 controls the time from the application of the treatment liquid to the adhesion of the ink, and the dot size of the treatment liquid. Also, the amount of processing liquid adhered per scan is controlled by a combination of controls of the carriage unit 30 and the head unit 40 .

The drying unit 50 controls the temperature of various heaters such as an IR heater, pre-heater, platen heater, and after-heater.

The inkjet recording apparatus 100 described above alternately repeats an operation of moving the carriage 2 on which the inkjet head 3 is mounted in the main scanning direction and a conveying operation (sub-scanning). At this time, when performing each pass, the controller 10 controls the carriage unit 30 to move the inkjet head 3 in the main scanning direction, and controls the head unit 40 to move predetermined nozzle holes of the inkjet head 3. A droplet of the treatment liquid or the ink composition is ejected from the recording medium 1 to adhere the droplet of the ink composition to the recording medium 1 . Further, the controller 10 controls the transport unit 50 to transport the recording medium 1 in the transport direction by a predetermined transport amount during the transport operation.

By alternately repeating the pass (main scan) and the transport operation (sub-scan), the recording area on which a plurality of droplets (dots) are adhered is gradually transported. Then, the after-heater 5 dries the droplets adhered to the recording medium to complete the image. After that, the completed recorded material may be wound into a roll by a winding mechanism (not shown) or transported by a flatbed mechanism (not shown). Main scanning is also called a pass. This is a serial type recording method. Main scanning is also called scanning in distinction from sub-scanning.

FIG. 3 is a perspective view showing an example of the configuration around the carriage of the recording apparatus of FIG. It is a part of an example of the configuration of a serial type inkjet recording apparatus. A configuration 100a around the carriage includes a carriage 2, an inkjet head 3 mounted on the carriage 2, a member 3a that is a part of the inkjet head 3 and includes nozzles that eject ink, an ink container (not shown), and an ink supply path (not shown) such as an ink supply pipe for supplying ink from the ink container to the inkjet head 3 . The ink container may be provided at a place other than the carriage 4 or may be provided on the carriage. A platen 4 disposed below the carriage 2 for transporting the recording medium P, a carriage movement mechanism 2a for moving the carriage 2 relative to the recording medium P, and a sub-scanning direction (transportation mechanism) for the recording medium P. direction), and a controller CONT for controlling the operation of the carriage 2 and the like. The direction of S1-S2 is the main scanning direction, and the direction of T1→T2 is the sub-scanning direction. One main scan is performed in one of the main scan directions (horizontal direction of the apparatus).

FIG. 4 is a diagram showing an example of arrangement of heads (inkjet heads) mounted on a carriage of a serial type printing apparatus. A first head, a second head, and a third head are arranged in this order on the carriage from the upstream side to the downstream side in the sub-scanning direction, which is the conveying direction of the recording medium. The head moves in the main scanning direction by a carriage and performs main scanning in which ink is ejected and adhered to the recording medium. Main scanning is performed in one of the left and right directions in the drawing in one main scan. By alternately repeating main scanning and sub-scanning, the printing medium is conveyed little by little, and printing progresses. The composition filled in the nozzle rows of the first head is ejected by main scanning and adheres to the recording medium. As the main scanning and sub-scanning are alternately repeated and recording progresses, the composition filled in the second nozzle row adheres to the recording medium, and then the composition filled in the third nozzle row adheres to the recording medium. adheres to the recording medium.

The area where the head moves while facing the print medium in one main scan is called the print area of the main scan. The print area of one main scan is a strip-shaped area whose length in the sub-scanning direction is the length of the nozzle row of the head in the sub-scanning direction and which extends in the main scanning direction. For example, when recording is performed by ejecting a certain composition from one nozzle row of the first head, the recording area of the composition in one main scan is the length of the one nozzle row of the first head in the sub-scanning direction. It is a band-shaped area extending in the main scanning direction at a height of 0.5 mm.

One head is equipped with five nozzle rows, and different compositions can be filled and discharged for each nozzle row. In this case, a plurality of compositions ejected from one head can be applied to the recording area of the main scan in the same main scan. The number of heads and the number of nozzle rows provided in the heads are not limited to those shown in the figure.

