JP2007321034A - Uv-curable ink composition for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a UV-curable ink composition for inkjet recording, excellent in the curability of both a low density thin film part and a high density thick film part in the region of a printed image, excellent in adhesiveness to a material to be printed, little in the odor of the printed image, and excellent in the color reproducibility of a full-color printed matter. <P>SOLUTION: The UV-curable ink composition for inkjet recording contains a mixture of oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethylester and oxy-phenyl-acetic acid 2-[2-hydroxy-ethoxy]-ethylester, and an acylphosphine oxide compound as the photopolymerization initiator, and an amine as the photoinitiator aid. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ultraviolet curable ink composition for ink jet recording, and more particularly to a process color ink composition for ultraviolet curable ink jet recording suitable for full color printing on non-ink-absorbing materials such as metals and plastics. .

  Printing by an ink jet printer recording apparatus is a method in which ink is ejected from a nozzle and adhered to a recording material, and since the nozzle and the recording material are in a non-contact state, the surface has a curved surface or an irregular irregular shape. On the other hand, good printing can be performed. For this reason, the printing method is expected to be used in a wide range of industrial applications.

  Ink jet recording ink compositions used for such printing methods generally include aqueous dye inks using water as the main solvent and oily dye inks using organic solvents as the main solvent. However, problems when using conventional water-based dye inks in industrial applications include drying speed on non-absorbing materials, adhesion of printed images, and poor durability such as wear resistance, water resistance, and light resistance. On the other hand, since the oil-based dye ink uses a chromium complex dye containing a heavy metal such as chromium, there is a problem in terms of safety. Therefore, as an ink improved in these points, one is proposed an aqueous pigment ink and an oil pigment ink having good light resistance using a pigment as a colorant. In addition, in recent years, in industrial applications, ink containing a photocurable material is cured with an active energy ray such as ultraviolet rays and dried to solve the problem of drying speed and water resistance. Many water-based and oil-based inks with increased strength have been proposed. An active energy ray-curable ink composition for ink jet recording using a pigment having both of these two advantages has also been proposed.

  There are basically water-based pigment inks and oil-based pigment inks as pigment inks that are cured and dried with such active energy rays. Have the problem of not being able to give sufficient adhesion. A method of providing an ink receiving layer for imparting adhesiveness to these recording media has also been studied, but has a problem in practical use such that the process becomes bulky. For this reason, it is considered more advantageous to use an oil-based pigment ink that can be directly printed on the surface of a recording medium and has excellent durability and adhesion of a cured coating. Furthermore, in order to obtain adhesiveness, abrasion resistance, water resistance, etc. of printed matter, it is more advantageous to use an oil-based ultraviolet curable ink containing almost no non-polymerizable solvent such as an organic solvent, and as an active energy ray. In particular, the use of ultraviolet rays is convenient and convenient for installation and handling of equipment. Therefore, an oil-based UV-curable pigment-based ink jet recording ink composition that does not contain a non-polymerizable organic solvent and that is excellent in ejection stability, curability, durability, and storage stability is developed. It is requested.

  The printing process of an inkjet printer recording device that uses ultraviolet curable ink is the same as that of conventional inkjet printers for water-based inks. The print head scans the print medium to form a printed image, and the print head applies ink simultaneously for each color. As with conventional lithographic printing and flexographic printing devices, the print head is fixed and the printing medium moves to form a single-color image on the entire surface. A printing process has been proposed in which a process of irradiating ultraviolet rays is repeated, and a single color is imparted and cured in a color sequence.

  In the case of conventional printing processes such as lithographic printing and flexographic printing, there is no significant difference in the printed film thickness, although there is a difference in the size of printing pixels between the low density part and the high density part of the full-color print on the non-absorbing material. On the other hand, in the case of the ink jet printing process described above, the difference in film thickness between the low density portion and the high density portion is large because the change in density is expressed by the difference in print film thickness. In particular, in the case of an ink not containing a non-polymerizable organic solvent, the film thickness difference becomes larger.

