JP2011104865A - Clear ink for inkjet, ink set and method for inkjet print - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a clear ink for inkjet which reduces a curl to be generated. <P>SOLUTION: The clear ink for the inkjet of which an absorbance of a visible light region is 0.1 or less and contains water and L-carnitine. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an inkjet clear ink, an ink set, and an inkjet printing method.

  As an example of inkjet printing, there is inkjet printing using a transparent clear ink. As a technique using such an ink jet print, there is an ink jet print using a clear ink and a colored ink. Specifically, a technique for improving printing quality and fastness has been proposed by using an ink set having a clear ink and a colored ink containing a component that agglomerates a coloring material in a colored ink such as a polyvalent metal salt. ing. In addition, the clear ink containing a substance that improves the gloss of the print medium and the colored ink are used, and the clear ink is applied to the area of the print medium where the colored ink is not applied, thereby improving the gloss of the printed matter. Technology has been proposed.

  On the other hand, a print medium containing cellulose typified by plain paper is known as a print medium used for inkjet printing. When a large amount of colored ink is applied to a print medium containing cellulose, the print medium itself may change its shape with the passage of time due to the influence of moisture in the ink. As this shape change, a phenomenon in which the print medium gradually warps, so-called curl, is known.

  When an image is formed on a print medium containing cellulose such as plain paper using the ink set as described above, the amount of water applied per unit area tends to increase as compared with the case where the color ink is used alone. When using an ink set, curling is very likely to occur.

  As a method for reducing curling when using such an ink set, Patent Document 1 proposes a clear ink containing betaine. In the embodiment, a clear ink containing N, N, N-trimethylglycine is proposed. Are listed. Patent Document 2 proposes reducing curl using an ink set having a clear ink containing trimethylolpropane and a colored ink.

Special table 2008-514747 gazette JP 2004-209758 A

  When the present inventors examined the techniques described in Patent Document 1 and Patent Document 2, it was confirmed that curl was reduced at a certain level. However, in recent years, there has been a strong demand in the market for an ink set that can achieve curl reduction at a higher level and a clear ink used in the ink set.

  Therefore, an object of the present invention is to provide a novel ink jet liquid composition having high curl reduction ability, an ink set having the liquid composition, and an ink jet printing method.

  The present invention is an ink-jet clear ink having an absorbance in the visible light region of 0.1 or less, comprising water and L-carnitine.

  ADVANTAGE OF THE INVENTION According to this invention, the clear ink for inkjet which has high curl suppression ability, the ink set which has this clear ink, and the inkjet printing method can be provided.

  The inkjet clear ink of the present invention contains L-carnitine.

  As a result of studies, the present inventors have found that a high curl suppression ability can be obtained by using an inkjet clear ink containing L-carnitine. The present inventors speculate that the present invention has achieved high curl suppressing ability as follows. First, a mechanism that causes curling will be described.

  Print media containing cellulose, such as plain paper, can be obtained by evaporating water in a state where tension is applied in the direction of stretching the print media during paper making to form hydrogen bonds between cellulose. When moisture is imparted to such a print medium containing cellulose, hydrogen bonds between celluloses are broken, the print medium swells, and the tension applied to the print medium is relaxed. Thereafter, as the water evaporates, the print media shrinks and again forms hydrogen bonds between the cellulose (cellulose recombination occurs). Since the recombination of cellulose occurs in a state where no tension is applied, that is, in a state where no force is applied in the direction in which the print medium is stretched, the recombination of the cellulose is relatively contracted compared to before applying water. Happens in the state. For this reason, the shape before applying water cannot be restored, and curling occurs.

  On the other hand, when a clear ink containing L-carnitine is applied to the print medium, L-carnitine enters between the celluloses. Since L-carnitine is a compound having deliquescence, it is easy to take up moisture in the print medium and in the atmosphere, and it is easy to retain moisture. Therefore, recombination of cellulose can be suppressed and curling can be suppressed.

  Since L-carnitine is a highly deliquescent compound, it easily breaks the hydration state of other substances. For example, when an ink containing a color material and the type and amount of the color material has different thresholds but L-carnitine of a certain amount or more is prepared, L-carnitine in the ink affects the dissolved or dispersed state of the color material. And insolubilizes or precipitates the coloring material. In order to reduce the influence of the compound represented by the above formula (1) on the color material, the clear ink of the present invention does not contain the color material or substantially does not contain the color material. Therefore, the clear ink for inkjet of the present invention has an absorbance in the visible region of 0.1 or less. In the present invention, “absorbance in the visible region is 0.1 or less” means that the absorbance is 0.1 or less over a range of 400 nm to 700 nm when a visible light absorption spectrum is measured using a cell having an optical path length of 1 cm. Refers to that.

