JP2014172224A - Inkjet printer, print method and ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet printer for properly satisfying both a condition for enhancing adhesiveness of ink to media and a condition for properly preventing oozing, when using solvent UV ink.SOLUTION: The inkjet printer comprises an inkjet head 13 for injecting ink including at least a pigment, an ultraviolet curable resin curable by an ultraviolet ray, a photoinitiator, a volatile organic solvent and a ketone-based or terpene-based substance, having viscosity of 3 mPa sec-18 mPa sec (the room temperature 25°C) and having the viscosity of 20 mPa sec or more in a state of volatilizing-removing the volatile organic solvent, from a plurality of discharge ports, a print heater 17 being heating means for volatilizing-removing the volatile organic solvent included in an ink drop by heating the ink drop impacted on a media surface and UV radiation means 16 for radiating the ultraviolet ray to the ink drop from which the volatile organic solvent is volatilizing-removed on the media surface.

Description

  The present invention relates to an inkjet printer, a printing method, and ink.

Solvent inks and UV (ultraviolet) curable inks can be cited as inks used in ink jet printers. Solvent ink is mainly a pigment and binder resin dispersed in a volatile solvent. The ink is jetted from the inkjet head onto the surface of the medium (printing medium), and the volatile solvent is volatilized by a heater at the bottom of the medium. As a result, the image is printed with the ink fixed on the surface of the medium.
On the other hand, a UV (ultraviolet) curable ink is composed of a pigment, an ultraviolet curable resin (monomer or / and oligomer), a polymerization initiator, and the like. After UV ink is jetted onto a medium from an inkjet head, ultraviolet irradiation means is used. The resin is cured by irradiating with ultraviolet rays to fix the ink on the media surface and print an image.

International Publication No. 2004/094150 JP 2010-280828 A JP 2009-280466 A

Printed using the solvent ink has an advantage that glossiness may be obtained because the viscosity of the ejected ink is low, the applied ink is thin, and the surface is flat. However, since the content of the volatile organic solvent is higher than 80 wt% (weight percentage), ink bleeds out when it hits the medium, resulting in a problem that the image is not fine. Further, it is necessary to use vinyl chloride, rubber or dedicated paper as a medium, and there is a disadvantage that the selectivity of the material of the medium is narrow.
In Japanese Patent Application Laid-Open No. 2004-133826, the applicant of the present application uses an ink jet printer including a pyrite heater for preheating a support and a heater for early heating of ink landed on a platen (recording medium) on the support. Is disclosed.
On the other hand, UV curable ink does not contain VOC (volatile organic compound), so it is environmentally friendly, and the viscosity of the ink is high, so that the ejected ink does not spread and a high-definition image can be obtained. . However, since the viscosity is high, there is a problem that clogging occurs in the inkjet head, and in order to stably eject ink from the inkjet head, for example, measures are taken to reduce the viscosity of the ejected ink by heating the inkjet head. ing. However, the ink that has landed on the surface of the media has a temperature drop and a viscosity that immediately rises, so that the ejected ink is difficult to spread, and the surface is uneven. Furthermore, since UV rays are cured immediately by a UV lamp installed integrally with the inkjet head, the unevenness is fixed as it is, the image quality is likely to be mat-like, and curing fringes are likely to occur in the scanning direction of the head. There were drawbacks. Therefore, it is conceivable to reduce the unevenness of the ink droplet surface by adding an organic solvent to the UV curable ink to reduce the unevenness of the ink droplet surface, but there is a concern that the thickness of the ink droplet becomes thin and the UV sensitivity decreases.

  Therefore, the applicant has previously filed a patent application for an ink and an ink jet printer that can print a high-definition image with no unevenness, high flatness, and glossiness. Reference 2). In Patent Document 2, a volatile organic solvent is added to a UV curable ink having a viscosity of 20 mPa · sec or more (room temperature 25 ° C.), which includes at least a pigment, an ultraviolet curable resin that is cured by ultraviolet rays, and a photopolymerization initiator. It is disclosed that an ink having a viscosity of 3 mPa · sec or more and 18 mPa · sec (room temperature 25 ° C.) or less is used. In addition, it is disclosed that by using such an ink, an inkjet printer can print a high-definition image having no unevenness, high flatness, and gloss.

  In addition, the configuration of the ink and ink jet printer disclosed in Patent Document 2 can print high-definition images with high flatness and gloss while suppressing the occurrence of bleeding. Application is expected. Therefore, for the ink disclosed in Patent Document 2 or the similar ink, it is desired to find characteristics more suitable for various applications through further intensive research. SUMMARY An advantage of some aspects of the invention is that it provides an ink jet printer, a printing method, and ink that can solve the above-described problems.

