JP5935140B2 - Active energy ray curable inkjet ink cured film - Google Patents

Description

  The present invention relates to an active energy ray-curable inkjet ink cured film.

  Conventionally, active energy ray-curable ink-jet inks have been mounted on high-speed printing type signage printers because of their faster drying compared to their solvent types. In addition, it has been mounted on a flat bed type printer compatible with various types of substrates in terms of excellent substrate adhesion. And the development of ink-jet ink according to the application has been advanced.

  These ink jet printers have been adapted to increase in size, film thickness, and density by scanning the head multiple times. In recent years, head technology capable of ejecting minute droplets at a high frequency has been established with the development of head technology. By realizing this technology, inkjet printing, which was inferior to existing printing methods in terms of productivity and image quality, has the advantage of digitization and increased the possibility of replacing existing printing methods.

  Furthermore, a 1 Pass type printer has emerged in which at least two ink jet heads are ejected and then cured simultaneously. This enables cost reduction and high productivity of the printing apparatus, and further accelerates the replacement from the existing printing method.

  However, in order to realize an alternative from the existing printing method to the ink jet printing method, not only the productivity at the printing speed required by the existing market but also the image quality and the same quality of the ink cured film are required. In order to achieve high image quality, in addition to the above-described printing with fine droplets, it was also important to improve landing accuracy. Up until now, head manufacturers from each company have made improvements in order to achieve these fine droplets, high frequency, and good landing accuracy. However, it is particularly important to achieve both low viscosity and good flowability of the ink. Has been done.

  Active energy ray curable inkjet printing, on the other hand, can strongly express images based on the thickness of its film thickness, so it has been developed to replace the label market, which is good at flexographic printing and UV-curable offset printing, among existing printing. Has advanced. However, in the label market, there is a high demand for food packaging, and it has been required to establish safety by reducing the mixing of chemical substances derived from ink, similar to gravure printing. In the EU market in particular, there are regulatory thresholds for the migration of chemical substances into food contents. In the Japanese market, there is no regulation value, but in actual food packaging applications, it was found that there was a high evasion feeling for severe odors, and it was essential to reduce residues such as initiators mainly composed of monomers.

  However, as is generally known, cured films using radical reactions such as UV curing are extremely complex reactions that proceed while competing with various substances such as oxygen during the reaction. In the cured film after irradiation, a considerably large amount of monomers and initiators remained unreacted and caused migration and odor. Furthermore, low viscosity for the purpose of achieving high landing accuracy so far requires the use of low molecular weight materials, so that low molecular materials such as monomers remaining in the cured film penetrate the substrate after curing. However, the odor of the printed matter is becoming stronger because it causes migration and is derived from the residual raw material.

  Prior art document 1 examines an old-style active energy ray curable ink jet system that cures by a shuttle type. However, this means is a shuttle system (a system in which the head scans a plurality of times and prints and simultaneously irradiates ultraviolet rays). Therefore, productivity is very poor, and when used in a 1-pass printer, even when nitrogen is used, the amount of monomer remaining in the cured film is large, so it is difficult to use in food applications (migration) Value) and odor.

  Moreover, in the prior art document 2, a hybrid type invention of water and active energy ray curing is carried out. In the present invention, since the monomer and the initiator are substantially water-soluble, the residual component easily penetrates into the food from the cured film, the migration value becomes high, and the ink film (cured film) that is originally necessary. The water resistance was extremely low, and practically it could not be used for food packaging applications.

  On the other hand, Documents 3 and 4 show techniques for curing at an oxygen concentration below the atmospheric environment in 1-pass printing. However, since the present invention aims at improving curability, the amount of the initiator is excessive with respect to the monomer, and after curing, a great odor is emitted from the cured film, and at the same time, the landing accuracy is poor due to high viscosity. Therefore, it was not possible to obtain a level of image quality that could replace the existing printing.

JP 2003-260790 A Japanese Patent Laid-Open No. 2007-144585 JP 2008-068516 A JP 2008-105387 A

  The present invention achieves low odor and low residual rate while maintaining the same level of productivity and high image quality as existing printing, and can cure food packaging by curing active energy ray-curable inkjet ink. The object is to provide a membrane.

That is, the present invention is a method for producing an active energy ray-curable inkjet ink cured film that is cured by a one-pass printing method using an active energy ray-curable inkjet ink containing a colorant, a monomer, and an initiator. ,
The monomer contains a polyfunctional monomer having two or more functions, and
A monomer having a molecular weight of 300 or more is not contained, or a monomer having a molecular weight of 300 or more is 15% by weight or less based on the total weight of the ink;
0 ≦ monofunctional monomer amount / polyfunctional monomer amount ≦ 0.2 (weight ratio),
0.02 ≦ initiator amount / monomer amount ≦ 0.16 (weight ratio),
The bifunctional or higher polyfunctional monomer contains 2- (2-hydroxyethoxy) ethyl acrylate (VEEA), and the VEEA contains 10 to 60% by weight of the entire inkjet ink,
The initiator comprises bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide;
The ink viscosity is 20 mPa · s or less,
The present invention relates to a method for producing an active energy ray-curable inkjet ink cured film, wherein the oxygen concentration at the time of irradiation with active energy rays is cured in an atmosphere less than the oxygen concentration in the atmosphere.

