Inkjet recording method

Abstract

To provide an inkjet recording method capable of achieving homogeneous matted finish in observation at various angles.SOLUTION: An inkjet recording method has an overcoat layer forming process of forming an overcoat layer on a color layer which is formed on a recording medium by radiation curable white ink composition and radiation curable clear ink composition, the overcoat layer forming process having: an ejecting process O in which the radiation curable white ink composition and the radiation curable clear ink composition are ejected from an inkjet head O and attached to the recording medium; and an irradiation process O in which the radiation curable white ink composition and the radiation curable clear ink composition attached to the recording medium are irradiated with radiation to obtain the overcoat layer, wherein a coverage of the overcoat layer with respect to the recording medium is less than 100%.SELECTED DRAWING: Figure 3

Description

【Technical Field】 【0001】 The present invention relates to an inkjet recording method. 【Background Art】 【0002】 The inkjet recording method can record high-definition images with a relatively simple device and has been rapidly developed in various fields. As one of them, in order to赋予 high added value to the recording material, recording materials having a matte finish, or recording materials having both a matte finish and a gloss finish have been developed, and attempts have been made to improve their quality. 【0003】 For example, in Patent Document 1, for the purpose of performing printing having smoothness on the surface while forming a high-definition image without crushing the edges of ink dots, a head that discharges a photocurable ink, a light irradiation device that irradiates light, and a predetermined control unit that controls the discharge amount of the photocurable ink and the waiting time from the landing timing of the photocurable ink on the printing medium to the irradiation of light are provided. The control unit described in the recording device of Patent Document 1 creates a recording material with a gloss finish or a matte finish by controlling the discharge amount and the waiting time. 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2018-111211 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 Patent Document 1 describes how irradiating the ink with ultraviolet light immediately after it lands on the printing medium can cure the ink before the ink dots flatten, thereby achieving a matte finish with less gloss. However, it has become clear that simply curing the ink before the dots flatten to create irregularities on the surface of the recording does not result in a matte finish depending on the viewing angle. [Means for solving the problem] 【0006】 The present invention provides an inkjet recording method comprising an overcoat layer formation step of forming an overcoat layer on a color layer formed on a recording medium using a radiation-curable white ink composition and a radiation-curable clear ink composition, wherein the overcoat layer formation step comprises an ejection step O of ejecting the radiation-curable white ink composition and the radiation-curable clear ink composition from an inkjet head O and adhering them to a recording medium, and an irradiation step O of irradiating the radiation-curable white ink composition and the radiation-curable clear ink composition adhering to the recording medium with radiation to obtain the overcoat layer, wherein the coverage rate of the overcoat layer on the recording medium is less than 100%. [Brief explanation of the drawing] 【0007】 [Figure 1] This is a schematic diagram illustrating how a recording with an uneven surface appears when created using conventional methods. [Figure 2] This embodiment is a schematic diagram illustrating the appearance of a recording material with an overcoat layer formed on its surface. [Figure 3] This figure shows an example of a schematic cross-sectional view of the recording device of this embodiment. [Figure 4] This figure shows another example of a schematic cross-sectional view of the recording device of this embodiment. [Modes for carrying out the invention] 【0008】 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. 【0009】 1. Inkjet recording method The inkjet recording method of this embodiment (hereinafter also simply referred to as "this recording method") has an overcoat layer formation step in which an overcoat layer is formed on a color layer formed on a recording medium using a radiation-curable white ink composition (hereinafter also simply referred to as "white ink composition") and a radiation-curable clear ink composition (hereinafter also simply referred to as "clear ink composition"). The overcoat layer formation step comprises an ejection step O in which the radiation-curable white ink composition and the radiation-curable clear ink composition are ejected from an inkjet head O and adhered to a recording medium, and an irradiation step O in which radiation is irradiated onto the radiation-curable white ink composition and the radiation-curable clear ink composition adhered to the recording medium to obtain the overcoat layer, wherein the coverage rate of the overcoat layer on the recording medium is less than 100%. 