WO2007023735A1

WO2007023735A1 - Inkjet ink set, image-forming method using same, and inkjet recorder

Info

Publication number: WO2007023735A1
Application number: PCT/JP2006/316212
Authority: WO
Inventors: Wataru Ishikawa
Original assignee: Konica Minolta Medical & Graphic, Inc.
Priority date: 2005-08-24
Filing date: 2006-08-18
Publication date: 2007-03-01
Also published as: JPWO2007023735A1

Abstract

Disclosed is an inkjet ink set which enables to form a very fine image on a transparent recoding medium having no ink absorption or on a recoding medium with low brightness. Also disclosed are an image-forming method using such an inkjet ink set, and an inkjet recorder. Specifically disclosed is an inkjet ink set including a white ink and a color ink containing at least a coloring agent, which is characterized in that the surface tension of the white ink is higher than that of the color ink. Also specifically disclosed is an inkjet ink set including a white ink and a color ink containing at least a coloring agent, a polymerizable compound and a photopolymerization initiator, which is characterized in that the surface tension of the white ink is higher than that of the color ink.

Description

Specification

Ink jet ink set, image forming method using the same, and ink jet recording apparatus

Technical field

The present invention relates to an inkjet ink set, an image forming method using the same, and an ink jet recording apparatus.

Background art

[0002] Inkjet recording methods are attracting attention as a technology that enables easy and inexpensive image creation and enables high-quality recording that can be adequately handled in various printing fields with the recent improvement in image quality. .

By the way, as a method for forming a reflection image on a transparent recording medium (base material), when printing using white ink and color ink, first, a white background is formed on the transparent base material with white ink. From “surface printing”, which forms an image with color inks such as yellow, magenta, cyan, black, etc., and the final image is printed with the surface strength, and with white ink that is formed with color ink on a transparent substrate. There is a method called “back printing” in which the final image is viewed through a transparent substrate.

[0004] In the ink jet recording method, these images can be similarly produced by using white ink and color ink. The white ink for ink jet is used for a transparent recording medium or a recording medium with low brightness. Therefore, it is an effective method that can obtain a clear full-color image similar to that when recording on a white medium, particularly when used in combination with a color ink.

[0005] In that case, in the ink jet recording method in which an image is created with dots, the color ink needs to maintain a dot size that matches the resolution on the substrate in order to create a more precise image. In particular, when color ink is printed on white ink such as surface printing, the dot diameter of the color ink depends on the characteristics of the white ink. If the dot diameter of the color ink becomes smaller than the dot size that matches the resolution, a gap is created between the dots, causing image defects.

[0006] On the other hand, it is non-ink-absorbing and can be fixed on a recording medium such as a film or metal and printed. As the ink for ink jet, there is an ultraviolet curable ink composition containing a colorant (coloring material), an ultraviolet curing agent, a photopolymerization initiator, and the like. These colorants, ultraviolet curable white inkjet ink using titanium oxide as a white pigment has been proposed (For example, refer to Patent Documents 1 to 3.) ₀ However, these are combined with color inks It is not premised on the use, but is described with respect to the optimal combination for obtaining a clear full-color image with visibility using white ink and color ink.

Patent Document 1: Japanese Patent Laid-Open No. 62-64874

Patent Document 2: JP 2000-336295 A

Patent Document 3: Japanese Patent Application Laid-Open No. 2001-207098

Disclosure of the invention

Problems to be solved by the invention

[0007] The present invention has been made in view of the above problems, and its object is to achieve a high-definition image even on a recording medium, which is ink-absorptive, non-V, transparent recording medium and low in brightness! Ink jet ink sets that can be obtained, an image forming method using the ink set, and an ink jet recording apparatus are provided.

Means for solving the problem

[0008] The above object of the present invention has been achieved by the following constitution.

[0009] 1. In an inkjet ink set including at least a color ink containing a colorant and a white ink, the surface tension value of the white ink is higher than the surface tension value of the color ink. Ink set.

[0010] 2. In an inkjet ink set comprising a color ink containing at least a colorant, a polymerizable polymer and a photopolymerization initiator, and a white ink, the surface tension value of the white ink has a surface of the color ink. An ink set for inkjet which is higher than a tension value.

[0011] 3. The surface tension value force of the white ink is characterized in that it is +0.5 mNZm or more and + lOmNZm or less with respect to the surface tension value of the force ink having the highest surface tension among the color inks. Or The ink set for inkjet according to 2.

[0012] 4. The surface tension value of the white ink is +0.5 mNZm or more and +3. OmNZm or less with respect to the surface tension value of the force ink having the highest surface tension among the color inks. The ink set for inkjet according to 1 or 2 above.