The active energy ray-curable inkjet ink cured film according to the invention is characterized in that the monomer contains a monomer having a main skeleton of EO (ethylene oxide) or PO (propylene oxide) in an amount of 30 to 100% by weight. It relates to the manufacturing method. The above active energy ray-curable type, wherein the monomer having EO (ethylene oxide) or PO (propylene oxide) as a main skeleton contains 2- (2-hydroxyethoxy) ethyl acrylate or dipropylene glycol diacrylate The present invention relates to a method for producing an inkjet ink cured film.
Moreover, this invention relates to the manufacturing method of the said active energy ray hardening-type inkjet ink cured film whose oxygen concentration at the time of the active energy ray irradiation after ink landing is 0.5-10 volume%.
In the present invention, the initiator further comprises 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide , oligo [2-hydroxy-2-methyl-1- {4- (1-methylvinyl) phenyl} propanone], 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) - butanone -1 Contact and characterized in that it comprises at least one selected from 4,4'-diethylamino benzophenone above The present invention relates to a method for producing an active energy ray-curable inkjet ink cured film.
In addition, the present invention further includes an inhibitor, and as the inhibitor, at least one selected from a hindered phenol compound, a phenothiazine compound, a hindered amine compound, and a phosphorus compound is contained in the ink in an amount of 0.1 to 2. It is related with the manufacturing method of the said active energy ray hardening-type inkjet ink cured film characterized by including 0 weight%.
The present invention also relates to the above-mentioned method for producing an active energy ray-curable inkjet ink cured film, wherein the active energy ray curing is curing by irradiating an LED lamp having an emission spectrum from ultraviolet to visible light.
Further, in the present invention, the active energy ray-curable inkjet ink cured film is characterized in that the active energy ray curing is a curing in which a metal halide lamp is irradiated after irradiating an LED lamp having an emission spectrum from ultraviolet to visible light. It relates to the manufacturing method.
The present invention also relates to a method for producing the above active energy ray-curable inkjet ink cured film, wherein the ink is ejected by an inkjet head having an appropriate amount of ink liquid at 1 Pass printing of 6 to 14 pL.

  According to the present invention, it has been possible to provide an active energy ray-curable inkjet ink cured film having a print quality equivalent to that of existing printing and a productivity equivalent to that of the existing printing, and having a low residual rate and low odor.

  Hereinafter, the active energy ray-curable inkjet ink cured film of this embodiment will be described. Unless otherwise specified, “part” and “%” represent “part by weight” and “% by weight”.

(Active energy ray-curable inkjet ink)
The active energy ray-curable inkjet ink composition may contain a colorant such as a pigment, a pigment dispersant, a monomer, an initiator, an additive, and the like (hereinafter referred to as “active energy ray-curable inkjet ink of this embodiment”. “Composition” may be referred to as “ink” or “ink composition”). Hereinafter, first, the inkjet ink of the present invention will be described.

(Coloring agent)
As the colorant, generally known solubility or salt increasing dyes or pigments can be used. Among them, a pigment can be suitably selected from the suppression of the coloration itself and durability. Furthermore, as a pigment, the pigment generally used for the ink composition of a printing use and a coating use can be used. Specifically, inorganic pigments or organic pigments such as carbon black, titanium oxide, and calcium carbonate can be used.

In particular, as a pigment component that achieves both non-migration and color reproducibility, among others, for example, as a colorant used in magenta ink, C.I. I. Pigment violet 19, C.I. I. Pigment red 81 series, C.I. I. Pigment red 122, 176, 185, 169, 202, 269, etc.
For example, as yellow ink, C.I. I. Pigment yellow 120, 139, 150, 151, 155, 180, 185, etc.
For example, as cyan ink, C.I. I. Pigment Blue 15: 3, 15: 4,
For example, as other color inks, C.I. I. Pigment green 7, 36, C.I. I. Pigment orange 43, C.I. I. Pigment violet 23,
As other inks, C.I. I. Pigment black 7, surface-treated titanium oxide, and carbon black can be preferably used.

(Pigment dispersant)
The pigment dispersant is roughly classified into a pigment dispersion aid and a resin-type pigment dispersant.

  The pigment dispersing aid is a compound obtained by introducing an organic pigment as a base skeleton and introducing a substituent such as a sulfonic acid, a sulfonamide group, an aminomethyl group, or a phthalimidomethyl group into a side chain, or a metal salt compound.

  The main chain skeleton of the resin-type pigment dispersant is not particularly limited, and examples thereof include a polyurethane skeleton, a polyacryl skeleton, a polyester skeleton, a polyamide skeleton, a polyimide skeleton, and a polyurea skeleton. Among these, a polyurethane skeleton, a polyacryl skeleton, and a polyester skeleton are preferable from the viewpoint of storage stability of the ink composition. The structure is not particularly limited, and examples include a random structure, a block structure, a comb structure, a star structure, etc., and a block structure or a comb structure in terms of reducing the viscosity of the ink and storage stability. Is preferred.

  The addition amount of the resin-type pigment dispersant is arbitrarily selected in order to ensure the desired stability. The fluidity of the ink is excellent when the effective component of the resin-type pigment dispersant (that is, the solid content (nonvolatile content) of the resin-type pigment dispersant is 20 to 150% by weight with respect to 100% by weight of the pigment. Within the range, the dispersion stability of the ink is good, and the quality is equivalent to the initial value even after a long period of time, and when the active ingredient of the resin type pigment dispersant is 30% by weight to 100% by weight with respect to 100% by weight of the pigment, Dispersion becomes very stable, and stable discharge property is exhibited even in a high frequency region of 20 kHz or higher, so that high accuracy and high productivity can be realized, and more preferably 30% by weight to 70% by weight.

(monomer)
The monomer can be freely selected as long as it does not interfere with the purpose. The “monomer” as defined in the present specification refers to a compound that undergoes a polymerization reaction directly or via a photopolymerization initiator after irradiation with active energy rays. Specific examples include monofunctional monomers and polyfunctional monomers having two or more functions. Among them, acrylic monomers, vinyl monomers, vinyl ether monomers, vinyl ester monomers, heterogeneous monomers including acrylic and vinyl in the molecule, allyl ethers. And monomers and allyl ester monomers. Monofunctional and polyfunctional monomers are preferred from the viewpoint of ink curability, and monofunctional acrylic monomers, bifunctional acrylic monomers, acrylics and vinyls from the viewpoints of lowering ink viscosity, reducing the residual amount of cured film, and odor. Is preferably used.

