JP2003251796A - Imaging method and final printed matter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink jet imaging method and a final printed matter in which a high resolution image can be reproduced stably on any recording material. <P>SOLUTION: In the imaging method and the final printed matter where an active light beam curing ink is ejected from a plurality of recording heads each having a plurality of nozzles capable of selective control of ink drop ejection, an inert gas substitutes for the curing atmosphere after the ink is shot. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method and final printed matter by an inkjet recording method capable of stably reproducing a high-definition image on any recording material.

[0002]

2. Description of the Related Art In recent years, the inkjet recording method has been simple and easy.
Since it is possible to create images at low cost, it has been applied to various printing fields such as photography, various printing, marking, and special printing such as color filters. Emit particularly fine dots
Using a recording device to control, ink with improved color reproduction range, durability and emission suitability, and special paper with dramatically improved ink absorbency, color material coloring, surface gloss, etc. It is also possible to obtain comparable image quality. The improvement in image quality of today's inkjet recording system is achieved only when all the recording devices, inks, and special papers are prepared.

However, the ink jet system that requires special paper has problems that the recording medium is limited and the cost of the recording medium is increased. Therefore, many attempts have been made to record on a transfer medium different from dedicated paper by an inkjet method. Specifically, there are a phase change inkjet method using a solid wax ink at room temperature, a solvent inkjet method using an ink mainly composed of a quick-drying organic solvent, and a UV inkjet method of crosslinking by UV light after recording. .

Among them, the UV ink jet system has been attracting attention in recent years because it has a relatively low odor as compared with the solvent type ink jet system, and can perform recording on a recording medium having a fast drying property and no ink absorbing property. Japanese Examined Patent Publication No. 5-54667,
JP-A-6-200204, Special Table 2000-50477
No. 8 discloses a UV-curable inkjet ink.

However, even when these inks are used, the dot diameter after landing changes greatly depending on the type of recording material and the working environment, and a high-definition image can be formed on all recording materials. Was impossible. Moreover, there is a problem that the discharge is not stable depending on the working environment.

Particularly in thin film plastic films used in soft packaging such as food packaging and adhesive labels, the dot diameter is completely changed due to a great change in the wettability of the ink, which makes it impossible to form a high-definition image. It was possible.

Due to the above-mentioned problems, the UV ink jet system has not been put to practical use in soft packaging printing or label printing.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming method by ink jet recording and a final printed matter which can stably reproduce a high-definition image on any recording material.

[0009]

The above objects of the present invention have been achieved by the following constitutions.

1. In an image forming method of ejecting ink that is cured by an actinic ray by a plurality of recording heads having a plurality of nozzles that can selectively control ejection of ink droplets, the curing atmosphere after ink landing is replaced with an inert gas. Image forming method.

2. 2. The image forming method as described in 1 above, wherein the oxygen concentration in the curing atmosphere after the ink has landed is controlled to be 0.1% to 10% by replacement with an inert gas.

3. 3. The image forming method as described in 1 or 2 above, wherein a recording device having a recording head of at least four colors is used.

4. The final printed material, wherein the recording material used in the image forming method according to any one of 1 to 3 is a non-absorbent material.

5. The final printed material, wherein the recording material used in the image forming method described in any one of 1 to 3 above is a shrink film.

6. The final printed material, wherein the recording material used in the image forming method described in any one of 1 to 3 above is an adhesive label.

The present invention will be described in more detail. The inkjet recording ink used in the present invention comprises at least a polymerizable monomer and an initiator.

<Image formation> In the image forming method of the present invention, the ink composition is ejected onto a recording material by an ink jet recording method to draw an image, and then the ink is cured by irradiating with actinic rays such as ultraviolet rays.

In the present invention, the ink composition is ejected from a plurality of recording heads having a plurality of nozzles.

In terms of ejection stability, it is preferable to heat the head and the ink to lower the ink viscosity and eject the ink. Since the actinic radiation curable ink generally has a higher viscosity than the water-based ink, the fluctuation range of viscosity due to temperature fluctuation is large. Viscosity fluctuations directly affect the droplet size and droplet ejection speed, causing image quality deterioration.
It is necessary to keep the ink temperature as constant as possible.

