JP2011207960A - Active energy ray-curable white inkjet ink composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a white ink composition which is used in active energy ray-curable inkjet printing and has excellent whiteness and concealing properties of printed matter and excellent curability on printing.SOLUTION: The active energy ray-curable white inkjet ink composition includes at least a white pigment (A), a polymerizable monomer (B), an acylphosphine oxide-based photopolymerization initiator (C-1), and a photopolymerization initiator (C-2) other than the acylphosphine oxide-based photopolymerization initiator.

Description

  The present invention relates to a white ink composition used for active energy ray-curable ink jet printing, wherein the printed material has excellent whiteness and concealing properties and excellent curability during printing.

  Conventionally, ink compositions used for ink-jet printing are diverse, such as solvent-type, water-type, and oil-based types, but many non-absorbable substrates such as plastic and glass and paper substrates can be used. In recent years, the demand for an active energy ray-curable ink composition has increased due to the fact that the conventionally required ink drying step is not required and the productivity is high, the amount of volatilization of the solvent is reduced, and the environment is friendly.

  On the other hand, some of the above non-absorbing substrates are transparent or colored, and when printed on these substrates with color ink as they are, an image with poor color developability is obtained. Therefore, it is known to use a white ink in addition to a normal color ink for the purpose of improving the color developability and the design of the printed matter. For example, by printing white ink on a transparent substrate or a colored substrate in advance and then performing normal printing, it is possible to block the influence of the color of the substrate and improve the color developability of the printed matter.

  The active energy ray-curable white inkjet ink composition used for such purposes has not only high hiding properties and coloring power, but also low viscosity, stable ejection properties, which are necessary as an active energy ray-curable inkjet ink composition, High curability for active energy rays is required.

So far, active energy ray-curable white inkjet ink compositions as shown in Patent Documents 1 to 3 have been reported. Among these, Patent Documents 1 and 2 are examples of a cation type active energy ray curable white inkjet ink composition. Generally, a cation type active energy ray curable inkjet ink composition is cured under the influence of heat and humidity. The properties are known to change, and the curability may be inferior depending on the printing environment.
Moreover, although patent document 3 is an example of a radical type active energy ray hardening-type white inkjet ink composition, sclerosis | hardenability may be inferior depending on printed matter, such as a printing rate and a film thickness.
In addition, although Patent Document 4 reports a photopolymerization initiator used for an active energy ray-curable inkjet ink containing an inorganic pigment, there is no example relating to a white ink composition in the specification. When developed in a white ink composition, the desired curability may not be obtained depending on the conditions of the printed matter, as in Patent Document 3. As described above, an active energy ray-curable white inkjet ink composition having high curability is not obtained regardless of printing conditions.

JP 2004-059627 A JP 2008-081517 A JP 2008-308692 A JP 2008-081594 A

  The present invention provides a white ink composition used for active energy ray curable ink jet printing, wherein the printed material has excellent whiteness and concealing properties, and excellent curability during printing. To do.

  The present inventor is a white ink composition used for active energy ray-curable ink jet printing, wherein the printed material has excellent whiteness and concealing properties, and has excellent curability during printing. As a result of intensive studies to provide the ink composition, the ink composition contains an acylphosphine oxide photopolymerization initiator (C-1) and a photopolymerization initiator (C-2) that is not an acylphosphine oxide. The present invention has been accomplished by finding that the above problems can be solved.

That is, the present invention relates to the following inventions (1) to (7).
(1) At least a white pigment (A), a polymerizable monomer (B), an acylphosphine oxide photopolymerization initiator (C-1), and a photopolymerization initiator (C-2) that is not an acylphosphine oxide An active energy ray-curable white inkjet ink composition characterized by the above.
(2) The active energy ray-curable white inkjet ink composition according to (1), wherein the white pigment (A) is contained in an amount of 10 to 20% based on the total amount of the ink composition.
(3) The total content of the acylphosphine oxide photopolymerization initiator (C-1) and the non-acylphosphine oxide photopolymerization initiator (C-2) is 5 to 15 with respect to the total amount of the ink composition. % Of the active energy ray-curable white inkjet ink composition according to any one of (1) to (2).
(4) The ratio of the content of the acylphosphine oxide photopolymerization initiator (C-1) and the photopolymerization initiator (C-2) that is not acylphosphine oxide is 1: 1 to 3: 1. The active energy ray-curable white inkjet ink composition according to any one of (1) to (3).
(5) The acylphosphine oxide photopolymerization initiator (C-1) contains only 2,4,6-trimethylbenzoyldiphenylphosphine oxide, according to any one of (1) to (4) Active energy ray-curable white inkjet ink composition.
(6) The activity according to any one of (1) to (5), characterized in that it contains no aminoacetophenone photopolymerization initiator as the photopolymerization initiator (C-2) that is not acylphosphine oxide. Energy ray curable white inkjet ink composition.
(7) It contains oligo (2-hydroxy-2-methyl-1- (4- (1-methylvinyl) phenyl) propanone) as a photopolymerization initiator (C-2) that is not an acylphosphine oxide type. The active energy ray-curable white inkjet ink composition according to any one of (1) to (6).