  The monomer content is preferably 50 to 95% by weight in the ink from the viewpoints of curability and ejection stability. More preferably, it is 60-95 weight%, More preferably, it is 70-95 weight%.

As the monomer, it is preferable to use a bifunctional monomer, and from the viewpoint of curability, it is preferable to use a monomer having EO (ethylene oxide) or PO (propylene oxide) as the main skeleton. The monomer having EO or PO as the main skeleton refers to a monomer containing an EO or PO group in a portion other than a reactive group such as an acryloyl group, a vinyl group, or a vinyl ether group. Specifically, VEEA (2-acrylic acid (2-vinyl Rokishietokishi) ethyl), bifunctional monomers are preferably selected from DPGDA (dipropylene glycol diacrylate). Since these bifunctional monomers easily propagate radicals from the initiator, it seems that the reaction speed between the initiator and the monomer is improved. By using alone or in combination, the monomer and the initiator in the cured film even in high-speed printing. The residual amount of can be reduced.

  The addition amount of the bifunctional monomer is preferably 30 to 100% by weight, more preferably 40 to 100% by weight, and more preferably 50 to 100% by weight in the monomer component in the ink from the viewpoint of low viscosity and low residual amount. Particularly preferred.

  In particular, when VEEA is used as the monomer, the reactivity is greatly improved, so that the initiator to be blended can be reduced, and the residual ratio is also reduced, so that it can be suitably used. The amount of VEEA added is preferably 10 to 60% by weight, more preferably 15 to 45% by weight, and particularly preferably 20 to 30% by weight in the ink.

  The monomer used in the present invention preferably has a molecular weight of less than 300. Until now, countermeasures against migration and odor have been dealt with by simply using high molecular weight raw materials. EUPIA (EUROPIAN PRINTING INK ASSOCIATION) published EuPIA Guideline on Printing Inks applied to the non-food contact surface of food packaging materials and articles (November 2011-corrigendum July 2012-) Raw materials with a molecular weight of 1000 or more are recommended. However, the high molecular weight component causes a decrease in image quality due to an increase in ink viscosity and a decrease in polymerization reactivity (hardening failure) for inkjet inks. In the present invention, it has been found that it is preferable to use a monomer having a molecular weight of 300 or less in order to lower the residual ratio after curing. Moreover, since these monomers have a relatively low viscosity, they are excellent in ejection stability and can be stably ejected even in high-speed printing. If it has these performances, it will not be restrict | limited to the said exemplary monomer.

For the above reasons, a monomer having a molecular weight of more than 300 can be blended. However, when blended in a large amount, the viscosity may increase or the reactivity may be deteriorated. In the present invention, a monomer having a molecular weight of 300 or more is preferable for suppressing the viscosity to 15% or less in the ink composition in order to achieve high image quality by lowering the viscosity and realizing a lower residual ratio.
These monomers may be used alone or in combination of two or more as required.

  In addition, vinyl monomers are extremely effective in reducing viscosity due to their low intermolecular forces, and can be used. However, acrylic monomers and vinyl monomers coexist in the ink and a large amount of vinyl monomers are present. In this case, since the radical propagation speed from the acrylic monomer to the vinyl monomer is slow, a large amount of monomer may remain in the cured film after irradiation with active energy rays. Therefore, the compounding amount of the vinyl monomer is preferably 30% by weight or less in the ink, and more preferably 10% by weight or less.

  In addition to the above-mentioned monomers, oligomers and prepolymers can be used for the ink composition, but for reasons such as ink viscosity and residual amount in the cured film, the ink composition contains 15% by weight or less, further 5% by weight or less. More preferably.

In the present invention, the ratio of the monofunctional monomer to the polyfunctional monomer is preferably 0% ≦ monofunctional monomer amount / polyfunctional monomer amount ≦ 20%. In the said range, the residual amount of the unreacted monomer in a cured film can be suppressed, and the cured film with a low migration value and reduced odor can be obtained.
Furthermore, it is preferable that 0% ≦ monofunctional monomer amount / polyfunctional monomer amount ≦ 15%. Monofunctional monomers are useful for lowering viscosity for the purpose of achieving high landing accuracy, but have poor reactivity. The less the monofunctional monomer is added, the lower the residual rate in the cured film, which is preferable.

(Initiator)
An initiator refers to all compounds that generate radically active species that initiate a polymerization reaction upon irradiation with active energy rays, and includes a sensitizer in addition to a photoradical polymerization initiator. The initiator can be freely selected depending on the curing speed, cured coating film properties, and coloring material.
Specifically, as an initiator, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, 2,4-diethylthioxanthone, 2-isopropylthioxanthone Oligo [2-hydroxy-2-methyl-1- {4- (1-methylvinyl) phenyl} propanone], 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1, 2-Dimethylamino-2- (4-methyl-benzyl) -1- (4-morpholin-4-yl-phenyl) -butan-1-one, [4- [4-methylphenyl] thio] phenyl] phenyl Methanone, ethyl 4- (dimethylamino) benzoate, 1- [4- (2-hydroxyethoxy) phenyl] -2 Hydroxy-2-methyl-1-4,4'-bis - (dimethylamino) benzophenone, 4,4'-diethylamino benzophenone and the like.
Among them, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenyl It is preferable to contain at least one of phosphine oxides. By using the above initiator, the radicals generated at an oxygen concentration below the atmospheric concentration are trapped by oxygen and the polymerization reaction of the monomers in the ink can proceed efficiently without causing a termination reaction. Since the residual amount of monomer in the film can be effectively reduced, it can be suitably used.

In addition, when printing is performed with a thick film thickness exceeding 5 μm, which is peculiar to inkjet printing, uneven curing may occur. In the case of printing with a 1-pass printer, the amount of energy ray irradiation to the ink placed in the lower layer at the time of irradiation with active energy rays (ink printed in the printing order first) is attenuated, so it is placed in the lower layer (printing order). Then, it is preferable to design the curing sensitivity higher as the color printed earlier.
As a specific design method, for example, the content of the initiator contained in the ink printed earlier can be increased more than the ink printed later.

