JP2013031946A - Image forming method and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method by an inkjet recording system which can form a solid image uniformly while maintaining the resolution thereof by using a small amount of an active energy ray curable ink with respect to even a recording medium formed of a polyolefin resin and having low wetting tension, and to provide an image forming apparatus.SOLUTION: The image forming method includes, in this order, steps for: ejecting ink containing an active energy ray curable material and a coloring material by the inkjet recording system on a surface of a recording medium to form an image; thickening an ink droplet constituting the image; compressing the thickened ink by a compressing member; irradiating the ink droplet with an active energy ray while the ink droplet is compressed to cure the ink droplet; and separating the compressing member from the ink droplet.

Description

  The present invention relates to an image forming method and an image forming apparatus.

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 technique can form an image by directly attaching ink to a recording medium, recording can be performed with a simpler apparatus configuration than indirect recording using a photoconductor such as electrophotographic recording, and can be recorded on the recording medium. 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.
Since most of the components of ink used in the ink jet recording method are liquid components, the difference in 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, since osmotic drying cannot be used, evaporation drying occurs, causing problems such as set-off when superimposed, particularly 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 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 for polyolefin materials with low wetting tension, compared to materials with high wetting tension. An equivalent image density cannot be obtained without using this ink. 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.
In general, for such a material having a low wetting tension, a surface treatment is generally performed on the surface of the recording medium in order to improve the wettability of the ink. Even in the case of polyolefin-based materials, the spread of ink is poor compared with, for example, PET (polyethylene terephthalate), and a large amount of ink is required.

  Patent Documents 1 to 3 are cited as documents related to the known technology similar to the present invention. In Patent Documents 1 and 2, after an image is formed on an intermediate transfer member, the viscosity is increased and transferred to a recording medium. However, in this method, the ink surface in a thickened state and the recording medium come into contact with each other, so that the binding property between the recording medium and the ink droplet is weak, and there is a problem in abrasion resistance and fixing property. In particular, in a recording medium made of a material having low wettability with respect to ink, an image is easily peeled off. Moreover, in patent document 3, the ink containing a phase change component is used, it is made to thicken and pressurize and flatten by a temperature difference. However, since the ink is solidified at room temperature, it is difficult to stably eject the ink with an inkjet head, and it takes time to change the temperature after landing. In addition, the binding force to a recording medium with poor ink wettability is also reduced. Furthermore, since the pressurizing part and the curing part are separated, the ink adheres to the pressurizing member when the ink surface is peeled off from the pressurizing part.

A film made of a polyolefin resin such as polyethylene or polypropylene has a very low wetting tension (about 20 mN / m). Corona-treated polypropylene films are also commercially available [for example, manufactured by Toyobo Co., Ltd .: Pyrene Film-OT (P2161)], and the wetting tension is about 40 mN / m, which is a level that is not problematic for normal printing. Yes. On the other hand, in the image forming method based on the ink jet recording method, for example, when a solid portion is formed, it is necessary that the ejected ink droplet spreads by wetting the surface of the recording medium by the surface tension, and adjacent ink droplets are connected.
However, in the case of the ink jet recording method, ink droplets do not spread even in the above-mentioned corona-treated film. Therefore, in order to form a solid portion, it is necessary to eject ink at a high density so that the ink droplets are connected. As a result, it was necessary to discharge more ink than necessary when forming the solid portion, which was not only disadvantageous in terms of cost, but also obtained an image with a large unevenness on the surface shape after curing and a low glossiness. .
Accordingly, the present invention can form a uniform solid image while maintaining the resolution using a small amount of active energy ray-curable ink even for a recording medium made of a polyolefin resin having a low wetting tension. An object of the present invention is to provide an image forming method and an image forming apparatus using an inkjet recording method.

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 coloring material on the surface of a recording medium by an ink jet recording method, a step of increasing the viscosity of ink droplets constituting the image, and a thickening An image forming method comprising: a step of pressing an ink droplet with a pressing member; a step of irradiating an active energy ray in a pressed state to cure the ink droplet; and a step of peeling the pressing member.
2) The image forming method according to 1), wherein the step of thickening the ink droplets is performed by irradiation with active energy rays.
3) The image forming method according to 1) or 2), wherein a member that transmits active energy rays is used as the pressing member.
4) The image forming method according to any one of 1) to 3), wherein the recording medium is a film made of a polyolefin resin.
5) A means for 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 ink jet recording method, a means for thickening ink droplets constituting the image, a thickening An image forming apparatus comprising: means for pressing an ink droplet with a pressing member; means for irradiating an active energy ray in a pressed state to cure the ink droplet; and means for peeling the pressing member.
6) The image forming apparatus according to 5), wherein the means for thickening ink droplets is an active energy ray irradiation device.
7) The image forming apparatus according to 5) or 6), wherein the pressing member is a member that transmits active energy rays.
8) The image forming apparatus according to 7), wherein the pressing member is an endless belt, and an active energy ray irradiation device is provided inside.