On the other hand, a line-type inkjet recording device may be used as the recording device. For example, in the recording apparatus of FIG. 1, the inkjet head 3 extends in the width direction of the recording medium (rear-to-front direction in FIG. 1), and the length of the inkjet head in the width direction is the length of the recording area in the width direction of the recording medium. It is configured as a line head that is longer than or equal to The line head is fixed in position during recording. Printing is performed by performing one scanning (main scanning) in which ink is ejected from the line head while the printing medium is conveyed and adheres to the printing medium. This is a line type recording method. By arranging a plurality of line heads from the upstream side to the downstream side in the conveying direction of the recording medium and ejecting a different composition for each line head, recording can be performed using a plurality of types of compositions. When the recording apparatus is a line-type inkjet recording apparatus, the configuration of the recording apparatus other than the configuration of the inkjet head and the recording method can be the same as that shown in FIG.

〔recoding media〕
In this embodiment, it is preferable to use a non-absorbent or low-absorbent recording medium as the recording medium 1 . A non-absorbent recording medium or a low-absorbent recording medium tends to have lower filling properties due to repelling of the water-based ink composition as the absorption is lower or as the non-absorption is lower. Therefore, it is advantageous to use the inkjet recording method according to the present embodiment for such a recording medium. A non-absorbent recording medium or a low-absorbent recording medium is useful because the recording medium itself has water resistance and durability, and the recorded matter can be used for various purposes.

Here, the term "low-absorbent recording medium" or "non-absorbent recording medium" refers to a recording medium having a water absorption of 10 mL/m ² or less from the start of contact until 30 msec in the Bristow method. The Bristow method is the most popular method for measuring liquid absorption in a short period of time, and is also adopted by the Japan Pulp and Paper Institute (JAPAN TAPPI). For details of the test method, refer to Standard No. 2000 of "JAPAN TAPPI Paper Pulp Test Method 2000". 51 "Paper and paperboard--Liquid absorbency test method--Bristow method".

Non-absorbent recording media or low-absorbent recording media can also be classified according to the wettability of the recording surface to water. For example, 0.5 μL of water droplets are dropped on the recording surface of the recording medium, and the rate of decrease in the contact angle (comparison between the contact angle at 0.5 milliseconds after impact and the contact angle at 5 seconds after impact) is measured. can be characterized. More specifically, as the property of the recording medium, the non-absorbent property of the "non-absorbent recording medium" refers to the above-mentioned decrease rate of less than 1%, and the low absorbency of the "low-absorbent recording medium" is the above-mentioned refers to a rate of decrease of 1% or more and less than 5%. In addition, absorbability means that the rate of decrease is 5% or more. The contact angle can be measured using a portable contact angle meter PCA-1 (manufactured by Kyowa Interface Science Co., Ltd.) or the like.

Examples of low-absorbency recording media include, but are not limited to, coated paper having a coating layer for receiving oil ink on the surface. Coated paper is not particularly limited, but includes recording paper such as art paper, coated paper, and matte paper.

Examples of non-absorbent recording media include, but are not limited to, plastic films having no ink-absorbing layer, substrates such as paper coated with plastic, and plastic films adhered. is mentioned. The plastics mentioned here include polyvinyl chloride, polyethylene terephthalate, polycarbonate, polystyrene, polyurethane, polyethylene, polypropylene and the like.

In addition to the recording media described above, non-ink-absorbing or low-ink-absorbing recording media such as plates of metals such as iron, silver, copper, and aluminum, and glass can also be used.
The width of the recording medium in the main scanning direction is preferably 50 cm or more, more preferably 70 cm or more, even more preferably 80 cm or more, even more preferably 100 cm or more, and particularly preferably 130 cm or more. The width of the recording medium in the main scanning direction is preferably 500 cm or less, more preferably 400 cm or less, still more preferably 300 cm or less, and particularly preferably 200 cm or less. When the width of the recording medium in the main scanning direction is within the above range, it is possible to record a useful recorded material for display or the like. It is preferable in that it can be reduced. Moreover, it is preferable because the maximum time for one scan can easily be set to what will be described later.