  Moreover, it is preferable to use together 2 or more types of initiators which absorb different wavelengths. The active energy ray irradiated after printing can be sufficiently utilized within a wide wavelength range, and the residual monomer amount is greatly reduced, which is preferable.

  The initiator is preferably used at 1 to 25% by weight in the ink, more preferably 2 to 20% by weight, and particularly preferably 3 to 13% by weight. When designed within the above range, both high-speed curability, low migration, and low odor can be achieved.

(Initiator / monomer ratio)
By controlling the initiator / monomer ratio in the ink to 2% ≦ initiator amount / monomer amount ≦ 16% or less, it is possible to achieve both the residual monomer amount in the cured film and odor reduction. In the present invention, at the time of curing, an active energy ray is irradiated at an oxygen concentration equal to or lower than the atmospheric concentration, and an object is to reduce the residual amount by advancing the radical polymerization reaction efficiently. By controlling the initiator / monomer ratio in the ink to 2% ≦ initiator amount / monomer amount, the residual monomer amount can be kept below a certain level. Moreover, the odor of the remaining initiator can be reduced by controlling the initiator / nomer ratio in the ink so that the amount of initiator / monomer amount ≦ 16% or less.

(Additive)
You may add an additive to the ink of this embodiment as needed. Examples of the additive include an inhibitor, a surface tension adjuster, and an organic solvent.

(Banner)
Inhibitors are preferably used in order to increase the viscosity stability of the ink over time, the ejection properties after the time, and the on-machine viscosity stability in the recording apparatus. As the inhibitor, hindered phenol compounds, phenothiazine compounds, hindered amine compounds, and phosphorus compounds are particularly preferably used.

  Among these, in terms of solubility in ink and the color of the inhibitor itself, as a hindered phenol compound, Seiko Chemical Co., Ltd. “BHT Swanox”, “Nonflex Alba”, Honshu Chemical Co., Ltd. “H-BHT”, “Phenothiazine” manufactured by Seiko Chemical Co., Ltd., “Phenothiazine” manufactured by Sakai Chemical Industry Co., Ltd., “HO-TEMPO” manufactured by Evonik Degussa Co., and “Triphenylphosphine” manufactured by BASF Co., Ltd. are used as phosphorus compounds. Selected. These inhibitors may be used alone or in combination of two or more as required.

  The amount of the inhibitor added is preferably 0.1 to 2.0% by weight in the ink, more preferably 0.1 to 1.5% by weight, and particularly preferably 0.1 to 1% by weight. Within the above range, it is possible to achieve both the storage stability of the ink, the curability in high-speed printing at 1 Pass, and the reduction in the migration value of the inhibitor.

(Surface tension regulator)
It is preferable to add a surface tension adjusting agent in order to improve the wetting and spreading property to the substrate.
The surface tension adjusting agent is preferably a silicone type from the viewpoint of prevention of flipping due to compatibility. More preferably, the residual rate of a cured film can be reduced by using the surface tension regulator which has reactivity, such as an acryloyl group.

  The amount of the surface tension modifier added is preferably 0.01 to 5% by weight in the ink, more preferably 0.01 to 3% by weight, and particularly preferably 0.1 to 2% by weight. When it is 0.01% by weight or more, wetting and spreading are good, and when it is 5% by weight or less, the surface tension adjusting agent is sufficiently oriented at the ink interface and exhibits a sufficient effect. One or more surface tension modifiers may be used as necessary.

(Organic solvent)
Although it does not specifically limit as an organic solvent, The glycol monoacetates, glycol diacetates, glycols, glycol ethers, lactic acid esters, etc. which are generally used with a solvent-type inkjet ink can be mix | blended. However, since there is a high possibility that the organic solvent remains in the cured film and the risk of migration increases, the blending amount is preferably 10% by weight or less in the ink, and particularly preferably 3% by weight or less. These organic solvents may be used alone or in combination of two or more as required.

(Moisture management)
The present invention is characterized by containing substantially no water. “Substantially no water” means that the ink composition does not intentionally contain water, and does not exclude a trace amount of water contained in each component. When water is contained in the ink, radicals generated during irradiation with active energy rays are trapped, the polymerization reaction does not proceed efficiently, and the residual ratio of the initiator and monomer in the cured film tends to increase.

  In addition to intentionally not adding water, the water content in the ink composition is preferably 1.0% by weight or less, and the raw materials and manufacturing process are controlled so that it is 0.5% by weight or less. Are preferably produced.

(About ink manufacturing method)
The ink composition is preferably prepared by adding a monomer, an initiator, and other additives to a pigment dispersion in which a monomer, a pigment dispersant, and a pigment are dispersed using an ordinary dispersing machine such as a sand mill. By this method, it is possible to sufficiently disperse using a normal disperser, so that excessive dispersion energy is not applied and a large dispersion time is not required. For this reason, it is possible to prepare an ink that hardly deteriorates during dispersion of the ink component and is excellent in stability.

  As the conditions for preparing the pigment dispersion, it is preferable to use fine beads. Specifically, it is preferable to use fine beads of 0.1 mm to 2 mm in order to produce a stable dispersion with low viscosity. Furthermore, it is preferable to use fine beads having a size of 0.1 mm to 1 mm because a dispersion with improved productivity and good ink jet discharge can be produced.

  The ink composition is preferably filtered with a filter after being dispersed by a disperser. From the viewpoint of inkjet discharge stability, the pore size of the filter is preferably 3 μm or less, more preferably 1 μm or less.