In the case of using radical polymerization type ultraviolet curable ink in a printed image having such a film thickness difference, polymerization is caused by oxygen dissolved in the ink from the interface between air and ink in the thin film portion of the printed image. It is well known that it is inhibited. Inhibition of polymerization by oxygen occurs on the surface of the printed film, but it is particularly large in thin films. As a measure to mitigate polymerization inhibition, the addition of specific initiators, the increase of polyfunctional monomers, the increase of photopolymerization initiators, the initiation of photons Auxiliary agents are used in combination.
Also, in the thick film portion of the printed image, depending on the photocurable material and photopolymerization initiator in the ink used, the absorption coefficient for ultraviolet rays is large, so most of it is absorbed on the surface of the coating film, and in the film thickness direction. Uniform curing is not performed, and in particular, the coating film strength at a portion far from the coating film surface and close to the substrate may be insufficient.
As described above, the curability of the ultraviolet curable ink is determined by the photocurable material and the photopolymerization initiator to be used. However, in the case of an inkjet recording ink that requires a low viscosity to ensure dischargeability, it is reactive. The use of a polyfunctional monomer having a high viscosity, good curability and high coating strength is suppressed due to its high viscosity, and more than 70% of the monomer is generally formed using a monofunctional or bifunctional monomer. Is. For this reason, for improving the curability, the composition of the photopolymerization initiator has a higher degree of freedom in selection and has a greater influence on the curability. This is why the selection of the photoinitiator composition is particularly important.

  The photopolymerization initiator is a constituent material of ink that greatly affects the odor and color reproducibility of a cured and dried printed image. For this reason, it is also important to select a photopolymerization initiator composition in consideration of the color and odor (volatility) of the photopolymerization initiator itself and the color and odor of the decomposition product of the photopolymerization initiator caused by ultraviolet irradiation. In particular, for printing applications such as labels, packages, and CDs in which it is essential to reduce the odor of the printed matter, it is important to select a photopolymerization initiator in consideration of the odor.

  In order to enhance the curability of the ultraviolet curable ink, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholinopropan-1-one (Irgacure 907: manufactured by Ciba Specialty Chemicals) is used as a photopolymerization initiator. An ink using a combination of an α-aminoketone photopolymerization initiator) and isopropylthioxanthone has been proposed (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3). In addition, an ink is proposed in which an α-aminoketone photopolymerization initiator and diethylthioxanthone are used in combination with a photopolymerization initiator, and an amine is added as a photoinitiator assistant (see, for example, Patent Document 4). Furthermore, Japanese Patent Application Laid-Open No. 2003-25707 proposes an ink using isopropylthioxanthone and an amine (photoinitiator aid) in combination (for example, see Patent Document 5). In addition, as an example in which a photopolymerization initiator with good surface curability and a photopolymerization initiator with good internal curability are used in combination, an α-hydroxyketone initiator and an acylphosphine oxide initiator are used in combination. (See, for example, Patent Document 6) 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1 (Irgacure 369: α-aminoketone manufactured by Ciba Specialty Chemicals) Ink has been proposed in which a photopolymerization initiator) and an acylphosphine oxide initiator are used in combination (for example, see Patent Document 7). In addition, as an ink that takes into account the odor of printed matter, an initiator containing a hydroxyethoxy group as a low-odor photopolymerization initiator having a small decomposition product odor (Irgacure 2529: α-hydroxyketone photopolymerization started by Ciba Specialty Chemicals) An ink using an agent has been proposed (see, for example, Patent Document 8).

  However, the ink using thioxanthone as the photopolymerization initiator is colored yellow in the cured product, so when used for cyan and magenta inks for process colors, the hue becomes yellow and the color of the full color print There is a problem that the reproducibility region becomes narrow. In addition, the ink using Irgacure 907 as a photopolymerization initiator has a problem that the odor of the photopolymerization initiator decomposition product is large, and the ink using Irgacure 369 is colored yellow because the photopolymerization initiator decomposition product is colored yellow. Similar to the ink using the ink, there is a problem that the color reproducibility region of the full-color printed material becomes narrow. Furthermore, the curability of the ultraviolet curable jet ink composition by the combination of the conventional photopolymerization initiators in the thin film and the thick film is not always satisfactory as the ink for the ink jet recording system, and the selection of the photopolymerization initiator. The combination was not appropriate.

