JP7527824B2 - Ink composition, dispersion liquid used therein, laminate having ink cured film layer formed thereon, image forming method, and method for producing printed matter - Google Patents

Description

The present invention relates to an ink composition, a dispersion liquid used therein, a laminate on which an ink cured film layer that is the cured film of the ink composition is formed, an image forming method, and a method for producing a printed matter.

Active energy ray-curable ink compositions that are cured by ultraviolet rays, electron beams, or other active energy rays are being developed. Active energy ray-curable ink compositions are used in a wide range of fields, such as inkjet printing, because they have excellent performance, such as the fact that they do not contain volatile solvents and therefore do not volatilize much of the components that are harmful to the environment, and that they can be printed on a variety of substrates.

Inkjet printing can easily and inexpensively create images regardless of the material or shape of the substrate, so it is used in a variety of fields, from regular printing of logos, figures, photographic images, etc., to special printing of markings, color filters, etc., and there are high expectations that it will be able to produce better printed matter when combined with the performance of active energy ray-curable ink compositions. Recently, there has been a demand for inkjet printing on a variety of substrates that are stretched or bent after printing.

In recent years, from the viewpoint of environmental protection, the light source for active energy ray-curable ink compositions is being replaced from mercury lamps and metal halide lamps to light-emitting diodes (LEDs), and from the viewpoint of production efficiency, there is a demand for ink compositions that can be sufficiently cured even when the irradiation energy of the LED is small.

For example, Patent Documents 1 and 2 disclose photocurable inkjet ink compositions that contain a specific amine compound. According to Patent Documents 1 and 2, these ink compositions have excellent curing properties in response to LED light and good adhesion to a specific sheet.

JP 2009-35650 A Patent No. 5618997

Now, yellow colorants are colorants that produce a yellow color by absorbing light with relatively short wavelengths, such as blue and purple. For example, by including a colorant that has a high absorbance of light with wavelengths of about 360 nm to 400 nm, such as Pigment Yellow 155, the ink composition has excellent color rendering.

However, the present inventors have found that coloring materials that have a high absorbance of light with wavelengths of about 360 nm to 400 nm also absorb the light rays used to cure the ink composition, which can reduce the curability of the ink composition.

The present invention has been made in consideration of the above circumstances, and aims to provide an ink composition that can form a cured film with excellent curability, even if the ink composition contains a yellow colorant that has a high absorbance of light of a specific wavelength.

As a result of intensive research into solving the above problems, the inventors discovered that the above problems could be solved by an ink composition containing a specific polymerizable compound and a photopolymerization initiator, and thus completed the present invention. Specifically, the present invention provides the following:

(1) A yellow-based ink composition that is cured by light, comprising a photopolymerizable compound, a photopolymerization initiator, and a yellow-based colorant,
a sample for evaluating absorbance is prepared by diluting the yellow colorant with ethyl diglycol acetate so that the concentration of the yellow colorant is 0.005%, and the sample for evaluating absorbance is irradiated with light to measure the absorbance, the absorbance being 1.54 or more at a wavelength of 395 nm as defined by the following general formula:
A ₃₉₅ =-log ₁₀ (I/I ₀ )...(1)
(In formula (1), _A395 is the absorbance at a wavelength of 395 nm, _I0 is the incident light intensity at a wavelength of 395 nm, and I is the transmitted light intensity at a wavelength of 395 nm.)
The photopolymerizable compound includes a polymerizable compound A,
The polymerizable compound A is a polymerizable compound having a repeating sequence having a structure containing an amino group and an ether group, and having two or more (meth)acrylate groups,
The ink composition, wherein the photopolymerization initiator contains at least a hydrogen abstraction type initiator.

(2) The yellow ink composition according to (1), wherein the yellow colorant includes at least one selected from the group consisting of C.I. Pigment Yellow 155, C.I. Pigment Yellow 120, C.I. Pigment Yellow 151, C.I. Pigment Yellow 154, and C.I. Pigment Yellow 180.

(3) The yellow ink composition according to (1) or (2), wherein the molecular weight of the photopolymerization initiator is 1,000 or less.

(4) The yellow ink composition according to any one of (1) to (3), wherein the photopolymerizable compound further includes a monofunctional polymerizable compound.

(5) A yellow ink composition according to any one of (1) to (4), which is cured by light having a wavelength of 385 nm or more and 395 nm or less.

(6) A laminate having a substrate and an ink cured film layer formed of a cured film of the yellow ink composition described in any one of (1) to (5).

(7) An image forming method for forming an image and/or a relief image on a substrate using a yellow ink composition described in any one of (1) to (5).

