JP2012200905A - Image forming method and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method and an image forming device, for forming a uniform solid image with a small quantity of ink, on a recording medium made of polyolefin resin or the like with low wetting tension.SOLUTION: (1) The image forming method includes: a step of forming an image by jetting ink containing active energy-ray curable material and color material, on a surface of the recording medium by an inkjet recording method; a step of performing discharge treatment; and a step of curing the ink by irradiation with active energy rays, the steps being performed in this order. (2) The image forming device includes: a jetting means for jetting the ink containing the active energy-ray curable material or color material on the recording medium, by the inkjet recording method; a discharge treatment means performing the discharge treatment; and a curing means curing the ink by irradiation with active energy rays.

Description

  The present invention relates to an image forming method and an image forming apparatus using an ink jet recording system.

The ink jet recording technique is a technique that uses a pressure on-demand system, a charge control system, or the like to form ink droplets through minute nozzles and attach them to a recording medium such as paper according to image information. This recording technique is suitably used for image forming apparatuses such as printers, facsimiles, and copying machines. In addition, since this recording technology can form an image by directly depositing ink on a recording medium, recording can be performed with a simple apparatus configuration compared to indirect recording using a photoconductor such as electrophotographic recording. Further development is expected as an image recording method.
The recording method using the ink jet recording technology is a low noise printing method, and according to the image signal, ink is directly ejected onto a printing material (recording medium) such as paper, cloth, and plastic sheet to print characters. A method of printing images and images (also called a direct discharge method) is the mainstream. In addition, it is a printing method that is also expected from industrial applications because it does not require a plate for printing and can efficiently produce printed matter with a small number of copies. However, for use in industrial applications, images must be formed on various recording media. However, the current mainstream direct discharge method has not obtained satisfactory results. That is, the ink jet recording by the direct discharge method is an image forming method in which the limit of the recording medium is large.

One specific limitation is the influence of ink permeability of the recording medium.
The ink used in the ink jet recording method is mostly a liquid component, and therefore the difference in the absorption and permeability of the recording medium with respect to the ink affects the image reproducibility. In particular, if a recording medium that does not penetrate liquid (non-ink penetrable) is used, ink droplets printed adjacent to each other are mixed (bleeding), and ink droplets that have landed first are attracted to ink droplets that have landed later. Image formation is very difficult because the phenomenon of beading (beading) is likely to occur, and furthermore, penetration drying cannot be used, and evaporation drying results in problems such as set-off when superimposed, especially high-speed recording. In this case, the drying property cannot be secured. On the other hand, for example, there is a method of printing on a non-permeable recording medium by using an ink containing an ultraviolet curable resin and irradiating and curing the ultraviolet ray after printing.

In the ultraviolet curable ink, the entire ink including the pigment is cured, so that an image can be formed even with a non-permeable recording medium. However, the way the ink spreads on the recording medium is affected by the wetting tension on the surface of the recording medium, and the ink does not spread sufficiently to polyolefin materials such as polyethylene and polypropylene which have low wetting tension. An image density equivalent to that of a high material cannot be obtained unless a large amount of ink is used. In addition, in a solid portion where adjacent ink droplets need to be combined, there is a problem that when the ink droplets are combined, the ink droplets move due to a slight difference in surface condition of the material, and unevenness is likely to occur.
Usually, for such a material having a low wetting tension, surface treatment is generally performed on the surface of the recording medium in order to improve the wettability of the ink. Such a processing apparatus is incorporated in the inside. However, even if the recording medium has been processed, the polyolefin-based material has a poor ink spread compared to, for example, PET (polyethylene terephthalate), and requires a large amount of ink.

  An object of the present invention is to provide an image forming method and an image forming apparatus capable of forming a uniform solid image with a small amount of ink even on a recording medium made of a polyolefin resin having a low wetting tension.

The above problems are solved by the following inventions 1) to 8).
1) A step of forming an image by ejecting ink containing an active energy ray-curable material and a color material on the surface of a recording medium by an inkjet recording method, a step of performing a discharge treatment, and irradiating and curing an active energy ray An image forming method comprising: steps, and performing each step in this order.
2) The image forming method according to 1), wherein the discharge treatment is a corona discharge treatment.
3) The image forming method according to 1) or 2), wherein the recording medium is a film made of a polyolefin resin.
4) The image forming method according to any one of 1) to 3), wherein discharge treatment is also performed before the step of forming the image.
5) A discharge means for discharging an ink containing an active energy ray-curable material and a coloring material to the recording medium by an ink jet recording method, a discharge treatment means for performing a discharge process, and a curing means for irradiating and curing the active energy ray. And an image forming apparatus configured to perform discharge treatment and curing after ink ejection.
6) The image forming apparatus according to 5), wherein the ejection unit is a line-type inkjet head fixedly installed in a direction perpendicular to the conveyance direction of the recording medium.
7) The image forming apparatus according to 5) or 6), wherein the discharge processing unit is set so that the discharge process can be performed before the ink is discharged.

  The present invention can provide an image forming method and an image forming apparatus capable of forming a uniform solid image with a small amount of ink even on a recording medium made of a polyolefin resin having a low wetting tension.