【0010】 Conventionally, matte finishes using radiation-curable ink compositions have been achieved by placing particles of a clear ink composition on the surface of the image. However, when using only a clear ink composition to achieve a matte finish, there was a problem in that the matte finish appeared unevenly depending on the positional relationship between the observer and the light source when viewing the recorded material. In particular, when the light source was positioned behind the observer, the light mainly traveled to the opposite side without diffuse reflection, resulting in a glossy appearance, making it difficult to achieve a uniform matte finish. 【0011】 To explain this point, Figure 1 shows a schematic diagram illustrating the appearance of a recording material with surface irregularities formed by a conventional method. Figure 1 shows a cross-section of a recording material with surface irregularities, and S1 shows a magnified portion of that cross-section. The recording material 1' obtained by the conventional method shown in Figure 1 has a color layer 3 on a recording medium 2, and on the color layer 3, there are irregularities 4 (overcoat layer) formed with clear ink. In such a recording material 1', when standing at viewpoint A on the light source L side, the angle of incidence of light from the light source L becomes large when observing the recording material 1', so the amount of light diffusely reflected from the surface of the irregularities 4 of the overcoat layer decreases, and it may not appear matte. 【0012】 On the other hand, when standing at viewpoint B opposite the light source L, it becomes easier to observe diffusely reflected light, making the surface appear more matte. Thus, when the surface (overcoat layer) is formed using conventional methods with clear ink, the difference in the light reflected by the recorded material becomes significant when viewed from the light source side versus the opposite side. Therefore, depending on the viewing angle, the surface may not appear matte. 【0013】 In contrast, the recording method of this embodiment involves ejecting a white ink composition and a clear ink composition onto the color layer to form an overcoat layer on the color layer on the recording medium. 【0014】 As a result, as shown in Figure 2, the recording material 1 obtained by this embodiment has a color layer 3 on the recording medium 2, and on the color layer 3 there are irregularities 4 formed with a clear ink composition and irregularities 5 formed with a white ink composition as an overcoat layer. With such a recording material 1, when standing at viewpoint A on the side of the light source L, the diffuse reflection of light on the surface of the irregularities 5 formed with white ink is noticeable, making it appear matte. On the other hand, even when standing at viewpoint B on the opposite side of the light source L, the diffuse reflection of light on the surfaces of both the irregularities 5 of white ink and the irregularities 4 of clear ink can be observed, making it appear matte. As a result, a recording material that appears matte regardless of the position of the light source relative to the recording material, and regardless of the angle from which the recording material is viewed, can be obtained. 【0015】 The following describes the steps included in the recording method according to this embodiment, the ink composition used therein, and the recording apparatus. 【0016】 1.1. Overcoat layer formation process The overcoat layer formation step of this recording method includes an ejection step O in which a white ink composition and a clear ink composition are ejected from an inkjet head O and adhered to a recording medium, and an irradiation step O in which radiation is irradiated onto the white ink composition and clear ink composition adhered to the recording medium to obtain an overcoat layer. By using a white ink composition and a clear ink composition in the overcoat layer formation step, the resulting recording material has a homogeneous matte finish. 【0017】 Although the overcoat layer is referred to as a "layer" for convenience, as shown in Figure 2, it may be a convex portion of the white ink composition and the clear ink composition, and does not need to be a coating film. 【0018】 The coverage rate of the overcoat layer on the recording medium is less than 100%. By setting the coverage rate of the overcoat layer within the above range, the recorded material becomes uniformly matte, resulting in superior image quality. In this specification, the coverage rate on the recording medium refers to the ratio of the area covered by the cured product of the ink composition on the surface of the printing medium. The method for determining the coverage rate is not particularly limited as long as it can calculate the ratio of the area. For example, the coverage rate may be calculated by observing the surface of the recorded material from a direction perpendicular to it using an optical microscope and analyzing the resulting image with analysis software. The method for controlling the coverage rate is not particularly limited, but it can be controlled by, for example, the amount of ink per drop, the duty cycle, etc. 