  The content of L-carnitine is preferably 5% by mass or more and 40% by mass or less, more preferably 20% by mass or more and 40% by mass or less, based on the total mass of the clear ink. When the content is more than 40% by mass, the ejection stability may be lowered.

(Polyvalent saturated alcohol)
The clear ink of the present invention may contain a polyvalent saturated alcohol. In the present invention, the polyvalent saturated alcohol may have a valence of 2 or more, but is preferably 2 or more and 6 or less. Examples of the polyvalent saturated alcohol include trimethylol-substituted C2-C4 lower alkane, glycerin, saccharide, and glycol. Specific examples of the trimethylol-substituted lower alkane having 2 to 4 carbon atoms include trimethylolpropane and trimethylolethane. Specific examples of glycerin include diglycerin and polyglycerin. Specific examples of the saccharide include lactose, sucrose, maltitol, sorbitol, mannitol and the like. Specific examples of glycols include polyethylene glycol and polypropylene glycol. The molecular weight of polyethylene glycol is preferably 200 or more and 600 or less.

  The mass ratio of L-carnitine to polyvalent saturated alcohol in the clear ink of the present invention is preferably 1: 3 to 3: 1, and more preferably 1: 1 to 3: 1. The content of the polyvalent saturated alcohol is preferably 5% by mass or more and 20% by mass or less based on the total mass of the ink.

(Components that aggregate colorants)
The ink-jet clear ink of the present invention preferably contains a component that aggregates the color materials contained in the color ink described later. When the clear ink contains a component that aggregates the color material, the print quality and the robustness of the image can be improved when used as an ink set of the clear ink and the colored ink.

  Examples of the component that aggregates the coloring material that can be used in the present invention include cationic polymers and polyvalent metal salts.

  As the cationic polymer, for example, polyallylamine hydrochloride, polyaminesulfone hydrochloride, polyvinylamine hydrochloride, chitosan acetate and the like can be suitably used.

In the present invention, the polyvalent metal salt comprises a metal ion and an anion. Examples of the metal ions include divalent metal ions such as Ca ²⁺ , Cu ²⁺ , Ni ²⁺ , Mg ²⁺ , and Zn ²⁺ , and trivalent metal ions such as Al ³⁺ , Fe ³⁺ , and Cr ³⁺ . Examples of the anion include Cl ⁻ , NO ₃ ⁻ , I ⁻ , Br ⁻ , ClO ₃ ⁻ , SO ₄ ²⁻ , CO ₃ ²⁻ , CH ₃ COO ⁻ , and HCOO ⁻ .

In the present invention, Ca ²⁺ , Mg ²⁺ , Sr ²⁺ , Al ³⁺ , and Y ³⁺ are particularly preferable as a metal ion from the viewpoint of reactivity, colorability, and ease of handling, and more preferably Ca. ²⁺ is used. As the anion, NO ₃ from the viewpoint of solubility and the like ^- are particularly preferred. Examples of the polyvalent metal salt composed of the metal ion and the anion include calcium nitrate. The content of the polyvalent metal salt in the clear ink is preferably 0.01% by mass or more and 20% by mass or less, and preferably 5.0% by mass or more and 15% by mass or less with respect to the total mass of the clear ink. More preferred.

  Further, a nonionic surfactant may be added to the clear ink of the present invention. As the nonionic surfactant, those listed below can be suitably used. Ethylene oxide adduct of acetylene glycol (for example, acetylenol EH; manufactured by Kawaken Fine Chemical). Ethylene oxide adducts of acetylene or alkanes (eg, Surfinol 104, 82, 465, 485; manufactured by Air Products). Tergitol 15-S-5, Tergitol 15-S-7 (both manufactured by Union Carbide Company). The content of the nonionic surfactant is preferably 0.1% by mass or more and 10.0% by mass or less with respect to the total mass of the clear ink.

  In addition to the above-described components, additives such as a pH adjuster, a rust inhibitor, a preservative, and a fungicide can be added to the clear ink of the present invention as necessary.

(Water and water-soluble organic solvents)
The ink-jet clear ink of the present invention contains water, but may be a mixture of water and a water-soluble organic solvent. Although it does not specifically limit as a water-soluble organic solvent, Specifically, C1-C4 alkyl alcohols, such as methyl alcohol and ethyl alcohol; N-methyl-2-pyrrolidone, 2-pyrrolidone, etc. are mentioned, for example. . Moreover, it is preferable to use deionized water as water.