[0013] 5. The ink set for inkjet according to any one of 2 to 4, wherein the polymerizable compound is a cationic polymerizable compound.

[0014] 6. The white ink force The ink set for inkjet according to any one of 1 to 5 above, wherein the ink contains titanium oxide as a colorant.

[0015] 7. The inkjet ink set as described in 6 above, wherein the titanium oxide has an average particle size of 50 nm or more and 500 nm or less.

[0016] 8. The ink set for inkjet according to any one of 1 to 7, wherein the surface tension value of each of the color ink and the white ink is 20 mNZm or more and 60 mNZm or less.

[0017] 9. Image formation in which ink jet ink is ejected onto a recording medium from the ink jet recording head using the ink jet ink set described in any one of 1 to 8 above, and printing is performed on the recording medium. A method for forming an image, characterized in that the surface tension value of a white ink image cured by irradiation with actinic rays is 30 mNZm or more and 60 mNZm or less.

[0018] 10. An image in which ink jet ink is ejected onto a recording medium from the ink jet recording head using the ink set for ink jet recording according to any one of 1 to 8 above, and printing is performed on the recording medium. An image forming method, wherein the ink jet ink is irradiated with an actinic ray for 0.001 seconds or more and 1.0 seconds or less after the ink jet ink has landed on a recording medium. Forming method.

[0019] 11. Image formation in which ink jet ink is ejected onto a recording medium using an ink jet ink set according to any one of 1 to 8 above from an ink jet recording head, and printing is performed on the recording medium. A method for forming an image, wherein the inkjet recording head force is a line head system.

[0020] 12. An ink jet recording apparatus for use in the image forming method according to any one of 9 to 11, wherein the inkjet ink and the inkjet recording head are disposed at 35 ° C or higher and 100 ° C or lower. An ink jet recording apparatus, wherein the ink jet ink is ejected from the ink jet recording head after being heated. The invention's effect

[0021] According to the present invention, an ink jet ink set capable of obtaining a high-definition image even on a transparent recording medium having no ink absorbability or a recording medium having low brightness, an image forming method using the ink set, and an ink jet recording The equipment could be provided.

Brief Description of Drawings

FIG. 1 is a schematic diagram showing an example of a main configuration of an ink jet recording apparatus.

FIG. 2 is a schematic diagram showing another example of the main configuration of the ink jet recording apparatus.

Explanation of symbols

[0023] 1 Recording device

2 Head carriage

3 Recording head

4 Irradiation means

P Recording medium

BEST MODE FOR CARRYING OUT THE INVENTION

[0024] As a result of intensive studies in view of the above problems, the present inventors have determined that the surface tension value of the white ink in an ink-jet ink set including at least a color ink containing a colorant and a white ink is An inkjet ink set characterized by having a surface tension value higher than that of the color ink, or an inkjet ink set comprising a color ink containing at least a colorant, a polymerizable compound and a photopolymerization initiator, and a white ink. The ink set for inkjet, which has a surface tension value of white ink higher than that of the color ink, enables high-definition recording even for transparent recording media that do not absorb ink or recording media with low brightness. It was found that an inkjet ink set capable of obtaining an image could be realized, and the present invention was reached.

[0025] As described above, according to the present invention, in the ink jet ink set including the color ink containing the colorant and the white ink, the surface tension value of the white ink is set higher than the surface tension value of the color ink. Thus, it has been found that a high-definition image can be obtained even on a transparent recording medium or a recording medium with low brightness. [0026] Further, by using an ink set for an inkjet including a color ink containing a polymerizable compound, a photopolymerization initiator, and a white ink, the surface tension value of the white ink is determined from the surface tension value of the color ink. It is a feature of the present invention that a high-definition image can be obtained even if a substrate having no ink absorbability is set to a substrate having a low ink absorbability by setting it to a high value.

[0027] The drying step can be omitted by using the ink jet ink set that also has an actinic ray curable ink force of the present invention. Therefore, it is possible to form a high-density image with a large amount of ink shot on a recording medium with high ink absorbency, and since it is cured instantaneously after landing, the fiber is rough! It's sharp! ヽ High-definition images can be formed.

[0028] As the types of these actinic ray curable inks, it is more preferable to use a cationic actinic ray curable ink from the viewpoints of curability, safety, and recording medium compatibility.

[0029] Hereinafter, materials, image forming methods, and the like used in the ink jet ink (hereinafter also simply referred to as ink) constituting the ink jet ink set of the present invention will be described in more detail.