(8) A method for producing a printed matter by forming an image and/or a relief image on a substrate using a yellow ink composition described in any one of (1) to (5).

The yellow ink composition of the present invention can form a cured film with excellent curability, even if the yellow ink composition contains a yellow colorant that has a high absorbance of light of a specific wavelength.

Specific embodiments of the present invention are described in detail below, but the present invention is not limited to the following embodiments and can be modified as appropriate within the scope of the invention.

<Yellow Ink Composition>
A yellow ink composition according to one embodiment of the present invention is a yellow ink composition that contains a photopolymerizable compound and a photopolymerization initiator. The photopolymerizable compound contains polymerizable compound A. In this specification, the term "polymerizable compound" is used as a concept that also includes compounds that are called monomers, oligomers, or polymers depending on their molecular weight.

[Light-ray polymerizable compound]
The photopolymerizable compound is a compound having an ethylenically unsaturated double bond that is polymerized by light such as far ultraviolet light, ultraviolet light, near ultraviolet light, visible light, and infrared light. Polymerizable compounds included in the photopolymerizable compound Let us explain A.

(Polymerizable compound A)
The polymerizable compound A is a polymerizable compound having a repeating sequence with a structure containing an amino group and an ether group, and having two or more (meth)acrylate groups. A yellow ink composition containing a polymerizable compound A having a repeating sequence with a structure containing an amino group and an ether group, and having two or more (meth)acrylate groups, can form a cured film that can achieve both curability, stretchability, and reduced tackiness. In this specification, (meth)acrylate means acrylate or methacrylate. These may be used alone or in combination.

The polymerizable compound A may be any polymerizable compound having a repeating sequence with a structure containing an amino group and an ether group and having two or more (meth)acrylate groups. Specific examples include CN371NS (manufactured by Sartomer), Genomer 5275 (manufactured by Rahn), and Genomer 5271 (manufactured by Rahn).

The polymerizable compound A may be a monomer (low molecular weight) or may be a compound called an oligomer or polymer depending on the molecular weight. The molecular weight of the polymerizable compound A is not particularly limited, but the molecular weight is preferably 50 or more, and more preferably 70 or more. The molecular weight is preferably 1500 or less, and more preferably 1000 or less.

The total content of polymerizable compound A is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, based on the total amount of the yellow-based ink composition. By having the total content of polymerizable compound A be 1% by mass or more based on the total amount of the yellow-based ink composition, the curability of the cured film can be improved.

The total content of polymerizable compound A is preferably 15% by mass or less, more preferably 13% by mass or less, and even more preferably 11% by mass or less, based on the total amount of the yellow-based ink composition. By having the total content of polymerizable compound A be 15% by mass or less based on the total amount of the yellow-based ink composition, the extensibility of the cured film can be improved.

The total content of polymerizable compound A is preferably 1% by mass or more, more preferably 2% by mass or more, and most preferably 3% by mass or more, based on the total amount of the photopolymerizable compounds. By having the total content of polymerizable compound A be 1% by mass or more based on the total amount of the yellow ink composition, the extensibility of the curing property can be improved.

(Other polymerizable compounds)
In addition to the above-mentioned polymerizable compound A, other monofunctional polymerizable compounds and/or polyfunctional polymerizable compounds may be appropriately added within the range in which the object of the present invention can be achieved.

Examples of monofunctional polymerizable compounds include 4-tert-butylcyclohexyl (meth)acrylate (TBCH), 3,3,5-triethylcyclohexyl (meth)acrylate (TMCHA), trimethylolpropane formal (meth)acrylate (CTFA), benzyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, γ-butyrolactone (meth)acrylate, cresol (meth)acrylate, 2-acryloyloxyethyl phthalate, 2-acryloyloxyethyl-2-hydroxyethyl phthalate, 2-acryloyloxyethyl hexahydrophthalate, 2-acryloyloxypropyl phthalate, paracumylphenoxyethylene glycol (meth)acrylate, nonylphenoxypolyethylene glycol Examples of the acrylate include ricolin (meth)acrylate, 1-adamantyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, acryloylmorpholine, N-vinylcaprolactam, imide (meth)acrylate, isooctyl (meth)acrylate, tridecyl (meth)acrylate, lauryl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, stearyl (meth)acrylate, isodecyl (meth)acrylate, caprolactone (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, 2-methoxyethyl (meth)acrylate, ethylcarbitol (meth)acrylate, 2-ethylhexyl (meth)acrylate, and those having various modifications such as alkoxy modification and caprolactone modification in these (meth)acrylates. By including a monofunctional polymerizable compound, the curability of the cured film can be improved.