FIG. 4 is a diagram for explaining an image forming operation according to the present invention. FIG. 3 is a diagram illustrating a state of ink droplets ejected on a recording medium surface made of a material having a low wetting tension. The figure which shows the state which discharged the ink droplet further between the ink droplets. The figure which shows the relationship of the pigment density | concentration of ink, ink layer thickness, and optical density. 1 is a diagram illustrating an example of an image forming apparatus of the present invention. The figure which shows an example of the apparatus which performs a corona discharge process before ink discharge. The figure which shows an example of the apparatus which performed the process before and after ink discharge with one corona discharge processing apparatus.

Hereinafter, the present invention will be described in detail.
The present invention uses an ink containing an active energy ray-curable material and a coloring material, discharges the ink by an ink jet recording method, forms an image, performs discharge treatment, and then irradiates active energy rays. To be cured.
FIG. 1 is a diagram for explaining an image forming operation according to the present invention, and shows an example of the present invention. First, the recording medium is conveyed from the paper feeding unit to the ink ejection unit, and then ink droplets are ejected from the ink ejection head according to the image pattern. Next, ink droplets spread on the recording medium by the treatment by the corona discharge treatment device, and in this state, are cured by the ultraviolet rays emitted from the ultraviolet irradiation device (high pressure mercury lamp). Therefore, even on a recording medium having a low surface wetting tension and difficult to spread ink, it can be cured with ink droplets wet and spread, so that an image can be efficiently formed with a small amount of ink.
As shown in FIG. 2, the ink droplets ejected on the surface of the recording medium made of a material having a low wetting tension are in a raised state without being wetted and spread on the recording medium. In this state, since the ink droplets do not spread over time, in order to fill the gaps between the ink droplets, it is necessary to further eject ink droplets between the ink droplets as shown in FIG. On the other hand, in the present invention, the ink droplets wet and spread by performing the discharge treatment (see FIG. 2), so that the gap between the ink droplets can be filled, and an image can be efficiently formed with a small amount of ink.

The reason why the ink droplet spreads by performing the discharge process on the recording medium on which the ink droplet is ejected is that high-energy electrons or ions released by the discharge collide with the ink droplet and spread it, Electrons and ions that collide with the surface of the recording medium generate radicals and ions that react with the surrounding ozone, oxygen, nitrogen, moisture, and other polar functions such as carbonyl, carboxyl, hydroxyl, and cyano groups. It is conceivable that the group is introduced to the surface of the recording medium and the wettability is improved.
If the resistance value of the material constituting the ink is low, the discharge concentrates on the ink droplets and uniform processing is difficult. Therefore, it is desirable that the component constituting the ink is an electrically insulating material or a high resistance material. . Water-based inks are low in resistance because water is the main component, and are not suitable for the image forming method of the present invention. However, the monomer used in the active energy ray-curable ink has high electric resistance, so that the image formation of the present invention is performed. Suitable for the method.
The time for performing the discharge treatment cannot be simply specified because it varies depending on the output of the apparatus. However, in the case of the corona treatment apparatus used in the examples described later, 0.01 to 1.0 sec is preferable, and 0.15 -0.2 sec is more preferable. Excessive processing may cause physical damage to the film surface, resulting in cloudiness. If the processing is insufficient, the effect will be insufficient. What is necessary is just to determine suitably.

Discharge treatment methods often used for surface modification of plastic films and the like include corona discharge treatment and plasma discharge treatment, both of which modify the surface by collision of high-energy electrons and ions due to discharge. However, compared with plasma discharge, corona discharge has a feature that can be carried out at a low cost, and is often used in pre-processing of printing.
Also in the present invention, it is preferable in terms of cost to employ corona discharge. In the corona discharge treatment apparatus, a treatment film is passed between an insulated electrode and a dielectric roll, and a high frequency (about 40 kHz) high voltage is applied to generate a corona discharge. Corona discharge causes a gas component such as oxygen to become an active plasma state, and accelerated electrons in the corona discharge collide with the resin surface forming the recording medium, causing molecular chain scission and addition of oxygen-containing functional groups on the resin surface. At this time, ozone is generated by corona discharge, and oxidization causes rust and odor of the metal parts. Therefore, an ozone removing filter composed of a suction device and activated carbon is required for the discharge part.
The corona discharge treatment apparatus used in the present invention is not particularly limited in form and output as long as it is discharged by corona discharge. Further, a plasma discharge treatment apparatus may be used instead of the corona discharge treatment apparatus. In order to cause plasma discharge, there are a type that is performed at high pressure and a low pressure under atmospheric pressure, and either type may be used.

A film made of a polyolefin resin has a very low wetting tension of about 20 mN / m. Since the printability is low as it is, there are also films subjected to corona discharge treatment, for example, commercially available as treated polypropylene films. A specific example is Toyobo Co., Ltd .: Pyrene Film-OT (P2161), which has a wetting tension of about 40 mN / m, which is at a level that is not problematic for printing. However, since the effect of the commercially available film decreases with time, it is preferable to perform a corona discharge treatment immediately before printing.
On the other hand, in the image forming method using the ink jet recording method, for example, when forming a solid portion, the ejected ink droplets wet and spread on the surface of the recording medium, so that adjacent ink droplets are combined (the space between the ink droplets is filled). )There is a need. However, in the case of the ink jet recording method, even if a corona discharge-treated polypropylene film is used, ink droplets do not spread, so that solid portions can be formed unless high-density ink ejection is performed until the ink droplets are combined. Can not. For this reason, in a recording medium having a low wetting tension such as a polypropylene film, it is necessary to eject more ink than necessary when forming a solid portion, which is not only disadvantageous in terms of cost, but also the surface shape after curing. Because of the large irregularities, only images with low gloss were obtained. In the case of a resin film such as PET (polyethylene terephthalate), if corona discharge treatment is performed, the ink droplets are sufficiently wet and spread, and a solid portion can be formed with a necessary amount of ink.
In the present invention, since the ink droplets can be spread by a discharge process even on a recording medium having a low wetting tension such as a polypropylene film, a solid portion can be formed with an amount of ink equivalent to that of PET, etc. Can also be a glossy surface with less irregularities.