(Ink viscosity)
The viscosity of the ink used in the present invention at 25 ° C. is preferably 20 mP · s or less. By controlling the viscosity of the ink to 20 mP · s or less, the ejection speed increases and the landing system can be enhanced, thus improving the beading (fusion between dots) caused by poor landing and improving the image quality. Can be improved. Furthermore, it is preferable that the viscosity in 25 degreeC is 5-15 mP * s. If it is 5 mP · s or more, the discharge is stable, and if it is 15 mPa · s or less, the discharge accuracy is excellent and the image quality is excellent.
The viscosity can be measured by reading the viscosity at 20 rpm in a 25 ° C. environment using a TVE25L viscometer manufactured by Toki Sangyo Co., Ltd.

(Active energy ray curing method)
The term “active energy rays” as used in the present invention is a general term for ionizing radiation, light, and the like, such as electron beams, α rays, γ rays, X rays, neutron rays or ultraviolet rays. Among these, electron beams and ultraviolet rays are preferable because they are not dangerous to human bodies, are easy to handle, and are widely used industrially. Among these, an ultraviolet lamp or an LED lamp having an emission spectrum from ultraviolet to visible light can be more suitably used from the viewpoint of reducing damage to a plastic substrate such as a packaging material.

These illuminance and integrated light quantity can be arbitrarily selected for the purpose of reducing the residual rate, but in our experimental data, iron-doped metal halide lamps, gallium lamps, and LED lamps should be selected. Is preferred. These lamps can be used alone, but when a plurality of these lamps are used in combination, a remarkable reduction in the residual rate can be realized. Specifically, there are a case where a metal halide lamp is irradiated after LED irradiation, a case where a gallium lamp is irradiated after irradiation with an LED lamp, and a case where a metal halide lamp is irradiated after irradiation with a gallium lamp.

(What is 1Pass printing)
The inkjet printing method of “1 Pass printing” in this specification is a printing method that completes printing (printing) once on a medium to be printed, and is suitable for business printing that requires a printing speed. In recent years, productivity is a very important factor in using inkjet printing as an alternative to conventional offset printing, and 1-pass curable inkjet printing is expected. Furthermore, among 1 Pass curable ink-jet printing, if high-speed printing such as 25 m / M (meter / min) and 50 m / M becomes possible, it is said that it will lead to expanded use as an alternative to offset and gravure printing. .

(About oxygen concentration during curing)
In the present invention, it is preferable to cure in an environment where the oxygen concentration upon irradiation with active energy rays after ink landing is less than the atmospheric concentration. Specifically, it can be confirmed that the oxygen concentration is less than the atmospheric concentration by actually measuring using an oxygen concentration meter in the vicinity of the active energy ray irradiation environment. As a means for controlling the oxygen concentration, the atmosphere is replaced with an inert gas such as nitrogen or argon gas. In particular, nitrogen gas can be suitably used because it is available at a low cost. These inert gases can be obtained by purchasing a commercially available gas cylinder or the like.

  In the present invention, the amount of residual monomer can be reduced more effectively by curing in an environment having an oxygen concentration of 0.5 to 10%. Within this concentration range, a gas separation method using a hollow filter such as a gas separation module is preferable because it can be sufficiently supplied by cheaper and simple means.

(Unreacted monomer in the cured film)
The unreacted monomer in the present invention refers to a monomer that is analyzed that the monomer extracted from the cured film and the monomer blended in the ink component are the same.
For identification and quantification of monomers and initiators, for example, GCMS (Gas Chromatography Mass Spectrometry, LCMS (Liquid Chromatography Mass Spectrometry), HPLC (High Efficiency Liquid Chromatography) can be suitably used. Can be arbitrarily selected for ease of quantification.

The method for measuring the unreacted monomer is specifically as described in the examples. For example, the cured film is cut into a 1 cm square together with the base material, and 100 ml of methyl ethyl ketone in a sealed container at 60 ° C. for 3 days. Immerse and extract the remaining components in the cured film. Two days later, methyl ethyl ketone stirred and homogenized was taken out from the container, and the extracted components were identified by GCMS (Shimadzu Corporation GCMS-QP2010Plus) and HPLC (Shimadzu Corporation). The amount of unreacted monomer and initiator remaining in the cured film is calculated by preparing and quantifying each compound.
(What is the residual rate)
Monomer or initiator residuals are analyzed using means as described in the examples. The ratio of raw materials such as monomers and initiator remaining in the cured film is shown with respect to the cured film weight (g). This residual rate greatly correlates with the migration value in a migration test defined by the EU for food packaging applications, and reduction of the residual rate is essential for food packaging. Further, in the present invention, an ink obtained by blending a large amount of a monomer having a relatively low molecular weight is used, as described above, in order to design a low viscosity ink.
Monomers having a relatively low molecular weight generally have an odor. Therefore, if the residual ratio is high, an odor is generated from the cured film, which is a subject of claims. Especially for markets with strict quality standards such as Japan, it is essential to reduce the residual rate. In other words, for the food packaging market, providing a cured film that reduces the low-molecular components (unreacted components) remaining in the cured film as much as possible is the key to replace the existing market in response to market demand. It can be said that there is.

(Resolution and printing speed)
The image quality of piezo-driven ink jet printing of the normal 1 Pass method is determined by the resolution expressed in dpi (dots per inch) and the number of gradations in one dot or drop volume. Of these, in general, the horizontal resolution with respect to the printing direction of the print image (flow of the printing substrate) is determined by the density of the nozzles in which the ink in the head is ejected. On the other hand, the resolution in the printing direction is determined by the frequency of ink ejected by driving a piezo, generally called frequency. The resolution in the printing direction varies depending on the specifications of the heads of each company, but there are two types, a binary specification in which 1 dot is represented by one drop volume (droplet) and a gradation specification formed from a plurality of droplets. In order to replace the existing printing market, it is indispensable to achieve both quality and productivity. However, in the binary mode, the printing speed is fast, but a high-definition image cannot be obtained. However, the printing speed is extremely lowered and the productivity is deteriorated.

