JP2012016870A - Printer and printing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cure the same extent even between inks where the absorption degree of light energy differs when using ink which is cured by absorbing light energy.SOLUTION: The printer includes (A) a black ink nozzle which jets a black ink drop cured by the irradiation of a medium by the energy of light, (B) a color ink nozzle which jets a color ink drop other than the black ink drop cured by the irradiation of the medium by the energy of light, (C) an irradiation unit which irradiates the medium with the light, and (D) a control unit which controls to jet the black ink drop to a pixel of the medium a plurality of times when a dot of black is formed in the pixel, and then cure the black ink drop by irradiating the pixel with the light every time when the black ink drop is jetted, and controls to jet the color ink drop once to the pixel when a dot of a color is formed in the pixel of the medium, and then cure the color ink drop by irradiating the pixel to which the color ink drop is jetted with the light.

Description

  The present invention relates to a printing apparatus and a printing method.

  2. Description of the Related Art Printing apparatuses that perform printing by ejecting ultraviolet curable ink that is cured by absorbing light such as ultraviolet rays have been developed. Such an ink contains at least a curing component that is cured by light such as ultraviolet rays and a pigment having a color to be expressed.

JP 2008-265263 A JP 2004-291459 A JP 2005-335073 A International Publication No. 2005/105452

  For example, when an ultraviolet curable ink containing a pigment that easily absorbs ultraviolet rays such as black is used, most of the ultraviolet rays are absorbed by the pigment. As a result, ultraviolet rays do not reach the curable component and are harder to cure than ultraviolet curable inks containing pigments of other colors. As a result, the degree of curing differs between an ink containing a pigment that easily absorbs ultraviolet rays and an ink that does not, and the glossiness of the printed matter is different. Therefore, even when ink that is hard to be cured by ultraviolet rays or the like is used, it is desirable that the ink be cured to the same extent as inks of other colors.

  The present invention has been made in view of such circumstances, and in the case of using ink that is cured by absorbing light energy, the same degree is obtained even between inks having different degrees of light energy absorption. It aims to be able to be cured.

The main invention for achieving the above object is:
(A) a black ink nozzle that ejects black ink droplets that are cured by irradiation energy of light onto a medium;
(B) a color ink droplet of a color other than the black ink droplet, the color ink nozzle ejecting the color ink droplet cured by the irradiation energy of the light onto the medium;
(C) an irradiation unit for irradiating the medium with light;
(D) When forming black dots on the pixels of the medium, the black ink droplets are ejected to the pixels a plurality of times, and the pixels are irradiated with the light each time the black ink droplets are ejected. Cure the drops,
When forming color dots on the pixels of the medium, the color ink droplets are ejected once to the pixels, and the light is applied to the pixels on which the color ink droplets are ejected to cure the color ink droplets. A control unit;
Is a printing apparatus.

  Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

1 is an overall configuration block diagram of a printer 1. FIG. 1 is a perspective view of a printer 1. FIG. It is a figure explaining the structure of a head. It is a figure explaining a drive signal. FIG. 3 is a diagram illustrating an arrangement of nozzles provided on the lower surface of a head 41. It is a figure explaining ejection of black ink. It is a figure explaining ejection of a color ink. FIG. 8A is a diagram for explaining how dots are formed with black ink, and FIG. 8B is a diagram for explaining how dots are formed with color ink. It is a table | surface explaining the composition of the ink used in this embodiment. It is a figure explaining the printing duty in 2nd Embodiment. It is a schematic side view of the printer 1 in 5th Embodiment. FIG. 10 is a schematic top view of a printer 1 in a fifth embodiment.

  At least the following matters will become clear from the description of the present specification and the accompanying drawings.

(A) a black ink nozzle that ejects black ink droplets that are cured by irradiation energy of light onto a medium;
(B) a color ink droplet of a color other than the black ink droplet, the color ink nozzle ejecting the color ink droplet cured by the irradiation energy of the light onto the medium;
(C) an irradiation unit for irradiating the medium with light;
(D) When forming black dots on the pixels of the medium, the black ink droplets are ejected to the pixels a plurality of times, and the pixels are irradiated with the light each time the black ink droplets are ejected. Cure the drops,
When forming color dots on the pixels of the medium, the color ink droplets are ejected once to the pixels, and the light is applied to the pixels on which the color ink droplets are ejected to cure the color ink droplets. A control unit;
A printing apparatus comprising:
In this way, in the case of using ink that is cured by absorbing light energy, it can be cured to the same extent even between inks having different degrees of light energy absorption.

In such a printing apparatus, it is desirable that the mass of the maximum black ink droplet ejected is smaller than the mass of the maximum color ink droplet ejected.
By doing so, the black ink which is hard to be cured is ejected with a small ink and cured with each ejection, so that it can be cured to the same degree as other easily curable inks.

The concentration of the pigment contained in the black ink may be lower than the concentration of the pigment contained in the color ink.
By doing so, the concentration of the pigment that easily absorbs light is lowered for the black ink and is cured each time it is ejected, so that it can be cured to the same extent as other easily curable inks.

The first print mode for ejecting the color ink droplets and the second print mode for not ejecting the color ink droplets, and the mass of the largest black ink droplet ejected in the second print mode is: It is desirable that the mass of the largest black ink droplet ejected in the first printing mode is larger.
In so-called monochrome mode printing in which no color ink droplets are ejected, color mixing with other color inks does not occur, so the size of the black ink dots can be increased.

Further, it is desirable that the black ink droplets and the color ink droplets are temporarily cured.
By doing in this way, a black ink drop and a color ink drop can be temporarily hardened appropriately.

Furthermore, a yellow ink nozzle row that ejects yellow ink droplets that are cured by the irradiation energy of the light onto the medium is provided, and the control unit forms the yellow dots on the pixels when the yellow dots are formed on the pixels of the medium. It is desirable that the yellow ink droplets are ejected a plurality of times, and the light is applied to the pixels each time the yellow ink droplets are ejected to cure the yellow ink droplets.
In this way, even when using a yellow ink that contains a pigment that absorbs more ultraviolet rays and is relatively hard to cure, it is ejected in multiple times and cured each time it is ejected. It can be cured to the same extent as easy ink.

