Patent Grant
11787179
This application is the U.S. National Phase under 35 U.S.C. § 371 of International Application PCT/JP2019/040291, filed Oct. 11, 2019, which claims priority to Japanese Patent Application No. JP2018-197387, filed Oct. 19, 2018. The International Application was published under PCT Article 21(2) in a language other than English.
The present invention relates to an inkjet printing device.
As described in Patent Literature 1, an art of irradiating ultraviolet light at low oxygen concentration onto an ink on a target base printing material immediately after it has been inkjet-printed, to polymerize the surface layer of the ink, and then irradiating an electron beam (hereinafter also referred to as “EB”) to polymerize the deep part and thereby cure the entirety of the ink, is known.
Also, as described in Patent Literature 2, an art of applying corona discharge treatment in an ambience of below 20000 ppm in oxygen concentration to an ink on a target base printing material immediately after it has been inkjet-printed, to polymerize the surface layer of the ink, and then irradiating an electron beam to polymerize its deep part and thereby cure the entirety of the ink, is known.
While these curing means reportedly do not require compounding of a photopolymerization initiator into the ink, they do require an ambience of low oxygen concentration.
The aforementioned background arts, while allowing an energy beam polymerizable ink containing no photopolymerization initiator to be cured without fail, still require a region of particularly low oxygen concentration to be formed. Particularly in the case of the invention described in Patent Literature 1, ultraviolet light may have to be irradiated after all, which makes it difficult, in practice, to cure the surface layer of the energy beam-curable ink containing no photopolymerization initiator.
Furthermore, in the case of using corona discharge treatment, performing the treatment in a stable manner is difficult unless the distance between the electrodes is sufficiently reduced to around several millimeters. In this case, depending on the thickness of the printing paper and degree of vertical movement of the printing paper, the printed ink may contact the electrodes before its surface cures, and disturb the printing as a result. Also, depending on the intensity of corona discharge treatment, the surface of the paper or other target base printing material may change its property where the ink is not deposited.
An object of the present invention is to obtain a device that allows the ink used in printing to be cured without fail, even when it contains no photopolymerization initiator, without modifying the property of the surface of the target base printing material.
As a result of studying in earnest to achieve the aforementioned object, the inventors of the present invention completed the invention as described below.
According to the printing device proposed by the present invention, a device that can achieve inkjet-printed images having good cured film resistance by, after two or more colored inks have been printed, allowing the surface of the printed inks to be cured by atmospheric-pressure plasma and then irradiated with an electron beam (EB) and cured so that the ink dots will be cured without fail both on the surface and inside, is obtained.
Also, the device can achieve images having good cured film resistance because, when atmospheric-pressure plasma is irradiated after each color has been printed and an electron beam (EB) is irradiated after all colors have been printed, the dots of different colored inks will not smudge even when overlaid and thus high-quality images can be achieved as a result, while the dots will also be cured without fail both on the surface and inside.
In addition, the device irradiates atmospheric-pressure plasma to actively cure inks, while also preventing the paths of inks from being disturbed or the shapes of printed inks from being disturbed by air flows on the target printing surface.
The device proposed by the present invention is explained in detail below.
<Inkjet Printing Part>
For the inkjet printing part under the present invention, a structure comprising any of various known inkjet nozzles for printing inks of two or more colors, or a structure comprising a nozzle conforming to any known inkjet method, may be adopted.
And, for the inkjet printing part, which prints on coated paper, plain paper, various resin films, laminate films having metal layers and metal compound layers, and other known target base printing materials that can be inkjet-printed, one based on any known operating principle may be adopted.
Such inkjet printing part may be fitted with an inkjet nozzle head in such a way that it moves in the direction perpendicular to the moving direction of the target base printing material and in the direction parallel to the surface of the target base printing material, or may have a fixed inkjet nozzle like a line-head type.
Here, it should be noted that, while the target base printing material to be conveyed can be supported with backup rollers that turn at a constant speed, backup rollers need not be provided.
