Active energy ray-curable ink composition, artificial leather, and inkjet printing method

Abstract

To provide an active energy ray-curable ink composition using a thiol-ene reaction, capable of forming a coating film having strength sufficient for a flexible material such as an artificial leather, and capable of inkjet printing.SOLUTION: An active energy ray-curable ink composition contains a polyfunctional thiol compound (A), a bifunctional monomer (B), a radical cyclopolymerizable monomer (C), and a photoinitiator (D). The thiol compound (A) has viscosity of 40-3,000 mPa s at 25°C. The bifunctional monomer (B) has two reactive groups including a vinyl group and at least one of the reactive group is an acrylic group. A glass-transition temperature of a homopolymer of the bifunctional monomer (B) is 65-150°C.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an active energy ray-curable ink composition. The present invention also relates to an artificial leather having a cured coating film of the active energy ray-curable ink composition. The present invention further relates to an inkjet printing method using the active energy ray-curable ink composition. [Background technology]

[0002] In recent years, printing methods using inkjet recording systems have become widespread because they allow easy printing and are suitable for on-demand printing, and are also adopted for printing on substrates other than paper (e.g., artificial leather). Since artificial leather is a low-absorbency / non-absorbency substrate, an active energy ray-curable ink composition is suitable for inkjet printing on artificial leather.

[0003] Active energy ray-curable ink compositions typically utilize radical polymerization of a (meth)acrylate compound. However, while this radical polymerization enables the ink coating to be cured in a short time, it has the disadvantages of a low reaction rate and being affected by oxygen inhibition. On the other hand, active energy ray-curable ink compositions utilizing a thiol-ene reaction are known (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-218447 A [Patent Document 2] JP 2012-167246 A Summary of the Invention [Problem to be solved by the invention]

[0005] Artificial leather is a flexible substrate. The cured coating film of the active energy ray curable ink composition utilizing the thiol-ene reaction contains sulfur atoms and therefore has high bending resistance. Therefore, it is considered that the active energy ray curable ink composition is suitable for printing on flexible substrates such as artificial leather. Therefore, the present inventors have conducted extensive research into the application of the active energy ray curable ink composition utilizing the thiol-ene reaction to inkjet printing on artificial leather. As a result, it has been found that there are problems with the active energy ray curable ink composition utilizing the thiol-ene reaction, such as the difficulty in preparing an active energy ray curable ink composition having a viscosity that can be discharged by the inkjet method, and the difficulty in forming a cured coating film with sufficient strength.

[0006] The present invention has been made in consideration of the above-mentioned points, and an object of the present invention is to provide an active energy ray-curable ink composition that utilizes a thiol-ene reaction, which is capable of forming a coating film with sufficient strength on flexible materials such as artificial leather and is capable of being inkjet printed. [Means for solving the problem]

[0007] The active energy ray-curable ink composition according to the present invention contains a polyfunctional thiol compound (A), a bifunctional monomer (B), a radical cyclopolymerizable monomer (C), and a photopolymerization initiator (D). The thiol compound (A) has a viscosity of 40 mPa·s to 3000 mPa·s at 25°C. The bifunctional monomer (B) has two reactive groups containing a vinyl group, and at least one of the reactive groups is an acrylic group. The glass transition temperature of a homopolymer of the bifunctional monomer (B) is 65°C to 150°C.

[0008] From another aspect, the artificial leather according to the present invention includes a cured coating film of the above-mentioned active energy ray-curable ink composition.

[0009] From another aspect, an inkjet printing method according to the present invention includes a step of applying the above-mentioned active energy ray-curable ink composition to a substrate by an inkjet system to form a coating film of the active energy ray-curable ink composition, and a step of irradiating the coating film with active energy rays to cure it. Effect of the Invention

[0010] According to the present invention, it is possible to provide an active energy ray-curable ink composition that utilizes a thiol-ene reaction, and that is capable of forming a coating film with sufficient strength on flexible materials such as artificial leather and that is capable of being inkjet printed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The active energy ray-curable ink composition according to the present invention contains a polyfunctional thiol compound (A), a bifunctional monomer (B), a radical cyclopolymerizable monomer (C), and a photopolymerization initiator (D). The thiol compound (A) has a viscosity of 40 mPa·s to 3000 mPa·s at 25°C. The bifunctional monomer (B) has two reactive groups including a vinyl group, and at least one of the reactive groups is an acrylic group. The glass transition temperature of a homopolymer of the bifunctional monomer (B) is 65°C to 150°C. In this specification, the numerical range indicated by "A to B" includes A and B.

