WO2002057377A1

WO2002057377A1 - Ink for ink-jet printing and method of ink fixation

Info

Publication number: WO2002057377A1
Application number: PCT/JP2001/000370
Authority: WO
Inventors: Taisaburo Sakai
Original assignee: Taisaburo Sakai
Priority date: 2001-01-19
Filing date: 2001-01-19
Publication date: 2002-07-25

Abstract

A water-based ink for ink-jet printing which contains a soluble vat dye; and a method of ink fixation which comprises printing a paper with the water-based ink by ink-jet printing and then irradiating the ink dots on the paper with a laser light to insolubilize the colorant and thereby fix the ink. By this method, an ink-jet print can be obtained which is free from ink dot blurring, has a bright color, and is comparable in durability (water resistance and light resistance) to conventional printed matters.

Description

Description Ink jet printing ink and ink fixing method

The present invention relates to an ink used for an ink jet printing method and a method for fixing the ink. More specifically, the present invention relates to an ink for ink jet printing for fixing ink by insolubilizing a soluble vat dye dissolved in an ink solvent by irradiating a laser to ink dots on ink-jet printed paper and a fixing method thereof.

Background art

The ink jet printing method discharges minute droplets of ink from nozzles and adheres them to the surface of a printing material such as paper to print a character or an image. Various ink jet printing methods have been proposed, for example, a method called the continuous method is disclosed in US Pat. Nos. 3,298,030 and 3,596,275. In the drop-on-demand method, for example, US Pat. No. 3,946,398 discloses a method in which deformation of a piezo element is applied to a driving force of ink ejection. Further, an ink jet printing method in which ink droplets are ejected by utilizing thermal energy is disclosed in US Pat. No. 4,251,824. Although each of these patent publications proposes a method of ejecting ink droplets, it does not describe an ink composition suitable for an ink jet printing method.

In the ink jet printing method, the ink is ejected from the fine nozzle orifice as fine droplets at a high frequency of more than kilohertz and at a high speed, and the ink droplet ejection stability is determined by the viscosity of the ink and the surface tension. Greatly affected by Therefore, it is desirable that the viscosity of the ink be as small as possible, and that the surface tension of the ink be as large as possible.

For the above reasons, water is generally used as an ink jet printing ink. An aqueous ink as a main solvent is used. A water-soluble dye is added to the ink as a coloring material. (For example, acid dyes, direct dyes, basic dyes, etc.) However, printed matter printed with an aqueous ink containing such a water-soluble dye has a problem in that the colorant has low water resistance. In addition, the light resistance was weak, and the preservability of the printed matter was insufficient.

In order to solve this problem, many proposals have been made to use an aqueous ink in which a pigment is dispersed (for example, Japanese Patent Application Laid-Open No. 56-147589). According to this method, although the robustness of the printed ink is satisfactory, the following problem arises when used as an ink for inkjet printing.

First, water-based inks that use pigments as coloring materials have the drawback that bright colors cannot be obtained, and cannot print beautiful colors. Ink-jet printing is a new printing technology that has only been in practice for a few years. The ink jet printing method is used as a printer that outputs the image on the display screen of a personal computer to a hard copy because it is compatible with digital signals. The display screen of a personal computer can express a beautiful color image, and it is clear that ink that cannot reproduce this sharp color on paper has a fatal drawback. Due to this drawback, the aqueous ink in which the pigment is dispersed is not evaluated as an ink for inkjet, even if the color material has excellent fastness.

The reason why a vivid color cannot be obtained with an aqueous ink in which a pigment is dispersed is explained as follows. Ink jet inks need to maintain the ink viscosity as low as possible, and do not add high-viscosity vehicles to the ink, unlike plate printing inks. On the other hand, pigments are used as colorants in plate printing inks.When preparing plate printing inks, pigment particles are kneaded with a vehicle for a long time in a kneader called an ink conditioner, and facial particles are removed. Due to miniaturization, irregular reflection of light is suppressed. The fact that the individual facial particles are covered by the vehicle also helps maintain color clarity due to the refractive index.