  Used in active energy ray-curable ink jet printing by including an acylphosphine oxide photopolymerization initiator (C-1) and a photopolymerization initiator (C-2) that is not an acylphosphine oxide in the ink composition. Thus, it was possible to obtain an ink composition in which the printed material had excellent whiteness and concealment and excellent curability during printing.

  In the present invention, two types of photopolymerization initiators, an acylphosphine oxide photopolymerization initiator and a photopolymerization initiator that is not acylphosphine oxide, are used in combination with a white active energy ray-curable inkjet ink composition. As a result, it is possible to obtain an ink composition excellent not only in whiteness and concealment of printed matter but also in curability.

  In the present specification, “whiteness” means that when a white ink composition is cured to produce a printed material, the printed material is not yellowish due to the components contained in the ink composition, and the whiteness inherent to the white pigment is obtained. It represents that the printed matter that has it is obtained.

  Generally, in a white active energy ray-curable inkjet ink composition, the white pigment contained in the ink composition reflects light regardless of the wavelength, and the active energy ray is not easily transmitted to the inside of the printed matter. The polymerization reaction by the initiator becomes insufficient, resulting in poor curing.

  Here, the active energy transmitted into the white printed matter is obtained by including in the ink composition an acylphosphine oxide-based photopolymerization initiator that has a wide light absorption region from the near ultraviolet to the visible region and is excellent in radical generation efficiency. It can react without missing a line, and as a result, excellent curability can be expressed.

  On the other hand, it is known that benzoyl radicals, which are generated by cleavage of acylphosphine oxide photopolymerization initiators and trigger the polymerization reaction, have the property of being easily combined with oxygen. In such a case, poor curing may occur due to the influence of oxygen on the surface of the coating film. Therefore, by using a photopolymerization initiator different from the acylphosphine oxide photopolymerization initiator and including a plurality of photopolymerization initiators having different characteristics in the ink composition, it is excellent regardless of the printing rate and film thickness. A white ink composition having high curability can be obtained.

  Thus, in order to obtain excellent curability irrespective of the printing rate and film thickness of the printed matter, an acylphosphine oxide photopolymerization initiator (C-1) and a photopolymerization initiator that is not an acylphosphine oxide ( The ratio of the blending amount of C-2) is important. The ratio in which the acylphosphine oxide photopolymerization initiator (C-1) is blended with the photopolymerization initiator (C-2) that is not an acylphosphine oxide photopolymerization initiator other than the acylphosphine oxide photopolymerization initiator is used. When agent (C-2) is 1, it is preferably 1 to 3, and more preferably 1 to 2. Here, if the ratio of the acylphosphine oxide photopolymerization initiator (C-1) to the photopolymerization initiator (C-2) that is not an acylphosphine oxide is less than 1, the acylphosphine oxide photopolymerization starts The effect of the agent (C-1) is reduced, and poor curing occurs in printed matter with a high printing rate or thick film. On the other hand, when it is larger than 3, the influence of the photopolymerization initiator (C-2) that is not an acylphosphine oxide is reduced, resulting in poor printing and poor curing in a thin printed matter.

  In order to develop excellent curability, it is necessary to consider the contents of the acylphosphine oxide photopolymerization initiator (C-1) and the photopolymerization initiator (C-2) that is not acylphosphine oxide. There is. In the present invention, the total content of the acylphosphine oxide photopolymerization initiator (C-1) and the non-acylphosphine oxide photopolymerization initiator (C-2) is 4 with respect to the total amount of the ink composition. It is preferably -14%, and more preferably 6-12%. Here, when the total content is less than 4%, the curability is remarkably deteriorated, which is not preferable. When the total content is more than 14% by weight, the curing rate does not change from that of the content of 14% by weight, and the dissolution remains. In some cases, even when heat is applied to dissolve the undissolved residue, there is a problem that the viscosity of the ink composition is increased and the dischargeability is deteriorated.

  As the acylphosphine oxide photopolymerization initiator (C-1) contained in the ink composition of the present invention, conventionally known materials can be used. Specific examples include 2,4,6-trimethylbenzoyl diphenylphosphine oxide and bis (2,4,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide. These materials may be used alone or in combination, but the ink composition has good storage stability, the photopolymerization initiator itself is small in yellowness, and has whiteness. In view of obtaining excellent printed matter, it is preferable to use 2,4,6-trimethylbenzoyldiphenylphosphine oxide alone.

  Examples of commercially available acylphosphine oxide photopolymerization initiators (C-1) include “Lucirin TPO, DAROCURETPO, Irgacure 819” manufactured by BASF, “Dido UV Cure APO” manufactured by Daido Kasei Kogyo Co., Ltd., “ SB-PI 718, 719 ".