  In addition, as an invention partially related to the present invention described below, the present applicant has also filed an application regarding an ink containing a coloring material and a predetermined ketone compound (Patent Document 3). However, the ink used in Patent Document 3 is completely different in basic configuration from the ink in the present invention.

  The inventor of the present application conducted intensive research on the more preferable characteristics of the ink disclosed in Patent Document 2 or the solvent UV ink (SUV ink) which is the same ink. In this earnest study, attention was paid to the adhesiveness of ink to media.

  The solvent UV ink may be used, for example, when printing on a large vinyl chloride sheet for outdoor advertising. In such applications, for example, high weather resistance and scratch resistance are required for the media after printing. And in order to implement | achieve high weather resistance, abrasion resistance, etc., it is thought that it is necessary to fully improve the adhesiveness of the ink with respect to a medium, for example.

  In this regard, in the case where printing is performed using the solvent UV ink, in order to increase the adhesion of the ink after curing to the medium, for example, the volatile organic solvent contained in the ink and the surface of the medium are allowed to pass for a certain period of time. It is conceivable to allow ink to penetrate into the inside of the medium. For example, when using media such as vinyl chloride sheets, the surface of the media will be eroded to some extent if the volatile organic solvent (for example, n-hexane) contained in the ink is sufficiently brought into contact with the surface of the media. Thus, it is considered that the adhesive property of the ink after curing is greatly improved.

  However, on the other hand, when printing using solvent UV ink, in order to print without causing bleeding, the volatile organic solvent can be removed immediately after the ink droplets have landed on the media. is necessary. In this case, since only the monomer or the like remains immediately after landing on the medium, the ink does not penetrate into the inside of the medium, for example, the state where the medium and the volatile organic solvent are sufficiently in contact with each other In comparison, the adhesiveness decreases. Therefore, when printing is performed using the solvent UV ink, the condition for improving the adhesion of the ink to the medium and the condition for appropriately preventing bleeding are usually in a trade-off relationship. As a result, in the conventional ink configuration, it is sometimes difficult to achieve both of these conditions appropriately.

  In order to improve the adhesion of the ink to the media, the contact time between the volatile organic solvent contained in the ink and the surface of the media is not increased, but the content of the volatile organic solvent in the ink is increased. It is also possible. However, in this case as well, the increase in the content of the volatile organic solvent is a condition in which bleeding is more likely to occur. For example, when a large amount of volatile organic solvent is to be volatilized and removed in a short time, it is necessary to increase the heating temperature of the media. Therefore, in this case, the heat resistance temperature of the media may be exceeded, and problems such as cockling may occur. Accordingly, in this case as well, it is difficult to properly balance the condition for improving the adhesion of the ink to the medium and the condition for appropriately preventing bleeding.

  Based on the recognition of such problems, the inventors of the present application have further conducted intensive research and appropriately increased the adhesion of the ink to the media by adding a ketone-based or terpene-based substance to the solvent UV ink. Found to get. In addition, it has been found that the above trade-off problem can be solved and the conditions for improving the adhesion of the ink to the medium and the conditions for appropriately preventing the bleeding can be appropriately made compatible. In order to solve the above problems, the present invention has the following configuration.

  (Configuration 1) 3 mPa containing a support for supporting a medium, at least a pigment, an ultraviolet curable resin cured by ultraviolet rays, a photopolymerization initiator, a volatile organic solvent, and a ketone or terpene material. A plurality of inks having a viscosity of sec to 18 mPa · sec (room temperature 25 ° C.) and having a viscosity of 20 mPa · sec or more (room temperature 25 ° C.) in a state where the volatile organic solvent is volatilized and removed. An ink jet head that ejects ink droplets from the outlet and lands on the surface of the media, and is located on at least one of the back side and the front side of the media, and heats the ink droplets that have landed on the media surface, and is included in the ink droplets A heating means for volatilizing and removing the volatile organic solvent, and ink droplets from which the volatile organic solvent on the media surface has been volatilized and removed are irradiated with ultraviolet rays to thereby produce the ink. And a UV irradiation means for curing the.