On the other hand, in the case of water-based ink jet inks containing pigments, only the dentists are dispersed in water, so after ink-jet printing on paper, naked pigment particles adhere to the paper. It is in the state that it is. Since the pigment particle diameter is 1 to 10 / m and is larger than the wavelength of visible light (0.4 to 0.8〃m), irregular reflection of light on the surface of the pigment particles that have been pulverized into an irregular shape will occur. It appears and the color looks dull. It is thought that the color appears turbid due to pseudo-absorption, due to the fact that light repeatedly diffuses and attenuates gradually in the gaps between the pigment particles, causing pseudo-absorption. Therefore, a clear color cannot be obtained with an aqueous ink containing a pigment.

If the pigment particles are further finely crushed and the particle size is made smaller than the wavelength of visible light, clear and transparent colors can be obtained, and this problem seems to be easily solved, but it does not actually happen . When the fine particles of the ordinary pigment having a particle diameter of 1 to 10 / im are made finer, the surface area of the particles is remarkably increased, and the attractive force between the particles becomes relatively large, so-called secondary aggregation occurs. Secondary agglomeration is a phenomenon in which fine particles stick together and solidify in a dumpling shape. To prevent this, there are measures such as adding a large amount of a surfactant, but it is not preferable to lower the surface tension of the ink for ink jet. In addition, the addition of a surfactant tends to generate air bubbles in the ink, causing undesirable side effects such as adversely affecting ink ejection. Due to these drawbacks, aqueous inks containing pigments are not evaluated as ink jet inks even though they have excellent fastness properties.

In order to solve this problem, there has been proposed a method of insolubilizing the water-soluble dye of the ink on paper after inkjet printing using an aqueous ink containing a water-soluble dye. According to this method, a printed matter having excellent durability can be obtained while maintaining the clear color of the water-soluble dye. The soluble vat dye is obtained by reducing the insoluble vat dye to a leuco form and stabilizing the leuco form by esterifying the OH group of the leuco form with concentrated sulfuric acid. Since sulfuric acid is a dibasic acid, the remaining acid group is modified to a water-soluble sodium salt. Since the esterification reaction is a reversible reaction, the ester compound is hydrolyzed to regenerate the original compound. As described in Patent Gazette 1995-No. 294777 and Published Patent Gazette No. 10-550 / 570, this soluble vat dye does not have mature energy or light energy. , The original insoluble dye can be regenerated.

Published Japanese Patent Publication No. Heisei 10-No. 3570570 describes an ink jet recording using a water-based ink containing a soluble vat dye, and then irradiates the ink dots on the paper with ultraviolet rays from a UV lamp to emit a soluble vat. There has been proposed a method for insolubilizing dyes and dyes, that is, performing ink fixing to obtain printed matter having excellent water fastness and light fastness. According to this method, a printed matter having excellent fastness can be obtained, and at the same time, a bright color and a transparent color which cannot be obtained with the pigment ink can be obtained. It is considered that the pigment regenerated from the water-soluble dye in the ink is very fine particles, so that the same clear color and transparent color as the dye can be obtained. However, since the UV irradiation time required for insolubilizing the dye was as long as 60 seconds, the disadvantage that the ink dots on the paper spread during that time has not been solved.

In ink jet printing, the ink dots begin to bleed immediately after they land on the paper. is there. Prevention of ink bleeding is a very important issue in ink jet printing, since high-quality images cannot be printed if ink bleeds occur. In ink jet printing, the volume of the ejected ink droplets is 5 to 10 picoliters, and the amount of energy required to insolubilize the ink's soluble vat dye is It is slight. However, it was found that high energy density was required, and it was not possible to concentrate high-density energy on a minute local area by UV irradiation with a UV lamp. Disclosure of the invention

The present inventor has now found that laser irradiation is extremely effective as a means for locally applying high-density energy to ink dots adhering to the paper surface. Laser light is a type of coherent electromagnetic wave of a single wavelength and has good convergence, so it can be focused with a lens to reduce the diameter; With a laser, it is easy to concentrate the energy density by 10,000 times. Therefore, focusing on the ink dots that land on the paper surface, laser irradiation for 1 / 10,000 to 1/10 seconds can almost instantaneously insolubilize soluble vat dyes. Was. This makes it possible to perform ink jet printing on bleeding paper such as rough paper without causing bleeding of ink.