【0019】 In the overcoat layer, the coverage rate of the white ink composition on the recording medium may preferably be 50% by area or less, 40% by area or less, 30% by area or less, 20% by area or less, 15% by area or less, or 10% by area or less. Also, in the overcoat layer, the coverage rate of the white ink composition on the recording medium may preferably be 1% by area or more, 3% by area or more, 5% by area or more, 10% by area or more, or 15% by area or more. The smaller the coverage rate of the white ink composition, the more the change in the color tone of the obtained recording can be suppressed. Also, the larger the coverage rate of the white ink composition, the more the matte feeling of the obtained recording tends to improve. 【0020】 In the overcoat layer, the coverage rate of the clear ink composition on the recording medium may preferably be 5% by area or more, 10% by area or more, or 20% by area or more. In the overcoat layer, the coverage rate of the clear ink composition on the recording medium may preferably be 99% by area or less, 97% by area or less, 95% by area or less, 90% by area or less, 85% by area or less, 70% by area or less, 60% by area or less, or 50% by area or less. The smaller the coverage rate of the clear ink composition, the more the influence on the texture of the obtained recording material can be suppressed. Also, the larger the coverage rate of the clear ink composition, the more the matte feeling of the obtained recording tends to improve. 【0021】 The coverage rate of the overcoat layer may preferably be less than 100 area%, may be 90 area% or less, may be 80 area% or less, may be 70 area% or less, may be 60 area% or less, or may be 50 area% or less. Further, the coverage rate of the overcoat layer may preferably be 10 area% or more, may be 20 area% or more, may be 30 area% or more, or may be 40 area% or more. The lower the coverage rate of the overcoat layer, the more likely it is to suppress the tendency for the resulting recording to appear whitish. Also, the higher the coverage rate of the overcoat layer, the more likely it is to improve the matte feeling of the resulting recording. 【0022】 In the overcoat layer, the cured product of the white ink composition and the cured product of the clear ink composition may be arranged side by side parallel to the surface of the recording medium, or may be deposited overlapping on the recording medium. Also, the order in which the overcoat layer forming step is performed for each ink composition may be performed first for the white ink composition or may be performed first for the clear ink composition. 【0023】 Furthermore, Duty is cited as a parameter representing the coating state with respect to the recording medium. In this specification, "Duty" is a value obtained by the following formula (1). Duty (%) = number of actually printed dots / (vertical resolution × horizontal resolution) × 100 (1) (In the formula, the "number of actually printed dots" is the number of actually printed dots per unit area, and the "vertical resolution" and "horizontal resolution" are the resolutions per unit area, respectively.) 【0024】 In this recording method, it is preferable that the duty cycle of the overcoat layer on the recording material is less than 100%. When the duty cycle of the overcoat layer is within the above range, the matte finish of the resulting recording material tends to be further improved. From a similar viewpoint, it is preferable that the duty cycle of the overcoat layer on the recording material be 95% or less, more preferably 90% or less, even more preferably 85% or less, and even more preferably 80% or less. Furthermore, the duty cycle of the overcoat layer on the recording material may be 20% or more, 30% or more, or 50% or more. 【0025】 The duty cycle of the white ink composition in the recording material is preferably 1% to 40%, more preferably 3% to 30%, and even more preferably 5% to 20%, from the viewpoint of improving the matte feel of the recording material while suppressing the whitening of the image in the color layer. 【0026】 Furthermore, the duty cycle of the clear ink composition in the recording material is preferably 5% to 90%, more preferably 10% to 80%, and even more preferably 20% to 60%, from the viewpoint of improving the matte feel of the recording material while suppressing the development of a glossy finish. 【0027】 1.1.1.Discharge process O The ejection process O is a process of ejecting the white ink composition and the clear ink composition onto the color layer formed on the recording medium, respectively, and adhering them to the color layer and / or the recording medium. More specifically, the pressure generating means is driven to eject the white ink composition or the clear ink composition filled in the pressure generating chamber of the inkjet head O from the nozzle. This ejection method is also called the inkjet method. 