JP5724481B2 - UV curable ink jet ink and ink jet recording method - Google Patents

Description

  The present invention relates to an ultraviolet curable ink jet ink and an ink jet recording method.

  Conventionally, various methods have been used as a recording method for forming an image on a recording medium such as paper based on an image data signal. Among these, the ink jet method is an inexpensive device, and ink is ejected only to a required image portion and an image is directly formed on a recording medium. Therefore, the ink can be used efficiently and the running cost is low. Furthermore, the inkjet method is excellent as a recording method because of its low noise.

  In recent years, in an inkjet recording method, an ultraviolet curable inkjet ink that is cured when irradiated with ultraviolet rays has been used as an ink that can provide good water resistance, solvent resistance, and scratch resistance.

  For example, Patent Document 1 discloses 2- (vinyloxyethoxy) ethyl (meth) acrylate, 2-hydroxypropyl acrylate, carbon black as a pigment, 2-methyl-2-morpholino (4-thiol as a photopolymerization initiator). Methylphenyl) propan-1-one and a copolymer of styrene / acrylic acid / butyl acrylate (acid value = 30, weight average molecular weight = 6000) as an additive for active energy ray-curable inkjet printing An ink is disclosed.

Japanese Patent No. 3461501

  However, the active energy ray-curable ink jet printing ink disclosed in Patent Document 1 may be inferior in its curability and the abrasion resistance and stretchability (elongation) of a cured film obtained by curing the ink. For this reason, it is difficult to obtain an ultraviolet curable ink jet ink excellent in all of these performances, which causes a practical problem.

  Accordingly, it is an object of the present invention to provide an ultraviolet curable ink jet ink excellent in ink curability and a rub resistance and stretchability of a cured film, and an ink jet recording method using the same.

The present inventors have intensively studied to solve the above problems. A monomer (hereinafter referred to as “monomer A”) represented by the following general formula (I), which includes 2- (vinyloxyethoxy) ethyl (meth) acrylate used in Patent Document 1, is ultraviolet light. By containing it in a curable inkjet ink (hereinafter also simply referred to as “ink”), the ink has a low viscosity, and has high sensitivity to irradiated ultraviolet rays, and therefore tends to have good curability. The present inventors have found that.
_{^{CH 2 = CR 1 -COOR 2 -O}} -CH = CH-R 3 ··· (I)
(In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is a divalent organic residue having 2 to 20 carbon atoms, and R ³ is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms. Group.)

  However, the present inventors have found that various problems occur in the obtained ink simply by adding the monomer A such as 2- (vinyloxyethoxy) ethyl (meth) acrylate to the ink. Hereinafter, this knowledge will be described in detail.

  First, simply adding the monomer A such as 2- (vinyloxyethoxy) ethyl (meth) acrylate to the ink cannot improve the various performances of the ink described above.

  As a result of pursuing an ink composition in which the various performances described above are satisfactory, it has been found that the content of monomer A in the ink, for example, 2- (vinyloxyethoxy) ethyl (meth) acrylate, is important. When the content of 2- (vinyloxyethoxy) ethyl (meth) acrylate in the ink exceeds a certain amount, addition of a polymerizable compound that imparts extensibility is restricted, and thus an ink having excellent extensibility is obtained. I can't. In addition to this, the photopolymerization initiator is difficult to dissolve in the ink, and the amount of addition is limited, thereby preventing an increase in sensitivity due to the photopolymerization initiator, resulting in an ink having poor curability. . In this case, if the photopolymerization initiator is excessively added, the photopolymerization initiator is precipitated, resulting in image defects and defective ink ejection from the print head.

  On the other hand, when the content of 2- (vinyloxyethoxy) ethyl (meth) acrylate in the ink is less than a certain amount, the cured film (coating film) of the ink becomes too soft and is inferior in abrasion resistance. In addition, since the minimum sensitivity required for ultraviolet curable ink cannot be maintained, the resulting ink is inferior in curability.

  Therefore, the present inventors conducted further diligent studies and found that the content of the monomer (A) exists such that various performances of the ink are relatively good. Specifically, when the content is within a predetermined range, the curability is relatively good. In this case, the discharge stability is also excellent.

  Second, in order to obtain an ink having better curability and excellent rub resistance and stretchability (elongation) of the cured film, the content of the monomer (A) is set within a predetermined range as described above. In addition, further ink composition improvements are needed. For example, when an image is formed using ink on the surface of a vehicle body or the like, a certain degree of extensibility (elongation) is required for the cured film of the ink.

  Therefore, as a result of further intensive studies by the present inventors, it is desired that the molar number average glass transition temperature (Tg) of the monofunctional (meth) acrylate monomer (including monomer A) in the ink is within a predetermined range. It was found that an ink of 1 was obtained. This finding is that when the content of 2- (vinyloxyethoxy) ethyl (meth) acrylate is below a certain amount, the cause of inferior abrasion resistance is sought, and the strength of the cured film is insufficient as the cause. This is based on the finding that the strength depends on the average number Tg of moles.

  From the above, it contains a monofunctional (meth) acrylate monomer containing a predetermined amount of monomer A, and the mole average Tg of the monofunctional (meth) acrylate monomer contained in the ink is within a predetermined range. The inventors have found that the above problems can be solved by using an ultraviolet curable inkjet ink, and have completed the present invention.

That is, the present invention is as follows.
[1]
A UV-curable ink-jet ink comprising a monofunctional (meth) acrylate monomer and a photopolymerization initiator, wherein the monofunctional (meth) acrylate monomer has the following general formula (I):
_{^{CH 2 = CR 1 -COOR 2 -O}} -CH = CH-R 3 ··· (I)
(In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is a divalent organic residue having 2 to 20 carbon atoms, and R ³ is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms. Group.)
The content of the monomer A is 10 to 75% by mass with respect to the total mass of the ink, and the cured product of the monofunctional (meth) acrylate monomer contained in the ink An ultraviolet curable inkjet ink having a molar average Tg of from 6 to 37 ° C.
[2]
The ultraviolet curable inkjet ink according to [1], wherein the monomer A is 2- (vinyloxyethoxy) ethyl (meth) acrylate.
[3]
The ultraviolet curable inkjet ink according to [1] or [2], wherein the photopolymerization initiator includes 8 to 11% by mass of an acylphosphine oxide photopolymerization initiator based on the total mass of the ink.
[4]
The ultraviolet curable ink-jet ink according to [3], further comprising 1 to 3% by mass of a thioxanthone-based initiator based on the total mass of the ink as the photopolymerization initiator.
[5]
The ultraviolet curable inkjet ink according to any one of [1] to [4], wherein the monomer of the monofunctional (meth) acrylate contains 5 to 55% by mass of phenoxyethyl acrylate with respect to the total mass of the ink. .
[6]
For ultraviolet curable inkjets according to any one of [1] to [5], which can be cured by irradiating ultraviolet rays having an emission peak wavelength in the range of 365 to 410 nm with an irradiation energy of 350 mJ / cm ² or less. ink.
[7]
The ultraviolet curable inkjet ink according to any one of [1] to [6], wherein the content of the monomer of the monofunctional (meth) acrylate is 50% by mass or more based on the total mass of the ink.
[8]
An inkjet recording method of forming an image by ejecting the ultraviolet curable inkjet ink according to any one of [1] to [7] onto a recording medium.

1 is a block diagram illustrating a configuration of a line printer that is an example of a recording apparatus used in the present embodiment. FIG. 2 is a schematic view around a recording area in one embodiment of the line printer of FIG. 1.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. In addition, this invention is not restrict | limited to the following embodiment, A various deformation | transformation can be implemented within the range of the summary.

  In this specification, “(meth) acrylate” means at least one of acrylate and its corresponding methacrylate, and “(meth) acryl” means at least one of acryl and its corresponding methacryl. The term “oligomer” refers to a low polymer having a weight average molecular weight of 10,000 or less obtained by polymerization of monomers. In addition, the value obtained by measuring with a mass spectrometry is employ | adopted for the weight average molecular weight in this specification.

  In this specification, “curability” refers to a property of curing in response to light. “Discharge stability” refers to the property of ejecting stable ink droplets from the nozzles without clogging the nozzles. “Abrasion resistance” is a physical force that prevents the coloring material from peeling off from the image surface when a physical force such as rubbing acts on the surface of the image formed by recording. This refers to the resistance of the image surface to. “Extensible” can be rephrased as the elongation of a cured film (coating film) of ink, and refers to the property that the cured film elongates without causing cracks when a recorded material produced by curing the ink coating film is pulled.

  Further, in this specification, “color ink” refers to all colored inks excluding colorless and transparent clear ink. “Main curing” refers to curing the dots formed on the recording medium to a curing state necessary for using the printed material. “Temporary curing” means temporary pinning of ink, which means curing before main curing in order to prevent dot bleeding and color mixing. Generally, the conversion rate in temporary curing is temporary curing. It is lower than the conversion rate by the main curing performed after the step. In addition, said conversion rate means the rate in which the polymeric compound contained in an ink converts into a hardened | cured material, and can be paraphrased with the hardening degree of the ink by light irradiation.