In the active energy ray-curable ink, the monomer itself, which is a vehicle component of the ink, is cured by active energy rays such as ultraviolet rays, so that an image can be formed on a resin film having no absorption layer. However, compared with water-based ink, for example, a curable monomer or oligomer is used instead of water, and therefore, it becomes expensive. Therefore, the supply cost can be reduced by increasing the concentration of the pigment, which is a color material, so that an image having the same density can be obtained with a small amount of ink. The pigment concentration also has restrictions such as dispersibility, curability, and low viscosity, and there is a limit to increasing the concentration as an inkjet ink, but a major problem is that when an image is formed on a resin film, it is ejected. Whether or not the ink droplets can be spread thinly to form an image.
For example, in the case of black ink, if a sufficient density is obtained with an ink layer thickness of about 5 to 7 μm, a necessary optical density can be obtained with a pigment density of about 2 to 3% by mass. However, when the ink layer thickness is about 2 to 3 μm, the concentration needs to be 5% by mass or more. In this case, it is necessary to form a uniform solid image with an ink hitting amount corresponding to 2 to 3 μm by the ink jet recording method.

For example, when an ink droplet of 5 pL is ejected to form an image with a head having a resolution of 600 dpi, the average ink layer thickness is about 2.8 μm. For this purpose, an ink droplet of 5 pL is a dot of about 60 to 70 μm. The ink dot needs to have a diameter. However, since the film made of polyolefin resin does not spread so much, a solid portion cannot be formed with an ink layer thickness of about 2 to 3 μm. Therefore, it is necessary to increase the ink droplet ejection amount so as to fill the space between the dots. However, the effect is limited even when a high-concentration ink having a pigment concentration of 5% by mass or more is used, and an unnecessarily thick layer thickness is required for forming a solid part. Therefore, a low-concentration ink was used. It will not be different from the thing.
On the other hand, in the present invention, since a uniform solid portion can be formed with a small amount of ink applied, high-density ink can be used efficiently. Accordingly, the use of high-density ink can reduce the amount of ink monomer used when obtaining an image having an optical density equivalent to that of low-density ink, thereby reducing supply costs.

FIG. 4 is a graph showing the relationship between the ink pigment density, ink layer thickness, and optical density.
When the target value of optical density (OD) is 1.7, the target can be achieved with 5% by mass of ink if the ink layer thickness required to form a uniform solid portion is about 3.5 μm or less. If an ink layer thickness of about 6 μm is required, 5% by mass of ink is unnecessary, and about 3% by mass is sufficient. Conversely, in order to efficiently use an ink having a high pigment concentration of 5% by mass or more, the ink layer may be formed with an ink amount that provides an ink layer thickness that provides a required optical density.
In the present invention, since it is possible to form a uniform image with such a thin layer, it is possible to efficiently use ink with a high pigment concentration, and it is possible to reduce the ink cost.

FIG. 5 is a diagram showing an example of the image forming apparatus of the present invention, and a continuous sheet is used as a recording medium. The sheet is transported by winding the sheet from the sheet feeding unit side toward the sheet discharging unit side, and after the ink is ejected by the ink ejection unit to form an image, the corona discharge processing device, which is an ink droplet expansion unit, is used. Corona discharge is performed to spread the ink droplets to a necessary extent, and then the ink is cured by irradiating ultraviolet rays with an ultraviolet irradiation device (high pressure mercury lamp) as a curing means to form an image.
The corona discharge treatment need not be performed in the case of a recording medium in which ink droplets are sufficiently spread to spread, and it is preferable to select whether or not the treatment is performed depending on the material of the recording medium and the state of wet tension of the surface. Further, the conveyance speed and the intensity (voltage) of corona discharge may be adjusted so that the adjustment can be made according to the state of the surface of each recording medium.
It is also possible to form a full-color image by arranging a plurality of ink ejection means in the recording medium conveyance direction and sequentially ejecting yellow, cyan, magenta, and black inks.

There are two types of inkjet recording head arrangement: a serial type that discharges while moving in a direction perpendicular to the recording medium conveyance direction, and a line type that is fixedly installed and discharges ink simultaneously in the width direction of the recording medium. There is. In the serial type, since the image is formed while moving the head in the width direction of the recording medium in a state where the conveyance of the recording medium is stopped, the print density of ejection can be varied in both the conveyance direction and the width direction. There is a degree. Therefore, in order to correct the difference in the wetting tension of the resin film with respect to the ink, it is possible to set the minimum required amount of ink applied for each recording medium by changing the print density in the vertical and horizontal directions of the image and forming the printed portion. is there.
On the other hand, with a line-type head, the print density in the transport direction can be adjusted, but the print density in the width direction cannot be adjusted. When the wetting tension of the recording medium is corrected by adjusting the printing density only in one direction, the streaks become more noticeable especially for recording media with low wetting tension made of polyolefin resin. It is difficult to form with ink. However, according to the present invention, the difference in the ink droplet spread caused by the difference in the wetting tension of the recording medium can be corrected by the expansion means by the discharge process, so there is no need to change the ink density by changing the print density. Even with a line-type head, it is possible to form an image with no streaking.

