JP2000117960A - Ink jet printing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet printing method by which it is possible to increase the adhesion of ink to a material to be printed after curing and print an image with high transparency when the material to be printed is light- transmissible and print an image with high gloss and chroma when the material is light-reflective. SOLUTION: Ink jet printing is performed on a material to be printed 3 using ink containing at least, pigment, a water-soluble ultraviolet polymerizable substance and a water-soluble photopolymerization initiator in an aqueous medium. In this case, the face to be printed of the material to be printed 3 is printed in such a way that the face is covered with a single-tier ink layer by making numerous single color ink droplets to adhere to the face, and the monochromatic solid printing process is adopted. Further in this case, when a static contact angle γw to pure water on the face to be printed satisfies γw<=60 deg. and an ink volume to be imparted per unit area during printing a monochromatic image solidly is given as VL (pl/cm2) and the ink volume to be absorbed by the face to be printed is given as VR (pl/cm2), the ink and the material to be printed 3 which satisfy conditions VR<=VL×0.5 are used to perform the printing process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for printing on a printing material with an aqueous ultraviolet curable ink using an ink jet printer. More specifically, a water-soluble dye or a pigment dispersed in an aqueous system as a coloring material component, a water-soluble polymerizable compound that is effectively polymerized by ultraviolet light as a binder component, and a water-soluble photopolymerization initiator are aqueous-based. Using an inkjet ink contained in the medium, the cured ink has a high adhesion to the printing material, and if the printing material is light-transmissive, prints with excellent transparency. The present invention relates to an ink jet printing method capable of printing with high gloss and saturation if it is reflective.

[0002]

2. Description of the Related Art A water-based ink containing a water-soluble dye as a coloring material has been used as an ink-jet ink. However, there is often a limit in improving the water resistance and light fastness of the aqueous ink alone using the water-soluble dye, and an aqueous ink using a pigment instead of the water-soluble dye is being studied.

[0003] In order to obtain higher water resistance, etc.,
An aqueous UV-curable pigment ink has been used as a UV-curable pigment ink. For example, JP-A-7-224241 discloses an aqueous UV-curable pigment ink.

[0004]

However, when a general ink-jet recording material is printed with pigment ink, the pigment particles are scattered on the surface of the medium, and the transparency and sufficient gloss of the ink layer can be obtained. There was a problem that there might not be. In particular, when the ink jet technology is used for a light transmission type medium such as an OHP that illuminates from behind and illuminates an image with light from behind, highly transparent printing is required, and such a requirement is sufficiently satisfied. Demand for pigment inks is increasing. In addition, for media for industrial use such as illuminated signboards and color liquid crystal panels, printing having both light resistance and transparency is required, and application of inkjet printing using pigment ink in such fields is being studied. .

[0005]

When printing is performed using an ink containing a pigment and an ultraviolet curable resin, the aggregation of the pigment at the time of fixing is reduced, and the refractive index difference between the resin and the pigment is small. Because of the reduction, the transparency is improved to some extent.
However, it has been found that when this ultraviolet-curable ink is printed on a recording material having sufficient ink absorbency, such as a general inkjet OHP film, no sufficient effect can be obtained.

On the other hand, in printing on a non-ink-absorbing medium with a UV-curable aqueous ink, when the medium has poor wettability with the ink, it is necessary to reduce the surface tension of the ink. Further, even in such a case, it is difficult to obtain a uniform ink layer at a high resolution, and the use of the obtained printed matter is sometimes limited.

The present invention has been made in view of the problem in using such an ultraviolet curable ink for printing by an ink-jet method. The cured ink has a high adhesive force to a printing material, and the printing material is hardly used. It is an object of the present invention to provide an ink jet printing method that enables printing with excellent transparency if the material is light transmissive, and high gloss and saturation if the material to be printed is light reflective. .

[0008]

According to the ink jet printing method of the present invention, printing is performed by using an ink containing at least a pigment, a water-soluble UV-polymerizable substance and a water-soluble photopolymerization initiator in an aqueous medium. In a printing method for performing ink-jet printing on a material, a case where a large number of ink droplets of one color are adhered to a printing surface of a printing material and printing is performed so as to cover the printing surface with one ink layer is considered. When the solid printing is performed, the static contact angle γ _{w of the} printing surface with respect to pure water is

[0009]

## EQU3 ## where γ _w ≦ 60 degrees (1) is satisfied, and the ink volume per unit area applied when printing one solid color is VL (pl / cm ² ),
The volume of the ink that can be absorbed by the printing surface is expressed as VR (pl /
cm ² )

[0010]

## EQU4 ## The printing is performed using an ink and a printing material that satisfy the condition of VR ≦ VL × 0.5 (2).

According to the present invention, it is possible to obtain good wettability on a printing surface of a printing material even when a non-ink-absorbing printing material is used in inkjet printing using an aqueous ultraviolet curable ink. And good ink-jet printing becomes possible.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION "One color solid printing" in the present invention
Refers to printing under the printing conditions necessary for one ink layer formed using one color ink as described above to be formed so as to cover the entire printing surface of the printing material, for example, The amount of ink applied when a uniform ink layer having a predetermined layer thickness is formed using the same printing material is calculated by the following equation.
It is as arranged in.