It is preferable that the monofunctional polymerizable compound contains a monofunctional polymerizable compound that has a glass transition temperature Tg of 25°C to 60°C when polymerized. By containing a monofunctional polymerizable compound that has a glass transition temperature Tg of 25°C to 60°C when polymerized, the tack of the cured film can be reduced and the stretchability of the cured film can be improved. Examples of monofunctional polymerizable compounds that have a glass transition temperature Tg of 25°C to 60°C when polymerized include 4-tert-butylcyclohexyl (meth)acrylate (TBCH), 3,3,5-triethylcyclohexyl (meth)acrylate (TMCHA), trimethylolpropane formal (meth)acrylate (CTFA), etc. The glass transition point of the polymer obtained by polymerization refers to the glass transition point of a polymer prepared by mixing 9 g of monofunctional polymerizable compound A with a photopolymerization initiator such as Irgacure 184 (1-hydroxycyclohexyl-phenyl ketone) and curing with a metal halide lamp, and measuring the glass transition point using the DSC method (differential scanning calorimeter) described in JIS K7121 at a heating rate of 10°C/min.

Examples of polyfunctional polymerizable compounds include trimethylolpropane tri(meth)acrylate, 1,6-hexanediol di(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, polyalkylene glycol di(meth)acrylate, alkoxylated bisphenol A di(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, 1,4-butanediol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dimethyloltricyclodecane di(meth)acrylate, pentaerythritol tri(meth)acrylate, glycerin tri(meth)acrylate, and (meth)acrylates of these with different numbers of modifications, different types of modifications, and different structures.

The total content of the polyfunctional polymerizable compounds is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more, based on the total amount of the photopolymerizable compounds. By having the total content of the polyfunctional polymerizable compounds be 3% by mass or more based on the total amount of the photopolymerizable compounds, the curability of the cured film can be improved.

The total content of the polyfunctional polymerizable compounds is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more, based on the total amount of the photopolymerizable compounds. By having the total content of the polyfunctional polymerizable compounds be 3% by mass or more based on the total amount of the photopolymerizable compounds, the curability of the cured film can be improved.

The total content of the polyfunctional polymerizable compounds is preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less, based on the total amount of the photopolymerizable compounds. By having the total content of the polyfunctional polymerizable compounds be 35% by mass or less based on the total amount of the photopolymerizable compounds, the stretchability of the cured film can be improved.

[Photopolymerization initiator]
The yellow ink composition of this embodiment contains a photopolymerization initiator that is a hydrogen abstraction initiator. The hydrogen abstraction initiator is a photopolymerization initiator that excites hydrogen and generates radicals when irradiated with light.

The light may be any of far ultraviolet, ultraviolet, near ultraviolet, infrared, etc., as long as it is an energy ray capable of initiating a polymerization reaction of radicals, cations, anions, etc., but curing by ultraviolet irradiation is preferred in terms of the curing speed, availability of an irradiation device, cost, etc. As the hydrogen abstraction initiator, a conventionally known hydrogen abstraction initiator can be used. Specific examples of hydrogen abstraction initiators include aromatic ketones including thioxanthone, etc., α-aminoalkylphenones, α-hydroxyketones, aromatic onium salts, organic peroxides, thio compounds, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon-halogen bond, and alkylamine compounds. Among them, 2,4-diethylthioxanthen-9-one (thioxanthone-based photopolymerization initiator) and 4-benzoyl 4'-methyldiphenyl sulfide are preferred.

The amount of photopolymerization initiator in this embodiment may be any amount that can properly initiate the photopolymerization reaction of the photopolymerizable compound, and is preferably 1.0% by mass or more, and more preferably 3.0% by mass or more, based on the entire yellow ink composition. Also, it is preferably 20.0% by mass or less based on the entire yellow ink composition.

The content ratio of the photopolymerization initiator to the photopolymerizable compound is preferably 0.001 or more in terms of the mass ratio of photopolymerization initiator/photopolymerizable compound. By having the mass ratio of photopolymerization initiator/photopolymerizable compound of 0.001 or more, the curability of the cured film can be improved more effectively. The content ratio of the photopolymerization initiator to the photopolymerizable compound is preferably 0.1 or less in terms of the mass ratio of photopolymerization initiator/photopolymerizable compound. By having the mass ratio of polymerization initiator/photopolymerizable compound of 0.1 or less, the stretchability of the cured film can be improved more effectively.

The molecular weight of the photopolymerization initiator is preferably 1000 or less, more preferably 700 or less, and even more preferably 500 or less. The dispersibility of the photopolymerization initiator in the yellow ink composition is improved, and the photopolymerization initiator can be uniformly dispersed, so that the curability of the cured film becomes uniform throughout the entire cured film.