[0012] [Multifunctional thiol compound (A)] The polyfunctional thiol compound (A) is a thiol component for the thiol-ene reaction. When the polyfunctional thiol compound (A) has two or more mercapto groups (-SH groups), the curability of the active energy ray-curable ink composition can be improved, and the strength of the cured coating film of the active energy ray-curable ink composition can be increased. The number of mercapto groups that the polyfunctional thiol compound (A) has is preferably 2 to 6, more preferably 2 to 3, and even more preferably 3. That is, the polyfunctional thiol compound (A) is preferably bifunctional to hexafunctional, more preferably bifunctional to trifunctional, and even more preferably trifunctional.

[0013] The viscosity of the polyfunctional thiol compound (A) at 25°C is 40 mPa·s to 3000 mPa·s. By using a polyfunctional thiol compound (A) having such a viscosity, the viscosity of the active energy ray curable ink composition can be adjusted to a viscosity suitable for inkjet printing. The viscosity of the polyfunctional thiol compound (A) at 25°C is preferably 40 mPa·s to 1,000 mPa·s, more preferably 40 mPa·s to 600 mPa·s, and even more preferably 40 mPa·s to 200 mPa·s. The viscosity of the polyfunctional thiol compound (A) at 25°C can be measured using a rotational viscometer equipped with a cone plate (i.e., an E-type viscometer).

[0014] It is particularly preferable that the polyfunctional thiol compound (A) is a difunctional to tetrafunctional thiol compound, and that the viscosity of the polyfunctional thiol compound (A) at 25° C. is 40 mPa·s to 500 mPa·s.

[0015] The type of polyfunctional thiol compound (A) may be any polyfunctional thiol compound that satisfies the above viscosity, and is not particularly limited. Examples of polyfunctional thiol compounds (A) include trimethylolpropane tris(3-mercaptopropionate) (available as "TMMP" manufactured by SC Organic Chemical Industry Co., Ltd., viscosity at 25°C: about 150 mPa·s), trimethylolpropane tris(3-mercaptobutyrate) (available as "Kalends MT (registered trademark) TPMB" manufactured by Resonac Corporation), and pentaerythritol tetrakis(3-mercaptopropionate) (available as "PEMP" manufactured by SC Organic Chemical Industry Co., Ltd., viscosity at 25°C: about 500 mPa·s). ), pentaerythritol tetrakis(3-mercaptobutyrate) (available as "KarendsMT® PE1" from Resonac), tetraethylene glycol bis(3-mercaptopropionate) (available as "EGMP-4" from SC Organic Chemicals, viscosity at 25°C: approximately 50 mPa·s), 1,4-butanediol bis(3-mercaptopropionate) (available as "BDMP" from SC Organic Chemicals), trimethylolpropane dipropanethiol (available as "Multhiol" from SC Organic Chemicals, viscosity at 25°C: approximately 50 mPa·s from SC Organic Chemicals), Examples of suitable mercaptopropionate include pentaerythritol tripropanethiol (available as "Multhiol Y-2" manufactured by SC Organic Chemical Industries, Ltd., viscosity at 25° C.: about 60 mPa·s), pentaerythritol tetrapropanethiol (available as "Multhiol Y-4" manufactured by SC Organic Chemical Industries, Ltd., viscosity at 25° C.: about 100 mPa·s), dipentaerythritol hexakis(3-mercaptopropionate) (available as "DPMP" manufactured by SC Organic Chemical Industries, Ltd., viscosity at 25° C.: about 2200 to 3000 mPa·s), and 1,4-bis(3-mercaptobutyryloxy)butane (available as "KarenzMT (registered trademark) BD1" manufactured by Resonac Corporation).

[0016] Among these, trimethylolpropane tris(3-mercaptopropionate), tetraethylene glycol bis(3-mercaptopropionate), trimethylolpropane dipropanethiol, and pentaerythritol trippropanethiol are preferred, and trimethylolpropane tris(3-mercaptopropionate) is more preferred. These may be used alone or in combination of two or more.