The basic method of irradiating actinic rays is disclosed in Japanese Patent Laid-Open No.
No. 0-132767. according to this,
Light sources are provided on both sides of the head unit, and the head and light sources are scanned by the shuttle system. Irradiation is performed after a certain time has elapsed after the ink has landed. Further, curing is completed by another light source that is not driven. US Patent No. 6,14
No. 5,979 discloses an irradiation method using an optical fiber or a method in which a collimated light source is applied to a mirror surface provided on the side surface of the head unit to irradiate the recording section with UV light. In the image forming method of the present invention,
Any of these irradiation methods can be used.

In the image forming method of the present invention, the curing atmosphere after the ink has landed is replaced with an inert gas. The inert gas may be any gas that is inert to the ink that is cured by irradiation with light, and examples thereof include nitrogen, carbon dioxide gas, and argon gas. Preferably, the oxygen concentration in the curing atmosphere after ink landing is controlled to 0.1% to 10%. Japanese Patent Laid-Open No. 2-310025 discloses a three-dimensional molding apparatus using an inkjet recording under an inert atmosphere.
The purpose is different from the present invention.

In the present invention, the curing atmosphere after the ink has landed refers to the atmosphere in the space of at least 10 cm ³ centering on the spot where the ink has landed, but more preferably the atmosphere in the space of the entire image forming apparatus. Say. Therefore, the replacement of the curing atmosphere after the ink has landed with an inert gas means that the space is replaced with an inert gas after the ink has landed, during the ink curing means, that is, during irradiation with actinic rays.

The present inventor has found that a high-definition image can be stably recorded on any recording material by suppressing the oxygen concentration in the curing atmosphere and forming an image by ejecting using a plurality of recording heads. By suppressing and controlling the oxygen concentration in the curing atmosphere, the diameter of the ink dots ejected from the nozzles of each recording head and formed on the recording material can be kept constant regardless of the type of recording material. This effect is particularly remarkable when the recording material is non-absorbent. Further, when an image is formed by using recording heads of four colors or more, color blur is significantly suppressed. Further, in the present invention, it was also found that the ejection of ink is very stable by suppressing the oxygen concentration.

The oxygen concentration in the curing atmosphere is 0.1% to 10%.
Examples of the means for controlling the temperature include, but are not limited to, a method in which the image forming apparatus is closed and the atmosphere is nitrogen. As a nitrogen supply means, for example, there is a method of using a nitrogen cylinder or a device of separating only nitrogen gas from the air by utilizing the difference in permeability between oxygen and nitrogen with respect to the hollow fiber membrane.

In the present invention, the types of light sources used for irradiation include ultraviolet rays such as UV-A, UV-B and UV-C,
In addition to vacuum ultraviolet rays and visible light, γ rays, β rays and the like can be used. Examples of light sources include high pressure mercury lamps, metal halide lamps, electrodeless lamps, low pressure mercury lamps, and UV.
There are lasers, xenon flash lamps, insect traps, black lights, germicidal lamps, cold cathode tubes, LEDs and the like, but not limited to these.

According to the present invention, even for various recording materials having different surface wettability, water absorbency, and thickness, the dot diameter of the deposited ink can be kept constant and a high-definition image can be stably formed. Therefore, it is preferable to change the irradiation and curing conditions depending on the type of recording material.

<Ink> As the polymerizable monomer that can be used in the ink of the present invention, various (meth) acrylate monomers can be used. For example, isoamyl acrylate, stearyl acrylate, lauryl acrylate, octyl acrylate, decyl acrylate, isomyrstil acrylate, isostearyl acrylate, 2-ethylhexyl-diglycol acrylate,
2-hydroxybutyl acrylate, 2-acryloyloxyethyl hexahydrophthalic acid, butoxyethyl acrylate, ethoxydiethylene glycol acrylate, methoxydiethylene glycol acrylate, methoxypolyethylene glycol acrylate, methoxypropylene glycol acrylate, phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, isobor Nyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-
Acryloyloxyethyl succinic acid, 2-acryloyloxyethyl phthalic acid, 2-acryloyloxyethyl-2-
Hydroxyethyl-phthalic acid, lactone-modified flexible acrylate, monofunctional monomers such as t-butylcyclohexyl acrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, tripropylene glycol diacrylate, polypropylene glycol di Acrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9
Nonanediol diacrylate, neopentyl glycol diacrylate, dimethylol-tricyclodecane diacrylate, EO adduct diacrylate of bisphenol A, PO adduct diacrylate of bisphenol A, neopentyl glycol diacrylate hydroxypivalate, polytetramethylene Bifunctional monomers such as glycol diacrylate, trimethylolpropane triacrylate, EO-modified trimethylolpropane triacrylate, pentaerythritol triacrylate,
Pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, ditrimethylolpropane tetraacrylate, glycerin propoxytriacrylate, caprolactone modified trimethylolpropane triacrylate, pentaerythritol ethoxytetraacrylate, caprolactam modified dipentaerythritol hexaacrylate, etc. Functional monomers may be mentioned.