  The content of the acylphosphine oxide photopolymerization initiator (C-1) needs to consider the content of the photopolymerization initiator (C-2) other than the acylphosphine oxide photopolymerization initiator as described above. However, it is preferably 1 to 12%, more preferably 2 to 10%, and particularly preferably 4 to 8% with respect to the total amount of the ink composition. Here, if the content is less than 1%, the curability is deteriorated, and if the content exceeds 12%, dissolution residue occurs or the viscosity of the ink composition increases, which is not preferable.

  The non-acylphosphine oxide photopolymerization initiator (C-2) used in the present invention can be freely selected from known materials excluding acylphosphine oxide photopolymerization initiators. In particular, those of molecular cleavage type or hydrogen abstraction type are suitable for the present invention. Specifically, benzoin isobutyl ether, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, 2-benzyl-2-dimethylamino-1- ( 4-morpholinophenyl) -butan-1-one, 2-methyl-1- (4-methylthiophenyl) -2-morpholinopropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl -1-phenylpropan-1-one, oligo (2-hydroxy-2-methyl-1- (4- (1-methylvinyl) phenyl) propanone), 4-benzoyl-4′-methyl-diphenyl sulfide, 1, 2-octanedione, 1- (4- (phenylthio) -2,2- (O-benzoyloxime)), Zone in ethyl ether, benzyl dimethyl ketal, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, benzophenone, 4-phenyl benzophenone, and the like isophthalic phenone.

Among these photopolymerization initiators, oxygen inhibition is unlikely to occur, and the curability of the acylphosphine oxide photopolymerization initiator (C-1) can be suitably supplemented. The radical generation efficiency is high and the curability of the ink composition is high. 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl, in that the photopolymerization initiator itself has a small yellowishness and a printed matter with excellent whiteness can be obtained. It is preferable to select an α-hydroxyketone photopolymerization initiator such as propan-1-one or oligo (2-hydroxy-2-methyl-1- (4- (1-methylvinyl) phenyl) propanone). It is particularly preferred to select (2-hydroxy-2-methyl-1- (4- (1-methylvinyl) phenyl) propanone).
On the other hand, 2-methyl-1- (4-methylthiophenyl) -2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butan-1-one As for aminoacetophenone photopolymerization initiators such as these, while it is possible to obtain ink compositions with excellent curability, the photopolymerization initiators themselves are strongly yellowish and have poor whiteness prints. The ink composition of the present invention is preferably not contained.

  The photopolymerization initiators (C-2) that are not acylphosphine oxides may be used alone or in combination of two or more.

  The content of the photopolymerization initiator (C-2) that is not an acylphosphine oxide is preferably 1 to 10%, more preferably 2.5 to 8%, based on the total amount of the ink composition. Here, if the content is less than 1%, the curability of the ink composition is deteriorated, and if it is more than 10%, the dissolution residue and the viscosity of the ink composition increase, which is not preferable. In addition, as described above, the content of the photopolymerization initiator (C-2) that is not an acylphosphine oxide system needs to be set in consideration of the content of the acylphosphine oxide photopolymerization initiator (C-1). is there.

  For the photopolymerization initiator (C-2) which is not an acylphosphine oxide, trimethylamine, methyldimethanolamine, triethanolamine, p-diethylaminoacetophenone, ethyl p-dimethylaminobenzoate, p- Amines such as isoamyl dimethylaminobenzoate, N, N-dimethylbenzylamine and 4,4′-bis (diethylamino) benzophenone can be used in combination. These sensitizers are preferably selected from those having excellent solubility in the ink composition.

  When these sensitizers are used, the content is preferably 0.5 to 5% with respect to the total amount of the ink composition. When the content is less than 0.5%, the function as a sensitizer cannot be exhibited, and when the content is more than 5%, the sensitizer increases with respect to the photopolymerization initiator. This is not preferable because the ink composition is too low and the curability of the ink composition is lowered, and the sensitizer itself has a yellowish color, resulting in a printed matter having inferior whiteness.

The white pigment (A) in the present invention is not limited as long as the ink composition can be made white, and examples thereof include inorganic white pigments, organic white pigments, and white polymer fine particles.
Among these, inorganic white pigments include carbonates of alkaline earth metals such as titanium oxide, zinc oxide, alumina, calcium carbonate, silicic acid, calcium silicate, lead white, talc, clay, etc. Bisstyryl derivative white pigments disclosed in JP-A Nos. 11-130975 and 2004-250559, and alkylene bismelamine derivative white pigments disclosed in JP-A Nos. 11-14365 and 2001-234093.

  Of these, titanium oxide is preferably used as the white pigment (A) in terms of concealability and colorability. Titanium oxide has crystal forms such as a rutile type, anatase type, and brookite type, and any of them can be suitably used in the present invention, but a rutile type having low light transmittance and high concealability is more preferably used. It is done.

  When rutile type titanium oxide is selected, the selection of the photopolymerization initiator is important because of its poor light transmission. In the present invention, since the ink composition contains a photopolymerization initiator (C-2) other than the acylphosphine oxide photopolymerization initiator (C-1) and the acylphosphine oxide photopolymerization initiator, Even if rutile type titanium oxide having poor light transmittance is used, sufficient curability can be exhibited.

