JP2006312682A - Active ray cured composition, active ray cured ink, image forming method using it, and ink jet recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method and an ink jet recording apparatus which can record high definition images very stably to various recording materials also under various circumstances in which adhesiveness is good, character quality is excellent, and there is no generation of color mixture by an active ray cured composition having no generation of wrinkles and an active ray cured ink using it. <P>SOLUTION: The active ray cured composition comprises a radical polymerization monomer, a radical polymerization initiator, and an oxetane ring containing compound, wherein the content of the oxetane ring containing compound is 1-20 mass% of the total amount of the active ray cured composition, wherein the activity ray cured composition contains a basic compound further, and wherein it is a desirable aspect that the viscosity at 25°C of the active ray cured composition is 7-50 mPa s. In addition, the active ray cured ink using the activity ray cured composition, the image forming method and the ink jet recording apparatus are provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an actinic ray curable composition capable of obtaining good curability and adhesion without generating wrinkles in various recording materials under various environments, and an actinic ray curable composition (ink) using the same. Inkjet ink), an image forming method, and an inkjet recording apparatus.

  In recent years, the inkjet recording method can be easily and inexpensively created images, and thus has been applied to various printing fields such as photographs, various printing, marking, and special printing such as color filters. In particular, the recording device that discharges and controls fine dots, the ink with improved color reproduction gamut, durability, and dischargeability, and the ink absorption, the coloring of the coloring material, the surface gloss, etc. have been dramatically improved. It is also possible to obtain image quality comparable to silver halide photography using special paper. The image quality improvement of today's ink jet recording system is achieved only when all of the recording apparatus, ink, and special paper are available.

  However, in an inkjet system that requires special paper, the recording material is limited, and the cost of the recording material increases. Therefore, many attempts have been made to record on a recording material different from the dedicated paper by the ink jet method. Specifically, a phase change inkjet method using a wax ink that is solid at room temperature, a solvent-based inkjet method that uses an ink mainly composed of a fast-drying organic solvent, and a UV inkjet method that uses an ultraviolet (UV) light to crosslink after recording. Etc.

  Among them, the UV inkjet method has been attracting attention in recent years because it has a relatively low odor compared to the solvent-based inkjet method, and can be recorded on a recording material that does not dry quickly and absorbs ink. (For example, refer to Patent Documents 1 and 2).

  However, even if these inks are used, it is impossible to form high-definition images on various recording materials depending on the type of recording material and the working environment.

In recent years, there has also been disclosed an active energy ray-curable resin composition using an oxetane compound and a cationic photopolymerization initiator in combination with a radical polymerizable compound and a radical photopolymerization initiator (see, for example, Patent Documents 3 and 4). .
JP-A-9-302269 JP 2002-128865 A JP 2004-331872 A JP 2005-15739 A

  The present invention has been made in view of the above problems, and its purpose is to provide an actinic ray curable composition that does not generate wrinkles even under various environments, and an actinic ray curable ink using the same. Provided are an image forming method and an ink jet recording apparatus capable of recording a high-definition image very stably with excellent adhesion to various recording materials, excellent character quality, and no color mixing. There is.

  The above object of the present invention is achieved by the following configurations.

(Claim 1)
An actinic ray curable composition comprising a radical polymerizable monomer, a radical polymerization initiator, and an oxetane ring-containing compound.

(Claim 2)
2. The actinic ray curable composition according to claim 1, wherein the content of the oxetane ring-containing compound is 1 to 20% by mass of the total amount of the actinic ray curable composition.

(Claim 3)
The actinic ray curable composition according to claim 1 or 2, comprising at least one basic compound.

(Claim 4)
The actinic ray curable composition according to any one of claims 1 to 3, wherein the viscosity at 25 ° C is 7 to 50 mPa · s.

(Claim 5)
The actinic ray curable ink according to any one of claims 1 to 4, wherein the actinic ray curable composition contains a pigment.

(Claim 6)
6. An image forming method for printing by ejecting the actinic ray curable ink according to claim 5 onto a recording material from an ink jet recording head, wherein the recording material is a polyvinyl chloride film.

(Claim 7)
The inkjet recording apparatus used in the image forming method according to claim 6, wherein the actinic ray curable ink and the recording head are heated to 35 to 100 ° C. and then discharged.

  According to the actinic ray curable composition, the actinic ray curable ink, the image forming method using the actinic ray curable ink, and the ink jet recording apparatus of the present invention, the adhesiveness to various recording materials even in various printing environments. The image quality is good, no wrinkles occur, the character quality is excellent, color mixing does not occur, and high-definition images can be recorded very stably.

  As an actinic ray curable composition (hereinafter also simply referred to as a composition), a radically polymerizable monomer, a cationically polymerizable monomer, a radical polymerization initiator, and a cationic polymerization start, as described in the above-mentioned known patent documents 1 to 4 Although the composition containing the agent is well known, there are some problems such as generation of wrinkles due to curing shrinkage due to curing environment (temperature, humidity, etc.), poor curability, and poor adhesion to the recording material. .