In addition, polymerizable oligomers can be blended in the same manner as the monomers. As the polymerizable oligomer,
Epoxy acrylate, aliphatic urethane acrylate,
Aromatic urethane acrylates, polyester acrylates, linear acrylic oligomers and the like can be mentioned.

In the present invention, it is particularly preferable to use a monofunctional, difunctional, trifunctional or higher polyfunctional monomer in combination as the polymerizable monomer. The monofunctional monomer has a large effect of reducing the shrinkage rate at the time of curing, has a low viscosity, and can easily obtain the ejection stability at the time of inkjet recording. The bifunctional monomer is preferably added because it has an appropriate sensitivity and excellent adhesion to various recording materials. A trifunctional or higher polyfunctional monomer provides sensitivity and film strength after curing. By using these three in combination, curling and waviness due to curing shrinkage can be prevented, adhesion and followability to a substrate, and high sensitivity and high image quality can be achieved. In particular, it is very effective in the case of a shrink film that shrinks the substrate itself after printing.

The monofunctional monomer is 5 to 5 parts of the total ink composition.
It is preferable to contain 40% by mass, 5 to 40% by mass of the bifunctional monomer, and 5 to 30% by mass of the polyfunctional monomer having three or more functional groups. As for the monomers to be used in combination, a combination in which the difference between the maximum value and the minimum value of the solubility parameter (SP value) is 1 or more is preferable in terms of adhesion to various substrates and curling due to curing shrinkage. . More preferably, it is 1.5 or more.

From the viewpoint of safety to workers or environment such as sensitization, skin irritation, eye irritation, mutagenicity and toxicity, among the above monomers, isoamyl acrylate, stearyl acrylate, lauryl acrylate, Octyl acrylate, decyl acrylate, isomystil acrylate, isostearyl acrylate, ethoxydiethylene glycol acrylate, methoxy polyethylene glycol acrylate, methoxypropylene glycol acrylate, isobornyl acrylate, lactone modified flexible acrylate, tetraethylene glycol diacrylate, polyethylene glycol di Acrylate, polypropylene glycol diacrylate, EO-modified trimethylolpropane triacrylate, dipenta Risuri hexaacrylate,
Ditrimethylolpropane tetraacrylate, glycerin propoxytriacrylate, caprolactone-modified trimethylolpropane triacrylate, pentaerythritol ethoxytetraacrylate, and caprolactam-modified dipentaerythritol hexaacrylate are preferable.

Further, among these, stearyl acrylate, lauryl acrylate, isostearyl acrylate, ethoxydiethylene glycol acrylate, isobornyl acrylate, tetraethylene glycol diacrylate, EO-modified trimethylolpropane triacrylate, glycerin propoxytriacrylate, caprolactone-modified trimethylolpropane. Particularly preferred are triacrylate and caprolactam-modified dipentaerythritol hexaacrylate.

As the photoinitiator, conventionally known initiators such as aryl alkyl ketone, oxime ketone, S-phenyl thiobenzoate, titanocene, aromatic ketone, thioxanthone, benzyl and quinone derivatives and ketocoumarins can be used. For more information on initiators, see "Applications and Markets of UV / EB Curing Technology" (CMC Publishing, edited by Yoneho Tabata / edited by Radtech Study Group). Among them, acyl phosphine oxide and acyl phosphonate have high sensitivity and their absorption is reduced by photocleavage of the initiator, so that they are suitable for internal curing in an ink image having a thickness of 5 to 12 μm per color as in an inkjet method. Especially effective. In particular,
Bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide and bis (2,6-dimethoxybenzoyl) -2,4,4-trimethyl-pentylphosphine oxide are preferable.