[0013]

## EQU5 ## Ink amount to be applied to solid color printing = resolution number ×
Resolution number x 1 dot droplet volume / area (inch square)

[0014]

[Table 1]

On the other hand, in order to form an ultraviolet-cured product from ink on a printing surface of a printing material in a good condition, a sufficient amount of the ink supplied on the printing surface of the printing material must be coated. It is necessary to remain on the surface to be printed without being absorbed in the printing material.
The value of R (the volume of the ink (liquid) that can be absorbed by the printing surface) needs to be sufficiently smaller than the above VL. Therefore, in the present invention, a combination of a printing material and an ink that can provide a VR sufficiently smaller than the VL, that is, a VR that satisfies the expression (2) is used. As shown in Table 1, VL is an amount mainly depending on the resolution of the printer and the volume of ink droplets per dot, and can be adjusted by changing these conditions. Whether satisfactory solid printing has been achieved can be determined by the naked eye and under a microscope that the entire surface has a uniform density and that fine particles having a high density due to agglomeration of color material particles are not observed.

The VR is a method of printing one to three solid colors on a printing material by variously changing the size of ink droplets.
It is a numerical value that can be obtained by measuring the amount of ink absorbed per unit area from the dry state of the surface after 0 minutes.

The numerical values for the resolution and the ink droplets shown in Table 1 show typical conditions in one-color solid printing, and are not limited to these. Further, the condition of the formula (2) relating to the solid printing in the present invention defines the condition relating to the combination of the printing material and the ink, and in actual printing, the same region with two or more colors of ink is used. Solid printing, printing with dots that are not solid printing,
Various print modes are applied according to print information, such as a mixture of solid printing and dot printing. For example, when printing with dots is included, printing may be performed such that one ink droplet has an amount smaller than the amount shown in Table 1. In that case, coalescence between adjacent dots (overlap at the periphery)
Is reduced, but the condition of equation (2) is still effective as a working condition for obtaining transparency. In addition, in normal color image printing, two or more colors of ink are applied to a unit area. Become.
Therefore, in printing using the method of the present invention, the printing material does not absorb the entire amount of ink applied inside, and the unabsorbed ink remains on the surface in a sufficient amount and is cured by ultraviolet rays. Be established.

When a light-transmissive printing material is used in the method of the present invention, it is considered that sufficient transparency is obtained for the following reasons.

For example, when printing on a printing material having poor wettability with water-based ink or poor absorption,
Generally, it is performed by providing a receiving layer having an ink absorbing property. However, if there is a receiving layer having sufficient ink absorbency, components other than the pigment particles in the ink (for example,
A phenomenon occurs in which the aqueous medium containing a water-soluble polymerizable compound or the like penetrates into the receiving layer. As a result, even if the pigment particles remain on the surface and the water-soluble polymerizable compound is polymerized by irradiation with ultraviolet light, a sufficient amount of the polymerizable compound does not remain on the surface or in the vicinity thereof. The function of wrapping and fixing the particles is no longer performed. Then, the cured film particles formed on the surface of the pigment particles cause light scattering, and the adhesive force of the pigment particles does not appear. On the other hand, when the relationship of the above-mentioned formula (2) is satisfied, it is ensured that a sufficient amount of the water-soluble polymerizable compound and water-soluble polymerization initiator in the ink remains on the medium surface together with the pigment. It is believed that UV curing gives sufficient transparency, gloss and adhesion.

On the other hand, a printing material that satisfies the condition of the above formula (2) usually has non-ink absorption or low ink absorption. In printing on such a printing medium, in addition to the condition of the expression (2), the expression (1) is satisfied so as to satisfy the expression (1).
The wettability between the ink and the substrate must be controlled. The combination of the ink and the printing material that satisfies the formula (1) can be achieved by adjusting the physical properties of at least one of them, and the physical property of the printing surface of the printing material is the condition of the formula (1). It is preferable to select a material that satisfies the above condition or to obtain a surface of the printing material by printing.

For reference, Table 2 shows the static contact angles of general-purpose plastics with pure water. These plastics have a static contact angle to pure water of 70 degrees or more. That is, it can be said that these general-purpose plastics have low wettability to water.

[0022]

[Table 2]

Accordingly, in order to print on a plastic sheet with an ink containing at least water, the surface tension of the ink itself is reduced by, for example, adding a surfactant to the ink to reduce the ink on the sheet. A method has been taken to increase the spread of wetness. At the same time, (1) an organic solvent which is miscible with water such as methyl ethyl ketone and γ-butyrolactone and has an affinity for plastic is mixed with water and used as a solvent component of the ink. A method of adding such a quick-drying solvent to the ink to rapidly evaporate the solvent component of the ink on the sheet and increase the viscosity to prevent uneven diffusion was also used. However, these methods can draw low-resolution images with large dots, such as those used to print codes, but the accuracy of the finish is completely insufficient for precise images or solid printing that requires high uniformity. It was something.

In the present invention, a desired printing result with high resolution is preferably obtained by selecting a printing material capable of satisfying the relationship of the expression (1) or by obtaining the material by surface treatment. In particular, when the purpose is transparent printing on a light-transmissive printing material, the printing is performed within a range that does not lose the smoothness of the surface of the printing material, or including increasing the surface smoothness. It is effective to perform surface treatment of the material.

The ink and the base material satisfy the above formulas (1) and (2)
In the relationship represented by, the ink droplets that fly and land from the nozzle spread on the printing surface of the printing material,
Adjacent droplets can effectively coalesce to form a smooth droplet layer. Deviating from this relationship, the droplets shrink and coalesce with each other, which may not form a uniform liquid film. As a result, smoothness and uniformity as an image cannot be obtained, and when transparency is required, light scattering is extremely increased, so that transparency may actually be lost.