  In this configuration, a ketone-based or terpene-based substance (hereinafter referred to as a ketone compound or the like) is an additive added to the ink, and functions as, for example, a media penetrating agent that allows the ink to penetrate into the media. Further, as the medium, for example, a medium whose surface is eroded by the ketone compound or the like is used. As such a medium, for example, a sheet such as vinyl chloride or a medium such as tarpaulin can be suitably used. In addition, for example, the above-mentioned ketone compound is further added to the solvent UV ink (SUV ink) in which a volatile organic solvent is added to a UV curable ink having a viscosity of 20 mPa · sec or more (room temperature 25 ° C.). Ink. In this ink, the content of the volatile organic solvent is preferably 30% by weight or more and 90% by weight or less, for example. For example, n-hexane can be suitably used as the volatile organic solvent. Moreover, it is preferable that the content rate of the said ketone compound etc. shall be 5-10 weight%, for example.

  In such a configuration, for example, the viscosity of the ink used is 3 mPa · sec or more and 18 mPa · sec or less, so that the ink jet can be favorably ejected without causing clogging. Further, the surfaces of the plurality of ink droplets that have landed on the medium (printing medium) have gentle irregularities. Further, ink that has a viscosity of 20 mPa · sec or more (room temperature 25 ° C.) in a state where the volatile organic solvent is volatilized and removed (for example, an ink containing a high-viscosity UV curable resin of 20 mPa · sec or more) is used for landing. Thereafter, the volatile organic solvent is immediately removed by volatilization with a heating means, whereby the viscosity of the ink can be increased to a viscosity at which bleeding does not easily occur. Further, it is possible to appropriately prevent the ink from bleeding even before the ink is cured by irradiating with ultraviolet rays.

  Further, in the state where the volatile organic solvent is removed by the heating means, the ink state is sufficiently high in viscosity so as not to cause bleeding, but is not cured. Therefore, the ink dots can be gradually spread and flattened on the medium. Therefore, in such a configuration, for example, before the ink is cured by irradiation with ultraviolet rays, the unevenness of the surface of the ink dots can be eliminated and the surface can be sufficiently and appropriately flattened. Further, a high-gloss and high-quality image can be obtained by curing and fixing with ultraviolet rays. Therefore, with this configuration, for example, it is possible to appropriately prevent both ink bleeding and appropriately flattening ink dots. In addition, this makes it possible to appropriately obtain a high-definition image with glossiness. In addition, when configured in this way, the thickness of the landed ink droplets is large, so that there is an advantage that the ultraviolet curing sensitivity is excellent. In addition, for example, it is possible to print on various media such as plastics such as PET, PP, PC, and acrylic, metal, or glass.

  In addition, in such a configuration, by using an ink to which a ketone compound or the like is added, for example, even when the volatile organic solvent is volatilized and removed immediately after landing of the ink droplet, the surface of the medium is appropriately eroded by the ink. be able to. In addition, this makes it possible to improve the adhesion of the ink to the medium while suppressing the occurrence of bleeding. Therefore, with this configuration, for example, in the case of using an ink containing an ultraviolet curable resin and a volatile organic solvent (hereinafter, referred to as a solvent UV ink or the like), the conditions for improving the adhesion of the ink to the medium and bleeding are reduced. It is possible to more appropriately balance the conditions to prevent appropriately.

  Further, when configured in this manner, for example, it is not necessary to increase the content of the volatile organic solvent in the ink in order to improve the adhesiveness of the ink. Therefore, for example, it is not necessary to excessively increase the heating temperature of the media. Therefore, if comprised in this way, it can also prevent appropriately that problems, such as cockling, arise by the heating of a medium, for example. For example, the heating means preferably performs heating so that the temperature of the support (platen or the like) is, for example, 40 to 60 ° C. More preferably, this temperature is 40-50 degreeC, for example. With this configuration, for example, even when using a medium having a low heat-resistant temperature (such as a vinyl chloride medium), conditions for improving the adhesion of the ink to the medium while appropriately suppressing the occurrence of cockling, and bleeding It is possible to properly satisfy both conditions for appropriately preventing the occurrence of the problem.

  In this configuration, when a ketone substance is used as an additive, for example, 2-heptanone, 2-octanone, 2-nonanone, 3-nonanone, 2-decanone, 2-undecanone, 5-dodecanone, etc. are used. Can be considered. When a terpene-based substance is used as an additive, for example, sesquiterpenes (bp = 220 ° C. to 250 ° C.), dipentene (bp = 165 ° C. to 183 ° C.), α-terpineol (b .P = 225 ° C.), D-limonene (bp = 175 ° C.), and the like.