In the present invention, ink droplets are wetted and spread by discharge treatment after ink discharge, but in the case of a film made of a polyolefin resin in particular, if the wetting tension is not increased appropriately before ink discharge, it will be expanded later. If the ink droplets cannot be sufficiently spread even if the discharge treatment is performed, or if the ink droplets are uneven in the initial state, the state will be expanded as it is, causing problems such as remaining unevenness. There is. Therefore, if necessary, the corona discharge treatment may be performed before ink discharge to prevent unevenness and insufficient spread.
FIG. 6 is a diagram illustrating an example of an apparatus that performs corona discharge treatment before ink discharge. The recording medium transported by the transport means is subjected to surface treatment by the corona discharge processing apparatus, and then the ink is discharged. Next, the apparatus performs processing by a corona discharge processing device which is an ink droplet expanding means, wets and spreads ink droplets to a necessary state, and finally cures by a curing device to form an image.
The apparatus shown in FIG. 6 has two corona discharge treatment apparatuses, but simplification of the apparatus can be achieved by performing both treatments with one corona discharge treatment apparatus. An example is shown in FIG. 7. For example, when a continuous sheet is used as a recording medium, as shown in FIG. 7A, the sheet is first set on the paper discharge side and the corona discharge process is performed. After the corona discharge process for the entire sheet is completed, the conveying means of the apparatus is switched, and ink is ejected by the ink ejecting means as shown in FIG. 7B. After that, the corona discharge treatment apparatus used for the pre-processing is used as the ink droplet expanding means, and then cured by the curing means to complete the image. Here, a color image can also be formed by arranging a plurality of ink discharge means.

The ink that is cured by absorbing active energy rays such as ultraviolet rays used in the present invention contains active energy ray-curable materials and coloring materials as main components, and usually also contains a photoinitiator. In addition, additives such as leveling agents, reaction accelerators, reaction inhibitors, and sensitizers may be included. The ultraviolet curable ink is roughly classified into a radical polymerizable ink containing a radical polymerizable compound and a cationic polymerizable ink containing a cationic polymerizable compound as a polymerizable compound which is an ultraviolet curable material. Are also applicable, and mixtures thereof may be used.
In the present invention, colored inks mainly containing black, cyan, magenta, yellow, etc. are used, but in addition to white, it is also possible to use light-colored inks that enrich tone expression. is there. Moreover, you may use the thing containing the clear ink or white pigment which does not contain a color material as a pre-processing agent.

Examples of the epoxy compound used in the cationic polymerization type ink include bisphenol A type epoxy compound, bisphenol BA type epoxy compound, bisphenol F type epoxy compound, bisphenol AD type epoxy compound, phenol novolac type epoxy compound, cresol novolac type epoxy compound, and alicyclic ring. Examples thereof include a formula epoxy compound, a fluorene epoxy compound, a naphthalene epoxy compound, a glycidyl ester compound, a glycidyl amine compound, a heterocyclic epoxy compound, and an α-olefin epoxy compound.
In particular, the alicyclic epoxy compound has a low viscosity and a high curing rate, and can be suitably used for a cationic polymerization type ink. Specific examples thereof include 3,4-epoxycyclohexenylmethyl-3 ′, 4′-epoxycyclohexenecarboxylate and its ε-caprolactone modification, bis- (3,4-epoxycyclohexylmethyl) adipate, 1,2: 8,9-diepoxy limonene, vinylcyclohexene monooxide, 1,2-epoxy-4-vinylcyclohexane.

The oxetane compound used in the cationic polymerization type ink may be appropriately selected according to the properties required for the ink. In particular, when adhesion to a substrate is important, 3-ethyl-3- (phenoxymethyl) ) Oxetane can be preferably used.
The cationic polymerization type ink can be mixed with a vinyl ether compound as necessary. Suitable vinyl ether compounds include, for example, 2-ethylhexyl vinyl ether, butanediol-1,4-divinyl ether, cyclohexanedimethanol monovinyl ether, diethylene glycol monovinyl ether, diethylene glycol divinyl ether, dipropylene glycol monovinyl ether, dipropylene glycol divinyl ether, methyl Vinyl ether, ethyl vinyl ether, propyl vinyl ether, isobutyl vinyl ether, dodecyl vinyl ether, octadecyl vinyl ether, hexanediol divinyl ether, hydroxyethyl vinyl ether, hydroxybutyl vinyl ether, triethylene glycol divinyl ether, vinyl-4-hydroxybutyl ether, vinyl cyclohexyl Ether, vinyl propionate, vinyl carbazole, vinyl pyrrolidone.

In the cationic polymerization type ink, propenyl ether and butenyl ether can be blended as a reactive component, if necessary. Examples thereof include 1-dodecyl-1-propenyl ether, 1-dodecyl-1-butenyl ether, 1-butenoxymethyl-2-norbornene, 1,4-di (1-butenoxy) butane, 1,10-di ( Examples include 1-butenoxy) decane, 1,4-di (1-butenoxymethyl) cyclohexane, diethylene glycol di (1-butenyl) ether, 1,2,3-tri (1-butenoxy) propane, propenyl ether propylene carbonate, and the like.
The cationic polymerization initiator applicable to the cationic polymerization type ink may be a compound that generates a substance that initiates polymerization by receiving energy rays such as ultraviolet rays, and is an onium salt such as arylsulfonium salt or aryliodonium. A salt can be suitably used. Furthermore, if necessary, photosensitizers such as anthracene compounds such as N-vinylcarbazole, thioxanthone compounds, and 9,10-dibutoxyanthracene can be used in combination.