  Moreover, when using titanium oxide by this invention, surface treatment can be performed as needed in order to stabilize dispersion and improve weather resistance. A well-known thing can be arbitrarily used for the surface treatment method and the surface treating agent.

  Specific examples of titanium oxide include “Taipeku CR-50, 50-2, 57, 80, 90, 93, 95, 953, 97, 60, 60-2, 63, 67, 58, 58- manufactured by Ishihara Sangyo Co., Ltd. 2, 85 "" Tipekes R-820, 830, 930, 550, 630, 680, 670, 580, 780, 780-2, 850, 855 "," Tipekes A-100, 220 "," Tipekes W-10 "," Tipekes " PF-740, 744 "" TTO-55 (A), 55 (B), 55 (C), 55 (D), 55 (S), 55 (N), 51 (A), 51 (C) " "TTO-S-1, 2", "TTO-M-1, 2", "Titanics JR-301, 403, 405, 600A, 605, 600E, 603, 805, 806, 701, 800, 808" manufactured by Teika "Titanic EN-1, C, 3, 4, 5 ", DuPont" Taipyua R-900,902,960,706,931 ', and the like.

  The average particle diameter when the white pigment (A) of the present invention is dispersed in the ink composition is preferably 50 to 500 nm, and more preferably 100 to 350 nm. Here, when the average particle size of the white pigment (A) is less than 50 nm, the dispersion stability is deteriorated even when the dispersion stabilization treatment is performed. As a result, the storage stability of the ink composition is deteriorated, and at the time of printing. It becomes difficult to obtain sufficient concealment. On the contrary, when the average particle diameter of the white pigment (A) exceeds 500 nm, the inkjet discharge property is deteriorated, which is not preferable.

  Note that Microtrac UPA (manufactured by Microtrac) was used to measure the average particle diameter of the white pigment (A) in the ink composition. Further, methyl ethyl ketone was used as a dispersion medium.

  The content of the white pigment (A) of the present invention is preferably 10 to 20%, more preferably 12 to 18%, based on the total amount of the ink composition. Here, when the content is less than 10%, the concealability of the printed matter is insufficient, and when the content exceeds 20%, the viscosity of the ink composition cannot be within a suitable range, and as a result Discharging becomes impossible.

  In the present invention, it is preferable to add a dispersant in order to improve the dispersion stability of the white pigment (A) and the storage stability of the ink composition. Examples of the dispersant include a hydroxyl group-containing carboxylic acid ester, a salt of a long-chain polyaminoamide and a high molecular weight acid ester, a salt of a high molecular weight polycarboxylic acid, a salt of a long chain polyaminoamide and a polar acid ester, a high molecular weight unsaturated acid ester, Molecular copolymer, modified polyurethane, modified polyacrylate, polyether ester type anionic activator, naphthalene sulfonic acid formalin condensate salt, aromatic sulfonic acid formalin condensate salt, polyoxyethylene alkyl phosphate ester, polyoxyethylene nonyl Phenyl ether, stearylamine acetate, etc. can be used.

  Specific examples of the dispersant include “Anti-Terra-U (polyaminoamide phosphate)”, “Anti-Terra-203 / 204 (high molecular weight polycarboxylate)”, “Disperbyk-101” (polyamino) manufactured by BYK Chemie. Amide phosphate and acid ester), 107 (hydroxyl group-containing carboxylic acid ester), 110, 111 (copolymerization product containing acid group), 130 (polyamide), 145, 161, 162, 163, 164, 165, 166, 170 (Polymer copolymer) ”,“ 400 ”,“ Bykumen ”(high molecular weight unsaturated acid ester),“ BYK-P104, P105 (high molecular weight unsaturated acid polycarboxylic acid) ”,“ P104S, 240S (high molecular weight) Unsaturated acid polycarboxylic acid and silicon system "," Lactimon (long chain amine and unsaturated) Acid polycarboxylic acid and silicon) ”.

  Also, “Efka CHEMICALS” “Efka 44, 46, 47, 48, 49, 54, 63, 64, 65, 66, 71, 701, 764, 766”, “Efka Polymer 100 (modified polyacrylate), 150 (aliphatic) System modified polymer), 400, 401, 402, 403, 450, 451, 452, 453 (modified polyacrylate), 745 (copper phthalocyanine system) "," Floren TG-710 (urethane oligomer) "," Flownon "manufactured by Kyoeisha Chemical Co., Ltd. “SH-290, SP-1000”, “Polyflow No. 50E, No. 300 (acrylic copolymer)”, “Disparon KS-860, 873SN, 874 (polymer dispersing agent), # 2150 (manufactured by Enomoto Kasei Co., Ltd.) Aliphatic polyvalent carboxylic acid), # 7004 (polyether ester type) " That.