The inkjet nozzle, or nozzles, is/are constituted by one or more nozzles corresponding to one or more colors. Printing data is calculated to obtain an accurate printing location for each color (location at which the ink is ejected from each nozzle), after which an ejection timing for each colored ink from each inkjet nozzle is obtained to allow for printing at this printing location, and inkjet printing is performed based on this calculation result.
(Plasma Ejection Port (Provided as One Piece with Inkjet Nozzle Head)
The plasma ejection port under the present invention is designed to introduce atmospheric-pressure plasma formed by the atmospheric-pressure plasma irradiation device 10 shown in
The atmospheric-pressure plasma irradiation device 10 shown in
Under the present invention, the plasma ejection port is intended, after inks of multiple colors have been printed, to simultaneously cure these multiple inks all together.
A plasma ejection port for performing this atmospheric-pressure plasma irradiation may be provided, in the case that the multi-color serial head method is adopted, on the same head as an inkjet nozzle on the downstream side relative to the movement of the target base printing material, or it may be provided separately from the inkjet head so that it can be moved, etc., as desired. Also, a plasma ejection port that ejects atmospheric-pressure plasma may be provided as one piece with an inkjet nozzle of the line head method.
Under both the serial head method and the line head method, a configuration in which a plasma ejection port is provided on the same head as the inkjet nozzle is possible, where inkjet nozzles for two or more given colors are provided on the same head as a plasma ejection port, and one or more such heads are installed. Also, inkjet nozzles N assigned to multiple colors, respectively, may be provided on the same head as plasma ejection ports 21, as shown in
Furthermore, as shown in
It should be noted that the layouts shown in
Here, the basic structure of the line head method is one where, as shown in
Furthermore, a cover C for covering each plasma ejection port 21 may be provided and the plasma ejection port may be provided in a manner oriented into the cover so as to increase the concentration of atmospheric-pressure plasma in the ambience inside the cover.
Also, the atmospheric-pressure plasma used under the present invention includes all gases resulting from the plasma modification of material gases.
When each plasma ejection port itself is provided between or near inkjet printing nozzles for different colors and moves with these nozzles as one piece, it will irradiate atmospheric-pressure plasma onto inks immediately after they have been printed, and therefore one that irradiates atmospheric-pressure plasma over a range of preferably 1 to 10 mm, or more preferably 1 to 5 mm, in diameter may be adopted.
During printing, the inkjet nozzles may be moved back and forth with respect to the surface of the target base printing material. In this case, a nozzle that ejects atmospheric-pressure plasma may be provided for each set, and between sets, of nozzles assigned to multiple colors, among the inkjet nozzles for multi-color printing. Furthermore, not only between the color-specific nozzles, but nozzles that eject atmospheric-pressure plasma may also be provided, one each, on the outer sides (outer sides in the width direction of the target base printing material) of the nozzles positioned at both ends of the arranged color-specific nozzles.
Similarly, when inkjet nozzles are provided based on the line head method, a plasma ejection port may be provided in such a way that it can eject atmospheric-pressure plasma onto multiple colored inks after the multiple colored inks have been printed.
However, cured inks must not collect at the opening part of the inkjet nozzle N due to the atmospheric-pressure plasma ejected from the plasma ejection port 21 that ejects atmospheric-pressure plasma. Accordingly, the atmospheric-pressure plasma to be ejected from the plasma ejection port 21 that ejects atmospheric-pressure plasma must be ejected from the plasma ejection port 21 for atmospheric-pressure plasma which is provided in a manner described in A or B below, so that it will contact uncured inks deposited on the surface of the target base printing material S but will not contact the inkjet nozzle N:
A. As shown in
B. As shown in
If the device in
In the cases of
As a result, the next colored ink, when ejected, will not mix with the previous colored ink whose surface has already been cured to some degree by atmospheric-pressure plasma, and consequently the printed outlines will become clearer.