As a method for satisfying the expression (1), the surface of the base material having a desired shape such as a sheet shape which can constitute the printing material is formed on the surface to be the printing surface so as to increase _γo with respect to the aqueous liquid. A method of performing the treatment is preferred, which ensures that the ink spreads wet. That is, it is effective to use a water-soluble polymer compound, a metal oxide, or the like having a water-absorptive ink absorbency in the range of the condition (1).

As another method for satisfying the expression (1),
Physical surface treatments such as oxygen plasma oxidation, electron beam irradiation, irradiation of far ultraviolet rays near 200 nm, flame (flame) treatment, vapor deposition of silicon oxide, aluminum oxide, and the like, and sputtering are effective.

In the water-based ink of the present invention using an ultraviolet curable substance, for example, the following two ink material constitutions and a printing method corresponding thereto can be adopted. The printing method includes a solvent removal process (evaporation, heat drying,
Washing).

The first ink material composition is a composition comprising a pigment as a coloring material, water, a liquid water-soluble polymerizable compound, and a water-soluble photoinitiator. Here, since the liquid water-soluble polymerizable compound also exhibits slow drying properties, a non-volatile hydrophilic solvent used in general water-based inkjet ink is not used. The second ink material composition is a composition comprising a pigment as a coloring material, water, a water-soluble organic solvent, a liquid water-soluble ultraviolet curable resin, and a water-soluble photoinitiator.

Hereinafter, each component will be described.

<Water-soluble polymerizable substance that is cured by ultraviolet rays> As the water-soluble polymerizable substance that is cured by ultraviolet rays, a monofunctional or polyfunctional polymerizable compound can be used. Among them, a compound having two or more acryloyl groups in one molecule and having a solubility in water of 10% by weight or more is desired. Moreover, it is soluble in water and has low viscosity,
Very few substances are photopolymerizable and have excellent physical properties of the cured film. Among the polyfunctional substances soluble in water, compounds having a polyethylene glycol structure are typical substances. However, even though these are water-soluble, the water resistance of the coating film is poor, and there is also a limitation on the base material that adheres well. Acrylic esters derived from epichlorohydrin adducts of polyhydric alcohols, a group of compounds generally called epoxy acrylates, have high water solubility, fast ultraviolet curing speed, and excellent coating physical properties, but have many hydroxyl groups. Therefore, there is a characteristic that the viscosity is slightly high. For this reason, use in ink may be restricted.

By using a non-volatile UV-polymerizable compound which is liquid, hydrophilic, has high hygroscopicity and is non-volatile, it is possible to form the first aqueous ink-jet ink containing no non-volatile organic solvent. .

One of the polyfunctional polymerizable compounds is a (meth) acrylic ester of a polyhydric alcohol. Water-soluble compounds in this group include polyethylene glycol # 200 diacrylate and polyethylene glycol # 200 diacrylate, which are acrylates of polyethylene glycol. Further, a water-soluble epoxy acrylate represented by the following compounds can also be used.

[0034]

Embedded image And the like.

A nonionic water-soluble polymerizable compound can also be used. Examples of such a polymerizable compound include (meth) acrylates of polyols having two or more hydroxyl groups such as monosaccharides and disaccharides; Examples thereof include (meth) acrylates such as ethanolamine, diethanolamine, trishydroxyaminomethane, and trishydroxyaminoethane. These have some of the basic elements of the present invention of water solubility and polymerizability,
Preferred compounds.

An acrylate having the following structure is particularly preferably used as a component of the ink in the present invention because it has high reactivity and low viscosity.

[0037]

Embedded image

[0038]

Embedded image

[0039]

Embedded image

Each of the compounds of the formulas (5) to (17) satisfies the requirements of low viscosity, high reactivity, and water solubility, and makes it easy to use a polyfunctional, high-viscosity oligomer. The content of the reactive substance in it can be increased.

The content of these polymerizable compounds in the ink is 1 to 40% by weight, preferably the same as the content of the coloring material or 5 times the content of the coloring material. That is, if the coloring material is 3% by weight, the content is preferably 3 to 15% by weight.

<Photopolymerization Initiator> The ink used in the present invention contains a polymerizable compound which also has the above-mentioned function as a solvent, and a water-soluble photopolymerization initiator is used for photopolymerization of the polymerizable compound. The agent is used in combination. As the water-soluble (hydrophilic) photopolymerization initiator, the following quaternary ammonium salt type water-soluble photopolymerization initiators can be used.

[0043]

Embedded image

Since these compounds have a quaternary ammonium salt structure, they have high water solubility.

[0045]

Embedded image

The compounds of the formulas (21) to (24) do not have a dissociable group, so that problems with co-solubility with the coloring material hardly occur, and are particularly preferable compounds in that sense.

The content of the photopolymerization initiator in the ink is 0.1.
It can be 1 to 10% by weight, preferably 0.3 to 3% by weight.

<Pigment> It is essential that the pigment used as a coloring material in the ink used in the present invention should be one in which the dispersion state of fine particles in the liquid medium is stably maintained. The basic element in the present invention is that it is dispersed in an aqueous medium and the particle size distribution as a dispersion is 2 particles in average particle diameter.
It is within a range of 5 nm to 250 nm, and the viscosity of the final ink can be adjusted to a range that does not affect the ejection, and the compatibility with components essential for ultraviolet curability is satisfied.

In order to obtain such a pigment dispersion, a method using a polymer dispersant as a base material disclosed in JP-A-10-168151 or the like is suitable. Surfactants disclosed in JP-A-8-209048 and the like are also suitable.