JP 2001-207098 A JP 2002-187343 A JP 2004-18656 A JP 2001-288387 A JP 2003-025707 A JP 2001-525479 A JP 2002-241647 A JP 2005-154537 A

  The present invention is excellent in curability of both a low-concentration thin film portion and a high-concentration thick film portion in a printed image area, adhesion to a substrate to be printed, less odor of a printed image, and full-color printed matter. An object of the present invention is to provide an ultraviolet curable process color jet ink having excellent color reproducibility.

  As a result of examining the coexistence of curability of a thin film portion and a thick film portion by a combination of various photopolymerization initiators having low volatility and low odor of a printed image after curing and drying, specific photopolymerization is performed. The inventors have found that it is effective to combine an initiator and a specific photoinitiator aid, and have reached the present invention.

That is, the present invention relates to a pigment, a photopolymerizable compound having an ethylenic double bond, and oxy-phenyl-acetic acid 2- [2-oxo-2-phenyl-acetoxy-ethoxy] -ethyl ester as a photopolymerization initiator. And oxy-phenyl-acetic acid 2- [2-hydroxy-ethoxy] -ethyl ester, an acylphosphine oxide compound, and an amine as a photoinitiator, an ultraviolet curable ink jet A recording ink composition is provided.
The ultraviolet curable ink jet recording ink of the present invention comprises, as a photopolymerization initiator, oxy-phenyl-acetic acid 2- [2-oxo-2-phenyl-acetoxy-ethoxy] -ethyl ester having good thin film curability. A mixture of oxy-phenyl-acetic acid 2- [2-hydroxy-ethoxy] -ethyl ester and an acyl phosphine oxide compound with good thick film curability are used in combination, and an amine is added as a photoinitiator. Therefore, the curability in both the thin film portion and the thick film portion of the printed image region and the adhesion between the thick film portion and the recording material are good. Furthermore, since the mixture and compound contained in these photopolymerization initiators have a low odor, the odor of the formed printed image can also be kept small.

  The ink composition for ultraviolet curable ink jet recording of the present invention has less odor of a cured and dried printed image, curability of both a low concentration thin film portion and a high concentration thick film portion, adhesion to a substrate to be printed, It is excellent in color reproducibility of a full-color printed material and is suitable as an ultraviolet curable process color ink composition used in an ink jet recording method.

  Next, while showing embodiment of this invention, this invention is demonstrated still in detail.

  Oxy-phenyl-acetic acid 2- [2-oxo-2-phenyl-acetoxy-ethoxy] -ethyl ester and oxy-phenyl-acetic acid 2- [2 used as the first photopolymerization initiator in the present invention The mixture of -hydroxy-ethoxy] -ethyl ester has very little residual odor after curing and drying. Moreover, since it has a main absorption region on the short wavelength side, it is an initiator with good thin film curability and surface curability. However, when used alone, the curability with thick films is insufficient, and when blended in a large amount, the surface absorption becomes too large, and the adhesion to the substrate to be printed is particularly low when forming thick films. Tend to be. As a photopolymerization initiator using the mixture, there is Irgacure 754 manufactured by Ciba Specialty Chemicals.

Examples of the acylphosphine oxide compound used as the second photopolymerization initiator in the present invention include bis (2,4,6 trimethylbenzoyl) -phenylphosphine oxide (trade name: Irgacure 819, manufactured by Ciba Specialty Chemicals). ) And 2,4,6 trimethylbenzoyl-diphenylphosphine oxide (manufactured by BASF, various product names: lucillin TPO). Since the acylphosphine oxide photopolymerization initiator is an initiator having a broad absorption characteristic having an absorption region on the long wavelength side, it is suitable for a colored ink containing a high concentration of a colorant, and particularly thick. It is an initiator excellent in film curability (internal curability). However, the thin film curability and surface curability are insufficient, and the solubility in compounds containing ethylenic double bonds is not large. Therefore, a large amount in the ink for the purpose of achieving sufficient curability alone. In some cases, it may be deposited in ink due to low-temperature storage and cause ejection failure.

