JP2016089139A - Inkjet ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide ink fixing tightly to a coarse surface and porous backing with good coloring without being influenced by the color of backing or roughness of fiber, because similar coloring is requested without depending on backing for printing ink including inkjet ink.SOLUTION: Water based inkjet ink providing coloring close to the color printed on a blank paper by applying titanium oxide as additive to dye-based inkjet ink is provided.SELECTED DRAWING: None

Description

The present invention relates to an aqueous inkjet ink, and more particularly to an aqueous dye ink made using a natural dye.

Conventionally, water-based inkjet inks are often used in which various water-based dyes are dissolved in water or a water-soluble solvent. Ink-jet ink using a dye forms an image by dyeing fibers of a substrate such as paper. However, a substrate with a wide fiber gap such as corrugated cardboard or a porous surface such as a cookie penetrates faster than the dye is colored, resulting in insufficient surface image formation and good color development. Cannot be obtained, and there is a problem that the printing density is lowered. This problem is particularly noticeable when a coloring material with weak color development such as a natural dye is used, and obtaining a good color development as the dye concentration increases is an important issue.

With respect to a substrate that is difficult to dye, it is studied to secure the printing density by stabilizing the fixability and color development on a printed material by using a pigment instead of a dye as a colorant. JP-A-9-227812 discloses a pigment and There has been proposed an ink that contains colloidal silica to improve dischargeability and fixability. Japanese Patent No. 3428742 discloses an ink that behaves as a pseudo pigment by adsorbing a dye on the silica surface. In addition to silica, there is shown an ink prepared by mixing adsorbed magnesium carbonate or calcium carbonate in edible oil and fat according to Japanese Patent Application Laid-Open No. 2001-011355. However, in the case of inks using these pigments, in the case of coarse fibers, the pigments pass between the fibers, resulting in a decrease in the density of the appearance due to insufficient concealment of the base, and it is necessary to disperse the pigments for inkjet discharge However, it is necessary to select an edible dispersant, and it is difficult to increase the pigment concentration.

JP-A-9-227812 Japanese Patent No. 3428742 JP2001-011355

Printing inks such as inkjet inks are required to have the same color regardless of the substrate. Provided is an ink that can be firmly fixed even on a coarse substrate or a porous substrate, and exhibits good color development without being affected by the color of the base or the roughness of the fibers.

As means for solving the above problems, in ink-jet inks mainly composed of water-based dyes, coloration close to the color printed on white paper can be obtained by adding titanium oxide as an additive.

It was found that the hue is hardly changed by adding titanium oxide to the aqueous dye ink regardless of the base material. It has been found that the color of the background is suppressed due to the concealing property of titanium oxide, and the brightness and the like are suppressed, and it is considered that the dye acts on the titanium oxide to behave as a pseudo pigment. It was shown that the hue is difficult to change. Titanium oxide is characterized by a greater hiding property than silica, magnesium carbonate, and the like. The refractive index n of silica or the like is 1.4 to 1.6, whereas titanium oxide is 2.5 to 2 .7, which is considered to contribute to the prevention of transmission of the background color.

The inkjet ink in the present invention contains an aqueous dye, water, and at least titanium oxide as an additive.

(Water-based dye)
Various dyes can be used as the dye according to the target color, but water-based inks using an aqueous dispersion medium are preferred, and such water-based inks are water-soluble. The dyes are used.

Examples of water-soluble dyes include acridine dyes, aniline black dyes, anthraquinone dyes, azine dyes, azomethine dyes, benzoquinone dyes, naphthoquinone dyes, indigoid dyes, indophenol dyes, indoaniline dyes, indamine dyes, leuco dyes, and naphthalimide dyes. , Nigrosine dye, indulin dye, nitro dye, nitroso dye, oxazine dye, dioxazine dye, oxidation dye, phthalocyanine dye, polymethine dye, quinophthalone dye, triacrylmethane dye, diacrylmethane dye, thiazine dye, thiazole dye, xanthine dye, One or more of cyan dyes can be mentioned.