Further, a green ink nozzle array that ejects green ink droplets that are cured by the irradiation energy of the light onto a medium, and the control unit forms the green dot on the pixel when the green dot is formed on the pixel of the medium. Preferably, the green ink droplet is ejected a plurality of times, and the pixel is irradiated with the light each time the green ink droplet is ejected to cure the green ink droplet.
In this way, even when using a green ink that contains a pigment that absorbs more ultraviolet rays and is relatively hard to cure, it is ejected in multiple times and cured each time it is ejected. It can be cured to the same extent as easy ink.

Black ink droplets that are cured by light irradiation energy are ejected to the pixels of the medium a plurality of times, and each time the black ink droplets are ejected, the pixels are irradiated with the light to cure the black ink droplets to form black dots. To do
A color ink droplet that is cured by light irradiation energy is ejected once onto the pixels of the medium, and the color ink droplet is cured by irradiating the light onto the pixel that ejects the color ink droplet to form a color dot. And
Including printing method.
In this way, in the case of using ink that is cured by absorbing light energy, it can be cured to the same extent even between inks having different degrees of light energy absorption.

=== First Embodiment ===
Hereinafter, an embodiment will be described by taking a printing system in which a printer and a computer are connected as an example.

  FIG. 1 is a block diagram of the overall configuration of the printer 1. FIG. 2 is a perspective view of the printer 1. The computer 60 is communicably connected to the printer 1 and outputs print data for causing the printer 1 to print an image to the printer 1. The computer 60 is installed with a program (printer driver) for converting image data output from the application program into print data. The printer driver is recorded on a recording medium (computer-readable recording medium) such as a CD-ROM or can be downloaded to a computer via the Internet.

  The controller 10 is a control unit for controlling the printer 1. The interface unit 11 is for transmitting and receiving data between the computer 60 and the printer 1. The CPU 12 is an arithmetic processing unit for controlling the entire printer 1. The memory 13 is for securing an area for storing a program of the CPU 12, a work area, and the like. The CPU 12 controls each unit by the unit control circuit 14. The detector group 50 monitors the situation in the printer 1, and the controller 10 controls each unit based on the detection result.

The transport unit 20 feeds the medium S to a printable position, and transports the medium S by a predetermined transport amount in the transport direction (predetermined direction) during printing.
The carriage unit 30 is for moving the head 41 in a movement direction that intersects the conveyance direction, and includes a carriage 31.

  The head unit 40 is for ejecting ink onto the medium S and has a head 41. The head 41 is moved in the movement direction by the carriage 31. A plurality of nozzles, which are ink ejecting portions, are provided on the lower surface of the head 41, and each nozzle is provided with an ink chamber (not shown) containing ink.

  The drive signal generation circuit 70 generates a drive signal that is applied to a drive element such as a piezo element included in the head to eject ink droplets. The drive signal generation circuit 70 includes a DAC (not shown). Then, an analog voltage signal is generated based on digital data relating to the waveform of the drive signal sent from the unit control circuit 14. The drive signal generation circuit 70 also includes an amplifier circuit (not shown), and performs power amplification on the generated voltage signal to generate a drive signal. The drive signal generation circuit 70 generates a drive signal COM_A supplied to the black ink nozzle row and a drive signal COM_B supplied to the color ink nozzle row. Here, “color ink” refers to cyan ink, magenta ink, and yellow ink.

  The ultraviolet irradiation unit 80 is a unit composed of an LED that irradiates ultraviolet rays, and moves in the moving direction of the head together with the head 41 as will be described later. Then, the ultraviolet curable ink is cured.

  FIG. 3 is a diagram illustrating the structure of the head. In the drawing, the nozzle Nz, the piezo element PZT, the ink supply path 402, the nozzle communication path 404, and the elastic plate 406 of the head 41 are shown.

  Ink drops are supplied to the ink supply path 402 from an ink tank (not shown). These ink droplets and the like are supplied to the nozzle communication path 404. A drive pulse of a drive signal described later is applied to the piezo element PZT. When the drive pulse is applied, the piezo element PZT expands and contracts according to the signal of the drive pulse and vibrates the elastic plate 406. An amount of ink droplets corresponding to the amplitude of the drive pulse is ejected from the nozzle Nz.

  FIG. 4 is a diagram for explaining drive signals. In the present embodiment, the drive signal for ejecting color ink is different from the drive signal for ejecting black ink. As described later, this is because one black ink dot is formed by overlapping a plurality of ink droplets, while one color ink dot is formed by one ink droplet. When the size of the black ink dots and the color ink dots are substantially the same under these conditions, it is necessary to make the black ink droplets smaller than the color ink droplets.

  For these reasons, the drive signals of both are generated differently. However, in the present embodiment, only the amplitude of the drive pulse in the drive signal is varied, so the drive signal will be described here by taking the black ink drive signal COM_A as an example. The color ink drive signal COM_B is obtained by increasing the magnitude of the drive pulse of the black ink drive signal COM_A.

  The drive signal COM_A is repeatedly generated every repetition period T. A period T that is a repetition period corresponds to a period during which the sheet S is conveyed by one pixel area. For example, if the printing resolution in the transport direction is set to 360 dpi, the period T corresponds to a period for transporting the paper S for 1/360 inch. Then, on the basis of the pixel data included in the print data, the drive pulse PS1 or PS2 of each section included in the period T is applied to the piezo element PZT, so that no dot is formed in one pixel region, Dots can be formed.