[Yellow colorants]
The yellow ink composition of this embodiment contains a yellow colorant. By containing a colorant, the cured film can be preferably used as a cured film for decoration. The colorant may be a dye, an inorganic pigment, or an organic pigment.

Specifically, a sample for absorbance evaluation is prepared by diluting the yellow colorant with ethyl diglycol acetate so that the concentration of the yellow colorant is 0.005%, and the absorbance, as defined by the following general formula at a wavelength of 395 nm, measured by irradiating the sample for absorbance evaluation with light is 1.54 or more. By having an absorbance of 1.54 or more at a wavelength of 395 nm, as defined by the general formula, the yellow ink composition has excellent color rendering properties.

A ₃₉₅ =-log ₁₀ (I/I ₀ )...(1)
(In formula (1), _A395 is the absorbance at a wavelength of 395 nm, _I0 is the incident light intensity at a wavelength of 395 nm, and I is the transmitted light intensity at a wavelength of 395 nm.)

If the absorbance of the sample for evaluating absorbance made from a yellow colorant is 1.54 or more, the yellow ink composition containing the yellow colorant is a yellow ink composition with excellent color rendering.

Specific examples of such yellow colorants include at least one selected from the group consisting of Pigment Yellow 155 (absorbance: 2.46), Pigment Yellow 120 (absorbance: 1.96), Pigment Yellow 151 (absorbance: 2.08), Pigment Yellow 154 (absorbance: 1.52), and C.I. Pigment Yellow 180 (absorbance: 2.32). The absorbance in parentheses is the absorbance of the sample for absorbance evaluation at a wavelength of 395 nm.

The absorbance defined by the general formula at a wavelength of 395 nm is preferably 1.54 or more, more preferably 1.60 or more, even more preferably 1.80 or more, and even more preferably 2.00 or more.

When a pigment is used as the yellow colorant in the yellow ink composition of this embodiment, the preferred dispersed particle size of the pigment is preferably 10 nm or more in terms of the volume average particle size measured by the laser scattering method. The preferred dispersed particle size of the pigment in the yellow ink composition of this embodiment is preferably 300 nm or less in terms of the volume average particle size measured by the laser scattering method. By setting the volume average particle size to 10 nm or more, 300 nm or less, or 10 nm or more and 300 nm or less, it is possible to maintain light resistance, and it is possible to stabilize the dispersion, which makes it possible to reduce the possibility of pigment settling and head clogging or deflection when ejecting the yellow ink composition in a recording device, thereby making it possible to make a more preferred yellow ink composition.

In this embodiment, when a pigment is used, its content may be adjusted as appropriate. Although it varies depending on the type of pigment, the content of the pigment in the total amount of the yellow-based ink composition is preferably 0.1% by mass or more, and more preferably 0.2% by mass or more, in the case of an organic pigment, in order to achieve both dispersibility and coloring power. Also, in the case of an organic pigment, it is preferably 20.0% by mass or less, and more preferably 10.0% by mass or less, in order to achieve both dispersibility and coloring power.

[Dispersant]
The yellow ink composition of this embodiment may contain a dispersant as necessary. Examples of dispersants include polymer dispersants. The main chain of this polymer dispersant is made of polyester, polyacrylic, polyurethane, polyamine, polycaprolactone, or the like, and the polymer dispersant preferably has a polar group such as an amino group, a carboxyl group, a sulfone group, or a hydroxyl group, or a salt thereof, as a side chain.

Preferred polymeric dispersants are polyester-based dispersants, and specific examples include Solsperse 33000, Solsperse 32000, and Solsperse 24000 manufactured by Lubrizol Japan; Disperbyk168, BYKJET-9150, BYKJET-9151, and BYKJET-9152 manufactured by BYK-Chemie; Ajisper PB821 manufactured by Ajinomoto Fine-Techno Co., Ltd.; and TEGO Dispers 685 manufactured by Evonik Japan.

[Surface conditioner]
The yellow ink composition of this embodiment may further contain a surface conditioner. The surface conditioner is not particularly limited, but specific examples include dimethylpolysiloxane-containing products manufactured by BYK-Chemie KK, such as "BYK-306", "BYK-333", "BYK-371", "BYK-377", "BYK-UV3570", and "BYK-UV3500", and products manufactured by Evonik Degussa Japan Ltd., such as "TegoRad2010", "TegoRad2100", "TegoRad2200N", and "TegoRad2300".

The content of the surface conditioner is preferably 0.1% by mass or more based on the total amount of the yellow-based ink composition. The content of the surface conditioner is preferably 5.0% by mass or less based on the total amount of the yellow-based ink composition. By setting the content to 0.1% by mass or more or 5.0% by mass or less, the yellow-based ink composition has favorable wettability with respect to thermoplastic resin substrates and the like, and when recording (forming an image) on the substrate, the yellow-based ink composition can wet and spread without causing repelling, making it possible to make a particularly favorable yellow-based ink composition.