  In particular, when a pigment is contained in the composition defined in the present invention and used as an actinic ray curable ink (hereinafter also simply referred to as ink), the ink viscosity depends on the storage environment (temperature, humidity, etc.) of the ink. The dispersion of ink is reduced, the discharge stability, which is the biggest problem in ink jet recording, is very good, and the dot diameter after the ink has landed on the recording material without being affected by the curing environment This is an epoch-making structure that can be easily controlled and can form high-quality images with high reproducibility.

  Furthermore, by using a basic compound, the ejection stability becomes better, and it is very effective particularly when the photopolymerizable compound has the structure of the present invention, and can form a high-quality image with good reproducibility. it can.

  Hereinafter, the present invention will be described in more detail.

(Radically polymerizable monomer)
First, the radical polymerizable monomer according to the present invention will be described.

  The composition of the present invention preferably contains a monomer or oligomer of (meth) acrylate. Any known (meth) acrylate monomer or oligomer may be used.

  For example, i-amyl acrylate, stearyl acrylate, lauryl acrylate, octyl acrylate, decyl acrylate, i-myristyl acrylate, i-stearyl acrylate, 2-ethylhexyl diglycol acrylate, 2-hydroxybutyl acrylate, 2-acryloyloxyethyl hexa Hydrophthalic acid, butoxyethyl acrylate, ethoxydiethylene glycol acrylate, methoxydiethylene glycol acrylate, methoxypolyethylene glycol acrylate, methoxypropylene glycol acrylate, phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, i-bornyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxy Propyl acrylate, 2- Droxy-3-phenoxypropyl acrylate, 2-acryloyloxyethyl succinic acid, 2-acryloyloxyethyl phthalic acid, 2-acryloyloxyethyl-2-hydroxyethyl-phthalic acid, lactone-modified flexible acrylate, t- Monofunctional monomers such as butylcyclohexyl acrylate; triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, tripropylene glycol diacrylate, polypropylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6- Hexanediol diacrylate, 1,9-nonanediol diacrylate, neopentyl glycol diacrylate, dimethylol-tricyclodecane diacrylate, bis Bifunctional monomers such as EO (ethylene oxide) adduct diacrylate of enol A, PO (propylene oxide) adduct diacrylate of bisphenol A, neopentyl glycol diacrylate of hydroxypivalate, polytetramethylene glycol diacrylate, etc .; trimethylolpropane tri Acrylate, EO-modified trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, ditrimethylolpropane tetraacrylate, glycerin propoxytriacrylate, caprolactone-modified trimethylolpropane triacrylate, pentaerythritol ethoxytetraacrylate Caprolactam-modified dipenta A trifunctional or higher polyfunctional monomer such as erythritol hexaacrylate is exemplified.

  In addition, polymerizable oligomers can be blended in the same manner as the monomer. Examples of the polymerizable oligomer include epoxy acrylate, aliphatic urethane acrylate, aromatic urethane acrylate, polyester acrylate, and linear acrylic oligomer.

  Among the above monomers, i-amyl acrylate, stearyl acrylate, lauryl acrylate, octyl acrylate, decyl acrylate, i-mil are particularly preferred from the viewpoints of sensitization, skin irritation, eye irritation, mutagenicity, toxicity, etc. Still acrylate, i-stearyl acrylate, ethoxydiethylene glycol acrylate, methoxypolyethylene glycol acrylate, methoxypropylene glycol acrylate, isobornyl acrylate, lactone-modified flexible acrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, EO-modified trimethylolpropane triacrylate, dipentaerythritol hexaacrylate, ditrimethylo Propane tetraacrylate, glycerol propoxy triacrylate, caprolactone modified trimethylolpropane triacrylate, pentaerythritol tetraacrylate, caprolactam modified dipentaerythritol hexaacrylate preferred. Furthermore, among these, stearyl acrylate, lauryl acrylate, i-stearyl acrylate, ethoxydiethylene glycol acrylate, i-bornyl acrylate, tetraethylene glycol diacrylate, EO-modified trimethylolpropane triacrylate, glycerin propoxytriacrylate, cowprolactone-modified tri Methylolpropane triacrylate and caprolactam-modified dipentaerythritol hexaacrylate are particularly preferred.

(Radical polymerization initiator)
In the present invention, a radical polymerization initiator is used. As the radical polymerization initiator, conventionally known photo radical generators such as aryl alkyl ketone, oxime ketone, S-phenyl thiobenzoate, titanocene, aromatic ketone, thioxanthone, benzyl, quinone derivatives, ketocoumarins and the like can be used. This is detailed in “Application and Market of UV / EB Curing Technology” (CMC Publishing Co., Ltd., supervised by Yoneho Tabata / edited by Radtech Study Group).