[0017] The content of the polyfunctional thiol compound (A) may be appropriately set in consideration of the total amount (mol) of mercapto groups contained in the active energy ray curable ink composition and the total amount (mol) of double bonds contained in the active energy ray curable ink composition. The ratio of the total amount (mol) of double bonds contained in the active energy ray curable ink composition to the total amount (mol) of mercapto groups contained in the active energy ray curable ink composition [i.e., the ratio expressed as the total amount (mol) of double bonds contained in the active energy ray curable ink composition / the total amount (mol) of mercapto groups contained in the active energy ray curable ink composition] is preferably 0.5 to 2.0, more preferably 0.8 to 1.5, even more preferably 1.0 to 1.4, and particularly preferably 1.1 to 1.3.

[0018] In the active energy ray curable ink composition according to this embodiment, the thiol-ene reaction and the polymerization reaction compete with each other, but the thiol-ene reaction occurs much more predominantly. From the viewpoint of causing the thiol-ene reaction to occur more predominantly and from the viewpoint of the bending resistance of the obtained cured coating film, the content of the polyfunctional thiol compound (A) in the active energy ray curable ink composition according to this embodiment is preferably 35% by mass or more, more preferably 40% by mass or more, and even more preferably 42% by mass or more. On the other hand, from the viewpoint of the viscosity of the active energy ray curable ink composition according to this embodiment, the content of the polyfunctional thiol compound (A) in the active energy ray curable ink composition according to this embodiment is preferably 65% ​​by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less.

[0019] [Bifunctional Monomer (B)] The bifunctional monomer (B) is an ene component for the thiol-ene reaction. The bifunctional monomer (B) has two reactive groups containing a vinyl group. Examples of the reactive groups include an acrylic group, a vinyl ether group, an allyl group, and an allyl ether group. In the bifunctional monomer (B), at least one reactive group is an acrylic group. This can enhance the curability of the active energy ray-curable ink composition, and can also enhance the strength of the cured coating film of the active energy ray-curable ink composition.

[0020] In addition, the glass transition temperature (Tg) of the homopolymer of the bifunctional monomer (B) is 65°C to 150°C. Tg is the temperature at which the interaction between the segments in the molecule weakens and the segments in the molecule start to move in micro-Brownian motion when the polymer is heated (i.e., when thermal energy is applied to the polymer). Therefore, it is an index of the strength of the interaction between the segments in the molecule of the homopolymer of the bifunctional monomer (particularly, the segment between the two reactive groups of the bifunctional monomer). When the bifunctional monomer (B) has a Tg in the above range, the curability of the active energy ray-curable ink composition can be improved, and the strength of the cured coating film of the active energy ray-curable ink composition can be increased. The Tg of the homopolymer of the bifunctional monomer (B) can be determined by performing differential scanning calorimetry (DSC) measurement.

[0021] Examples of bifunctional monomers (B) include neopentyl glycol diacrylate (NPDA, homopolymer Tg: 117°C), nonanediol diacrylate (NDDA, homopolymer Tg: 68°C), and 2-(2-vinyloxyethoxy)ethyl acrylate (VEEA, homopolymer Tg: 91°C). These can be used alone or in combination of two or more. It is known that the Tg of the homopolymer of VEEA differs depending on the polymerization method because the reactivity of the two reactive groups differs. Here, the Tg of the homopolymer obtained by carrying out UV radical polymerization and UV cationic polymerization is used so that both reactive groups undergo polymerization reaction.

[0022] The homopolymer of the bifunctional monomer (B) preferably has a Tg of 66° C. or higher, more preferably 67° C. or higher. The homopolymer of the bifunctional monomer (B) preferably has a Tg of 140° C. or lower, more preferably 135° C. or lower, even more preferably 130° C. or lower, and particularly preferably 120° C. or lower.

[0023] From the viewpoint of storage stability of the actinic energy ray-curable ink composition according to the present invention, it is preferable that both of the two reactive groups of the bifunctional monomer (B) are acrylic groups. As the bifunctional monomer (B), NPDA and NDDA are particularly preferable.