  According to the present invention, it is possible to form a uniform solid image while maintaining the resolution using a small amount of active energy ray-curable ink even on a recording medium made of a polyolefin resin or the like having a low wetting tension. It is possible to provide an image forming method and an image forming apparatus using a simple ink jet recording method.

FIG. 3 is a diagram illustrating an example of an image forming method according to the present invention. The figure which shows typically the mode of the ink drop in each process in this invention. FIG. 6 is a diagram showing another example of the image forming method of the present invention. The figure which showed the relationship between the pigment density | concentration of an ink, ink layer thickness (average thickness), and optical density (OD).

Hereinafter, the present invention will be described in detail.
In the image forming method of the present invention, an ink containing an active energy ray-curable material and a color material is ejected onto a recording medium by an ink jet recording method, and then an ink droplet constituting the image is thickened. The thickened ink droplet is pressed and flattened by a pressing member, and in this state, the active energy ray is irradiated to cure the ink droplet, and then the pressing member is peeled off.
As described above, the present invention provides an image forming method in which an image is directly formed on a recording medium without being transferred, flattened by pressing in a thickened semi-cured state, and further completely cured before peeling. It has been done.
According to the image forming method of the present invention, it is possible to form a solid portion with an amount of ink equivalent to that of polyethylene terephthalate (PET) even on a recording medium made of a polyolefin resin or the like having a low wetting tension. A glossy surface with less unevenness can be obtained.
In addition, by moderately thickening the ink droplets and pressing and deforming, the ink droplets can be appropriately spread and filled by flattening, and the image can be prevented from being crushed due to excessive deformation of the ink droplets. It is possible to achieve both the formation of a solid portion with a small amount of ink and the maintenance of resolution.

An example of the image forming method of the present invention will be described with reference to FIG.
A recording medium is fed from a paper feeding device, conveyed to an ink ejection unit having an ink ejection head, and ink droplets are ejected according to an image pattern. Next, active energy rays (ultraviolet rays in FIG. 1) are irradiated to thicken the ink droplets (in FIG. 1, a high-pressure mercury lamp is used as the ultraviolet irradiation device). If it is completely cured, flattening by pressing becomes difficult, and thus the viscosity is increased to the extent that the dot exhibits an elastic behavior of flattening while maintaining its shape as a dot against external pressure. Then, after the viscosity is increased, the ink droplet is flattened by pressing with a pressing member. Since the intensity and irradiation time of the active energy rays necessary for thickening vary depending on the type of ink, they are appropriately set so as to obtain an appropriate thickened state (see Examples described later).
Although flattening is performed without increasing the viscosity, in this case, the ink droplet behaves as a liquid with respect to the pressing force, so that the deformation amount increases, and the deformation amount cannot be controlled by the pressing force. As a result, the thin line reproducibility is lost due to excessive crushing of the ink droplets, resulting in an image in which the resolution before pressing cannot be maintained. Therefore, the step of increasing the viscosity of the ink droplet is essential.

Pressing ink droplets with a pressing member in a thickened state can spread the ink droplets to the required extent on a recording medium with low ink wettability, so an image can be formed with the minimum amount of ink required can do.
Furthermore, since the ink droplets are cured by irradiating the active energy rays in the pressed state and the pressing member is peeled off after the curing, the ink droplets can be prevented from being separated, so that the ink adhesion to the pressing member surface can be suppressed. . Moreover, since the surface of the ink droplet is cured in a state where it is covered with the pressing member, it is possible to efficiently cure without eliminating the inhibition factor such as oxygen inhibition, and the surface property of the pressing member is transferred. Since it can be cured, the surface smoothness after curing can be controlled.
In FIG. 1, a high-pressure mercury lamp is built in a pressing member (roller) that can transmit active energy rays so that it can be cured by being irradiated with ultraviolet rays while being pressed.

FIG. 2 schematically illustrates the state of ink droplets in each of the steps (a) to (e). In the pressing step (c), following the ejection step (a) and the thickening step (b). The ink droplets are flattened to control the size and spread to the required extent. When pressed without thickening, the ink droplets in the liquid state cannot maintain the dot shape, and are connected even at the thin line portion as shown in (f), and the necessary resolution cannot be maintained. On the other hand, when the viscosity is increased moderately, as shown in (c), when the ink droplets are flattened by pressing, the adjacent ink droplets are connected at the solid portion to form a uniform ink layer. It is possible to maintain a resolvable state without excessive line collapse.
Next, in the curing step (d), by curing in a pressed state, it is possible to prevent the ink droplets from separating into two layers and adhering to the pressing member side when the pressing member is peeled off. And in a peeling process (e), it can be made to peel at the interface of an ink drop and a press member, and since it can peel in the state in which the surface property of the press member was transcribe | transferred, a smooth surface can be formed. When peeled without being cured, as shown in (g), the ink droplets separated into two layers adhere to the surface of the pressing member, and the surface property of the pressing member cannot be transferred, forming a smooth surface. Can not.