<Printing Condition> The most important requirement in the present application is that the relationship between the printing base material and the ink is satisfied so as to satisfy the above-described expressions (1) and (2). These conditions, if expressed qualitatively, do not mean that a printing material capable of absorbing ink quickly and sufficiently can be prepared as conventionally performed by the ink jet method. Lack of such absorptivity is an essential requirement for achieving the printing targeted in the present invention. The present invention is characterized in that the amount of ink that can be absorbed by a printing material is suppressed more than the total amount of ink applied in solid printing.

As a result of various experimental studies, in order to obtain a substantially transparent printing result using the aqueous ultraviolet curable ink, it is necessary to perform printing while satisfying the relationship of the above formula (1). As described above, it is easy to set the amount of ink that can be absorbed by the printing material to be １ ／ of the total amount of ink of one color to be provided by the following means. In order to satisfy such conditions, the water-based ink has good wettability, but the surface has been modified such that the amount of penetrated absorption has been suppressed, or the wettability is good, but there is no permeability. What is necessary is just to prepare a base material.

Here, a material method for performing surface modification such that the amount of permeated absorption is suppressed will be described. Preferred surface modifiers are hydrophilic resins for coating. Examples include polyvinyl alcohol, aqueous polyurethane, aqueous polyester, polyvinyl acetal, cross-linked polyethylene oxide, cross-linked water-soluble polyamide, alcohol-soluble polyamide, hydrophilic melamine resin, and hydrophilic acrylic resin. These resins are preferably used as a crosslinked product thereof in terms of moisture resistance and water resistance of the printed matter. Aldehydes, melamines, polyepoxides, block isocyanates, aluminum alkoxides, and the like are used for crosslinking. Such a surface modification has a certain ink absorption capacity but cannot have a quick absorption rate.

In the printing method of the present invention, the ink absorption amount of the printing material is suppressed, and the ink curing method by ultraviolet irradiation (ultraviolet curing method) is used. No longer. Therefore, most methods known as surface modification methods for a predetermined hydrophilic surface of metal or plastic can be basically applied. For example, an inorganic coating, such as applying a metal oxide such as silica, alumina, or magnesia from the gas phase, or applying a noble metal such as gold, silver, or copper, is also effective in adjusting the wettability to the surface. If the condition of the formula (1) is satisfied and the ultraviolet curing method is adopted, pigment ink printing can be achieved with excellent transparency in the transparent substrate and excellent saturation, density and brightness in the reflective substrate. .

<Solvent> The aqueous medium used in the present invention may be one formed with water alone as described above,
It may be formed by mixing a water-soluble organic solvent with water as required. When a water-soluble organic solvent is used, the drying step after printing becomes more effective. The water-soluble organic solvent having a property of being relatively easily evaporated and dried is a water-soluble organic solvent having a boiling point at atmospheric pressure of about 190 ° C. or less. Examples thereof include ethylene glycol, diethylene glycol, triethylene glycol, tripropylene glycol, glycerin, 1,2,4-butanetriol, 1,2,6 hexanetriol, 1,2,2
5-pentanetriol, 1,2-butanediol, 1,
3-butanediol, 1,4-butanediol, dimethyl sulfoxide, diacetone alcohol, glycerin monoallyl ether, propylene glycol, butylene glycol, polyethylene glycol 300, thiodiglycol, N-methyl 2-pyrrolidone, 2-pyrrolidone, γ -Butyrolactone, 1,3-dimethyl-2-imidazolidinone, sulfolane, trimethylolpropane, trimethylolethane, neopentyl glycol,
Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monoallyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoether, propylene glycol monomethyl ether, Dipropylene glycol monomethyl ether, β
-Dihydroxyethylurea, urea, acetonylacetone, pentaerythritol, 1,4-cyclohexadiol and the like.

The non-volatile solvent which is difficult to evaporate and dry is desirably removed by washing with water after printing. Solvents that can be used when using such a process also include hexylene glycol, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol monophenyl ether, diethylene glycol diethyl ether, diethylene glycol monobutyl ether, Diethylene glycol monoisobutyl ether, triethylene glycol monobutyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, propylene glycol monobutyl ether,
Dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, glycerin monoacetate, briserine diacetate, glycerin triacetate, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, cyclohexanol , 1,2-cyclohexanediol, 1
-Butanol, 3-methyl-1,5-pentadiol,
3-hexene-2,5-diol, 2,3-butanediol, 1,5-pentanediol, 2,4-pentanediol, 2,5-hexanediol, and the like.

In the present invention, as described above as the first constitution, since the polymerizable oligomer has the function of preventing water as a solvent from evaporating, when the polymerizable oligomer is added in a high content, May be configured without using the above-mentioned solvents as a solvent. When using solvents,
The total amount of the water-soluble solvent is generally 5 to 40% by weight based on the whole ink. Two or more water-soluble solvents can be used in combination within a range that does not impair the effects of the present invention.

<Color Ink> Next, the color ink used for color recording will be described. As a coloring material of the color ink, an organic pigment, for example, a pigment dispersion dispersed with a dispersant can be applied. In addition, conventionally known direct dyes, acid dyes, reactive dyes, and metal complexes and polyvalent metal salts thereof can be used in combination with the pigment. However,
Irradiates ultraviolet rays after recording, so dyes that are stable to light,
Organic pigments are preferred.

<Pigment> As an organic pigment having a hue as a process color used in a color ink, as a yellow pigment, there may be mentioned Pigment Yellow 1, 2, 3, 1
2, Pigment Yellow 13, Pigment Yellow 1
4, Pigment Yellow 16, Pigment Yellow 1
7, Pigment Yellow 55, Pigment Yellow 7
3, Pigment Yellow 74, Pigment Yellow 7
5, Pigment Yellow 83, Pigment Yellow 9
3, Pigment Yellow-95, Pigment Yellow 9
7, Pigment Yellow 98, Pigment Yellow 10
9, Pigment Yellow 110, Pigment Yellow 1
14, Pigment Yellow 128, Pigment Yellow 138, Pigment Yellow 139, Pigment Yellow 150, Pigment Yellow 151, Pigment Yellow 154, Pigment Yellow 180 and the like.