  The drive signal COM_A has a first drive pulse PS1 generated in the section T1 in the repetition period and a second drive pulse PS2 generated in the section T2. The first drive pulse PS1 is a fine vibration pulse, and is a drive pulse for finely vibrating the ink surface (ink meniscus) of the nozzle. When this pulse is applied, ink is not ejected from the nozzle. On the other hand, the second drive pulse PS2 is a pulse for ink ejection, and is a drive pulse for ejecting ink from the nozzles. When this pulse is applied, ink is ejected from the nozzle.

  In the drawing, Vh is shown as the amplitude of the second drive pulse PS2. When this amplitude is increased, large size ink droplets are ejected, and when the amplitude is decreased, small size ink droplets are ejected. Therefore, the magnitude of Vh of the second drive pulse PS2 of the color ink drive signal COM_B is set to be larger than the magnitude of Vh of the second drive pulse PS2 of the black ink drive signal COM_A. By doing so, the size of the black ink droplet can be made smaller than the size of the color ink droplet.

  FIG. 5 is a diagram illustrating an arrangement of nozzles provided on the lower surface of the head 41. In addition, the figure is the figure which looked at the nozzle virtually from the upper surface of the head 41. FIG. On the lower surface of the head 41, four nozzle rows are formed in which 180 nozzles are arranged at a predetermined interval (nozzle pitch D) in the transport direction. As shown in the drawing, a black nozzle row K for ejecting black ink, a cyan nozzle row C for ejecting cyan ink, a magenta nozzle row M for ejecting magenta ink, and a yellow nozzle row Y for ejecting yellow ink are arranged in the moving direction. It is out. Note that the 180 nozzles in each nozzle row are numbered sequentially from the nozzles on the downstream side in the transport direction (# 1 to # 180).

  In such a printer 1, dot formation processing in which ink droplets are intermittently ejected from the head 41 moving along the moving direction to form dots on the medium, and the medium is conveyed with respect to the head 41 in the conveying direction. The conveyance process is repeated. By doing so, dots can be formed by dot formation processing at positions on the medium different from the positions of the dots formed by the previous dot formation processing, and a two-dimensional image is printed on the medium Can do. The operation in which the head 41 moves once in the movement direction while ejecting ink droplets (corresponding to one dot formation processing / ejection operation) is referred to as “pass”.

  The head in this embodiment is also provided with an ultraviolet irradiation unit 80. The ultraviolet irradiation unit 80 includes a first LED assembly 81 and a second LED assembly 82. Each LED assembly is composed of a plurality of LEDs. These LED assemblies emit ultraviolet light having a peak at a wavelength of 395 nm.

  The first LED assembly 81 and the second LED assembly 82 are provided on both sides in the moving direction of the head 41 as shown in the figure. The light is always lit during the printing operation. In this way, the ink ejected from each nozzle row and landed on the medium can be cured each time. That is, the ink that has landed on the medium can be cured for each pass.

  FIG. 6 is a diagram for explaining black ink ejection. On the left side of the figure, the relative movement of the nozzle column with respect to the medium is shown, and on the right side of the figure, the number of the formation target nozzle corresponding to the row number and column number of the pixel is shown.

  In the figure, a black ink nozzle row K, a yellow ink nozzle row Y, a magenta ink nozzle row M, and a cyan ink nozzle row C are shown as color ink nozzle rows. Here, for simplicity of explanation, the number of nozzles belonging to one nozzle row is reduced to eight. Further, D is shown as the inter-nozzle distance. Here, it is assumed that the medium is transported by a transport amount of 4D / 3.

  On the right side of the figure, nozzle numbers that can eject ink droplets for each pixel are shown. For example, “7” and “3” are shown in the pixel in the first row and the first column, which indicates that the No. 7 nozzle and No. 3 nozzle can eject ink droplets to the pixel. Yes. For example, “6” and “2” are shown in the pixel in the second row and the second column. This is because the sixth nozzle and the second nozzle can eject ink droplets to the pixel. Is shown.

  One ink droplet is ejected in one pass for one pixel. Therefore, in the example shown in this figure, dots are formed in two passes so that two ink droplets are ejected to one pixel.

  In this way, for the black ink, two ink droplets are ejected to each pixel as shown in FIG. One dot is formed by two ink droplets.

  FIG. 7 is a diagram illustrating the ejection of color ink. Also in this drawing, the relative movement of the nozzle row with respect to the medium is shown on the left side, and the number of the formation target nozzle corresponding to the row number and column number of the pixel is shown on the right side of the drawing.

Since both the black ink nozzle row and the color ink nozzle row are integrated in the head, if the medium is transported as shown in FIG. For the pixel, the No. 7 nozzle and the No. 3 nozzle can eject ink droplets to the pixel. That is, two ink droplets can be ejected in two passes. However, in this embodiment, regarding color ink, only one ink droplet is ejected to one pixel, and therefore, ink is not ejected in the second pass of the first pass and the second pass in one pixel. (In the figure, “x” is shown as meaning not to inject).
In this way, for color ink, one ink droplet is ejected to each pixel. One dot is formed by one ink droplet.

Through the above-described operation, a plurality of ink droplets are ejected to one pixel as black ink droplets. At that time, the pixels are irradiated with ultraviolet rays every time the black ink droplet is ejected, and are cured each time the ink is ejected. Here, since the size of the black ink droplet is smaller than the size of the color ink droplet, one black ink droplet is reliably cured on the medium.
By doing so, even between inks having different degrees of ultraviolet absorption, it can be appropriately cured to the same extent.

  FIG. 8A is a diagram for explaining how dots are formed with black ink. FIG. 8B is a diagram illustrating a state in which dots are formed with color ink. Each drawing shows an ink droplet that has landed on one pixel. As shown in the figure, a black dot is composed of a plurality of ink droplets. Further, the color ink dots are formed by one ink droplet.

  Here, regarding black ink, a dot is formed by two ink droplets per pixel, but a dot may be formed by ejecting a plurality of ink droplets per pixel.