  Among them, acyl phosphine oxide and acyl phosphonate have high sensitivity and absorption is reduced by photocleavage of the initiator, so that it is particularly suitable for internal curing in an ink image having a thickness of 5 to 12 μm per color as in the ink jet method. It is valid. Specifically, bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide, and the like are preferable. Further, as in the case of the above-mentioned monomer, in consideration of safety, 1-hydroxycyclohexyl-phenylketone, 2-methyl-1 (4-methylthiophenyl) -2-morpholinopropan-1-one, bis (2, 6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide, 2-hydroxy-2-methyl-1-phenylpropan-1-one (Darocur (registered trademark) 1173) is preferably used. A preferable addition amount is 1 to 20% by mass, preferably 5 to 10% by mass, based on the entire ink composition.

  In the present invention, no cationic polymerization initiator is used.

(Oxetane ring-containing compound)
Examples of the oxetane ring-containing compound according to the present invention include compounds having one or more oxetane rings in the molecule.

  Examples of one oxetane ring-containing compound in the molecule include compounds represented by the following general formula (1).

In the general formula (1), Z represents an oxygen atom or a sulfur atom. R ¹ is a hydrogen atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms such as methyl, ethyl, propyl or butyl, a fluoroalkyl group having 1 to 6 carbon atoms, an allyl group, an aryl group, a furyl group or a thienyl group. R ² represents an alkyl group having 1 to 6 carbon atoms such as methyl, ethyl, propyl or butyl, 1-propenyl, 2-propenyl, 2-methyl-1-propenyl, 2-methyl-2-propenyl, An alkenyl group having 1 to 6 carbon atoms such as 1-butenyl, 2-butenyl or 3-butenyl, an aryl group such as phenyl, benzyl, fluorobenzyl, methoxybenzyl or phenoxyethyl, propylcarbonyl, butylcarbonyl or pentylcarbonyl C1-C6 alkylcarbonyl group, ethoxycarbonyl, propoxycarbonyl, or butoxycarbonyl Represents an alkoxycarbamoyl group having 1 to 6 carbon atoms such as ethoxycarbamoyl, propylcarbamoyl or butylpentylcarbamoyl.

As the oxetane ring-containing compound, in general formula (1), those in which R ¹ is a lower alkyl group, particularly an ethyl group, R ² is a butyl group, a phenyl group or a benzyl group, and Z is an oxygen atom are preferable.

  Examples of the compound having two or more oxetane rings in the molecule include compounds represented by the following general formulas (2) and (8).

In general formula (2), m represents 2, 3 or 4, and Z represents an oxygen atom or a sulfur atom. R ³ is a hydrogen atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms such as methyl, ethyl, propyl or butyl, a phenyl group, a fluoroalkyl group having 1 to 6 carbon atoms, an allyl group, an aryl group or a furyl group. R ⁴ represents, for example, a linear or branched alkylene group having 1 to 12 carbon atoms, a linear or branched poly (alkyleneoxy) group represented by the general formula (3), or the following general formula (4), (5 ) And (6) represents a polyvalent group selected from the group consisting of.

[Wherein R ⁵ represents a lower alkyl group such as methyl, ethyl or propyl. ]

In General formula (4), n represents 0 or the integer of 1-2000. R ⁶ represents a group selected from the group consisting of an alkyl group having 1 to 10 carbon atoms such as methyl, ethyl, propyl or butyl and the following general formula (7). R ⁷ represents an alkyl group having 1 to 10 carbon atoms such as methyl, ethyl, propyl or butyl.

In the formula, j represents 0 or an integer of 1 to 100. R ⁸ represents an alkyl group having 1 to 10 carbon atoms.

In the general formula (5), R ⁹ is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms such as methyl, ethyl, propyl or butyl, an alkoxy group having 1 to 10 carbon atoms, a halogen atom, a nitro group, or cyano. Represents a group, a mercapto group, a lower alkylcarboxylate group or a carboxyl group.

In the general formula (6), R ¹⁰ represents an oxygen atom, a sulfur atom, NH, SO, SO ₂ , CH ₂ , C (CH ₃ ) ₂ or C (CF ₃ ) ₂ .

As the oxetane ring-containing compound, in the above general formula (2), R ³ is a lower alkyl group, particularly an ethyl group, R ⁴ is a group in which R ⁹ in the general formula (5) is a hydrogen atom, a hexamethylene group, In the formula (3), it is preferable that R ⁵ is an ethyl group, R ⁷ and R ⁸ are each a methyl group, and Z is an oxygen atom.

In General formula (8), r represents the integer of 25-200. R ¹¹ represents an alkyl group or a trialkylsilyl group having 1 to 4 carbon atoms, R ¹ and R ⁸ has the same meaning as R ⁸ of R ¹ and formula respectively the formula (1) (7).

  In the present invention, two or more kinds of one or more oxetane ring-containing compounds may be used in combination in these molecules.

  The oxetane ring-containing compound is preferably 1 to 20% by mass of the total amount of the composition of the present invention. When the amount of the oxetane ring-containing compound is more than 20% by mass, the curability is deteriorated, and when it is less than 1% by mass, the curability is improved, but the adhesiveness to the recording material is weak and the resistance as a printed matter is not preferable. Absent.