  The photoinitiator used in the present invention is not itself activated by ultraviolet irradiation, but when used in combination with a photopolymerization initiator, the initiation reaction is promoted more than the photopolymerization initiator alone, and the curing reaction proceeds efficiently. Is. The amine used as the photoinitiator aid can be widely used as a photoinitiator aid for conventional UV curable inks, paints, etc., but in particular the amine as the photoinitiator aid used in the present invention. The tertiary compound is preferably a tertiary amine, for example, an aliphatic amine such as triethanolamine, methyldiethanolamine, triisopropanolamine, 4,4′-diethylaminobenzophenone, ethyl 2-dimethylaminobenzoate, 4-dimethylamino. And aromatic amines such as ethyl benzoate and isoamyl 4-dimethylaminobenzoate. The amine used in the present invention is more preferably an aromatic tertiary amine.

As described above, oxy-phenyl-acetic acid 2- [2-oxo-2-phenyl-acetoxy-ethoxy] -ethyl ester and oxy-phenyl-acetic acid 2- [2-hydroxy-ethoxy] -ethyl ester When the mixture is used as a photopolymerization initiator, it has good thin film curability and surface curability, but is inferior in thick film curability and adhesion to a substrate to be printed. Therefore, by using the initiator together with a photopolymerization initiator using an acyl phosphine oxide compound having an absorption region on the long wavelength side and excellent in thick film curability (internal curability), a thin film portion, a thick film An ink having a partially improved curability can be obtained. However, as an ultraviolet curable ink composition for ink jet recording that is susceptible to polymerization inhibition by oxygen due to its low viscosity, it cannot be said that its curability in a thin film is practically sufficient.
In the present invention, by combining the above two types of photopolymerization initiators and further containing an amine as a photoinitiator aid, both the low-concentration thin film portion and the high-concentration thick film portion are included in the printed image area. An ink having excellent curability and adhesion to a substrate to be printed, less odor of a cured and dried printed image, and excellent color reproducibility of a full color print can be obtained. The blending amount of the aromatic tertiary amine is preferably 1 to 5% by mass. If the amount is less than 1% by mass, the curability tends to be insufficient. If the amount exceeds 5% by mass, the storage stability of the ink tends to decrease, the printed film tends to yellow, and the odor of the printed matter tends to increase. is there.

  In general, the higher the content of the photopolymerization initiator, the better the curability of the ink, but it causes an increase in ink viscosity and poor low-temperature storage stability due to precipitation. In addition, a photopolymerization initiator that has good solubility and hardly causes an increase in viscosity and poor low-temperature stability may be incorporated in a large amount. However, an unreacted photopolymerization initiator or a photopolymerization initiator decomposition product may be used. May cause problems such as an increase in odor of the cured film and a decrease in the strength of the cured film. Therefore, the content of the photopolymerization initiator in the ink is preferably used in the range of 5 to 15% by weight, and even when importance is attached to the coating film curability, the content is more preferably in the range of 7 to 13%. It is preferable to study the optimum blending while changing the type and combination of the photopolymerization initiator in the range of%. The photopolymerization initiator composition of the present invention can be used in combination with another initiator for the purpose of further improving the curability.

  Examples of the pigment used in the ultraviolet curable ink composition for inkjet recording of the present invention include inorganic pigments such as carbon black, titanium oxide and iron oxide, insoluble azo pigments, soluble azo pigments, phthalocyanine pigments, quinacridone pigments, perylene pigments, Examples thereof include organic pigments such as indoline pigments, benzimidazolone pigments, pyranthrone pigments, thioindigo pigments, and quinophthalone pigments. The content of the pigment in the ink is preferably in the range of 2 to 20% by mass in order to obtain a sufficient image density and light resistance of the printed image.