  In this specification, the “recording device” means a device that forms an image on a recording medium. The “inkjet recording apparatus” means an apparatus that forms an image on a recording medium by an inkjet method among the recording apparatuses, and corresponds to, for example, a printer (1) described later. The recording control device means a device that controls the recording device, and corresponds to, for example, a computer (110) in which a printer driver is installed, which will be described later.

[UV curable inkjet ink]
One embodiment of the present invention relates to an ultraviolet curable inkjet ink. The ultraviolet curable inkjet ink is an ultraviolet curable inkjet ink containing a monofunctional (meth) acrylate monomer containing the monomer A represented by the general formula (I), and the content of the monomer A Is 10 to 75% by mass with respect to the total mass of the ink, and the ultraviolet curing is such that the average number of moles Tg of the monofunctional (meth) acrylate monomer contained in the ink is 6 to 37 ° C. Type ink jet ink. Here, the “mol number average Tg in the cured product of monofunctional (meth) acrylate monomer” in this specification is contained in the ink in the Tg of the cured product when each monomer is a cured product (homopolymer). It is calculated by adding each other a value obtained by multiplying the number of moles of each monomer (percentage in terms of moles) with respect to the total number of moles of monofunctional (meth) acrylate monomers. Moreover, Tg of the cured product of each monomer is measured by a differential thermal analyzer (DSC).

  Hereinafter, additives (components) contained in or capable of being contained in the ultraviolet curable inkjet ink of the present embodiment will be described.

(Polymerizable compound)
The polymerizable compound contained in the ink of this embodiment can be polymerized at the time of ultraviolet irradiation by the action of a photopolymerization initiator described later, and the printed ink can be cured.

(1. Monomer A)
The monomer A, which is an essential polymerizable compound in the present embodiment, is a compound belonging to a vinyl ether group-containing (meth) acrylic ester. The monomer A is contained in a monofunctional (meth) acrylate monomer described later, and is represented by the following general formula (I).
_{^{CH 2 = CR 1 -COOR 2 -O}} -CH = CH-R 3 ··· (I)
(In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is a divalent organic residue having 2 to 20 carbon atoms, and R ³ is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms. Group.)

  When the ink contains the monomer A, the curability of the ink can be improved.

In the above general formula (I), the divalent organic residue having 2 to 20 carbon atoms represented by R ² is a linear, branched or cyclic substituted having 2 to 20 carbon atoms. May be an alkylene group, an optionally substituted alkylene group having an oxygen atom by an ether bond and / or an ester bond in the structure, and an optionally substituted divalent alkylene group having 6 to 11 carbon atoms. Aromatic groups are preferred. Among these, C2-C6 alkylene groups such as ethylene group, n-propylene group, isopropylene group, and butylene group, oxyethylene group, oxy n-propylene group, oxyisopropylene group, and oxybutylene group An alkylene group having 2 to 9 carbon atoms having an oxygen atom due to an ether bond in the structure is preferably used.

In the above general formula (I), the monovalent organic residue having 1 to 11 carbon atoms represented by R ³ is a linear, branched or cyclic substituted having 1 to 10 carbon atoms. Suitable alkyl groups and optionally substituted aromatic groups having 6 to 11 carbon atoms are preferred. Among these, C6-C2 aromatic groups, such as a C1-C2 alkyl group which is a methyl group or an ethyl group, a phenyl group, and a benzyl group, are used suitably.

  When each of the organic residues is an optionally substituted group, the substituent is divided into a group containing a carbon atom and a group not containing a carbon atom. First, when the substituent is a group containing a carbon atom, the carbon atom is counted in the carbon number of the organic residue. Examples of the group containing a carbon atom include, but are not limited to, a carboxyl group and an alkoxy group. Next, examples of the group not containing a carbon atom include, but are not limited to, a hydroxyl group and a halo group.

  Examples of the monomer A include, but are not limited to, for example, 2-vinyloxyethyl (meth) acrylate, 3-vinyloxypropyl (meth) acrylate, 1-methyl-2-vinyloxyethyl (meth) acrylate, (meth ) 2-vinyloxypropyl acrylate, 4-vinyloxybutyl (meth) acrylate, 1-methyl-3-vinyloxypropyl (meth) acrylate, 1-vinyloxymethylpropyl (meth) acrylate, (meth) acrylic acid 2-methyl-3-vinyloxypropyl, 1,1-dimethyl-2-vinyloxyethyl (meth) acrylate, 3-vinyloxybutyl (meth) acrylate, 1-methyl-2-vinyloxypropyl (meth) acrylate, ( 2-vinyloxybutyl (meth) acrylate, 4-vinyloxycyclohexyl (meth) acrylate 6-vinyloxyhexyl (meth) acrylate, 4-vinyloxymethylcyclohexylmethyl (meth) acrylate, 3-vinyloxymethylcyclohexylmethyl (meth) acrylate, 2-vinyloxymethylcyclohexylmethyl (meth) acrylate, P-vinyloxymethylphenylmethyl (meth) acrylate, m-vinyloxymethylphenylmethyl (meth) acrylate, o-vinyloxymethylphenylmethyl (meth) acrylate, 2- (vinyloxyethoxy) (meth) acrylate ) Ethyl, 2- (vinyloxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxy) propyl (meth) acrylate, 2- (vinyloxyethoxy) isopropyl (meth) acrylate, (meth) acryl Acid 2- (vinyloxyisopropoxy) propyl (Meth) acrylic acid 2- (vinyloxyisopropoxy) isopropyl, (meth) acrylic acid 2- (vinyloxyethoxyethoxy) ethyl, (meth) acrylic acid 2- (vinyloxyethoxyisopropoxy) ethyl, (meth) acrylic 2- (Vinyloxyisopropoxyethoxy) ethyl acid, 2- (vinyloxyisopropoxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyethoxy) propyl (meth) acrylate, (meth) acrylic acid 2 -(Vinyloxyethoxyisopropoxy) propyl, (meth) acrylic acid 2- (vinyloxyisopropoxyethoxy) propyl, (meth) acrylic acid 2- (vinyloxyisopropoxyisopropoxy) propyl, (meth) acrylic acid 2- (Vinyloxyethoxyethoxy) isopropyl, 2- (vinyloxyethoxyisopropoxy) isopropyl (meth) acrylate, 2- (vinyloxyisopropoxyethoxy) isopropyl (meth) acrylate, 2- (vinyloxyisopropoxyisopropoxy) isopropyl (meth) acrylate, ( (Meth) acrylic acid 2- (vinyloxyethoxyethoxyethoxy) ethyl, (meth) acrylic acid 2- (vinyloxyethoxyethoxyethoxyethoxy) ethyl, (meth) acrylic acid 2- (isopropenoxyethoxy) ethyl, (meth) 2- (isopropenoxyethoxyethoxyethoxy) ethyl acrylate, 2- (isopropenoxyethoxyethoxyethoxy) ethyl (meth) acrylate, 2- (isopropenoxyethoxyethoxyethoxyethoxy) ethyl (meth) acrylate, (meth ) Acrylic acid Ethylene glycol monovinyl ether, and (meth) acrylic acid polypropylene glycol monovinyl ether.

  Among these, because of low viscosity, high flash point, and excellent curability, 2- (vinyloxyethoxy) ethyl (meth) acrylate, that is, 2- (vinyloxyethoxy) ethyl acrylate and methacrylic acid At least one of 2- (vinyloxyethoxy) ethyl is preferable, and 2- (vinyloxyethoxy) ethyl acrylate is more preferable. Examples of 2- (vinyloxyethoxy) ethyl (meth) acrylate include 2- (2-vinyloxyethoxy) ethyl (meth) acrylate and 2- (1-vinyloxyethoxy) ethyl (meth) acrylate. Examples of 2- (vinyloxyethoxy) ethyl acrylate include 2- (2-vinyloxyethoxy) ethyl acrylate (hereinafter also referred to as “VEEA”) and 2- (1-vinyloxyethoxy) ethyl acrylate. It is done.

  The content of the monomer A is in the range of 10 to 75% by mass, preferably in the range of 40 to 75% by mass, and in the range of 55 to 75% by mass with respect to the total mass (100% by mass) of the ink. More preferably, it is more preferably in the range of 65 to 70% by mass. When the content is within the above range, the curability and ejection stability of the ink are excellent, and the viscosity, abrasion resistance, and extensibility are also excellent.

  The method for producing monomer A is not limited to the following, but is a method of esterifying (meth) acrylic acid and a hydroxyl group-containing vinyl ether (production method B), and a (meth) acrylic acid halide and a hydroxyl group-containing vinyl ether are esterified. Method (Production Method C), Method of Esterification of (Meth) acrylic Anhydride and Hydroxyl-Containing Vinyl Ether (Production Method D), Method of Transesterification of (Meth) Acrylic Acid Ester and Hydroxyl-Containing Vinyl Ether (Production Method E), ( Method of esterifying (meth) acrylic acid and halogen-containing vinyl ether (Production Method F), Method of esterifying (meth) acrylic acid alkali (earth) metal salt and halogen-containing vinyl ether (Production Method G), hydroxyl group-containing (Metal) ) Method of vinyl exchange between acrylic acid ester and vinyl carboxylate (Production method H), Hydroxic acid Containing (meth) How to ether exchange and acrylic acid ester and an alkyl vinyl ether (Process I).