Examples of magenta pigments include Pigment Red 5, Pigment Red 7, Pigment 12, Pigment 48 (Ca), Pigment Red 48 (Mn), Pigment Red 57: 1, Pigment Red 57 (Sr),
Pigment Trend 57: 2, Pigment Red 122,
Pigment Red 123, Pigment Red 168, Pigment 184, Pigment Red 202, Pigment Red 238, and the like are applied.

Examples of cyan pigments include Pigment Blue 1, Pigment Blue 2, Pigment Blue 3, Pigment Blue 16, Pigment Blue 22, Pigment Blue 60, Pigment Blue 15: 2, Pigment 1
5: 3, put blue 1, put blue 60, etc. are applied.

The subject of the present application is basically the achievement of transparency and adhesion in fine particle pigment ink. However, it does not hinder the use of the dye, and when the dye is used, a favorable effect is obtained except for slight fading due to ultraviolet rays. That is, they are saturation, density, and brightness.

Dyes are basically weak in light resistance, but by selecting the wavelength and intensity of light used for ultraviolet curing, the fading of the dye is minimized and the dye can be practically applied in many cases. The dyes that can be used in combination with the pigment include the following.

As the yellow dyes, Acid Yellow 11, Acid Yellow 17, Acid Yellow 23,
Acid yellow 23, acid yellow 25, acid yellow 29, acid yellow 42, acid yellow 49, acid yellow 61, acid yellow 7
1, Direct Yellow 12, Direct Yellow 2
4, Direct Yellow 26, Direct Yellow 4
4, Direct Yellow 86, Direct Yellow 8
7, Direct Yellow 98, Direct Yellow 10
0, Direct Yellow 130, Direct Yellow 8
6, Direct Yellow 132, Direct Yellow 1
42, and so on.

As magenta (red) dyes, Acid Red 1, Acid Red 6, Acid Red 8, Acid Red 32, Acid Red 35, Acid Red 37, Acid Red 51, Acid Red 52, Acid Red 80, Acid Red 85 Acid Red 87, Acid Red 92, Acid Red 94, Acid Red 115, Acid Red 180, Acid Red 254, Acid Red 256, Acid Red 289, Acid Red 315, Acid Red 31
7, Direct Red 1, Direct Red 4, Direct Red 13, Direct Red 17, Direct Red 23, Direct Red 28, Direct Red 3
1, direct red 62, direct red 79, direct red 81, direct red 89, direct red 227, direct red 240, direct red 242, direct red 243, and the like.

As cyan dyes, Acid Blue 9,
Acid Blue 22, Acid Blue 40, Acid Blue 59, Acid Blue 93, Acid Blue 10
2, Acid Blue 104, Acid Blue 113, Acid Blue 117, Acid Blue 120, Acid Blue 167, Acid Blue 229, Acid Blue 234, Acid Blue 254, Direct Blue 6,
Direct Blue 22, Direct Blue 25, Direct Blue 71, Direct Blue 78, Direct Blue 86, Direct Blue 90, Direct Blue 1
06, Direct Blue 199, and the like.

Not only these existing coloring materials but also newly developed compounds satisfying hue, light resistance and solubility can be applied to the constitution of the present invention without great difficulty.

The weight of the pigment in the ink as the pure content of the pigment is preferably 0.5 to 10.0% by weight.
When a dye is used in combination, the content is preferably 0.1 to 5% by weight.

<Pigment Particle Size of Ink> Conventional ink,
In the use of pigments for paints and plastics, it has been said that if the particle size of the pigments is less than about 0.2 microns, the transparency will begin to greatly improve. However, when the average particle size is set to 0.
A general inkjet pigment ink of only 2 microns or less may result in extremely poor transparency. On the other hand, according to the method of the present invention, in addition to the transparency based on the particle size of the pigment, excellent transparency is exhibited by the curing of the ultraviolet-polymerizable compound. Therefore, if the printing method of the present invention is used, the average particle size of the pigment particles is 25 nm.
It only has to be in the range of about 250 nm. Although this range also depends on the use of the printed matter, it gives a printed matter that is sufficiently transparent in a general sense. Of course, the pigment particle size is desirably small, but if the method of the present invention is used, it is not always necessary to reduce the particle diameter to 100 nm or less.

<Method of Making Ink> The ink may be mixed with the raw materials to be used in any order, but the mixing is carried out promptly without maintaining a non-uniform state for a long time. When a pigment dispersion is used, stirring is further carried out so as not to impair the uniformity.

<Printer System> In the print system embodying the present invention, an ultraviolet irradiation device is required for the ink jet mechanism. The ultraviolet irradiation device is typically arranged at a position as illustrated in FIG. UV light
The recording paper exiting the print station is irradiated from above or below, or both above and below. Such selection is of course possible in the case of transparent substrates. The time interval from the print head to the irradiation area is best performed in a time zone in which the ink components remain uniform before the ink completely penetrates the recording paper.
In this sense, under the printing conditions of the present invention in which the penetration ability of the base material is suppressed, the allowable range of the timing is large. Even if there are many types of recording base materials, the curable irradiation can be surely performed because their penetration is suppressed.