In FIG. 1, active energy rays (ultraviolet rays) are irradiated as a means for thickening ink. Thickening by active energy ray irradiation is performed instantaneously, and there is almost no change in the viscosity of the ink until the active energy ray is irradiated. Therefore, this is excellent in terms of ink ejection stability and high speed.
A preferable range of the irradiation amount (integrated light amount) in the case of using ultraviolet rays varies depending on the types of monomers and photoinitiators used in the ink, the ink formulation (mixing ratio), and the like. There are inks that are easy to cure and inks that are difficult to cure. Generally, the irradiation amount (integrated light amount) requires about 3 to 30% of the irradiation amount necessary for complete curing, and 8 to 10%. The degree is preferred. If the irradiation amount is too large, the degree of thickening becomes high, and a larger pressing force is required to deform the state to a necessary state, which places a burden on the apparatus. On the other hand, if the amount of irradiation is too small, the degree of thickening is low, and it is necessary to use a low pressing force in order to avoid excessive deformation, but it is difficult to uniformly apply a low pressure. It becomes easy.

  As a thickening means other than the active energy ray, it is also possible to use, for example, a change in viscosity due to temperature. However, the viscosity that can be ejected by the inkjet head is 20 mPa · s or less, and it is difficult to increase the viscosity by changing the temperature. The ink is heated at 50-60 mPa · s at room temperature, and the head is heated to 50-60 ° C. When printing, the thickening cannot be expected. Therefore, when using a viscosity change, it is necessary to use an ink containing a solid wax component at room temperature so that a large viscosity change can be obtained even with a small temperature difference.

The pressing member is preferably a member that can transmit active energy rays in order to cure ink droplets in a pressed state.
Further, if the recording medium is transparent, it is possible to cure by irradiating active energy rays from the recording medium side, but if opaque, it is necessary to cure by irradiating active energy rays from the pressing member side. Therefore, for example, when the active energy ray is ultraviolet light, it is preferably a transparent member that does not absorb ultraviolet light.
As long as the active energy ray is transmitted, there are no particular restrictions on the material, and glass or resin can be used. The shape may be a roller as shown in FIG. 1 or a belt as shown in FIG.

The pressure for pressing is linear pressure: 100 to 1000 N / m, preferably about 200 to 500 N / m. In the case of a roller, the material and outer diameter are determined so that a uniform pressure can be applied in the axial direction.
FIG. 1 shows a configuration in which a curing means (high-pressure mercury lamp) is built in a transparent glass roller and is cured while being in contact between two rollers facing the roller, and deforms the thickened ink. The pressure for this is determined by the pressure between the glass roller and the first roller in contact therewith. In order to apply a uniform pressure in the axial direction, the surface of the lower pressing roller is desirably elastically deformed, and a rubber roller is desirable. The outer diameter of the roller is not particularly limited, but it is necessary to obtain sufficient core strength according to the length in consideration of the influence of deflection in the axial direction. If the width is about 300 mm, a steel material such as SUS is used as the core material, and the thickness of the elastic rubber layer is added to about 10 to 30 mm, so that the outer diameter is about 20 to 50 mm.

FIG. 3 shows another example of the image forming method of the present invention. In this example, after forming an image by an ink jet recording method, the ink droplets are thickened by an ultraviolet irradiation device (LED). An endless belt that moves at the same speed as the recording medium is used as the pressure-pressing member for the ink droplets after thickening. The endless belt and the recording medium are in contact with each other by being sandwiched between the rollers, and an appropriate pressure necessary for pressing is applied to the ink droplets, and the ultraviolet irradiation device installed inside the endless belt in this state The ink droplets are cured by (LED), and the endless belt is separated from the recording medium after curing.
The endless belt is made of a transparent material that can transmit ultraviolet rays. The endless belt is irradiated with ultraviolet rays through the endless belt, and the ink droplets on the recording medium are cured in a pressed state. Since a thin endless belt can be used, active energy rays can be transmitted efficiently.
Also, the endless belt system of FIG. 3 is configured to have a strength equivalent to that of the above-described pressing roller of FIG. 1 because it is pressed and deformed between the rollers that start contact with the endless belt. preferable.
In FIG. 3, since the thickening before pressing is also performed by ultraviolet irradiation, a shielding plate is provided so as not to be affected by ultraviolet leakage. An LED type ultraviolet irradiation device is preferable because it generates little heat and has little thermal damage to a thin endless belt material.