  In the above-described embodiment, only black ink is configured to form dots with two ink droplets per pixel, and is cured by the ultraviolet irradiation unit each time one ink droplet is ejected. Further, the same operation may be performed for another color of ink that is difficult to cure. Specifically, with respect to yellow ink containing a yellow pigment, a dot is composed of a plurality of ink droplets per pixel, and is cured by an ultraviolet irradiation unit each time one ink droplet is ejected. Also good. Also, in the case of having a green ink nozzle row for ejecting green ink containing a green pigment, a dot is formed by a plurality of ink droplets in one pixel, and each time one ink droplet is ejected, ultraviolet rays are used. It is good also as hardening by an irradiation unit.

<About black ink>
In the present embodiment, the black ink is an ink that contains a black color material such as carbon black and is used for printing a black image. The content concentration of the black color material in the black ink is not particularly limited, and so-called light black ink having a low content concentration is also included in the black ink.

<Ink composition>
-Radiation curable ink composition Next, an example of the composition of the radiation curable ink (including the ultraviolet curable ink) used in the present embodiment will be described.

-Polymerizable compound The radiation-curable ink composition according to this embodiment contains a polymerizable compound. Examples of the polymerizable compound include monofunctional monomers, bifunctional monomers, trifunctional monomers, urethane acrylate oligomers, and amino acrylates shown below.

  The monofunctional monomer is not particularly limited. For example, (2-methyl-2-ethyl-1,3-dioxolan-4-yl) methyl (meth) acrylate, (2-methyl-2-isobutyl-1,3- Dioxolan-4-yl) methyl (meth) acrylate, phenoxyethyl (meth) acrylate, isobornyl (meth) acrylate, methoxydiethylene glycol mono (meth) acrylate, (meth) acryloylmorpholine, dicyclopentenyloxyethyl (meth) acrylate, di Cyclopentenyl (meth) acrylate, dicyclopentanyl (meth) acrylate, isobornyl (meth) acrylate, trimethylolpropane formal mono (meth) acrylate, adamantyl (meth) acrylate, oxetane (meth) acrylate Over DOO, 3,3,5-trimethylcyclohexane (meth) acrylate. These polymerizable compounds can be used alone or in combination of two or more. In this specification, the description of (meth) acrylate indicates acrylate or methacrylate.

  The bifunctional monomer is not particularly limited, and examples thereof include alkylene glycol di (meth) acrylate and di (meth) acrylate having an alicyclic structure. Examples of the alkylene glycol di (meth) acrylate include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, and 1,9-nonanediol. Di (meth) acrylate, polyethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 2-hydroxy-1, Examples include 3-di (meth) acryloxypropane. Examples of the di (meth) acrylate having an alicyclic structure include tricyclodecane dimethanol di (meth) acrylate, dioxane glycol di (meth) acrylate, isocyanuric acid EO-modified di (meth) acrylate, and dimethylol tricyclo. Examples include decanedi (meth) acrylate and 1,3-adamantanediol di (meth) acrylate. These polymerizable compounds can be used alone or in combination of two or more.

  The trifunctional monomer is not particularly limited. For example, trimethylolpropane tri (meth) acrylate, trimethylolpropane EO-modified tri (meth) acrylate, trimethylolpropane PO-modified tri (meth) acrylate, and glycerin PO-modified tri (meth). Examples thereof include acrylate and isocyanuric acid EO-modified tri (meth) acrylate.

  Moreover, as another polymeric compound, the N-vinyl compound may be included. Examples of the N-vinyl compound include N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, N-vinylpyrrolidone, N-vinylcaprolactam, and derivatives thereof.

  Moreover, the urethane type oligomer may be included as a polymeric compound. The urethane-based oligomer means one having at least one urethane bond and radically polymerizable unsaturated double bond in the molecule. Here, the oligomer used in this embodiment is a small number of units substantially or conceptually obtained from a molecule having a small relative molecular mass (synonymous with molecular weight), generally about 2 to 20 times. Molecules with a medium relative molecular mass with a repetitive structure of about twice.

  Examples of the urethane oligomer include oligomers produced by an addition reaction between a polyol and a polyisocyanate and a polyhydroxy compound. Examples of urethane oligomers include polyester urethane acrylate, polyether urethane acrylate, polybutadiene urethane acrylate, and polyol urethane acrylate. Specifically, examples of the urethane oligomer include CN963J75, CN964, CN965, CN966J75 (all available from SARTOMER).

  Moreover, amino acrylate may be included as a polymeric compound. As aminoacrylate, what is obtained by making bifunctional (meth) acrylate and an amine compound react is mentioned.

  Examples of the bifunctional acrylate include propylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, and 1,6-hexanediol di (meth). Acrylate, 1,9-nonanediol di (meth) acrylate, alkylene glycol di (meth) acrylate such as neopentyl glycol di (meth) acrylate, di (meth) acrylate of bisphenol S ethylene oxide adduct, ethylene of bisphenol F Di (meth) acrylate of oxide adduct, di (meth) acrylate of ethylene oxide adduct of bisphenol A, di (meth) acrylate of ethylene oxide adduct of thiobisphenol, ethylene of brominated bisphenol A Bisphenol alkylene oxide adduct di (meth) acrylate such as di (meth) acrylate of oxide adduct, polyalkylene glycol di (meth) acrylate such as polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, hydroxypivalin Examples include di (meth) acrylate of acid neopentyl glycol ester.

  Examples of amine compounds include ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, n-pentylamine, isopentylamine, n-hexylamine, cyclohexylamine, n-heptylamine, and n-octylamine. Monofunctional amine compounds such as 2-ethylhexylamine, n-nonylamine, n-decylamine, n-dodecylamine, n-tetradecylamine, n-hexadecylamine, n-octadecylamine, benzylamine, phenethylamine, diethylenetriamine, triethylene Ethylenetetramine, tetraethylenepentamine, 1,6-hexamethylenediamine, 1,8-octamethylenediamine, 1,12-dodecamethylenediamine, o-phenylenediamine, p-phenylenediamine , M-phenylenediamine, o-xylylenediamine, p-xylylenediamine, m-xylylenediamine, menthanediamine, bis (4-amino-3-methylcyclohexylnomethane, 1,3-diaminocyclohexane, isophoronediamine And polyfunctional amine compounds such as spiroacetal-based diamines, and also high molecular weight type polyfunctional amine compounds such as polyethyleneimine, polyvinylamine, and polyallylamine.