It should be noted that, in other inkjet printing devices, ink jet nozzles N for all colors used in printing may be provided on the print head and multiple plasma ejection ports 21 corresponding to the respective colors may also be provided on the same head, as shown in
(Plasma Ejection Port (Provided Separately from Inkjet Nozzle))
Under the present invention, the plasma ejection port may be provided separately from the inkjet nozzle head. In this case, one or more heads, each printing only one color, will be placed along the moving direction of the target base printing material. Alternatively, one or more plasma ejection devices will be provided on the downstream side of a head or heads combining multiple colors.
In
After the first colored ink has been printed by this inkjet nozzle N, the target base printing material is conveyed to a plasma treatment device 40 similar to the plasma treatment device shown in
And, the generated atmospheric-pressure plasma P travels through a plasma ejection tube 43 and is irradiated on the ink on the target base printing material. Here, a cover 45 may be provided to increase the concentration of atmospheric-pressure plasma inside the cover 45.
When inkjet printing is performed based on the line head method, a plasma treatment device may be provided for, and on the downstream side of, each head conforming to the line head method and used for printing one colored ink, or a plasma treatment device may be provided for, and on the downstream side of, each head used for printing two or more colored inks. And, a plasma treatment device may be provided on the downstream side of the foregoing so that, once all colored inks have been printed, atmospheric-pressure plasma can be ejected onto all of the colored inks.
Also, a backup roller 44 may be provided on the side of the target base printing material S opposite to the plasma ejection tube 43, where this roller is grounded or an electric charge opposite to that carried by the atmospheric-pressure plasma is applied to it, so that atmospheric-pressure plasma will exist on the surface of the target base printing material S at high concentration.
It should be noted that
Alternatively, in
And, although this is not illustrated, the aforementioned printing with an inkjet ink using the inkjet nozzle N shown in
In
For the front-end plasma treatment device 30 that shares a common basic constitution with the plasma treatment device 40, a plasma treatment device comprising a discharge space, into which atmospheric-pressure plasma generation gas G is introduced, and which has an ejection port and is formed by an insulator 32, as well as a pair of discharge electrodes 31 that are facing each other over a spacing of approx. 0.5 to 5.0 mm to generate an electric field in this discharge space, is used.
This plasma treatment device is such that plasma generation gas G is supplied to the discharge space, while the pressure inside the discharge space is maintained near atmospheric pressure, and a voltage is further applied to the pair of discharge electrodes 31, and when a voltage exceeding the discharge starting voltage is applied to generate discharge in the discharge space, atmospheric-pressure plasma P will generate in the discharge space.
And, the generated atmospheric-pressure plasma P travels through a plasma ejection tube 33 and irradiates the ink on the target base printing material. Here, a cover 35 may be provided to increase the concentration of atmospheric-pressure plasma inside the cover 35.
Also, a backup roller 34 may be provided on the side of the target base printing material S opposite to the plasma ejection tube 33, where this backup roller is grounded or an electric charge opposite to that carried by the atmospheric-pressure plasma is applied to it, so that atmospheric-pressure plasma will exist on the surface of the target base printing material S at high concentration.
(Installation of Device for Grounding or Charging)
For each inkjet nozzle and/or nozzle that ejects atmospheric-pressure plasma, a backup roller or bar that supports the non-printing surface of the target base printing material may be provided at a position facing the nozzle via the target base printing material. And, this backup roller or bar may be grounded or charged to the polarity opposite to the polarity of the plasma particles beforehand, so that an electric charge that attracts atmospheric-pressure plasma and improves the plasma density at the ink surface on the target base printing material can be applied to cause the plasma ejected from the plasma ejection port to change its direction and hit the ink on the target base printing material.
Also, a small cover may be provided in a manner enclosing the plasma ejection port and uncured ink on the target base printing material, so that plasma can be ejected into the cover to cause the plasma present inside the cover to move toward the top of the target base printing material.
By keeping air flows containing plasma from directly blowing against the ink, as described above, the possibility of individual ink dots or their outlines spreading as a result of air flows blowing against the uncured ink on the target base printing material can be reduced.