  In recent years, heads capable of eliminating this trade-off and capable of high-frequency printing in a gradation mode have started to be marketed, and the existing printing market is expected. In particular, when an image quality comparable to that of existing printing is obtained, it is preferable to control the minimum drop volume as small as possible, and it is essential that the minimum drop volume is about 10 pL or less. In order to obtain a higher quality image, it is necessary to form an image using droplets of 6 pL or less.

  On the other hand, as a major problem with active energy ray-curable ink-jet inks, there is no problem with solid printing that prints at 100% of the head drive, but when printing is performed using a drop volume of 10 pL or less in order to obtain a high quality image. Although the image quality was improved, it was found that the residual ratio increased and the migration value increased even though the amount of ink deposited per unit area was small compared to solid printing. This is because small droplets have a large surface area and thus are susceptible to oxygen inhibition during curing, and initiator and monomer radicals are trapped, causing reaction inhibition.

  In order to achieve both high image quality and high productivity to replace existing printing, a resolution of 360 × 360 dpi or higher is suitably used as a print mode, and 600 × 600 dpi or higher is used depending on the application. Further, it is preferable that the gradation used therein contains a drop volume of 6 pL or less, since the image quality can be remarkably improved. In order to cure ink having a drop volume of 10 pL or less, the oxygen concentration at the time of curing is preferably within 1 to 10%, and the initiator / monomer ratio is controlled to 5% to 14%. Thus, it was found that the image quality and the low residual rate can be improved more effectively.

  Specific examples of the inkjet head include Kyocera and Xaar heads, but there is no particular limitation as long as the head can print with a drop volume of 10 pL or less in order to obtain high resolution.

  Although the printing speed depends on the frequency of the head, in the case of label use, printing is generally performed at 35 to 40 m / min. Therefore, in the present invention, printing can be performed at a printing speed of 40 m / min or more. preferable. A printing speed of 50 m / min or more is more preferable.

It is the know-how of an inkjet head that the drop volume can be reduced and printed at a high frequency, and it is the know-how of ink that obtains flow characteristics that can be followed. The purpose of the present invention is to obtain a cured film with a low odor and a low residual rate that can be used for food packaging while realizing this high image quality and high printing speed. It shows that it can be obtained by controlling various factors such as curing environment.

(Printing substrate)
In this invention, the film and paper base material which are generally used for a label and a packaging material can be used. For label applications, tack paper and tack film sold by bonding adhesive and separate paper can be used. It is also possible to use a base material having a function of barriering gas and liquid, such as an aluminum vapor deposition film. However, in the present invention, since the purpose is to reduce the residual ratio of the ink raw material, It can also be used particularly effectively for general coated papers and films that are highly likely to penetrate and mix.

  In the case of a highly penetrating substrate, the residual rate can be more effectively reduced by inserting at least one temporary curing or main curing step within 0.5 seconds from the first ink landing. preferable.

In order to control the permeability of the ink, it is also effective to modify the surface of the base material such as anchor coating or corona treatment. In particular, corona treatment tends to be considered to promote penetration because the surface of the base material is generally polarized to improve the wettability of the ink. However, in practice, changing only the surface state can be suitably used because it is possible to modify only the surface of the coating layer and to suppress the permeation if it is a substrate having a coating layer.

  EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, the aspect of this invention is not limited to these examples.

1. Preparation of Pigment Dispersion Prior to the preparation of the ink composition, various pigment dispersions were prepared as follows.

(Preparation of pigment dispersion A)
The following materials were stirred with a high speed mixer or the like until uniform, and then the obtained mill base was dispersed with a horizontal sand mill for about 1 hour to prepare pigment dispersion A.

Pigment: Phthalocyanine pigment (Toyocolor)
"LIONOL BLUE FG-7400-G" 30.0 parts Pigment dispersant: Solsperse 32000 (manufactured by Lubrizol) 15.0 parts Monomer: 64.0 parts dipropylene glycol diacrylate

(Preparation of pigment dispersion B)
Similar to Pigment Dispersion A, Pigment Dispersion B having the following composition was prepared.

Pigment: Quinacridone pigment (manufactured by Clariant)
“Inkjet Magenta E5B02” 30.0 parts Pigment dispersant: Solsperse 32000 (manufactured by Lubrizol) 15.0 parts Monomer: 64.0 parts dipropylene glycol diacrylate

(Preparation of pigment dispersion C)
Similar to Pigment Dispersion A, Pigment Dispersion C having the following composition was prepared.

Pigment: Benzimidazolone pigment (manufactured by Clariant)
“Noveperm Yellow P-HG” 30.0 parts Pigment dispersant: Solsperse 32000 (manufactured by Lubrizol) 15.0 parts Monomer: 64.0 parts dipropylene glycol diacrylate

(Preparation of pigment dispersion D)
Similar to Pigment Dispersion A, Pigment Dispersion D having the following composition was prepared.

Pigment: Carbon black pigment (Degussa)
“Special Black 350” 30.0 parts Pigment Dispersant: Solsperse 32000 (manufactured by Lubrizol) 15.0 parts Monomer: Dipropylene glycol acrylate 64.0 parts

2. Preparation of ink composition Using each of the previously prepared color pigment dispersions A to D, the monomer, the initiator, the stabilizer, and the surface conditioner were sequentially stirred so that the ink formulation shown in Table 1 was obtained. Added and mixed gently until the initiator dissolved. For example, # 1 represents a four-color ink set of cyan, magenta, yellow, and black. In addition, the compounding quantity of the component described in the table | surface is all "weight part." Then, it filtered with the 1 micrometer membrane filter about the obtained liquid mixture, and obtained the inkjet ink composition by removing a coarse particle.

  The raw material components of the ink described in Table 1 are as follows.