(Configuration 2) The ketone-based or terpene-based substance is a ketone compound represented by the following general formula (1).
R ¹ —CO—R ² (1)
[In General Formula (1), R ¹ and R ² each independently represents an alkyl group having 1 to 10 carbon atoms. However, the total carbon number of R ¹ and R ² is 5 to 11, and when the total carbon number of R ¹ and R ² is 6 or more, R ¹ and R ² may form a ring. ]
The inventor of the present application has studied the ketone compound represented by the general formula (1) as a substance capable of more appropriately satisfying the conditions for improving the adhesiveness of the ink to the medium and the conditions for appropriately preventing bleeding by intensive research. It was found that it is preferable to use If comprised in this way, the conditions which improve the adhesiveness of the ink with respect to a medium, for example, and the conditions which prevent a bleeding appropriately can be compatible more appropriately.

  (Configuration 3) The ketone compound is 2-heptanone or 2-octanone. The inventor of the present application has found that these ketone compounds have appropriate and sufficient media attack properties in experiments and the like in earnest research, for example, when a vinyl chloride medium is used. If comprised in this way, the adhesiveness of the ink with respect to a medium can be improved more appropriately, for example. Moreover, when using solvent UV ink etc. by this, the conditions which improve the adhesiveness of the ink with respect to a medium, and the conditions which prevent a blurring more appropriately can be compatible more appropriately.

(Configuration 4) The boiling point of the ketone-based or terpene-based substance is 150 ° C to 250 ° C. If comprised in this way, the conditions which improve the adhesiveness of the ink with respect to a medium, for example, and the conditions which prevent a bleeding appropriately can be compatible more appropriately.
In addition, when the boiling point (bp) of the ketone compound or the like used as the additive is less than 150 ° C., there is a concern that the nozzle may be dried. In addition, the medium may be dried before the medium such as vinyl chloride is sufficiently dissolved, and the adhesion of the ink to the medium may not be sufficiently increased. In addition, when the boiling point of a ketone compound or the like used as an additive exceeds 250 ° C., the ink is difficult to dry, and bleeding may not be prevented appropriately.

  (Configuration 5) At least 3 mPa · sec to 18 mPa · sec (room temperature) including at least a pigment, an ultraviolet curable resin cured by ultraviolet rays, a photopolymerization initiator, a volatile organic solvent, and a ketone or terpene material. 25 degrees Celsius) or less, and in a state where the volatile organic solvent is volatilized and removed, an ink having a viscosity of 20 mPa · sec or more (room temperature 25 degrees Celsius) is ejected from a plurality of ejection ports of the inkjet head. The ink droplets are landed on the media surface, and the ink droplets landed on the media surface are heated by heating means located on at least one of the back side and the front side of the media to volatilize the volatile organic solvent contained in the ink droplets. After the removal, the ink droplets are irradiated with ultraviolet rays by UV irradiation means, and the ink droplets are cured and fixed on the media surface. Printing wherein the printing images comprising a sequence of a plurality of ink droplets. If comprised in this way, the effect similar to the structure 1 can be acquired, for example.

  (Configuration 6) At least 3 mPa · sec to 18 mPa · sec (room temperature) including at least a pigment, an ultraviolet curable resin cured by ultraviolet rays, a photopolymerization initiator, a volatile organic solvent, and a ketone or terpene substance. An ink having a viscosity of 20 mPa · sec or more (room temperature 25 ° C.) in a state where the volatile organic solvent is volatilized and removed. If comprised in this way, the effect similar to the structure 1 can be acquired, for example.

  According to the present invention, for example, in the case of using a solvent UV ink or the like, it is possible to appropriately achieve both a condition for improving the adhesion of the ink to the medium and a condition for appropriately preventing bleeding.

1 is a schematic top view showing a main part of an inkjet printer according to an embodiment of the present invention. 1 is a schematic side view showing an inkjet printer according to an embodiment of the present invention.