Further, “Demol RN, N (Naphthalenesulfonic acid formalin condensate sodium salt), MS, C, SN-B (aromatic sulfonic acid formalin condensate sodium salt), EP”, “Homogenol L-18 (poly) Carboxylic acid type polymer), “Emulgen 920, 930, 931, 935, 950, 985 (polyoxyethylene nonyl phenyl ether)”, “Acetamine 24 (coconut amine acetate), 86 (stearyl amine acetate)”, manufactured by Lubrizol "Solsperse 5000 (phthalocyanine ammonium salt type), 13940 (polyesteramine type), 17000 (fatty acid amine type), 24000GR, 32000, 33000, 39000, 41000, 53000", Nikko Chemical's "Nikkor T106 (poly Oxyethylene sorbitan monooleate), MYS-IEX (polyoxyethylene monostearate), Hexagline 4-0 (hexaglyceryl tetraoleate) ", Ajinomoto Fine Techno Co., Ltd." Azisper PB821, 822, 824, 827, 711 ", Tego Examples thereof include “TEGODisper685” manufactured by Chemiservice.
The above dispersants may be used alone or in combination of two or more.

  The amount of the dispersant added to the white pigment (A) is preferably 3 to 50% by weight. Here, when the addition amount is less than 3%, the ability as a dispersant cannot be exhibited, and the dispersion stability of the white pigment (A) and the storage stability of the ink composition are deteriorated. On the other hand, if it is 50% or more, the viscosity of the ink composition cannot be kept within a suitable range, and as a result, ejection cannot be performed.

  As a polymerizable monomer (B) used by this invention, a conventionally well-known material can be used as needed.

Specific examples of the polymerizable monomer (B) include benzyl (meth) acrylate, (ethoxy (or propoxy)) 2-phenoxyethyl (meth) acrylate, dicyclopentenyl (oxyethyl) (meth) acrylate as a monofunctional monomer, Phenoxydiethylene glycol (meth) acrylate, 2-methoxyethyl (meth) acrylate, methoxytriethylene glycol (meth) acrylate, 2-ethoxyethyl (meth) acrylate, ethoxyethoxyethyl (meth) acrylate, methoxydipropylene glycol (meth) acrylate , Dipropylene glycol (meth) acrylate, β-carboxylethyl (meth) acrylate, trimethylolpropane formal (meth) acrylate, isoamyl (meth) acrylate, Chlohexyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentanyl (meth) acrylate, isooctyl (meth) acrylate, lauryl (meth) acrylate, 2-hydroxy-3-phenoxypropyl ( (Meth) acrylate, 1,4-cyclohexanedimethanol (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, acryloylmorpholine, N-vinylcaprolactam N-vinylpyrrolidone, N-vinylformamide, and N-acryloyloxyethyl hexahydrophthalimide.
Polyfunctional monomers include dimethylol tricyclodecane di (meth) acrylate, (ethoxy (or propoxy)) bisphenol A di (meth) acrylate, cyclohexanedimethanol di (meth) acrylate, (poly) ethylene glycol di ( (Meth) acrylate, (ethoxy (or propoxy)) 1,6-hexanediol di (meth) acrylate, (ethoxy (or propoxy)) neopentyl glycol di (meth) acrylate, hydroxypivalate neopentyl glycol di (meth) ) Acrylate, dipropylene glycol di (meth) acrylate, (neopentyl glycol modified) trimethylolpropane di (meth) acrylate, tripropylene glycol di (meth) acrylate, dicyclopentanyl di (meth) acrylate Examples include rate, pentaerythritol tri (or tetra) (meth) acrylate, trimethylolpropane tri (or tetra) (meth) acrylate, tetramethylolmethane tri (or tetra) (meth) acrylate, and dipentaerythritol hexa (meth) acrylate. be able to.
The above materials may be used alone or in combination of two or more.

Of these, in the present invention, (ethoxy (or propoxy)) 2-phenoxyethyl acrylate, ethoxyethoxyethyl acrylate, isobornyl acrylate, isooctyl acrylate, lauryl acrylate, N-vinylcaprolactam, N-acryloyl as a monofunctional monomer Oxyethylhexahydrophthalimide and dimethylol tricyclodecane diacrylate, (ethoxy (or propoxy)) bisphenol A diacrylate, (ethoxy (or propoxy)) neopentyl glycol diacrylate, hydroxypivalic acid as polyfunctional monomer Neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate It can be used bets more suitably.
As described above, in the present invention, it is preferable that the content of the white pigment (A) is 10 to 20% with respect to the total amount of the ink composition. It becomes difficult. However, by selecting the suitable polymerizable monomer, the viscosity of the ink composition can be within a suitable range.
In addition, the polymerizable monomer is preferably used in terms of high-speed curability and cured film performance.

  In the present invention, in order to increase the curability of the ink composition and the strength of the printed material, it is desirable to use a monofunctional monomer and a polyfunctional monomer together, and the amount of the monofunctional monomer is 30 to 99% with respect to the entire polymerizable monomer. It is preferably 40 to 95%, more preferably 50 to 90%.