As the component of the radical polymerization type ink, various known radical polymerizable monomers that cause a polymerization reaction with an initiation species generated from a radical polymerization initiator can be used.
Examples of the radical polymerizable monomer include (meth) acrylates, (meth) acrylamides, aromatic vinyl compounds, vinyl ethers, and compounds having an internal double bond (such as maleic acid).
Hereinafter, monofunctional and polyfunctional radically polymerizable compounds are exemplified.

  Specific examples of the monofunctional (meth) acrylate include hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, tert-octyl (meth) acrylate, isoamyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) ) Acrylate, stearyl (meth) acrylate, isostearyl (meth) acrylate, cyclohexyl (meth) acrylate, 4-n-butylcyclohexyl (meth) acrylate, bornyl (meth) acrylate, isobornyl (meth) acrylate, benzyl (meth) acrylate 2-ethylhexyl diglycol (meth) acrylate, butoxyethyl (meth) acrylate, 2-chloroethyl (meth) acrylate, 4-bromobutyl (meth) acrylate, cyano Chill (meth) acrylate, butoxymethyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, alkoxymethyl (meth) acrylate, alkoxyethyl (meth) acrylate, 2- (2-methoxyethoxy) ethyl (meth) acrylate, 2 -(2-butoxyethoxy) ethyl (meth) acrylate, 2,2,2-trifluoroethyl (meth) acrylate, 1H, 1H, 2H, 2H-perfluorodecyl (meth) acrylate, 4-butylphenyl (meth) Acrylate, phenyl (meth) acrylate, 2,3,4,5-tetramethylphenyl (meth) acrylate, 4-chlorophenyl (meth) acrylate, phenoxymethyl (meth) acrylate, phenoxyethyl (meth) acrylate, 2-phenoxy Chill (meth) acrylate, glycidyl (meth) acrylate, glycidyloxybutyl (meth) acrylate, glycidyloxyethyl (meth) acrylate, glycidyloxypropyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, hydroxyalkyl ( (Meth) acrylate, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, dimethyl Aminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, diethylaminopropyl (meth) acrylate, trimethoxy Sisilylpropyl (meth) acrylate, trimethylsilylpropyl (meth) acrylate, polyethylene oxide monomethyl ether (meth) acrylate, oligoethylene oxide monomethyl ether (meth) acrylate, polyethylene oxide (meth) acrylate, oligoethylene oxide (meth) acrylate, oligoethylene oxide mono Alkyl ether (meth) acrylate, polyethylene oxide monoalkyl ether (meth) acrylate, dipropylene glycol (meth) acrylate, polypropylene oxide monoalkyl ether (meth) acrylate, oligopropylene oxide monoalkyl ether (meth) acrylate, 2-methacryloyl Loxyethyl succinic acid, 2-methacryloyloxyhexahydrofur Phosphoric acid, 2-methacryloyloxyethyl-2-hydroxypropyl phthalate, butoxydiethylene glycol (meth) acrylate, trifluoroethyl (meth) acrylate, perfluorooctylethyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) ) Acrylate, ethylene oxide modified phenol (meth) acrylate, ethylene oxide modified cresol (meth) acrylate, ethylene oxide modified nonylphenol (meth) acrylate, propylene oxide modified nonylphenol (meth) acrylate, ethylene oxide modified-2-ethylhexyl (meth) acrylate, and the like. .

  Specific examples of monofunctional (meth) acrylamide include (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-propyl (meth) acrylamide, and Nn-butyl (meth). Acrylamide, Nt-butyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N-methylol (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N -Diethyl (meth) acrylamide, (meth) acryloylmorpholine, etc. are mentioned.

  Specific examples of monofunctional aromatic vinyl compounds include styrene, methyl styrene, dimethyl styrene, trimethyl styrene, ethyl styrene, isopropyl styrene, chloromethyl styrene, methoxy styrene, acetoxy styrene, chloro styrene, dichloro styrene, bromo styrene, Vinyl benzoic acid methyl ester, 3-methylstyrene, 4-methylstyrene, 3-ethylstyrene, 4-ethylstyrene, 3-propylstyrene, 4-propylstyrene, 3-butylstyrene, 4-butylstyrene, 3-hexylstyrene 4-hexylstyrene, 3-octylstyrene, 4-octylstyrene, 3- (2-ethylhexyl) styrene, 4- (2-ethylhexyl) styrene, allylstyrene, isopropenylstyrene, butenylstyrene Octenyl styrene, 4-t-butoxycarbonyl styrene, 4-methoxystyrene, and a 4-t-butoxystyrene.

  Specific examples of the monofunctional vinyl ether include methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, n-butyl vinyl ether, t-butyl vinyl ether, 2-ethylhexyl vinyl ether, n-nonyl vinyl ether, lauryl vinyl ether, cyclohexyl vinyl ether, cyclohexyl methyl vinyl ether, 4 -Methylcyclohexyl methyl vinyl ether, benzyl vinyl ether, dicyclopentenyl vinyl ether, 2-dicyclopentenoxyethyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinyl ether, butoxyethyl vinyl ether, methoxyethoxyethyl vinyl ether, ethoxyethoxyethyl vinyl ether, methoxypolyethylene glycol vinyl A , Tetrahydrofurfuryl vinyl ether, 2-hydroxyethyl vinyl ether, 2-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 4-hydroxymethylcyclohexyl methyl vinyl ether, diethylene glycol monovinyl ether, polyethylene glycol vinyl ether, chloroethyl vinyl ether, chlorobutyl vinyl ether, chloro Examples thereof include ethoxyethyl vinyl ether, phenylethyl vinyl ether, phenoxy polyethylene glycol vinyl ether and the like.