UV light widely used as the active energy ray is suitable, and examples of the light source 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. Since a lamp that irradiates ultraviolet rays generates heat and the recording medium may be deformed, it is desirable to have a cooling mechanism such as a cold mirror, a cold filter, and a workpiece cooling.
As the metal halide in the metal halide lamp, metal halides such as Pb, Sn, and Fe are used. Metal halide is effective as a light source for curing the pretreatment agent because of its wide wavelength range.

  Active energy ray-curable ink containing an active energy ray-curable material forms an image on a resin film that does not have an absorption layer because the monomer itself, which is a vehicle component of the ink, is cured by active energy rays such as ultraviolet rays. can do. However, it becomes expensive because a curable monomer or oligomer is used instead of water in the water-based ink. Therefore, it is necessary to increase the density of the color material so that an image having the same density can be obtained with a small amount of ink. When a pigment is used as a coloring material, there is a limit to increasing the concentration of the pigment in terms of dispersibility, curability, low viscosity, etc., but when forming an image on a resin film, the ejected ink droplets If it is possible to form an image by thinning the film, the cost can be reduced.

For example, in the case of black ink using a pigment as a color material, a pigment concentration of about 2 to 3% by weight is sufficient if a sufficient optical density is obtained with an ink layer thickness of about 5 to 7 μm. However, when the ink layer thickness is about 2 to 3 μm, the pigment concentration needs to be 5% by weight or more.
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, the ink droplet has a dot diameter of about 60 to 70 μm. Need to be ink dots. However, especially in the case of a polyolefin resin film, since the dot diameter does not increase that 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 amount of ink droplets deposited so as to fill the space between the dots. In other words, the effect is limited even when a high-concentration ink having a pigment concentration of 5% by weight or more is used, and the layer thickness for forming the solid portion is increased, which is different from the case using a low-concentration ink. There will be no.
On the other hand, in the image forming method of the present invention, a uniform solid portion can be formed with a small amount of ink applied, so that high-concentration ink can be used efficiently, and as a result, monomer consumption is reduced. This can reduce supply costs.

FIG. 4 shows the relationship between the pigment concentration, the ink layer thickness (average thickness), and the optical density (OD: measured with a reflection spectral densitometer X-Rite 939 manufactured by X-Rite). It can be seen that it is necessary to form a uniform solid portion with a thin layer in order to make the best use of.
When the target value of OD is 1.7, if the ink layer thickness required to form a uniform solid portion is 3.5 μm or less, the target can be achieved with an ink having a pigment concentration of 5% by weight. When an ink layer thickness of about 6 μm is required, an ink having a pigment concentration of about 3% by weight is sufficient.
On the other hand, in order to efficiently use an ink having a high pigment concentration of 5% by weight or more, it is necessary to form a uniform ink layer with an ink amount equal to or less than the ink layer thickness at which a necessary concentration is obtained.
In the image forming method of the present invention, since uniform image formation with such a thin layer is possible, ink with a high pigment concentration can be efficiently used, and ink cost can be reduced.

The arrangement of the heads of the image forming apparatus of the ink jet recording method includes a serial type that ejects while moving in a direction perpendicular to the conveyance direction of the recording medium, and an ink ejection that is fixedly installed in the width direction of the recording medium at the same time. There is a line type to do. The serial type head forms an image while moving the head in the width direction of the recording medium in a state where the conveyance of the recording medium is stopped. Therefore, the print density of the ejection is changed both in the transport direction and in the width direction. There is a degree of freedom. Therefore, in order to correct the difference in the wetting tension of the resin film with respect to the ink, printing can be performed by changing the printing density in the vertical and horizontal directions of the image, and the minimum amount of ink applied that can form a solid portion can be set for each recording medium. .
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 in only one direction, the lines become particularly noticeable for recording media with low surface tension such as polyolefin resin, and a uniform solid image can be obtained with a small amount of ink. It is difficult to form with.
However, in the image forming method of 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 pressure deformation after thickening. This is unnecessary, and an image having no streaks can be formed even with a line-type head.

The ultraviolet curable ink, which is a typical example of the active energy ray curable ink, contains at least a polymerizable compound, a photoinitiator, and a color material as main components. In addition, additives such as a leveling agent, reaction accelerator, reaction inhibitor, and sensitizer may be included. The ultraviolet curable ink is roughly classified into a radical polymerization ink containing a radical polymerizable compound and a cation polymerization ink containing a cationic polymerizable compound. In the present invention, any ink can be applied and mixed. A system may be used.
In the present invention, colored inks containing mainly color materials such as black, cyan, magenta, and yellow are mainly used. However, in addition to white, light-colored inks that enrich gradation expression can be used in combination. It is.

