JP6447814B2 - Photo-curable inkjet ink - Google Patents

Description

  The present invention relates to an inkjet ink having photocurability.

  In order to improve the resistance of the film formed by the inkjet printing method to various solvents, that is, the solvent resistance, a photocurable inkjet ink in which a radically polymerizable oligomer or monomer is mixed with a radical photopolymerization initiator is used as an inkjet ink. It has been proposed that the film after printing is irradiated with light to cause the oligomer or the like to undergo photocuring reaction (polymerization or crosslinking).

Examples of the radical polymerizable oligomer may be collectively referred to as a urethane acrylate oligomer or a urethane methacrylate oligomer (hereinafter referred to as “urethane (meth) acrylate oligomer”). ] Is mainly used (Patent Documents 1, 2, etc.).
According to the inventor's study, a film excellent in solvent resistance against an alkyl halide solvent such as chloroform can be formed by using the photocurable inkjet ink using the urethane (meth) acrylate oligomer.

  However, since urethane (meth) acrylate oligomers tend to form hydrogen bonds in the same molecule or between different molecules, the oxygen atom of the C═O group and the hydrogen atom of the N—H group constituting the amide bond in the molecule. If the urethane (meth) acrylate oligomer is used alone, the viscosity of the photocurable inkjet ink becomes too high and may not be used for inkjet printing.

Therefore, it is common to use various radical polymerizable monomers that function as reactive diluents together with urethane (meth) acrylate oligomers.
For example, Patent Document 1 proposes to use various monofunctional or bifunctional or higher polyfunctional monomers together with a urethane (meth) acrylate oligomer.
However, when only a monofunctional monomer that can function well as a reactive diluent is used due to its low viscosity, the crosslinking density of the film after the photocuring reaction decreases as the blending ratio increases, and the solvent resistance of the film There is a problem that the property and strength are lowered.

On the other hand, when a polyfunctional monomer having two or more functions is used, the crosslink density of the coating can be increased to improve the solvent resistance and strength.
In particular, according to the inventor's study, for example, by using different types and combinations of polyfunctional monomers depending on the types and combinations of solvents that may come into contact with the coating, the solvent resistance is improved by specializing in specific solvents. It is possible to form a coating film having improved resistance to solvents of two or more different types of solvents.

However, since the polyfunctional monomer has a higher viscosity than the monofunctional monomer, it cannot function sufficiently as a reactive diluent.
Therefore, in order to adjust the viscosity of the photocurable inkjet ink to a range suitable for inkjet printing, Patent Document 1 further discloses ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), methanol, ethanol, isopropanol (IPA). There is a description that non-reactive diluents such as alcohols may be blended as appropriate.

  However, according to the inventor's study, the photocurable inkjet ink containing various non-reactive diluents described in Patent Document 1 has insufficient storage stability. For example, if it is stored at a high temperature for a long time, the radical polymerization reaction occurs in the dark. In other words, the viscosity is increased and the nozzles of the ink jet printer are clogged, and in severe cases, they are solidified during storage.

In addition, for example, MEK, methanol, ethanol, IPA, etc. are too fast to evaporate, so even when the increase in viscosity during storage is not so large, the nozzles of the inkjet printer are likely to be clogged when used for inkjet printing. There is also a problem.
Furthermore, since acetone and MEK are too soluble in plastics, etc., the plastic parts of the ink jet printer head, etc. are dissolved, and contamination of the photo-curable ink jet ink due to mixing of the dissolved plastics is likely to occur. There is also a problem.

In Patent Document 2, it has been studied to improve the discharge property of the photocurable inkjet ink by improving the polyurethane (meth) acrylate itself or to improve the solvent resistance of the coating film. ) Only by modification of acrylate, there is a limit to the effect of improving the above properties.

Japanese Patent Laid-Open No. 2001-131453 Japanese Patent No. 4993151

An object of the present invention is a photo-curable inkjet which is excellent in storage stability and hardly causes clogging or contamination at the nozzle of an inkjet printer and can form a film excellent in solvent resistance and strength against various solvents. To provide ink.

