JP2008081594A - Ultraviolet ray-curable ink-jet ink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultraviolet ray-curable ink-jet ink excellent in storage stability and heat stability. <P>SOLUTION: The ultraviolet ray-curable ink-jet ink comprises a pigment, a reactive monomer and/or a reactive oligomer and a photopolymerization initiator, and the pigment is an inorganic pigment and the photopolymerization initiator is a hydroxyketone or an acylphosphine oxide. The content of the inorganic pigment is preferably 0.1-10 wt.%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ultraviolet curable inkjet ink. More specifically, the present invention relates to an ultraviolet curable ink jet ink excellent in storage stability and thermal stability.

  In recent years, ink jet printing using an ultraviolet curable resin has been studied as a technique other than water-based or solvent-based ink jet printing. This ultraviolet curable resin has a feature that the resin is instantly cured when irradiated with ultraviolet rays, and therefore has an advantage that an ink receiving layer is not required for the recording substrate. Because of this merit, the use of the ultraviolet curable resin is not limited to coloring on paper, but its application as a coloring material to various materials such as film, plastic, metal and glass is being studied.

  Further, since the ultraviolet curable resin becomes a cured film excellent in scratch hardness and adhesion to the base material, the recorded matter can be used both outdoors and indoors. However, when compared with indoor use, for example, when used outdoors such as building materials and signboards, excellent resistance that can cope with all natural conditions is required. Examples thereof include light resistance, heat resistance, water resistance and acid resistance. The recorded material must be capable of holding the image without discoloration and fading for a certain period. In general, an ultraviolet curable resin is excellent in weather resistance as compared with other resins, but is not sufficient.

  For this reason, research has been conducted on ink jet inks used outdoors, and organic pigments having better light resistance than dyes have begun to be used as colorants. However, in outdoor applications, since it will be exposed to sunlight for a long time, fading cannot be avoided even when organic pigments are used. In the case of outdoor use, light resistance that hardly fades after exposure outdoors for 5 to 10 years is necessary. Therefore, there is a method of using an inorganic pigment having excellent light resistance as compared with an organic pigment as a colorant. .

  By the way, since it is necessary for ink jet printing to discharge ink droplets uniformly, the dispersion stability of a pigment becomes important. Furthermore, since the ultraviolet curable resin is used by heating at the time of ejection, the ink is also required to have thermal stability. This is because if the ink is denatured or denatured by this heating, stable ejection becomes impossible. However, the ultraviolet curable resin containing an inorganic pigment is inferior in thermal stability to that containing an organic pigment. The reason for this is not clear, but inorganic pigments are in an active state because there are more polar groups on the surface of the pigment than organic pigments, and radicals are generated by the interaction with the photopolymerization initiator. It is thought that it will harden. This phenomenon is known to occur when heat is applied.

  In Patent Document 1, in order to realize long-term storage stability, an ink composition comprising a plurality of liquids each independently containing a set of compounds that react by mixing to form aggregates or thicken. Is described. However, when mixing inks consisting of multiple liquids, if the ink compatibility is not fully considered, the dissolved or dispersed state of the ink contents (for example, pigments, etc.) will become unstable, and the stability of the ink will be reduced. There is a risk of deterioration. In Patent Document 2, C.I. I. It is described that the discharge stability of ink is improved by using a polymer dispersant containing Pigment Yellow 180 and having a basic adsorbing group. Patent Document 3 describes that the discharge stability and the storage stability are improved by containing a pigment having a specific surface hydrophilicity and a basic compound. However, the inorganic pigment is not described, and when the inorganic pigment is used, there is a possibility that the ejection stability and storage stability of the ink may be lowered due to the above-mentioned reasons.

JP 2006-36932 A JP 2004-2528 A JP 2005-255765 A

  An object of the present invention is to provide an ultraviolet curable ink jet ink excellent in storage stability and thermal stability.

  The present invention has been made by finding that the storage stability and thermal stability of an ink are dramatically improved by combining an inorganic pigment and a specific photopolymerization initiator.