Further, like the above-mentioned monomers, 1-hydroxy-cyclohexyl-phenyl-ketone and 2-methyl-methyl ether are selected in consideration of safety to workers or the environment.
1 [4- (methylthio) phenyl] -2-morpholinopropan-1-one, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethyl-pentylphosphine oxide, 2-hydroxy-2- Methyl-1-phenyl-propan-1-one (Darocur (R) 117
3) is preferably used. The preferable addition amount is 1 to 6% by mass, and preferably 2 to 5% by mass of the whole ink composition. In the present invention, it is preferable to divide the irradiation into two stages by changing the wavelength or the intensity from the viewpoint of improving the adhesiveness / following property of the ink film to the substrate, and the initiator is also a combination of two or more kinds having different absorption wavelengths. Is particularly preferable.

In addition, when coloring the ink composition,
Add colorant. As the coloring material, a coloring material that can be dissolved or dispersed in the main component of the polymerizable compound can be used, but a pigment is preferable from the viewpoint of weather resistance. As the pigment, C.I. I Pigment Yellow-1,3,1
2, 13, 14, 17, 81, 83, 87, 95, 10
9, 42, C.I. I Pigment Orange-16, 36,
38, C.I. I Pigment Red-5, 22, 38, 4
8: 1, 48: 2, 48: 4, 49: 1, 53: 1, 5
7: 1, 63: 1, 144, 146, 185, 101, C.I. I Pigment Violet-19, 23, C.I. I Pigment Blue-15: 1, 15:
3,15: 4,18,60,27,29, C.I. I Pigment Green-7, 36, C.I. I Pigment White-6, 18, 2
1, C.I. I Pigment Black-7 can be used, but is not limited thereto.

A ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, a paint shaker or the like can be used to disperse the pigment. It is also possible to add a dispersant when dispersing the pigment. A polymer dispersant is preferably used as the dispersant, but Avec is used as the polymer dispersant.
The Solsperse series of ia company is mentioned. It is also possible to use synergists corresponding to various pigments as the 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 a solvent or a polymerizable compound, but the radiation-curable ink used in the present invention is preferably solvent-free because it reacts and cures immediately after the ink hits. If the solvent remains in the cured image, problems of solvent resistance deterioration and residual solvent VOC occur. Therefore, it is preferable in view of dispersion suitability that the dispersion medium is selected from a polymerizable compound, not a solvent, and a monomer having the lowest viscosity among them.

The dispersion has an average particle size of 0.08 to 0.5 μm.
And the maximum particle size is 0.3 to 10 μm,
A pigment, a dispersant, so that the thickness is preferably 0.3 to 3 μm,
Set the dispersion medium selection, dispersion conditions, and filtration conditions. By controlling the particle size, clogging of the head nozzle can be suppressed, and the storage stability of the ink, the transparency of the ink, and the curing sensitivity can be maintained. Color material is 1% by mass to 1% of the total ink
An addition amount of 0 mass% is preferable.

<< Other Components >> In order to enhance the storage stability of the ink composition, a polymerization inhibitor is added in an amount of 200 to 20000 ppm.
It can be added. UV curable ink is heated,
Since it is preferable to lower the viscosity and then to inject, it is preferable to add a polymerization inhibitor in order to prevent head clogging due to thermal polymerization.

In addition to these, a surfactant, a leveling additive, a matting agent, a polyester resin for adjusting the physical properties of the film, a polyurethane resin, a vinyl resin, if necessary,
Acrylic resins, rubber resins, and waxes can be added. In order to improve the adhesion to the recording medium, it is also effective to add an extremely small amount of organic solvent. in this case,
Addition is effective within a range that does not cause problems of solvent resistance and VOC, and its amount is 0.1 to 5%, preferably 0.1 to 5%.
3%.

Further, due to the light shielding effect of the ink coloring material,
As a means for preventing sensitivity, it is possible to combine a cationically polymerizable monomer having a long initiator life with an initiator to prepare a radical / cation hybrid type curable ink.

As the recording material, in addition to ordinary non-coated paper, coated paper and the like, various non-absorbent materials used for so-called soft packaging can be used. Examples include PET film, OPS film, OPP film, ONy film, PVC film, PE film, TAC film. Other plastics include polycarbonate, acrylic resin, ABS, polyacetal, P
VA, rubber, etc. can be used. Further, it is also applicable to metals and glasses.

Among these recording materials, especially PET film, OPS film, OP which can be shrunk by heat
The configuration of the present invention is effective when forming an image on a P film, an ONy film, or a PVC film. With these recording materials, a shrinking step is performed after the image formation to form the final printed matter, so it is necessary to stably form a high-definition image in which the dot diameter and color bleeding are more controlled. Also,
The present invention is also particularly effective in the case of forming an image on an adhesive label whose surface is coated with various kinds of materials as described above.