Examples of the polymerizable compound used in the cationic polymerization type ink include an epoxy compound and an oxetane compound.
Examples of the epoxy compound include bisphenol A type epoxy, bisphenol BA type epoxy, bisphenol F type epoxy, bisphenol AD type epoxy, phenol novolac type epoxy, cresol novolac type epoxy, alicyclic epoxy, fluorene type epoxy, naphthalene type epoxy, glycidyl. Examples include ester compounds, glycidylamine compounds, heterocyclic epoxies, α-olefin epoxies, and the like.
In particular, alicyclic epoxy compounds are preferred because of their low viscosity and fast curing speed. Specific examples include 3,4-epoxycyclohexenylmethyl-3 ′, 4′-epoxycyclohexenecarboxylate and its ε-caprolactone modified product, bis- (3,4-epoxycyclohexylmethyl) adipate, 1, 2: 8. , 9-diepoxy limonene, vinylcyclohexene monooxide-1,2-epoxy-4-vinylcyclohexane.
The oxetane compound may be appropriately selected according to the properties required for the ink, and 3-ethyl-3- (phenoxymethyl) oxetane is suitable when adhesion to the substrate is particularly important. .

  The cationic polymerization type ink can be mixed with a vinyl ether compound as required. Preferred vinyl ethers 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 divinyl ether, dodecyl vinyl ether, ethyl vinyl ether, hexanediol. Divinyl ether, hydroxybutyl vinyl ether, hydroxyethyl vinyl ether, isobutyl vinyl ether, methyl vinyl ether, octadecyl vinyl ether, propyl vinyl ether, triethylene glycol divinyl ether, vinyl-4-hydroxybutyl ether, vinyl cyclohexyl ether, vinyl propionate, vinylcarba Lumpur, Binirubiroridon the like.

  If necessary, the cationic polymerization type ink may further contain propenyl ether and butenyl ether as reactive components. For example, 1-dodecyl-1-propenyl ether, 1-dodecyl-1-butenyl ether, 1-butenoxymethyl-2-norbornene, 1-4-di (1-butenoxy) butane, 1,10-di (1-butenoxy) Preferred are 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 that can be applied to the cationic polymerization type ink may be any compound that generates a substance that initiates polymerization upon irradiation with an active energy ray such as ultraviolet rays, and is an onium salt such as arylsulfonium salt or aryliodonium. Salts are preferred. Furthermore, if necessary, photosensitizers such as anthracene compounds such as N-vinylcarbazole, thioxanthone compounds, and 9,10-dibutoxyanthracene can be used in combination.

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

  Examples of monofunctional (meth) acrylates that can be used in radical polymerization inks include hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, tert-octyl (meth) acrylate, isoamyl ( (Meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, tridecyl (meth) acrylate, lauryl (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 (2-methyl-2-ethyl-1,3-dioxolan-4-yl) methyl (meth) acrylate, butoxyethyl (meth) acrylate, 2-chloroethyl (meth) acrylate, 4-bromobutyl (meth) acrylate , Cyanoethyl (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, Feni (Meth) acrylate, 2,3,4,5-tetramethylphenyl (meth) acrylate, 4-chlorophenyl (meth) acrylate, phenoxymethyl (meth) acrylate, phenoxyethyl (meth) acrylate, glycidyl (meth) acrylate, Sidyloxybutyl (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, dimethylamino Noethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, diethylaminopropyl (meth) acrylate, trimethoxysilylpropyl (meth) acrylate, trimethylsilylpropyl (meth) acrylate, polyethylene oxide monomethyl ether (meta ) Acrylate, oligoethylene oxide monomethyl ether (meth) acrylate, polyethylene oxide (meth) acrylate, oligoethylene oxide (meth) acrylate, oligoethylene oxide monoalkyl ether (meth) acrylate, polyethylene oxide monoalkyl ether (meth) acrylate, dipropylene glycol ( (Meth) acrylate, polypropylene oxide monoalkyl -Ter (meth) acrylate, oligopropylene oxide monoalkyl ether (meth) acrylate, 2-methacryloyloxyethyl succinic acid, 2-methacryloyloxyhexahydrophthalic acid, 2-methacryloyloxyethyl-2-hydroxypropyl phthalate, butoxy Diethylene glycol (meth) acrylate, trifluoroethyl (meth) acrylate, perfluorooctylethyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, EO-modified phenol (meth) acrylate, EO-modified cresol (meth) Acrylate, EO-modified nonylphenol (meth) acrylate, PO-modified nonylphenol (meth) acrylate, EO-modified-2-ethylhexyl (meth) acrylate, capro Ton modified tetrahydrofurfuryl (meth) acrylate, caprolactone (meth) acrylate.