  In order to impart resistance to printed matter, oligomers and prepolymers can be used in the ink composition of the present invention. Specific examples of oligomers and prepolymers include “Ebecryl 230, 244, 245, 270, 280 / 15IB, 284, 285, 4830, 4835, 4858, 4883, 8402, 8803, 8800, 254, 264, 265, manufactured by Daicel UCB. 294 / 35HD, 1259, 1264, 4866, 9260, 8210, 1290.1290K, 5129, 2000, 2001, 2002, 2100, KRM7222, KRM7735, 4842, 210, 215, 4827, 4849, 6700, 6700-20T, 204 205, 6602, 220, 4450, 770, IRR567, 81, 84, 83, 80, 657, 800, 805, 808, 810, 812, 1657, 1810, IRR302, 450, 67 830, 835, 870, 1830, 1870, 2870, IRR267, 813, IRR483, 811, 436, 438, 446, 505, 524, 525, 554W, 584, 586, 745, 767, 1701, 1755, 740 / 40TP 600, 601, 604, 605, 607, 608, 609, 600 / 25TO, 616, 645, 648, 860, 1606, 1608, 1629, 1940, 2958, 2959, 3200, 3201, 3404, 3411, 3412, 3415 3500, 3502, 3600, 3603, 3604, 3605, 3608, 3700, 3700-20H, 3700-20T, 3700-25R, 3701, 3701-20T, 3703, 3702, RDX63182, 6040, RR419 ”, manufactured by Sartomer,“ CN104, CN120, CN124, CN136, CN151, CN2270, CN2271E, CN435, CN454, CN970, CN971, CN972, CN9782, CN981, CN9873, CN99L, A8787 , LR8986, PE56F, PE44F, LR8800, PE46T, LR8907, PO43F, PO77F, PE55F, LR8967, LR8981, LR8982, LR8992, LR9004, LR8956, LR8985, LR8987, UP35D, UA19T, F83L63 , LR8869, LR8889, LR899 , LR8996, LR9013, LR9019, PO9026V, PE9027V, manufactured by Cognis, "Photomer 3005, 3015, 3016, 3072, 3982, 3215, 5010, 5429, 5430, 5432, 5562, 5806, 5930, 6008, 6010, 6019, 6184 6210, 6217, 6230, 6891, 6892, 6893-20R, 6363, 6572, 3660, manufactured by Negami Kogyo Co., Ltd. “Art Resin UN-9000HP, 9000PEP, 9200A, 7600, 5200, 1003, 1255, 3320HA, 3320HB, 3320HC” 3320HS, 901T, 1200TPK, 6060PTM, 6060P "," Nippon Gosei UV-6630B, 7000B, 7510B, 7 " 461TE, 3000B, 3200B, 3210EA, 3310B, 3500BA, 3520TL, 3700B, 6100B, 6640B, 1400B, 1700B, 6300B, 7550B, 7605B, 7610B, 7620EA, 7630B, 7640B, 2000B, 2010B, 2250EA, 2750B, Nippon Kayaku “Kayarad R-280, R-146, R131, R-205, EX2320, R190, R130, R-300, C-0011, TCR-1234, ZFR-1122, UX-2201, UX-2301, UX3204, UX-3301, UX-4101, UX-6101, UX-7101, MAX-5101, MAX-5100, MAX-3510, UX-4101 ”and the like.

  The ink composition of the present invention may contain an organic solvent in order to reduce the viscosity and improve the wetting and spreading property to the substrate.

  Organic solvents include ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl Ether acetate, ethylene glycol monomethyl ether propionate, ethylene glycol monoethyl ether propionate, ethylene glycol monobutyl ether propionate, diethyl diglycol, diethylene glycol dialkyl ether, tetraethylene glycol dialkyl Ether, diethylene glycol monomethyl ether propionate, diethylene glycol monoethyl ether propionate, diethylene glycol monobutyl ether propionate, propylene glycol monomethyl ether propionate, dipropylene glycol monomethyl ether propionate, ethylene glycol monomethyl ether butyrate, ethylene glycol Monoethyl ether butyrate, ethylene glycol monobutyl ether butyrate, diethylene glycol monomethyl ether butyrate, diethylene glycol monoethyl ether butyrate, diethylene glycol monobutyl ether butyrate, propylene glycol monomethyl ether butyrate, dipropylene glycol monomethyl ether Glycol monoacetates such as tyrate, ethylene glycol diacetate, diethylene glycol diacetate, propylene glycol diacetate, dipropylene glycol diacetate, ethylene glycol acetate propionate, ethylene glycol acetate butyrate, ethylene glycol propionate butyrate, ethylene Glycol dipropionate, ethylene glycol acetate dibutyrate, diethylene glycol acetate propionate, diethylene glycol acetate butyrate, diethylene glycol propionate butyrate, diethylene glycol dipropionate, diethylene glycol acetate dibutyrate, propylene glycol acetate propionate, propylene glycol Acetate butyrate, propylene glycol propionate butyrate, propylene glycol dipropionate, propylene glycol acetate dibutyrate, dipropylene glycol acetate propionate, dipropylene glycol acetate butyrate, dipropylene glycol propionate butyrate, dipropylene Glycol diacetates such as glycol dipropionate and dipropylene glycol acetate dibutyrate, glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol and dipropylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol Monobutyl ether, diethylene Cole monoethyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, propylene glycol n-propyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene Examples include glycol ethers such as glycol monobutyl ether and tripropylene glycol monomethyl ether, and lactic acid esters such as methyl lactate, ethyl lactate, propyl lactate, and butyl lactate. Among these, tetraethylene glycol dialkyl ether, ethylene glycol monobutyl ether acetate, and diethyl diglycol are preferable.