[0043]

Examples Example 1 << Ink Composition >> Ink compositions of the present invention shown in Table 1 were prepared. In Table 1, the added compounds are as follows. Photopolymerizable compound 1: Lauryl acrylate (monofunctional) Photopolymerizable compound 2: Bisphenol A glycidyl ether methacrylic acid adduct (bifunctional) Photopolymerizable compound 3: Tetraethylene glycol diacrylate (bifunctional) Photopolymerizable compound 4 : Trimethylolpropane triacrylate (trifunctional) Photopolymerizable compound 5: Caprolactam-modified dipentaerythritol hexaacrylate (hexafunctional) Initiator 1: Irgacure 651 Ciba Specialty
Chemicals Initiator 2: Irgacure 369 Ciba Specialty
Chemicals Initiator Aid 1: Diethylthioxanthone

[0044]

[Table 1]

The ink viscosity shown in Table 1 was 34 mPa · s as measured by melt viscosity at 25 ° C. using a rotational viscometer (EDL model manufactured by Tokimec).

<Inkjet recording> Recording was performed on nine kinds of recording materials having a width of 600 mm shown in Tables 2 and 3 by an inkjet recording apparatus using a piezo type inkjet nozzle. The ink supply system was composed of an ink tank, a supply pipe, an anterior chamber ink tank immediately before the head, a pipe with a filter, and a piezo head. The anterior chamber tank and the head were thermally insulated and heated to 38 ° C. The piezo head uses 8 to 30 pl multi-size dots for 720 x 7
It was driven and ejected so that it could be ejected at a resolution of 20 dpi (dpi is 1 inch, that is, the number of dots per 2.54 cm). The irradiation conditions after landing were as shown in Tables 2 and 3.

Further, the entire recording apparatus is hermetically sealed, and a nitrogen generator using a nitrogen gas cylinder or a hollow fiber membrane or a PSA (Pressure Swing Addo) using activated carbon is used.
nitrogen gas was injected into the system by the rption method, and the oxygen concentration in the system was controlled as shown in Tables 2 and 3. As a comparison, evaluation was also made when nitrogen gas was not injected.

<< Evaluation Items >> [Character Quality] 8-point characters were printed at the target K density, and the character was rugged and the shape of 1 dot for each color was magnified and evaluated with a magnifying glass. ◎: No shading, dot shape is a perfect circle ○: Slight shading is visible. The dot shape is a perfect circle Δ: Roughness is visible and the dot shape is slightly disturbed (a level that can be used at the last minute) × ... Roughness is visible and the dot shape is also poor.

[Color mixing (bleeding)] An image pattern in which 8-point characters were arranged on a solid image having a target density of M and 1 dot for each color were output, and the quality after 10 minutes was magnified with a loupe and visually evaluated. ◎: No shading, dot shape is a perfect circle ○: Slight shading is visible. The dot shape is a perfect circle Δ: Roughness is visible and the dot shape is slightly disturbed (a level that can be used at the last minute) × ... Roughness is visible and the dot shape is also poor.

[0050]

[Table 2]

[0051]

[Table 3]

As is clear from Tables 2 and 3, the image forming method of the present invention can stably reproduce a high-definition image on any recording material.

[0053]

According to the present invention, it is possible to provide an image forming method by inkjet recording and a final printed matter which can stably reproduce a high-definition image on any recording material.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09F 3/10 B41J 3/04 101Z

Claims (6)

[Claims] 1. An image forming method for ejecting ink that is cured by an actinic ray by a plurality of recording heads having a plurality of nozzles capable of selectively controlling ejection of ink droplets, wherein a curing atmosphere after the ink is landed is an inert gas. An image forming method characterized by replacement. 2. The image forming method according to claim 1, wherein the oxygen concentration in the curing atmosphere after the ink has landed is controlled to be 0.1% to 10% by replacement with an inert gas. 3. The image forming method according to claim 1, wherein a recording device having a recording head of at least four colors is used. 4. The final printed material, wherein the recording material used in the image forming method according to claim 1 is a non-absorbent material. 5. The final printed material, wherein the recording material used in the image forming method according to claim 1 is a shrink film. 6. The final printed material, wherein the recording material used in the image forming method according to claim 1 is an adhesive label.