  Various (meth) acrylates can be used as the compound having an ethylenic double bond used in the present invention. Specific examples include monofunctional (meth) acrylates having one ethylenic double bond, polyfunctional (meth) acrylates having two or more ethylenic double bonds, and (meth) acrylate oligomers. Can be used in combination with more than one type. In order to obtain good curability, the content of the compound having one ethylenic double bond is preferably 20% by mass or less based on the total amount of the photopolymerizable compound. Furthermore, it is preferable to contain a (meth) acrylate oligomer or a trifunctional or higher polyfunctional acrylate, but these have a high viscosity, and in particular, the (meth) acrylate oligomer has a higher viscosity than the monomer. It is preferable to use in the range of 2 to 20% by mass with respect to the total amount of compounds having a bond.

  Examples of the monofunctional (meth) acrylate that can be used in the present invention include methyl, ethyl, propyl, butyl, amyl, 2-ethylhexyl, isooctyl, nonyl, dodecyl, hexadecyl, octadecyl, cyclohexyl, benzyl, methoxyethyl, butoxyethyl, And (meth) acrylate having a substituent such as phenoxyethyl, nonylphenoxyethyl, glycidyl, dimethylaminoethyl, diethylaminoethyl, isobornyl, dicyclopentanyl, dicyclopentenyl, dicyclopentenyloxyethyl and the like. Two or more of these can be used in combination.

  Examples of the polyfunctional (meth) acrylate include 1,3-butylene glycol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, and 1,6-hexanediol. Di (meth) such as neopentyl glycol, 1,8-octanediol, 1,9-nonanediol, tricyclodecane dimethanol, ethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol Di (meth) acrylate of diol obtained by adding 4 mol or more of ethylene oxide or propylene oxide to 1 mol of acrylate, tris (2-hydroxyethyl) isocyanurate di (meth) acrylate, neopentyl glycol , Di (meth) acrylate of diol obtained by adding 2 mol of ethylene oxide or propylene oxide to 1 mol of bisphenol A, and triol obtained by adding 3 mol or more of ethylene oxide or propylene oxide to 1 mol of trimethylolpropane. Di or tri (meth) acrylate, di (meth) acrylate of diol obtained by adding 4 mol or more of ethylene oxide or propylene oxide to 1 mol of bisphenol A, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) Acrylate, poly (meth) acrylate of dipentaerythritol, ethylene oxide modified phosphoric acid (meth) acrylate, ethylene oxide modified alkyl phosphoric acid (meth) acrylate, etc. It is. Two or more of these can be used in combination.

  Examples of the (meth) acrylate oligomer that can be used in the present invention include urethane (meth) acrylate oligomers, epoxy (meth) acrylate oligomers, polyester (meth) acrylate oligomers, and the like.

  In the ink composition for ink jet recording of the present invention, a polymerization inhibitor such as hydroquinone, methoquinone, P-methoxyphenol, nitrosamine salt or the like is added in an amount of 0.01 to 0.5% by mass in the ink in order to enhance the storage stability of the ink. You may add in the range.

For the purpose of enhancing the dispersion stability of the pigment, it is preferable to use a polymer dispersant as the dispersant used in the ink composition for ink jet recording of the present invention.
Specific examples include Ajinomoto Fine Techno's Ajisper PB821, PB822, PB817, Avisia's Solsper's 24000GR, 32000, Disparon DA-703-50, DA-705, DA-725 manufactured by Enomoto Kasei. It is not limited to. Further, the amount of the polymer dispersant used is preferably in the range of 10 to 80% by mass, particularly preferably in the range of 20 to 60% by mass with respect to the pigment. When the amount used is too small, the dispersion stability is insufficient, and when it is too large, the viscosity of the ink is increased, which is not preferable from the viewpoint of ejection stability.

  In addition, the ink composition of the present invention includes additives such as modified silicone oil for the purpose of adjusting the surface tension for good ink discharge and imparting wettability and adhesiveness to the substrate to be printed. Non-reactive resins and the like can be blended.