【0028】 In the ejection process O, the inkjet head O can be a line head that records using a line method or a serial head that records using a serial method. Of these, the inkjet head O is preferably a line inkjet head. 【0029】 In a line-type inkjet 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 inkjet 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. 【0030】 In a 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. The carriage is then moved along the main scanning direction (the lateral direction, width direction of the recording medium), and ink droplets are ejected from the nozzle opening of the head in conjunction with this movement, thereby recording an image on the recording medium. 【0031】 1.1.2.Irradiation process O The irradiation process involves irradiating the white ink composition and clear ink composition attached to the recording medium with radiation. When irradiated with radiation, the monomer polymerization reaction begins, causing the composition to harden and a coating film to form. At this time, if a photopolymerization initiator is present, it generates active species (initiators) such as radicals, acids, and bases, and the monomer polymerization reaction is promoted by the function of these initiators. In addition, if a photosensitizer is present, it absorbs radiation and becomes excited, and by coming into contact with the photopolymerization initiator, it promotes the decomposition of the photopolymerization initiator, thereby achieving a more effective hardening reaction. 【0032】 Examples of radiation used in the irradiation process include ultraviolet rays, infrared rays, visible light, and X-rays. The radiation source is located downstream of the inkjet head and irradiates the composition. While there are no particular limitations on the radiation source, examples include ultraviolet light-emitting diodes (UV light-emitting diodes). Using UV light-emitting diodes allows for miniaturization of the device and reduction of costs. UV light-emitting diodes as UV sources are particularly advantageous when installed inside an inkjet device because of their small size. 【0033】 1.2. Color layer formation process This recording method includes a color layer formation step in which a color layer is formed using a radiation-curable color ink composition (hereinafter also simply referred to as "color ink composition"). The color layer formation step includes an ejection step C in which the radiation-curable color ink composition is ejected from an inkjet head C and attached to the recording medium, and an irradiation step C in which radiation is irradiated onto the radiation-curable color ink composition attached to the recording medium to obtain a color layer. The overcoat layer formation step is performed after the color layer formation step. By forming an overcoat layer on top of the color layer, the image formed by the color layer can be finished with a matte texture. 【0034】 1.2.1.Discharge process C The ejection process C is a process of ejecting and adhering various color ink compositions onto a recording medium. More specifically, an inkjet method is used in which a pressure generating means is driven to eject a white ink composition or a clear ink composition filled in the pressure generating chamber of the inkjet head C from the nozzle. 【0035】 In the ejection process C, the inkjet heads C used include line heads that record using a line method and serial heads that record using a serial method. Generally, when inkjet head O is a line head, inkjet head C is also a line head, and when inkjet head O is a serial head, inkjet head C is also a serial head. 【0036】 1.2.2. Irradiation process C Irradiation step C involves irradiating the color ink composition attached to the recording medium with radiation. When irradiated with radiation, the color ink composition hardens and a coating film is formed. At this time, as with irradiation step O, it is preferable to use a color ink composition that contains a photosensitizer to promote the hardening reaction of the ink composition. 【0037】 Regarding the radiation used in irradiation step C, the same radiation and radiation source as in irradiation step O can be used. Furthermore, while there are no particular restrictions on the radiation source, for example, an ultraviolet light-emitting diode, which is advantageous for miniaturization, may be used. 【0038】 1.3. Radiation-curable ink compositions The radiation-curable ink composition used in this embodiment (hereinafter also referred to as "ink composition") contains a polymerizable compound as an essential component, and may further contain a photopolymerization initiator, colorant, dispersant, surfactant, polymerization inhibitor, etc., as needed. For example, the radiation-curable color ink composition that forms the color layer may contain a colorant and a polymerizable compound, the radiation-curable clear ink composition used when forming the overcoat layer may not contain a colorant but may contain at least a polymerizable compound, and the radiation-curable white ink composition may contain at least a white pigment and a polymerizable compound. 