  The content of the water-soluble organic solvent in the inkjet clear ink of the present invention is preferably 3% by mass or more and 50% by mass or less with respect to the total mass of the clear ink. In addition, the amount of water in the inkjet clear ink is preferably 50% by mass or more and 95% by mass or less with respect to the total mass of the clear ink.

  The clear ink for inkjet of the present invention is preferably used as a set of clear ink and colored ink (an ink set having clear ink and colored ink) in combination with colored ink. Hereinafter, the components constituting the colored ink of the present invention will be described in detail.

<Colored ink>
Unlike the above-described clear ink, the colored ink of the present invention is an ink containing a color material that is a compound having absorption in the visible light region and water that is a medium for dissolving or dispersing the color material.

  Examples of the color material that can be used in the ink of the present invention include a water-soluble color material (hereinafter also referred to as a dye) or a water-insoluble color material (hereinafter also referred to as a pigment). Further, in the present invention, any color material exhibiting any color development characteristic such as black, yellow, magenta, and cyan can be used.

  The content of the coloring material in the ink of the present invention is preferably 1% by mass or more and 15% by weight or less, and more preferably 1% by mass or more and 10% by weight or less with respect to the total mass of the colored ink.

  The dye that can be used in the ink of the present invention is not particularly limited, and examples thereof include direct dyes, acid dyes, reactive dyes, and basic dyes. Specifically, a color index (CI) number can be used. In the present invention, even dyes not described in the color index can be used as long as they have water solubility.

  The pigment that can be used in the present invention is not particularly limited, and either a black pigment or a color pigment can be used. Moreover, carbon black is suitable as the black pigment. Since the pigment is insoluble in water, when the pigment is used as the color material, the pigment is dispersed in the ink. In the present invention, the method of dispersing the pigment in water is not particularly limited, and the following methods can be used. Specifically, a method of dispersing a pigment using a dispersant (resin dispersion method), a method of introducing a hydrophilic group on the surface of the pigment, and improving the dispersibility of the pigment itself to disperse the pigment (self-dispersion method) ) Etc. can be used.

  Moreover, when the resin dispersion system mentioned above in this invention is used, water-soluble resin can be used preferably as a dispersing agent. It does not specifically limit as water-soluble resin which can be used for this invention, Any thing may be used. Further, the content of the water-soluble resin is preferably 0.1% by mass or more and 5% by mass or less with respect to the total mass of the colored ink, and the weight average molecular weight is preferably 1,000 or more and 30,000 or less.

  The colored ink of the present invention may contain the deionized water and the water-soluble organic solvent mentioned as the aqueous medium that can be used for the ink-jet clear ink. The content of the water-soluble organic solvent in the colored ink of the present invention is preferably 3% by mass or more and 50% by mass or less with respect to the total mass of the colored ink. The amount of water in the colored ink is preferably 50% by mass or more and 95% by mass or less with respect to the total mass of the colored ink.

(Other ingredients)
In addition to the above components, a surfactant may be added to the colored ink of the present invention as necessary. As the surfactant that can be used in the present invention, nonionic surfactants such as polyoxyethylene alkyl ethers can be suitably used. Further, in addition to the above-described components, various additives such as a pH adjuster, a rust inhibitor, a preservative, and a fungicide can be added to the ink of the present invention as necessary. .

<Inkjet printing method>
The ink jet printing method using the ink set of the present invention is a method of applying a colored ink and a clear ink to a print medium so that the colored ink and the clear ink are in contact with each other. By using the above printing method, if the clear ink contains a component that aggregates the coloring material, the aggregation of the coloring material in the colored ink can be increased, so that the fixing property of the coloring material is improved. And bleeding that occurs when the colored ink and the clear ink come into contact with each other can be reduced.

  In the present invention, an ink jet printing method is used when applying ink to a print medium, but a method other than the ink jet printing method may be used when applying clear ink to a print medium. Specific examples include application methods using a roller coating method, a bar coating method, and a spray coating method. It is preferable to apply clear ink to the entire printing surface of the print medium using an application method because the colored ink and the clear ink come into contact with each other regardless of the shape of the image formed by the colored ink.