(Basic compound)
In addition to the said structure, it is preferable to use a basic compound for the composition of this invention. By containing the basic compound, not only the ejection stability becomes good, but also the generation of wrinkles due to curing shrinkage is suppressed even under low humidity.

  As the basic compound, any known compounds can be used, and representative examples include basic alkali metal compounds, basic alkaline earth metal compounds, and basic organic compounds such as amines.

  Basic alkali metal compounds include alkali metal hydroxides (lithium hydroxide, sodium hydroxide, potassium hydroxide, etc.), alkali metal carbonates (lithium carbonate, sodium carbonate, potassium carbonate, etc.), alkali metal alcoholates. (Sodium methoxide, sodium ethoxide, potassium methoxide, potassium ethoxide, etc.). Similarly, basic alkaline earth metal compounds include alkaline earth metal hydroxides (magnesium hydroxide, calcium hydroxide, etc.), alkali metal carbonates (magnesium carbonate, calcium carbonate, etc.), and alkali metals. Alcoholate (magnesium methoxide, etc.).

  Examples of the basic organic compound include nitrogen-containing heterocyclic compounds such as amine, quinoline and quinolidine. Among these, amines are preferable from the viewpoint of compatibility with the photopolymerization monomer, for example, octylamine, naphthylamine, Xylenediamine, dibenzylamine, diphenylamine, dibutylamine, dioctylamine, dimethylaniline, quinuclidine, tributylamine, trioctylamine, tetramethylethylenediamine, tetramethyl-1,6-hexamethylenediamine, hexamethylenetetramine, triethanolamine, etc. Is mentioned.

  The concentration in the presence of the basic compound is preferably in the range of 10 to 1000 ppm by mass, particularly 20 to 500 ppm by mass with respect to the total amount of the photopolymerizable monomer. In addition, a basic compound may be used individually or may be used together.

(Pigment)
The actinic ray curable ink of the present invention contains various known dyes or pigments together with the actinic ray curable composition described above, and preferably contains a pigment.

  The pigments that can be preferably used are listed below, but the present invention is not limited thereto.

C. I Pigment Yellow-1, 3, 12, 13, 14, 17, 81, 83, 87, 95, 109, 42,
C. I Pigment Orange-16, 36, 38,
C. I Pigment Red-5, 22, 38, 48: 1, 48: 2, 48: 4, 49: 1, 53: 1, 57: 1, 63: 1, 144, 146, 185, 101,
C. I Pigment Violet-19, 23,
C. I Pigment Blue-15: 1, 15: 3, 15: 4, 18, 60, 27, 29,
C. I Pigment Green-7, 36,
C. I Pigment White-6, 18, 21,
C. I Pigment Black-7.

  In the present invention, it is preferable to use white ink for the purpose of enhancing the color concealment property on a transparent substrate such as a plastic film. In particular, in soft packaging printing and label printing, it is preferable to use white ink, but since the discharge amount increases, there is a limit to the amount of use from the viewpoint of discharge stability, curl of recording material, and wrinkle generation. is there.

  For the dispersion of the pigment, for example, a ball mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet jet mill, paint shaker, or the like can be used. Further, it is possible to add a dispersant when dispersing the pigment. As the dispersant, a polymer dispersant is preferably used, and examples of the polymer dispersant include Avecia's Solsperse series and Ajinomoto Fine-Techno's PB series. Moreover, it is also possible to use a synergist corresponding to various pigments as a dispersion aid. These dispersants and dispersion aids are preferably added in an amount of 1 to 50 parts by mass with respect to 100 parts by mass of the pigment.

  The dispersion medium is used using a solvent or a polymerizable compound. However, the radiation curable ink used in the present invention is preferably solvent-free because it reacts and cures immediately after ink landing. If the solvent remains in the cured image, the solvent resistance deteriorates and the VOC (volatile organic compound) problem of the remaining solvent arises. Therefore, it is preferable in view of dispersibility that the dispersion medium is not a solvent but a polymerizable compound, and among them, a monomer having the lowest viscosity is selected.

  The pigment is preferably dispersed so that the average particle diameter of the pigment particles is 0.08 to 0.5 μm, and the maximum particle diameter is 0.3 to 10 μm, preferably 0.3 to 3 μm. The selection of the dispersion medium, the dispersion conditions, and the filtration conditions are appropriately set. By controlling the particle size, clogging of the head nozzle can be suppressed, and ink storage stability, ink transparency, and curing sensitivity can be maintained.

  The ink of the present invention preferably has a colorant concentration of 1 to 10% by mass of the entire ink.

  Various additives other than those described above can be used in the ink of the present invention. For example, surfactants, leveling additives, matting agents, polyester resins for adjusting film properties, polyurethane resins, vinyl resins, acrylic resins, rubber resins, and waxes can be added.

  The ink of the present invention preferably has a viscosity of 7 to 50 mPa · s at 25 ° C., in order to stabilize ejection and obtain good curability regardless of the curing environment (temperature / humidity).