The present invention is a radical polymerizable hexafunctional urethane (meth) acrylate oligomer,
1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, neopentyl glycol diacrylate, dipropylene glycol diacrylate, ethoxylated (4) bisphenol A diacrylate, ethoxylated (30) bisphenol A diacrylate, From the group consisting of tris (2-hydroxyethyl) isocyanurate triacrylate, ethoxylated (3) trimethylolpropane triacrylate, propoxylated (3) trimethylolpropane triacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol hexaacrylate selected, two or more radical polymerizable a chestnut rates monomers,
Including a radical photopolymerization initiator, and a non-reactive diluent,
The non-reactive diluent is represented by the formula (1):
_{C n H 2n + 1 O- [} CH 2 CH (CH 3) O] m -H (1)
[In formula, n shows 1-3 and m shows the number of 1-3. ]
Is a photocurable inkjet ink which is a glycol ether represented by the formula:

According to the present invention, a photocurable inkjet that is excellent in storage stability and hardly clogged or contaminated with nozzles of an inkjet printer, and can form a film excellent in solvent resistance and strength against various solvents. Ink can be provided.

The photocurable inkjet ink of the present invention is a radical polymerizable hexafunctional urethane (meth) acrylate oligomer,
1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, neopentyl glycol diacrylate, dipropylene glycol diacrylate, ethoxylated (4) bisphenol A diacrylate, ethoxylated (30) bisphenol A diacrylate, From the group consisting of tris (2-hydroxyethyl) isocyanurate triacrylate, ethoxylated (3) trimethylolpropane triacrylate, propoxylated (3) trimethylolpropane triacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol hexaacrylate selected, two or more radical polymerizable a chestnut rates monomers,
Including a radical photopolymerization initiator, and a non-reactive diluent,
The non-reactive diluent is represented by the formula (1):
_{C n H 2n + 1 O- [} CH 2 CH (CH 3) O] m -H (1)
[In formula, n shows 1-3 and m shows the number of 1-3. ]
It is the glycol ether represented by these.

The glycol ethers of the above formula (1) are urethane (meth) acrylate oligomers and various monomers, as well as pigments, dispersants, and other components that constitute a photocurable inkjet ink. It has dispersibility and improves the storage stability of the photo-curable inkjet ink, so that, for example, even when stored at a high temperature for a long time, it is difficult to increase in viscosity or solidify.

  In addition, the glycol ethers of formula (1) have a slower evaporation rate than MEK and IPA, and an appropriate evaporation rate as a non-reactive diluent for photo-curable inkjet ink (relative evaluation assuming that the evaporation rate of butyl acetate is 1). Therefore, it is difficult to cause clogging or the like at the nozzles of the ink jet printer when used for ink jet printing, in combination with the fact that the viscosity is hardly increased as described above.

Furthermore, since the glycol ethers of formula (1) are not as soluble in plastics as acetone and MEK, they can dissolve the plastic parts of inkjet printer heads, and are photo-curable inkjets by mixing dissolved plastics. It is difficult to cause ink contamination.
Moreover, according to the photocurable ink-jet ink of the present invention by adjusting the urethane (meth) type of acrylate oligomer Hi chestnut rates monomers and combinations, form a film excellent in resistance and strength, and the like for various solvents It becomes possible to do.

<Glycol ethers>
Examples of the glycol ether of the formula (1) used as a non-reactive diluent in the present invention include propylene glycol monomethyl ether (n = 1, m = 1), dipropylene glycol monomethyl ether (n = 1, m = 2). ), Tripropylene glycol monomethyl ether (n = 1, m = 3), propylene glycol monopropyl ether (n = 3, m = 1), dipropylene glycol monopropyl ether (n = 3, m = 2), etc. A seed | species or 2 or more types is mentioned.

In particular, propylene glycol monomethyl wherein n = 1 and m = 1 in formula (1) in terms of solubility and dispersibility in each component constituting the photocurable ink-jet ink, evaporation rate, solubility in plastics, etc. Ether (also known as 1-methoxy-2-propanol) is preferred.
The blending ratio of the glycol ethers is the remaining amount of other components described below. That is, the urethane (meth) acrylate oligomer and other components are blended at a predetermined ratio, and the blending ratio may be set so that the total amount of glycol ethers added is 100% by mass.

In addition, as the non- reactive diluent, a range that does not inhibit the above-described effect by using the glycol ether of the formula (1), specifically, a range of 20% by mass or less of the total amount of the non-reactive diluent, Other non-reactive diluents may be used in combination. Examples of such other non-reactive diluents include the aforementioned ketones and alcohols, and further water.
In this case, the blending ratio of the non-reactive diluent may be set so that the total of the glycol ethers of (1) and the other non-reactive diluent falls within the above range.