【0039】 1.3.1. Polymerizable compounds Polymerizable compounds are compounds that harden when irradiated with radiation. Polymerizable compounds include monofunctional monomers having one polymerizable functional group and polyfunctional monomers having multiple polymerizable functional groups, and may also include oligomers having one or more polymerizable functional groups as needed. A single polymerizable compound may be used alone, or two or more may be used in combination. 【0040】 Examples of monofunctional monomers include aromatic monofunctional monomers, nitrogen-containing monofunctional monomers, and aliphatic group-containing monofunctional monomers. Examples of polyfunctional monomers include vinyl ether group-containing (meth)acrylates and polyfunctional (meth)acrylates. 【0041】 The polymerizable compound content may be 10% to 99% by mass, 20% to 95% by mass, 30% to 90% by mass, or 40% to 80% by mass, based on the total amount of the ink composition. 【0042】 1.3.2. 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. The photopolymerization initiator may be used alone or in combination of two or more types. 【0043】 The content of the photopolymerization initiator is preferably 1.0% by mass or more and 10.0% by mass or less, more preferably 1.0% by mass or more and 8.0% by mass or less, and even more preferably 2.0% by mass or more and 7.0% by mass or less, based on the total amount of the ink composition. 【0044】 1.3.3. Colorants The ink composition of this recording method may optionally contain a colorant. The colorant may be at least one of pigments and dyes. One type of colorant may be used alone, or two or more types may be used in combination. 【0045】 The pigments are not particularly limited and include, for example, inorganic pigments and organic pigments. Examples of inorganic pigments include carbon blacks (CI Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black, as well as iron oxide and titanium dioxide. Furthermore, examples of organic pigments include azo pigments such as insoluble azo pigments, condensed azo pigments, azo lakes, and chelated azo pigments; polycyclic pigments such as phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments; dye chelates (e.g., basic dye type chelates, acid dye type chelates, etc.); dye lakes (basic dye type lakes, acid dye type lakes); nitro pigments; nitroso pigments; aniline black; and daylight fluorescent pigments. 【0046】 Dyes may be used as colorants. The dyes are not particularly limited and may include, for example, acid dyes, direct dyes, reactive dyes, and basic dyes. 【0047】 The amount of colorant is not particularly limited and can be adjusted as appropriate according to the characteristics of the ink composition being prepared. For example, the amount of colorant may be 0% to 30% by mass or 1% to 25% by mass relative to the total amount of the ink composition. 【0048】 1.3.4. Fluorescent whitening agents Fluorescent whitening agents are substances that absorb light of a specific wavelength and emit light in a different wavelength range. Examples of such wavelength ranges include those that absorb light in the 300-400 nm range and emit light in the 400-500 nm range. Examples of such fluorescent whitening agents include naphthalene benzoxazolyl derivatives, thiophene benzoxazolyl derivatives, stilbene benzoxazolyl derivatives, coumarin derivatives, styrene biphenyl derivatives, pyrazolone derivatives, stilbene derivatives, styrene and biphenyl styryl derivatives, bis(benzazole-2-yl) derivatives, carbostyryl, naphthalimide, dibenzothiophene-5,5'-dioxide derivatives, pyrene derivatives, and pyridotriazole. Note that a single fluorescent whitening agent may be used, or two or more may be used in combination. 【0049】 In this recording method, it is preferable that the clear ink composition contained in the overcoat layer contains a fluorescent whitening agent. When the clear ink composition contains a fluorescent whitening agent, the clear ink composition emits white light, which tends to further improve the matte finish of the resulting recording. 【0050】 Furthermore, the amount of fluorescent whitening agent contained in the clear ink composition may be, for example, 0.1% by mass or more and 1.0% by mass or less, or 0.1% by mass or more and 0.5% by mass or less, based on the total amount of the clear ink composition. 【0051】 1.3.5. Surfactants Examples of surfactants include acetylene glycol-based surfactants, fluorine-based surfactants, and silicone-based surfactants. Note that a single surfactant may be used alone, or two or more may be used in combination. 【0052】 Examples of acetylene glycol-based surfactants include 2,4,7,9-tetramethyl-5-decine-4,7-diol and its alkylene oxide adduct, and 2,4-dimethyl-5-decine-4-ol and its alkylene oxide adduct. Commercially available acetylene glycol-based surfactants may be used. Examples of commercially available products include the Orfin® 104 series (product name) and E series (product name) manufactured by Nisshin Chemical Industry Co., Ltd., and the Surfinol® series (product name) manufactured by Air Products and Chemicals Inc. 