[Ink surface tension]

The surface tension value of the ink defined in the present invention is a static surface tension value (m N / m at a temperature of 25 ° C.) by a platinum plate method using a surface tension meter (for example, Kyowa Interface Science Co., Ltd .: CBVP-Z). ). In addition, the surface tension value of the formed image with the white ink cured by irradiation with actinic rays was determined by measuring the contact angles with water, methylene iodide and -tromethane on the cured ink image surface, It can be calculated according to the calculation formula described in the Journal of the Society, 8 pp. 131 (1972) and obtained as the solid surface tension value (mNZm) of the ink image.

In the present invention, the means for setting the surface tension value of the ink before emission defined above and the surface tension value of the ink cured by actinic ray irradiation as a condition defined in the present invention is particularly limited. However, by appropriately adjusting the type and addition amount of the surfactant, the type and addition amount of the pigment dispersant described above, the type and addition amount of the polymerizable component, and the type and addition amount of the polymerization initiator, Can be realized.

[0032] The surfactant that is one of the means for adjusting the respective surface tension values will be described. [0033] The surfactant that can be used in the present invention is not particularly limited. For example, dialkyl sulfosuccinates, alkylnaphthalene sulfonates, fatty acid salts and other cationic surfactants, polyoxyethylene alkyls Nonionic surfactants such as ethers, polyoxyethylene alkyl ethers, acetylene glycols, polyoxyethylene 'polyoxypropylene block copolymers, alkylamine salts, quaternary ammonium salts, etc. Examples include cationic surfactants and silicone oils.

[0034] In the present invention, it is particularly preferable to use a silicone oil. For example, an amino-modified silicone oil, an epoxy-modified silicone oil, a carboxy-modified silicone oil, a polyether-modified silicone oil, dimethylpolysiloxane. Polyether-modified silicone oil, polyether-modified silicone oil, alkoxy-modified silicone oil, fluorine-modified silicone oil, methylstyrene-modified silicone oil, olefin-modified silicone oil, alcohol-modified Examples include silicone oil.

[0035] The surface tension value of the color ink and the white ink constituting the ink-jet ink set of the present invention is preferably adjusted to 20 to 60 mNZm, particularly preferably 25 to 45 mN / m for the color ink and the white ink. Then, it is 35-50mN / m.

[0036] At this time, in the inkjet ink set, it is necessary to adjust the ink physical properties so that the surface tension value of the white ink is higher than the surface tension value of the force ink, and the surface tension value of the white ink is If the surface tension value of the color ink is lower, when the color ink is placed on the white ink, the dots are not sufficiently filled, resulting in an image defect.

[0037] [Color ink]

In the inkjet ink set of the present invention, it is preferable that the color ink is at least one selected from yellow, magenta, cyan, and black power. More preferably, the four colors of yellow, magenta, cyan, and black are used. It is preferable that the ink is composed of a color ink. Depending on the application and image quality, light yellow, light magenta, light cyan and other light color inks with low colorant concentration, specific color inks such as red, blue, green, orange and violet, gold, silver, etc. Metal gloss ink etc. Used.

[0038] [Colorant]

As the colorant contained in the color ink, various colorants such as pigments and dyes that can be dissolved or dispersed in the main component constituting the color ink can be used. I like it.

[0039] As the pigment contained in the color ink according to the present invention, a chromatic organic pigment can be used. Organic pigments include insoluble azo pigments such as toluidine red, toluidine maroon, hansaiero ichi, benzidine yellow, pyrazolone red, soluble azo pigments such as ritodo, heliobordeaux, pigment scarlet, permanent red 2B, alizarin, indanthron , Derivatives from vat dyes such as thioindigo maroon, phthalocyanine organic pigments such as phthalocyanine blue and phthalocyanine green, quinacridone organic pigments such as quinacridone red and quinacridone magenta, and perylene organic pigments such as perylene red and perylene scarlet, Isoindolinone yellow and isoindolinone organic pigments such as isoindolinone orange, bilanthrone organic pigments such as pyranthrone red and pyranthrone orange, Indigo organic pigments, condensed azo organic pigments, benzimidazolone organic pigments, quinophthalone organic pigments such as quinophthalone yellow, isoindoline organic pigments such as isoindolin yellow, and other pigments such as flavanthlon yellow and acylamide Yellow, nickel azo yellow, copper azomethine yellow, perinone orange, anthrone orange, dianslaquinol red, dioxazine violet and the like.