  Examples of the bifunctional (meth) acrylate that can be used in the radical polymerization type ink include tripropylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, 1,3- Butanediol di (meth) acrylate, diethylene glycol di (meth) acrylate, caprolactone-modified hydroxypivalic acid neopentyl glycol ester di (meth) acrylate, propoxylated pentyl glycol di (meth) acrylate, 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, butyl Tylpropanediol (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, hydroxypivalate neopentyl glycol di (meth) acrylate, EO-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 di (meth) acrylate DOO, 1,9-nonane di (meth) acrylate, propoxylated ethoxylated bisphenol A di (meth) acrylate, tricyclodecane di (meth) acrylate.

  Examples of tri- or higher functional (meth) acrylates that can be used in radical polymerization inks include trimethylolpropane tri (meth) acrylate, trimethylolethane tri (meth) acrylate, and 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 tri (meth) acrylate Rate, sorbitol tri (meth) acrylate, propoxylated trimethylolpropane tri (meth) acrylate, ethoxylated glycerin tri (meth) acrylate, tris (2-hydroxyethyl) isocyanurate tri (meth) acrylate, ethoxylated trimethylolpropane tri (Meth) acrylate, propoxylated glyceryl tri (meth) acrylate, (meth) acrylate of ε-caprolactone modified dipentaerythritol, pentaerythritol tetra (meth) acrylate, ethoxylated pentaerythritol tetra (meth) acrylate, dipentaerythritol hydroxypenta (Meth) acrylate, penta (meth) acrylate ester, dipentaerythritol hexa (meth) acrylate and the like.

  Examples of monofunctional (meth) acrylamides that can be used in radical polymerization inks include (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-propyl (meth) acrylamide, N -N-butyl (meth) acrylamide, Nt-butyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N-methylol (meth) acrylamide, N, N-dimethyl ( And (meth) acrylamide, N, N-diethyl (meth) acrylamide, (meth) acryloylmorpholine, and the like.

  Examples of monofunctional aromatic vinyls that can be used in radical polymerization inks include styrene, methylstyrene, dimethylstyrene, trimethylstyrene, ethylstyrene, isopropylstyrene, chloromethylstyrene, methoxystyrene, acetoxystyrene, chlorostyrene, Chlorstyrene, bromostyrene, vinyl benzoic acid methyl ester, 3-methylstyrene, 4-methylstyrene, 3-ethylstyrene, 4-ethylstyrene, 3-propylstyrene, 4-propylstyrene, 3-butylstyrene, 4-butyl Styrene, 3-hexylstyrene, 4-hexylstyrene, 3-octylstyrene, 4-octylstyrene, 3- (2-ethylhexyl) styrene, 4- (2-ethylhexyl) styrene, allylstyrene, isopropenyls Ren, butenylstyrene, octenyl styrene, 4-t-butoxycarbonyl styrene, 4-methoxystyrene, and a 4-t-butoxystyrene.

  Examples of monofunctional vinyl ethers that can be used in the radical polymerization type ink 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, Cyclohexylmethyl 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 , Methoxypolye Lenglycol vinyl ether, 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 Chloroethoxyethyl vinyl ether, phenylethyl vinyl ether, phenoxypolyethylene glycol vinyl ether, and the like.

  Examples of polyfunctional vinyl ethers that can be used in radical polymerization inks 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. Divinyl ethers such as bisphenol F alkylene oxide divinyl ether; trimethylolethane trivinyl ether, trimethylolpropane trivinyl ether, ditrimethylolpropane tetravinyl ether, glycerin trivinyl ether, pentaerythritol tetravinyl ether, dipentaerythritol pentavinyl ether, di Intererythritol hexavinyl 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 Examples thereof include oxide-added pentaerythritol tetravinyl ether, ethylene oxide-added dipentaerythritol hexavinyl ether, and propylene oxide-added dipentaerythritol hexavinyl ether.

  As the vinyl ether compound, a di- or trivinyl ether compound is preferable from the viewpoint of curability, adhesion to a recording medium, surface hardness of the formed image, and the like, and a divinyl ether compound is particularly preferable.

  Water and a solvent may be added to the ink to reduce the viscosity and increase the speed. The solvent is not particularly limited as long as it dissolves the constituent components of the ink and evaporates quickly after printing, but a solvent containing ketone and / or alcohol as the main solvent is preferable. Examples thereof include acetone, methyl ethyl ketone, methyl isobutyl ketone, methanol, ethanol, isopropanol and the like. These may be used alone or in admixture of two or more, but are preferably used as a mixed solvent with water.