【0053】 Examples of fluorinated surfactants include perfluoroalkyl sulfonates, perfluoroalkyl carboxylates, perfluoroalkyl phosphate esters, perfluoroalkyl ethylene oxide adducts, perfluoroalkyl betaines, and perfluoroalkylamine oxide compounds. Commercially available fluorine-based surfactants may be used. Examples of commercially available products include S-144 (product name) and S-145 (product name) manufactured by Asahi Glass Co., Ltd. 【0054】 Examples of silicone-based surfactants include polysiloxane compounds and polyether-modified organosiloxanes. Commercially available silicone-based surfactants may be used. Examples of commercially available products include BYK® series 306, 307, 333, 341, 345, 346, 347, 348, and 349 (all product names) manufactured by BYK Chemie Japan Co., Ltd. 【0055】 The surfactant content is preferably 0.05% by mass or more and 2.5% by mass or less, more preferably 0.1% by mass or more and 1.5% by mass or less, and even more preferably 0.3% by mass or more and 1.0% by mass or less, relative to the total amount of the ink composition. 【0056】 1.4. Recording media The recording medium used in the inkjet recording method of this embodiment is not particularly limited, and examples include absorbent recording media, low-absorbent recording media, or non-absorbent recording media. From the viewpoint of more reliably achieving the effects of the present invention, the material of the recording medium is preferably non-absorbent or low-absorbent on both its front and back surfaces, and more preferably non-absorbent. 【0057】 Examples of non-absorbent recording media include polymer films and plates such as polyvinyl chloride, polyethylene terephthalate, polycarbonate, polystyrene, polyurethane, polyethylene, polypropylene, polyvinyl acetal, and blends of two or more thereof; films and plates of cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, etc.; metal foils and plates of iron, silver, copper, aluminum, etc., or plates and films with these metals deposited on them; alloy foils and plates of stainless steel, brass, etc.; and glass plates. 【0058】 Examples of low-absorption recording media include those having a coating layer (receiving layer) on the surface for receiving liquids. For example, these include films or plates coated with a hydrophilic polymer, or those coated with particles such as silica or titanium together with a binder (e.g., a hydrophilic polymer such as polyvinyl alcohol or polyvinylpyrrolidone). Furthermore, examples of low-absorption recording media with paper as the substrate include printing papers such as art paper, coated paper, and matte paper. 【0059】 Non-absorbent or low-absorbent recording media refer to recording media that do not absorb ink (liquid) at all or absorb very little. Quantitatively, non-absorbent or low-absorbent recording media are defined as "in the Bristow method, from the start of contact for 30 msec 1 / 2 Up to 10 mL / m² of water absorption capacity 2 This refers to "recording media as described below." 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." In contrast, absorbent recording media refer to recording media that do not fall under non-absorbent or low-absorbent categories. 【0060】 The recording medium may be colorless and transparent, semi-transparent, colored and transparent, chromatic and opaque, achromatic and opaque, etc. Furthermore, the recording medium itself may be colored, semi-transparent, or transparent. 【0061】 2. Inkjet recording device An inkjet recording apparatus (hereinafter also simply referred to as "recording apparatus") that can be used in this recording method includes: a first line inkjet head unit that ejects a color ink composition and adheres it to a recording medium; a first irradiation unit that irradiates the color ink composition adhered to the recording medium with radiation to form a color layer; a second line inkjet head unit that ejects a radiation-curable white ink composition and a clear ink composition and adheres them onto the color layer on the recording medium; and a second irradiation unit that irradiates the white ink composition and the clear ink composition adhered to the color layer with radiation to form an overcoat layer. 【0062】 Inkjet recording can be performed using either a line method or a serial method, but the line method is preferred. The line method is a recording method in which an inkjet head fixed to an inkjet recording device and having a width greater than or equal to the recording width of the recording medium is used to move the recording medium along the vertical direction (transport direction) of the recording medium, and ink droplets are ejected from the nozzles of the inkjet head in conjunction with this movement to form an image on the recording medium. The serial method, on the other hand, is a method of recording by performing main scans multiple times. Incidentally, an inkjet head used in the serial method is called a serial inkjet head or serial head, and an inkjet head used in the line method is called a line inkjet head or line head. 