[0040] For example, CI pigment yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 109, 110, 117, 120, 125, 12 8, 129, 137, 138, 139, 147, 148, 150, 151, 153, 154, 155, 166, 168, 1 80, 185, CI pigment orange 16, 36, 43, 51, 55, 59, 61 CI pigment lead 9, 48, 49, 52, 53, 57, 97, 122, 123, 147, 149, 168, 177, 180, 192, 202, 206, 215, 216, 217, 220, 223, 224 , 226, 227, 228, 238, 240, C.I.Pigment Novelette 19, 23, 29, 30, 37, 40, 50, CI Pigment Blue 15, 1 5: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64, CI Pigment Green 7, 36, CI Pigme N Brown 23, 25, 26, CI Big Men Black 7, 26, 28

In addition to the above, newly synthesized pigments can also be used. Furthermore, these pigments may be surface-treated. Examples of the surface treatment method include treatment with a coupling agent such as alcohol, acid, base, and silane compound, polymer graft treatment, and plasma treatment. The colorant used in the present invention is preferably one having a low content of organic and inorganic impurities. Generally, it is desirable to use the purified product because it contains a large amount of impurities.

[0042] Among the above pigments, quinacridone organic pigments, phthalocyanine organic pigments, benzimidazolone organic pigments, isoindolinone organic pigments, condensed azo organic pigments, quinophthalone organic pigments, isoindoline organic pigments Pigments are preferred because of their excellent light resistance.

[0043] The organic pigment is preferably a fine pigment having an average particle diameter of 10 to 200 nm as measured by laser scattering. When the average particle size of the pigment is less than lOnm, the concentration is increased due to the smaller particle size, resulting in a decrease in light resistance, and when it exceeds 200 nm, it is difficult to maintain stable dispersion. Precipitation is likely to occur.

[0044] The colorant used in the color ink according to the present invention is used in the range of 0.1 to 30% by mass, preferably 1 to 15% by mass, based on the total mass of the ink.

[White ink colorant]

As the colorant used in the white ink according to the present invention, inorganic and Z or organic white pigments can be used. Examples of inorganic white pigments include sulfates of alkaline earth metals such as barium sulfate, carbonates of alkaline earth metals such as calcium carbonate, silicas such as fine powdered kainate and synthetic silicate, calcium karate, alumina, Examples include alumina hydrate, titanium oxide, zinc oxide, talc, and clay. Titanium oxide is also preferred for its hiding power and tinting strength.

[0046] Examples of the organic white pigment include organic compound salts disclosed in JP-A-11 129613 and alkylene bismelamine derivatives disclosed in JP-A-11 140365 and JP2001-234093. Specific examples of the white pigments include Shigenox OWP, ShigenoxOWPL, ShigenoxFWP, ShigenoxFWG, ShigenoxUL, ShigenoxU (all of which are trade names of NOC and CKOR Chemical Co., Ltd.). [0047] (Titanium oxide)

There are three crystal forms of acid-titanium, anatase type, rutile type and brookite type, but they can be broadly classified into anatase type and rutile type. The anatase type has a small specific gravity and a small particle size, while the rutile type has a high refractive index and high concealment. In the present invention, any of them may be used, but it is preferable to select them according to their use, and the specific gravity is small and the particle size is easily reduced. By using the anatase type, dispersion stability and Ink storage stability and emission are improved. In addition, the combined use of anatase type, which can use two or more different crystal forms, and rutile type, which has high tinting strength, can reduce the amount of acid titan added, resulting in improved ink storage and ejection properties. Become good.

[0048] As the surface treatment method of titanium oxide, aqueous treatment, gas phase treatment, etc. are performed, but as the surface treatment agent, alumina / silica treatment is generally used, and untreated, alumina treatment, alumina / silica is used. There is a thing of processing.

[0049] The average particle diameter of titanium oxide is preferably 50 to 500 nm. When the average particle diameter is less than 50 nm, sufficient concealability cannot be obtained, and when it exceeds 500 nm, the ink storage stability and emission properties tend to deteriorate. More preferably, it is 100 300.

[0050] The amount of titanium oxide added is preferably in the range of 350% by mass in the ink composition. If it is less than 3% by mass, sufficient concealing properties cannot be obtained, and 50% by mass is not obtained. If it exceeds, the ink storage and emission properties tend to deteriorate. More preferably, it is 5 20 mass%.

[0051] For the dispersion of the colorant, for example, a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, a paint shaker, or the like can be used. It is also possible to add a dispersant when dispersing the colorant. As the dispersion medium, a solvent or a polymerizable compound is used.

[0052] [Dispersant]

The dispersant used for dispersing the colorant according to the present invention improves the dispersibility of the colorant in the ink composition, thereby improving the mixing at the time of ink preparation, and the storage stability and emission properties of the ink after preparation. Of course, it has a function of adjusting the surface tension value of the ink.