However, in order to achieve the best possible effect of using the glycol ether of formula (1) as a non-reactive diluent, only the glycol ether of formula (1) is used alone (two or more glycol ethers). Including the case where a combination is used), and is preferably used as a non-reactive diluent.
<Urethane (meth) acrylate oligomer>
As the urethane (meth) acrylate oligomer, for example, a (meth) acrylic monomer is urethane-bonded to a polyester-based or polyether-based base resin, and (meth) acrylic is a residue of the (meth) acrylic monomer in the molecule. various hexafunctional oligomers having six to yloxy group as a functional group can be used.

According to in the molecular as functional group (meth) acryloyloxy groups in six have hexafunctional urethane (meth) acrylate oligomer, Ya those of the (meth) acryloyloxy group and monofunctional with only one , 2 or more, than those with in less than 6 range, by photocuring, it is possible to form a film excellent in solvent resistance and strength.

In addition, as a hexafunctional urethane (meth) acrylate oligomer, in order to suppress an increase in the viscosity of the photocurable inkjet ink, it is preferable to use one having a viscosity as small as possible.
Such hexafunctional urethane (meth) Specific examples of the acrylate oligomer, for example if sub Toma (SARTOMER) manufactured by aliphatic urethane acrylate der Ru C N968 [polyester, hexafunctional, viscosity (60 ° C.): 0. 350 Pa · s ] .

The mixing ratio of the hexafunctional urethane (meth) acrylate oligomer is more than 10 wt% of the total amount of the photocurable ink-jet ink, particularly 13 preferably has a weight% or more, and preferably 1 to 5% by weight.
If the blending ratio of the urethane (meth) acrylate oligomer is less than this range, a film excellent in solvent resistance against an alkyl halide solvent such as chloroform may not be formed.

On the other hand, if the blending ratio of the urethane (meth) acrylate oligomer exceeds the above range, the viscosity of the photocurable inkjet ink may be too high to be used for inkjet printing.
<Aguri rate monomer>
The A chestnut rates monomer, the following which can be copolymerized with the urethane (meth) acrylate oligomer, two or more bifunctional or more polyfunctional A chestnut rates monomers can be used.

That is, the A chestnut rates monomers bifunctional or higher polyfunctional, 1, 6-hexanediol diacrylate [Sartomer Co. SR238, etc.], 1,9-nonanediol diacrylate, neopentyl glycol diacrylate [Sartomer SR247, etc.], dipropylene glycol diacrylate (SR508, manufactured by Sartomer), ethoxylated (4) bisphenol A diacrylate [SR601, manufactured by Sartomer], ethoxylated (30) bisphenol A diacrylate, manufactured by Sartomer CD9038, etc.], tris (2-hydroxyethyl) isocyanurate triacrylate (SR368, manufactured by Sartomer), ethoxylated (3) trimethylolpropane triacrylate (SR454, manufactured by Sartomer), propoxylation (3) Two types of trimethylolpropane triacrylate [SR492 manufactured by Sartomer, etc.], dipentaerythritol pentaacrylate [SR399 manufactured by Sartomer], and dipentaerythritol hexaacrylate [DPHA manufactured by Sartomer] The above is mentioned.
By using two or more of the above bifunctional or higher polyfunctional acrylate monomers, the solvent resistance and strength of the coating can be improved .

Further, as described above, the type and combination of polyfunctional monomers can be properly used according to the type and combination of solvents that may come into contact with the coating.
For example the alcohol-based solvents such as ethanol and good solvent resistance to both alkyl halides solvents such as chloroform considering applying the coating, the A chestnut rates monomer, among the 1,6 -Two types of hexanediol diacrylate and dipropylene glycol diacrylate are preferably used in combination.

The mixing ratio of the bifunctional or higher polyfunctional A chestnut rates monomer, or 32 wt% of the total amount of the photocurable ink-jet ink is preferably in particular 34 mass% or more, 40 wt% or less, especially 38 wt% or less Is preferred.
A chestnut rate proportion of the monomers is less than this range increasingly proportion of relatively urethane (meth) acrylate oligomer, the viscosity of the photocurable inkjet ink becomes too high it may not be used in ink jet printing.