  Among these, since the desired effect can be further exhibited in this embodiment, the production method E is preferable.

  Monomer A may be a single compound or a combination of two or more compounds.

(2. Monofunctional (meth) acrylate monomers and oligomers)
The ink of the present embodiment contains a monofunctional (meth) acrylate monomer. In particular, the ink of the present embodiment contains the monomer A, which is one type of monofunctional (meth) acrylate monomer. In the present specification, the monomer of monofunctional (meth) acrylate includes monomer A unless otherwise specified.

  In addition to the monofunctional (meth) acrylate monomer, the ink of the present embodiment may further include at least one of a monofunctional (meth) acrylate oligomer, a urethane oligomer, and an epoxy oligomer.

  Monofunctional (meth) acrylate monomers (excluding monomer A) and oligomers are not limited to the following, but include, for example, isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) Acrylate, decyl (meth) acrylate, isomyristyl (meth) acrylate, isostearyl (meth) acrylate, 2-ethylhexyl-diglycol (meth) acrylate, ethyl carbitol (meth) acrylate, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (Meth) acrylate, methoxydiethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate Phenoxyethyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4- Hydroxybutyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, lactone-modified flexible (meth) acrylate, cyclohexyl (meth) acrylate, t-butylcyclohexyl (meth) acrylate, dicyclopentanyl ( Examples include meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, and oligomers thereof.

  Ink contains monofunctional (meth) acrylate monomers (and oligomers), resulting in low viscosity inks, excellent solubility of photopolymerization initiators and other additives, and ejection stability during inkjet recording. It is easy to be done. Furthermore, in order to increase the toughness, heat resistance, and chemical resistance of the ink coating, a monofunctional (meth) acrylate monomer (and oligomer) and a bifunctional (meth) acrylate monomer (and oligomer) described later are used in combination. It is more preferable.

  Furthermore, the monomer (and oligomer) of the monofunctional (meth) acrylate preferably has one or more skeletons selected from the group consisting of an aromatic ring skeleton, a saturated alicyclic skeleton, and an unsaturated alicyclic skeleton. Thereby, the viscosity of the ink can be reduced.

  Examples of monofunctional (meth) acrylate monomers and oligomers having an aromatic ring skeleton include phenoxyethyl (meth) acrylate and 2-hydroxy-3-phenoxypropyl (meth) acrylate. Examples of the monofunctional (meth) acrylate monomer and oligomer having a saturated alicyclic skeleton include isobornyl (meth) acrylate, t-butylcyclohexyl (meth) acrylate, and dicyclopentanyl (meth) acrylate. Examples of the monofunctional (meth) acrylate monomer and oligomer having an unsaturated alicyclic skeleton include dicyclopentenyloxyethyl (meth) acrylate.

  Among the above, the monomer (and oligomer) of the monofunctional (meth) acrylate excluding the monomer A can bring the mole number average Tg of the monofunctional (meth) acrylate contained in the ink into a desired range. A compound having a number average Tg of 37 ° C. or less may be contained. Among them, excellent adhesion and adhesion to the recording medium are imparted, the flexibility of the ink coating film is improved, the viscosity of the ink can be reduced, and acylphosphine oxide photopolymerization is initiated. Since the solubility of the agent is excellent, at least one of phenoxyethyl acrylate (Tg = −22 ° C.) and 4-hydroxybutyl acrylate (Tg = −80 ° C.) is preferable. More preferable is phenoxyethyl acrylate because it can reduce odor in addition to the above.

  The content of the monofunctional (meth) acrylate monomer is preferably 50% by mass or more, and more preferably 65 to 70% by mass with respect to the total mass (100% by mass) of the ink. When the content is 50% by mass or more, the contribution of the monofunctional (meth) acrylate to the entire ink is increased, so that the properties of the cured film can be improved due to the mole average Tg.

When the monofunctional (meth) acrylate monomer contains the phenoxyethyl acrylate, the lower limit of the phenoxyethyl acrylate content is preferably 5% by mass or more with respect to the total mass (100% by mass) of the ink. Yes, more preferably 10% by mass or more, still more preferably 15% by mass or more. When the lower limit value of the content is within the above range, the ink curability is further improved. Further, the upper limit of the content of phenoxyethyl acrylate is preferably 55% by mass or less, more preferably 40% by mass or less, and more preferably 35% by mass or less with respect to the total mass (100% by mass) of the ink. More preferably, it is still more preferably 30% by mass or less. When the upper limit value of the content is within the above range, a relatively large amount of other components in the ink composition can be contained.
In addition, when the ink of the present embodiment further includes a monofunctional (meth) acrylate oligomer in addition to the monofunctional (meth) acrylate monomer, the content of the monofunctional (meth) acrylate monomer and oligomer is preferable. The range is the same as the preferred range of the above content.

The molar average Tg of the monofunctional (meth) acrylate monomer contained in the ink is preferably 6 to 37 ° C, more preferably 10 to 30 ° C, and still more preferably 20 to 30 ° C. When the mole average Tg is within the above range, as described above, an ink having extremely good curability and excellent rub resistance and stretchability (elongation) of the cured film can be obtained.
In addition, when the ink of the present embodiment further includes a monofunctional (meth) acrylate oligomer in addition to the monofunctional (meth) acrylate monomer, the molar average Tg of the monofunctional (meth) acrylate monomer and oligomer is preferable. The range is the same as the preferable range of the mole average Tg.

  The relationship between the mole average Tg and the composition of the monofunctional (meth) acrylate monomer (and oligomer) will be described in detail. As described above, the Tg of 2- (2-vinyloxyethoxy) ethyl acrylate, which is a preferred compound among monomers A, is 39 ° C., while the monofunctional (meth) acrylate monomer (and oligomer) contained in the ink The mole number average Tg is preferably 6 to 37 ° C. Therefore, the ink of the present embodiment substantially contains other monofunctional (meth) acrylate monomers (and oligomers) even though it contains 2- (vinyloxyethoxy) ethyl acrylate. At that time, if the content of the other monofunctional (meth) acrylate is combined with that of 2- (2-vinyloxyethoxy) ethyl acrylate, the molar number average Tg is within the above preferable range. Good. In addition, the above-mentioned mole number average Tg depends on the Tg of the other monofunctional (meth) acrylate and the content of 2- (vinyloxyethoxy) ethyl acrylate, and so on. The content of acrylate is not particularly limited.

  The above monofunctional (meth) acrylate monomers and oligomers may be used alone or in combination of two or more.

(3. Polymerizable compounds other than monofunctional (meth) acrylate monomers and oligomers)
In addition to the above monofunctional (meth) acrylate monomers and oligomers, various conventionally known monomers and oligomers such as monofunctional and bifunctional or more polyfunctional can also be used (hereinafter referred to as “other polymerizability”). Compound "). Examples of the monomer include unsaturated carboxylic acids such as (meth) acrylic acid, itaconic acid, crotonic acid, isocrotonic acid and maleic acid, salts or esters thereof, urethane, amide and anhydride thereof, acrylonitrile, styrene, various types Unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes. Examples of the oligomer include oligomers formed from the above monomers such as linear acrylic oligomers, epoxy (meth) acrylate, oxetane (meth) acrylate, aliphatic urethane (meth) acrylate, and aromatic urethane (meth). Acrylate and polyester (meth) acrylate are mentioned.

  Moreover, an N-vinyl compound may be included as another monofunctional monomer or polyfunctional monomer. Examples of the N-vinyl compound include N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, and derivatives thereof.

  Of the other polymerizable compounds, esters of (meth) acrylic acid, that is, (meth) acrylates are preferable (except for monofunctional ones).

  Among the (meth) acrylates, examples of the bifunctional (meth) acrylate include triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, and dipropylene glycol di ( (Meth) acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, dicyclopentanyl di (meth) acrylate, 1,6-hexanediol di (Meth) acrylate, 1,9-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, tricyclodecane dimethylol di (meth) acrylate, bisphenol A EO Oxide) adduct di (meth) acrylate, PO (propylene oxide) adduct di (meth) acrylate of bisphenol A, neopentyl glycol di (meth) acrylate hydroxypivalate, polytetramethylene glycol di (meth) acrylate, and Examples thereof include acrylated amine compounds obtained by reacting 1,6-hexanediol di (meth) acrylate and amine compounds. In addition, as a commercial item of the acrylated amine compound obtained by reacting 1,6-hexanediol di (meth) acrylate and an amine compound, EBECRYL 7100 (containing compound of 2 amino groups and 2 acryloyl groups, Cytec) (Trade name, manufactured by Cytech, Inc.).

  Among the above (meth) acrylates, trifunctional or more polyfunctional (meth) acrylates include, for example, trimethylolpropane tri (meth) acrylate, EO-modified trimethylolpropane tri (meth) acrylate, and pentaerythritol tri (meth) acrylate. , Isocyanuric acid EO-modified tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, glycerin propoxytri (meth) acrylate, cowprolactone modified tri Methylolpropane tri (meth) acrylate, pentaerythritol ethoxytetra (meth) acrylate, and caprolactam-modified dipentaerythritol hexa (meth) a Relate and the like.