[0053] The chemical structure includes, for example, a hydroxyl group-containing carboxylic acid ester and a long-chain polyaminoamide. And salts of high molecular weight acid esters, salts of high molecular weight polycarboxylic acids, salts of long-chain polyaminoamides and polar acid esters, high molecular weight unsaturated acid esters, high molecular weight copolymers, modified polyurethanes, modified polyacrylates, poly Ether ester type cation activator, naphthalene sulfonic acid formalin condensate salt, aromatic sulfonic acid formalin condensate salt, polyoxyethylene alkyl phosphate ester, polyoxyethylene nonyl phenyl ether, stearylamine acetate, pigment derivative Etc.

[0054] In particular, as a dispersant for dispersing acid-titanium, a high molecular weight copolymer or a high molecular weight polyester acid amide amine salt is used, so that dispersion stability, ink storage stability, and emission properties are further improved. Become.

[0055] The addition amount of the activator is 0.1 to 30% by mass, more preferably 5 to 20% by mass with respect to the colorant.

Use in the range of%.

[Curable ink containing a polymerizable compound]

As another form of the ink in the present invention, a curable ink containing a polymerizable compound and a photoinitiator is one feature, and various curable inks can be used.

1S Among these, it is preferable to use a cationic curable ink from the viewpoints of curability, safety, and substrate compatibility.

[0057] The curable ink contains a colorant, a polymerizable compound, and a photopolymerization initiator, and a polymerization inhibitor, a surfactant, a resin, a solvent, and the like are appropriately blended as necessary.

[0058] As the cationic curable ink, various known ink yarns can be used. For example, JP-A-6-9714, JP-A-2001-31892, 2001-40068, 2 001-55507, 2001-310938, 2001-310937, 2001-220526, 2003-183551, 2004-59627, 2004-108778, 2005 — The power of No. 41893 is mentioned. Examples of the radical curable ink include ink compositions described in JP-A-7-159983, JP-B-7-31399, JP-A-8-224982, and JP-A-10-863. Togashi.

It is also possible to combine a cationic polymerizable compound and a radical polymerizable compound into a radical-cation hybrid type hard ink. [0060] The curable ink according to the present invention has a viscosity of 7 to 50 mPa · s at 25 ° C, so that ejection is stable without adversely affecting the curing environment (temperature'humidity), Preferable because of good curability! / !.

[Image Forming Method]

An image forming method using the curable inkjet ink set according to the present invention will be described.

As the ink discharge conditions, it is preferable from the viewpoint of discharge stability that the recording head and ink are heated to 35 to 100 ° C. and discharged. The ink composition has a large viscosity fluctuation range due to temperature fluctuations. Viscosity fluctuations directly affect the droplet size and droplet ejection speed, causing image quality deterioration, so keep the temperature constant while raising the ink temperature. is required. The control range of the ink temperature is the set temperature ± 5 ° C, preferably the set temperature ± 2 ° C, more preferably the set temperature 1 ° C.

[0063] In the image forming method of the present invention, as an irradiation condition of active light, active light is irradiated for 0.001 to 2.0 seconds after ink has landed on the recording medium. More preferably, it is 0.001 to 1.0 seconds. In order to form high-definition images, it is particularly important that the irradiation timing is as fast as possible.

[0064] A basic method of actinic ray irradiation is disclosed in JP-A-60-132767. According to this, a light source is provided on both sides of the head unit, and the head and the light source are scanned by the shuttle method. Irradiation is performed after a certain period of time after ink landing. Further, the curing is completed by another light source that is not driven. In the specification of US Pat. No. 6,145,979, a method using an optical fiber as an irradiation method is a method in which a collimated light source is applied to a mirror surface provided on the side surface of the head unit and the recording unit is irradiated with ultraviolet rays. It is disclosed. Any of these irradiation methods can be used in the image forming method of the present invention.

[0065] In addition, actinic ray irradiation is divided into two stages. First, actinic rays are irradiated in the above-described manner for 0.001 to 2.0 seconds after ink landing. Irradiation is also a preferred embodiment. By dividing the irradiation of actinic rays into two stages, it is possible to further suppress the shrinkage of the recording medium that occurs during ink hardening. [0066] Conventionally, in the actinic ray curable ink jet method, a light source with a high illuminance in which the total power consumption of the light source exceeds lkW'hr has been generally used to suppress dot spreading and bleeding after ink landing. . However, when these light sources are used, especially for printing on shrink labels, etc., the shrinkage of the recording medium is so great that it cannot be used in practice.