(Recording material)
As a recording material that can be used in the present invention, various non-absorbable plastics and films used for so-called soft packaging can be used in addition to ordinary uncoated paper, coated paper, and the like. Examples of various plastic films include polyethylene terephthalate (PET) film, stretched polystyrene (OPS) film, stretched polypropylene (OPP) film, stretched nylon (ONy) film, polyvinyl chloride (PVC) film, polyethylene (PE) film, An acetyl cellulose (TAC) film etc. can be mentioned. Other plastics that can be used include polycarbonate (PC), acrylic resin, ABS (acrylic butadiene styrene resin), polyacetal, PVA (polyvinyl alcohol), and rubbers. It can also be applied to metals and glasses. Especially, when a PVC film is used, the effect of the present invention is particularly great.

  The surface energy of these various plastic films varies greatly depending on the characteristics of the material, and it has been a problem that the dot diameter after ink landing changes depending on the recording material. With the configuration of the present invention, a good high-definition image can be formed on a wide range of recording materials having a surface energy of 35 to 60 mN / m, including OPP films having a low surface energy, OPS films, and PET having a relatively large surface energy. .

  In the present invention, it is more advantageous to use a long (web) recording material in terms of the cost of the recording material such as packaging cost and production cost, the efficiency of creating the print, and the ability to cope with printing of various sizes. It is.

(Image forming method)
Next, the image forming method of the present invention will be described.

In the image forming method of the present invention, the ink is ejected and drawn on a recording material by an ink jet recording method, and then the ink is cured by irradiation with actinic rays such as ultraviolet rays.

(Total ink film thickness after ink landing)
In the present invention, the total ink film thickness after the ink has landed on the recording material and cured by irradiation with actinic rays is preferably 2 to 25 μm. In the actinic ray curable ink jet recording in the screen printing field, the total ink film thickness currently exceeds 25 μm, but in the flexible packaging printing field where the recording material is often a thin plastic material, the recording material described above is used. In addition to the problem of curling and wrinkles, there is a problem that the waist and texture of the entire printed matter changes, so that it is not preferable to eject ink with an excessive film thickness.

  Here, the “total ink film thickness” means the maximum value of the film thickness of the ink drawn on the recording material, and may be a single color or other two-color overlay (secondary color), three-color overlay, Even when recording is performed by an ink-jet recording method of color overlap (white ink base), the meaning of the total ink film thickness is the same.

(Ink ejection conditions)
As the ink ejection conditions, it is preferable from the viewpoint of ejection stability that the recording head and ink are heated to 35 to 100 ° C. and ejected. Actinic radiation curable ink has a large viscosity fluctuation range due to temperature fluctuation, and the viscosity fluctuation directly affects the droplet size and droplet ejection speed, causing image quality degradation. Must be kept constant. The control range of the ink temperature is set temperature ± 5 ° C., preferably set temperature ± 2 ° C., more preferably set temperature ± 1 ° C.

  In the present invention, it is preferable that the amount of liquid droplets discharged from each nozzle is 2 to 15 pl. Originally, in order to form a high-definition image, it is necessary for the amount of droplets to be within this range, but when discharging with this amount of droplets, the above-described discharge stability becomes particularly severe. According to the present invention, even when the ink is ejected with a small droplet amount such as 2 to 15 pl, the ejection stability is improved and a high-definition image can be stably formed.

(Light irradiation conditions after ink landing)
In the image forming method of the present invention, it is preferable that the actinic ray is irradiated between 0.001 second and 1.0 second after ink landing, and more preferably between 0.001 second and 0.5 second. In order to form a high-definition image, it is particularly important that the irradiation timing is as early as possible.

  As a method for irradiating actinic rays, the basic method is disclosed in JP-A-60-132767. According to this, the light source is provided on both sides of the head unit, and the head and the light source are scanned by the shuttle method. Irradiation is performed after a certain period of time after ink landing. Further, the curing is completed by another light source that is not driven. US Pat. No. 6,145,979 discloses a method using an optical fiber as an irradiation method and a method of irradiating a recording unit with UV light by applying a collimated light source to a mirror surface provided on the side surface of the head unit. In the present invention, any of these irradiation methods can be used.

  In addition, the irradiation of actinic rays is divided into two stages. First, actinic rays are irradiated by the above-described method within 0.001 to 2.0 seconds after ink landing, and actinic rays are further irradiated after all printing is completed. The method is also a preferred embodiment. By dividing the irradiation of actinic rays into two stages, it is possible to further suppress the shrinkage of the recording material that occurs during ink curing.

  Conventionally, in the UV ink jet system, a light source with high illuminance in which the total power consumption of the light source exceeds 1 kW · hr is usually used in order to suppress dot spreading and bleeding after ink landing. However, when these light sources are used, particularly in printing on a shrink label or the like, the shrinkage of the recording material is so large that it cannot be used practically.

(Inkjet recording device)
Next, an ink jet recording apparatus (hereinafter simply referred to as a recording apparatus) will be described.

  Hereinafter, a recording apparatus according to the present invention will be described with reference to the drawings as appropriate. Note that the recording apparatus in the drawing is merely one aspect of the recording apparatus of the present invention, and is not limited to this drawing.