On the other hand, A chestnut rate when the mixing ratio of the monomer exceeds the above range becomes smaller proportion of relatively urethane (meth) acrylate oligomers, especially solvent resistance to such alkyl halide solvents such as chloroform There is a possibility that an excellent film cannot be formed.
<Photoradical polymerization initiator>
As the radical photopolymerization initiator, any of various compounds capable of generating radicals by irradiation with light having an arbitrary wavelength and causing the urethane (meth) acrylate oligomer and the monomer to undergo radical polymerization reaction can be used. .

Examples of such radical photopolymerization initiators include one or more of the following compounds.
Benzophenone, hydroxybenzophenone, 2-chlorobenzophenone, 4,4'-dichlorobenzophenone, 4,4'-bisdiethylaminobenzophenone (Michler ketone), 4,4'-bisdimethylaminobenzophenone (Michler ketone), 4-methoxy-4'- Dimethylaminobenzophenone, benzophenones such as benzophenone compounds represented by the general formula (1) of JP-A-2008-280427, or salts thereof.

  Thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2-isopropylthioxanthone, 1-chloro-4-propoxythioxanthone, 2,4-diethylthioxanthone, 4-isopropylthioxanthone, isopropoxychlorothioxanthone, general formulas of Patent Document 1 ( Or a salt thereof such as a thioxanthone compound represented by 2).

Anthraquinones such as ethyl anthraquinone, benzanthraquinone, aminoanthraquinone and chloroanthraquinone.
Acetophenones such as acetophenone, 2,2-diethoxyacetophenone, 2,2-dimethoxyphenylacetophenone, 4'-dimethylaminoacetophenone, dimethylhydroxyacetophenone.

  2- (o-chlorophenyl) -4,5-diphenylimidazole dimer, 2- (o-chlorophenyl) -4,5-di (m-methoxyphenyl) imidazole dimer, 2- (o-fluorophenyl) -4,5-diphenylimidazole dimer, 2- (o-methoxyphenyl) -4,5-diphenylimidazole dimer, 2- (p-methoxyphenyl) -4,5-diphenylimidazole dimer, 2 -Di (p-methoxyphenyl) -5-phenylimidazole dimer, 2- (2,4-dimethoxyphenyl) -4,5-diphenylimidazole dimer, 2,4,5-triarylimidazole dimer Imidazoles such as

Benzyldimethyl ketal, 2-benzyl-2-dimethylamino- 1- (4-morpholinophenylbutane) -1-one, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholinopropane-1- ON, 2-hydroxy-2-methyl-1-phenyl-1-one, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one, 9,10-phenanthrenequinone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-propyl ether, benzoin isobutyl ether Benzoins such as benzoin-n-butyl ether.

Acridine derivatives such as 9-phenylacridine and 1,7-bis (9,9'-acridinyl) heptane.
Bisacylphosphine oxide, bisphenylphosphine oxide, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis (2,6-dimethoxybenzoyl) ) Phosphine oxides such as -2,4,4-trimethylpentylphosphine oxide.

  2,2-dimethoxy-1,2-diphenylethane-1-one, 2-hydroxy-1- {4- [4- (2-hydroxy-2-methylpropionyl) benzyl] phenyl} 2-methylpropane-1- ON, 2-dimethylamino-2- (4-methylbenzyl) -1- (4-morpholin-4-yl-phenyl) butan-1-one, 1- (4-isopropylphenyl) -2-hydroxy-2 -Methylpropan-1-one, methylbenzoyl formate, azobisisobutyronitrile, benzoyl peroxide, di-tert-butyl peroxide, 1-hydroxycyclohexyl phenyl ketone, 2,4,6-trihalomethyltriazine, benzyl, methyl Benzoyl, methyl benzoylformate, 2-benzyl-2-dimethylamino-4-morpholinob Rofenon like.

Although the blending ratio of the photo radical polymerization initiator can be arbitrarily set, in consideration of imparting good photo curability to the photo curable inkjet ink, 0.1% by mass or more of the total amount of the photo curable inkjet ink, In particular, it is preferably 0.5% by mass or more, more preferably 10% by mass or less, and particularly preferably 8% by mass or less.
<Sensitizer>
You may mix | blend a sensitizer with the photocurable inkjet ink of this invention as needed.