<Ultraviolet irradiation lamp> The ultraviolet irradiation lamp is preferably a low-pressure mercury lamp, a high-pressure mercury lamp, a mercury lamp coated with a phosphor, or the like, in which the vapor pressure of mercury is 1 to 10 Pa during operation. The emission spectrum of these mercury lamps in the ultraviolet region is from 184 nm to 4
It is in the range of 50 nm, and is suitable for efficiently reacting a polymerizable substance in a black or colored ink. In addition, since a small power supply can be used even when the power supply is mounted on the printer, it is also suitable in that sense. Mercury lamps include metal-hide lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, xenon flash lamps, deep UV lamps,
UV lasers and the like are practically used, and the emission wavelength range includes the above range. Therefore, if a power supply size, an input intensity, a lamp shape, and the like are permitted, they are basically applicable. The light source is selected according to the sensitivity of the catalyst used.

The required ultraviolet light intensity is 2 to 50 mW / cm
A degree of ² is desirable from the position of the polymerization rate. If the integrated irradiation amount is insufficient, the adhesion of the fixed ink to the recording paper will not be sufficient. Further, in color recording, there is a shortage in the robustness of the printing ink, which is the object of the present invention, such as insufficient water resistance.

<Printing Step> The printing method of the present invention preferably basically has the following steps. (1) Step of printing on the base material with an ink jet printer (2) Step of irradiating the base material with ultraviolet rays to polymerize the polymerizable substance in the ink (3) Step of removing the solvent component in the base material ) May be before or after (2).

In the present invention, it is preferable to use the step (3) in order to remove the unevaporated solvent component because the ink receiving capacity of the ink receiving layer is not sufficient and the solvent remains near the surface.

However, as described above, when the water-soluble and relatively volatile organic solvent is used, or when the water-soluble organic solvent is not used, the step (3) may be omitted. is there. For removing the solvent component, a heating method such as a microwave oscillator, a far-infrared lamp, or the like can be employed. When a non-volatile solvent is used, washing with water is the simplest and most effective method if it is a substrate resistant to water after ultraviolet curing.

By fixing the ink with ultraviolet rays, good fixing, abrasion resistance, water resistance and the like can be obtained. At the same time, deformation of the paper itself such as curl and cockle is suppressed, which is preferable for handling and storage.

Hereinafter, the present invention will be described more specifically with reference to Examples.
The measurement of the average particle diameter is a numerical value obtained by a dynamic light scattering method. Ink formulation example 1 (Ink set 1: Ink not containing water-soluble organic solvent)

[0078]

[Table 3] *) Pigment Yellow 74 dispersion; average particle diameter: 110 nm; dispersant: water-soluble polyurethane resin (number average molecular weight 3000)

[0079]

[Table 4] *) Pigment Red 122 dispersion; average particle diameter: 90 nm; dispersant: water-soluble polyurethane resin (number average molecular weight 3000)

[0080]

[Table 5] *) Pigment Blue 15: 3 dispersion; average particle diameter: 75 nm; dispersant: water-soluble polyurethane resin (number average molecular weight 3000)

[0081]

[Table 6] *) Pigment Black 7 dispersion; average particle diameter: 95 nm, dispersant: water-soluble polyurethane resin (number average molecular weight 3000) Ink formulation example 2 (Ink set 2: Ink containing water-soluble organic solvent)

[0082]

[Table 7] *) Pigment Yellow 93 dispersion; average particle diameter: 135 nm; dispersant: alkali-soluble acrylic resin (number average molecular weight 5300)

[0083]

[Table 8] *) Permanent Carmine GG-2105 (Pigment Tread 238) dispersion; average particle size: 115 nm

[0084]

[Table 9] *) Pigment Blue 15: 3 dispersion; average particle diameter: 75 nm; dispersant: alkali-soluble acrylic resin (number average molecular weight 5300)

[0085]

[Table 10] *) Pigment Black 7 dispersion; average particle diameter: 95 nm; dispersant: alkali-soluble acrylic resin (number average molecular weight 5300) Ink formulation example 3 (Ink set 3: Ink containing water-soluble organic solvent)

[0086]

[Table 11] *) Pigment Yellow 128 dispersion; average particle diameter: 123 nm; dispersant: Phosphanol RE610 (HLB = 12.6, manufactured by Toho Chemical)

[0087]

[Table 12] *) Pigment Red 122 dispersion; average particle diameter: 140 nm; dispersant: Phosphanol RE610 (HLB = 12.6, manufactured by Toho Chemical)

[0088]

[Table 13] *) Pigment Blue 15: 3 dispersion; average particle diameter: 110 nm; dispersant: Phosphanol RE610 (HLB = 12.6, manufactured by Toho Chemical)

[0089]

[Table 14] *) Pigment Black 7 dispersion; average particle diameter: 95 nm; dispersant: Phosphanol RE610 (HLB = 12.6, manufactured by Toho Chemical)

Example 1 A 75 micron polyethylene terephthalate film was used as a base material, and a crosslinkable water-soluble polyamide resin was used.
Paratoluenesulfonic acid was added as a cross-linking agent to Toresin FS500 (water dispersion manufactured by Teikoku Chemical Sangyo) (100 parts of water dispersion: cross-linking agent = 100: 2 (parts by weight)), and applied with a wire bar coater # 10. Dry at 20 ° C. for 15 minutes. In this way, a printing material 1 having a hydrophilic polyamide resin layer having a thickness of 4 microns was prepared. The contact angle of the film surface to pure water was 30 degrees. The amount of ink that this film can absorb is approximately 1 ×
It was 10 ⁵ pl / cm ² (= 1 ml / m ² ). The coating showed good water resistance.