[Matting agent]
The yellow ink composition of this embodiment may contain a matting agent as necessary. As the matting agent, for example, various powders such as silica, alumina, calcium carbonate, etc. The matting agents may be used alone or in combination of two or more kinds.

[Other additives]
The yellow ink composition of this embodiment may further contain various other additives such as a plasticizer, a polymerization inhibitor, a light stabilizer, an antioxidant, etc. A solvent may also be added within the range in which the object of the present invention can be achieved.

In addition, from the viewpoint of inkjet ejection properties and ejection stability, the surface tension of the yellow ink composition of this embodiment is preferably 20 mN/m or more at 40°C. In addition, the surface tension at 40°C is preferably 40 mN/m or less.

<Dispersion>
The dispersion liquid of this embodiment is a dispersion liquid used in the yellow ink composition of the above embodiment. Specifically, it contains a photopolymerizable compound and, if necessary, a colorant, but does not contain a photopolymerization initiator. The dispersion liquid of this embodiment is a dispersion liquid in a preliminary stage of the production of the yellow ink composition of the above embodiment. In addition, except for the photopolymerization initiator, the photopolymerizable compound, colorant, dispersant, surface conditioner, matting agent, and various additives contained in the dispersion liquid are the same as those in the yellow ink composition of the above embodiment. By using the dispersion liquid of this embodiment, the yellow ink composition of the above embodiment can be produced.

<Method of producing yellow ink composition>
The method for producing the yellow ink composition of this embodiment is not particularly limited, and a conventionally known method can be used. When a granular colorant, granular matting agent, or the like is used, the yellow ink composition of this embodiment is obtained by dispersing the colorant, the photopolymerizable compound, the photopolymerization initiator, the dispersant, and the like using a dispersing machine, and then adding a surface conditioner, etc., as necessary, and stirring uniformly, and further filtering with a filter.

<Method of manufacturing laminate>
The laminate of this embodiment is produced by printing the yellow ink composition onto a substrate, preferably by inkjet printing, and then curing the composition with light. Printing can be performed by a conventionally known method such as offset printing, gravure printing, spraying, or brushing, but inkjet printing is preferred in terms of its ability to handle small lots and a wide variety of products. When printing by inkjet printing, the inkjet head may be heated or may be left at room temperature.

The yellow ink composition of this embodiment can be used to form images on a substrate. For example, various images can be formed on a substrate by preparing an ink set of ink compositions each containing coloring materials of various hues, printing using an inkjet method, and then curing the ink compositions. The ink composition that forms such a cured film and the image forming method that forms an image on a substrate are also within the scope of the present invention. In this specification, the term "image" refers to a decorative image that can be recognized visually, including characters, diagrams, figures, symbols, photographs, etc., consisting of a single color or multiple colors, and also includes, for example, patterns consisting of wood grain, stone grain, cloth grain, sand grain, geometric patterns, and characters.

[Base material]
The substrate is not particularly limited, and any absorbent such as coated paper, uncoated paper, or cloth, or non-absorbent substrate can be used. Specifically, examples of uncoated paper include saw paper, medium-quality paper, and fine paper; examples of coated paper include coated paper, art paper, cast paper, light-weight coated paper, and lightly coated paper; examples of absorbent such as cloth include cotton, chemical fiber fabric, silk, hemp, cloth, nonwoven fabric, and leather; examples of non-absorbent substrates include polyester resin, polypropylene synthetic paper, vinyl chloride resin, polyimide resin, metal, metal foil coated paper, glass, synthetic rubber, and natural rubber. In addition, the ink composition of the present embodiment is not limited to the case where a substrate having no flexibility such as metal is used as the recording medium, and even when a substrate having flexibility is used as the recording medium, cracking of the cured film caused by bending of the substrate having flexibility can be effectively suppressed. Incidentally, "having flexibility" means that it is possible to bend the material to a radius of curvature of usually 1 m at room temperature, preferably 50 cm, more preferably 30 cm, further preferably 10 cm, and particularly preferably 5 cm.