Hereinafter, an ink, an ink jet printer, and a printing method according to the present invention will be described with reference to the drawings.
First, the ink of the present invention will be described.
<Ink>
The ink of the present invention comprises a monomer (55 to 88% by weight) and an oligomer (0 to 15% by weight), a photopolymerization initiator (6 to 13% by weight), a sensitizer (3 to 30% by weight), a colorant ( Pigment) (3 to 6% by weight) and additives (1 to 8% by weight; dispersant, leveling agent, polymerization inhibitor), and high viscosity UV curable type having a viscosity (25 ° C.) of 30 to 300 mPa · sec. 60 to 85% by weight of n-hexane having a viscosity of 0.32 (20 ° C.) and a boiling point of 69 ° C. is added to the ink, and a ketone compound (ketone-based substance) represented by the following general formula (1) is added to the ink. The viscosity at 25 ° C. is 10 mPa · sec by adding 10% by weight to 10% by weight.
R ¹ —CO—R ² (1)
[In General Formula (1), R ¹ and R ² each independently represents an alkyl group having 1 to 10 carbon atoms. However, the total carbon number of R ¹ and R ² is 5 to 11, and when the total carbon number of R ¹ and R ² is 6 or more, R ¹ and R ² may form a ring. ]
As such an ink, for example, a UV curable ink having a viscosity before addition of n-hexane of about 30 mPa · sec (25 ° C.) is added so that the content in the whole ink becomes 75% by weight. Examples include inks having a viscosity of 8 mPa · sec by adding hexane and further adding a ketone compound.
The monomers and oligomers are ultraviolet curable resins that are cured by ultraviolet rays. The ink may be an ink obtained by further adding the ketone compound to a solvent UV ink (SUV ink) in which a volatile organic solvent is added to a UV curable ink.

  The ink of the present invention uses a UV curable ink composed of a monomer and / or oligomer, a photopolymerization initiator, a sensitizer, a colorant and an additive having a viscosity of 20 mPa · sec or more (room temperature 25 ° C.), The viscosity of the ink is adjusted to 3 mPa · sec to 18 mPa · sec by appropriately adjusting the contents of the volatile organic solvent and the ketone compound. The viscosity of the UV curable ink is preferably 20 mPa · sec or more (room temperature 25 ° C.), more preferably 50 mPa · sec (room temperature 25 ° C.) or more. If it is less than 20 mPa · sec (room temperature 25 ° C.), the bleeding is severe and the speed is high. Bleeding is observed at 20 mPa · sec (room temperature 25 ° C.) or more and less than 50 mPa · sec (room temperature 25 ° C.), but the bleeding speed is low, and the fineness of the image is not lost until it is cured by irradiation with ultraviolet rays. By controlling the time until irradiation, a high-definition image can be obtained. At 50 mPa · sec (room temperature 25 ° C.) or higher, bleeding is not noticeable, at 100 mPa · sec (room temperature 25 ° C.) or higher there is almost no bleeding, and at 1000 mPa · sec (room temperature 25 ° C.) or higher, there is no bleeding.

The content of the volatile organic solvent is preferably 30% by weight or more and 90% by weight or less, and more preferably 50% by weight or more and 70% by weight or less.
In addition, other volatile organic solvents may be used instead of n-hexane, the contact angle is smaller than the UV curable ink, the viscosity is 5 mPa · sec or less, preferably 2 mPa · sec or less, and the boiling point is The organic solvent can be appropriately selected from volatile organic solvents at 200 ° C. or lower, preferably 160 ° C. or lower. For example, isoparaffin hydrocarbons (Idemitsu Kosan IP solvent 1016, IP solvent 1620, etc.), ketones such as cyclohexanone, aromatic hydrocarbons such as toluene and xylene, esters such as dipropylene glycol and monomethyl ether acetate, etc. be able to. Moreover, you may mix and use not only one type but a several volatile organic solvent.

  The pigment, monomer and / or oligomer, and photopolymerization initiator are not particularly limited, and various conventionally known ones can be appropriately selected and used. Further, various additives such as a sensitizer, a dispersant, a leveling agent, a polymerization inhibitor, and the like can be appropriately selected from known ones.

  Since the ink of the present invention contains a volatile organic solvent, the ink viscosity at room temperature can be lowered. Furthermore, by quickly removing the volatile organic solvent by volatilization before UV curing, it is possible to print a high-quality image having a high flatness of the surface of the ink droplet and a glossy feeling.

  Further, as described above, the ink of the present invention contains the ketone compound represented by the general formula (1). Therefore, when a medium (for example, vinyl chloride medium) whose material is eroded by the ketone compound is used, the ketone compound functions as a medium penetrant that allows ink to penetrate into the medium. In this case, even when the volatile organic solvent is volatilized and removed immediately after the ink droplets have landed, the surface of the medium can be appropriately eroded by the ink so that the ink can permeate the medium. In addition, this makes it possible to improve the adhesion of the ink to the medium while suppressing the occurrence of bleeding. Therefore, if comprised in this way, the conditions which improve the adhesiveness of the ink with respect to a medium, for example, and the conditions which prevent a bleeding appropriately can be made compatible appropriately.