【0063】 Figures 3 and 4 are schematic cross-sectional views showing an example of an inkjet recording apparatus according to this embodiment. In Figure 3, the recording apparatus 100 includes a first line inkjet head unit 10, a first irradiation unit 20, a second line inkjet 30, and a second irradiation unit 40. The first line inkjet head unit 10, the first irradiation unit 20, the second line inkjet head unit 30, and the second irradiation unit 40 may be arranged in this order along the transport direction F1 of the recording medium P. 【0064】 Furthermore, the recording device 100 may have an upstream transport roller 50, a downstream transport roller 60, and a belt 70 as a configuration for transporting the recording medium P from the upstream side D1 in the transport direction to the downstream side D2 in the transport direction. 【0065】 2.1. First Line Inkjet Head Unit The first line inkjet head unit 10 ejects a color ink composition and adheres it to the recording medium P. This allows a color layer to be formed on the recording medium P. In this embodiment, a combination of multiple line inkjet heads configured for a predetermined purpose is called a "unit". For example, as shown in Figure 3, the first line inkjet head unit 10 of the recording device 100 in this embodiment may have one independent line inkjet head 10a to d for each color such as cyan, magenta, yellow, orange, black, and white. By using such a first line inkjet head unit 10, a color layer can be formed. 【0066】 2.2.First irradiation section The first irradiation unit 20 irradiates the color ink composition attached to the recording medium P with radiation to form a color layer. The polymerizable compounds in the color ink composition polymerize due to the first irradiation unit 20, forming a color layer. 【0067】 In Figures 3 and 4, the first irradiation unit 20 is positioned upstream of the second line inkjet head unit 30 in direction F. If there are multiple first line inkjet head units 10, the first irradiation unit 20 may be positioned downstream of those first line inkjet head units 10 in direction F. This allows the color ink composition attached to the recording medium P to be irradiated with radiation by multiple first line inkjet head units 10 at once, making it possible to miniaturize the recording device. 【0068】 Furthermore, if there are multiple first-line inkjet head units 10, the first irradiation unit 20 may be arranged between the multiple first-line inkjet head units 10, for example, between the first-line inkjet heads 10a to d. By arranging it between each head, radiation can be irradiated to each color ink composition immediately after it adheres to the recording medium P, which tends to improve the image quality of the recorded material. 【0069】 2.3. Second Line Inkjet Head Unit The second line inkjet head unit 30 ejects the white ink composition and the clear ink composition and adheres them to the color layer formed on the recording medium P. This second line inkjet head unit 30 forms an overcoat layer on the color layer. The overcoat layer formed by the radiation-curable white ink composition and the clear ink composition allows the resulting recording to have a uniform matte finish. 【0070】 The second line inkjet head unit 30 ejects the white ink composition and the clear ink composition and adheres them to the color layer and / or recording medium P. This second line inkjet head unit 30 forms the overcoat layer. In forming the overcoat layer, the recording device 100 may have separate second line inkjet head units 30 for the white ink composition and the clear ink composition. 【0071】 In Figure 3, the second line inkjet head unit 30 may include a second A line inkjet head 30a that ejects a white ink composition and a second B line inkjet head 30b that ejects a clear ink composition. The second A line inkjet head 30a is positioned downstream D2 in the transport direction of the recording medium P from the second B line inkjet head 30b. The second A line inkjet head 30a is an inkjet head that ejects a white ink composition, and the second B line inkjet head 30b is an inkjet head that ejects a clear ink composition. 【0072】 In Figure 4, the second line inkjet head unit 30 includes a second A line inkjet head 30a and a second B line inkjet head 30b. In Figure 4, the second B line inkjet head 30b is positioned downstream D2 of the transport direction of the recording medium P relative to the second A line inkjet head 30a. Regardless of the order in which the second A line inkjet head 30a and the second B line inkjet head 30b are positioned, a uniform matte-finish recording can be obtained even when observed from various angles. 【0073】 2.4.Second irradiation section The second irradiation unit 40 irradiates the white ink composition and clear ink composition attached to the color layer formed on the recording medium P with radiation to form an overcoat layer. The polymerizable compounds in the color ink composition polymerize due to the second irradiation unit 40, forming an overcoat layer. 