[0067] In the present invention, even when a light source with an hourly power consumption of 1 kW or less is used, a high-definition image can be formed, and the shrinkage of the recording medium can be kept within a practically acceptable level. Examples of light sources that consume less than 1 kW per hour include, but are not limited to, fluorescent tubes, cold cathode tubes, and LEDs.

[Inkjet recording apparatus]

The ink jet recording apparatus of the present invention will be described below with reference to the drawings as appropriate. Note that the recording apparatus in the drawings is merely one aspect of the inkjet recording apparatus of the present invention, and the inkjet recording apparatus of the present invention is not limited to this drawing.

[0069] Fig. 1 is a schematic view seen from above showing an example of a main configuration of an ink jet recording apparatus of the present invention. The recording apparatus includes a head carriage 2, a recording head 3, an actinic ray irradiation means 4, and the like.

The head scanning means (not shown) in FIG. 1 scans the recording head 3 held by the head carriage 2 by reciprocating the head carriage 2 in the Y direction in FIG.

[0071] The head carriage 2 is installed on the upper side of the recording medium P, and corresponds to the number of colors used for image printing on the recording medium P (not shown, further on the vertical direction head carriage 2 on the paper surface). Then, a plurality of recording heads 3 to be described later are stored and the discharge ports are arranged on the lower side. The head carriage 2 is installed with respect to the recording apparatus main body in such a manner that it can reciprocate in the Y direction in FIG. 1, and reciprocates in the Y direction in FIG. 1 by driving the head scanning means.

In FIG. 1, the head carriage 2 is white (W), yellow (Y), magenta (M), cyan (C), black (K), light yellow (Ly), light magenta (Lm), Drawing as if the light cyan (Lc), light black (Lk), and white (W) recording heads 3 were to be stored! The number of colors is determined as appropriate It is what

[0073] The recording head 3 includes a discharge means (not shown) provided with a plurality of actinic ray curable inks (for example, UV curable ink) supplied by an ink supply means (not shown). By operation, the ink is discharged toward the recording medium P. The active light curable ink ejected by the recording head 3 is composed of a coloring material, a polymerizable monomer, an initiator, and the like, and the initiator acts as a catalyst when irradiated with ultraviolet rays. The crosslinking of the monomer has the property of being cured by a polymerization reaction.

[0074] During a scan in which the recording head 3 moves from one end of the recording medium P to the other end of the recording medium P in the Y direction in FIG. The actinic ray curable ink is ejected as ink droplets onto the possible region, and the ink droplets are landed on the landable region. Next, the recording medium P is slightly moved downstream in the X direction (sub-scanning direction), and the above operation is repeated to form an image.

At this time, white is ejected only from the recording head at the leading end in the sub-scanning direction, thereby forming a “printed” image.

[0076] The above operation is repeated, and the actinic ray curable ink is ejected from the recording head 3 in conjunction with the head scanning unit and the conveying unit, thereby forming an aggregate of actinic ray curable ink droplets on the recording medium P. An image is formed.

[0077] The irradiation means 4 includes an ultraviolet lamp that emits ultraviolet light in a specific wavelength region with stable exposure energy and a filter that transmits ultraviolet light of a specific wavelength. Here, mercury lamps, metal halide lamps, excimer lasers, ultraviolet lasers, cold cathode tubes, black lights, LEDs (light emitting diodes), etc. can be applied as ultraviolet lamps, such as strip metal halide lamps, cold cathodes. A tube, mercury lamp or black light is preferred. In particular, a low-pressure mercury lamp, a cold cathode tube, a hot cathode tube, and a germicidal lamp that emit ultraviolet light having a wavelength of 254 nm are preferable because they prevent bleeding and control the dot diameter efficiently. By using black light as the radiation source of the irradiation means 4, the irradiation means 4 for curing the actinic ray curable ink can be produced at low cost.

The irradiating means 4 is a recording device (active light curable ink-in type) in a landable area where the recording head 3 ejects actinic light curable ink by a single scan driven by the head scanning means. Kudget printer) It has almost the same shape as the maximum one that can be set in 1 or larger than the landable area. The irradiation means 4 is installed on both sides of the head carriage 2 so as to be fixed substantially parallel to the recording medium P.

Here, the wavelength of the ultraviolet rays irradiated by the irradiation means 4 can be appropriately changed by replacing the ultraviolet lamp or filter provided in the irradiation means 4.

[0080] The actinic ray curable ink composition according to the present invention has very excellent ejection stability and is particularly effective when an image is formed using a line head type recording apparatus.

FIG. 2 is a schematic diagram showing another example of the configuration of the main part of the ink jet recording apparatus.