  FIG. 1 is a front view showing the configuration of the main part of the recording apparatus of the present invention. The recording apparatus 1 includes a head carriage 2, a recording head 3, an irradiation unit 4, a platen unit 5, and the like. In the recording apparatus 1, the platen unit 5 is installed under the recording material P. The platen unit 5 has a function of absorbing ultraviolet rays, and absorbs excess ultraviolet rays that have passed through the recording material P. As a result, a high-definition image can be reproduced very stably.

  The recording material P is guided by the guide member 6 and moves from the near side to the far side in FIG. 1 by the operation of the conveying means (not shown). A head scanning unit (not shown) scans the recording head 3 held by the head carriage 2 by reciprocating the head carriage 2 in the Y direction in FIG.

  The head carriage 2 is installed on the upper side of the recording material P, and stores a plurality of recording heads 3 to be described later according to the number of colors used for image printing on the recording material P, with the discharge ports arranged on the lower side. The head carriage 2 is installed with respect to the main body of the recording apparatus 1 in such a manner that it can reciprocate in the Y direction in FIG. 1, and reciprocates in the Y direction in FIG. 1 by driving the head scanning means.

  In FIG. 1, the head carriage 2 is white (W), yellow (Y), magenta (M), cyan (C), black (K), light yellow (Ly), light magenta (Lm), and light cyan (Lc). In the drawing, the recording head 3 for light black (Lk) and white (W) is drawn. However, in practice, the number of colors of the recording head 3 stored in the head carriage 2 is appropriately determined. Is.

  The recording head 3 has a discharge port by operating a discharge means (not shown) provided with a plurality of actinic ray curable inks (for example, UV curable ink) supplied by an ink supply means (not shown). To the recording material P. The discharged UV curable ink is composed of a coloring material, a polymerizable monomer, an initiator, and the like. The monomer is crosslinked and polymerized when the initiator acts as a catalyst when irradiated with ultraviolet rays. It has the property of being cured by reaction.

  The recording head 3 has a certain area (landing possible area) in the recording material P during scanning that moves from one end of the recording material P to the other end of the recording material P in the Y direction in FIG. On the other hand, UV curable ink is ejected as ink droplets, and ink droplets are landed on the landable area.

  The above scanning is performed as many times as necessary, and after the UV curable ink is discharged toward one landing possible region, the recording material P is appropriately moved from the front to the back in FIG. While performing scanning, the recording head 3 discharges the UV curable ink to the next landable area adjacent to the rearward direction in FIG.

  By repeating the above-described operation and ejecting the UV curable ink from the recording head 3 in conjunction with the head scanning unit and the conveying unit, an image composed of an aggregate of UV curable ink droplets is formed on the recording material P.

  The irradiation unit 4 includes an ultraviolet lamp that emits ultraviolet light in a specific wavelength region with stable exposure energy and a filter that transmits ultraviolet light of a specific wavelength. Here, as the ultraviolet lamp, a mercury lamp, a metal halide lamp, an excimer laser, an ultraviolet laser, a cold cathode tube, a hot cathode tube, a black light, an LED (light emitting diode) and the like can be applied. A cathode tube, a hot cathode tube, a mercury lamp or a black light is preferred. The irradiation means 4 is fixed on both sides of the head carriage 2 so as to be substantially parallel to the recording material P.

  The irradiating means 4 has substantially the same shape as the maximum one that can be set by the recording apparatus (UV inkjet printer) 1 among the landable areas in which the recording head 3 ejects UV curable ink by a single scan driven by the head scanning means. Or it has a larger shape than the landable area.

  As described above, as a means for adjusting the illuminance of the ink discharge portion, the entire recording head 3 is shielded from light, but in addition, the ink of the recording head 3 is determined from the distance h1 between the irradiation means 4 and the recording material P. It is effective to increase the distance h2 between the ejection unit 31 and the recording material P (h1 <h2) or to increase the distance d between the recording head 3 and the irradiation unit 4 (d is increased). Further, it is more preferable to provide a bellows structure 7 between the recording head 3 and the irradiation means 4.

  Here, the wavelength of the ultraviolet rays irradiated by the irradiation means 4 can be changed as appropriate by replacing the ultraviolet lamp or filter provided in the irradiation means 4.

  The ink of the present invention has excellent ejection stability and is particularly effective when an image is formed using a line head type recording apparatus.

  FIG. 2 is a top view illustrating another example of the configuration of the main part of the ink jet recording apparatus.

  The ink jet recording apparatus shown in FIG. 2 is called a line head system, and a plurality of ink jet recording heads 3 of each color are fixedly arranged on the head carriage 2 so as to cover the entire width of the recording material P. ing.

  On the other hand, on the downstream side of the head carriage 2, there is provided irradiation means 4 arranged so as to cover the entire width of the recording material P and cover the entire area of the ink printing surface. As the ultraviolet lamp used in the illuminating means 4, the same one as described in FIG. 1 can be used.