The sensitizer becomes excited by irradiation with ultraviolet rays and functions to interact with the photoradical polymerization initiator to help generate radicals in the photoradical polymerization initiator.
For example, when an LED is used as a light source, the wavelength range thereof is narrow, and therefore it is preferable to add a sensitizer in order to improve the sensitivity by expanding the wavelength range having sensitivity, that is, to sensitize.

  Examples of the sensitizer include thioxanthones such as 2,4-diethylthioxanthone, 1-chloro-4-propoxythioxanthone, and a mixture of 2-isopropylthioxanthone and 4-isopropylthioxanthone among the above-mentioned photo radical polymerization initiators or the like. Salts, eutectic mixtures of benzophenone and 2,3- and 4-methylbenzophenone, methyl-2-benzophenone, benzophenone, 4-benzoyl-4'-methylphenyl sulfide, 4-methylbenzophenone, 4-phenylbenzophenone, and other benzophenones Or a salt thereof, 2-ethylanthraquinone, 4,4'-bisdiethylaminobenzophenone (Michler's ketone) and the like.

  Other sensitizers include, for example, benzoate compounds such as ethyl-4- (dimethylamino) benzoate and 2-ethyl-4- (dimethylaminobenzoate), naphthalenebenzoxazolyl derivatives, thiophenebenzoxazolyl derivatives, Stilbene benzoxazolyl derivatives, coumarin derivatives, styrene biphenyl derivatives, pyrazolone derivatives, stilbene derivatives, styryl derivatives of benzene and biphenyl, bis (benzazol-2-yl) derivatives, carbostyril, naphthalimide, dibenzothiophene-5,5′- Dioxide derivatives, pyrene derivatives, pyridotriazole, ethyl p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, ethanolamine, diethanolamine, triethanolamine, etc. It is.

As the sensitizer, among the various sensitizers described above, those having an absorption wavelength range suitable for sensitization according to the wavelength range of light from the light source and the absorption wavelength range of the radical photopolymerization initiator Can be used alone or in combination of two or more.
Although the blending ratio of the sensitizer can be arbitrarily set, in consideration of obtaining a good sensitizing effect, it is 0.01% by mass or more, particularly 0.5% by mass or more of the total amount of the photocurable inkjet ink. Is preferably 5% by mass or less, and particularly preferably 4% by mass or less.

<Colorant>
You may mix | blend a coloring agent with the photocurable inkjet ink of this invention.
Examples of the colorant include various pigments and dyes. As the colorant, any colorant corresponding to the color of the photocurable inkjet ink can be used. In particular, various inorganic pigments and / or organic pigments are preferable in consideration of improving the light resistance, weather resistance and the like of printing.

Among these, as inorganic pigments, various carbon blacks such as metal compounds such as titanium oxide and iron oxide, or neutral, acidic, basic, etc. produced by known methods such as contact method, furnace method, thermal method, etc. 1 type, or 2 or more types.
Examples of organic pigments include azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, or chelate azo pigments), and polycyclic pigments (eg, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazines). Pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc.), dye chelates (eg basic dye chelate, acid dye chelate, etc.), nitro pigments, nitroso pigments, aniline black, etc. Can be mentioned.

One or more pigments can be used depending on the color of the photocurable inkjet ink. The pigment may be treated on the surface in order to improve the dispersion stability in the photocurable ink-jet ink.
Specific examples of the pigment include the following various pigments.
(Yellow pigment)
C. I. Pigment Yellow 1, 2, 3, 12, 13, 14, 14C, 16, 17, 20, 24, 73, 74, 75, 83, 86, 93, 94, 95, 97, 98, 109, 110, 114, 117, 120, 125, 128, 129, 130, 137, 138, 139, 147, 148, 150, 151, 154, 155, 166, 168, 180, 185, 213, 214
(Magenta pigment)
C. I. Pigment Red 5, 7, 9, 12, 48 (Ca), 48 (Mn), 49, 52, 53, 57 (Ca), 57: 1, 97, 112, 122, 123, 149, 168, 177, 178 179, 184, 202, 206, 207, 209, 242, 254, 255
(Cyan pigment)
C. I. Pigment Blue 1, 2, 3, 15, 15: 1, 15: 3, 15: 4, 15: 6, 15:34, 16, 22, 60
(Black pigment)
C. I. Pigment Black 7
(Orange pigment)
C. I. Pigment Orange 36, 43, 51, 55, 59, 61, 71, 74
(Green pigment)
C. I. Pigment Green 7, 36
(Violet pigment)
C. I. Pigment Violet 19, 23, 29, 30, 37, 40, 50
The blending ratio of the colorant can be arbitrarily set according to the type of the colorant and the color of the photocurable inkjet ink.