SP32000: Solsperse 32000 (manufactured by Lubrizol)
・ LA: Lauryl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.)
VEEA: 2- (2-vinyloxyethoxy) ethyl acrylate (manufactured by Nippon Shokubai Co., Ltd.)
・ DPGDA: Dipropylene glycol diacrylate (manufactured by BASF)
DCP-A: Tricyclodecane dimethanol diacrylate (manufactured by Kyoeisha Chemical Co., Ltd.)
DPHA: Dipentaerythritol hexaacrylate (manufactured by Toagosei Co., Ltd.)
Irg819: bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide (manufactured by BASF)
Irg369: 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1 (manufactured by BASF)
ESACURE ONE: oligo [2-hydroxy-2-methyl-1- {4- (1-methylvinyl) phenyl} propanone] (manufactured by Lamberti)
EAB: 4,4′-diethylaminobenzophenone (manufactured by Daido Kasei Kogyo Co., Ltd.)
・ TPO: 2,4,6-trimethylbenzoyldiphenylphosphine oxide (manufactured by BASF)
・ Phenothiazine: Phenothiazine (Seiko Chemical Co., Ltd.)
UV3510: BYK-UV3510 (manufactured by BYK Chemie)

(Viscosity measurement)
The viscosity of the prepared ink was a TVE25L viscometer manufactured by Toki Sangyo Co., Ltd. The measurement conditions were set in a 25 ° C. circulating chiller environment, after adjusting to a rotation speed suitable for measurement (20 rpm for inks of 20 mP · s or less, and 10 rpm for inks with a viscosity higher than 20 mP · s). The measured value after the minute was used as the viscosity.

(Examples 1 to 20 and Comparative Examples 1 to 4)
3. Inkjet printing Next, as shown in Tables 2 and 3, printing was performed at the printing speeds listed in Tables 2 and 3 using the inkjet ink composition prepared previously, as shown in Tables 2 and 3.
The ink printing order was cyan, magenta, yellow, and black.
-Kyocera: on a PET K2411 manufactured by Lintec under the printing conditions of a frequency of 20 kHz, a head temperature of 40 ° C., an ink droplet amount of 6 to 14 pl, and 600 × 600 dpi using an inkjet discharge device loaded with a head (KJ4A) manufactured by Kyocera Corporation. The ink composition was discharged.
-TEC: onto a PET K2411 manufactured by Lintec under the printing conditions of a frequency of 5 kHz, a head temperature of 40 ° C., an ink droplet amount of 42 pl, and 150 × 150 dpi using an inkjet discharge device loaded with a head (CA3) manufactured by Toshiba Tec Corporation The ink composition was discharged.
After ink landing, as shown in Tables 2 and 3, ultraviolet curing was performed using one of the following lamps to obtain a cured film.
-LED + Metahara: One LED lamp (385 nm, 10 m / sec, integrated light quantity 566 mw / cm ² ) manufactured by Integration Technology, followed by one 160 W / cm metal halide lamp manufactured by Harrison Toshiba Lighting, at a conveyor speed of 50 m / min, 1 Pass UV cured.
Meta-harass + meta-harass: UV cured with two 160 W / cm metal halide lamps manufactured by Harrison Toshiba Lighting Corporation at a conveyor speed of 50 m / min and 1 Pass.

(Oxygen concentration)
When performing UV curing, the oxygen concentration during curing shown in Tables 2 and 3 was adjusted by feeding the nitrogen-enriched air generated by changing the flow rate of the gas separation module SEPAREL MJ-G530C manufactured by DIC into the apparatus. . The oxygen concentration described here is the oxygen concentration on the surface of the printed material when subjected to ultraviolet irradiation. The oxygen concentration was measured by installing a combustion exhaust gas oxygen concentration meter HT-1200N (manufactured by Hodaka Co., Ltd.) immediately before the ultraviolet irradiation unit and recording the average value.

4). In addition to the evaluation of the cured film, various evaluations were performed on the cured film according to the method described below.

(Extraction of unreacted monomer and initiator remaining in cured film and calculation of amount)
A4 size cured film on which sample number 5 (bicycle) of high-definition color digital standard image data (ISO / JIS-SCID JISX 9201 compliant JSA-00001) is printed using four colors of CYAN, MAGENTA, YELLOW, and BLACK. The entire substrate was cut into a 1 cm square and immersed in 100 ml of methyl ethyl ketone in a sealed container for 3 days at 60 ° C. to extract residual components in the cured film. Two days later, methyl ethyl ketone stirred and homogenized was taken out of the container, and the extracted components were identified by GCMS (GCMS-QP2010 Plus manufactured by Shimadzu Corporation) and HPLC (manufactured by Shimadzu Corporation). An amount of unreacted monomer / initiator remaining in the cured film was calculated by preparing a calibration curve of the detected compound and quantifying each compound.

(Cured film weight)
The cured film weight was calculated as follows.
Cured film weight = printed material after printing (cured film + base material) weight−base material weight before printing

(Monomer residual rate)
The residual ratio of unreacted monomer remaining in the cured film was calculated as follows.
Monomer residual ratio = total amount of extracted monomers (g) / weight of cured film (g)
(Initiator residual rate)
The residual ratio of unreacted initiator remaining in the cured film was calculated as follows.
Initiator residual ratio = total amount of extracted initiator (g) / weight of cured film (g)

As a result of evaluating the printed materials for food packaging according to EUPIA guidance (EuPIA Guideline on Printing Inks applied to the non-food contact surface of food packaging materials and articles), the migration value into the food substitute evaluation liquid In order to fall below the lower limit of the above, it is known that the standard is satisfied by setting the residual amount of the monomer and initiator remaining in the cured product to a certain value or less. From the results, in the present invention, the residual monomer ratio was determined to be 0.5% or less, and the residual initiator ratio was 10% or less as the residual practical use level.

(Odor)
The evaluation of odor was judged using a printed material immediately after printing and curing. The evaluation criteria are as follows.
○: There is almost no odor and there is no fear of impairing the taste and flavor of food △: Immediately after printing, the odor of the monomer or initiator is faint, but no odor is felt after 1 hour, the taste and flavor of food ×: The odor of the monomer or initiator is strong and the odor can be felt even after 1 day from printing, which may impair the taste and flavor of the food.

