Inkjet recording device

Abstract

To provide a recording device capable of suppressing hardening inhibition while ensuring downsizing.SOLUTION: An ink jet recording device comprises: an ink jet head which discharges a radiation ray-curable ink jet composition and makes the same adhere onto a recording medium; and an irradiation unit which irradiates with radiation ray the recording medium to which the radiation ray-curable ink jet composition adheres with an inactive gas supplied thereto. The irradiation unit has a nozzle surface that discharges the inactive gas, and the irradiation surface that performs irradiation of the radiation ray in the order of a conveying direction of the recording medium. A distance h1 from the recording medium to the nozzle surface and a distance h2 from the recording medium to the irradiation surface satisfy a relation of h1>h2.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an inkjet recording apparatus.

Background Art

[0002] The inkjet recording method uses a relatively simple apparatus and can record high-definition images, and has been rapidly developed in various fields. Among them, various studies have been made on the curing method of radiation-curable ink. For example, Patent Document 1 discloses an inkjet recording method including a step of efficiently curing inkjet ink by irradiating active rays in an atmosphere with less oxygen.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, it is disclosed that the LED light source unit is surrounded by an inert gas blanket 2 and the atmosphere in the blanket is made an oxygen-deficient atmosphere. However, although it is for the purpose of reducing the inhibitory effect of oxygen, using such a blanket inevitably increases the size of the recording apparatus.

Means for Solving the Problems

[0005] The inkjet recording apparatus of the present invention comprises an inkjet head that ejects a radiation-curable inkjet composition and adheres it to a recording medium, and an irradiation unit that irradiates the recording medium to which the radiation-curable inkjet composition is attached with radiation while supplying an inert gas, wherein the irradiation unit has a nozzle surface for ejecting the inert gas and an irradiation surface for irradiating with radiation in the order of the transport direction of the recording medium, and the distance h1 from the recording medium to the nozzle surface and the distance h2 from the recording medium to the irradiation surface satisfy the relationship h1 > h2. [Brief explanation of the drawing]

[0006] [Figure 1] This is a schematic diagram showing one aspect of the inkjet recording apparatus of this embodiment. [Figure 2] This is a schematic diagram showing another embodiment of the inkjet recording apparatus of this embodiment. [Modes for carrying out the invention]

[0007] The embodiments of the present invention (hereinafter referred to as "these embodiments") will be described in detail below, with reference to the drawings as necessary. However, the present invention is not limited thereto, and various modifications are possible without departing from its essence. In the drawings, the same elements will be denoted by the same reference numerals, and redundant explanations will be omitted. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings. Moreover, the dimensional ratios in the drawings are not limited to those shown.

[0008] 1. Inkjet recording device The inkjet recording apparatus of this embodiment comprises an inkjet head that ejects a radiation-curable inkjet composition (hereinafter also simply referred to as "ink composition") and adheres it to a recording medium, and an irradiation unit that irradiates the recording medium to which the ink composition is attached with radiation while supplying an inert gas. The irradiation unit has a nozzle surface for ejecting the inert gas and an irradiation surface for irradiating radiation, in the order of the transport direction of the recording medium, and the distance h1 from the recording medium to the nozzle surface and the distance h2 from the recording medium to the irradiation surface satisfy the relationship h1 > h2.

[0009] In conventional recording devices, the space between the recording medium and the UV irradiation area is relatively large, making the ink composition ejected onto the recording medium susceptible to polymerization inhibition by oxygen. From the perspective of suppressing such polymerization inhibition, it has been considered to perform UV irradiation in an area enclosed by a blanket or similar material to cure under conditions of low oxygen concentration. However, this is undesirable because it increases the size of the device. On the other hand, if the device is not enclosed by a blanket, the space in the UV irradiation area is large, the efficiency of oxygen concentration reduction by inert gas is poor, and polymerization inhibition is difficult to achieve. In particular, sufficient oxygen inhibition prevention effect cannot be obtained when the printing speed is increased, and the amount of inert gas used increases, requiring a large gas generator.

[0010] In contrast, this embodiment uses an irradiation unit configured such that the nozzle surface that discharges the inert gas and the irradiation surface that irradiates with radiation satisfy a predetermined relationship. This makes it possible to improve the efficiency of oxygen concentration reduction by the inert gas without having to surround it with a blanket or the like.

[0011] Figure 1 shows a schematic diagram of the inkjet recording apparatus of this embodiment. As shown in Figure 1, the inkjet recording apparatus 100 includes an irradiation unit 10, an inkjet head 20, and a transport unit 30. Each component will be described in detail below.