  In this line head system, the head carriage 2 and the irradiation means 4 are fixed, only the recording material P is conveyed, and ink is ejected and cured to form an image.

  Nitrogen gas can be blown between the ultraviolet lamp and the recording material.

  Examples of the present invention will be specifically described below, but the embodiments of the present invention are not limited to these examples. Unless otherwise specified, “part” in the examples represents “part by mass” and “%” represents “% by mass”.

<Preparation of ink composition set>
According to the following method, ink composition sets 1 to 6 having the compositions shown in Tables 1 to 6 were prepared.

  5 parts of a dispersant (PB822: manufactured by Ajinomoto Fine Techno Co., Ltd.) and each photopolymerizable compound shown in Tables 1 to 6 were placed in a stainless beaker and stirred and mixed for 1 hour while heating on a hot plate at 65 ° C. And dissolved. Next, after adding the coloring materials described in Tables 1 to 6 to this solution, the solution was placed in a plastic bottle together with 200 g of zirconia beads having a diameter of 1 mm and sealed, and subjected to dispersion treatment for 2 hours using a paint shaker. Next, the zirconia beads are removed, and various radically polymerizable monomers, radical polymerization initiators, oxetane ring-containing compounds, basic compounds, surfactants and other various additives are added in combinations shown in Tables 1 to 6, and Ink composition sets 1 to 6 were obtained by filtration through a 0.8 μm membrane filter to prevent printer clogging.

  The ink viscosity of each color of each ink composition set prepared above is as follows. The viscosity was expressed as the viscosity width at the maximum and minimum viscosity of each color ink at 25 ° C.

Ink composition set 1: 16 to 19 mPa · s
Ink composition set 2: 30 to 32 mPa · s
Ink composition set 3: 28 to 31 mPa · s
Ink composition set 4: 30 to 33 mPa · s
Ink composition set 5: 28-30 mPa · s
Ink composition set 6: 32 to 35 mPa · s
Details of each ink, each compound, and display described in Tables 1 to 6 are as follows.

K: dark black ink, C: dark cyan ink, M: dark magenta ink Y: dark yellow ink, W: white ink, Lk: light black ink Lc: light cyan ink, Lm: light magenta ink, Ly: light yellow ink Color material 1: C.I. I. pigment Black 7
Color material 2: C.I. I. pigment Blue 15: 3
Color material 3: C.I. I. pigment Red 57: 1
Color material 4: C.I. I. pigment Yellow 13
Coloring material 5: Titanium oxide (anatase type, average particle size 0.20 μm)
[Radically polymerizable monomer]
A-1: EO-modified trimethylolpropane triacrylate (trifunctional)
A-2: Caprolactam-modified dipentaerythritol hexaacrylate (hexafunctional)
A-3: Tetraethylene glycol (EO-containing) diacrylate (bifunctional)
[Radical polymerization initiator]
I-1800: Irgacure 1800 (Ciba Specialty Chemicals)
I-651: Irgacure 651 (Ciba Specialty Chemicals)
[Oxetane ring-containing compound]
OXT-211: 3-ethyl-3- (phenoxymethyl) oxetane (manufactured by Toagosei Co., Ltd.)
OXT-221: Di [1-ethyl (3-oxetanyl)] methyl ether (manufactured by Toagosei Co., Ltd.)
RSOX: Toagosei Co., Ltd. [Photoacid generator]
SP152: Asahi Denka Co., Ltd. [Surfactant]
F178k: Megafax F178k (perfluoroalkyl group-containing acrylic oligomer, manufactured by Dainippon Ink & Chemicals, Inc.)
F1405: Megafax F1405 (perfluoroalkyl group-containing ethylene oxide adduct, manufactured by Dainippon Ink & Chemicals, Inc.)
F470: Megafax F470 (perfluoroalkyl group-containing acrylic oligomer, manufactured by Dainippon Ink & Chemicals, Inc.)
TF907: Megafax EXP TF907 (perfluoroalkyl group-containing ethylene oxide adduct, manufactured by Dainippon Ink & Chemicals, Inc.)
[Dispersant]
PB822: Ajinomoto Fine Techno Co., Ltd. (supra)
[Other additives]
* 1: γ-caprolactone (reagent, manufactured by Kanto Chemical Co., Inc.)
* 2: N-ethyldiethanolamine (basic compound)
* 3: Propylene carbonate (reagent, manufactured by Kanto Chemical Co., Inc.)
* 4: Tributylamine (basic compound)

<Inkjet image formation>
Each ink composition set 1 to 3 prepared above is loaded into an ink jet recording apparatus having the structure shown in FIG. 1 equipped with a piezo type ink jet nozzle, and has a width of 600 mm and a length having each surface energy shown in Table 7. The following image recording was continuously performed on each long recording material of 500 m. The ink supply system was composed of an ink tank, a supply pipe, a front chamber ink tank immediately before the head, a pipe with a filter, and a piezo head. The ink was insulated from the front chamber tank to the head portion and heated at 50 ° C. The piezo head was driven so that 2-15 pl multi-size dots could be ejected at a resolution of 720 × 720 dpi (dpi represents 1 inch, that is, the number of dots per 2.54 cm), and each ink was ejected continuously. After each ink landed, the ink was cured by irradiating with ultraviolet rays from each irradiation light source shown in Table 7 instantly (less than 0.5 seconds after landing) by the lamp units on both sides of the carriage. When the total ink film thickness was measured after image recording, it was in the range of 2.3 to 13 μm.