  The content of the other polymerizable compound is preferably 10 to 35% by mass with respect to the total mass (100% by mass) of the ink. When the content is within the above range, the additive is excellent in solubility, and the ink coating film is excellent in toughness, heat resistance, and chemical resistance.

  Said other polymeric compound may be used individually by 1 type, and may use 2 or more types together.

(Photopolymerization initiator)
The ink of this embodiment includes a photopolymerization initiator. The photopolymerization initiator is used to form a print by curing the ink present on the surface of the recording medium by photopolymerization by irradiation with ultraviolet rays. By using ultraviolet rays (UV) among the radiation, the safety is excellent and the cost of the light source lamp can be suppressed.

  A photopolymerization initiator for improving ink characteristics, particularly curability, was examined. As a result, the inventors of the present application have found that the use of an acylphosphine oxide photopolymerization initiator can make the ink curability extremely excellent.

  In addition, by using a combination of an acylphosphine oxide photopolymerization initiator and a thioxanthone photopolymerization initiator, not only can the ink have excellent curability, but also prevent coloring of the cured film at the initial stage after ink jet recording. The present inventors have found that this is also possible.

  Thus, the above photopolymerization initiator preferably contains an acyl phosphine oxide photopolymerization initiator, and more preferably contains an acyl phosphine oxide photopolymerization initiator and a thioxanthone photopolymerization initiator. preferable.

  Further, the content of the photopolymerization initiator is preferably 10 to 13% by mass, and more preferably 11 to 13% by mass with respect to the total mass (100% by mass) of the ink. In particular, when the above preferred compounds are used as the photopolymerization initiator in the above preferred contents, the ink curability and ejection stability are extremely excellent.

(1. Acylphosphine oxide photopolymerization initiator)
As described above, the photopolymerization initiator in the present embodiment preferably includes an acyl phosphine oxide photopolymerization initiator (hereinafter also simply referred to as “acyl phosphine oxide”). Thereby, the curability of the ink can be particularly improved.

Although this acyl phosphine oxide is not particularly limited, for example, 2,4,6-trimethylbenzoyl diphenyl phosphine oxide, 2,4,6-triethylbenzoyl diphenyl phosphine oxide, 2,4,6-triphenylbenzoyl diphenyl Examples include phosphine oxide, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, and bis- (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide.
Examples of commercially available acylphosphine oxide photopolymerization initiators include DAROCUR TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), IRGACURE 819 (bis (2,4,6-trimethylbenzoyl)) -Phenylphosphine oxide) and CGI 403 (bis (2,6-dimethoxybenzoyl) -2,4,4-trimethyl-pentylphosphine oxide).

  Moreover, it is preferable that said acyl phosphine oxide contains a monoacyl phosphine oxide. As a result, the photopolymerization initiator is sufficiently dissolved and curing proceeds sufficiently, and the curability of the ink is excellent.

  Although it does not specifically limit as this monoacyl phosphine oxide, For example, 2,4,6-trimethylbenzoyl diphenyl phosphine oxide, 2,4,6-triethyl benzoyl diphenyl phosphine oxide, 2,4,6-triphenyl benzoyl A diphenylphosphine oxide is mentioned. Among these, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide is preferable.

  Examples of commercially available monoacylphosphine oxides include DAROCUR TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide).

The photopolymerization initiator in the present embodiment is monoacyl phosphine oxide or monoacyl since it has excellent solubility in a polymerizable compound and internal curability of the ink coating film, and the initial coloration degree is small. A mixture of phosphine oxide and bisacyl phosphine oxide is preferred.
The bisacylphosphine oxide is not particularly limited, and examples thereof include bis- (2,4,6-trimethylbenzoyl) -phenylphosphine oxide and bis- (2,6-dimethoxybenzoyl) -2,4. , 4-trimethylpentylphosphine oxide. Among these, bis- (2,4,6-trimethylbenzoyl) -phenylphosphine oxide is preferable.

  The acylphosphine oxide content is preferably in the range of 8 to 11% by mass relative to the total mass (100% by mass) of the ink. When the content is within the above range, the curability of the ink is excellent and the initial coloring degree of the cured film is small.

(2. Thioxanthone photopolymerization initiator)
As described above, the photopolymerization initiator in the present embodiment preferably contains a thioxanthone photopolymerization initiator (hereinafter also simply referred to as “thioxanthone”) together with the acylphosphine oxide photopolymerization initiator. Thereby, it is excellent in sclerosis | hardenability of an ink, and coloring of the initial cured film after inkjet recording can be prevented (the initial coloring amount of a cured film becomes small).

  Among thioxanthones, 2,4-diethylthioxanthone is preferable because of its excellent sensitizing effect on acylphosphine oxide, solubility in polymerizable compounds, and safety.

  As a commercially available product of thioxanthone, for example, KAYACURE DETX-S (2,4-diethylthioxanthone) (trade name, manufactured by Nippon Kayaku Co., Ltd.) ITX (manufactured by BASF), Quantacure CTX (Aceto Chemical).

  The content of thioxanthone is preferably in the range of 1 to 3% by mass relative to the total mass (100% by mass) of the ink. When the content is within the above range, the curability of the ink is excellent, and the initial coloring degree of the cured film becomes small.

[Color material]
The ink of this embodiment may further include a color material. As the color material, at least one of a pigment and a dye can be used.

(Pigment)
In the present embodiment, the light resistance of the ink can be improved by using a pigment as the color material. As the pigment, both inorganic pigments and organic pigments can be used.

  As the inorganic pigment, carbon black (CI pigment black 7) such as furnace black, lamp black, acetylene black and channel black, iron oxide, and titanium oxide can be used.

  Organic pigments include insoluble azo pigments, condensed azo pigments, azo lakes and chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc. Polycyclic pigments, dye chelates (eg basic dye chelates, acid dye chelates, etc.), dye rakes (basic dye rakes, acid dye rakes), nitro pigments, nitroso pigments, aniline black, daylight A fluorescent pigment is mentioned.

  More specifically, as carbon black used as black ink, No. 2300, no. 900, MCF88, No. 33, no. 40, no. 45, no. 52, MA7, MA8, MA100, no. 2200B and the like (trade names manufactured by Mitsubishi Chemical Corporation), Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700 and the like (trade names manufactured by Columbia Columbia) , Rega 1 400R, Rega 1 330R, Rega 1 660R, Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch K 1400, etc. Name), Color Black FW1, Color Black FW2, Color Black FW2V, Colo Black FW18, Color Black FW200, Color B1ack S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Special Beck Degussa brand name).

  Examples of pigments used in white ink include C.I. I. Pigment white 6, 18, and 21. Moreover, the metal atom containing compound which can be used as a white pigment can also be used, for example, the metal oxide, barium sulfate, and calcium carbonate which are conventionally used as a white pigment are mentioned. Although it does not restrict | limit especially as said metal oxide, For example, titanium dioxide, a zinc oxide, a silica, an alumina, magnesium oxide etc. are mentioned.

  Examples of pigments used in yellow ink 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 pigments used in magenta ink include 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 pigments used for cyan ink include 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, or C.I. I. Bat Blue 4,60.

  Examples of pigments other than magenta, cyan and yellow include C.I. I. Pigment Green 7, 10, or C.I. I. Pigment brown 3, 5, 25, 26, or C.I. I. Pigment orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 63.

  The said pigment may be used individually by 1 type, and may use 2 or more types together.

  When using said pigment, the average particle diameter has preferable 2 micrometers or less, and its 30-300 nm is more preferable. When the average particle diameter is in the above range, the ink can be more excellent in reliability such as ejection stability and dispersion stability, and an image with excellent image quality can be formed. Here, the average particle diameter in the present specification is measured by a dynamic light scattering method.

(dye)
In the present embodiment, a dye can be used as the color material. The dye is not particularly limited, and acid dyes, direct dyes, reactive dyes, and basic dyes can be used. Examples of the dye include C.I. I. Acid Yellow 17, 23, 42, 44, 79, 142, C.I. I. Acid Red 52, 80, 82, 249, 254, 289, C.I. I. Acid Blue 9, 45, 249, C.I. I. Acid Black 1, 2, 24, 94, C.I. I. Food Black 1, 2, C.I. I. Direct Yellow 1,12,24,33,50,55,58,86,132,142,144,173, C.I. I. Direct Red 1,4,9,80,81,225,227, C.I. I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C.I. I. Directed Black 19, 38, 51, 71, 154, 168, 171, 195, C.I. I. Reactive Red 14, 32, 55, 79, 249, C.I. I. Reactive black 3, 4, and 35 are mentioned.

  The said dye may be used individually by 1 type, and may use 2 or more types together.

  The content of the color material has good color developability and can reduce the inhibition of curing of the ink coating film due to light absorption of the color material itself, so that the content of the color material is 1.5 to the total mass (100% by mass) of the ink. A range of 6% by mass (in the case of white, 15 to 30% by mass) is preferable.