[0012] 1.1. Inkjet head The inkjet head 20 is a means for ejecting an ink composition and adhering it to the recording medium M. The inkjet head 20 has nozzles on the nozzle plate surface 21 facing the recording medium M, and ejects the ink composition from these nozzles. The nozzles may be arranged in a row.

[0013] The recording device 100 of this embodiment may have a separate, independent inkjet head 20 for each color, such as cyan, magenta, yellow, black, and white. Alternatively, one inkjet head 20 may be configured to eject two or more ink compositions.

[0014] One method for ejecting an ink composition from a nozzle is to drive a pressure generating means to eject the composition filled in the pressure generating chamber of the inkjet head from the nozzle. This ejection method is also called the inkjet method. There are no particular limitations on the method of applying pressure to the ink composition in the nozzle, but examples include the piezo method, which ejects droplets of the ink composition using a piezoelectric element, and the thermal method, which ejects droplets by heating.

[0015] Furthermore, the inkjet head 20 used in the ejection process can be a line head that records using a line method or a serial head that records using a serial method. Among these, the line head is preferred. This makes it possible to improve the printing speed.

[0016] In a line-type system using a line head, for example, an inkjet head with a width greater than the recording width of the recording medium is fixed to the recording device. The recording medium is then moved along the sub-scanning direction (the vertical direction of the recording medium, the transport direction), and ink droplets are ejected from the nozzles of the inkjet head in conjunction with this movement, thereby recording an image on the recording medium.

[0017] In the serial method using a serial head, for example, an inkjet head is mounted on a carriage that can move in the width direction of the recording medium. Then, the carriage is moved along the main scanning direction (the lateral direction, width direction of the recording medium), and ink droplets are ejected from the nozzle openings of the head in conjunction with this movement, so that an image can be recorded on the recording medium.

[0018] Among these, from the viewpoint of winding up the recording medium to which ink has been attached and enabling high-speed and large-volume printing, it is preferable to use the line method. In the case of the line method, while continuously feeding the recording medium in the sub-scanning direction, the line head continuously performs recording and radiation irradiation in one pass, and the recording medium to which ink has been attached can be wound up downstream. Note that the form of the recording apparatus shown in FIG. 1 shows an example of the line method.

[0019] 1.2. Irradiation Unit The irradiation unit 10 is means for irradiating radiation in a state where an inert gas is supplied onto the recording medium to which the ink composition has been attached. The irradiation unit 10 has, in the order of the conveyance direction F of the recording medium, a nozzle surface 11 for discharging an inert gas and an irradiation surface 12 for irradiating radiation. Note that the “unit” means that the nozzle surface 11 for discharging an inert gas and the irradiation surface 12 for irradiating radiation are integrally formed.

[0020] Thereby, the recording medium conveyed in the conveyance direction F first passes under the nozzle surface of the inkjet head 20, and an image is formed. Next, by passing under the nozzle surface 11 of the inert gas of the irradiation unit 10, a space with a low oxygen concentration is created in the vicinity of the surface to which the ink composition has been attached. And finally, by passing under the irradiation surface 12 of the inert gas of the irradiation unit 10, the ink composition attached to the recording medium is cured by radiation.

[0021] In particular, for the irradiation unit 10 used in this embodiment, the distance h1 from the recording medium to the nozzle surface 11 and the distance h2 from the recording medium to the irradiation surface 12 satisfy the relationship h1 > h2. In this way, by making the distance h2 from the recording medium M to the irradiation surface 12 shorter than the distance h1 from the recording medium M to the nozzle surface 11 of the inert gas downstream, the inert gas supplied from the nozzle surface 11 and filling immediately below the nozzle surface 11 can easily flow into the area immediately below the irradiation surface 12 along the flow in the transport direction F. Therefore, it becomes possible to create a space with a low oxygen concentration in the vicinity of the surface to which the ink composition adheres, and thereby, the efficiency of reducing the oxygen concentration by the inert gas can be improved without being surrounded by a blanket or the like.