[Inkjet recording method]
The ink jet recording method according to the present embodiment uses the ink set described above, and has an ink application step of applying the first ink composition and the second ink composition of the ink set to a heated recording medium. The recording method will be described step by step below. Either a serial type recording method or a line type recording method can be used.

(Treatment liquid adhering step)
The inkjet recording method according to this embodiment includes a step of applying a treatment liquid to a recording medium. The treatment liquid application step is a step of applying a treatment liquid containing an aggregating agent for aggregating the ink composition onto the recording medium. The aggregating agent has the function of reacting with the pigment contained in the ink composition and the pigment dispersing resin that may be contained in the ink composition to aggregate the pigment. As a result, it is possible to suppress the occurrence of bleeding and the like in an image recorded using the ink composition, and an image having excellent image quality can be obtained. The method of applying the treatment liquid is not limited, and an inkjet method, a roll coating method, a spray method, or the like can be used. Among these, the inkjet method is preferred.

In this embodiment, the treatment liquid is preferably applied before or during the main scanning to the recording area to which the ink composition has been applied during the main scanning, and the former is more preferred. Note that the timing of adhesion of the processing liquid is not limited to the above-described mode.

(Ink composition adhesion step)
The ink composition application step is a step of ejecting an ink set containing a first ink composition and a second ink composition from an inkjet head and applying the ink set to a low-absorbent or non-absorbent recording medium 1. be. There is no limitation on the order of ejecting the first ink composition and the second ink composition.

As an example of the serial type recording method according to the present embodiment, the ink adhesion step includes main scanning in which the ink composition is ejected while changing the relative position between the inkjet head 3 and the recording medium 1 in the main scanning direction, and sub-scanning for changing the relative positions of the carriage 2 and the recording medium 1 in the intersecting sub-scanning direction. Then, the image of the first ink composition and the image of the second ink composition are recorded on the recording medium so as to overlap each other. As a result, recording can be performed on a wide recording medium without using a large head such as a line head.

Preferably, the ink composition application step is performed by performing multiple main scans in which the ink composition is ejected while changing the relative position between the ink jet head provided with the ink set and the recording medium in the main scan direction.
For example, a serial type recording method using the configuration of the head (inkjet head) shown in FIG. 4 can be used. For example, if one nozzle row of the first head mounted on the carriage shown in FIG. Just do it. In this case, the treatment liquid is applied to the recording medium, and as the printing progresses, the first ink is applied to the areas to which the treatment liquid has been applied, and the second ink is applied to the areas to which the first ink has been applied. In such a case, an inkjet head for ejecting the first ink and an inkjet head for ejecting the second ink are mounted on the same carriage. In this case, the configuration of the recording apparatus can be simplified as compared with the case where the first head and the second head are mounted on separate carriages, which is preferable. On the other hand, since the first ink is deposited and the second ink is deposited by the same movement of the carriage, it is necessary to pay attention to the alignment of the first ink image and the second ink image, and the present invention is particularly useful. be. In such an example, the first ink and the second ink may be ejected from the heads mounted on the same carriage, and the arrangement of the heads is not limited to the above.

Preferably, the maximum time for one main scan is 0.8 seconds or longer. The “maximum time for one scan” refers to the time during which one point of the inkjet head faces the print medium in one scan when printing is performed from end to end in the scanning direction of the print medium. When performing the recording method, scanning may be performed for a time shorter than the maximum time for one scan according to the image to be recorded. The maximum time for one scan is more preferably 0.8 to 5 seconds, more preferably 0.8 to 4 seconds, still more preferably 1 to 3 seconds, and particularly preferably is 1.5 to 2.5 seconds.
When the maximum time for one scan is equal to or less than the above range, it is preferable in that image positional deviation can be further reduced. In addition, when the maximum time for one scan is equal to or greater than the above range, it is possible to create a printed material useful for display on a wide recording medium, which is preferable. On the other hand, if the maximum scanning time is long, the ink in the nozzles during scanning is likely to dry, and misalignment of the image is likely to occur. . The average scanning speed in scanning is preferably 60 to 100 cm/sec.