  Specific examples of the bifunctional (meth) acrylate include 1,6-hexanediol di (meth) acrylate, 1,10-decanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 2,4- Dimethyl-1,5-pentanediol di (meth) acrylate, butylethylpropanediol di (meth) acrylate, ethoxylated cyclohexanemethanol di (meth) acrylate, polyethylene glycol di (meth) acrylate, oligoethylene glycol di (meth) Acrylate, ethylene glycol di (meth) acrylate, 2-ethyl-2-butyl-butanediol di (meth) acrylate, hydroxypivalic acid neopentyl glycol di (meth) acrylate, ethylene oxide modified bisphenol A di (Meth) acrylate, bisphenol F polyethoxydi (meth) acrylate, polypropylene glycol di (meth) acrylate, oligopropylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 2-ethyl-2-butylpropanediol Examples include di (meth) acrylate, 1,9-nonanedi (meth) acrylate, propoxylated ethoxylated bisphenol A di (meth) acrylate, and tricyclodecane di (meth) acrylate.

  Specific examples of trifunctional (meth) acrylates include trimethylolpropane tri (meth) acrylate, trimethylolethane tri (meth) acrylate, trimethylolpropane ethoxytriacrylate, trimethylolpropane alkylene oxide modified tri (meth) acrylate , Pentaerythritol tri (meth) acrylate, dipentaerythritol tri (meth) acrylate, trimethylolpropane tris [(meth) acryloyloxypropyl] ether, isocyanuric acid alkylene oxide modified tri (meth) acrylate, propionate dipentaerythritol tri ( (Meth) acrylate, tris [(meth) acryloyloxyethyl] isocyanurate, hydroxypivalaldehyde-modified dimethylolpropane Li (meth) acrylate, sorbitol tri (meth) acrylate, propoxylated trimethylolpropane tri (meth) acrylate, ethoxylated glycerin tri (meth) acrylate is Kyora.

Specific examples of polyfunctional vinyl ethers include ethylene glycol divinyl ether, diethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, butylene glycol divinyl ether, hexanediol divinyl ether, bisphenol A alkylene oxide divinyl ether, bisphenol F alkylene oxide. Divinyl ethers such as divinyl ether; trimethylolethane trivinyl ether, trimethylolpropane trivinyl ether, ditrimethylolpropane tetravinyl ether, glycerin trivinyl ether, pentaerythritol tetravinyl ether, dipentaerythritol pentavinyl ether, dipentaerythritol hexa Trivinyl ethers such as nyl ether, ethylene oxide-added trimethylolpropane trivinyl ether, propylene oxide-added trimethylolpropane trivinyl ether; ethylene oxide-added ditrimethylolpropane tetravinyl ether, propylene oxide-added ditrimethylolpropane tetravinyl ether, ethylene oxide-added pentaerythritol tetravinyl ether Propylene oxide-added pentaerythritol tetravinyl ether, ethylene oxide-added dipentaerythritol hexavinyl ether, propylene oxide-added dipentaerythritol hexavinyl ether, and the like.
Among the above, as the vinyl ether compound, di- or trivinyl ether compounds are preferable from the viewpoints of curability, adhesion to a recording medium, surface hardness of the formed image, and the like, and divinyl ether compounds are particularly preferable.

The blending ratio of the active energy ray-curable monomer in the ink is preferably about 10 to 70% by mass.
Among the above monomers, a monomer having a relatively low viscosity having an unsaturated double bond capable of radical polymerization in the molecular structure is preferable. For example, monoethyl 2-ethylhexyl (meth) acrylate (EHA), 2-hydroxyethyl (Meth) acrylate (HEA), 2-hydroxypropyl (meth) acrylate (HPA), caprolactone-modified tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, tetrahydrofurfuryl (meth) ) Acrylate, lauryl (meth) acrylate, 2-phenoxyethyl (meth) acrylate, isodecyl (meth) acrylate, isooctyl (meth) acrylate, tridecyl (meth) acrylate, caprolactone (meth) acrylate, Toxylated nonylphenol (meth) acrylate, bifunctional tripropylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, neopentyl glycol Hydroxypivalate ester di (meth) acrylate (MANDA) and hydroxypivalate neopentyl glycol ester di (meth) acrylate (HPNDA), 1,3-butanediol di (meth) acrylate (BGDA), 1,4-butanediol di (Meth) acrylate (BUDA), 1,6-hexanediol di (meth) acrylate (HDDA), 1,9-nonanediol di (meth) acrylate, diethyleneglycol Di (meth) acrylate (DEGDA), neopentyl glycol di (meth) acrylate (NPGDA), tripropylene glycol di (meth) acrylate (TPGDA), caprolactone-modified hydroxypivalic acid neopentyl glycol ester di (meth) acrylate, propoxylation Neopentyl glycol di (meth) acrylate, ethoxy-modified bisphenol A di (meth) acrylate, polyethylene glycol 200 di (meth) acrylate, polyethylene glycol 400 di (meth) acrylate, multifunctional trimethylolpropane tri (meth) acrylate ( TMPTA), pentaerythritol tri (meth) acrylate (PETA), dipentaerythritol hexa (meth) acrylate (DPHA), triary Isocyanate, ε-caprolactone modified dipentaerythritol (meth) acrylate, tris (2-hydroxyethyl) isocyanurate tri (meth) acrylate, ethoxylated trimethylolpropane tri (meth) acrylate, propoxylated trimethylolpropane tri (meth) ) Acrylate, propoxylated glyceryl tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, dipentaerythritol hydroxypenta (meth) acrylate, ethoxylated pentaerythritol tetra (meth) acrylate, penta (Meth) acrylate ester etc. are mentioned.

