JP2003342503A - Black ink for ink-jet recording and method for forming image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a black ink forming an image having a high density, a high sensitivity and good adhesion to a substrate even when a UV light source of relatively low illuminance suitable for a method for ink-jet recording from the ink side is used. <P>SOLUTION: The black ink for ink-jet recording forms an image by jetting the black ink curable with irradiation of energy rays according to an ink-jet method on a substrate and then irradiating the substrate from the side of an ink-jetted surface with the energy rays. The ink comprises at least a colorant reproducing black color and a photopolymerization initiator having a photosensitive wavelength in the ultraviolet part. The transmission density corresponding to a contact print image at 360 nm is ≤1.30 for components except the photopolymerization initiator in the ink and ≥0.15 for the photopolymerization initiator component in the ink. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a black ink for ink jet recording which is capable of reacting and curing by irradiation with energy rays (mainly ultraviolet rays) and an image forming method using this ink composition, and more particularly, a plurality of black inks. The present invention relates to an inkjet technique capable of forming an image with high sensitivity and good adhesion even when an image formed of color is formed.

[0002]

2. Description of the Related Art In recent years, the inkjet recording method has been simple and easy.
Since you can make images at low cost, you can print photos,
It has been applied to various printing fields such as special printing such as marking and color filters. In particular, a recording device that emits and controls fine dots, ink that has improved color reproduction range, durability, and emission suitability, and special paper that dramatically improves ink absorbency, color material coloring, surface gloss, etc. Using
It is also possible to obtain image quality comparable to silver salt photography.

However, the improvement in image quality of today's ink jet recording system is achieved only when all of the recording apparatus, ink and special paper are prepared.

Inkjet systems that require special paper have problems that the recording medium is limited and the cost of the recording medium is increased. Therefore, many attempts have been made to record an image on a transfer medium that is not a dedicated paper by an inkjet method.

Specifically, a phase change ink jet system using a wax ink which is solid at room temperature, a solvent type ink jet system using an ink mainly composed of a quick-drying organic solvent, and crosslinking by ultraviolet (UV) light immediately after image formation. For example, a UV inkjet method.

Among them, the UV ink jet method has been attracting attention in recent years because it has less odor than the solvent ink jet method, is quick-drying, and can record an image on a recording medium having no ink absorption. The UV inkjet ink is classified into a solvent-containing type containing water and an organic solvent and a substantially solvent-free type. In the former case, the solvent remains after UV curing, resulting in deterioration of the physical properties of the film and VOC (Vola
Problems such as volatilization of tile organic compounds) occur. In that respect, the latter is the durability of the finished image while suppressing bleeding by curing immediately after impact,
VOC-free can be achieved.

An ultraviolet curable ink capable of being ejected and ejected from a minute hole by heating for image formation is disclosed in JP-A-61-164836, and a solventless ink having a similar constitution is disclosed in JP-A-5-214279. JP-A-5-21428
No. 0, special table 2000-504778, WO99 / 29
No. 787, WO 99/29788.

As a problem of the above-mentioned method, there is a problem that crosslinking by UV light is insufficient and often causes defective curing inside the ink forming an image. The composition of the ink that is on the outer side inside the ink, that is, the photopolymerization initiator,
The UV light absorption of the pigment, resin, or monomer reduces the light intensity, and accordingly the amount of radicals generated decreases and the reactivity decreases. This causes problems such as poor adhesion with the substrate, deterioration of image durability, and migration due to unreacted monomers.

This problem is generally remarkable in a black ink using carbon black having a strong absorption in the ultraviolet region. Further, as the type of image, a dark color image portion using a plurality of colors is used, and in this area, the amount of ink is the maximum adhesion amount or an amount close to it, so that a problem easily occurs.

As a countermeasure, UV light irradiation from the substrate side can be considered, but nevertheless, in a paper medium or a transparent film, U or polystyrene such as polystyrene or PET mainly containing an aromatic compound is used.
A medium that absorbs V light may not have a sufficient effect. Further, as shown in Japanese Patent Application Laid-Open No. 9-314981, a method of using an electron beam with an acceleration voltage of 10 to 100 kV is also conceivable, but the device cost becomes very high and there is a problem in practicability.

In addition to this, it is effective to reduce the amount of ink adhered, but it is likely to lead to a reduction in image density, that is, a reduction in the color reproduction area. Especially, in commercial printing such as packaging printing and POP, which requires a catch-eye property. , It is important to secure the color gamut,
There are many problems.