  The production of the ultraviolet curable jet ink composition of the present invention comprises a compound having an ethylenic double bond such as a pigment and (meth) acrylate, and a mixture containing a polymer dispersant and a resin as necessary, such as a bead mill. After the pigment is dispersed using an ordinary disperser, a photopolymerization initiator is added, and an additive such as a surface tension adjuster is added as necessary, followed by stirring and dissolution. A compound having an ethylenic double bond such as (meth) acrylate in which a photopolymerization initiator is dissolved after preparing a high-concentration pigment dispersion (mill base) using an ordinary dispersing machine such as a bead mill in advance. Can be prepared by stirring and mixing.

  Hereinafter, the present invention will be described in more detail by way of examples. The present invention is not limited by the following examples. In addition, the part in an Example below represents a mass part.

Example 1
(Adjustment of high density cyan dispersion)
Fastgen Blue 5412SD 10 parts (Dainippon Ink Chemicals phthalocyanine pigment CI Pigment Blue 15: 3)
Polymer dispersant “Ajisper PB821” 3 parts Dipropylene glycol diacrylate 87 parts was stirred and mixed with a stirrer for 1 hour, and then treated with a bead mill for 4 hours to prepare a high-concentration cyan dispersion.

(Cyan ink adjustment)
Epoxy acrylate oligomer 8 parts Ethylene oxide addition (3 mol) Trimethylolpropane triacrylate 28 parts Dipropylene glycol diacrylate 28 parts Isooctyl acrylate 16 parts KF-351A 0.2 part (manufactured by Shin-Etsu Chemical Polyether Silicone Oil)
To the above mixture, 20 parts of the high-concentration cyan dispersion was added to a solution prepared by adding the following photopolymerization initiator and heating and dissolving the photopolymerization initiator at 60 ° C., followed by thorough mixing, and then a 1.2 μm membrane. The ink for jet printer was produced by filtering with a filter.
"Irgacure 819" 4 parts (Ciba Specialty Chemicals)
"Irgacure 754" 4 parts (Ciba Specialty Chemicals)
3 parts ethyl dimethylaminobenzoate (Nippon Kayaku Co., Ltd.)

(Example 2 to Example 3, Comparative Example 1 to Comparative Example 5)
Instead of the photopolymerization initiator composition used in Example 1, a table. Using the composition and amount of the photopolymerization initiator shown in 1, UV-curable ink jet recording ink compositions corresponding to the remaining examples and comparative examples were prepared.
About the produced ultraviolet curable ink composition for inkjet recording, the characteristic was measured and evaluated by the method shown below. The photopolymerization initiator composition used for the cyan ink, the ink viscosity (25 ° C.), the odor of the cured film, the curability of the thin film and the thick film, and the evaluation results of the adhesion are shown. Ink viscosity, cured coating odor, ink curability and adhesion were evaluated by the following methods.

[Viscosity measurement method]
The viscosity at 25 ° C. of the inks prepared in each Example and Comparative Example was measured with an E-type viscometer.

[Thin film curability evaluation method]
The ink prepared in each example and comparative example was applied to a polycarbonate plate (trade name: Lexan, manufactured by Asahi Glass) with a spin coater so that the ink had a thickness of about 2 μm, and a conveyor type ultraviolet irradiation device (one metal halide lamp manufactured by Nippon Batteries) : Output 120 W / cm), ultraviolet rays were irradiated at an irradiation energy of 0.2 j / cm 2, and the number of passes at which the surface was not damaged was evaluated by a rubbing test using a nonwoven fabric (trade name: Bencott manufactured by Asahi Kasei).

[Thick film curability evaluation method]
The ink produced in each example and comparative example was applied to a polycarbonate plate (trade name: Lexan, manufactured by Asahi Glass) with a spin coater so that the ink had a thickness of about 6 μm, and a conveyor type ultraviolet irradiation device (metal halide lamp 1 manufactured by Nippon Batteries). The number of passes at which the surface was not damaged by a rubbing test using a non-woven fabric (trade name: Bencott manufactured by Asahi Kasei) was evaluated.