  In this case, for example, it is not necessary to increase the content of the volatile organic solvent in the ink in order to improve the adhesion of the ink. Therefore, the drying property of the ink is not lowered in order to improve the adhesive property of the ink. This also makes it possible to appropriately increase the drying property of the ink. Further, since it is not necessary to excessively increase the heating temperature of the media under the conditions for increasing the adhesiveness of the ink, problems such as cockling can be appropriately prevented. In addition, for example, even when using a medium having a low heat-resistant temperature (such as a vinyl chloride medium), the conditions for improving the ink adhesion to the medium and the bleeding are appropriately suppressed while appropriately suppressing the occurrence of cockling. It is possible to properly balance the conditions to prevent the failure.

  Here, as said ketone compound, 2-heptanone or 2-octanone can be used conveniently, for example. By using such a ketone compound, it is possible to appropriately improve the media attack of the ink, particularly when using a vinyl chloride medium. In addition, this makes it possible to more appropriately satisfy the conditions for improving the adhesion of the ink to the medium and the conditions for appropriately preventing bleeding. Moreover, as said ketone compound, it is also considered to use 2-nonanone, 3-nonanone, 2-decanone, 2-undecanone, 5-dodecanone etc., for example. Even when these ketone compounds are used, the media attack property can be appropriately exhibited in the ink.

  In the ink of the present invention, for example, a terpene-based substance may be used as an additive instead of a ketone compound. In this case, examples of the terpene-based substance additive include sesquiterpenes (bp = 220 ° C. to 250 ° C.), dipentene (bp = 165 ° C. to 183 ° C.), α-terpineol (b .P = 225 ° C.), D-limonene (bp = 175 ° C.), and the like. Even when these substances are used as additives, it is possible to appropriately satisfy both conditions for improving the adhesiveness of the ink to the medium and conditions for appropriately preventing bleeding.

  Moreover, when using any substance as a ketone type | system | group or a terpene type substance, it is preferable that the boiling point of the substance shall be 150 to 250 degreeC. If comprised in this way, the conditions which improve the adhesiveness of the ink with respect to a medium, for example, and the conditions which prevent a bleeding appropriately can be compatible more appropriately.

Next, the ink jet printer and the printing method of the present invention will be described. FIG. 1 is a schematic top view of an essential part of an ink jet printer showing an embodiment of the present invention, and FIG. 2 is a side view thereof.
<Inkjet printer>
An ink jet printer 10 according to the present invention includes a platen (support) 12 that supports a medium (recording medium) 11 and ink that is ejected from a plurality of ejection openings onto the surface of the medium 11 while moving in the X direction (left and right in the drawing). An ink jet head 13 for landing droplets, and a print heater (heating means) that is positioned on the back side of the medium 11 and that heats the ink droplets that have landed on the surface of the medium 11 to volatilize and remove the volatile organic solvent contained in the ink droplets. ) 17 and UV irradiation means arranged in front of the moving direction (Y direction) of the medium 11 and irradiating the ink droplet from which the volatile organic solvent on the surface of the medium 1 is volatilized and removed by irradiating the ink droplet with ultraviolet rays. 16.

  The ink-jet head 13 has a structure in which ink droplets are ejected from a nozzle (not shown) arranged side by side by a piezo method or the like, and is fixed to a unit base 14 and travel means (see FIG. It is possible to travel on the guide rail 15 in the X direction. The traveling means includes an electric motor and an electronic circuit for controlling the motor.

  The ink to be used is a volatilization of the UV curable ink having a viscosity of 20 mPa · sec or more (room temperature 25 ° C.) comprising the pigment, the ultraviolet curable resin curable by ultraviolet rays, and the photopolymerization initiator shown in the embodiment of the present invention. An ink characterized by having a viscosity of 3 mPa · sec or more and 18 mPa · sec or less to which a water-soluble organic solvent and the above-described ketone compound are added.

  The medium 11 is supported by a platen 12 and is sandwiched between a pinch roller (not shown) and a feed roller (not shown), and the inkjet head 13 ejects ink droplets from one end of the medium 11 in the X direction. At the same time as traveling to the end, the roller rotates and is conveyed in the Y direction. The media 11 can be made of almost all materials such as plastic materials such as PET, PP, PC, and acrylic, metals, glass, vinyl chloride, rubber materials, or paper for solvent ink.