[Light curing]
The light beam for forming a cured film (hereinafter, sometimes referred to as "cured film") obtained by curing an ink composition including the yellow-based ink composition of this embodiment is preferably a light beam containing light having a wavelength of 385 nm or more and 395 nm or less irradiated from a light source. Incidentally, "light having a wavelength of 385 nm or more and 395 nm or less" may be light containing light having a wavelength of less than 385 nm and/or light having a wavelength of more than 395 nm. "Light containing light having a wavelength of 385 nm or more and 395 nm or less" is preferably 30% or more of the total light beam, more preferably 50% or more, even more preferably 70% or more, and even more preferably 90% or more. In this specification, the term "cured film" does not mean only a yellow-based cured film obtained by curing only a yellow-based ink composition. The term "yellow-based cured film" includes a yellow-based cured film obtained by curing only a yellow-based ink composition, but also includes a cured film obtained by curing an ink set of a plurality of ink compositions including a yellow-based ink composition (for example, an ink set including YMCK inks and/or white inks).

The light source is not particularly limited, and examples thereof include a high-pressure mercury lamp, a metal halide lamp, a low-pressure mercury lamp, an ultra-high-pressure mercury lamp, an ultraviolet laser, sunlight, an LED, etc. By using these light sources and irradiating light so that the integrated light amount is 100 mJ/ ^cm2 or more, preferably 200 mJ/cm2 or ^more , the yellow-based ink composition can be instantaneously cured.

From the viewpoint of energy saving, high degree of freedom in designing the printing device, and production efficiency, it is more preferable to use an LED as the light source. In particular, since the yellow ink composition of this embodiment is an ink composition that can form a cured film having curability, even an LED with a relatively small irradiation energy can effectively cure the ink composition.

The light source may be any light source that excites hydrogen with the photopolymerization initiator described above to generate radicals. The light may be any energy ray, such as far ultraviolet, ultraviolet, near ultraviolet, or infrared, as long as it is capable of initiating polymerization reactions of radicals, cations, anions, etc. However, curing by ultraviolet irradiation is preferred from the standpoint of curing speed, availability of light sources, cost, etc.

[Cured film]
A cured film is obtained by polymerizing the yellow ink composition of the present embodiment described above by light. The thickness of the cured film is preferably 1 μm or more. Also, the thickness of the cured film is preferably 100 μm or less. By making the thickness 1 μm or more, the color density of the cured film containing the coloring material is not reduced, and the design and decorativeness are improved, and physical properties such as adhesion and extensibility are improved, which is more preferable. By making the thickness 100 μm or less, the ink composition can be sufficiently cured in a shorter time when the ink composition is irradiated with light, which is more preferable.

The thickness of the cured film can be measured by applying the yellow ink composition of this embodiment to a PET film (A4300, manufactured by Toyobo Co., Ltd.) under the same application conditions as for the prepared cured film, and measuring the thickness of the obtained cured film with a micrometer. In this specification, the thickness of the cured film is measured by measuring 10 points per sample, and the average of these is taken as the thickness (average thickness). The same applies to the protective layer and primer described below.

An image can also be formed by an ink set of a plurality of ink compositions including a yellow-based ink composition. Furthermore, by adjusting conditions such as the amount of ink composition ejected and the time from ejection of the ink composition to irradiation with light, the thickness of the cured film can be intentionally made uneven to form a relief image with relief. Specifically, relief can be imparted by increasing or decreasing the amount of ejection depending on the ejection location, or relief differences can be imparted from other locations by repeating the ejection of the ink composition and irradiation with light at the same location. Such an image forming method for forming an image and/or relief image on a substrate and a method for manufacturing a printed matter are also within the scope of the present invention. It is preferable to form such relief images by the inkjet method because the conditions can be easily adjusted.

[Other layers]
An overcoat layer for protecting the cured film formed by the yellow ink composition of this embodiment may be provided on the surface of the cured film. This overcoat layer may be formed using a conventionally known overcoat composition, or a clear ink composition to which no coloring material is added in the yellow ink composition of this embodiment may be used as the composition for the overcoat layer.

The cured film formed by the yellow ink composition of this embodiment may be provided with a primer layer in order to improve adhesion to the substrate. This primer layer may be formed using a conventionally known primer composition, or a clear ink composition to which no coloring material is added may be used as the composition for the primer layer in the yellow ink composition of this embodiment.

When forming an overcoat layer and/or a primer layer on a substrate, any method may be used to form these layers, such as spray application, application using a towel, sponge, nonwoven fabric, tissue, etc., dispenser application, brush application, gravure printing, flexographic printing, silk screen printing, inkjet printing, thermal transfer printing, etc.

The overcoat layer is not limited to being formed on the surface of a layer made of a cured film of an ink composition, but may be formed directly on the surface of the substrate, or may be formed on the surface of a primer layer formed on the surface of the substrate.

The thickness of the overcoat layer is preferably 1 μm or more. By making it 1 μm or more, it is preferable because the cured film can be adequately protected. In addition, the thickness of the overcoat layer is preferably 100 μm or less. By making it 100 μm or less, the drying time for forming the overcoat layer is shortened, and it is preferable because it is possible to achieve excellent productivity.