[0024] The viscosity of the bifunctional monomer (B) at 25° C. is preferably 15 mPa·s or less, and more preferably 10 mPa·s or less. The viscosity of the bifunctional monomer (B) at 25° C. can be measured using an E-type viscometer.

[0025] It is particularly preferable that the ratio of the total amount (mol) of double bonds contained in the active energy ray-curable ink composition to the total amount (mol) of mercapto groups contained in the active energy ray-curable ink composition according to the present invention is 0.8 to 1.5, and the molar ratio of the radical cyclic polymerizable monomer (C) to the bifunctional monomer (B) is 0.7 to 1.5.

[0026] The content of the bifunctional monomer (B) in the active energy ray-curable ink composition is preferably 15% by mass to 40% by mass, and more preferably 20% by mass to 38% by mass.

[0027] [Radical cyclopolymerizable monomer (C)] Cyclopolymerization is a reaction in which a monomer containing two appropriately positioned radically polymerizable groups is polymerized, resulting in the formation of rings in the polymer backbone by alternating intermolecular and intramolecular reactions. Thus, the radically cyclopolymerizable monomer (C) has two radically polymerizable groups and is the ene component for the thiol-ene reaction.

[0028] While the polyfunctional thiol compound (A) has a high viscosity, the radical cyclopolymerizable monomer (C) has an extremely low viscosity (for example, the viscosity of methyl α-allyloxymethylacrylate at 25°C is 1.57 mPa·s), and therefore also plays a role in significantly reducing the viscosity of the active energy beam-curable ink composition to make it suitable for inkjet printing. In addition, the homopolymer of the radical cyclopolymerizable monomer (C) has a ring structure due to cyclization during polymerization, and therefore has a high Tg (for example, the Tg of the homopolymer of methyl α-allyloxymethylacrylate is 84°C), which contributes to improving the strength of the cured coating film of the active energy beam-curable ink composition.

[0029] Examples of radical cyclic polymerizable monomers include α-(unsaturated alkoxyalkyl)acrylates such as α-allyloxymethyl methyl acrylate (AOMA), α-allyloxymethyl ethyl acrylate, and α-allyloxyethyl methyl acrylate. These can be used alone or in combination of two or more. Among them, AOMA is preferred.

[0030] The Tg of the homopolymer of the radical cyclopolymerizable monomer (C) is preferably 10° C. or higher, more preferably 60° C. to 200° C., and further preferably 80° C. to 180° C. The Tg of the homopolymer of the radical cyclopolymerizable monomer (C) can be determined by DSC measurement.

[0031] The viscosity of the radical cyclopolymerizable monomer (C) at 25° C. is preferably 5.0 mPa s or less, more preferably 3.0 mPa s or less, and further preferably 2.0 mPa s or less. The viscosity of the radical cyclopolymerizable monomer (C) at 25° C. can be measured using an E-type viscometer.

[0032] It is particularly preferable that the radical cyclopolymerizable monomer (C) is an α-(unsaturated alkoxyalkyl)acrylate, and that the viscosity of the radical cyclopolymerizable monomer (C) at 25° C. is 5.0 mPa·s or less.

[0033] Regarding the proportion of the bifunctional monomer (B) and the radical cyclopolymerizable monomer (C) used, the higher the molar ratio of the radical cyclopolymerizable monomer (C) to the bifunctional monomer (B), the higher the abrasion resistance. Therefore, the molar ratio of the radical cyclopolymerizable monomer (C) to the bifunctional monomer (B) is preferably 0.5 to 3.0, more preferably 0.8 to 2.0, and even more preferably 1.0 to 1.5.

[0034] The content of the radical cyclopolymerizable monomer (C) in the active energy ray-curable ink composition is preferably 10% by mass to 35% by mass, and more preferably 12% by mass to 30% by mass.

[0035] [Photopolymerization initiator (D)] The photopolymerization initiator (D) is a component that generates radicals by irradiation with active energy rays to initiate polymerization. However, in the present invention, the radicals generated by the photopolymerization initiator (D) by irradiation with active energy rays are utilized in the thiol-ene reaction. The active energy rays are, for example, ultraviolet rays, electron beams, α rays, β rays, γ rays, X-rays, etc., and preferably ultraviolet rays. The photopolymerization initiator (D) may be either an intramolecular bond cleavage type or an intramolecular hydrogen abstraction type, and the intramolecular cleavage type is preferred.