Also, by providing such backup roller or bar, the density of atmospheric-pressure plasma can be lowered simultaneously in the ambience of the inkjet nozzle and its surroundings. As a result, depositing/collection of cured ink on the inkjet nozzle can be prevented.
(Atmospheric-Pressure Plasma Irradiation Device)
For the plasma irradiation device that supplies plasma to the plasma ejection port, a remote atmospheric-pressure plasma irradiation device may be adopted. Plasma is a high-energy gas that generates when discharge is caused by applying high voltage between electrodes. Atmospheric-pressure plasma is a type of plasma generated under atmospheric pressure, and normally used for such purposes as hydrophilizing the surfaces of material.
For such device, a plasma treatment device comprising a discharge space with an outlet, as well as discharge electrodes facing each other over a spacing of approx. 0.5 to 5.0 mm to generate an electric field in this discharge space, like the one shown in
The target base printing material can be plasma-treated by blowing against it this atmospheric-pressure plasma P jetted from the ejection port. For such plasma irradiation device, the RT series or APT series manufactured by Sekisui Chemical Co., Ltd., any appropriate plasma treatment device offered by Yamato Material Co., Ltd., or the like, or any of plasma irradiation devices used with the devices described in Japanese Patent Laid-open No. 2004-207145, Japanese Patent Laid-open No. Hei 11-260597, and Japanese Patent Laid-open No. Hei 3-219082, may also be used.
Also, for the gases used for atmospheric-pressure plasma, air, oxygen, nitrogen, etc., may be adopted.
It should be noted that the aforementioned spacing between the electrodes depends on the applied voltage, and a high-frequency, pulse-wave, microwave or other electric field is applied to the electrodes to generate plasma.
Above all, preferably pulse waves are applied in consideration of the fact that the time needed for an electric field to rise and fall (rise and fall refer to voltage increasing and decreasing continuously) is preferably short. Here, the time needed for an electric field to rise and fall is preferably 10 μs or shorter, or more preferably 50 ns to 5 μs.
The electric field intensity that generates between the electrodes in the plasma irradiation device is 1 kV/cm or higher or preferably 20 kV/cm or higher, and/or no higher than 1000 kV/cm or preferably no higher than 300 kV/cm.
Also, when an electric field is applied using pulse waves, their frequency is preferably 0.5 kHz or higher, but it may be around 10 to 20 MHz, or around 50 to 150 MHz.
Furthermore, the electric power applied between the electrodes is 40 W/cm or lower, or preferably 30 W/cm or lower.
It is better that the aforementioned electrodes do not come in direct contact with the gas, in order to achieve stable plasma discharge. For this reason, desirably the electrode surface is coated or otherwise covered with an insulating film using any known means. Such insulating film may be quartz, alumina, or other glass material, or ceramic material, for example. Depending on the situation, barium titanate, silicon oxide, aluminum nitride, silicon nitride, silicon carbide, or other dielectric body with a dielectric constant of 2000 or lower may also be adopted.
A remote atmospheric-pressure plasma irradiation part such as those discussed above is one, for example, comprising an atmospheric-pressure plasma irradiation part, a unit including a plasma ejection tube, etc., and a power supply part, among the aforementioned known devices. Based on the above device, multiple parts that eject atmospheric-pressure plasma may further be arranged in their width direction, or each nozzle may further be shaped as a slit, in order to treat the target base printing material uniformly in the width direction.
A schematic view of a cross-section of such remote atmospheric-pressure plasma irradiation part is shown in
It should be noted that the atmospheric-pressure plasma ejected from the nozzle that ejects atmospheric-pressure plasma may irradiate beforehand the printing surface of the target base printing material to be supplied to the inkjet nozzle, on the upstream side of the inkjet nozzle. This allows the atmospheric-pressure plasma to remain briefly on the printing surface of the target base printing material, so that inkjet printing can be performed while the plasma still remains. As a result, the ink that has deposited on the surface of the target base printing material can be cured, albeit slightly, at the deposited part.