In addition, by adjusting conditions such as the amount of ink composition ejected when forming the overcoat layer and the time between ejecting the ink composition and irradiating the light, it is possible to impart unevenness to the overcoat layer.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these descriptions in any way.

<Preparation of Ink Composition>
Table 1 shows the parts by mass of the photopolymerizable compound, photopolymerization initiator, polymerization inhibitor, polymer dispersant, additives, and pigment (pigment dispersion) in the total amount of the ink composition in the examples, comparative examples, and reference examples.

In Table 1, TMCHA stands for "3,3,5-trimethylcyclohexyl acrylate" with a Tg of 52°C (corresponding to a monofunctional polymerizable compound).

In Table 1, DPHA stands for "dipentaerythritol hexaacrylate" (corresponding to a multifunctional photopolymerizable compound).

In Table 1, 1,6HDA is "1,6-hexanediol diacrylate" (corresponding to a multifunctional photopolymerizable compound).

In Table 1, TMPTA stands for "trimethylolpropane triacrylate" (corresponding to a multifunctional photopolymerizable compound).

In Table 1, "Genomer 5271 (amine acrylate)" is a polymerizable compound A that has a repeating sequence with a structure containing an amino group and an ether group and has two or more (meth)acrylate groups.

In Table 1, "gamma-butyrolactone" is a water-soluble organic solvent.

In Table 1, "JRCURE TPO" is diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (molecular weight: 348.37), a photopolymerization initiator.

In Table 1, "DETX" is 2,4-diethylthioxanthone (molecular weight 268.3), a hydrogen abstraction type photopolymerization initiator.

In Table 1, "SpeedCURE BMS" is 4-benzoyl 4'-methyldiphenyl sulfide (molecular weight 304.41), a photopolymerization initiator.

In Table 1, "ANTAGE TDP" is phenothiazine (manufactured by Kawaguchi Chemical Industry Co., Ltd.), a polymerization inhibitor.

In Table 1, "BYK-UV3570" refers to BYK-UV3570 (polyester-modified polydimethylsiloxane solution (active ingredient 70%)) manufactured by BYK Japan, a surfactant.

In Table 1, "Ye (PY155) base D/P=0.5, Pig 12% (TBCH)" is a yellow mill base made by adding TBCH (4-(1,1-dimethylethyl acrylate) so that the dispersant/pigment ratio of yellow pigment (Pigment Yellow 155) is 0.5 and the yellow pigment is 12%, and then dispersing it with a paint shaker (manufactured by Asada Iron Works Co., Ltd.).

A sample for absorbance evaluation was created by diluting "Ye (PY155) base D/P = 0.5, Pig 12% (TBCH)" with ethyl diglycol acetate so that the concentration of Pigment Yellow 155 was 0.005%. The absorbance of the sample for absorbance evaluation was measured at a wavelength of 395 nm and was found to be 2.46.

In Table 1, "Ye (PY150) base D/P=0.5, Pig 12% (TBCH)" refers to a yellow mill base made by adding TBCH (4-(1,1-dimethylethyl acrylate) so that the dispersant/pigment ratio of yellow pigment (Pigment Yellow 150) is 0.5 and the yellow pigment is 12%, and then dispersing using a paint shaker (manufactured by Asada Iron Works Co., Ltd.).

A sample for absorbance evaluation was prepared by diluting "Ye (PY150) base D/P = 0.5, Pig 12% (TBCH)" with ethyl diglycol acetate so that the concentration of Pigment Yellow 150 was 0.005%. The absorbance of the sample for absorbance evaluation was measured at a wavelength of 395 nm and found to be 0.96.

<Odor test>
An odor test was carried out on the ink compositions of the Examples, Comparative Examples, and Reference Examples. Specifically, the ink composition was diluted with polyethylene glycol (ink composition:polyethylene glycol=1:1000), and five subjects were asked to smell it and perform a sensory evaluation. If the majority of the subjects judged it to have "no odor", it was marked as "○", and if the majority of the subjects judged it to have "unpleasant odor" or "slight odor", it was marked as "×" (in the table, it is marked as "odor"). The measurement results are shown in Table 1.

[Production of Laminate]
A laminate was produced using vinyl chloride having a thickness of 80 μm as a substrate. Each evaluation sample consisting of a cured film was produced on the surface of the substrate by the inkjet method using the ink composition shown in Table 1. Then, the ink composition was cured with an integrated light amount of 240 mJ using a UV-LED lamp (wavelength 395 nm). The integrated light amount and peak illuminance were measured using an ultraviolet light meter UV Power Puck 2 (manufactured by EIT Corporation). In this way, a cured film was produced.