[0036] As the photopolymerization initiator (D), a known initiator used in an active energy ray-curable ink composition may be used. Examples of the initiator include an acylphosphine oxide-based initiator, an acetophenone-based initiator, a benzoin-based initiator, a benzophenone-based initiator, and a thioxanthone-based initiator.

[0037] Acylphosphine oxide-based polymerization initiators are preferred because they have particularly high curability, and examples thereof include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, and ethylphenyl(2,4,6-trimethylbenzoyl)phosphinate. Among these, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide and 2,4,6-trimethylbenzoyldiphenylphosphine oxide are preferred. The photopolymerization initiator (D) can be used alone or in combination of two or more.

[0038] The content of the photopolymerization initiator (D) in the active energy ray-curable ink composition may be appropriately determined depending on the type of the photopolymerization initiator (D). The content of the photopolymerization initiator (D) in the active energy ray-curable ink composition is, for example, 0.1% by mass to 15% by mass, preferably 0.5% by mass to 10% by mass, and more preferably 1.0% by mass to 5.0% by mass.

[0039] [Optional ingredients] The active energy ray-curable ink composition of the present invention may contain components other than those described above (hereinafter also referred to as "optional components") within the range that does not significantly impair the effects of the present invention.

[0040] Examples of optional components include ultraviolet absorbers. Examples of ultraviolet absorbers include benzotriazole (BTZ)-based ultraviolet absorbers (e.g., "CHIGUARD5530" manufactured by Chitech Co., Ltd., "RIASORB UV-928" manufactured by Lianglong Japan Co., Ltd., etc.), malonic acid ester-based ultraviolet absorbers, oxalic acid anilide-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, and hydroxyphenyltriazine (HPT)-based ultraviolet absorbers.

[0041] An example of an optional component is a light stabilizer. As the light stabilizer, a NOR type hindered amine light stabilizer (e.g., bis(1-undecaneoxy-2,2,6,6-tetramethylpiperidin-4-yl)carbonate, etc.) is preferred because it has very little adverse effect on the properties of the active energy ray-curable ink composition according to the present invention.

[0042] An example of an optional component is a surface conditioner. As the surface conditioner, a polyether-based surface conditioner or a polysiloxane-based surface conditioner is preferred because they have very little adverse effect on the properties of the actinic energy ray-curable ink composition according to the present invention.

[0043] An example of an optional component is a polymerization inhibitor. As the polymerization inhibitor, a known one used in an active energy ray curable ink composition can be used. When the bifunctional monomer (B) has a vinyl ether group as a reactive group, it is advantageous to use a nitroso-based polymerization inhibitor (e.g., n-nitrosophenylhydroxylamine aluminum salt, etc.).

[0044] An example of an optional component is a coloring material. Thus, the active energy ray curable ink composition of the present invention can be used as a clear ink that does not contain a coloring material, but the active energy ray curable ink composition of the present invention may contain a coloring material. The coloring material may be a pigment or a dye. The pigment may be either an inorganic pigment or an organic pigment. The pigment and dye may be any of those known to be used in active energy ray curable ink compositions. The coloring material may be used alone or in combination of two or more kinds.

[0045] Other optional components include organic solvents, antioxidants, pH adjusters, bactericides, preservatives, deodorants, charge control agents, wetting agents, and the like.

[0046] [Characteristics of active energy ray-curable ink composition] In order for the active energy ray curable ink composition to be inkjet printable, its viscosity at 25°C must be 20 mPa·s or less. Therefore, the active energy ray curable ink composition of the present invention may have a viscosity of 20 mPa·s or less at 25°C, and may further have a viscosity of 18 mPa·s or less, and further may have a viscosity of 16 mPa·s or less. The viscosity of the active energy ray curable ink composition of the present invention at 25°C may be 5 mPa·s or more. Therefore, the active energy ray curable ink composition of the present invention is inkjet printable and can be suitably used as an inkjet ink. It can also be used in printing methods other than inkjet printing. The viscosity of the active energy ray curable ink composition of the present invention at 25°C can be measured using an E-type viscometer.