<Electron Beam Irradiation Part>
The function of the electron beam irradiation part under the present invention is to act on the colored inks whose surface has been cured by the irradiation of atmospheric-pressure plasma on the upstream thereof, either concurrently with inkjet printing or after inkjet printing, using the plasma ejection port provided as one piece with the inkjet nozzle, or plasma ejection port provided separately from the inkjet nozzle, and completely cure the inks internally and externally in their entirety. Adopting the electron beam irradiation part as described above, in combination with the adoption of atmospheric-pressure plasma ejection, eliminates the need for the inkjet ink composition to contain a polymerization initiator or related auxiliary agents, etc. Furthermore, high-contrast images can be formed without causing the boundaries of adjacent colors to smudge.
As for the electron beam generation device that constitutes the electron beam irradiation part, any known device may be adopted.
And, an introduction/irradiation device for irradiating the electron beam generated by the electron beam generation device, over the ink on the target base printing material, is provided.
Also, the ambience in which to irradiate the electron beam is preferably one of nitrogen, rare gas, or other inert gas, in the interest of facilitating the curing.
And, the target base printing material must be passed through the electron beam irradiation part in such a way that the electron beam generated by this electron beam generation device will be irradiated uniformly over the ink on the surface of the target base printing material. Inside the electron beam irradiation part, for example, the electron beam can be irradiated on the printing surface of the target base printing material in a manner irradiating in the shape of a curtain. It should be noted that an appropriate level of the acceleration voltage of electron beam, which can be changed in a timely manner according to the specific gravity and film thickness of the ink, is 20 to 300 kV. Preferably the irradiation quantity of electron beam is in a range of 0.1 to 20 Mrad.
Such electron beam irradiation part, in combination with the irradiation of atmospheric-pressure plasma, can cure energy beam-curable inkjet printing inks. Furthermore, there is no need to compound any polymerization initiator, curing agent, auxiliary polymerization initiation agent, etc., in the inks beforehand. The inks can be cured sufficiently without having to compound these components into the ink.
By supplying a polyethylene terephthalate film of 21 cm in width to a line-type inkjet printing device so that a printing speed of 12 m/min would be achieved, each of the compositions of Examples and Comparative Examples as shown in Table 1 below was printed and then cured under the respective conditions shown in Table 1. In the table, the compounding quantities of compositions are expressed in mass.
It should be noted that the examples where “Y” is indicated in “Plasma curing between colors with gas species N2” are examples where an atmospheric-pressure plasma whose gas species was nitrogen gas was irradiated from a slit of 300 mm in width at a gas flow rate of 30 L/min on the inkjet printing ink of each color after the entire color had been printed. “Y” in “EB irradiation, 30 kGray, 90 kV” indicates that, after all colors had been printed, an electron beam generated at a voltage of 90 kV was irradiated on the ink to 30 kGray in a nitrogen gas-purged ambience.
(Removal of Coating Film)
Using a Gakushin-type rubbing tester (manufactured by Daiei Kagaku Seiki Mfg. Co., Ltd.), the cured coating film surface was rubbed by moving a friction element, for which unbleached muslin No. 3 was used, back and forth 200 times over it with a 500-g load, and the coating film was evaluated for removal.
◯: The coating film was not removed.
Δ: The coating film was slightly removed.
X: The coating film was removed.
(Tackiness)
◯: When the coating film surface was touched with a finger, no tackiness was found on the coating film surface.
X: When the coating film surface was touched with a finger, tackiness was found on the coating film surface.
Pigment dispersant: Solsperse 39000 (manufactured by Lubrizol Corporation)
PO-modified NPGDA: Propoxylated modified (2) tripropylene glycol diacrylate (SR492, manufactured by Sartomer Co., Inc.)
EO(3)-modified trimethylolpropane triacrylate: (SR354, manufactured by Sartomer Co., Inc.)