  The content of the polymerizable compound is preferably 20% by mass or more, and more preferably 20% by mass or more and 95% by mass or less with respect to the total mass of the radiation curable ink composition.

-Photopolymerization initiator The radiation-curable ink composition according to this embodiment may contain a photopolymerization initiator. The photopolymerization initiator is a general term for compounds having a function of initiating a copolymerization reaction of the above-described polymerizable compound by irradiating the radiation curable ink composition discharged onto the recording medium with actinic radiation. .

  Examples of the photopolymerization initiator include known photopolymerization initiators such as alkylphenone photopolymerization initiators, acylphosphine oxide photopolymerization initiators, titanocene photopolymerization initiators, and thioxanthone photopolymerization initiators. It is done. Among these, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide having excellent compatibility with the above-mentioned reaction components, bis (2,4,6-trimethylbenzoyl) -phenylphosphine having a wide range of light absorption characteristics A molecular cleavage type such as fin oxide and a hydrogen abstraction type such as diethylthioxanthone are preferred. The reason why acylphosphine oxide-based photopolymerization initiators are preferable is that the structure of the chromophore changes greatly before and after photocleavage, so the change in absorption is large, and a short wavelength of absorption called photobleaching (photobleaching) is observed. Because it is. Moreover, it is because yellowing hardly occurs despite the absorption ranging from the UV to the VL region, and is excellent in internal curing. For this reason, it is particularly preferable for a transparent thick film or a pigmented coating film having a large hiding power. The reason why the thioxanthone photopolymerization initiator is preferable is that it reacts with oxygen remaining in the reaction system after photocleavage to lower the concentration of oxygen in the system. Since the degree of radical polymerization inhibition can be reduced as much as the oxygen concentration decreases, the surface curability can be improved. Further, it is particularly preferable to use an acyl phosphonic photopolymerization initiator and a thioxanthone photopolymerization initiator in combination. These photopolymerization initiators can be used singly or in combination of two or more, and each characteristic can be maximized.

  The content of the photopolymerization initiator is preferably 1% by mass or more and 20% by mass or less, more preferably 5% by mass or more and 15% by mass or less with respect to the total mass of the radiation curable ink composition.

Other Additives The radiation curable ink composition according to this embodiment can contain additives such as pigments, dispersants, slip agents, photosensitizers, polymerization inhibitors, and the like as necessary.

  The radiation curable ink composition according to the present embodiment is used with a pigment added thereto, but can function as a so-called clear ink as it is. Although it does not restrict | limit especially as a pigment which can be used in this embodiment, An inorganic pigment and an organic pigment are mentioned. As the inorganic pigment, in addition to titanium oxide and iron oxide, carbon black produced by a known method such as a contact method, a furnace method, or a thermal method can be used. On the other hand, organic pigments include azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments), polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinofullerone pigments, etc.) Nitro pigments, nitroso pigments, aniline black, and the like can be used.

  Among specific examples of pigments that can be used in the present embodiment, carbon black includes C.I. I. Pigment black 7, for example, No. available from Mitsubishi Chemical Corporation. 2300, no. 900, MCF88, No. 33, no. 40, no. 45, no. 52, MA7, MA8, MA100, no. Raven5750, 5250, 5000, 3500, 1255, 700, etc. available from Columbia Chemical Company 2200B, etc. Also, Regal400R, 330R, 660R, MoguL, available from Cabot 700, Monarch 800, 880, 900, 1000, 1100, 1300, 1400, etc. Also available from Degussa are ColorBlack FW1, FW2, FW2V, FW18, FW200, ColorBlackS150, S160. , S170, Printex35, U, V, 140U, Special Black6, 5, 4A, 4 and the like.

  Examples of pigments that can be used when the radiation curable ink composition according to this embodiment is a yellow ink include C.I. I. Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 120, 128, 129, 138, 150, 151, 154, 155, 180, 185, 213 and the like.

  Examples of pigments that can be used when the radiation curable ink composition according to the present embodiment is magenta ink include C.I. I. Pigment Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 112, 122, 123, 168, 184, 202, 209, C.I. I. Pigment violet 19 and the like.

  Examples of pigments that can be used when the radiation curable ink composition according to the present embodiment is cyan ink include C.I. I. Pigment blue 1, 2, 3, 15: 3, 15: 4, 16, 22, 60, and the like.

  Examples of pigments that can be used when the radiation curable ink composition according to this embodiment is a green ink include C.I. I. Pigment green 7, 8, 36, and the like.

  Examples of pigments that can be used when the radiation curable ink composition according to this embodiment is an orange ink include C.I. I. Pigment orange 51, 66 and the like.

  Examples of pigments that can be used when the radiation curable ink composition according to the present embodiment is white ink include basic lead carbonate, zinc oxide, titanium oxide, and strontium titanate.

  The average particle diameter of the pigment that can be used in the present embodiment is preferably in the range of 10 nm to 200 nm, more preferably in the range of 50 nm to 150 nm.

  The amount of the pigment that can be added to the radiation curable ink composition according to the present embodiment is 0.1% by mass or more and 25% by mass or less, more preferably, based on the total mass of the radiation curable ink composition. It is 0.5 mass% or more and 15 mass% or less.