The ink jet recording apparatus shown in FIG. 2 is called a line head system, and a plurality of ink jet recording heads 3 are fixedly arranged on the head carriage 2 so as to cover the entire width of the recording medium P. ing.

[0083] On the other hand, on the downstream side of the head carriage 2, the irradiation light source 8 composed of a light emitting diode having a maximum illuminance of 210 to 280 nm according to the present invention is also provided, for example, as shown in FIG. As shown in FIG. 2, there are provided irradiation means 4 arranged so as to cover the entire area of the ink printing surface by arranging four in the scanning direction and ten in the sub-scanning direction.

In this line head system, the head carriage 2 and the irradiation means 4 are fixed, and the recording medium

Only P is conveyed, and ink ejection and curing are performed to form an image.

[0085] In the image recording apparatus described above, the force V by which the ink set of the color ink and the white ink according to the present invention is used can be obtained. The effects of the invention can be obtained.

Example

[0086] Hereinafter, the present invention will be specifically described with reference to examples, but the embodiments of the present invention are not limited to these examples.

[0087] Example 1

According to the following method, ink composition sets 1 to 7 having compositional powers shown in Tables 1 to 7 were prepared.

[0088] The dispersant described in Table 1 and each photopolymerizable compound were placed in a stainless beaker, and a 65 ° C The mixture was stirred and mixed for 1 hour while being heated on a metal plate, and dissolved. Next, after adding colorants 1 to 5 described in Table 1 to this solution, 200 g of zircoyu beads having a diameter of 1 mm were placed in a plastic bottle and sealed, and subjected to a dispersion treatment with a paint shaker for 2 hours.

[0089] Next, the zirconium oxide beads are removed, and various additives such as a photopolymerization initiator, a fragrance, and a basic compound are added in the combinations shown in Table 1 to prevent clogging of the printer. Ink composition set 1 was prepared by filtration through a / zm membrane filter. The surfactant used was KF351, and the amount of surface tension listed in Table 8 was used for each.

[0090] Ink composition sets 2 to 7 were prepared in the same manner. As the surfactant used for each, the amount of surface tension shown in Table 8 was used. Ink composition set 2 is X-22-22272, ink composition set 3 is SDX1842, ink composition set 4 is SDX1843, ink composition set 5 is KF351, and ink composition set 6 is X-22. SDX1843 was used for 4272 and ink composition set 7, respectively.

[0091] [Table 1]

Inku composition (mass ^_0/0) 0920

Ink

Composition

Set 1

(Invention)

0093

Ink composition set 2 (invention)

Ink composition set 4 (invention)

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Ink composition set 5 (comparison)

Ink composition set 6

(Comparison)

[0098] Details of each compound used for preparing each ink composition set described in Tables 1 to 7 are as follows.

[0099] K: dark black ink

C: Dark cyan ink M: Dark magenta ink

Y: dark yellow ink

W: White ink

Lk: Light black ink

Lc: Light cyan ink

Lm: Light magenta ink

Ly: Light yellow ink

Colorant 1: C. I. pigment Black 7

Colorant 2: C. L pigment Blue 15: 3

Colorant 3: C. L pigment Red 122

Colorant 4: C. I. pigment Yellow 120

Colorant 5: C. L pigment White6 (Anatase-type titanium oxide average particle size 0.16 μm)

D1: Pigment dispersant Ajisper PB822 Ajinomoto Fine Technone Earth

D2: Pigment dispersant Disparon DA-7300 Made by Enomoto Kasei

EP—1: Alicyclic epoxy compound (chemical structure below)

OXT— 221: Oxetane compound made by Toagosei

OXT— 212: Oxetane compound manufactured by Toagosei Chemical Co., Ltd.

OXT— 101: Oxetane compound manufactured by Toagosei

TAS-A: Photopolymerization initiator (chemical structure below)

TIPA (triisopropanolamine): basic compound

KF351: Side-chain polyether-modified silicone oil manufactured by Shin-Etsu Silicone

X— 22— 4272: Polyethers modified with both ends polyether Shin-Etsu Silicone Co., Ltd.

SDX1843: Dimethylpolysiloxane copolymer Asahi Denka Kogyo Co., Ltd.

SDX1842: Dimethylpolysiloxane copolymer Asahi Denka Kogyo Co., Ltd.

Linalool: Air Freshener Takasago Inc.

[Chemical 1] EP-1

[0101] 《Performance evaluation》

[Inkjet image output]

Next, an image was recorded on a recording medium (polyethylene terephthalate film) by an ink jet recording apparatus having a piezo-type inkjet nozzle having a nozzle diameter of 23 μm and 128 nozzles.