  In the present invention, 4-methoxyphenol, hydroquinone, methylhydroquinone, t-butylhydroquinone, 2,5-t-butyl-4-methyl are used to improve the storage stability of the ink composition and the stability in the recording apparatus. It is preferable to use a polymerization inhibitor such as an aluminum salt of phenol, phenothiazine or N-nitrosophenylhydroxylamine. From the viewpoint of improving stability while maintaining curability, it is preferably blended at a ratio of 0.01 to 5 parts by weight with respect to the entire ink composition.

  In the ink composition of the present invention, additives such as a surface conditioner, a leveling agent, an ultraviolet absorber, and an antioxidant can be used as necessary in order to increase printability and printed matter resistance.

  The ink composition of the present invention is produced by thoroughly dispersing the white pigment (A), the polymerizable monomer (B), and the dispersant using a normal dispersing machine such as a sand mill. In the present invention, it is preferable to prepare a concentrated solution containing the white pigment (A) at a high concentration in advance and then dilute with the polymerizable monomer (B). This method enables sufficient dispersion even in dispersion using a normal disperser, and does not require excessive dispersion energy, and does not require a large amount of dispersion time, so that it is difficult to cause material deterioration during dispersion, and as a result An ink having excellent stability can be produced.

  In order to prevent clogging in the head, the ink composition of the present invention is preferably filtered through a filter having a pore size of 3 μm or less, preferably 1 μm or less after dispersion and / or after dissolution of the radical photopolymerization initiator.

The ink composition of the present invention preferably has a viscosity at 25 ° C. adjusted to 5 to 100 mPa · s. If it is this viscosity area | region, the stable discharge characteristic will be shown also in the head of the high frequency of 10-50 KHz especially from the head which has a frequency of normal 4-10 KHz.
When the viscosity is less than 5 mPa · s, a decrease in the followability of the discharge is recognized in the high-frequency head. When the viscosity exceeds 100 mPa · s, even if a mechanism for reducing the viscosity by heating is incorporated in the head, the discharge itself A drop occurs, the ejection stability becomes poor, and the ejection cannot be performed at all.

  The ink composition of the present invention preferably has an electric conductivity of 10 μS / cm or less in a piezo head and does not cause electrical corrosion inside the head. In the continuous type, it is necessary to adjust the electric conductivity by the electrolyte. In this case, it is necessary to adjust the electric conductivity to 0.5 mS / cm or more.

  In order to use the ink composition of the present invention, the ink composition is first supplied to a printer head of a printer for an ink jet recording system, discharged from the printer head onto a substrate, and then activated energy such as ultraviolet rays or electron beams. Irradiate the line. This quickly cures the composition on the print medium.

  In addition, when irradiating an ultraviolet-ray as a light source of an active energy ray, a high pressure mercury lamp, a metal halide lamp, a low pressure mercury lamp, an ultrahigh pressure mercury lamp, an ultraviolet laser, LED, and sunlight can be used, for example.

  Although there is no limitation in particular about the printing base material used by this invention, Plastic base materials, such as a polycarbonate, a hard vinyl chloride, a soft vinyl chloride, a polystyrene, a foamed polystyrene, PMMA, a polypropylene, polyethylene, PET, these mixed or modified goods, a fine paper And paper base materials such as art paper, coated paper and cast coated paper, and metal base materials such as glass and stainless steel.

[Example]
Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the embodiments of the present invention are not limited to these examples. In the following, all parts represent parts by weight. The detailed conditions of the following Examples and Comparative Examples are shown in Table 1 below, and the results are shown in Table 2.

(Creation of pigment dispersion)
Pigment Rutile type titanium oxide (“PF-740” manufactured by Ishihara Sangyo Co., Ltd.) 60.0 parts Pigment dispersant “Solsperse 32000” manufactured by Lubrizol 3.0 parts monomer 2-phenoxyethyl acrylate 37.0 parts After stirring with a mixer or the like until uniform, the obtained mill base was prepared by dispersing for about 1 hour in a horizontal sand mill.

  The materials listed in Table 1 were added and mixed with sequential stirring, mixed gently until the photopolymerization initiator was dissolved, then filtered through a membrane filter with a pore size of 1 μm to remove coarse particles, and inkjet ink A composition was obtained.

[Examples 2 to 15]
In the same manner as in Example 1, an inkjet ink composition was prepared as shown in Table 1.

[Comparative Examples 1 to 4]
In the same manner as in Example 1, an inkjet ink composition was prepared as shown in Table 1.