TPO: 2,4,6-trimethylbenzoyl diphenyl phosphine oxide (manufactured by Lamberti S.p.A)
Irgacure 184 (manufactured by BASF SE)
DETX: 2,4-diethyl thioxanthone (manufactured by Lambson Ltd.)
BYK333: Silicone additive (manufactured by BYK-Chemie GmbH)
According to Table 1 above, plasma-treating each color after that color had been printed, prevented the coating film from exhibiting tackiness and being removed even when rubbed with unbleached muslin No. 3, as is evident from the Examples. When plasma was not irradiated after printing, on the other hand, the coating film was slightly removed.
Also, when plasma was irradiated but EB was not, printing manifested some removal of the coating film and tackiness.
Table 2 shows that Example 8, where plasma treatment and EB irradiation were performed successively only after a successive inkjet printing of four colored inks, achieved printing free from removal of the coating film or tackiness.
By contrast, Comparative Example 6, where plasma irradiation was not performed, resulted in removal of the coating film, while Comparative Example 7 where EB curing was not performed resulted in removal of the coating film as well as poor outcome in terms of tackiness.
According to the Examples above, the device proposed by the present invention can achieve printing free from removal of the coating film or tackiness.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-197387 | Oct 2018 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/040291 | 10/11/2019 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2020/080310 | 4/23/2020 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5477784 | Floegel | Dec 1995 | A |
| 20060164487 | Kadomatsu et al. | Jul 2006 | A1 |
| 20100225696 | Shibata | Sep 2010 | A1 |
| 20150030823 | Stamatoukos et al. | Jan 2015 | A1 |
| 20150251453 | Nakai et al. | Sep 2015 | A1 |
| 20170028742 | Ohnishi | Feb 2017 | A1 |
| 20180147831 | Du Buf et al. | May 2018 | A1 |
| 20180154576 | Chen et al. | Jun 2018 | A1 |
| 20190322107 | Ozawa | Oct 2019 | A1 |
| Number | Date | Country |
|---|---|---|
| 102010029939 | Dec 2011 | DE |
| 2002253952 | Sep 2002 | JP |
| 2003200565 | Jul 2003 | JP |
| 2003218099 | Jul 2003 | JP |
| 2003300315 | Oct 2003 | JP |
| 2003311940 | Nov 2003 | JP |
| 2013129123 | Jul 2013 | JP |
| 2015153652 | Aug 2015 | JP |
| 2015180529 | Oct 2015 | JP |
| 2017132895 | Aug 2017 | JP |
| 2018094758 | Jun 2018 | JP |
| 2018099871 | Jun 2018 | JP |
| 6353618 | Jul 2018 | JP |
| 2018140784 | Sep 2018 | JP |
| 2011154184 | Dec 2011 | WO |
| 2015093609 | Jun 2015 | WO |
| 2018017058 | Jan 2018 | WO |
| 2018105621 | Jun 2018 | WO |
| Entry |
|---|
| Extended European Search Report (EESR) dated Jul. 6, 2022, issued for European counterpart patent application No. EP19872292.8 (9 pages). |
| Notification Concerning Transmittal of International Preliminary Report on Patentability (PCT/IB/326) and Notification of Transmittal of Translation of the International Preliminary Report on Patentability (PCT/IB/338) dated Apr. 15, 2021, with International Preliminary Report on Patentability (PCT/IB/373) and Written Opinion of the International Searching Authority (PCT/ISA/237), for corresponding international application PCT/JP2019/040291 (26 pages). |
| International Search Report (ISR) dated Jan. 7, 2020, issued for International application No. PCT/JP2019/040291. (2 pages). |
| A Notice of Reasons for Refusal issued by the Japanese Patent Office dated Jun. 7, 2022, for Japanese counterpart application No. 2018-197387. (3 pages). |
| A Notice of Reasons for Refusal issued by the Japanese Patent Office dated Dec. 20, 2022, for Japanese counterpart application No. 2018-197387. (2 pages). |
| Number | Date | Country | |
|---|---|---|---|
| 20210347170 A1 | Nov 2021 | US |