  That is, the present invention relates to an ultraviolet curable inkjet ink containing a pigment, a reactive monomer and / or a reactive oligomer, and a photopolymerization initiator, wherein the pigment is an inorganic pigment and the photopolymerization initiator is a hydroxyketone. Alternatively, the present invention relates to an ultraviolet curable inkjet ink which is an acylphosphine oxide.

  The inorganic pigment is preferably contained in an amount of 0.1 to 10% by weight.

  The photopolymerization initiator is preferably contained in an amount of 1 to 10% by weight.

  The present invention also relates to an outdoor ultraviolet curable inkjet ink comprising the ultraviolet curable inkjet ink.

  Since the ink of the present invention comprises a combination of an inorganic pigment and a specific photopolymerization initiator, it is excellent in storage stability and thermal stability, and can be stably ejected.

  The ink of the present invention comprises an inorganic pigment, a reactive monomer and / or a reactive oligomer, and a photopolymerization initiator of hydroxy ketones or acyl phosphine oxides.

  The pigment used in the present invention is not particularly limited as long as it is an inorganic pigment. Examples thereof include oxides, hydroxides, sulfides, ferrocyanides, chromates, carbonates, silicates, phosphates, carbons (carbon black) and metal powders. Of these, oxides, hydroxides, and ferrocyanides are preferable because they are clear, have coloring power, and are harmless.

  The pigment is preferably contained in an amount of 0.1 to 10% by weight, and more preferably 0.5 to 5% by weight. If the pigment content is less than 0.1% by weight, the ink concentration tends to be insufficient, and if it exceeds 10% by weight, ejection from the nozzle tends to be difficult.

  In the present invention, hydroxy ketones or acyl phosphine oxides are used as the photopolymerization initiator. By using a combination of an inorganic pigment and these photopolymerization initiators, the ink is less likely to aggregate even when stored for a long period of time, the viscosity does not change, and even when heated, it is difficult to gel. Therefore, storage stability and thermal stability are dramatically improved.

  Examples of photopolymerization initiators for the hydroxy ketones include 1-hydroxy-cyclohexyl-phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, and 1- {4- (2-hydroxyethoxy). -Phenyl} -2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1- {4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] -phenyl}- 2-methyl-propan-1-one and the like. Among these, 1- {4- (2-hydroxyethoxy) -phenyl} -2-hydroxy-2-methyl-1-propan-1-one and 2-hydroxy-1- {4 are highly reactive. -[4- (2-Hydroxy-2-methyl-propionyl) -benzyl] -phenyl} -2-methyl-propan-1-one is preferred.

  Examples of the photopolymerization initiator of the acylphosphine oxides include bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide and 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide. Of these, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide is preferable because of its high reactivity.

  Further, when these photopolymerization initiators are used, yellowing immediately after curing can be suppressed, so that there is an advantage that color matching is easy.

  The addition amount of the photopolymerization initiator is preferably 1 to 10% by weight, and more preferably 3 to 7% by weight. If the amount is less than 1% by weight, the ink tends not to be cured sufficiently. If the amount exceeds 10% by weight, an excess of the unreacted photopolymerization initiator remains in the cured film, and the cured film tends to deteriorate. is there.

  The ink used in the present invention contains a reactive monomer and / or a reactive oligomer in addition to the inorganic pigment and the photopolymerization initiator.

  Although it does not specifically limit as a reactive monomer and / or a reactive oligomer, It hardens | cures by irradiation of an ultraviolet-ray, and is what is called a ultraviolet curing resin.