  In the radiation curable ink composition according to this embodiment, a dispersant may be added for the purpose of improving the dispersibility of the pigment. Dispersing agents that can be used in this embodiment include Solsperse 3000, 5000, 9000, 12000, 13240, 17000, 24000, 26000, 28000, 36000 (above, manufactured by Lubrizol), DISCOL N-503, N-506, Examples thereof include polymer dispersants such as N-509, N-512, N-515, N-518, and N-520 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

  A slip agent may be added to the radiation curable ink composition according to this embodiment. The slip agent that can be used in this embodiment is preferably a silicone-based surfactant, more preferably a polyester-modified silicone or a polyether-modified silicone. Specifically, examples of the polyester-modified silicone include BYK-347, 348, BYK-UV3500, 3510, 3530 (above, manufactured by BYK Chemie Japan Co., Ltd.), and the polyether-modified silicone includes BYK. -3570 (made by Big Chemie Japan Co., Ltd.) and the like.

  A photosensitizer may be added to the radiation curable ink composition according to this embodiment. Photosensitizers that can be used in this embodiment include amine compounds (aliphatic amines, amines containing aromatic groups, piperidine, reaction products of epoxy resins and amines, triethanolamine triacrylate, etc.), urea compounds ( Allylthiourea, o-tolylthiourea, etc.), sulfur compounds (sodium diethyldithiophosphate, soluble salts of aromatic sulfinic acid, etc.), nitrile compounds (N, N-diethyl-p-aminobenzonitrile, etc.), phosphorus compounds (tri -N-butylphosphine, sodium diethyldithiophosphide, etc.), nitrogen compounds (Michler ketone, N-nitrisohydroxylamine derivative, oxazolidine compound, tetrahydro-1,3-oxazine compound, formaldehyde or acetaldehyde and diamine condensate, etc. , Chlorine compounds (carbon tetrachloride, hexachloroethane, etc.) and the like.

  A polymerization inhibitor may be added to the radiation curable ink composition according to this embodiment. Examples of the polymerization inhibitor that can be used in this embodiment include hydroquinone, benzoquinone, and p-methoxyphenol.

Physical properties (1) Viscosity The viscosity at 20 ° C. of the radiation curable ink composition according to this embodiment is preferably 5 mPa · s to 50 mPa · s, more preferably 20 mPa · s to 40 mPa · s. . When the viscosity at 20 ° C. of the radiation curable ink composition is within the above range, an appropriate amount of the radiation curable ink composition is ejected from the nozzle, and the flight bending and scattering of the radiation curable ink composition can be further reduced. Therefore, it can be suitably used for an ink jet recording apparatus. The viscosity was measured by using a viscoelasticity tester MCR-300 (manufactured by Pysica), increasing the Shear Rate to 10 to 1000 in an environment of 20 ° C., and reading the viscosity at Shear Rate 200 hours.

(2) Surface Tension The surface tension at 20 ° C. of the radiation curable ink composition according to this embodiment is preferably 20 mN / m or more and 30 mN / m or less. When the surface tension at 20 ° C. of the radiation curable ink composition is within the above range, the radiation curable ink composition is hardly wetted by the liquid-repellent treated nozzle. Accordingly, an appropriate amount of the radiation curable ink composition is ejected from the nozzle, and the flight bending and scattering of the radiation curable ink composition can be further reduced, so that it can be suitably used for an ink jet recording apparatus. The surface tension was measured by using an automatic surface tension meter CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.) to confirm the surface tension when the platinum plate was wetted with ink in an environment of 20 ° C.

Recording medium The recording medium used in the image forming method according to the present embodiment is preferably non-ink-absorbing or low-absorbing. When the image forming method of the present embodiment is used, a good image can be formed even if the recording medium is non-ink-absorbing or low-absorbing.

  As a non-ink-absorbing recording medium, for example, a plastic film coated on a substrate such as a plastic film or paper that has not been surface-treated for inkjet printing (that is, an ink-absorbing layer is not formed). And those having a plastic film adhered thereto. Examples of the plastic here include polyvinyl chloride, polyethylene terephthalate, polycarbonate, polystyrene, polyurethane, polyethylene, and polypropylene. Examples of the recording medium having low ink absorption include printing paper such as art paper, coated paper, and matte paper.

Here, in this specification, “ink non-absorbing or low-absorbing recording medium” means “the amount of water absorption from the start of contact to 30 msec ^1/2 in the Bristow method is 10 mL / m ² or less. Recording medium ". This Bristow method is the most popular method for measuring the amount of liquid absorbed in a short time, and is also adopted by the Japan Paper Pulp Technology Association (JAPAN TAPPI). For details of the test method, refer to Standard No. of “JAPAN TAPPI Paper Pulp Test Method 2000”. 51 "Paper and paperboard-Liquid absorbency test method-Bristow method". In the present specification, a non-ink-absorbing or low-absorbing recording medium is also referred to as “plastic medium”.

=== Second Embodiment ===
In the second embodiment, an ink that is hard to cure such as a black ink is common to the first embodiment in that dots are formed by multiple ejections per pixel and irradiation with ultraviolet rays. However, in the second embodiment, the mass percentage of the pigment contained in the black ink is set lower than the mass percentage contained in the color ink. Note that the size of the black ink droplets in the second embodiment is larger than the size of the black ink droplets in the first embodiment.

FIG. 9 is a table illustrating the composition of the ink used in this embodiment. Hereinafter, although the ink used in this embodiment is demonstrated concretely, it is not limited to these. Note that E ₉₀ in FIG. 9 is the ultraviolet irradiation energy necessary to cure the ink by 90%. The ink curing rate can be determined by the method described in JP-A-2004-216681, stage 0029.

-Preparation of pigment dispersion: 18 parts by mass of black pigment as a colorant (trade name “MICROLITH-WA Black C-WA” manufactured by Ciba Specialty Chemicals Co., Ltd.), 1.2 mass of Solsperse 36000 (manufactured by LUBRIZOL) as a dispersant Phenoxyethyl acrylate (Osaka Organic Chemical Co., Ltd., trade name “V # 192”) as a monofunctional monomer was added to the part to make 100 parts by mass, and the mixture was stirred to obtain a mixture. This mixture was subjected to a dispersion treatment for 6 hours together with zirconia beads (diameter 1.5 mm) using a sand mill (manufactured by Yaskawa Seisakusho Co., Ltd.). Then, the black pigment dispersion liquid was obtained by isolate | separating a zirconia bead with a separator. Similarly, a cyan pigment dispersion, a magenta pigment dispersion, and a yellow pigment dispersion were obtained.