[Dispersant]
When the ink of this embodiment contains a pigment, it may further contain a dispersant in order to improve pigment dispersibility. Although it does not specifically limit as a dispersing agent, For example, the dispersing agent currently used for preparing pigment dispersion liquids, such as a polymer dispersing agent, is mentioned. Specific examples thereof include polyoxyalkylene polyalkylene polyamines, vinyl polymers and copolymers, acrylic polymers and copolymers, polyesters, polyamides, polyimides, polyurethanes, amine polymers, silicon-containing polymers, sulfur-containing polymers, fluorine-containing polymers, and epoxies. The thing which has 1 or more types of resin as a main component is mentioned.
Commercially available polymer dispersants include Ajinomoto Fine Techno's Ajisper series (trade name), Solsperz series (Solsperse 36000, trade name) available from Lubrizol, BYK Chemie, etc. Dispersic series (trade name) and Disparon series (trade name) manufactured by Enomoto Kasei.

(Leveling agent)
The ink of this embodiment may further include a leveling agent (surfactant) because the wettability to the printing substrate becomes good. The leveling agent is not particularly limited. For example, as the silicone surfactant, polyester-modified silicone or polyether-modified silicone can be used, and it is particularly preferable to use polyether-modified polydimethylsiloxane or polyester-modified polydimethylsiloxane. preferable. Specific examples include BYK-347, BYK-348, BYK-UV3500, 3510, 3530, and 3570 (above, trade names manufactured by BYK Japan KK).

[Polymerization inhibitor]
The ink of this embodiment may further contain a polymerization inhibitor in order to improve the storage stability of the ink. Although it does not specifically limit as a polymerization inhibitor, For example, using IRGASTAB UV10 and UV22 (trade name made by BASF), hydroquinone monomethyl ether (MEHQ, trade name made by KANTO CHEMICAL CO., INC) is used. it can.

[Other additives]
The ink of this embodiment may contain additives (components) other than the additives listed above. Such components are not particularly limited, and may include, for example, conventionally known polymerization accelerators, penetration enhancers, wetting agents (humectants), and other additives. Examples of the other additives include conventionally known fixing agents, antifungal agents, preservatives, antioxidants, ultraviolet absorbers, chelating agents, pH adjusting agents, and thickeners.

[Physical properties of UV curable inkjet ink]
The ink of the present embodiment preferably has a viscosity at 20 ° C. of 9 to 15 mPa · s, and more preferably 10 to 14 mPa · s. When the viscosity is within the above range, the solubility of the photopolymerization initiator and other additives is excellent, and the ejection stability during ink jet recording is easily obtained. The viscosity in the present specification is a value measured using a rheometer MCR300 manufactured by DKSH Japan KK.

Moreover, it is preferable that the ink of this embodiment can be hardened | cured by irradiating the ultraviolet-ray which has the light emission peak wavelength in the range of 365-410 nm with the irradiation energy of 350 mJ / cm < ² > or less. The ink of the present embodiment can be cured by irradiating with a low irradiation energy of 350 mJ / cm ² or less, and thus has various advantageous effects. The integrated light quantity (irradiation energy) [mJ / cm ² ] is calculated from the product of the irradiation intensity [mW / cm ² ] and the irradiation duration [s] on the irradiated surface irradiated from the light source. The fact that the integrated light amount is small leads to a reduction in cost especially when the irradiation intensity is low, and particularly when the irradiation duration is short, the printing speed is increased, that is, the printing time is shortened. In particular, in the case of a commercial recording apparatus, since a reduction in printing time is required, the ink according to the present embodiment can exert an advantageous effect that is prominent in the field of commercial printing. The emission peak wavelength of ultraviolet light is more preferably 385 to 400 nm, and the irradiation energy is more preferably 100 to 200 mJ / cm ² . In addition, the integrated light quantity (irradiation energy) in this specification is measured by the method used in the below-mentioned Example.

As described above, the content of the monomer A in the ink of the present embodiment is 10 to 75% by mass. If it is less than the lower limit of 10% by mass, the minimum sensitivity required for an ultraviolet curable ink cannot be maintained, resulting in an ink having poor curability. In this case, if it is intended to obtain an ink having good curability, it is necessary to cure with an irradiation energy exceeding 350 mJ / cm ² , so that a large amount of irradiation energy is required, and the irradiation apparatus becomes large. The machine becomes larger, the cost becomes higher, and the running cost becomes higher.

  Thus, unlike the conventional ink, the ink of the present embodiment is an ink that can be sufficiently cured even with low irradiation energy.

[Recording medium]
The ultraviolet curable ink-jet ink of the present embodiment can be recorded by being ejected onto a recording medium by a recording method described later. Examples of the recording medium include an absorptive or non-absorbable recording medium. The recording methods of the following embodiments are widely used for recording media having various absorption performances, from non-absorbing recording media in which water-soluble ink penetration is difficult to absorbent recording media in which water-soluble ink penetration is easy. Applicable. However, when the ink is applied to a non-absorbable recording medium, it may be necessary to provide a drying step after being cured by irradiation with ultraviolet rays.

  The absorbent recording medium is not particularly limited. For example, plain paper such as electrophotographic paper having high water-based ink permeability, ink jet paper (an ink absorbing layer composed of silica particles or alumina particles, or polyvinyl alcohol). (Paper for exclusive use of ink jet equipped with an ink absorbing layer composed of a hydrophilic polymer such as PVA) or polyvinyl pyrrolidone (PVP)), art paper or coated paper used for general offset printing with relatively low permeability of water-based ink And cast paper.

  The non-absorbable recording medium is not particularly limited. For example, plastic films and plates such as polyvinyl chloride (PVC), polyethylene, polypropylene, polyethylene terephthalate (PET), iron, silver, copper, aluminum, and the like. Examples thereof include a metal plate, a metal plate produced by vapor deposition of these various metals, a plastic film, a plate made of an alloy such as stainless steel or brass.

[Recording device]
One embodiment of the present invention relates to a recording apparatus. The recording apparatus includes a head having a nozzle diameter of preferably 25 μm or less from which the ultraviolet curable inkjet ink of the above-described embodiment is discharged.

  Among the above recording apparatuses, an apparatus that forms an image on a recording medium by an ink jet method, that is, an ink jet recording apparatus is preferable because it can achieve downsizing and cost reduction and is excellent in image quality.

Hereinafter, the ink jet recording apparatus among the above recording apparatuses will be described in detail.
FIG. 1 is a block diagram illustrating a configuration of a line printer that is an example of a recording apparatus used in the present embodiment. FIG. 2 is a schematic view around the recording area in one embodiment of the line printer of FIG.

[1. Device configuration〕
As shown in FIG. 1, the printer 1 of the present embodiment is connected to a computer 110 that is an external device so as to be communicable.

The printer 1 is a recording apparatus that forms an image on a recording medium by discharging ultraviolet curable ink that is cured by irradiation with light (ultraviolet rays). At least one of the ultraviolet curable inks used in the recording apparatus is the ultraviolet curable inkjet ink according to the present embodiment.
In this specification, “on the recording medium” means being located on the surface of the recording medium and above the surface.

The printer 1 (recording apparatus) includes a transport unit 20 (transport unit) that transports a recording medium in the transport direction, and a part (first) of a head unit 30 that discharges ultraviolet curable color ink onto the recording medium. And a part of the irradiation unit 40 (first temporary curing irradiation unit) that temporarily cures the first coating film made of the color ink landed on the recording medium by first light irradiation. The head unit 30 is disposed on the downstream side of the first temporary curing irradiation section in the transport direction, and discharges the ultraviolet curable clear ink to at least a part of the first coating film (first part). Second print head), the first coating film that has been temporarily cured, and the second coating film that is made of the clear ink that has landed on at least a part of the first coating film. Irradiation unit to be cured Irradiation unit for carrying out main curing of part of 40 (second irradiation part for temporary curing), first cured coating film and second cured coating film by light irradiation from main curing light source 40 (a main curing irradiation unit). In addition to this, the above-described printer 1 (recording apparatus) optionally includes a detector group 50 and a controller 60.
In addition, said 1st light irradiation and 2nd light irradiation both mean the light irradiation from the light source for temporary hardening.

  The transport unit 20 is for transporting the recording medium in the transport direction. As illustrated in FIG. 2, the transport unit 20 includes, for example, an upstream transport roller 23 </ b> A and a downstream transport roller 23 </ b> B, and a belt 24.

  The head unit 30 is for ejecting ultraviolet curable ink toward a recording medium.

  The irradiation unit 40 irradiates light toward the dots of the ultraviolet curable ink landed on the recording medium S. Since the irradiation unit 40 in the present embodiment can suppress bleeding and prevent color mixing, the first pre-curing irradiation unit 42e and the first in the form shown in FIG. 2 provisional curing irradiation sections 42f and main curing irradiation sections 44 are provided.

  The detector group 50 includes a rotary encoder (not shown) and a paper detection sensor (not shown) as required.

  The controller 60 is a control unit for controlling the printer, and the controller 60 includes an interface unit 61, a CPU 62, a memory 63, and a unit control circuit 64. The interface unit 61 is for transmitting and receiving data between the computer 110 as an external device and the printer 1. The CPU 62 is an arithmetic processing unit for controlling the entire printer. The memory 63 is for securing an area for storing a program of the CPU 62, a work area, and the like, and includes storage elements such as a RAM and an EEPROM. The unit control circuit 64 controls each unit (each unit) based on the control of the CPU 62 according to a program stored in the memory 63.

  As described above, the printer 1 includes at least an ultraviolet curable color ink ejected first (hereinafter simply referred to as “color ink”) and an ultraviolet curable clear ink ejected later (hereinafter simply “clear ink”). The image can be formed (printing can be executed).