  Examples of the reactive monomer include hexafunctional acrylates such as dipentaerythritol hexaacrylate and modified products thereof; pentafunctional acrylates such as dipentaerythritol hydroxypentaacrylate; tetrafunctional acrylates such as pentaditrimethylolpropane tetraacrylate and pentaerythritol tetraacrylate. Trifunctional acrylates such as trimethylolpropane triacrylate, pentaerythritol triacrylate, tris (2-hydroxyethyl) isocyanurate triacrylate, glyceryl triacrylate; hydroxypivalate neopentyl glycol diacrylate, polytetramethylene glycol diacrylate, tri Methylolpropane acrylic acid benzoate, diethylene glycol Acrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol (200) diacrylate, polyethylene glycol (400) diacrylate, polyethylene glycol (600) diacrylate, neopentyl glycol diacrylate, 1,3-butanediol A bifunctional acrylate such as diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, dimethylol-tricyclodecane diacrylate, bisphenol A diacrylate; and Caprolactone acrylate, tridecyl acrylate, isodecyl acrylate, isooctyl acrylate, isomyristyl acrylate , Isostearyl acrylate, 2-ethylhexyl-diglycol diacrylate, 2-hydroxybutyl acrylate, 2-acryloyloxyethyl hexahydrophthalic acid, neopentyl flycol acrylate benzoate, isoamyl acrylate, lauryl acrylate, stearyl acrylate, Butoxyethyl acrylate, ethoxy-diethylene glycol acrylate, methoxy-triethylene glycol acrylate, methoxy-polyethylene glycol acrylate, methoxydipropylene glycol acrylate, phenoxyethyl acrylate, phenoxy-polyethylene glycol acrylate, nonylphenol acrylate, tetrahydrofurfuryl acrylate, isobornyl acrylate, 2-hydro Xylethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-acryloyloxyethyl-succinic acid, 2-acryloyloxyethyl-phthalic acid, 2-acryloyloxyethyl-2-hydroxy And monofunctional acrylates such as ethyl-phthalic acid. Furthermore, the reactive monomer which provided the functional group of phosphorus, fluorine, ethylene oxide, and propylene oxide to these is mentioned. These reactive monomers can be used alone or in combination. Among these, a bifunctional monomer is preferable in terms of excellent toughness and flexibility. Among them, an aliphatic reactive monomer composed of hydrocarbon, specifically 1,6-hexanediol diacrylate, neopentyl glycol diacrylate 1,3-butanediol diacrylate, 1 1,4-butanediol diacrylate and 1,9-nonanediol diacrylate are preferred.

  The reactive monomer is preferably contained in the ink in an amount of 50 to 85% by weight. If the amount is less than 50% by weight, the ink viscosity becomes high, which may cause ejection failure. If the amount exceeds 85% by weight, other chemicals necessary for curing may be insufficient, resulting in poor curing.

  Examples of the reactive oligomer include urethane acrylate, polyester acrylate, epoxy acrylate, silicon acrylate, and polybutadiene acrylate, which may be used alone or in combination. In addition, an oligomer means the 2-20 mer of a monomer. Of these, urethane acrylate is preferred because it is excellent in toughness, flexibility and adhesion. Among these, aliphatic urethane acrylates composed of hydrocarbons are more preferable in that they are hardly yellowed like reactive monomers.

  The reactive oligomer is preferably contained in the ink in an amount of 0.1% by weight or more, and more preferably 0.5% by weight or more. The upper limit is preferably 30% by weight, and more preferably 20% by weight. If the reactive oligomer is 0.1% by weight or more and 30% by weight or less, the toughness, flexibility and adhesion tend to be further improved.

  In addition, you may add a dispersing agent to the ink used by this invention as needed.

  Examples of the dispersant include an anionic compound, a cationic compound, a nonionic compound, an amphoteric compound, and a polymer compound, and these can be used alone or in combination.

  The amount of the dispersant added to the ink is appropriately determined according to the type of pigment to be dispersed, but is preferably 5 to 150% by weight, and preferably 30 to 80% by weight with respect to the pigment. Is more preferable. When the amount of the dispersant is less than 5% by weight, the pigment tends not to be dispersed well, and when the amount exceeds 150% by weight, the dispersant tends to inhibit the dispersion of the pigment or increase the ink cost.

  Furthermore, if necessary, a sensitizer for promoting the initiation reaction of the photopolymerization initiator, a heat stabilizer, an antioxidant, an antiseptic, an antifoaming agent, a penetrating agent, a resin binder, a resin emulsion, an antireduction agent, It is also possible to add additives such as leveling agents, pH adjusters, pigment derivatives, polymerization inhibitors, ultraviolet absorbers and light stabilizers.