For the application of laser, _c soluble vat dye choosing laser wavelength substance absorbs is leuco (Leuco) body vat dyes, one is the number of conjugated double bonds in a molecule small, its Molecular absorption shifts to shorter wavelengths. For this reason, vat dyes have absorption in the visible part (400-800 nm), whereas soluble vat dyes have absorption in the ultraviolet. This is convenient for laser applications, and high energy UV lasers can be used. Ultraviolet light has a large energy, and in addition to the thermal effect of the laser, it is thought that it also has the effect of photochemically exciting dye molecules to promote the hydrolysis of soluble vat dyes. It is thought that vat dyes are instantly insolubilized.

The chemical reaction process in which a soluble vat dye dissolved in water regenerates an insoluble dye (vat dye) by laser irradiation is as follows: Soluble

Vat dye

σ-ico field

Pigment

Insoluble dye)

The composition of the aqueous ink that can be fixed by the laser irradiation of the present invention is as follows:

60 to 80 parts by weight water

1 0-3 0 parts by weight High boiling polar organic solvent

1 to 10 parts by weight Soluble vat dye

1 0 0 The high-boiling-point polar organic solvent suppresses the evaporation of the ink solvent at the nozzle opening to prevent nozzle clogging. N-methyl-pyrrolidone or ,, Ν'-dimethyl-imidazolidinone can be used as the high boiling point polar organic solvent. As the laser oscillator, a solid-state laser is preferable, and a semiconductor laser is particularly suitable. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an explanatory view showing that ink droplets are ejected from nozzles of an ink jet printing head and then laser irradiation is performed on ink dots on the paper surface to fix the ink. BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a state in which a laser is applied to the ink dots on the paper surface, and the ink droplets and the ink dots are enlarged for ease of illustration.

After the ink droplets 2a, 2b, and 2c ejected from the ink jet recording head 1 land on the paper 6, the soluble vat dye in the ink is insolubilized by the laser beam 5 emitted from the laser element 4. Ink fixing is performed. Paper 6 moves in paper feed direction 7.

In order to prevent the ink from scattering, irradiate the laser to the ink dot 3c of the ink dots 3a, 3b and 3 where the ink is soaked in the paper. As the laser element, a semiconductor laser element made of gallium nitride having an output wavelength of 403 nm (output: 50 to 20 OmW) is used.

In this aqueous ink, when the pH is adjusted to the acidic side, the rate of hydrolysis of the soluble vat dye is remarkably increased, so that the ink fixing rate (dye insolubilization) can be increased. Use any of the following dyes as soluble vat dyes. Vat dye soluble vat dye

Power Index (Chemical Structural Formula)

C. I.7 0 6 00 (reddish yellow)

C. Bat Yellow 1

C. I.67 3 00 (greenish yellow)

CI Pat Yellow 2

(Yellow)

C. I.5 9 I 00 (reddish yellow)

C. Pat Yellow 4

CI6 0 5 3 0 (clear greenish yellow)

(Light yellow)

C. I.5 9 1 0 5 (clear

C. Shit orange 1 reddish yellow)

C.1.5 9 7 0 5 (clear

C. Pat orange 2 reddish yellow)

CI5 9 3 0 0 (clear reddish

G. bat orange 3 orange)

C. I.5 9 7 1 0 (reddish

C. Shiba orange 4 color)

C.I.7 3 3 3 5 Reddish

C.Pat orange 5 color)

(Yellow orange)

CI70 80 5 S0 ₃ Na,

C.I.Bat Orange 1 ί 0 (yellow

Orange)

(Clear red)

CI

(Clear magenta color)

C I.733 55

(Blue tint)

C.'Short Red 6

C

OCH: C I.67000

C.I.Bat Red 10

(Blue tint)

C. I.67 8 1 0 (clear

C.I.Bat red 38 CI.Magenta evening color

C. I.73 860

N a (clear I. Butt red 45 5 reddish)

C.I.73905

C.I.