The print heater (heating means) 17 is disposed inside the platen and on the back side of the medium 11 and heats the ink droplets that have landed on the surface of the medium 11 to volatilize and remove the volatile organic solvent contained in the ink droplets. To do. As the print heater 17, an electric heater, an infrared heater, or an electromagnetic induction (IH) heater can be used. The ink is ejected and landed on the medium surface, and at the same time, the volatile organic solvent contained in the ink is volatilized and removed. In addition, the temperature of the platen is kept constant. The lower limit of the heating temperature of the print heater is desirably a temperature at which the volatile organic solvent is sufficiently volatilized and removed before the medium 11 is sent to the UV irradiation means position, and is, for example, about 35 ° C. The upper limit is desirably determined from the heat resistance temperature of the media and the safety to the human body due to the higher temperature of the heater, and is, for example, about 80 ° C.
Further, the position of the heating means is not limited to the back side of the medium, and may be on the front side or both sides of the medium. When the heating means is provided on the surface side of the media, the heating means is positioned on the same guide rail 15 as the ink jet head, or in a position fixed and separated from the guide rail 15 in front of the Y direction (platen transport direction). can do. In the case where the heating means is provided on the same guide rail as the ink jet head, and when the unidirectional printing is performed, the heating means is provided behind the ink jet head in the traveling direction. Specifically, when ejecting ink while running the inkjet head to the right in the X direction, install it on the left side of the inkjet head, and when ejecting ink while running to the left in the X direction, install on the right side of the inkjet head. To do. Furthermore, in the case of bidirectional printing, the inkjet head is installed on the front and rear in the running direction, that is, on both the left and right sides of the inkjet head.

The UV irradiation means 16 has a built-in UVLED (abbreviation of Ultra Violet Light Emitting Diode; ultraviolet light-emitting diode), and the unit base 14 along with the inkjet head 13 in the moving direction (Y direction) of the medium 11 of the inkjet head 13. It is arranged on the side and can travel in the X direction by a moving means (not shown). The UV irradiation unit 16 irradiates the surface of the medium 11 conveyed by the conveying roller with ultraviolet rays by curing the ink droplets on the surface of the medium 11 after the ink droplets have landed from the ink jet head 13, and fixes them.
The UV irradiation means 16 is not particularly limited, but a UVLED lamp that can freely adjust the amount of irradiation light and control ON / OFF by changing the current and the emission pulse width and uses less power is used. Is the most suitable. However, by providing a shutter, the amount of UV light can be changed, so that other lamps such as a metal halide lamp, a xenon lamp, and high-pressure mercury can be used.

  As described above, the ink jet printer 10 according to the present invention has the ink of the present invention ejected from the ink jet head 13 onto the surface of the medium 11 supported on the platen (support) 12 and landed on the surface of the medium 11. The volatile organic solvent contained in the ink droplets is volatilized and removed by a print heater located on the back side of the media, and then the UV ink droplets are irradiated by UV irradiation means 16 to cure the UV ink droplets. 11 is fixed to the surface of the medium 11, and an image composed of an array of a plurality of UV ink droplets is formed on the surface of the medium 11. According to the ink jet printer of the present invention, the surface of the ink droplets can be flattened so that it has a gloss feeling, and since the ink of the present invention is used, there is no bleeding of the ink droplets and a high-definition image can be obtained. . Furthermore, by using the ink to which the above-described ketone compound or the like is added, it is possible to appropriately satisfy both the condition for improving the adhesion of the ink to the medium and the condition for appropriately preventing bleeding.

  In the ink jet printer in the above embodiment, the case where the ink jet head 13 and the UV irradiation means 16 are both fixed to the unit base has been described as an example. However, the present invention is not limited to this, and UV irradiation is performed. The means may be configured to be able to travel in the X direction by being fixed to another guide rail positioned forward in the Y direction while being separated and independent from the inkjet head, or may be configured to be positioned in front of the Y direction in the platen It is good also as a structure which fixes the UV lamp over the X direction full width. Examples of the UV lamp include discharge tubes such as a black light and a germicidal lamp.

<Printing method>
Next, a printing method using the ink of the present invention and the ink jet printer 10 will be described with reference to FIGS.
The printing method of the present invention is performed using the ink of the present invention as described above and an ink jet printer. The ink is ejected from a plurality of ejection openings of the ink jet head 13 to land ink droplets on the surface of the medium 11. The ink droplets landed on the surface of the medium 11 are heated by heating means located on the back side of the medium to volatilize and remove the volatile organic solvent contained in the ink droplets. The ink droplets are cured by being irradiated with ultraviolet rays and fixed on the surface of the medium 11, and an image composed of an array of a plurality of ink droplets is printed on the surface of the medium 11.