In this embodiment, an ink adhesion process can also be performed as a line type recording method. When the line type recording method is used, for example, the line type recording apparatus described above may be used for recording. In this case, the recording speed can be increased, which is preferable. Also in this case, it is possible to reduce the increase in misalignment between the image of the first ink and the image of the second ink during scanning, which is preferable.

(Heating process)
In the ink composition applying step, it is preferable to heat the recording medium 1 using a heating means and perform the ink applying step on the heated recording medium 1 . The means for heating the recording medium during the ink deposition process is not limited to the platen heater, and may be air blowing means for sending hot air to the recording medium or means for irradiating the recording medium with radiation that generates heat.

In the ink composition adhesion step, the surface temperature of the recording medium is preferably 27 to 50°C, more preferably 28 to 45°C, still more preferably 29 to 40°C, still more preferably 30 to 38°C, and 32 to 38°C. Especially preferred. The temperature is the surface temperature of the portion of the recording surface of the recording medium to which the ink adheres in the adhesion step, and is the average temperature during printing when the printing is performed for a long time. The surface temperature of the recording medium in the heating process is preferably 30° C. or higher.
The provision of the heating step is preferable because the image quality is excellent, and the abrasion resistance, the reduction of clogging, and the high gloss are excellent. On the other hand, during scanning, the ink in the nozzles of the inkjet head tends to dry due to the influence of heat, which causes fluctuations in the ejection speed of the ink and fluctuations in the timing at which the ink droplets leave the nozzles, resulting in misalignment of the image. Guess. However, according to the present embodiment, it is possible to reduce ink misalignment.

According to the inkjet recording method of the present embodiment, misalignment between the image of the first ink composition and the image of the second ink composition can be suppressed in the inkjet recording method performed by applying ink to a heated recording medium. .
In addition, it is preferable that the ink composition application step includes an air blowing step of blowing air to the recording medium by means of air blowing means. The sending process may be carried out as the heating process described above, or may be carried out by blowing normal temperature air without heat. The drying of the ink adhering to the recording medium can be accelerated by the blowing process, which is preferable because the image quality is excellent.

(Ink composition post-drying step)
After the ink composition is applied, the after-heater 5 dries the recording medium to which the ink composition is applied. As a result, the resin contained in the ink composition on the recording medium is melted to form a recorded matter with good fillability. At this time, the heating temperature of the recording medium by the after heater 5 is preferably 50 to 150°C, more preferably 70°C to 120°C, and still more preferably 80°C to 110°C. When the drying temperature is within the above range, the abrasion resistance tends to be further improved.

(Example)
Hereinafter, the present invention will be described more specifically using examples and comparative examples. The present invention is by no means limited by the following examples.

(Preparation of treatment liquid and ink composition)
Each material was mixed according to the composition (% by mass) shown in Table 1 below and sufficiently stirred to prepare various treatment liquids, first ink compositions and second ink compositions. Pigments, resins, and waxes are the respective solid contents in the ink or the like. In the examples, a white ink composition was prepared as the first ink composition, and a non-white ink composition, specifically a cyan ink composition, was prepared as the second ink composition. A dispersant resin (styrene-acrylic water-soluble resin) and a pigment:dispersant resin are mixed in advance with water at a mass ratio of 5:1, and stirred in a bead mill to prepare a pigment dispersion. Used for preparation. Pigment solids is the total solids of pigment and dispersant resin. When a hydrate of a polyvalent metal salt is used as the flocculant, the solid content is the solid content of the hydrate excluding water.

The ink materials shown in Table 1 are as follows.
Flocculant A: polyvalent metal salt "magnesium sulfate heptahydrate"
Flocculant B: cationic polymer "Catiomaster-PD-7"
Pigment (white ink): Pigment White 6 (titanium dioxide pigment)
Pigment (non-white ink): Pigment Blue 15:3
Resin: Styrene-acrylic "Joncryl 62" resin Emulsion wax: Polyethylene-based "AQ515" Wax emulsion surfactant: Silicon-based "BYK348"

The viscosities of the inks shown in Table 1 are values measured using an MCR300 rheometer (manufactured by Anton Paar) while maintaining the temperature of the ink at 20°C.