(Clear magenta)

C 1.6 0 0 1 0

Shipat Violet 1

(Clear purple)

C 1. 7 3 3 8 5 C I

(Critical 1.Bat Bio-Let 2

Magenta)

C. I. 7 3 3 9 5 (clear

C. Shibao Biolet 3 reddish purple)

C..I. 7 3 4 0 0

Na0 ₃ S * 0 O-SOoNa (purple)

C. I-Bat Bioreet 4

(Reddish purple)

(purple)

(鲊 light purple)

(Reddish blue)

(綠 taste 靑 color)

C.l.73055 (reddish blue)

CI Pat Blue 3

(Clear reddish blue)

(Blue)

1.6

C. I.6 9 825 (clear blue)

C.1. Bat Pull 6

(yellow)

color)

C I.5 9 83 0

C.I.Batch Gris

(Clear green)

CH ₃ 0 OCH ₃

(Dark green)

Light blue green)

(green)

(Reddish brown

C. I.6 90 1 5 (brown)

C.I.Bat Bra

CI.7 34 1 0 (reddish brown)

C. Back Brown 5

Na 0 ₃ S-0

C I.734 0 5

(Dark reddish brown)

C. Back Brown 7

C.I.73670 (blueish black)

C. Pat Black 1

(Blueish black)

(Blueish black)

NaOaS-0 0-S0 ₃ Na

C. I.69005

Hot rack 27

η _{ςο Μ} (olive color)

C. I 7 1 0 5 0

C. I Bat Green 8

(khaki)

C. I.6 9 5 2 5

I. Bat Black 2 5

Leave color)

Dyes suitable for Cyan (C), agenta (M), Yellow (Y), Black (K) are selected from the dyes listed above to make inks of each color. Currently available color printers for personal computers use CMYK 4-color inks, and print color images with different color tones from the display screen. In order to improve the color reproducibility of color printing, as proposed in U.S. Pat. By using these 7 color inks, a color printer with good color reproducibility can be made. As a reference example, soluble dye dyes for use in CMYRGBK 7 color inks are selected from the above dye list and indicated by I. structure number:

Cyan (C) ink C.1.67915 or C.1.67910

Magenta (M) ink C.1.73385 or C.1.73905

Yellow (Y) ink C.1.67300 or C.1.60530

Bed 00 ink C.1.73360 or C.1.59300

Green (G) ink C.1.59825 or C.1.59830

Blue (B) ink C.1.73000, C.1.73055, C.1.69800, C.1.73065 or C.1.69825

BlackOQ ink C.1.73670 Industrial applicability

Since the ink jet printing method is compatible with digital signals, it is used for printers that output information of a short time on a paper. The ink jet printing method combined with a computer can be used to reduce printing costs, and is considered to be the next-generation printing method. The ink jet printing method has a simple structure of the ink discharge head and is easy to integrate nozzles on a large scale. Therefore, it is suitable for multicolor printing, and can be used for high-speed printing.

In order for ink jet printing to replace plate printing, ink durability (robustness) must be improved to the same level as plate printing inks. At present, water-soluble dyes (base dyes, acid dyes, etc.) are used in inkjet printing inks, and the lightfastness of printed matter is poor and the water resistance is poor. In need, the inkjet printing method was limited to use as a personal printer.

By the ink for ink jet printing and the ink fixing method of the present invention, a printed matter having the same durability as that of conventional plate printing can be obtained on plain paper, and commercial printing by the ink jet printing method becomes possible.

Claims

The scope of the claims

1. After performing ink jet printing using an ink containing a soluble vat dye with water as the main solvent, the ink dots on the paper are irradiated with a laser to insolubilize the dye in a short time, and the ink dots are blurred. An ink fixing method for an ink jet printing ink, which is characterized in that the ink is fixed while preventing the ink.

2. The ink for ink jet printing according to claim 1, wherein the dye which can be insolubilized by the above-mentioned ink fixing method includes any one of the dyes represented by the following chemical formulas:

ε

o

Lis now AV.

O

2 7

2 8

M 0 _₃ S0 0-S0 ₃

H ₅

2 ⁿ 5

M0 ₃ S-0

M 0 ₃ S-0 0-S0 ₃ M

I

/.C00/l0df/I3d 3 4

Or CO

o

O'SOgM

H ₃ C 3 6

M.

(However, M in the formula represents sodium, potassium or lithium)