  Next, each image was formed in the same manner using the ink composition sets 4 to 6 using the line head type ink jet recording apparatus shown in FIG.

  Using the above two methods, printing was performed under three conditions of 10 ° C./20% RH (relative humidity), 25 ° C./50% RH, and 27 ° C./80% RH.

  In addition, the detail of each irradiation light source of Table 7 is as follows.

Irradiation light source A: High pressure mercury lamp VZero085 (manufactured by INTEGRATION TECHNOLOGY)
Irradiation light source B: Low-pressure mercury lamp (Iwasaki Electric Co., Ltd.)
Further, the illuminance of each irradiation light source was measured and displayed by measuring an integrated illuminance of 365 nm using UVPF-A1 manufactured by Iwasaki Electric Co., Ltd.

  Details of the abbreviations of the recording materials used are as follows.

OPP: Stretched polypropylene PET: Polyethylene terephthalate PVC: Polyvinyl chloride

<Evaluation of recorded images>
Each image recorded by the above image forming method was subjected to the following evaluations.

《Character quality》
Using each color ink of Y, M, C, and K, 6-point MS Mincho characters were printed at a target density, and the character roughness was magnified with a loupe, and character quality was evaluated according to the following criteria.

◎: No rusting ○: Slight rustling is visible △: Gashesiness is visible, but it can be recognized as a character and can be used at the last minute ×: A level where the rustling is severe and the character is distorted and cannot be used.

《Color mixing (bleeding, wrinkle)》
At 720 dpi (supra), printing is performed so that 1 dot of each color of Y, M, C, K is adjacent to each other, each adjacent color dot is enlarged with a magnifying glass, and the presence or absence of color mixing due to bleeding and occurrence of wrinkles is visually observed. The color mixture was evaluated according to the criteria of.

◎: Adjacent dot shape maintains a perfect circle and no bleeding or wrinkle occurs. ○: Adjacent dot shape maintains a substantially perfect circle, and almost no bleeding or wrinkle occurs. Δ: Adjacent dot is slightly blurred. Although the shape of the dot is slightly collapsed, the level that can be used at the last minute ×: The level where the adjacent dots are smeared and mixed, and there is a wrinkle in the overlapping part, and it cannot be used.

《Adhesion》
For the printed image produced above, a sample that does not scratch the printed surface at all, and in accordance with JIS K 5400, 11 cuts are made on the printed surface at 1 mm intervals vertically and horizontally, and a 1 mm square grid. 100 samples were prepared, cellotape (registered trademark) was affixed on each printing surface, quickly peeled off at an angle of 90 degrees, and the remaining print image or grid pattern remaining in accordance with the following criteria: It was evaluated. A sample cured at 25 ° C. and 45% RH was used.

○: No peeling of the printed image is observed even in the cross-cut test. Δ: Slight ink peeling is observed in the cross-cut test, but almost no peeling is observed unless the ink surface is scratched. It is easy to peel off with cello tape (registered trademark).

  Table 8 summarizes the evaluation results obtained as described above.

  As is apparent from Table 8, by using the actinic ray curable composition having the constitution according to the present invention, the character quality is improved with respect to various recording materials in various printing environments as compared with the comparative example. High-definition images can be recorded that are excellent and have no color mixing (bleeding, wrinkles).

It is a front view which shows an example of a structure of the principal part of the inkjet recording device of this invention. It is a top view which shows another example of a structure of the principal part of the inkjet recording device of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet recording device 2 Head carriage 3 Inkjet recording head 31 Ink ejection port 4 Irradiation means 5 Platen part 6 Guide member 7 Bellows structure P Recording material

Claims (7)

An actinic ray curable composition comprising a radical polymerizable monomer, a radical polymerization initiator, and an oxetane ring-containing compound. 2. The actinic ray curable composition according to claim 1, wherein the content of the oxetane ring-containing compound is 1 to 20% by mass of the total amount of the actinic ray curable composition. The actinic ray curable composition according to claim 1 or 2, comprising at least one basic compound. The actinic ray curable composition according to any one of claims 1 to 3, wherein the viscosity at 25 ° C is 7 to 50 mPa · s. The actinic ray curable ink according to any one of claims 1 to 4, wherein the actinic ray curable composition contains a pigment. 6. An image forming method for printing by ejecting the actinic ray curable ink according to claim 5 onto a recording material from an ink jet recording head, wherein the recording material is a polyvinyl chloride film. The inkjet recording apparatus used in the image forming method according to claim 6, wherein the actinic ray curable ink and the recording head are heated to 35 to 100 ° C. and then discharged.

Images