As shown in Tables 2 to 4, recording was performed by changing the combination of the treatment liquid and the ink composition used in the inkjet recording method and various conditions, and various evaluations were performed. The conditions of the recording method and the details of each evaluation test will be described below.

(recording test)
A modified Epson SC-S40650 machine was produced. As shown in FIG. 4, three heads are arranged on the upstream side, the downstream side, and the downstream side in the conveying direction of the recording medium. From the upstream, the first head, the second head, and the third head. One nozzle row of the first head was filled with the treatment liquid, one nozzle row of the second head was filled with white ink (first ink composition), and one nozzle row of the third head was filled with non-white ink (second ink composition). . The treatment liquid, the white ink, and the non-white ink can be adhered to the recording medium in this order. A common platen facing the three heads was provided with a platen heater. The platen heater was operated and the surface temperature of the recording medium during the adhesion process was taken as the value in the table. However, in the example at 25°C, the platen heater was stopped and no heating was performed. Secondary drying was performed with an after-heater downstream of the head. Secondary drying was performed at 85°C for about 30 seconds.
(recoding media)
LAGJET E-1000ZC (a transparent film manufactured by Lintec Corporation) was used as a recording medium. This was cut or pasted, and the width of the recording medium was set to the value shown in the table for each example. Due to the width of the recording medium, one scanning time was the value shown in the table.

The following recording conditions were used for the evaluation patterns other than the evaluation of image misregistration. For each treatment liquid and ink, the ink amount and dot density of dots were adjusted so that the maximum resolution was 1440×1400 dpi and the adhesion amount was the following value.
Ink: Adhesion amount of 12 mg/inch ² for each ink Treatment liquid: Adhesion amount of 10% by mass with respect to the total adhesion amount of the inks used

A recording pattern formed on the recording medium after recording was evaluated. The contents of each evaluation test are shown below.

<Image misalignment>
Using the nozzle row of the first ink, main scanning is performed from one end to the other end of the printable range in the main scanning direction of the recording medium in one main scan, and lines are drawn at one end and the other end, respectively. was recorded. Each line extends in the sub-scanning direction and has a length of 1 cm in the sub-scanning direction. Next, sub-scanning was performed and the carriage was returned. Next, using the nozzle row of the second ink, main scanning was performed from one end to the other end so as to overlap the line recorded with the first ink, and lines were recorded at one end and the other end. The second ink line also had a length of 1 cm in the sub-scanning direction. The line of the first ink and the line of the second ink were ejected at the same position so that the position in the main scanning direction theoretically overlapped. At this time, a line was similarly recorded on the next area in the sub-scanning direction of the recording medium with the first ink. Sub-scanning and carriage return are performed, and the line of the second ink is superimposed on the line of the first ink recorded in the previous main scanning and recorded in the next main scanning. This was done continuously for 30 minutes. Each time the carriage moved, nozzles were used to flush the recording medium in flushing boxes provided on both sides of the recording medium. After the recording, positional deviation in the main scanning direction between the line of the first ink and the line of the second ink was confirmed for each line recorded at the other end in the main scanning direction, and the maximum amount of deviation was confirmed. In any of the examples, the lines recorded at one end in the main scanning direction were not displaced.
A: The deviation amount is 0.1 mm or less.
B: The deviation amount is more than 0.1 mm and 0.3 mm or less.
C: The deviation amount is more than 0.3 mm and 0.6 mm or less.
D: The deviation amount is more than 0.6 mm.

<Image Edge Bleeding>
Each test pattern for evaluation had a size of 3.times.3 cm and was recorded over the entire recordable area of the recording medium in the main scanning direction with a gap of 1 cm between the patterns. The patterns were ejected at the same positions so that the patterns of the treatment liquid and the white ink theoretically overlapped. Patterns were also printed side by side in the sub-scanning direction with an interval of 1 cm between the patterns. No non-white ink was used. Nozzle flushing was performed for each main scan.
A recording test was continuously performed for 30 minutes, and each pattern was visually observed to see whether or not unevenness in density of white was observed at the ends in the main scanning direction compared to the inside of the white pattern.
A: There is no state in which unevenness in density is visible at the edges compared to the inside of the pattern.
B: There is a state in which uneven density is slightly visible at the edges compared to the inside of the pattern.
C: Conspicuous unevenness of density at the edges compared to the inside of the pattern.