<Dispersant>
When the colorant is a pigment, an arbitrary dispersant may be blended in the photocurable inkjet ink so as to improve the dispersibility of the pigment.
As the dispersant, a polyallylamine / polycaprolactone dispersant is particularly preferable.
A photocurable inkjet ink cannot use a dispersant having both a hydrophilic group and a hydrophobic group, such as an aqueous dispersant. Usually, a basic group obtained by oxidizing a pigment such as carbon black is used. Generally, it is dispersed in combination with a dispersing agent having As the basic group, amide, imide and the like are exclusively used.

The dispersant is required to be insoluble in the non-reactive diluent that forms the photocurable inkjet ink, that is, to be appropriately dissolved.
However, there are few dispersants that are insoluble in the glycol ethers of formula (1) used as non-reactive diluents in the present invention, and many dispersants cannot function sufficiently as dispersants. There is a problem that it is likely to precipitate or aggregate in a short period of time. In addition, amides and imides may be liberated to perform the same function as a sensitizer and the like, and the viscosity of the photocurable inkjet ink may be increased at an early stage.

In contrast, polyallylamine / polycaprolactone-based dispersants are insoluble in the glycol ethers of formula (1) and can disperse the pigments well in the photocurable inkjet ink over a long period of time. Therefore, there is no risk of the viscosity of the photocurable inkjet ink being increased at an early stage.
Examples of the polyallylamine / polycaprolactone-based dispersant include PB821 [acid value: 15 to 18 mgKOH / g, amine value: 8 to 11 mgKOH / of the Ajisper (registered trademark) series of dispersants manufactured by Ajinomoto Fine Techno Co., Ltd. g], PB822 [acid value: 12 to 15 mgKOH / g, amine value: 12 to 19 mgKOH / g], PB881 [acid value: 15 to 18 mgKOH / g, amine value: 12 to 19 mgKOH / g], etc. More than species.

The blending ratio of the dispersant is preferably 0.2 times or more, and preferably 0.8 times or less of the amount of the pigment.
According to the photocurable inkjet ink of the present invention containing each of the above components, as described above, by using the glycol ethers of the formula (1) as the non-reactive diluent, it is excellent in storage stability and inkjet. In addition to clogging and contamination at the nozzles of the printer, it is possible to form a film excellent in solvent resistance and strength against various solvents.

<Example 1>
The following components were blended and mixed in the proportions shown in Table 1, and then filtered using a 5 μm membrane filter to prepare a photocurable inkjet ink.
(Urethane acrylate oligomer)
Sartomer aliphatic urethane acrylate CN968 [polyester, hexafunctional, viscosity (60 ° C.): 0.350 Pa · s]
( Acrylate monomer)
1,6-hexanediol diacrylate [16HDDA, bifunctional, SR238 manufactured by Sartomer]
Dipropylene glycol diacrylate [DPGDA, bifunctional, SR508 manufactured by Sartomer]
(Non-reactive diluent)
Propylene glycol monomethyl ether (PGME) represented by the formula (1), wherein n = 1 and m = 1 in the formula (1)
(Photopolymerization initiator)
2,4,6-Trimethylbenzoyldiphenylphosphine oxide [SpeedCureTPO manufactured by Rambson Japan Ltd.]
(Pigment)
Carbon black (dispersant)
Polyallylamine / polycaprolactone-based dispersant [Ajisper PB821, manufactured by Ajinomoto Fine Techno Co., Ltd., acid value: 15 to 18 mgKOH / g, amine value: 8 to 11 mgKOH / g]

< Comparative Example 1 >
A photocurable inkjet ink was prepared in the same manner as in Example 1 except that the same amount of monofunctional ethoxylated phenylphenol acrylate (EPPA) was blended in place of DPGDA in the acrylate monomer.
<Example 2 >
A photocurable inkjet ink as in Example 1 except that the same amount of an imide dispersant (BYKJET 9151 manufactured by Big Chemie Japan Co., Ltd.) was used instead of the polyallylamine / polycaprolactone dispersant as a dispersant. Was prepared.