[0047] The active energy ray-curable ink composition of the present invention can form a cured coating film with sufficient strength on flexible materials such as artificial leather. This high-strength cured coating film has abrasion resistance. Therefore, the active energy ray-curable ink composition of the present invention can impart abrasion resistance to flexible materials such as artificial leather. Artificial leather is a material obtained by impregnating a nonwoven fabric made of microfibers such as nylon or polyester with a synthetic resin (e.g., urethane resin, etc.), or a material obtained by using the nonwoven fabric impregnated with a synthetic resin as a substrate and coating the surface of the substrate with a synthetic resin (e.g., urethane resin, vinyl chloride resin, etc.).

[0048] Examples of flexible materials other than artificial leather include synthetic leather, which uses a woven or knitted fabric made of natural fibers, nylon fibers, polyester fibers, etc. as a base material and has a synthetic resin applied to the surface of the base material; recycled leather, which is made by crushing cut scraps generated during the manufacturing process of natural leather, solidifying them into sheets, and applying a surface coating; polyurethane sheets; and polyvinyl chloride sheets.

[0049] [Uses of active energy ray-curable ink composition] By forming a cured coating film of the active energy ray curable ink composition according to the present invention on a substrate such as artificial leather, it is possible to impart abrasion resistance. Therefore, the active energy ray curable ink composition according to the present invention is suitable for overprint varnish (OPV), and is particularly suitable for OPV of artificial leather. When the active energy ray curable ink composition according to the present invention is used as an OPV, the active energy ray curable ink composition according to the present invention may be a clear ink that does not contain a coloring material.

[0050] Alternatively, the active energy ray-curable ink composition according to the present invention may be used for decorating artificial leather or the like, with or without containing a coloring material.

[0051] From another aspect, the present invention provides an artificial leather having a cured coating film of an active energy ray-curable ink composition. The active energy ray-curable ink composition is preferably an overprint varnish.

[0052] From another aspect, the present invention provides an inkjet printing method including a step of applying the above-mentioned active energy ray-curable ink composition to a substrate by an inkjet system to form a coating film of the active energy ray-curable ink composition (hereinafter also referred to as an "application step"), and a step of irradiating the coating film with active energy rays to cure it (hereinafter also referred to as an "irradiation step").

[0053] The coating process will be described. A suitable example of the substrate is artificial leather, but the substrate is not limited thereto. The substrate may be a substrate as flexible as artificial leather, such as synthetic leather, recycled leather, a polyurethane sheet, or a polyvinyl chloride sheet.

[0054] The active energy ray curable ink composition has a viscosity suitable for inkjet printing, even though it uses a polyfunctional thiol compound (A). Therefore, the coating step can be performed using a known inkjet recording device. Specifically, for example, the active energy ray curable ink composition is loaded into a known inkjet recording device. Coating is performed by ejecting the active energy ray curable ink composition in the form of fine droplets from the inkjet head of the inkjet recording device onto the surface of the substrate. This makes it possible to form a coating film of the active energy ray curable ink composition on the substrate. Note that the active energy ray curable ink composition or the substrate may be preheated before coating.

[0055] Next, the irradiation step will be described. The active energy rays used in the irradiation step include, for example, ultraviolet rays, electron beams, α rays, β rays, γ rays, X-rays, etc., and preferably ultraviolet rays. The ultraviolet rays are energy rays with a wavelength of 10 nm to 400 nm, and the ultraviolet rays are preferably UV-A with a wavelength of 315 nm to 400 nm. Therefore, it is preferable to appropriately select a photopolymerization initiator that initiates polymerization at this wavelength as the photopolymerization initiator (D) of the active energy ray-curable ink composition.

[0056] The coating film can be irradiated with active energy rays by a known method. Specifically, it can be irradiated with a known active energy ray irradiator used for curing active energy ray curable ink compositions. The amount of irradiation with active energy rays can be appropriately determined according to the type and amount of the photopolymerization initiator (D) as in the past.