[0102] The ink supply system used consisted of an ink tank, a supply pipe, a front chamber ink tank just before the head, a pipe with a filter, and a piezo head. Temperature sensors were installed near the front chamber tank and the nozzle of the piezo head, respectively, and the temperature was controlled so that the nozzle part was always 60 ± 2 ° C. The droplet size was about 7p1, and it was ejected at a resolution of 720 x 720dpi (dpi is 2.5 dots per 54cm), and was driven at a driving frequency of 10kHz.

[0103] As shown in Fig. 1, W (white) head on the downstream side of the piezo head carriage and Y (Ly), M (Lm), C (Lc), K (Lk) four-color heads (Ly) , Lm, Lc, and Lk, 8 colors) were arranged in this order with a full-color printer. That is, after white ink was printed and cured, color ink was printed and cured on the white ink to form an image. Cold cathode lamps with a wavelength of 308 nm (custom products manufactured by Hibeck) were mounted on both ends of the carriage, and the heads were run to irradiate ultraviolet rays within 1000 ms after ink landing. Exposure surface illumination is 15mWZc It was m ^2. The exposure energy was adjusted by changing the speed of the head carriage so that all ink was irradiated.

[Evaluation of formed image]

The following evaluation was performed for each full-color image output using the inkjet recording apparatus described above.

[0105] (Observation of solid lines)

A solid image of color ink was output with the above-described ink jet recording apparatus, and after irradiation with ultraviolet rays, the solid portion was visually observed and evaluated according to the following criteria.

[0106] ◎: Good without streaks

○: There are some streaks, but there is no problem with high-definition printing

△: Power with streaks What level of power can be used

X: Level where streaks are noticeable and cannot be used

(Beta banding observation)

[0107] A: Good without banding

○: There is some banding, but there is no problem with high-definition printing

△: Power with banding Somehow usable level

X: Banding is conspicuous and cannot be used

Table 8 shows the results of each evaluation.

[0108] [Table 8]

[0109] From Table 8, the ink composition set of the present invention was evaluated for both solid lines and banding. The value is clearly superior to the comparison.

Claims

The scope of the claims

[1] An inkjet ink set comprising a color ink containing at least a colorant and a white ink, wherein the surface tension value of the white ink is higher than the surface tension value of the color ink .

[2] In an inkjet ink set including a color ink containing at least a colorant, a polymerizable compound and a photopolymerization initiator, and a white ink, the surface tension value of the white ink is greater than the surface tension value of the color ink. Ink-jet ink set characterized by being high.

[3] The surface tension value of the white ink is +0.5 mNZm or more and + lOmNZm or less with respect to the surface tension value of the color ink having the highest surface tension among the color inks. The inkjet ink set according to item 1 or 2.

[4] The surface tension value of the white ink is +0.5 mNZm or more and + 3. OmNZm or less with respect to the surface tension value of the color ink having the highest surface tension among color inks. The inkjet ink set according to item 1 or 2 of the range.

[5] The inkjet ink set according to any one of [2] to [4], wherein the polymerizable compound is a cationically polymerizable compound.

[6] The inkjet ink set according to any one of [1] to [5], wherein the white ink contains titanium oxide as a colorant.

[7] The inkjet ink set according to item 6, wherein the titanium oxide titanium has an average particle diameter of 50 nm or more and 500 nm or less.

[8] The inkjet ink according to any one of claims 1 to 7, wherein the surface tension value of each of the color ink and the white ink is 20 mNZm or more and 60 m NZm or less. Ink set.

[9] Using the ink jet ink set according to any one of claims 1 to 8, the ink jet ink is ejected onto the recording medium from the ink jet recording head, and printing is performed on the recording medium. A method of forming an image, wherein the surface tension value of a white ink image cured by irradiation with actinic rays is 30 mNZm or more and 60 mNZm or less.

[10] The ink jet recording head according to any one of claims 1 to 8 An ink jet ink set is used to eject an ink jet ink onto a recording medium, and printing is performed on the recording medium. After the ink jet ink has landed on the recording medium, 0.001 An image forming method comprising irradiating the ink-jet ink with actinic rays for a period of from 2 seconds to 1.0 second.

[11] Using the inkjet ink set according to any one of claims 1 to 8, the inkjet ink is ejected onto the recording medium from the inkjet recording head, and printing is performed on the recording medium. An image forming method, wherein the inkjet recording head is a line head method.

[12] An inkjet recording apparatus for use in the image forming method according to any one of claims 9 to 11, wherein the inkjet ink and the inkjet recording head are at least 35 ° C. An ink jet recording apparatus wherein the ink jet ink is ejected from the ink jet recording head after being heated to 100 ° C. or lower.