Edible dyes refer to edible dyes that are soluble in water or that are stabilized without using a dispersant. If it corresponds to the said definition, it can select suitably from a synthetic food coloring and a natural food coloring. Examples of the synthetic food color include food red No. 2, food red No. 3, food yellow No. 4, food yellow No. 5, food green No. 3, food blue No. 1, food blue No. 2, and the like. Examples of natural pigments include caramel pigment, oyster pigment, turmeric pigment, safflower pigment, beech mushroom pigment, tomato pigment, β-carotene pigment, palm oil carotene, marigold pigment, anato pigment, capsicum pigment, gardenia pigment, monascus pigment, Beet red pigment, red radish pigment, grape skin pigment, anthocyanin pigment, spirulina pigment, perilla pigment, paprika pigment, cochineal pigment, squid ink pigment, copper chlorofoil and its sodium salt, iron chlorofoil and its sodium salt, riboflavin, riboflavin butyrate, One type or two or more types such as sodium riboflavin phosphate can be mentioned.

The blending ratio of the dye is preferably 1% by mass or more, particularly 10% by mass or more, and preferably 70% by mass or less, and particularly preferably 60% by mass or less, based on the total amount of the inkjet ink.
If the blending ratio is less than the above range, a clear print with a high color density may not be obtained. When the above range is exceeded, the dispersion stability in the water-based inkjet ink may be insufficient. In particular, in the case of edible dyes, the color development is poor, and in order to obtain the required color development, the blending ratio tends to increase. When the viscosity exceeds the above range, the viscosity increases and the ink jet suitability may decrease.

In addition, what is necessary is just to set arbitrarily the color taste and compounding ratio of each dye according to the color taste to express.

(solvent)
It is preferable to use water as the aqueous dispersion medium. Other aqueous media include sulfolane and low molecular weight polyethylene glycols. The mixing ratio of the aqueous dispersion medium is preferably 30% by mass or more, particularly preferably 40% by mass or more, more preferably 98% by mass or less, and particularly preferably 95% by mass or less of the total amount of the inkjet ink.

In addition to the aqueous dispersion medium, a water-soluble solvent can be used as a co-solvent. The selection of the water-soluble solvent depends on the required functions such as surface tension, viscosity, pigment, drying time and printing substrate. Suitable water-soluble solvents are ethylene glycol, propylene glycol, diethylene glycol, glycerin, dipropylene glycol, polypropylene glycol, amide, ether, carboxylic acid, ester, alcohol, organosulfide, organosulfoxide, alcohol derivative, carbitol, butyl carbitol , Cellosolve, ether derivatives, amino alcohols, ketones, N-methylpyrrolidinone, 2-pyrrolidone, cyclohexyl pyrrolidone, hydroxy ethers, amides, sulfoxides, such as dimethyl sulfoxide, lactones, mixtures thereof, and the like.

(Titanium oxide)
The particle size of titanium oxide is preferably 10 μm to 300 μm. If it is larger than 300 μm, the dispersion stability and the discharge property are inferior, and if it is smaller than 10 μm, the concealing property is inferior, and good color development cannot be obtained due to the influence of the underlying color. Any type of titanium oxide having various crystal forms such as rutile type and anatase type can be used. However, in consideration of improving the fastness of printing and preventing choking, etc. Fine particles of titanium oxide having a crystalline form are preferred.
Further, as fine particles of titanium oxide, it is also possible to use particles whose surface has been modified in order to improve dispersibility in ink.

(Other additives)
The water-based inkjet ink can use various additives depending on the required function.

[Surfactant]
Surfactants that can be added to the aqueous inkjet ink of the present invention can include anionic surfactants, cationic surfactants, amphoteric surfactants and nonionic surfactants.

[PH adjusters, antioxidants, UV absorbers, antiseptics, antifungal agents]
The aqueous ink of the present invention is preferably adjusted to be neutral or alkaline. Moreover, it is also possible to mix | blend antioxidant, a ultraviolet absorber, antiseptic | preservative, and an antifungal agent in order to prevent discoloration and a countermeasure against a change with time.