< Comparative Example 2 >
Light as in Example 1, except that the same amount of difunctional aliphatic urethane acrylate CN985 [polyester, viscosity (60 ° C.): 0.205 Pa · s] manufactured by Sartomer, which is bifunctional, was blended as a urethane acrylate oligomer. A curable inkjet ink was prepared.

<Comparative Example 3 >
A photocurable inkjet ink was prepared in the same manner as in Example 1 except that the same amount of propylene glycol monomethyl ether acetate (PGMAc) was used instead of PGME as a non-reactive diluent.
<Evaluation of storage stability at high temperature>
The photocurable inkjet ink prepared in each of the above Examples and Comparative Examples was put in a sealed container, kept at 45 ° C. in a dark place, and checked for the presence of residues after filtration after 1 week and 1 month, respectively. . The storage stability at high temperatures was evaluated according to the following criteria.

○: No residue was observed after 1 month.
Δ: No residue was observed after 1 week, but a residue was observed after 1 month.
X: Residue was seen after 1 week.
<Solvent resistance evaluation>
A sample was printed on the surface of the substrate using the photocurable inkjet ink prepared in each of the above Examples and Comparative Examples.

Next, this sample was dipped in ethanol or chloroform as a solvent at 23 ± 2 ° C. for 24 hours, then pulled up, and further rubbed with a Kimwipe soaked with the same solvent as that which had been dipped, followed by rubbing three times. The solvent resistance was evaluated according to the standard.
○: No change was observed in printing.
X : Even a slight chip was observed in the printing.
The results are shown in Table 2.

By selecting and using the glycol ethers represented by the formula (1) as non-reactive diluents from the results of Examples 1 and 2 and Comparative Example 3 in Table 2, other non-reactive diluents can be used. It was found that the storage stability at a higher temperature can be greatly improved than when used.
Further, from the result of Comparative Example 1 , when two kinds of acrylate monomers , one of which is a monofunctional ethoxylated phenylphenol acrylate, are used in combination, although good solvent resistance can be maintained with respect to an alcohol solvent. It was also found that the solvent resistance against the halogenated alkyl solvent is lowered.
From the results of Example 1 contrast, as acrylate monomer, either by combination of 1,6-hexanediol diacrylate and dipropylene glycol diacrylate is bifunctional, alcoholic solvent such as ethanol, and chloroform It has been found that the solvent resistance to both of the halogenated alkyl solvents such as can be improved .

Real Example 1, the results of Comparative Example 2, as the urethane acrylate oligomer, by using a six-functional instead that of bifunctional, it can be particularly improved solvent resistance to solvents halogenated alkyl type understood.
Furthermore, from the results of Examples 1 and 2, it is preferable to use a polyallylamine / polycaprolactone dispersant as a dispersant rather than a normal amide dispersant in order to further improve storage stability at high temperatures. I found out.

Claims (4)

Radical polymerizable hexafunctional urethane (meth) acrylate oligomer,
1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, neopentyl glycol diacrylate, dipropylene glycol diacrylate, ethoxylated (4) bisphenol A diacrylate, ethoxylated (30) bisphenol A diacrylate, From the group consisting of tris (2-hydroxyethyl) isocyanurate triacrylate, ethoxylated (3) trimethylolpropane triacrylate, propoxylated (3) trimethylolpropane triacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol hexaacrylate selected, two or more radical polymerizable a chestnut rates monomers,
Including a radical photopolymerization initiator, and a non-reactive diluent,
The non-reactive diluent is represented by the formula (1):
_{C n H 2n + 1 O- [} CH 2 CH (CH 3) O] m -H (1)
[In formula, n shows 1-3 and m shows the number of 1-3. ]
The photocurable inkjet ink which is glycol ethers represented by these.   The photocurable inkjet ink according to claim 1, comprising a polyallylamine / polycaprolactone dispersant. Before Kia chestnut rates monomer photocurable inkjet ink according to claim 1 or 2 which is two 1,6-hexanediol diacrylate and dipropylene glycol diacrylate. The photocurable inkjet ink according to any one of claims 1 to 3 , wherein a blending ratio of the urethane (meth) acrylate oligomer is 10% by mass or more and 15% by mass or less of a total amount of the photocurable inkjet ink. .