  FIG. 2 is a diagram schematically illustrating a configuration related to printing in the printer 1. FIG. 2 illustrates an embodiment in which the color ink is composed of a single type or a combination of two or more types. In the embodiment of FIG. 2, when the color ink is a combination of two or more kinds, the print head (not shown) for each color ink is placed at the position of the ink head COLOR in FIG. It is assumed that they are arranged in order downstream. As a specific example, a black ink head, a cyan ink head, a magenta ink head, and a yellow ink head are sequentially provided from the upstream side at the position of the ink head COLOR in FIG. As shown in FIG. 2, the color head COLOR and the clear ink head CL are provided in order from the upstream side in the transport direction.

  In the aspect shown in FIG. 2, the first temporary curing irradiation section 42e is provided on the downstream side in the transport direction of the ink head COLOR. In addition to the first temporary curing irradiation unit 42e, a second temporary curing irradiation unit 42f is provided on the downstream side in the transport direction of the clear ink head CL. Further, a main curing irradiation unit 44 is provided on the downstream side in the transport direction of the second temporary curing irradiation unit 42f.

[2. (Device operation)
The printer 1 that has received the print data from the computer 110, which is an external device, controls each unit (each unit), that is, the transport unit 20, the head unit 30, and the irradiation unit 40 by the controller 60, and the recording medium according to the print data Form an image on top. The controller 60 controls each unit based on the print data received from the computer 110 and forms an image on the recording medium. The situation in the printer 1 is monitored by the detector group 50, and the detector group 50 outputs the detection result to the controller 60. The controller 60 controls each unit based on the detection result output from the detector group 50.

  In the transport unit 20, when a transport motor (not shown) rotates, the upstream transport roller 23A and the downstream transport roller 23B shown in FIG. 2 rotate, and the belt 24 moves. The recording medium S fed by a paper feed roller (not shown) is conveyed by the belt 24 to a recordable area (area facing the print head). Then, the recording medium S that has passed through this area is discharged to the outside by the belt 24.

  At this time, the transport unit 20 (scanning unit) scans the recording medium S in the transport direction (scanning direction) relative to the head unit 30 (print head), while ink (an ultraviolet curable ink set described later). ) Is discharged from the head unit 30. Ink may be ejected while performing a scan for moving the head unit 30 relative to the recording medium S without conveying the recording medium S. Here, when the recording medium S is scanned with respect to the head unit 30, the side to which the recording medium S is conveyed is downstream, and the scanning with which the head unit 30 moves with respect to the recording medium S is performed. When performing, the direction in which the head unit 30 moves is the upstream side.

  Note that the recording medium S being conveyed may be electrostatically attracted or vacuum attracted to the belt 24. Further, in this specification, for convenience, the term “paper feeding” is used, but as the recording medium S in the present embodiment, a recording medium described later can be used.

  The head unit 30 discharges at least color ink and clear ink as ultraviolet curable ink for forming an image.

  The head unit 30 discharges each ink to the recording medium S being conveyed, thereby forming dots on the recording medium S (landing ink), forming a coating film, and forming an image. To do. The printer 1 is a line printer, and each print head (hereinafter simply referred to as “head”) of the head unit 30 can form an image corresponding to the width of the recording medium. Here, at least one of the heads included in the head unit 30 is for ejecting the ultraviolet curable ink-jet ink of the above embodiment, and the diameter of the nozzle is preferably 25 μm or less, more preferably 17 to 17 μm. 20 μm. When the nozzle diameter is within the above range, the ink according to the present embodiment has less tailing and mist, has excellent ejection stability, and leads to improvement in print quality.

  In the irradiation unit 40, the dots (landed ink) formed on the recording medium S are cured by receiving light irradiation from the irradiation unit 40.

  The first temporary curing irradiation section 42e shown in FIG. 2 temporarily cures dots corresponding to the first coating film formed on the recording medium S before the clear ink is landed thereon. The first light irradiation is performed. In the first temporary curing irradiation unit, it is only necessary to be able to perform temporary curing. Therefore, at least a part of the dots (droplets), for example, the dot surface may be cured. By performing this temporary curing, it is possible to prevent ink bleeding.

  Further, the second temporary curing irradiation section 42f shown in FIG. 2 can surely suppress bleeding of the color ink and the clear ink by irradiating the clear light with the second light and quickly curing it. Is. In FIG. 2, only the main curing irradiation unit 44 may be irradiated to the clear ink without providing the second temporary curing irradiation unit 42f.

  The main curing irradiation section 44 shown in FIG. 2 performs main curing of the color ink and the clear ink that have landed on the recording medium by light irradiation from a main curing light source. In other words, the main curing irradiation unit 44 performs light irradiation for main curing the dots (the first coating film and the second coating film using the clear ink) formed on the recording medium S. Further, the length of the main curing irradiation section 44 in the width direction of the recording medium S is equal to or larger than the width of the recording medium S. The main curing irradiation unit 44 then irradiates the dots formed by the heads of the head unit 30 with light.

  The main curing irradiation unit 44 includes a light emitting diode (LED) or a lamp as a main curing light source. The lamp is not particularly limited, and examples thereof include a metal halide lamp, a xenon lamp, a carbon arc lamp, a chemical lamp, a low pressure mercury lamp, and a high pressure mercury lamp.

  The first temporary curing irradiation unit 42e and the second temporary curing irradiation unit 42f have LEDs as a temporary curing light source. The LED can easily change the irradiation energy by controlling the magnitude of the input current.

  The light irradiation energy of the main curing by the main curing irradiation unit 44 is common between the ultraviolet curable color ink and the ultraviolet curable clear ink when the main curing is performed once. On the other hand, in order to make the light irradiation energy of the main curing different between the ultraviolet curable color ink and the ultraviolet curable clear ink, it is necessary to perform the main curing each time after each ink is landed on the recording medium. However, if the main curing is performed twice or more, it becomes complicated and the process of the recording method becomes complicated. Therefore, the main curing is preferably performed once.

  As shown in FIG. 2, the printer 1 further includes a second temporary curing irradiation unit 42 f between the clear ink head CL and the main curing irradiation unit 44. Bleed (color mixing) can be effectively suppressed.

The rotary encoder that can be provided in the detector group 50 detects the amount of rotation of the upstream transport roller 23A and the downstream transport roller 23B. The transport amount of the recording medium S can be detected based on the detection result of the rotary encoder. A paper detection sensor that can be provided in the detector group 50 detects the position of the leading end of the recording medium S being fed.
The operation of each part constituting the controller 60 is as described above.

The computer 110 is for installing a printer driver. The printer driver is a program for displaying a user interface on a display device (not shown) and converting image data output from an application program into print data (image formation data). The printer driver is recorded on a computer-readable recording medium such as a flexible disk FD or a CD-ROM. Alternatively, the printer driver can be downloaded to the computer 110 via the Internet. In addition, this program is comprised from the code | cord | chord for implement | achieving various functions.
Then, the computer 110 outputs print data corresponding to the image to the printer 1 in order to cause the printer 1 to form an image.

  In addition, as a type of the printer 1 (recording apparatus) in the present embodiment described above, there is a serial printer described later in addition to the line printer. These are different printer systems. Briefly speaking, a line printer is one in which printing is performed with the head fixed without moving. On the other hand, the serial printer performs printing while the head reciprocates (shuttle movement) in a direction orthogonal to the conveyance direction of the recording medium. Among these, in a line printer, an image is formed only by scanning the head once in a predetermined direction (single pass) with respect to a recording medium. When the recording medium is transported in a predetermined transport direction, the head is relatively scanned in the direction opposite to the transport direction. In other words, in the line printer, the recording medium passes under the head only once during recording. This is generally referred to as single pass printing.

(3. Modification) In the head unit 30, when there are two or more types of color ink heads, a plurality of heads are arranged side by side at the position of the color head COLOR as described with reference to FIG. Is not limited. For example, a mode in which a plurality of color heads are arranged in order in the transport direction as separate heads may be employed. In this modified example, the heads of the respective color inks may be arranged so as to be in contact with each other and adjacent to each other in the transport direction, or may be arranged at intervals.

  When the heads of the respective color inks are arranged at intervals, a first temporary curing irradiation unit for temporary curing may be provided for each head between the heads. That is, in the irradiation unit 40, the heads of the respective color inks and the first temporary curing irradiation units may be alternately provided (the first preliminary curing irradiation units are respectively provided downstream in the transport direction of the heads of the respective ink colors. Provided.)

  In the mode of FIG. 2 and the above modification, the printer 1 is a line printer, and each head of the head unit 30 can form dots corresponding to the width of the recording medium at a time.

  On the other hand, the recording method of the present invention may be performed by a serial printer. In this case, for example, as disclosed in Japanese Patent Application Laid-Open No. 2003-341021, ink is ejected and temporarily cured by a head and a temporary curing light source provided on the carriage, and then a book provided downstream in the transport direction from the carriage. The main curing may be performed with a curing light source.