(image quality)
Image quality is evaluated by printing sample number 5 (bicycle) of high-definition color digital standard image data (ISO / JIS-SCID JISX 9201 compliant JSA-00001) using four colors of CYAN, MAGENTA, YELLOW, and BLACK. It was evaluated with. The evaluation criteria are as follows.
○: Image quality exceeding practical quality in the label market △: Image quality equivalent to practical quality in the label market ×: Image quality less than practical quality in the label market

(character)
The evaluation of the character was judged by printing the character on the printing substrate with BLACK ink and evaluating the minimum point at which the character can be read. The evaluation criteria are as follows.
○: Can read 4pt characters △: Can read 8pt characters, but cannot read 4pt characters ×: Cannot read 8pt characters

(Examples 1 to 12, 19, 20)
Examples 13 to 18 are reference examples.
As shown in Table 2, in Examples 1 to 12, 19, and 20, the monomer residual ratio is 0.5% by weight or less and the initiator residual ratio is 10% by weight or less, and the odor of the cured film is hardly felt. Met. In addition, both the image quality and the characters were good, and the quality desirable as a food label was shown. Among them, Examples 1, 2, 4, 5, 7, and 8 have a monomer residual ratio of 0.3% by weight or less and an initiator residual ratio of 6% or less. In addition to being considered extremely unlikely to be mixed, high-quality and high-definition drawing in high-speed printing is possible, so it can be said that it is more preferable as a food label.

(Comparative Examples 1 to 4)
On the other hand, as shown in Table 3, in Comparative Example 1, the viscosity of the ink is very high, and the viscosity at the time of ejection is too high. Therefore, energy cannot be efficiently transmitted to the ink on the head, and the meniscus is not stable. Discharge was not stable, and image quality and character drawing quality were not practical. In Comparative Examples 2 and 3, the ratio of initiator amount / monomer amount is too low or too high. In Comparative Example 2, the initiator / monomer ratio is too low, the monomer curing is not sufficient, and a large amount of monomer remains in the cured film. Moreover, in the comparative example 3, since an initiator is excess with respect to a monomer, an initiator will remain in a large amount in a cured film. Both Comparative Examples 2 and 3 had a strong odor after printing and curing, and were unsuitable for use as a food label from the point of impairing the taste and flavor of the food and the risk of migration to food. In Comparative Example 4, curing was performed under atmospheric oxygen concentration (21%). However, since the surface of the cured film was greatly affected by the inhibition of curing by oxygen, a large amount of monomer remained in the cured film. For this reason, it was inappropriate for use as a food label.

Claims (9)

A method for producing an active energy ray-curable inkjet ink cured film that is cured by a 1-pass printing method using an active energy ray-curable inkjet ink containing a colorant, a monomer, and an initiator,
The monomer contains a polyfunctional monomer having two or more functions, and
A monomer having a molecular weight of 300 or more is not contained, or a monomer having a molecular weight of 300 or more is 15% by weight or less based on the total weight of the ink;
0 ≦ monofunctional monomer amount / polyfunctional monomer amount ≦ 0.2 (weight ratio),
0.02 ≦ initiator amount / monomer amount ≦ 0.16 (weight ratio),
The bifunctional or higher polyfunctional monomer contains 2- (2-hydroxyethoxy) ethyl acrylate (VEEA), and the VEEA contains 10 to 60% by weight of the entire inkjet ink,
The initiator comprises bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide;
The ink viscosity is 20 mPa · s or less,
A method for producing an active energy ray-curable inkjet ink cured film, wherein the oxygen concentration at the time of irradiation with active energy rays is cured in an atmosphere less than the oxygen concentration in the atmosphere.
2. The production of an active energy ray-curable inkjet ink cured film according to claim 1, wherein the monomer contains 30 to 100% by weight of a monomer having EO (ethylene oxide) or PO (propylene oxide) as a main skeleton in the monomer component. Method. The activity according to claim 2, wherein the monomer having EO (ethylene oxide) or PO (propylene oxide) as a main skeleton contains 2- (2-hydroxyethoxy) ethyl acrylate or dipropylene glycol diacrylate. A method for producing an energy ray curable inkjet ink cured film. The manufacturing method of the active energy ray hardening-type inkjet ink cured film in any one of Claims 1-3 whose oxygen concentration at the time of the active energy ray irradiation after ink landing is 0.5-10 volume%. The initiator is further 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide , oligo [2-hydroxy-2-methyl-1- {4- (1-methylvinyl) phenyl} propanone], 2-benzyl 2-dimethylamino-1- (4-morpholinophenyl) - butanone -1 Contact and, in any one of claims 1 to 5, characterized in that it comprises at least one selected from 4,4'-diethylamino benzophenone The manufacturing method of the active energy ray hardening-type inkjet ink cured film of description.   Furthermore, an inhibitor is included, and the inhibitor includes at least one selected from a hindered phenol compound, a phenothiazine compound, a hindered amine compound, and a phosphorus compound in an amount of 0.1 to 2.0% by weight in the ink. The manufacturing method of the active energy ray hardening-type inkjet ink cured film in any one of Claims 1-5 characterized by the above-mentioned.   The method for producing an active energy ray-curable inkjet ink cured film according to any one of claims 1 to 6, wherein the active energy ray curing is curing by irradiating an LED lamp having an emission spectrum from ultraviolet to visible light.   The active energy ray-curable inkjet ink according to any one of claims 1 to 7, wherein the active energy ray curing is a curing in which a metal halide lamp is irradiated after irradiating an LED lamp having an emission spectrum from ultraviolet to visible light. A method for producing a cured film.   The method for producing an active energy ray-curable inkjet ink cured film according to any one of claims 1 to 8, wherein the ink is ejected by an inkjet head having an appropriate amount of ink liquid at 1 Pass printing of 6 to 14 pL.