[0057] This allows a cured coating film of the active energy ray-curable ink composition to be formed on the substrate. This allows the substrate to be provided with scratch resistance and decoration. The active energy ray-curable ink composition is preferably used as an OPV. EXAMPLES

[0058] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0059] <Examples 1 to 3 and Comparative Examples 1 to 16> [Preparation of active energy ray curable ink] As a polyfunctional thiol compound, trifunctional thiol, trimethylolpropane tris(3-mercaptopropionate) ("TMMP" manufactured by SC Organic Chemicals) was prepared. In Comparative Examples 1 to 3, TMMP and a bifunctional monomer shown in Table 1 were mixed in a molar ratio of 2:3. In Comparative Example 4, TMMP and a monofunctional monomer shown in Table 1 were mixed in a molar ratio of 1:3. In Examples 1 to 3 and Comparative Examples 5 to 16, TMMP was mixed with a bifunctional monomer and a monofunctional monomer shown in Table 1 in a molar ratio of 1:1:1 (i.e., mixed so that the mole numbers of mercapto groups and reactive groups in the mixture were the same). In this manner, a monomer mixture was obtained.

[0060] To 100 parts by mass of the monomer mixture, 2 parts by mass of "Irgacure (registered trademark) 819" (bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide) manufactured by BASF was added as a polymerization initiator, and 0.2% by mass of "BYK-UV3510" manufactured by BYK was further added as a surface conditioner. The mixture was mixed uniformly to obtain an active energy ray-curable ink for each of the Examples and Comparative Examples.

[0061] [Measurement of Viscosity of Active Energy Ray-Curable Ink] The viscosity of active energy ray curable ink was measured at 25°C with a cone plate angle of 1°34' using a Toki Sangyo Co., Ltd. E-type viscometer "TVE-25L". The results are shown in Table 1. Note that if the viscosity at 25°C is 20 mPa·s or less, inkjet printing is possible, so viscosity of 20 mPa·s or less is marked as "Good", and viscosity of more than 20 mPa·s is marked as "Poor". Note that in the case of "Good", the lower the viscosity at 25°C, the easier it is to inkjet print.

[0062] [Evaluation of active energy ray curable ink] As a substrate, Teijin's artificial leather Cordley (registered trademark) (white) was prepared. The active energy ray curable ink prepared above was applied to the substrate with a wet thickness of 30 μm using a bar coater. Next, the active energy ray curable ink was reacted by irradiating the substrate with ultraviolet light of 2 J / s for 1 second using a UV-LED lamp with a wavelength of 385 nm. The state of the coating film after irradiation with ultraviolet light was evaluated according to the following criteria. (curable) 〇: The coating film does not deform when touched with a finger △: When the coating film is touched with a finger, part of the coating film is deformed. ×: The coating film is not cured. (tack) ◯: When the coating film is touched with a finger, there is no feeling of adhesion to the finger. △: When the coating film is touched with a finger, it feels like it sticks to the finger, but when it is removed, the coating film does not stick to the finger. ×: The coating adheres to the fingers.

[0063] For those where the coating film had hardened, Sakura Cray-Pas Ink Eraser 512 was run back and forth over the coating film 10 times, after which the condition of the coating film was observed and the strength of the coating film was evaluated according to the following criteria. (Coating strength) 〇: The coating is not damaged and there are almost no scratches. △: The coating is destroyed and many scratches occur. ×: The coating is destroyed.

[0064] [Table 1]

[0065] [Difunctional monomer abbreviation] NDDA: Nonanediol diacrylate (Tg of homopolymer: 68°C) NPDA: Neopentyl glycol diacrylate (Tg of homopolymer: 117°C) TMPDA: Trimethylolpropane diallyl ether NDDM: Nonanediol dimethacrylate ODE: 1,7-octadiene VEEA: 2-(2-vinyloxyethoxy)ethyl acrylate (Tg of homopolymer: 91°C) HDDA: Hexanediol diacrylate (Tg of homopolymer: 63°C) DAP: Diallyl phthalate DAE: Diallyl ether

[0066] [Monofunctional monomer abbreviation] AOMA: α-allyloxymethyl methyl acrylate PEA: Phenoxyethyl acrylate THFA: Tetrahydrofuryl acrylate CHA: Cyclohexyl acrylate BZA: Benzyl acrylate IBXA: Isobornyl acrylate NVC: N-vinylcaprolactam *Note that although methyl α-allyloxymethylacrylate has two polymerizable groups, one of them is consumed in a cyclization reaction within the molecule, so it is classified here as a monofunctional monomer.