  Commercially available products include KAYARAD TC-110S, R-128H, R-526, NPGDA, PEG400DA, MANDA, R-167, HX-220, HX-620, R-551, R-712, R-604, R- 684, GPO, TMPTA, THE-330, TPA-320, TPA-330, PET-30, RP-1040, T-1420, DPHA, DPHA-2C, D-310, D-330, DPCA-20, DPCA- 30, DPCA-60, DPCA-120, DN-0075, DN-2475, KAYAMER PM-2, PM-21, KS series HDDA, TPGDA, TMPTA, SR series 256, 257, 285, 335, 339A, 395, 440 495, 504, 111, 212, 213, 230, 2 59, 268, 272, 344, 349, 601, 602, 610, 9003, 368, 415, 444, 454, 492, 499, 502, 9020, 9035, 295, 355, 399E494, 9041203, 208, 242, 313, 604, 205, 206, 209, 210, 214, 231E239, 248, 252, 297, 348, 365C, 480, 9036, 350 (manufactured by Nippon Kayaku Co., Ltd.), beam set 770 (manufactured by Arakawa Chemical Co., Ltd.), etc. .

Monomers that are vehicle components of the ink can be used singly or in combination of two or more. All of these have good wettability to the recording medium and have excellent adhesion to a wide variety of recording media.
Furthermore, water and a solvent may be added to lower the viscosity and increase the speed. Any solvent may be used as long as it dissolves the ink constituents well and evaporates quickly after printing, but those containing ketone and / or alcohol as the main solvent are preferred, for example, acetone, methyl ethyl ketone, methyl isobutyl ketone. , Methanol, ethanol, isopropanol and the like are used alone or in combination, and further used as a mixed solvent with water as necessary.

The photoinitiator is usually blended in an amount of about 0.01 to 20% by mass relative to the total amount of vehicle.
Examples of photoinitiators include benzoin ether, acetophenone, benzophenone, benzophenone, thioxanthone, other special groups such as acylphosphine oxide, methylphenylglyoxylate, benzoin alkyl ether, benzylmethyl ketal, hydroxycyclohexyl Examples include phenyl ketone, p-isopropyl-a-hydroxyisobutylphenone, 1,1-dichloroacetophenone, 2-chlorothioxanthone and the like.

Examples of the photoinitiator include triethanolamine, ethyl 2-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, and polymerizable tertiary amine.
Specifically, BYCURE 10, 30, 55 (Stouffer), KAYACURE BP-100, BMS, DETX-S, CTX, 2-EAQ, DMBI, EPA (Nippon Kayaku), Irgacure 651, 184, 907, 369, 379 (Ciba-gigi), Darocur 1173, 1116, 953, 2959, 2273, 1664 (Merck), Sandre 1000 (Sand), Counter Cure CTX, Counter Cure BMS, ITX, PDO, BEA, DMB (Word Brenkin Sop), Sun Cure IP, BTTP (Japanese fats and oils), etc. are desirable. In addition, a photoinitiator-containing type photocurable resin may be used.

There is no restriction | limiting in particular in the coloring material of an ink, It can select suitably from well-known water-soluble dye, oil-soluble dye, a pigment, etc. and can be used. Among these, pigments that are well dispersed in the vehicle and have excellent weather resistance are desirable. For example, organic or inorganic pigments having the following numbers described in the color index can be used.
Pigment Red 3, 5, 19, 22, 31, 38, 43, 48: 1, 48: 2, 48: 3, 48: 4, 48: 5, 49: 1, 53: 1 as red or magenta pigment 57: 1, 57: 2, 58: 4, 63: 1, 81, 81: 1, 81: 2, 81: 3, 81: 4, 88, 104, 108, 112, 122, 123, 144, 146 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, 257, Pigment Violet 3, 19, 23, 29, 30, 37, 50, 88, Pigment Orange 13 16, 20, 36,
Pigment Blue 1, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 16, 17-1, 22, 27, 28, 29, 36, 60 as blue or cyan pigments ,
Examples of green pigments include Pigment Green 7, 26, 36, 50,
As the yellow pigment, Pigment Yellow 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 137, 138 139, 153, 154, 155, 157, 166, 167, 168, 180, 185, 193,
As the black pigment, Pigment Black 7, 28, 26,
Etc. can be used according to the purpose.