[Recording method]
One embodiment of the present invention relates to a recording method. The ultraviolet curable inkjet ink of the above embodiment can be used in the recording method of the present embodiment. The recording method can be applied to an inkjet method, and forms an image by ejecting the ultraviolet curable inkjet ink of the above embodiment onto a recording medium. More specifically, the recording method includes a discharge step of discharging the ink onto a recording medium, and a curing step of curing the ink by irradiating the ink discharged by the discharge step with ultraviolet rays. ,including. In this way, a coating film (cured film) is formed by the ink cured on the recording medium.

[Discharge process]
In the ejection step, ink is ejected onto the recording medium, and the ink adheres to the recording medium. The viscosity of the ink upon ejection is preferably 9 to 15 mPa · s, and more preferably 10 to 14 mPa · s. If the viscosity of the ink is as described above with the ink temperature set to room temperature (about 20 ° C.) or without heating the ink, the ink temperature may be set to room temperature or discharged without heating the ink. Good. On the other hand, the ink may be discharged with a preferable viscosity by heating the ink to a predetermined temperature. In this way, good discharge stability is realized.

  Since the ink of the present embodiment has a higher viscosity than the water-based ink used in a normal inkjet recording ink, the viscosity fluctuation due to temperature fluctuation during ejection is large. Such fluctuations in the viscosity of the ink have a great influence on the change in the droplet size and the change in the droplet discharge speed, which can cause image quality deterioration. Therefore, it is preferable to keep the temperature of the ink during ejection as constant as possible.

[Curing process]
Next, in the curing step, the ink ejected and adhered onto the recording medium is cured by irradiation with ultraviolet rays (light). This is because the photopolymerization initiator contained in the ink is decomposed by irradiation with ultraviolet rays to generate starting species such as radicals, acids, and bases, and the polymerization reaction of the polymerizable compound is accelerated by the function of the starting species. Because. Or it is because the polymerization reaction of a polymeric compound starts by irradiation of an ultraviolet-ray (light). At this time, if the sensitizing dye is present together with the photopolymerization initiator in the ink, the sensitizing dye in the system absorbs actinic radiation to be in an excited state and contacts the photopolymerization initiator to decompose the photopolymerization initiator. It can be accelerated and a more sensitive curing reaction can be achieved.

  As an ultraviolet ray source, a mercury lamp, a gas / solid laser, or the like is mainly used, and as a light source used for curing an ultraviolet curable inkjet ink, a mercury lamp or a metal halide lamp is widely known. On the other hand, there is a strong demand for mercury-free from the viewpoint of environmental protection, and replacement with a GaN-based semiconductor ultraviolet light-emitting device is very useful industrially and environmentally. Furthermore, an ultraviolet light emitting diode (UV-LED) and an ultraviolet laser diode (UV-LD) are small, have a long lifetime, high efficiency, and low cost, and are expected as light sources for ultraviolet curable ink jets. Among these, UV-LED is preferable.

Here, ultraviolet light having an emission peak wavelength of preferably in the range of 365 to 410 nm, more preferably in the range of 385 to 400 nm, is preferably 350 mJ / cm ² or less, more preferably 100 to 100 nm, using a UV-LED or the like. It is preferable to use an ink that can be cured by irradiation with an irradiation energy of 200 mJ / cm ² . In this case, a reduction in cost and an increase in printing speed, that is, a reduction in printing time can be realized. Such an ink can be obtained by including at least one of a photopolymerization initiator that decomposes upon irradiation with ultraviolet rays in the wavelength range and a polymerizable compound that starts polymerization upon irradiation with ultraviolet rays in the wavelength range.

  As described above, according to the above three embodiments, the ultraviolet curing is excellent in the ejection stability and curability of the ink, and also in the balance of the abrasion resistance and the stretchability of the cured film obtained by curing the ink. Ink jet ink, and an ink jet recording apparatus and ink jet recording method using the same can be provided. According to such an embodiment, it is possible to obtain an ultraviolet curable ink jet ink that is excellent not only in either one of the coating properties such as extensibility and abrasion resistance but also in both.

  Hereinafter, the embodiments of the present invention will be described more specifically by way of examples. However, the embodiments are not limited to these examples.

[Use ingredients]
The components used in the following examples and comparative examples are as follows.
[Pigment]
-FASTOGEN BLUE (color index name: pigment blue 15: 4, trade name made by DIC, abbreviated as cyan in the table)
SYMULER FAST YELLOW (Color index name: CI Pigment Yellow 180, trade name of DIC Corporation, abbreviated as yellow in the table)
MICROLITH-WA Black C-WA (color index name: CI Pigment Black 7, trade name manufactured by BASF, abbreviated as black in the table)
CROMOPHTAL PinkPT (SA) GLVO (Color index name: CI Pigment Red 122, trade name manufactured by BASF, abbreviated as magenta in the table)
Pigment white 06 (Titanium dioxide, trade name of Mikuni Color Ltd., abbreviated as white in the table)
[Dispersant]
SOLPERSE 36000 (Amine-based, trade name manufactured by Lubrizol, abbreviated as SOL36000 in the table)
(Polymerizable compound)
(1. Monofunctional acrylate monomer)
VEEA (2- (2-vinyloxyethoxy) ethyl acrylate, trade name of Nippon Shokubai Co., Ltd., abbreviated as VEEA in the table)
・ Biscoat # 192 (phenoxyethyl acrylate, trade name of OSAKA ORGANIC CHEMICAL INDUSTRY LTD., Abbreviated as PEA in the table)
4-HBA (4-hydroxybutyl acrylate, trade name of Osaka Organic Chemical Co., Ltd., abbreviated 4-HBA in the table)
IBXA (isobornyl acrylate, trade name of Osaka Organic Chemical Co., Ltd., abbreviated as IBXA in the table)
V # 155 (cyclohexyl acrylate, trade name of Osaka Organic Chemical Co., Ltd., abbreviated as CHA in the table)
ME-4S (Methoxypolyethylene glycol acrylate, trade name of Dai-ichi Kogyo Seiyaku Co., Ltd., abbreviated as MPEGA in the table)
V # 190 (Ethyl carbitol acrylate, trade name of Osaka Organic Chemical Company, abbreviated as ECA in the table)
(2. Polyfunctional acrylate monomer)
KAYARAD R-684 (Tricyclodecane dimethylol diacrylate, trade name of Nippon Kayaku Co., Ltd., abbreviated as R-684 in the table)
A-DPH (dipentaerythritol hexaacrylate, trade name of Shin-Nakamura Chemical Co., Ltd., abbreviated as A-DPH in the table)
NK ester A-9300 (ethoxylated isocyanuric acid triacrylate, trade name of SHIN-NAKAMURA CHEMICAL CO, LTD., Abbreviated as A-9300 in the table)
EBECRYL 7100 (compound containing 2 amino groups and 2 acryloyl groups, trade name of Cytech, Inc., abbreviated as EB7100 in the table)
[Polymerization inhibitor]
MEHQ (trade name manufactured by Kanto Chemical Co., Ltd., abbreviated as MEHQ in the table)
(Leveling agent)
Silicone surface conditioner BYK-UV3500 (trade name, manufactured by BYK, abbreviated as UV3500 in the table)
(Photopolymerization initiator)
IRGACURE 819 (trade name, manufactured by BASF, abbreviated as 819 in the table)
DAROCUR TPO (trade name manufactured by BASF, abbreviated as TPO in the table)
KAYACURE DETX-S (trade name, manufactured by Nippon Kayaku Co., Ltd., abbreviated as DETX-S in the table)

  The physical properties of the monofunctional acrylate monomer among the polymerizable compounds listed above are summarized in Table 1 below. In the following tables, “molecular weight” represents a weight average molecular weight.

[Examples 1-17, Comparative Examples 1-32]
First, a pigment dispersion is prepared by mixing the pigments and dispersants described in Tables 2 to 6 below, and VEEA or PEA so as to have the compositions (units: mass%) described in Tables 2 to 6. It was prepared (except for examples and comparative examples that do not contain a coloring material).
Next, the other components described in Tables 2 to 6 below were added to the prepared pigment dispersion so as to have the compositions (units: mass%) described in Tables 2 to 6, and this was added at high speed. By stirring with a water-cooled stirrer, ultraviolet curable ink jet inks of each color (cyan, magenta, yellow, black, white) were obtained. Moreover, about the example which does not contain a coloring material among an Example and a comparative example, each component described in following Table 2, Table 4-Table 6 is set to the composition (unit: Table: Table 2 and Table 4-Table 6). (Mass%), and this was stirred with a high-speed water-cooled stirrer to obtain a clear ultraviolet curable inkjet ink.

〔Evaluation item〕
(1. Ink curability)
Ink printing and curing were performed as follows. First, a PET film with a receiving layer is affixed and transported on a table of a transport unit configured to transport a test sample in a straight line, and ink is ejected from the inkjet head along the way. The printed sample was irradiated with light, and the curability at that time was confirmed by a finger erosion test.
Printing was performed at a resolution of 720 dpi × 720 dpi, and the ink weight at the time of printing was 14 ng / dot. The irradiation intensity of the printing surface of the irradiator was 1 W / cm ² . The print sample was printed with a size of 1 inch × 1 inch. The amount of energy was adjusted by changing the sample transport speed.
The ink of each Example and each Comparative Example was irradiated with ultraviolet rays having an emission peak wavelength of 395 nm, and the irradiation energy (unit: mJ / cm ² ) required for curing the ink was measured. Irradiation with ultraviolet rays required for curing is performed until the sticky print pattern is touched and no stickiness is felt. ).
The evaluation criteria are as follows. The evaluation results are shown in Table 8 to Table 13 below.
A: Integrated light quantity is 200 mJ / cm ² or less.
○: The integrated light quantity exceeds 200 mJ / cm ² and is 350 mJ / cm ² or less.
△: integrated light quantity is 500mJ / cm ² or less beyond the 350mJ / cm ^2.
X: Integrated light quantity is over 500 mJ / cm ² .