[0067] A comparison of Examples 1 to 3 and Comparative Examples 1 to 3 shows that it is difficult to reduce the viscosity of the ink when a monofunctional monomer is not used. A comparison of Examples 1 to 3 and Comparative Example 4 shows that the curability of the ink is insufficient when a bifunctional monomer is not used. A comparison of Examples 1 to 3 and Comparative Examples 10 to 16 shows that when AOMA is used as a monofunctional monomer, the ink viscosity can be significantly reduced and the strength of the cured coating film of the ink can be improved. In Comparative Example 13, the ink viscosity was reduced to a level suitable for inkjet printing, but the ink did not cure. This shows that when AOMA is used as a monofunctional monomer, the effect of reducing the ink viscosity and the effect of improving the curability can be significantly obtained. Furthermore, a comparison of Examples 1 to 3 and Comparative Examples 7 to 9 shows that depending on the type of bifunctional monomer, sufficient curability of the ink and a cured coating film with sufficient strength cannot be obtained. In particular, a comparison between Examples 1 to 3 and Comparative Example 7 indicates that the segment between the two polymerizable groups (reactive groups) of the bifunctional monomer contributes to the curability of the ink and the strength of the cured coating film, and that when the Tg of the bifunctional monomer is 65°C to 150°C, sufficient curability of the ink and a cured coating film of sufficient strength can be obtained.

[0068] Therefore, from the above, it can be seen that the present invention can provide an actinic ray-curable ink composition that can form a coating film with sufficient strength on flexible materials such as artificial leather and can be inkjet printed. [Industrial Applicability]

[0069] The active energy ray-curable ink composition of the present invention can be suitably used as an inkjet ink, and can be used in various applications including an overprint varnish for artificial leather.

Claims

1. The composition contains a polyfunctional thiol compound (A), a bifunctional monomer (B), a radical cyclopolymerizable monomer (C), and a photopolymerization initiator (D), The viscosity of the thiol compound (A) at 25° C. is 40 mPa·s to 3000 mPa·s, the bifunctional monomer (B) has two reactive groups each containing a vinyl group, and at least one of the reactive groups is an acrylic group; The actinic ray-curable ink composition, wherein the homopolymer of the bifunctional monomer (B) has a glass transition temperature of 65°C to 150°C.

2. 2. The active energy ray-curable ink composition according to claim 1, wherein the radical cyclopolymerizable monomer (C) is an α-(unsaturated alkoxyalkyl)acrylate, and the viscosity of the radical cyclopolymerizable monomer (C) at 25° C. is 5.0 mPa·s or less.

3. 2. The active energy ray-curable ink composition according to claim 1, wherein the radical cyclopolymerizable monomer (C) is methyl α-allyloxymethylacrylate.

4. The active energy ray-curable ink composition according to claim 1 , wherein the bifunctional monomer (B) is neopentyl glycol diacrylate or nonanediol diacrylate.

5. The polyfunctional thiol compound (A) is a difunctional to tetrafunctional thiol compound, and 2. The active energy ray-curable ink composition according to claim 1, wherein the polyfunctional thiol compound (A) has a viscosity at 25° C. of 40 mPa·s to 500 mPa·s.

6. 2. The active energy ray curable ink composition according to claim 1, wherein a ratio of a total amount (mol) of double bonds contained in the active energy ray curable ink composition to a total amount (mol) of mercapto groups contained in the active energy ray curable ink composition is 0.8 to 1.5, and a molar ratio of the radical cyclic polymerizable monomer (C) to the bifunctional monomer (B) is 0.7 to 1.

5.

7. The actinic ray-curable ink composition according to claim 1 , which is an ink-jet ink.

8. The active energy ray-curable ink composition according to claim 1 , which is an overprint varnish for artificial leather.

9. An artificial leather having a cured coating film of the active energy ray-curable ink composition according to claim 1.

10. A process for applying the active energy ray-curable ink composition according to claim 1 to a substrate by an inkjet system to form a coating film of the active energy ray-curable ink composition; a step of irradiating the coating film with active energy rays to cure the coating film; 2. An inkjet printing method comprising:

11. The inkjet printing method of claim 10, wherein the substrate is artificial leather.

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