<Clogging resistance (white)>
Recording was performed continuously for two hours under the conditions of the image edge bleeding test, and after the recording, an ejection test of the white nozzle row was performed.
A: No non-ejection nozzles B: 2% or less non-ejection nozzles C: More than 2% and 4% or less non-ejection nozzles D: More than 4% non-ejection nozzles

<Abrasion resistance (white)>
A pattern was recorded using only the treatment liquid and white ink. In the Gakushin abrasion resistance test, evaluation was performed by rubbing with a cloth 10 times with a load of 500 g.
A: There is neither peeling of the pattern portion nor color transfer to the cotton cloth.
B: The pattern portion is not peeled off, but there is some color transfer to the cotton cloth.
C: There is peeling of the pattern portion.

<Whiteness>
A pattern was recorded using only the treatment liquid and white ink. The whiteness (L*) of the image was measured with a spectrophotometer Gretag Macbeth Spectrolino (product name, manufactured by X-RITE). A black backing paper with an OD value of 2.1 was used as a base during the measurement.
A: L* value of 75 or more.
B: L* value of 70 or more and less than 75.
C: L* value less than 70;

<Image Quality (White)>
A pattern was recorded using only the treatment liquid and white ink. The pattern was evaluated visually.
A: There is no density unevenness in the pattern.
B: Slight unevenness of density is observed in the pattern.
C: Unevenness in density is conspicuous in the pattern.

The following findings were obtained from the results of Examples and Comparative Examples.
The solid content of the first ink is 5% by mass or more than that of the second ink, and the organic solvent content of the second ink is 7% by mass or more than that of the first ink. Excellent suppression of misalignment. On the other hand, all of the comparative examples that did not satisfy such conditions were inferior in suppressing image misregistration. Details are given below.
From the comparison between Examples 1 and 6 and 7 and between Examples 16 and 9, the lower the recording temperature in the ink adhesion step, the better the suppression of image misalignment and the better the clogging resistance. It is presumed that when the recording temperature was high, the drying of the nozzle progressed and affected clogging resistance and image misalignment. In addition, in the evaluation of image misalignment, no image misalignment occurred in the lines printed at one end in the main scanning direction. In addition, since the higher the recording temperature in the ink adhesion process, the better the image quality, it was found that the present invention is useful in that it is possible to suppress the image misalignment when performing the heating process to obtain excellent image quality.
From the comparison between Examples 1 and 11 and 12, and between Examples 17 and 3, the shorter the pass time in the ink adhesion process, the better in the image misalignment and image edge bleeding tests. On the other hand, the longer the pass time, the more useful the printed material can be for display. Therefore, it is found that the present invention is particularly useful in that it is possible to suppress misalignment of images even in printing with a long pass time. rice field.
Examples 1 to 13, 16, and 17, in which the first ink has a solids content of 5% by mass or more than the treatment liquid and the treatment liquid has an organic solvent content of 7% by mass or more than the first ink, Compared to Comparative Examples 1 to 3 and Examples 14 and 15, which do not satisfy such conditions, bleeding at the edge of the image can be suppressed, and these Examples suppress image misalignment between the first ink and the treatment liquid. I know it was done.
Examples 1 to 4, in which the difference in water content between the first ink and the second ink is within 5.5% by mass, compared to Example 9, in which the difference in water content is large, caused more image misalignment. I was able to suppress it.
Examples 1 to 4, in which the difference in viscosity at 20° C. between the first ink and the second ink is within 1 mPa s, compared to Examples 8 to 10, in which the difference in viscosity is more than 1 mPa s, are more accurate in the image position. It was possible to further suppress the deviation.
From Example 18, the effect of suppressing image misregistration was obtained even when the treatment liquid was not used.
From Reference Examples 1 and 2, the solid content of the first ink is 5% by mass or more than that of the second ink, and the organic solvent content of the second ink is 7% by mass or more than that of the first ink. In spite of the fact that the first ink and the second ink were used without the heating process, the suppression of image misregistration was not bad, but the image quality was inferior. From this, it was found that the present invention is necessary in terms of excellent suppression of image misregistration when a heating process is performed to obtain excellent image quality.