  The ink jet head unit is filled with the ink of the present invention having a viscosity of about 4 mPa · sec, and the ink jet head is run in the X direction to eject ink droplets onto the medium. In this case, since the ink of the present invention does not cause clogging, it is not particularly necessary to provide heating means such as a heater on the inkjet head. However, the inkjet head and ink are heated with warm water to lower the viscosity at the time of ejection. be able to.

  Next, the ink droplets ejected onto the medium 11 are immediately heated by a print heater located on the back side of the medium and holding the surface of the medium at 40 ° C. to 80 ° C. to evaporate and remove the volatile organic solvent. As a result, ink droplets made of UV-curable ink having a high viscosity of 30 mPa · sec are formed, and bleeding can be prevented.

  Next, the medium 11 is conveyed in the Y direction by the platen 12. The ink droplets on the surface of the medium from which the volatile organic solvent has been volatilized and removed are irradiated with ultraviolet rays by the UV irradiation means 16 located in front of the medium in the Y direction, and are cured and fixed on the surface of the medium 11. As a result, an image composed of an array of a plurality of ink droplets is formed on the surface of the medium 11.

  The ink, ink jet printer, and printing method of the present invention have been described above. However, the present invention is not limited to these examples, and can be appropriately changed as necessary without departing from the spirit of the present invention. .

DESCRIPTION OF SYMBOLS 10 Inkjet printer 11 Media 12 Platen 13 Inkjet head 14 Unit mount 15 Guide rail 16 UV irradiation means 17 Print heater

Claims (6)

A support for supporting the media;
At least 3 mPa · sec to 18 mPa · sec (room temperature 25 ° C.) including at least a pigment, an ultraviolet curable resin cured by ultraviolet rays, a photopolymerization initiator, a volatile organic solvent, and a ketone or terpene substance. Ink droplets having a viscosity of 20 mPa · sec or more (room temperature 25 ° C.) in a state where the volatile organic solvent has been volatilized and removed are ejected from a plurality of ejection openings onto the surface of the medium. An inkjet head for landing
Heating means that is located on at least one of the back side and the front side of the media and heats the ink droplets landed on the media surface to volatilize and remove the volatile organic solvent contained in the ink droplets;
An inkjet printer comprising: UV irradiation means for irradiating ultraviolet rays onto the ink droplets from which the volatile organic solvent on the surface of the medium has been volatilized and removed to cure the ink droplets. The inkjet printer according to claim 1, wherein the ketone-based or terpene-based substance is a ketone compound represented by the following general formula (1).
R ¹ —CO—R ² (1)
[In General Formula (1), R ¹ and R ² each independently represents an alkyl group having 1 to 10 carbon atoms. However, the total carbon number of R ¹ and R ² is 5 to 11, and when the total carbon number of R ¹ and R ² is 6 or more, R ¹ and R ² may form a ring. ]   The inkjet printer according to claim 2, wherein the ketone compound is 2-heptanone or 2-octanone.   The inkjet printer according to any one of claims 1 to 3, wherein a boiling point of the ketone-based or terpene-based substance is 150 ° C to 250 ° C. At least 3 mPa · sec to 18 mPa · sec (room temperature 25 ° C.) including at least a pigment, an ultraviolet curable resin cured by ultraviolet rays, a photopolymerization initiator, a volatile organic solvent, and a ketone or terpene substance. Ink with a viscosity of 20 mPa · sec or more (room temperature 25 ° C.) in a state where the volatile organic solvent is volatilized and removed is ejected from a plurality of ejection ports of the inkjet head onto the surface of the medium. Land ink drops,
After the ink droplets that have landed on the surface of the media are heated by heating means located on at least one of the back side and the front side of the media, the volatile organic solvent contained in the ink droplets is volatilized and removed,
The ink droplets are irradiated with ultraviolet rays by UV irradiation means to cure the ink droplets and fix them on the media surface,
A printing method comprising printing an image comprising an array of a plurality of ink droplets on the surface of the medium.   At least 3 mPa · sec to 18 mPa · sec (room temperature 25 ° C.) including at least a pigment, an ultraviolet curable resin cured by ultraviolet rays, a photopolymerization initiator, a volatile organic solvent, and a ketone or terpene substance. An ink having a viscosity of 20 mPa · sec or more (room temperature 25 ° C.) in a state where the volatile organic solvent is volatilized and removed.

Images