[0022] In other words, by satisfying the relationship h1 > h2, the volume of the space sandwiched between the irradiation surface 12 and the surface of the recording medium M is smaller than the volume of the space sandwiched between the nozzle surface 11 and the surface of the recording medium M. Therefore, by allowing a part of the inert gas supplied at the nozzle surface 11 to flow into the area immediately below the irradiation surface 12 along the flow in the transport direction F, it becomes possible to create a space with a low oxygen concentration in the vicinity of the surface to which the ink composition adheres. As a result, without being surrounded by a blanket or the like, in the space sandwiched between the irradiation surface 12 and the surface of the recording medium M, the efficiency of reducing the oxygen concentration by the inert gas can be improved, and the curing efficiency by radiation irradiation can be improved. Therefore, it is possible to provide an inkjet recording apparatus with excellent curing efficiency by an inert gas while downsizing the entire apparatus.

[0023] On the other hand, when the volume of the space sandwiched between the nozzle surface 11 and the surface of the recording medium M is approximately the same as the volume of the space sandwiched between the irradiation surface 12 and the surface of the recording medium M, or when the volume of the space sandwiched between the irradiation surface 12 and the surface of the recording medium M is configured to be larger, even if a part of the inert gas supplied at the nozzle surface 11 flows into the area immediately below the irradiation surface 12 along the flow in the transport direction F, the reduction in the oxygen concentration immediately below the irradiation surface 12 will be insufficient.

[0024] The ratio of the height of the value of h2 to that of h1 is not particularly limited as long as it satisfies the relationship h1 > h2. For example, the ratio of the height of the value of h2 to that of h1 is preferably 0.10 to 0.95 times, more preferably 0.20 to 0.85 times, and even more preferably 0.30 to 0.75 times.

[0025] Figure 2 shows a schematic diagram illustrating another embodiment of the inkjet recording device 100 of this embodiment. As shown in Figure 2, the recording device 100 of this embodiment may be equipped with a plurality of inkjet heads 20, and the irradiation unit 10 may be provided one by one corresponding to the inkjet heads 20.

[0026] More specifically, the recording device 100 of this embodiment may have a separate, independent inkjet head 20 for each color such as cyan, magenta, yellow, black, and white, and a single irradiation unit 10 corresponding to each inkjet head 20. This tends to further improve the image quality of the recorded material.

[0027] In particular, as described above, the irradiation unit of this embodiment can improve the efficiency of reducing oxygen concentration by an inert gas in the space sandwiched between the irradiation surface 12 and the surface of the recording medium M, without the need for a blanket or the like, and can improve the curing efficiency by radiation irradiation. As a result, the irradiation unit 10 can be miniaturized, and one irradiation unit 10 can be installed for each inkjet head 20.

[0028] On the other hand, in conventional recording devices that include blankets and the like, considering the practical limitations of the device size, it is reasonable to install one irradiation unit 10 to correspond to multiple inkjet heads 20, and it is practically difficult to install one irradiation unit 10 to correspond to one inkjet head 20.

[0029] 1.3. Conveying Section The recording device 100 of this embodiment may have a transport unit 30 for transporting the recording medium M. The transport unit 30 is not particularly limited as long as it is configured to transport the recording medium M in the transport direction F, but for example, in Figure 1, the transport unit 30 is shown that feeds out the roll-shaped recording medium M and rewinds the roll-shaped recording medium M.

[0030] 1.4. Recording media The recording medium used by the recording device 100 of this embodiment is not particularly limited, but a non-absorbent recording medium is preferred, for example. In particular, it is preferable that both the recording surface and the non-recording surface of the recording medium used in this embodiment are non-absorbent. By using such a recording medium, it is possible to obtain a recording material suitable for label applications and the like. Furthermore, because it is non-absorbent, the cured ink coating film adheres more easily to the non-recording surface, so the irregularities formed by the second ink work more effectively, and the peelability of the recording material tends to improve.

[0031] Examples of non-absorbent recording media include, but are not limited to, films and plates of plastics such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, and polyurethane; plates of metals such as iron, silver, copper, and aluminum; metal plates or plastic films made by vapor deposition of these metals; plates of alloys such as stainless steel and brass; and recording media in which films of plastics such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, and polyurethane are bonded (coated) to a paper substrate.

[0032] In this embodiment, non-absorbent means that the amount of water absorbed from the start of contact to 30 msec in the Bristow method is 10 mL / m². 2The following applies. Furthermore, a non-absorbent recording medium refers to a recording medium that possesses such non-absorbency. The Bristow method is the most widely used method for measuring liquid absorption in a short time and is also adopted by the Japan Paper & Pulp Technology Association (JAPAN TAPPI). Details of the test method are described in standard No. 51 "Paper and cardboard - Liquid absorbency test method - Bristow method" of the "JAPAN TAPPI Paper & Pulp Test Methods 2000 Edition".