  The ink used in the present invention can be obtained by mixing the materials to be used, further dispersing the mixture using a dispersing machine such as a roll mill, a ball mill, a colloid mill, a jet mill or a bead mill, followed by filtration. it can. Among these, a bead mill is preferable because it can be dispersed in a large amount in a short time.

  The viscosity of the ink is preferably 1 to 20 mPa · s, more preferably 2 to 15 mPa · s at the temperature discharged from the nozzle. If the viscosity is lower than 1 mPa · s, there is a possibility that the discharge amount becomes too large and the discharge becomes unstable due to the viscosity of the ink being too low, and if it exceeds 20 mPa · s, the viscosity of the ink is too high. There is a possibility that it cannot be discharged.

  Further, the surface tension at the time of ejection is preferably 20 to 40 dyne / cm, more preferably 25 to 35 dyne / cm, considering that it corresponds to various materials. If it is less than 10 dyne / cm, the wettability becomes too good, so that the image tends to blur, and it becomes difficult to supply ink to the printer head. If it exceeds 50 dyne / cm, the wettability deteriorates, so that the ink is repelled and the image tends to be streak-like.

  The ink jet recording apparatus using the ink of the present invention is not particularly limited. For example, continuous methods such as charge modulation method, microdot method, charge jet control method and ink mist method, stem-me method, pulse jet method, on-demand method such as bubble jet (registered trademark) method and electrostatic suction method Can also be adopted.

  Further, a head equipped in these ordinary ink jet printers may be equipped with a heating device, and the viscosity may be lowered by heating to discharge. The heating temperature is 25 to 150 ° C., preferably 30 to 70 ° C. The heating temperature is determined in consideration of the curability of the reactive oligomer to be used with respect to heat, and the heating temperature is set lower than the temperature at which curing starts with heat. The ultraviolet curable ink-jet ink of the present invention is excellent in heat resistance, so there is no hue change even when it is kept under heating for a long time.

  As conditions for ultraviolet irradiation, the output of the ultraviolet lamp is preferably 50 to 280 W / cm, more preferably 80 to 200 W / cm. When the output of the UV lamp is lower than 50 W / cm, the ink tends not to be cured sufficiently due to the peak intensity of UV light and insufficient accumulated light amount. When the output is higher than 280 W / cm, the substrate is deformed or melted by the heat of the UV lamp. In addition, the cured film of the ink tends to deteriorate.

  The irradiation time of ultraviolet rays is preferably 0.1 to 20 seconds, and more preferably 0.5 to 10 seconds. If the irradiation time of the ultraviolet lamp is longer than 20 seconds, the substrate tends to be deformed or melted by the heat of the ultraviolet lamp, and the cured film of the ultraviolet curable ink tends to deteriorate. The accumulated light quantity is insufficient, and the ultraviolet curable ink tends not to be sufficiently cured.

The amount of ink applied to the substrate is preferably ¹ to 200 g / m ² . More preferably, it is 5-150 g / m < ² >. If it is less than 1 g / m ² , it tends to be difficult to sufficiently color, and if it exceeds 200 g / m ² , there is a tendency to cause bleeding or poor curing due to too much applied amount. .

  Since the ink of the present invention contains a pigment and is extremely excellent in light resistance, it can be preferably used for exterior materials for buildings, signboards, signs, and the like used particularly outdoors.

  In addition, since the ink of the present invention is an ultraviolet curable ink, it has excellent adhesion to the substrate. The substrate is not particularly limited, and examples thereof include plastics, ceramics, glasses, wood, metals, and those obtained by subjecting them to primer treatment. Among these, metals are preferable in consideration of the use for outdoor use. Although it does not specifically limit as said metals, Plated steel plates, such as a normal steel plate and a Galvalume steel plate, steel plates, such as a coated steel plate and a stainless steel plate, an aluminum plate, a copper plate, etc. are mention | raise | lifted. Furthermore, after printing, post-processing such as top coating and embossing can be performed on the printed matter, and there is no particular limitation.

  The thickness and shape of the substrate are not particularly limited, and can be appropriately set according to the use, the place to be used, the form, and the like.