The ink jet printer having the arrangement shown in FIG.
Printing using a device equipped with an ultraviolet irradiation lamp on the linter
The test was performed. This test equipment uses the bubble jet method
Using one print head
Ink amount is 2.2 × 10 ⁶pl / cm^TwoWas set.
The installed lamp is Ushio's low-pressure mercury lamp UL1
-5DQ (input 50W, 90V, 0.6A). I
Time from when the ink is applied to when it enters the UV irradiation area
Is approximately 7 seconds, and
About 10 seconds.

Using the ink set 1, a solid pattern of one color (YMC) was printed on the material 1 to be printed, and the material was irradiated with ultraviolet rays. The obtained printed matter was evaporated and dried in a microwave irradiation device to obtain a desired printed matter. The transmission spectrum was measured using these printed materials. As a comparison, a printed material was prepared by performing printing in the same manner as described above without performing the surface treatment on the base material in Production Example 1 of the printing material, and the transmission spectrum was measured. Table 1 shows the above measurement results.
No. 5

To indicate preferable transparency means that the transmittance is 0 in a wavelength region where the coloring material itself should absorb, and 1 in a wavelength region where the coloring material does not absorb.

[0094]

[Table 15]

In the case of no surface treatment, coalescence of the ink droplets did not proceed and a smooth liquid film was not formed. Therefore, in order to evaluate the transmittance, the uniformity of the printed matter was extremely poor. It was in perfect condition.

Example 2 A 75 micron polyethylene terephthalate film was used as a base material, and a mixture of polyethylene glycol resin (molecular weight: 80,000) and glyoxal (polyethylene glycol: glyoxal =, 100: 3 (parts by weight)) was used as a wire bar. Apply with coater # 20, Celsius 1
It was dried at 25 degrees for 20 minutes. In this way, a printing material 2 having a polyethylene glycol resin layer having a thickness of 10 microns was prepared. This resin surface had a water-resistant surface due to crosslinking, and had a contact angle of 15 degrees with pure water. The amount of ink that can be absorbed is 4 × 10 ⁶ pl / cm ²
Met.

Using the ink set 2 and the printing material 2, a solid pattern of one color (YMC) was printed in the same manner as in Example 1, and ultraviolet irradiation was performed. The obtained printed matter was evaporated and dried with a far-infrared dryer to obtain a desired printed matter. Furthermore, a printed material was obtained by the same operation using a substrate (without surface treatment). The transmission spectrum was measured using these prints, and the results are shown in Table 16.

[0098]

[Table 16]

In the case of no surface treatment, coalescence of the ink droplets did not proceed and a smooth liquid film was not formed. Therefore, in order to evaluate the transmittance, the uniformity of the printed matter was extremely poor. It was in perfect condition.

Example 3 A 7059 glass plate having a thickness of 1.1 mm was used as a base material, and its surface was irradiated with an ultraviolet sterilizing lamp for 5 minutes, then ultrasonically cleaned with an alkaline cleaning agent, and then washed with water and dried to form a coating. A printing material was obtained. The contact angle of the surface-treated portion of the printing material to pure water was 13 degrees. Using this printing material, printing was performed in the following steps.

A bubble jet printing apparatus was prepared which can be printed on a substrate on a plate having no flexibility as shown in FIG. 2 and which is arranged so as to be capable of irradiating ultraviolet rays from above and below the substrate. A light source of 254 nm was arranged at the upper part, and a light source of 365 nm was arranged at the lower part. Using this, a printing test was performed on the base material 3 using the ink of Formulation Example 3. The mounted lamp is a high-pressure mercury lamp having an output characteristic of 5 mW / cm ² near the center wavelength in both the upper and lower directions. Using the inks of the ink set 3, a solid pattern of one color (YMC) was printed on the printing material 3 and irradiated with ultraviolet light.

The obtained printed matter (colored glass plate) was washed with water and then evaporated and dried in a microwave irradiation device. The transmission spectrum was measured using the colored glass plate thus obtained. These results are shown in Table 17.

[0103]

[Table 17]

Example 4 Denacol EX31 which is a water-soluble polyepoxide as a cross-linking agent for a polyvinyl alcohol resin (Molecular weight: 50,000, manufactured by Popal Kuraray, 50,000 in degree of saponification: 85%) was used as a base material.
4, and as a crosslinking reaction catalyst, zinc borofluoride hydrochloride was added (Denacol EX314: zinc borofluoride hydrochloride: 100: 5 (parts by weight)), and a wire bar coater # 3
0 and dried at 120 degrees Celsius for 15 minutes. Thus, a printing material 4 having a polyvinyl alcohol resin layer having a thickness of 10 μm was prepared. The contact angle of the film surface with pure water was 25 degrees. The amount of ink that this film can absorb is approximately 1 ×
It was 10 ⁶ pl / cm ² (= 10 ml / m ² ). The coating showed good water resistance.

In the same manner as in Example 1, a printing test was performed using the apparatus having the configuration shown in FIG. The used ink is
This is Ink Set 2. Printing and ultraviolet irradiation were performed in the same manner as in Example 1. The obtained printed matter was evaporated and dried in a hot air oven to obtain a desired printed matter. The transmission spectrum was measured using these printed materials. Table 18 shows the measurement results.