【0074】 In Figures 3 and 4, the second irradiation unit 40 is positioned downstream of the second line inkjet head unit 30 in direction F. The second line inkjet head unit 30 has at least one second A line inkjet head 30a and a second B line inkjet head 30b. Therefore, it is sufficient to position it in one location downstream of each inkjet head in direction F. This allows for simultaneous irradiation of the radiation-curable white ink composition and clear ink composition attached to the color layer and / or recording medium P, thus enabling a smaller recording device. In other words, as shown in Figures 3 and 4, from the viewpoint of miniaturizing the recording device 100 as a whole and improving the efficiency of inkjet recording, the second irradiation unit 40 does not necessarily have to be positioned between the second A line inkjet head 30a and the second B line inkjet head 30b. 【0075】 Alternatively, the second irradiation unit 40 may be independently positioned between each line inkjet head. By positioning it between each head, radiation can be irradiated immediately after either the white ink composition or the clear ink composition adheres to the recording medium P, which tends to result in a more uniform matte finish on the recorded material. 【0076】 2.5. Others The upstream transport roller 50 and the downstream transport roller 60, although not shown in the figure, rotate in conjunction with the rotation of the transport motor, thereby driving the belt 70 to transport the recording medium in direction F1. [Explanation of symbols] 【0077】 1...Recording material, 2...Recording medium, 3...Color layer, 4...Rubber pattern formed with clear ink, 5...Rubber pattern formed with white ink, 10...First line inkjet head unit, 10a, 10b, 10c, 10d...Line inkjet heads, 20...First irradiation unit, 30...Second line inkjet head unit, 30a...Second A line inkjet head, 30b...Second B line inkjet head, 40...Second irradiation unit, 50...Upstream transport roller, 60...Downstream transport roller, 70...Belt, 100...Recording device, F1...Transportation direction, P...Recording medium.

Claims

[Claim 1] The process includes an overcoat layer formation step in which an overcoat layer is formed on a recording medium using a radiation-curable white ink composition and a radiation-curable clear ink composition. The above-mentioned overcoat layer formation step is The ejection step O involves ejecting the radiation-curable white ink composition and the radiation-curable clear ink composition from the inkjet head O and adhering them to a recording medium. The process includes an irradiation step O in which radiation is irradiated onto the radiation-curable white ink composition and the radiation-curable clear ink composition attached to the recording medium to obtain the overcoat layer. The color layer has irregularities formed with the radiation-curable white ink composition, The coverage rate of the overcoat layer on the recording medium is less than 100%. Inkjet recording method. [Claim 2] The process includes a color layer formation step in which a color layer is formed using a radiation-curable color ink composition. The aforementioned color layer formation step is Discharge step C involves ejecting a radiation-curable color ink composition from an inkjet head C and adhering it to the recording medium, The process includes an irradiation step C in which radiation is irradiated onto the radiation-curable color ink composition attached to the recording medium to obtain a color layer, The above-mentioned overcoat layer formation step is performed after the color layer formation step. The inkjet recording method according to claim 1. [Claim 3] In the overcoat layer, the coverage rate of the radiation-curable white ink composition on the recording medium is 20% or less. The inkjet recording method according to claim 1 or 2. [Claim 4] The inkjet head O is a line inkjet head. The inkjet recording method according to claim 1 or 2. [Claim 5] The radiation-curable clear ink composition contains a fluorescent whitening agent. The inkjet recording method according to claim 1 or 2. [Claim 6] The process comprises forming an overcoat layer on a color layer formed on a recording medium using a radiation-curable white ink composition and a radiation-curable clear ink composition, The above-mentioned overcoat layer formation step is The ejection step O involves ejecting the radiation-curable white ink composition and the radiation-curable clear ink composition from the inkjet head O and adhering them to a recording medium. The process includes an irradiation step O in which radiation is irradiated onto the radiation-curable white ink composition and the radiation-curable clear ink composition attached to the recording medium to obtain the overcoat layer. In the overcoat layer, the cured product of the white ink composition and the cured product of the clear ink composition are arranged parallel to each other on the surface of the recording medium. The coverage rate of the overcoat layer on the recording medium is less than 100%. Inkjet recording method.

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