Examples of the photopolymerization initiator include benzoin ether series, acetophenone series, benzophenone series, thioxanthone series, and other special groups such as acylphosphine oxide and methylphenylglyoxylate. Specific examples include benzoin alkyl ether, benzyl methyl ketal, hydroxycyclohexyl phenyl ketone, p-isopropyl-α-hydroxyisobutylphenone, 1,1-dichloroacetophenone, 2-chlorothioxanthone and the like.
The blending amount of the photopolymerization initiator is preferably 0.01 to 10% by weight with respect to the active energy ray-curable material.

Examples of the photopolymerization initiation assistant include triethanolamine, ethyl 2-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, and polymerizable tertiary amine.
Specific examples include BiCure 10, 30, 55 (Stouffer), KAYACURE BP-100, KAYACURE BMS, KAYACURE DETX-S, KAYACURE CTX, KAYACURE 2-EAQ, KAYACURE DMBI, KAYACURE EPA, KAYACURE EPA, 184, 907, 369, 379 (Ciba-gigi), Darocur 1173, 1116, 953, 2959, 2273, 1664 (Merck), Sandre 1000 (Sand), Counter Cure CTX, Counter Cure BMS, Counter Cure ITX, Counter Cure PDO, Counter Cure BEA, DMB (Word Brenkin Sopp), Suncure IP, BTTP (Nippon Yushi) and the like can be mentioned. In addition, a photopolymerization initiator-containing type photocurable resin may be used.

There is no restriction | limiting in particular in a coloring material, It can select suitably from well-known water-soluble dye, oil-soluble dye, a pigment, etc., and can be used. Among these, oil-soluble dyes and pigments that are easily dispersed and dissolved in a water-insoluble medium are preferable, and pigments excellent in weather resistance are particularly preferable. In addition, two or more kinds of color materials can be appropriately mixed and used for color adjustment or the like.
The appropriate amount of pigment added is 1 to 20% by weight of the total ink. If it is less than 1% by weight, the image quality is deteriorated. If it is more than 20% by weight, the ink viscosity characteristics are adversely affected.

Examples of the pigment include those described below in the color index.
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 a blue or cyan pigment
Pigment Green 7, 26, 36, 50 as a green pigment
As yellow pigments, 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
Pigment Black 7, 28, 26 as black pigment

In order to further add functionality to the ink, leveling agent, polymerization accelerator, polymerization inhibitor, sensitizer, light stabilizer, surface treatment agent, surfactant, viscosity reducing agent, antioxidant, anti-aging Agents, plasticizers, preservatives, pH adjusters, antifoaming agents, humectants, dispersants, dyes, and the like can be mixed.
For mixing and dispersing the above-mentioned active energy ray-curable material, coloring material and other components, various known pulverization or dispersion devices can be used as appropriate, but a bead mill and a homogenizer are optimal.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited by these Examples.

Examples 1-4, Comparative Examples 1-3
<Image forming process>
As a recording medium, a single-sided corona-treated polypropylene film [Toyobo Co., Ltd .: Pyrene Film-OT (P2161)] was used, and a Ricoh Printing System Gen4 inkjet head was used for the corona-treated surface. The following black ink was adjusted by a discharge device so as to form a droplet of 5 pL, and discharged from a distance of 1 mm at a speed of 8 m / sec to form a 4 pt character image and a solid image (600 dpi × 600 dpi). .

<Black ink>
Inks were prepared by mixing and stirring the materials of the following formulation. The concentration of the colorant is about 5% by weight.
・ A mixture of the following low-molecular acrylate monomers (total 170 parts by weight)
Light acrylate PO-A (manufactured by Kyoeisha Chemical Co., Ltd.) 55 parts by weight Acrylyl morpholine ACMO (manufactured by Kojin Co., Ltd.) 55 parts by weight Trimethylolpropane ethoxytriacrylate TMPEOTA
(Daicel Cytec Co., Ltd.) ... 60 parts by weightAdditive: BYK UV3510 (manufactured by Big Chemie Japan) ... 0.2 parts by weightPhotoinitiator (Ciba, Irgacure 379) ... 20 parts by weight Coloring material: Carbon black pigment
(Degussa Special Black 350) ... 10 parts by weight

<Thickening process>
The image formed as described above was irradiated with ultraviolet rays using Sub Zero 085 (A bulb) manufactured by Integration Technology, and the state of ink droplets when the irradiation amount (integrated light amount) was changed was evaluated. The evaluation criteria are as follows.
In the case of “curing”, since there is a slight deformation that is not related to the object effect of the present invention, “curing” and “thickening” are distinguished by “the presence or absence of ink adhesion”. “Thickening” was divided into “high, medium, low, no change” depending on the degree of deformation and the spread of ink droplets.