[0106]

[Table 18]

Example 5 A resin-coated paper having a polyethylene layer laminated on the surface of a base paper
Pyronal, a hydrophilic polyester resin (Toyobo
Co., Ltd.) with a wire bar coater # 30.
After drying for 15 minutes, a printing material 5 was obtained. In addition, Polyester
The thickness of the resin layer was 13 μm. This chart sheet
The contact angle of the surface with pure water was 60 degrees. Also recording paper
The amount of ink that can be absorbed is approximately 0.
5 × 10 ⁶pl / cm^Two(= 5ml / m^Two)Met.

Using the same apparatus as in Example 1, a solid pattern of seven colors of YMCKRGB was printed using the ink set 3 and the printing material 5. The obtained printed matter is placed in a heating furnace for 3 hours.
Minutes and evaporated to dryness. Using these prints, image density and color measurement (saturation, lightness, hue) were performed. Also, rub the image area with a commercially available yellow marker,
Resistance was evaluated. As a result, good color reproduction and high abrasion performance were confirmed.

Comparative Example 1 The water-based pigment ink of Ink Set 2 was converted to CF102 (Cannon product), which is an OHP film for inkjet.
In the same manner as in Example 1, printing and ultraviolet irradiation were performed. CF- which is an OHP film for inkjet
At 102, the absorbable amount of the aqueous ink is 3 × 10 ⁶ p
1 / cm ² (= 30 ml / m ² ), which is sufficiently larger than the amount of ink applied in solid printing. Although the contact angle with pure water was difficult to measure accurately due to the absorption of water, the value was estimated to be 20 degrees or less from the initial shape of the droplet. In the OHP obtained in this way,
Pigment particles were deposited on the film surface, and the coalescence of the droplets was insufficient. Due to this, the transmitted light was strongly scattered, and the transparency as OHP was extremely insufficient. Table 1 shows the transmission spectrum measurement results.
It is shown in FIG.

[0110]

[Table 19]

In Table 19, the reason why the value in the absorption region is large is that the coalescence of the dots is insufficient, and a minute region through which light is directly transmitted remains. On the other hand, in the transmission region, light scattering reduced the transmittance.

[0112]

According to the present invention, an ink in which a pigment is dispersed in an aqueous medium is used to form a highly transparent ink for a non-absorbing substrate or a substrate having insufficient absorption. Printing with layers can be performed.

When the base material is a light-transmitting base material, it is possible to perform printing with less scattering and having both light resistance and transparency. In addition, in printing with a pigment ink, the adhesiveness is excellent, and in terms of chroma and lightness, these performances, which have been disadvantages of the conventional inkjet aqueous pigment ink, are improved.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a printer to which an inkjet printing method using an aqueous ultraviolet curable ink of the present invention can be applied.

FIG. 2 is a diagram schematically illustrating a printer to which an inkjet printing method using the aqueous ultraviolet curable ink of the present invention can be applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ink-jet print head 2 Printer main body 3 Printed material 4 Printed material to be discharged 5 Ultraviolet lamp 6 Transport base of printed material

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B41J 29/00 HF term (Reference) 2C056 EA04 EA09 FB02 FC01 FC06 HA44 HA46 2C061 AQ05 AS13 CK10 CK13 2H086 BA05 BA41 BA51 BA53 BA55 BA59 4J039 AB01 AD21 AE05 AE07 AF03 BB00 BC07 BC12 BC16 BC19 BC33 BC35 BE01 BE12 BE27 CA03 CA06 EA06 EA12 EA48 GA24

Claims (8)

[Claims] 1. A printing method for performing inkjet printing on a printing material using an ink containing at least a pigment, a water-soluble UV-polymerizable substance and a water-soluble photopolymerization initiator in an aqueous medium. When printing in such a manner that a large number of ink droplets of one color ink are attached to the printing surface of a material and the printing surface is covered with one ink layer, the printing surface is a solid color printing, Has a static contact angle γ _w with respect to pure water satisfying the following expression: γ _w ≦ 60 degrees (1), and the ink volume per unit area to be given when printing one solid color. VL (pl / cm ² ), where VR (pl / cm ² ) is the volume of ink that can be absorbed by the printing surface, the following equation is obtained: VR ≦ VL × 0.5 (2) An ink jet printing apparatus that performs printing using an ink and a material to be printed that satisfy the conditions. Printing method. 2. A printing method in which an aqueous ultraviolet curable ink is used to print on a printing surface of a printing material by an ink-jet method, wherein: (1) the printing surface of the printing material is printed under the conditions described in claim 1; A step of performing printing by an ink-jet method; (2) a step of irradiating the printing surface after printing in step (1) with ultraviolet light to cure the ink attached to the printing surface; and (3) the ultraviolet light. Curing the ink on the printing surface of the printing material by irradiation, and then removing a solvent component contained in the ink from the printing material. 3. The ink jet printing method according to claim 1, wherein the printing material has a light-transmitting sheet shape, and the ultraviolet irradiation is performed from both front and back surfaces of the sheet-shaped printing material. 4. The ink-jet printing method according to claim 2, wherein the removal of the solvent component in the printing material is performed using a drying device having a microwave oscillation device. 5. The ink jet printing method according to claim 2, wherein the removal of the solvent component in the printing material is performed by washing the printing material with water and a subsequent evaporative drying step. 6. The ink jet printing method according to claim 2, wherein the removal of the solvent component in the printing material is performed by irradiation with far infrared rays. 7. The pigment has an average particle diameter of 25 nm to 25.
The ultraviolet light source is dispersed in the aqueous medium as a fine particle dispersion in a range of 0 nm, and a light source having a wavelength near 254 nm and a light source having a wavelength near 365 nm are used in combination as an ultraviolet light source. Ink jet printing method. 8. The inkjet printing method according to claim 1, wherein the aqueous medium contains a water-soluble slow drying solvent.