Production of inkjet inks and evaluation tests in the following examples and comparative examples were carried out in an environment of a temperature of 25 ° C. and a relative humidity of 55%, unless otherwise specified.
<Creation of standard sample>
As the aqueous solvent, ultrapure water was used, and Lina Blue [Spirulina Pigment, manufactured by DIC Corporation] was used as a blue dye.
The ratio of water and dye was 6: 1, and 10 g of this was used as a standard sample to prepare Examples and Comparative Examples below.
<< Examples 1-5 >>
Examples 1 to 5 were prepared by adding 1 g each of titanium oxide having a particle size of 10 nm, 35 nm, 300 nm, 5 nm, and 500 nm to a standard sample.
<< Comparative Example 1 >>
The standard sample was used as Comparative Example 1.
<< Comparative Examples 2-4 >>
The silica shown in the prior patent was made to have a particle size of 10 nm, 35 nm, and 300 nm in the same manner as the titanium oxide of the example, and 0.4 g each was added to the standard sample to make Comparative Examples 1 to 3, respectively.
<< Comparative Example 5 >>
Comparative Example 4 was prepared by adding 0.4 g of magnesium carbonate shown in the prior patent to the standard sample in the same manner as the titanium oxide of the example.

<Evaluation>
Regarding Examples 1 to 3 and Comparative Examples 1 to 4, after a certain amount was dropped on two types of ordinary printing paper and cookie surface, a method of spreading on a thin film using a blade or a bar, L * a * b * was measured. Based on this L * a * b *,
From the value of Comparative Example 1 where the color difference between the plain paper and the cookie surface {ΔE * ab = [(ΔL *) ^ 2+ (Δa *) ^ 2+ (Δb *) ^ 2] ^ (1/2)} is a standard sample Is expressed as a relative color difference.
The greater the relative color difference, the greater the effect of the addition of particles, and the smaller the color difference between the plain paper and the cookie surface than the standard sample without addition. That is, it can be expressed that there is little hue change due to the selection of the base material. The relative color difference was evaluated according to the following criteria.
○ 5 or more △ 1 or more to less than 4 × 0 or more to less than 1

Using a piezo inkjet printer, printing was performed with the inkjet inks of Examples 1 to 5 and Comparative Examples 1 to 4, and then stopped for 2 minutes, and then the ruled lines were printed. By observing, the dischargeability of the ink droplets discharged from the nozzles of the inkjet head was evaluated according to the following criteria.
○: No fading was observed on the ruled line. Good discharge performance.
Δ: Slight fading was observed on the ruled lines in the initial stage of printing, but no fading was observed thereafter. The dischargeability was evaluated as a practical level.
X: Fading was observed on the ruled lines throughout the printing period. The dischargeability was evaluated as poor.

The results are shown in Table 1.

All of the blends of silica of Comparative Examples 2 to 4 have a change in relative color difference of less than 1 with respect to the standard sample, and are influenced by the color of the base. In Examples 1 to 5 in which titanium oxide is blended, the relative color difference changes by 1 or more, and it can be expressed that it is hardly affected by the color of the base. In particular, when the particle size is 10 nm or more, the change in relative color difference is large and less affected by the underlying color, and when the particle size is 300 nm or less, the discharge property is improved.

The present invention may show good color development without being bound by the printing substrate by blending ink with suppressed color material blending or blending titanium oxide with ink using a weak color material such as natural dyes. I can do it. In particular, in the field of edible inks where the use of synthetic dyes is restricted, natural dyes that are weakly colored can be easily selected, and by incorporating titanium oxide according to the present invention, good color development is exhibited even on porous bodies such as cookie surfaces. Inkjet ink can be supplied.

Claims (3)

Inkjet ink containing at least a dye, water, and titanium oxide The inkjet ink according to claim 1, wherein the dye is an edible dye. The inkjet ink according to claim 1 or 2, wherein the titanium oxide has a particle size of 10 nm to 300 nm.