〔Evaluation criteria〕
“Curing”: Does not deform when pressed. No ink adheres to the pressing member.
"Thickening"
High: Little deformation when pressed (only the tip of the ink droplet is deformed). Ink to the pressing member
There is adhesion.
Medium: Appropriately deformed when pressed (the entire ink droplet is deformed.
30% or less). Ink adheres to the pressing member.
Low: Appropriately deformed when pressed (the entire ink droplet is deformed. Ink droplet spread due to deformation)
60% or less). Ink adheres to the pressing member.
“No change”: Deforms greatly when pressed (the entire ink droplet is deformed.
Spread over 100%). Ink adheres to the pressing member.

Note that “the spread of ink droplets is 30% or less” means that “the ratio of the increase in the area of the printed portion after 10 seconds is 30% or less with respect to the area of the printed portion immediately after printing”. . The same applies to the case of 60% or less. The rate of increase can be obtained by observing with a digital microscope VHX-200 manufactured by Keyence Corporation.

<Pressing process><Curingprocess><Peelingprocess>
Next, the untreated surface of a polypropylene film [Toyobo Co., Ltd .: Pyrene Film-OT (P2161)] subjected to a single-sided corona treatment is used as a pressing member, and is brought into contact with the ink droplets having undergone the above thickening step and pressed. However, it was cured using Integration Technology: Sub Zero 085 (A bulb). The pressing was performed by passing the nip between a φ30 mm urethane roller and a φ50 mm SUS roller, which had a linear pressure of 400 N / m, at a feed rate of 188 mm / s. The film transmits ultraviolet rays.
Next, the pressing member was peeled off.

The following criteria were evaluated for the following items related to the 4pt character image and solid image that had undergone all the above steps.

[4pt character resolution]
○: Resolvable △: Partially collapsed ×: Collapsed

[Solid part of solid image]
○: Almost filled △: Intermediate level ×: Poorly filled, with many gaps

[Crushing of edges of solid images]
○: No protrusion Δ: Although there is protrusion, the edge is maintained.
×: Many protrusions

〔Comprehensive evaluation〕
◎: The above three points are all “◯” ○: The above three points include “△” X: The above three points include “×”

As can be seen from the results in Table 1, with the image forming method of the present invention, a solid image of 600 dpi × 600 dpi with a well-filled solid portion was obtained with an ink amount of 5 pL with respect to a polypropylene film having low wetting tension and poor wetness with respect to ink. It was possible to achieve both the formation and the resolution capable of resolving 4pt characters. That is, it was confirmed that a uniform solid image could be formed with a small amount of ink even on a recording medium made of a polyolefin resin having a low wetting tension.
Depending on the degree of hardening or thickening before pressing, the degree of filling of the solid part and the degree of crushing of the solid part edge change, but compared with Comparative Examples 1 and 2, which were completely cured before pressing, Partial filling has been improved. Further, although it was impossible to resolve in Comparative Example 3 in which the viscosity was not increased before pressing, it was found that sufficient resolution can be maintained in the present invention.
The OD value of the solid part was 1.7 in Example 3 and 1.2 in Comparative Example 1, and it was found that a sufficient image density can be obtained with a small amount of ink according to the present invention.
Further, in the process of Example 3, when the ink droplets were peeled off after being deformed without being cured and cured after peeling, the ink droplets separated into two layers adhered to the surface of the pressing member, and the image density was also reduced. Declined.
In addition, if an endless belt is produced with the film made from the polypropylene which carried out the single-sided corona treatment used in the said Example, and the untreated surface is used as a press member, it can also be set as an aspect like FIG.
Further, when the pressure is not applied after the thickening, the effect on the image is the same as that of the comparative example 1 because it is completely cured in two steps.

JP 2010-194875 A JP 2007-15241 A JP 2006-56199 A

Claims (8)

  A step of forming an image by ejecting an 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 thickening ink droplets constituting the image, a thickened ink An image forming method comprising: a step of pressing a droplet with a pressing member; a step of irradiating an active energy ray in a pressed state to cure the ink droplet; and a step of peeling the pressing member.   2. The image forming method according to claim 1, wherein the step of increasing the viscosity of the ink droplet is performed by irradiation with an active energy ray.   The image forming method according to claim 1, wherein a member that transmits active energy rays is used as the pressing member.   The image forming method according to claim 1, wherein the recording medium is a film made of a polyolefin resin.   Means for 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, means for thickening ink droplets constituting the image, and thickened ink An image forming apparatus comprising: means for pressing a droplet with a pressing member; means for irradiating an active energy ray in a pressed state to cure the ink droplet; and means for peeling the pressing member.   6. The image forming apparatus according to claim 5, wherein the means for thickening the ink droplet is an active energy ray irradiation device.   The image forming apparatus according to claim 5, wherein the pressing member is a member that transmits an active energy ray.   The image forming apparatus according to claim 7, wherein the pressing member is an endless belt, and an active energy ray irradiating device is provided inside.

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