[0033] 2. Recording Method The recording method of this embodiment is a recording method using the above-described inkjet recording apparatus, comprising: an ejection step of ejecting an ink composition and adhering it to a recording medium; and an irradiation step of irradiating the ink composition adhering to the recording medium with radiation to obtain a cured coating film of the ink composition, wherein in the irradiation step, radiation is irradiated while an inert gas is supplied to the recording medium to which the ink composition is adhering.

[0034] 2.1.Discharge process The ejection process is the process of ejecting the ink composition from the inkjet head 20 and adhering it to the recording medium M. More specifically, the pressure generating means is driven to eject the composition filled in the pressure generating chamber of the inkjet head from the nozzle.

[0035] From the viewpoint of winding up the ink-coated recording medium, it is preferable to use a line system in the ejection process. In the line system, the recording medium is continuously fed in the sub-scanning direction, and recording and radiation irradiation are continuously performed by the line head, and the ink-coated recording medium is wound up downstream. The recording device shown in Figure 1 is a line system.

[0036] The manner in which ink adheres, such as the Duty Cycle, during the ejection process is not particularly limited and can be adjusted as appropriate depending on the desired image.

[0037] 2.2.Irradiation process The irradiation process involves irradiating the ink adhering to the recording medium M with radiation from the irradiation surface 12 while flowing an inert gas from the nozzle surface 11 of the irradiation unit 10, thereby suppressing polymerization inhibition by oxygen and obtaining a cured ink coating film.

[0038] In this irradiation process, the ink composition attached to the recording medium is irradiated with radiation. When irradiated with radiation, the polymerization reaction of monomers begins, causing the composition to harden and a coating film to form. At this time, if a polymerization initiator is present, it generates active species (initiators) such as radicals, acids, and bases, and the polymerization reaction of monomers is promoted by the function of these initiators.

[0039] The irradiation step is a process of irradiating a radiation-curable inkjet composition attached to a recording medium with radiation to obtain a cured coating film of the radiation-curable inkjet composition. In particular, in this embodiment, in the irradiation step, radiation is irradiated while an inert gas is supplied to the recording medium to which the radiation-curable inkjet composition is attached.

[0040] Here, examples of radiation include ultraviolet rays, infrared rays, visible light, and X-rays. The radiation source is located downstream of the inkjet head and irradiates the composition with it. There are no particular limitations on the radiation source, but for example, a UV-LED can be used. Using such a radiation source makes it possible to miniaturize the device and reduce costs. Since UV-LEDs as ultraviolet sources are small, they can be installed inside the inkjet recording device.

[0041] In particular, the irradiation unit has a nozzle surface for discharging inert gas and an irradiation surface for irradiating radiation, in the order of the transport direction of the recording medium, and the distance h1 from the recording medium to the nozzle surface and the distance h2 from the recording medium to the irradiation surface satisfy the relationship h1 > h2. By performing the above irradiation process using such an irradiation unit, oxygen inhibition tends to be further suppressed.

[0042] 2.3.Lamination process The recording method of this embodiment may include a lamination step in which the recording material is stacked such that a recording surface to which the ink composition is attached faces a non-recording surface to which the ink composition is not attached.

[0043] The stacking method in the lamination process is not particularly limited, but examples include stacking single-sheet recordings one by one so that the recording surface and non-recording surface face each other, or stacking recordings continuously recorded on a long recording medium by winding them into a roll downstream of the recording device so that the recording surface and non-recording surface face each other. More specifically, the recordings can be wound into a winding body by winding them with a winding roller. Within this winding body, the recordings are wound up so that the recording surface and non-recording surface face each other.

[0044] 3. Ink composition In this embodiment, a radiation-curable inkjet ink composition refers to one that hardens when irradiated with radiation. Examples of radiation include ultraviolet rays, electron beams, infrared rays, visible light, and X-rays. Among these, ultraviolet rays are preferred because radiation sources are readily available and widely used, and materials suitable for curing by ultraviolet radiation are readily available and widely used.

[0045] The radiation-curable inkjet ink composition of this embodiment is not particularly limited, but may contain, for example, polymerizable compounds, photopolymerization initiators, polymerization inhibitors, slip agents, colorants, dispersants, etc. The ink composition may be an undercoat ink composition used for a base coat, an image-forming ink composition such as a color ink, or an overcoat ink composition.

[0046] 3.1. Polymerizable compounds The polymerizable compound comprises a monofunctional monomer and, if necessary, a polyfunctional monomer.