  The amount applied to the substrate is preferably 5 to 150 μm in terms of dry film thickness. If it is thinner than 5 μm, it tends to be difficult to sufficiently color, and if it exceeds 150 μm, the ink film thickness becomes too thick, so that the printed layer tends to crack or peel off. It may be applied to the entire surface or may be applied partially in a pattern.

  Further, as described above, since the applied ink is excellent in adhesion to the base material, it is difficult to peel off even if embossing or bending is performed as post-processing.

  EXAMPLES Next, although an Example is given and demonstrated about this invention, this invention is not necessarily limited to these Examples.

Example 1
As an inorganic pigment, 3 parts by weight of Sicotrans Yellow L1100 (C.I. Pigment Yellow 184, bismuth vanadate, manufactured by BASF), 3 parts by weight of a dispersant (Disperbyk-168, polymer compound, manufactured by Byk Chemie), reactivity 20 parts by weight of oligomer (CN985B88, aliphatic urethane acrylate, bifunctional, manufactured by Sartomer Co., Ltd.), 69 weights of reactive monomer (SR238F, 1,6-hexanediol diacrylate, bifunctional, manufactured by Sartomer Co., Ltd.) Part, and photopolymerization initiator (hydroxy ketones, 1- {4- (2-hydroxyethoxy) -phenyl} -2-hydroxy-2-methyl-1-propan-1-one, Ciba Specialty Chemicals Co., Ltd. 5 parts by weight)) and add a bead mill disperser. After it had dispersed, performing filtration impurity removal to produce a homogeneous yellow ink. The obtained ink was evaluated by the following evaluation method. The results are shown in Table 1.

Example 2
DAIPYROXIDE BLUE 9410 (Ci Pigment Blue 28, composite oxide, manufactured by Dainichi Seika Co., Ltd.) as an inorganic pigment, and photopolymerization initiator (acylphosphine oxides, bis (2,4,6-trimethylbenzoyl)) A blue ink was prepared in the same manner as in Example 1 except that -phenylphosphine oxide, manufactured by Ciba Specialty Chemicals Co., Ltd. was used. The obtained ink was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 1
Example 1 except that a photopolymerization initiator (aminoketones, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1, manufactured by Ciba Specialty Chemicals Co., Ltd.) was used. Similarly, an ink was produced. The obtained ink was evaluated in the same manner as in Example 1 using the obtained ink. The results are shown in Table 1.

Comparative Example 2
Example except that photopolymerization initiator (amino ketones, 2-methyl-1- {4- (methylthio) phenyl} -2-morpholinopropan-1-one, manufactured by Ciba Specialty Chemicals Co., Ltd.) was used. Ink was produced in the same manner as in Example 1. The obtained ink was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Evaluation Method (1) Thermal Stability The produced ink was stored in a constant temperature layer at 70 ° C., and the time until gelation was measured. The upper limit was 700 hours.

(2) Storage stability The prepared ink was stored in a constant temperature layer at 40 ° C. for 3 months, and the viscosity and aggregates of the ink were confirmed.
Viscosity: The ink immediately after preparation and after 3 months was measured with a B-type viscometer (measurement temperature 50 ° C.).
Aggregate: No. of ink immediately after preparation and after 3 months. The mixture was filtered with 5A quantitative filter paper (manufactured by Toyo Filter Paper Co., Ltd.) to confirm the presence or absence of aggregates.

Claims (4)

An ultraviolet curable ink jet ink containing a pigment, a reactive monomer and / or a reactive oligomer, and a photopolymerization initiator, wherein the pigment is an inorganic pigment, and the photopolymerization initiator is a hydroxyketone or acylphosphine oxide An ultraviolet curable ink for inkjet. The ultraviolet curable inkjet ink according to claim 1, wherein the inorganic pigment is contained in an amount of 0.1 to 10% by weight. The ultraviolet curable ink-jet ink according to claim 1, wherein the photopolymerization initiator is contained in an amount of 1 to 10% by weight. An outdoor ultraviolet curable inkjet ink comprising the ultraviolet curable inkjet ink according to claim 1, 2 or 3.