・ Preparation of radiation curable ink composition After mixing a polymerizable compound, a photopolymerization initiator, a slip agent, and a polymerization inhibitor so that the composition (mass%) shown in FIG. The black pigment dispersion was added dropwise with stirring so that the concentration of the black pigment was as shown in FIG. After completion of the dropwise addition, the mixture was stirred for 1 hour at room temperature, and further filtered through a 5 μm membrane filter to obtain a black radiation curable ink composition. Similarly, a cyan radiation curable ink composition, a magenta radiation curable ink composition, and a yellow radiation curable ink composition were obtained.

In addition, the component used in FIG. 9 is as follows.
(1) Polymerizable compound / phenoxyacrylate (Osaka Organic Chemical Industry Co., Ltd., trade name “V # 192”)
・ Dicyclopentenyloxyethyl acrylate (manufactured by Hitachi Chemical Co., Ltd., trade name “FA512AS”)
・ Dicyclopentenyl acrylate (manufactured by Hitachi Chemical Co., Ltd., trade name “FA511AS”)
・ N-Vinylcaprolactam (trade name “N-Vinylcaprolactam” manufactured by BASF)
Amino acrylate (Daicel Cytec Co., Ltd., trade name “EBECRYL 7100”)
・ Tripropylene glycol diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name “APG-200”)
・ Dipropylene glycol diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name “APG-100”)

(2) Polymerization inhibitor, p-methoxyphenol (manufactured by Kanto Chemical Co., Inc.)

(3) Slip agent BYK-UV3500 (by Big Chemie Japan Co., Ltd., polydimethylsiloxane having a polyether-modified acrylic group)

(4) Photopolymerization initiator IRGACURE 819 (Ciba Japan Co., Ltd., bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, photopolymerization initiator)
DAROCUR TPO (Ciba Japan Co., Ltd., 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, photopolymerization initiator)
・ DETX (Nippon Kayaku Co., Ltd., photopolymerization initiator)

(5) Dispersant: Solsperse 36000 (manufactured by LUBRIZOL)

(6) Pigment / MICROLITH-WA Black C-WA (manufactured by Ciba Specialty Chemicals Co., Ltd., black pigment)
・ IRGALITE BLUE GLVO (Ciba Specialty Chemicals, Cyan Pigment)
・ CROMOPHTAL PinkPT (SA) GLVO Ciba Specialty Chemicals Co., Ltd., magenta pigment ・ IRGALITE YELLOW LBG Ciba Specialty Chemicals Co., Ltd., yellow pigment

  As shown in FIG. 9, the mass percentage of the pigment of the black ink is the lowest compared to the other inks (cyan, magenta, yellow) (black is 1.80, cyan is 2. 00, magenta is 5.00, and yellow is 8.00). In this way, low pigment concentration ink can be ejected in multiple times and cured each time it is ejected, so that it can be cured to the same extent even between inks with different degrees of ultraviolet absorption. Become.

  FIG. 10 is a diagram for explaining the print duty in the second embodiment. In the figure, the print duty with respect to the image density is shown. The density is indicated by 255 gradations.

  The print duty indicates the percentage of pixels in which dots are formed when the total number of pixels per unit area (number of rows of pixels × number of columns) is 100% (corresponding to the density of image data). ). Usually, dots are formed in the image data with a printing duty of 0 to 100%.

  However, in the second embodiment, the black ink uses a low pigment concentration ink. Therefore, for black ink, 0 to 200% can be set as the print duty. Two ink droplets can be ejected per pixel. Based on the density, the black ink printing duty of 200% corresponds to the printing duty of other color inks of 100%.

=== Third Embodiment ===
In the above-described embodiment, the color ink other than black is mainly described as being ejected once per pixel. However, the present invention is not limited to this. That is, yellow Y, magenta M, and cyan C may be ejected a plurality of times per pixel.

=== Fourth Embodiment ===
In the above-described embodiment, the color printing mode in which not only the black ink but also the color ink is ejected in order to perform color printing has been described. However, a monochrome printing mode in which only the black ink is ejected may be provided.

  At this time, it is desirable that the size (mass) of the black ink droplet ejected in the monochrome printing mode is larger than the size of the black ink droplet ejected in the color printing mode. A technique for increasing the size of the black ink droplet can be realized by increasing the amplitude of the second drive pulse PS2 in the drive signal described above. When a plurality of sizes are used as the black ink droplets ejected in each printing mode, the mass of the largest black ink droplet ejected in the monochrome printing mode is larger than the mass of the largest black ink droplet ejected in the color printing mode. It is desirable to enlarge it.

  As described above, in the monochrome printing mode in which the color ink droplets are not ejected, color mixture with other color inks does not occur, and thus the size of the black ink droplets can be increased.

=== Fifth Embodiment ===
FIG. 11 is a schematic side view of the printer 1 according to the fifth embodiment. FIG. 12 is a schematic top view of the printer 1 according to the fifth embodiment.

  The transport roller 111A and the paper discharge roller 112A are connected to a motor (not shown), and the rotation of the motor is controlled by the controller 10. Then, the medium is conveyed in the conveyance direction by being sandwiched between the conveyance roller 111A and the first pressing roller 111B. Further, the medium is transported in the transport direction and discharged by being sandwiched between the paper discharge roller 112A and the second pressing roller 112B.

  In the fifth embodiment, the head unit 40 includes a black head unit 141K, a yellow head unit 141Y, a magenta head unit 141M, and a cyan head unit 141C. Furthermore, the head unit 40 includes a first black head unit 141K1 and a second black head unit 141K2. The position of the nozzle in the first black head unit 141K1 and the position of the nozzle in the second black head unit 141K2 are configured to coincide with each other in the width direction.