<Ejection test>
The surface of the cured film was visually inspected to evaluate the ink compositions of the Examples and Comparative Examples. When thin lines were correctly reproduced, it was marked with "○", when slight curvature was observed, it was marked with "△", and when the landing position was shifted and curvature was observed, it was marked with "×" (in the table, this is indicated as "ejection property").

<Curability test>
Curability was evaluated by rubbing the cured film with a cotton swab after curing to check for color transfer. The results are shown in Table 1. The case where no color transfer was observed with the cotton swab was marked with "○", the case where almost no color transfer was observed with the cotton swab was marked with "△", and the case where color transfer was observed with the cotton swab and substantially exceeded the allowable range was marked with "×" (indicated as "curability" in the table).

<Evaluation Results>
From Table 1, it can be seen that the ink compositions of Examples 1 to 6, which contain a yellow colorant with high absorbance at a specified wavelength (395 nm), are ink compositions capable of forming a cured film with excellent curability.

On the other hand, the ink composition of Comparative Example 1 has a repeating sequence having a structure containing an amino group and an ether group, does not contain a polymerizable compound A having two or more (meth)acrylate groups, and is therefore unable to form a cured film with sufficient curability.

In addition, the ink composition of Comparative Example 2 does not contain a hydrogen abstraction type photopolymerization initiator, and is therefore unable to form a cured film with sufficient curability.

The ink compositions of Reference Examples 1 to 3 were able to form cured films with excellent curability, but they contained Pigment Yellow 150 as a yellow colorant and did not contain any yellow colorant with an absorbance of 1.54 or more at a wavelength of 395 nm. Therefore, it is presumed that these ink compositions do not have high color rendering properties compared to the ink compositions of Examples 1 to 6.

On the other hand, Reference Example 2 has the same composition as Comparative Example 1 except for the yellow colorant, and Reference Example 3 has the same composition as Comparative Example 2 except for the yellow colorant, but Reference Examples 2 and 3 have good cured films, unlike Comparative Examples 1 and 2. From this, it can be seen that the decrease in curability cited as a problem of the present invention occurs only in the case of a yellow ink composition containing a predetermined yellow colorant that has a high absorbance of light of a predetermined wavelength, such as C.I. Pigment Yellow 155.

Claims (7)

A yellow-based ink composition that is cured by light, the yellow-based ink composition comprising a photopolymerizable compound, a photopolymerization initiator, and a yellow-based colorant,
a sample for evaluating absorbance is prepared by diluting the yellow colorant with ethyl diglycol acetate so that the concentration of the yellow colorant is 0.005%, and the sample for evaluating absorbance is irradiated with light to measure the absorbance, the absorbance being 1.54 or more at a wavelength of 395 nm as defined by the following general formula:
A ₃₉₅ =-log ₁₀ (I/I ₀ )...(1)
(In formula (1), _A395 is the absorbance at a wavelength of 395 nm, _I0 is the incident light intensity at a wavelength of 395 nm, and I is the transmitted light intensity at a wavelength of 395 nm.)
The photopolymerizable compound includes a polymerizable compound A,
the polymerizable compound A is an amine(meth)acrylate compound having a repeating sequence having a structure containing an amino group and an ether group, and having two or more (meth)acrylate groups that are polymerizable by light,
the photopolymerizable compound further contains a monofunctional polymerizable compound that is a (meth)acrylate compound having a (meth)acrylate group that is polymerized by light, and the glass transition temperature Tg of the polymer obtained by polymerization is 25° C. or more and 60° C. or less, in a proportion of 54.0% by mass or more based on the total amount of the ink composition;
The yellow ink composition, wherein the photopolymerization initiator contains at least a hydrogen abstraction type initiator. The yellow ink composition according to claim 1, wherein the yellow colorant includes at least one selected from the group consisting of C.I. Pigment Yellow 155, C.I. Pigment Yellow 120, C.I. Pigment Yellow 151, C.I. Pigment Yellow 154, and C.I. Pigment Yellow 180. The yellow ink composition according to claim 1 or 2, wherein the molecular weight of the photopolymerization initiator is 1000 or less. The yellow ink composition according to claim 1 , which is cured by exposure to light having a wavelength of 385 nm or more and 395 nm or less. A laminate comprising a substrate and a cured ink film layer, the cured ink film layer being the yellow ink composition according to claim 1 . An image forming method for forming an image and/or a relief image on a substrate, using the yellow ink composition according to any one of claims 1 to 4 . A method for producing a printed matter by forming an image and/or a relief image on a substrate using the yellow ink composition according to any one of claims 1 to 4 .