  Further, the order of applying the colored ink and the clear ink to the print medium is not particularly limited, but it is preferable to apply the clear ink to the print medium first. By applying the clear ink to the print medium in advance, the color ink is always applied to the print medium containing L-carnitine regardless of the printing interval between the clear ink and the color ink. Therefore, the occurrence of curling due to the evaporation of moisture in the colored ink can be reduced. In addition, when the clear ink contains a component that aggregates the color material, it is possible to cause an efficient aggregation reaction in which the influence of the penetration speed of the colored ink is reduced.

  When the clear ink is applied to the print medium by the inkjet method, the clear ink is preferably applied to the print medium at 25% duty or more, more preferably at 50% duty or more, particularly at 100% duty. preferable. By setting the duty of the clear ink within the above preferable range, it is possible to easily bring the L-carnitine and the colored ink in the clear ink into contact with each other. The duty in the present invention is the ratio of the position where the clear ink or colored ink is applied to the position where the clear ink or colored ink excluding the margin of the print medium can be applied.

  As print media used for inkjet printing, print media containing cellulose such as glossy paper, plain paper, matte paper, etc. are known. Any print media can be used by using the inkjet printing method of the present invention. The curl can be reduced even if it occurs.

  Print media such as glossy paper and matte paper have an ink receiving layer containing silica and alumina in addition to cellulose. When ink or clear ink is applied to a print medium having an ink receiving layer, the ink or clear ink is taken into the ink receiving layer, so that the amount of moisture applied to cellulose can be reduced and curling is suppressed. be able to. On the other hand, unlike glossy paper and matte paper, plain paper does not have an ink receiving layer having silica or alumina, and most of the material constituting the plain paper is cellulose. Therefore, a large amount of moisture is easily added to cellulose, and curling is likely to occur compared to glossy paper and matte paper. The effect of the present invention can be confirmed particularly remarkably when plain paper having the above-described characteristics is used.

  Next, the present invention will be described more specifically with reference to examples and comparative examples. In the text, “part” or “%” is based on mass unless otherwise specified.

<Adjustment of Clear Inks of Examples 1 to 6 and Comparative Examples 1 to 3>
The materials listed in Table 1 below were mixed, and further filtered under pressure with a membrane filter having a pore size of 0.2 microns to obtain clear inks 1-9. About the obtained clear inks 1-9, the absorbance measurement of visible region was performed using Hitachi spectrophotometer U-3300. As a result, the absorbance in the range of 400 nm to 700 nm was 0.1 or less for any clear ink. Moreover, it adjusted with deionized water so that the sum total of each component in each clear ink might be 100 parts.

<Curl evaluation of clear ink>
An ink tank filled with each clear ink is mounted on the ink cartridge of the inkjet printing apparatus MX-7600 (manufactured by Canon), and 100% of the area excluding 20 mm from the edge of A4 size plain paper (office planner, manufactured by Canon) Printing was performed with duty. Each printed matter on which clear ink was printed was allowed to stand for 1 day with the printed surface facing up in an environment of 50% humidity and 25 ° C., and then evaluated for curl. The curl of the printed matter was measured by the following method.

  The printed material was allowed to stand on a horizontal surface so that the surface on which the clear ink was printed faced up, and the height from the horizontal surface was measured at the four corners of the curled printed material. The curl value of the printed matter was calculated by averaging the heights from the obtained horizontal surface to the four corners of the printed matter. The curl values when using clear inks 1 to 9 are shown in Table 1 together with the clear ink composition.

Claims (9)

An ink-jet clear ink having an absorbance in the visible light region of 0.1 or less,
An ink-jet clear ink comprising water and L-carnitine.   The inkjet clear ink according to claim 1, wherein the content of L-carnitine is 20% by mass or more and 40% by mass or less based on the total mass of the clear ink.   The clear ink for inkjet according to claim 1 or 2, comprising a polyvalent metal salt.   The inkjet clear ink according to claim 3, wherein the content of the polyvalent metal salt is 5.0 mass% or more and 15 mass% or less based on the total mass of the clear ink.   The inkjet clear ink according to any one of claims 1 to 4, comprising a polyvalent saturated alcohol. An inkjet printing method for applying a clear ink for ink jet having an absorbance in a visible light region of 0.1 or less to a print medium and a colored ink containing water and a coloring material,
The inkjet clear ink includes water and L-carnitine,
An inkjet printing method comprising applying to a print medium such that the inkjet clear ink and the colored ink are in contact with each other.   The inkjet printing method according to claim 6, wherein the inkjet clear ink and the colored ink are applied to the print medium in this order.   The inkjet printing method according to claim 6 or 7, wherein the inkjet clear ink is applied to the print medium at 50% duty or more.   The ink-jet printing method according to claim 6, wherein the print medium is plain paper.