(Curing test)
Using the ink composition prepared above, the ink composition was ejected onto a polycarbonate plate by an inkjet ejection device equipped with a piezo head manufactured by Konica Minolta IJ. Immediately after ejection, a metal halide lamp (output 120 W / cm) manufactured by Harrison Toshiba Lighting was used to irradiate ultraviolet rays, and the maximum conveyor speed at which the printed material was cured was investigated. By performing this test under two conditions, one having a film thickness at the time of ejection of 10 μm and 2 μm, the curability of the thick film and the thin film was evaluated. The evaluation criteria at this time are as follows, and Δ or higher is considered to be good curability.
○: Cured even when the conveyor speed is faster than 10 m / min. Δ: Cured when the conveyor speed is 5 to 10 m / min. X: Not cured even when the conveyor speed is 5 m / min.

(Concealment)
Concealability was evaluated by measuring the transmission density of a coating film having a film thickness of 10 μm at the time of ejection prepared in the above curable test using a Macbeth TR-924 densitometer. The evaluation criteria at this time are as follows.
○: Transmission density is 0.6 or more Δ: Transmission density is 0.4 or more and less than 0.6 ×: Transmission density is less than 0.4

(Whiteness)
Using a 528 spectral densitometer manufactured by X-Rite, the hue (b * value) is measured with a viewing angle of 2 °, a D50 light source, and a Hunter calculation method for the coating film having a film thickness of 10 μm prepared in the above curable test. As a result, whiteness was evaluated. The evaluation criteria at this time are as follows.
◎: b * value is less than −1.5 ○: b * value is −1.5 or more and less than 0.0 Δ: b * value is 0.0 or more and less than 1.5 ×: b * value is 1.5 or more

Table 2 shows the evaluation results for the ink compositions prepared in Examples 1 to 15 and Comparative Examples 1 to 4. In Examples 1 to 15 in which the ink composition contained an acylphosphine oxide photopolymerization initiator (C-1) and a photopolymerization initiator (C-2) that was not an acylphosphine oxide, the film thickness during ejection was increased. Regardless, it was confirmed that it had excellent curability, and good results were obtained for the concealability and whiteness of the printed matter prepared from these ink compositions.
Further, only 2,4,6-trimethylbenzoyldiphenylphosphine oxide is contained as the acylphosphine oxide photopolymerization initiator (C-1), and oligo (C-2) is used as the non-acylphosphine oxide photopolymerization initiator (C-2). In Examples 1 and 2 containing 2-hydroxy-2-methyl-1- (4- (1-methylvinyl) phenyl) propanone), all of the properties of curability, concealability and whiteness are the best, The above photoinitiators have been shown to be preferred materials for these properties.

  On the other hand, in Comparative Examples 1 and 2 containing only the acylphosphine oxide photopolymerization initiator (C-1) as the photopolymerization initiator, the curability at a film thickness of 2 μm at the time of ejection is insufficient, and conversely In Comparative Examples 3 to 4 containing only a photopolymerization initiator (C-2) that is not an acylphosphine oxide type as an initiator, the curability at a discharge thickness of 10 μm was insufficient. From this result, in order to obtain excellent curability regardless of the film thickness, the acylphosphine oxide photopolymerization initiator (C-1) and the photopolymerization initiator (C-2) which is not acylphosphine oxide are used. It turns out that combined use is an essential condition.

  The active energy ray-curable white inkjet ink composition of the present invention has an excellent whiteness and concealment, and is excellent in curability during printing. Can be used for printing.

Claims (7)

  It contains at least a white pigment (A), a polymerizable monomer (B), an acylphosphine oxide photopolymerization initiator (C-1), and a photopolymerization initiator (C-2) that is not an acylphosphine oxide. An active energy ray-curable white inkjet ink composition.   2. The active energy ray-curable white inkjet ink composition according to claim 1, wherein the white pigment (A) is contained in an amount of 10 to 20% based on the total amount of the ink composition. The total content of the acylphosphine oxide photopolymerization initiator (C-1) and the non-acylphosphine oxide photopolymerization initiator (C-2) is 4 to 14% based on the total amount of the ink composition. The active energy ray-curable white inkjet ink composition according to claim 1, wherein the composition is an active energy ray-curable white inkjet ink composition.   The ratio of the content of the acylphosphine oxide photopolymerization initiator (C-1) and the non-acylphosphine oxide photopolymerization initiator (C-2) is 1: 1 to 3: 1. The active energy ray-curable white inkjet ink composition according to claim 1.   The active energy ray curing according to any one of claims 1 to 4, wherein the acylphosphine oxide photopolymerization initiator (C-1) contains only 2,4,6-trimethylbenzoyldiphenylphosphine oxide. Type white inkjet ink composition. The active energy ray-curable white color according to any one of claims 1 to 5, which does not contain an aminoacetophenone photopolymerization initiator as the photopolymerization initiator (C-2) that is not acylphosphine oxide. Inkjet ink composition.   It contains oligo (2-hydroxy-2-methyl-1- (4- (1-methylvinyl) phenyl) propanone) as a photopolymerization initiator (C-2) that is not an acylphosphine oxide type. The active energy ray-curable white inkjet ink composition according to claim 1.