[Adhesion evaluation method]
Using a cutter, the ink created in Examples 1 to 3 and Comparative Examples 1 to 5 was applied in a thickness of 6 μm onto a polycarbonate plate (trade name: Lexan manufactured by Asahi Glass Co., Ltd.), and the coating surface was cut into a cloth shape. Then, an adhesive tape (manufactured by Nichiban) was applied to the cut portion by rubbing 50 times while pressing it with a finger with a force of about 1 kg, and the peeled state of the coating film was visually evaluated.
○: Does not peel.
Δ: Partially peeled off.
X: Completely peeled off.

[Method for evaluating odor of cured film]
The odor of the cured film after the thick film curable evaluation was sensitively evaluated by 5 people, and the odor intensity was classified into 3 levels, giving 3 points, 2 points, and 1 point, respectively. Classified as "Large", "Medium" and "Small".
(Evaluation criteria)
Odor "Large" 15 to 12 points Odor "Medium" 11 to 8 points Odor "Small" 5 to 7 points

(Table 1)

The substance names and manufacturer names of the initiators in the abbreviated table are as follows.
Irg. 819 (Irgacure 819): Bis (2,4,6 trimethylbenzoyl) -phenylphosphine oxide Irg. Manufactured by Ciba Specialty Chemicals. 754 (Irgacure 754): oxy-phenyl-acetic acid 2- [2-oxo-2-phenyl-acetoxy-ethoxy] -ethyl ester and oxy-phenyl-acetic acid 2- [2- manufactured by Ciba Specialty Chemicals Hydroxy-ethoxy] -ethyl ester mixture EPA: Nippon Kayaku Co., Ltd. Ethyl dimethylaminobenzoate Irg. 127 (Irgacure 368): 2-hydroxy-1-{-4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] -phenyl} -2-methyl-propane-1 manufactured by Ciba Specialty Chemicals -On Irg. 2959 (Irgacure 2959): 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one manufactured by Ciba Specialty Chemicals

As described above, the inks of Examples 1, 2, and 3 had a small cured film odor, and had good thin film curability, thick film curability, and thick film cured film adhesiveness. In contrast, the inks of Comparative Example 1 and Comparative Example 3 have low viscosity and good thin film curability, but thick film curability or adhesion of the thick film cured film is poor. The ink of Comparative Example 2 has better thick film curability and better adhesion of the thick film cured film than Comparative Examples 1 and 3, but the thin film curability is poor. The inks of Comparative Example 4 and Comparative Example 5 using Irgacure 127 and Irgacure 2529 as low odor α-hydroxyketone initiators have good thin film curability, but have a high viscosity and thick film cured coating. The adhesion was poor. In addition, both photopolymerization initiators are not necessarily sufficiently soluble, have poor solubility stability compared to Irgacure 754 in a liquid state at room temperature, and are stored at a low temperature, especially when used in large amounts in ink. When driven, the risk of deposits clogging the nozzle and causing defective discharge increases. In addition, as described in the prior art, I-light using Irgacure 369 and Irgacure 907, which have low volatility among α-aminoacetophenone initiators that are less susceptible to oxygen inhibition and have good thin film curability, as main components. Since the polymerization initiators have problems in terms of coloring (yellowing) and odor of the decomposed products, they are not employed from the beginning in the examples and comparative examples.

Claims (2)

Pigment, photopolymerizable compound having ethylenic double bond, oxy-phenyl-acetic acid 2- [2-oxo-2-phenyl-acetoxy-ethoxy] -ethyl ester and oxy-phenyl- as photopolymerization initiator An ultraviolet curable ink composition for ink jet recording, comprising a mixture of an acetic acid 2- [2-hydroxy-ethoxy] -ethyl ester, an acyl phosphine oxide compound, and an amine as a photoinitiator. object. The ink composition for ultraviolet curable ink jet recording according to claim 1, wherein the amine is an aromatic tertiary amine and the content in the ink composition is 1 to 5 mass%.