  The ultraviolet irradiation unit 80 includes five LED assemblies 181C, 181M, 181Y, 181K1, and 181K2. Further, the ultraviolet irradiation unit 80 may further include an ultraviolet irradiation device 191 at the final stage.

  The arrangement order of the head units of each color is not limited to this. For example, two sets of head units may be prepared for cyan, magenta, and yellow.

  For cyan, magenta, and yellow, separate LED assemblies need not be provided. It is sufficient that at least the first black head unit 141K1 and the second black head unit 141K2 capable of individually curing the black ink ejected from the two black head units are provided.

=== Other Embodiments ===
<When forming dots of multiple sizes>
Both black ink dots and color ink dots may form dots of a plurality of sizes. In such a case, dots of a plurality of sizes can be formed by ejecting ink droplets of a plurality of sizes. At this time, the mass of the largest black ink droplet ejected is made smaller than the mass of the largest color ink droplet. As a method of reducing the mass of the ink droplet, it can be performed by adjusting the amplitude of the drive pulse as described with reference to FIG.

<Other devices>
In the above-described embodiment, the printer 1 has been described. However, the present invention is not limited to this, but fluid other than ink (liquid, liquid material in which particles of functional material are dispersed, flow like gel) It can also be embodied in a liquid ejecting apparatus that ejects or ejects a body. For example, color filter manufacturing apparatus, dyeing apparatus, fine processing apparatus, semiconductor manufacturing apparatus, surface processing apparatus, three-dimensional modeling machine, gas vaporizer, organic EL manufacturing apparatus (especially polymer EL manufacturing apparatus), display manufacturing apparatus, film formation You may apply the technique similar to the above-mentioned embodiment to the various apparatuses which applied inkjet technology, such as an apparatus and a DNA chip manufacturing apparatus. These methods and manufacturing methods are also within the scope of application.

<About the head>
In the above-described embodiment, ink is ejected using a piezoelectric element. However, the method for discharging the liquid is not limited to this. For example, other methods such as a method of generating bubbles in the nozzle by heat may be used.

  The above-described embodiments are for facilitating the understanding of the present invention, and are not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof.

  For example, in the first to fourth embodiments in the above-described embodiment, bleed or blur does not occur in the landed ink by irradiating the ultraviolet light by the irradiation unit provided in the head in the path where the ink is landed on the medium. Temporary curing, which is a degree of curing, may be performed. The ink curing rate in the temporary curing is less than 80%. In this case, irradiation is further performed after the temporary curing by irradiation in the pass where the ink is landed on the medium, and the main curing is performed (the ink curing rate is 80% or more). The main curing is a curing that cures to a curing rate suitable for using the printed matter. On the other hand, the ink may be cured until main curing by irradiation with an irradiation unit provided in the head in a path where the ink is landed on the medium. In the former case, another light source for main curing may be separately provided in the printer. In the latter case, the printer may not be provided with another light source for main curing. Also in the above-described fifth embodiment, temporary curing may be performed by irradiation performed by each LED assembly 181 in FIG. 11, or it may be performed up to main curing. In the case of performing main curing, there is no ultraviolet irradiation device 191. Also good.

1 printer, 10 controller,
11 interface, 12 CPU,
13 memory, 14 unit control circuit,
20 transport unit, 30 carriage unit,
40 head units, 41 heads,
50 detector groups, 60 computers,
80 UV irradiation unit

Claims (8)

(A) a black ink nozzle that ejects black ink droplets that are cured by irradiation energy of light onto a medium;
(B) a color ink droplet of a color other than the black ink droplet, the color ink nozzle ejecting the color ink droplet cured by the irradiation energy of the light onto the medium;
(C) an irradiation unit for irradiating the medium with light;
(D) When forming black dots on the pixels of the medium, the black ink droplets are ejected to the pixels a plurality of times, and the pixels are irradiated with the light each time the black ink droplets are ejected. Cure the drops,
When forming color dots on the pixels of the medium, the color ink droplets are ejected once to the pixels, and the light is applied to the pixels on which the color ink droplets are ejected to cure the color ink droplets. A control unit;
A printing apparatus comprising:   The printing apparatus according to claim 1, wherein a mass of the largest black ink droplet ejected is smaller than a mass of the largest color ink droplet ejected.   The printing apparatus according to claim 1, wherein the content concentration of the pigment contained in the black ink is lower than the content concentration of the pigment contained in the color ink. A first printing mode for ejecting the color ink droplets, and a second printing mode for ejecting the color ink droplets,
The printing according to any one of claims 1 to 3, wherein a mass of the largest black ink droplet ejected in the second printing mode is larger than a mass of the largest black ink droplet ejected in the first printing mode. apparatus.   The printing apparatus according to claim 1, wherein curing of the black ink droplet and curing of the color ink droplet is temporary curing. Furthermore, a yellow ink nozzle row that ejects yellow ink droplets that are cured by the irradiation energy of the light onto a medium,
When the yellow dot is formed on the pixel of the medium, the control unit ejects the yellow ink droplet a plurality of times, and irradiates the pixel with the light each time the yellow ink droplet is ejected. The printing apparatus according to claim 1, wherein the yellow ink droplet is cured. Furthermore, a green ink nozzle row that ejects green ink droplets that are cured by the irradiation energy of the light onto a medium,
When the green dot is formed on the pixel of the medium, the control unit ejects the green ink droplet a plurality of times, and irradiates the pixel with the light each time the green ink droplet is ejected. The printing apparatus according to claim 1, wherein the green ink droplet is cured. Black ink droplets that are cured by light irradiation energy are ejected to the pixels of the medium a plurality of times, and each time the black ink droplets are ejected, the pixels are irradiated with the light to cure the black ink droplets to form black dots. To do
A color ink droplet that is cured by light irradiation energy is ejected once onto the pixels of the medium, and the color ink droplet is cured by irradiating the light onto the pixel that ejects the color ink droplet to form a color dot. And
Including printing method.

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