(2. Ink viscosity)
The viscosity of the ink of each example and each comparative example was measured at 20 ° C. using a rheometer MCR300 manufactured by DKSH Japan.
The evaluation criteria are as follows. The evaluation results are shown in Table 8 to Table 13 below.
A: Less than 10 mPa · s.
○: 10 mPa · s or more and less than 14 mPa · s.
Δ: 14 mPa · s or more.

(3. Discharge stability)
Using an inkjet printer (PX-7500 (trade name) manufactured by Seiko Epson Corporation) equipped with a high-speed MACH head (180 nozzles per inch head, nozzle diameter 20 μm) capable of high-speed printing And evaluated. The high-speed MACH head was filled with the ink of each of the examples and comparative examples separately, and the ejection stability was judged by the number of nozzles clogged when the ink was ejected continuously for 5 minutes.
The evaluation criteria are as follows. The evaluation results are shown in Table 8 to Table 13 below.
A: There was no clogged nozzle.
○: There was a clogged nozzle, but it returned.
Δ: The number of clogged nozzles was 1 to 5.
X: The number of clogged nozzles exceeded 5.
The above-mentioned “returned” means that when there is a nozzle clogged with ink during printing, the ink can be ejected again by flushing the ink ejection port of the head. .

(4. Abrasion resistance)
The ink of each example and each comparative example was irradiated with ultraviolet light having an emission peak wavelength of 395 nm at an irradiation energy corresponding to twice the integrated light amount measured in the above-mentioned “1. Curability of ink”. A solid print pattern was prepared by curing the ink. In addition, the irradiation energy (integrated light amount) corresponds to twice the amount of energy necessary for curing the image surface. Other printing and curing methods and conditions are the same as those described in “1. Ink curability”.

The obtained solid print pattern was evaluated for rubbing resistance. In the evaluation, the printed surface was rubbed 100 times in a state where a load of 500 g was applied to the gold width using a Gakushin type wear fastness tester (trade name, manufactured by TESTER SANGYO CO., LTD.).
The evaluation criteria are as follows. The evaluation results are shown in Table 8 to Table 13 below.
A: There was no scratch on the rubbed solid print pattern surface, and no stain was observed.
○: There was no scratch on the rubbed solid print pattern surface.
Δ: Scratches were observed on the rubbed solid print pattern surface.
X: peeling was observed on the rubbed solid printed pattern surface, and many scratches were observed.

(5. Extensibility)
The ink of each Example and each Comparative Example was applied to a 10 mm × 100 mm test piece 3J IJ-180-10 (PVC (vinyl chloride) media) to a thickness of 10 μm. This coating film is irradiated with ultraviolet light having an emission peak wavelength of 395 nm at 200 mJ / cm ² , or when it is not cured with this energy, the energy required for curing is clarified by an axillary test. The ink was cured with energy to produce a cured film.
Using a tensile tester TENSILON (trade name, manufactured by ORIENTEC), each test piece with a cured film was pulled from both sides in the longitudinal direction, and the elongation rate when cracks occurred in the cured film (doubled) When it is elongated, the elongation rate is 100%.).
The evaluation criteria are as follows. The evaluation results are shown in Table 8 to Table 13 below.
A: Elongation rate is 40% or more.
○: The elongation is 30% or more and less than 40%.
Δ: Elongation is 10% or more and less than 30%.
X: Elongation rate is 0% or more and less than 10%.

  From the above Tables 8 to 13, UV curing, which contains 10 to 75% by mass of monomer A in the ink, and the average number Tg of monofunctional (meth) acrylate monomers contained in the ink is 6 to 37 ° C. It was found that all the examples of the ink jet inks were excellent in all evaluation items, and in particular, were excellent in curability, scratch resistance, and extensibility.

  On the other hand, in Comparative Examples 22 to 27 in which the content of the monomer A was less than 10% by mass in the ink, it was found that the curability and the abrasion resistance were very inferior, and the viscosity and the ejection stability were also inferior. The reason why the curability is inferior is considered to be due to the small amount of monomer A. In addition, when the monomer A is small, even if the mole number average Tg of the (meth) acrylate monomer is 6 to 37 ° C., the abrasion resistance is inferior, but the extensibility is not good. Whatever the value of the monomer mole average Tg, it is considered that both the abrasion resistance and the extensibility cannot be made excellent. Moreover, when there was little content of the monomer A, the viscosity became high and the tendency for it to be inferior to discharge stability was seen. The reason why the ejection stability is inferior is considered to be that when the amount of the monomer A is small, the surface tension becomes high as a result, making it difficult for the ink to fly.

  On the contrary, in Comparative Examples 28 to 32 in which the content of the monomer A exceeds 75% by mass in the ink, even if the mole number average Tg of the (meth) acrylate monomer is 6 to 37 ° C., the extensibility is very poor. In addition, it cannot be said that the rub resistance is good, and it is considered that the rub resistance and the extensibility cannot be made excellent regardless of the molar number average Tg of the (meth) acrylate monomer. . Moreover, it was difficult to lower the average number Tg of moles of the (meth) acrylate monomer. The reason why the extensibility is inferior is considered to be because the content of the monomer A is too large.

  In addition, it was found that in Comparative Examples 1 to 11 in which the mole number average Tg of the monofunctional (meth) acrylate monomer contained in the ink exceeds 37 ° C., the curability and the extensibility are very inferior. The reason for this is that the flexibility of the cured film is low due to the high mole number average Tg. In addition, in the comparative example in which content of PEA is less than 5%, it was found that the photopolymerization initiator had a long time for dissolution, and the photopolymerization initiator had poor solubility.

  In Comparative Examples 12 to 21, in which the molar average Tg of the monofunctional (meth) acrylate monomer contained in the ink is less than 6 ° C., the curability is extremely inferior, and the ejection stability and the abrasion resistance are also very high. I found it inferior. The reason why the abrasion resistance is inferior is that the film is soft due to the low mole number average Tg.

  DESCRIPTION OF SYMBOLS 1 ... Printer, 20 ... Conveyance unit, 23A ... Upstream conveyance roller, 23B ... Downstream conveyance roller, 24 ... Belt, 30 ... Head unit, 40 ... Irradiation unit, 42e ... First temporary curing irradiation part, 42f ... Second temporary curing irradiation unit, 44 ... main curing irradiation unit, 50 ... detector group, 60 ... controller, 61 ... interface unit, 62 ... CPU, 63 ... memory, 64 ... unit control circuit, 110 ... computer, CL: Clear ink head, COLOR: Color ink head, S: Recording medium.

Claims (8)

An ultraviolet curable ink-jet ink containing a monofunctional (meth) acrylate monomer and a photopolymerization initiator,
The monomer of the monofunctional (meth) acrylate has the following general formula (I):
_{^{CH 2 = CR 1 -COOR 2 -O}} -CH = CH-R 3 ··· (I)
(In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is a divalent organic residue having 2 to 20 carbon atoms, and R ³ is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms. Group.)
A monomer A represented by
The content of the monomer A is 10 to 75% by mass with respect to the total mass of the ink,
The molar average Tg in the cured product of the monofunctional (meth) acrylate monomer contained in the ink is 6 ° C. or higher and 28.5 ° C. or lower ,
The ultraviolet curable inkjet ink, wherein the total content of the monofunctional (meth) acrylate monomers contained in the ink is 50% by mass or more based on the total mass of the ink.   The ultraviolet curable inkjet ink according to claim 1, wherein the monomer A is 2- (vinyloxyethoxy) ethyl (meth) acrylate.   The ultraviolet curable ink-jet ink according to claim 1, comprising 8 to 11% by mass of an acylphosphine oxide photopolymerization initiator as the photopolymerization initiator based on the total mass of the ink.   The ultraviolet curable inkjet ink according to claim 3, further comprising 1 to 3% by mass of a thioxanthone-based initiator as the photopolymerization initiator based on the total mass of the ink.   The ultraviolet curable inkjet ink according to any one of claims 1 to 4, comprising 5 to 55% by mass of phenoxyethyl acrylate as a monomer of the monofunctional (meth) acrylate, based on a total mass of the ink. . The ultraviolet curable inkjet according to any one of claims 1 to 5, which can be cured by irradiating ultraviolet rays having an emission peak wavelength in a range of 365 to 410 nm with an irradiation energy of 350 mJ / cm ² or less. ink. The ultraviolet curable inkjet ink according to claim 1, wherein a content of the monomer of the monofunctional (meth) acrylate is 65 % by mass or more with respect to a total mass of the ink.   An ink jet recording method for forming an image by ejecting the ultraviolet curable ink jet ink according to claim 1 onto a recording medium.