The added amount of the pigment is preferably about 1 to 20 parts by weight. If it is 1 part by weight or more, the image quality will not deteriorate, and if it is 20 parts by weight or less, the ink viscosity characteristics will not be adversely affected. Further, two or more kinds of color materials may be appropriately mixed and used for color adjustment or the like.
In order to impart further functionality to the ink used in the present invention, various sensitizers, light stabilizers, surface treatment agents, surfactants, viscosity reducing agents, antioxidants, anti-aging agents, crosslinking accelerators, polymerization agents Inhibitors, plasticizers, preservatives, pH adjusters, antifoaming agents, humectants, dispersants, dyes and the like may be mixed.
Various known crushing or dispersing devices can be used for mixing and dispersing the vehicle, coloring material and other components without particular limitation, but a bead mill and a homogenizer are most suitable.

The light source used for the curing means is not particularly limited, but the light source that irradiates ultraviolet rays is the most common.
Examples thereof include a low-pressure mercury lamp, a high-pressure mercury lamp, a metal halide lamp, a hot cathode tube, a cold cathode tube, and an LED. However, in the case of an ultraviolet irradiation lamp, there is a possibility that heat will be generated and the recording medium may be deformed. Therefore, it is desirable to provide a cooling mechanism, for example, a cold mirror, a cold filter, a workpiece cooling, and the like.
Metal halide is effective as a light source for curing the pretreatment agent because of its wide wavelength range. The metal halide is a metal halide such as Pb, Sn, or Fe, and can be selected according to the absorption spectrum of the photoinitiator.

The ink discharge means is provided with a plurality of nozzles arranged in a row on the lower surface thereof and ink chambers corresponding to the respective nozzle positions, and the volume of each ink chamber is changed by an actuator at any timing from any nozzle. Ink droplets can be ejected.
The discharge head may be the above-described line type head or a serial type head. Further, there may be a temperature control means for adjusting the viscosity.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated further more concretely, this invention is not limited at all by these Examples.

In order to confirm the effect of the present invention, an ink dot image was formed under the following conditions, and the size of the dot diameter was measured and evaluated.
<Ink>
An ink having the following composition was prepared by a conventional method.
・ Mixed liquid of the following monomers: 170 parts by mass ・ Low molecular monomer acrylate
Light acrylate PO-A (2-phenoxyethyl acrylate)
(Kyoeisha Chemical Co., Ltd.) ... 70 parts by mass
Acryloylmorpholine ACMO (manufactured by Kojinsha) ... 50 parts by mass
Trimethylolpropane ethoxytriacrylate TMPEOTA
(Daicel Cytec Co., Ltd.) ... 50 parts by mass Photoinitiator (Ciba, Irgacure 379) ... 20 parts by mass Colorant: Carbon black pigment (Degussa Special Black 350)
... 10 parts by mass

<Recording medium>
As the recording medium, the following films (a) and (b) manufactured by Toyobo Co., Ltd. were used.
(A) Pyrene film-OT [OPP (P2161)]
... One side corona discharge treatment with polypropylene material (b) Polyester film [PET (E5100)]
... A single-sided corona discharge treatment with PET material

The corona discharge treated surface and the untreated surface of the recording medium were adjusted to have a waveform of 1 mm by adjusting the waveform so that the black ink became 8 pL droplets by an ejection device using a Gen4 head manufactured by Ricoh Printing System. It discharged at a speed of 8 m / sec from the distance, and was cured using Sub Zero 085 (A bulb) manufactured by Integration Technology.
Ten dot diameters were arbitrarily measured using a KEYENCE microscope VHX-200 to obtain an average dot diameter.
On the other hand, with respect to the ink droplets ejected on the corona discharge treated surface of the film (a), the feeding speed is changed under the conditions of a gap of 2 mm and 14 kV by a corona discharge device (Corona Scanner / manufactured by Shinko Electric Instrumentation Co., Ltd.). After changing the treatment time, the ultraviolet rays were irradiated and cured, and the dot diameter was measured in the same manner to obtain the average dot diameter.
The results are summarized in Table 1.

As can be seen from the results in Table 1, even with a polypropylene film made of a polyolefin resin that has low wetting tension and poor wetting with respect to ink, the image forming method of the present invention can provide a dot diameter equivalent to that of PET, resulting in ink droplets. The expansion effect was confirmed.
Further, when 5 pL ink droplets were ejected at 600 dpi using the ink having a pigment concentration of 5 mass% used in the examples, a solid image having an OD value of 1.7 could be obtained. When the discharge treatment as the expansion means was not performed, the adjacent dots were not combined, so that a solid image was not obtained, and the optical density of the image was an OD value of 1.2.

JP 2008-207528 A JP 2002-187343 A

Claims (7)

  A step of forming an image by ejecting ink containing an active energy ray-curable material and a coloring material on the surface of a recording medium by an ink jet recording method, a step of performing a discharge treatment, and a step of curing by irradiating active energy rays. And an image forming method characterized in that each step is performed in this order.   2. The image forming method according to claim 1, wherein the discharge process is a corona discharge process.   The image forming method according to claim 1, wherein the recording medium is a film made of a polyolefin resin.   The image forming method according to claim 1, wherein a discharge treatment is also performed before the step of forming the image.   Discharge means for ejecting ink containing an active energy ray-curable material and a colorant to a recording medium by an ink jet recording method, discharge processing means for performing discharge processing, and curing means for irradiating and curing active energy rays An image forming apparatus configured to perform discharge processing and curing after ink discharge.   6. The image forming apparatus according to claim 5, wherein the ejection unit is a line-type ink jet head fixedly installed in a direction perpendicular to the recording medium conveyance direction.   7. The image forming apparatus according to claim 5, wherein the discharge processing unit is set so that the discharge process can be performed before the ink is ejected.

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