DESCRIPTION OF SYMBOLS 1... Recording medium 2... Carriage 3... Inkjet head 4... Platen 4a... Platen heater 5... After heater 5a... Cooling fan 7... Preheater 8... IR heater 8a... Ventilation fan 10... CONTROLLER 11 INTERFACE 12 CPU 13 MEMORY 14 UNIT CONTROL CIRCUIT 20 CONVEYING UNIT 30 CARRIAGE UNIT 40 HEAD UNIT 50 DRYING UNIT 60 DETECTORS 90 COMPUTER , 100... Inkjet device.

Claims (13)

comprising a first ink composition and a second ink composition;
The first ink composition and the second ink composition are water-based inkjet ink compositions containing a solid content containing a coloring material and an organic solvent,
The solid content of the first ink composition is greater than that of the second ink composition by 5% by mass or more,
the organic solvent content of the second ink composition is greater than that of the first ink composition by 7% by mass or more;
It is used in an inkjet recording method in which ink is adhered to a heated recording medium.is used for recording together with a treatment liquid containing an aggregating agent for aggregating the components of the water-based inkjet ink composition,
The first ink composition has a solid content higher than that of the treatment liquid by 5% by mass or more,
The treatment liquid has an organic solvent content higher than that of the first ink composition by 7% by mass or more.
ink set. comprising a first ink composition and a second ink composition;
The first ink composition and the second ink composition are water-based inkjet ink compositions containing a solid content containing a coloring material and an organic solvent,
The solid content of the first ink composition is greater than that of the second ink composition by 5% by mass or more,
the organic solvent content of the second ink composition is greater than that of the first ink composition by 7% by mass or more;
the difference in water content between the first ink composition and the second ink composition is within 8% by mass;
An ink set for use in an inkjet recording method in which ink is applied to a heated recording medium. The difference in water content between the first ink composition and the second ink composition is within 8% by mass.
The ink set according to claim 1 . The difference in viscosity at 20° C. between the first ink composition and the second ink composition is within 1.5 mPa·s.
The ink set according to any one of claims 1 to 3. Each of the first ink composition and the second ink composition has a water content of 50% by mass or more,
The ink set according to any one of claims 1 to 4. The first ink composition has a solid content higher than that of the second ink composition by 5 to 13% by mass, and the second ink composition has an organic solvent content of 7 higher than that of the first ink composition. ~17 mass% more,
The ink set according to any one of claims 1 to 5. The first ink composition contains 10 to 22% by mass of solids and 15 to 27% by mass of organic solvent, and the second ink composition contains 5 to 12% by mass of solids and 23 to 38% by mass of organic solvent. %contains,
The ink set according to any one of claims 1 to 6. The first ink composition is a white ink composition containing a white colorant as a solid content, and the second ink composition is a non-white ink composition containing a non-white colorant as a solid content,
The ink set according to any one of claims 1 to 7. The organic solvent content of the second ink composition is greater than that of the first ink composition by 9% by mass or more,
The ink set according to any one of claims 1 to 8. Using the ink set according to any one of claims 1 to 9,
An inkjet recording method, comprising an ink applying step of applying the first ink composition and the second ink composition to a heated recording medium. The surface temperature of the recording medium when attached is 30 to 50 ° C.
The inkjet recording method according to claim 10. A step of applying a treatment liquid containing an aggregating agent for aggregating components of the water-based inkjet ink composition to the recording medium;
The inkjet recording method according to claim 10 or 11. The ink application step is performed by performing a plurality of main scans in which the ink composition is ejected while changing the relative position between the inkjet head provided with the ink set and the recording medium in the main scan direction, and one main scan is performed. a maximum time of 0.8 seconds or more;
The inkjet recording method according to any one of claims 10 to 12.

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