[0047] There are no particular limitations on the monofunctional monomers, but examples include monofunctional monomers having an alicyclic group, monofunctional monomers having an aromatic group, and monofunctional monomers having a nitrogen-containing heterocycle. Other monomers may also be used as monofunctional monomers.

[0048] The polyfunctional monomer is not particularly limited, but examples include vinyl group-containing (meth)acrylates and polyfunctional (meth)acrylates.

[0049] 3.2. Photopolymerization Initiators The photopolymerization initiator is not particularly limited as long as it generates an active species when irradiated with radiation, but known photopolymerization initiators include acylphosphine oxide-based photopolymerization initiators, alkylphenone-based polymerization initiators, titanocene-based polymerization initiators, and thioxanthone-based photopolymerization initiators. Among these, acylphosphine oxide-based photopolymerization initiators are preferred. Using such a photopolymerization initiator improves the curability of the ink, and in particular, the curability by the curing process using UV-LED light tends to be improved. The photopolymerization initiator may be used alone or in combination of two or more types.

[0050] 3.3 Polymerization Inhibitors Polymerization inhibitors include, but are not limited to, p-methoxyphenol, hydroquinone monomethyl ether (MEHQ), 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, hydroquinone, cresol, t-butylcatechol, 3,5-di-t-butyl-4-hydroxytoluene, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-butylphenol), and 4,4'-thiobis(3-methyl-6-t-butylphenol), hindered amine compounds, and others. Polymerization inhibitors may be used individually or in combination of two or more.

[0051] 3.4. Slip agent As the slip agent, a silicone-based surfactant is preferred, and a polyester-modified silicone or a polyether-modified silicone is more preferred. Examples of polyester-modified silicones include BYK-347, 348, BYK-UV3500, 3510, and 3530 (all manufactured by BYK Additives & Instruments), and an example of a polyether-modified silicone is BYK-3570 (manufactured by BYK Additives & Instruments). The slip agent may be used alone or in combination of two or more types.

[0052] 3.5. Colorants The colorant may be at least one of pigments and dyes. Depending on the type of colorant, a dispersant may also be used. The dispersant is not particularly limited, but examples include dispersants commonly used to prepare pigment dispersions, such as polymer dispersants. Specific examples include those mainly composed of one or more of the following: polyoxyalkylene, polyalkylene, polyamine, vinyl polymers and copolymers, acrylic polymers and copolymers, polyester, polyamide, polyimide, polyurethane, amino polymer, silicon-containing polymer, sulfur-containing polymer, fluorine-containing polymer, and epoxy resin. The dispersant may be used alone or in combination of two or more. [Explanation of Symbols]

[0053] 10...Irradiation unit, 11...Nozzle surface, 12...Irradiation surface, 20...Inkjet head, 21...Nozzle plate surface, 30...Transport unit, 100...Inkjet recording device, F...Transportation direction, h1...Distance, h2...Distance, M...Recording medium

Claims

1. An inkjet head that ejects a radiation-curable inkjet composition and deposits it onto a recording medium, The system comprises an irradiation unit that irradiates the recording medium on which the radiation-curable inkjet composition is attached with radiation while supplying an inert gas, Equipped with multiple inkjet heads, The irradiation unit is provided one by one, corresponding to the inkjet head. The irradiation unit has a nozzle surface for discharging the inert gas and an irradiation surface for irradiating the radiation, in the order of the transport direction of the recording medium. The irradiation unit has the nozzle surface for discharging the inert gas and the irradiation surface for irradiating the radiation integrally formed. An inkjet recording apparatus in which the distance h1 from the recording medium to the nozzle surface and the distance h2 from the recording medium to the irradiation surface satisfy the relationship h1 > h2.

2. The inkjet recording apparatus according to claim 1, wherein the inkjet head and the irradiation unit each have a width greater than or equal to the width of the recording medium.

3. The inkjet recording apparatus according to claim 1, wherein the inkjet head ejects droplets of the radiation-curable inkjet composition using either a piezoelectric method that ejects droplets of the radiation-curable inkjet composition using a piezoelectric element or a thermal method that ejects droplets by heating.

4. The inkjet recording apparatus according to claim 1, wherein two or more ink compositions are ejected from separate inkjet heads for each color, or one inkjet head ejects two or more radiation-curable inkjet compositions.

5. The inkjet recording apparatus according to claim 1, wherein the irradiation unit is not surrounded by a blanket.

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