Another effective measure is to increase the illuminance of the light source so as not to reduce the amount of radicals generated while reducing the concentration of the initiator to reduce the UV shading property of the ink itself. For this method, see FUSION UV Sem
inar 2001 9th Fusion UV Technology Seminar "Detailed UV Technology Breaking the Current State"

However, in the UV ink jet system, this method is not always promising. A high-output UV light source is expensive and requires exhaustion of generated ozone and heat. In addition, in order to suppress ink bleeding after landing, a light source is generally arranged near the head, but a high-output light source has a large space and mass, and the head carriage size and mass also increase. This is because there is a problem in terms of output.

In the end, at present, the recording medium is not limited, and no truly practical solution has been found which does not cause a decrease in image density, an increase in size of an image forming apparatus, and an increase in price. .

[0015]

The present invention has been made to solve the above problems.

That is, an object of the present invention is to use a UV light source suitable for an ink jet recording method, to use a substrate having a poor UV transparency, and to use a light source of relatively low illuminance from the ink side to obtain high density, It is to provide a black ink capable of forming an image having high sensitivity and good adhesion to a substrate, and an image forming method using the black ink.

[0017]

Means for Solving the Problems As a result of intensive studies by the present inventors, it was found that the object of the present invention can be achieved by adopting any one of the following constitutions.

[1] A black ink for inkjet recording, in which a black ink curable by irradiation with energy rays is jetted onto a substrate by an inkjet method, and then an energy ray is emitted from the ink jetting surface side to form an image. , The ink is composed of a coloring material that reproduces at least black and a photopolymerization initiator having a photosensitive wavelength in the ultraviolet region, and the transmission density corresponding to a solid image at 360 nm is a component excluding the photopolymerization initiator in the ink. 1.30 or less, and the photopolymerization initiator component in the ink is 0.15 or more, a black ink for inkjet recording.

[2] The black ink for ink jet recording according to [1], which contains titanium black as a coloring material.

[3] The black ink for ink jet recording according to [1] or [2], which contains at least two kinds of coloring materials.

[4] An image forming method for forming an image by jetting a black ink curable by irradiation of energy rays onto a substrate by an ink jet method, and then irradiating energy rays from the ink ejection surface side to form an image. The ink according to Item 1, 2 or 3 is used, and the ink adhesion amount in a solid image is such that the transmission density at 360 nm excluding the photopolymerization initiator component in the ink is 1.30 or less, and the photopolymerization initiator in the ink is An image forming method, which comprises ejecting and adhering ink onto a base material so that the component becomes 0.15 or more.

[5] The image forming method according to [4], wherein an ink having a hue other than black is jetted onto the base material to form an image having a plurality of colors including black.

[6] The image forming method according to [5], characterized in that the black ink is ejected last.

[7] The image forming method according to [5], wherein the black ink is first ejected.

[8] The image forming method according to any one of [4] to [7], wherein the amount of ink adhered to the solid image of black ink is ² to 20 g / m ² .

[0026]

[9] The image forming method according to any one of [5] to [8], wherein the maximum ink adhesion amount in a solid image of a plurality of colors is 6 to 60 g / m ² .

[10] The substrate has a transmission density at 360 nm of 0.20 or more [4]-

The image forming method according to any one of [9].

[11] The image forming method as described in any one of [4] to [10], wherein ultraviolet light having a main wavelength of 300 to 400 nm is used as the energy ray.

[12] The illuminance of energy rays is 5 to 2
000 mW / cm ² [4]-
The image forming method according to any one of [11].

The essence of the present invention is to use a black coloring material (titanium black or the like) having a good UV transmittance or a plurality of coloring materials of two or more kinds for a base material having a poor UV transmittance. After the ink is adhered to the substrate, ultraviolet rays having a relatively low illuminance are irradiated from the surface of the adhered ink, so that the sensitivity is high and the ink is well adhered to the substrate.

In the present invention, ultraviolet rays refer to light having a wavelength in a range usually used, which will be described later in detail. Further, the solid image means an image having a maximum image density and a uniform density.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION In order to explain the present invention in more detail, the compounds used in the present invention and the contents of the constituents will be described below.

[1] Ink Color Material In the present invention, a color material having a small ultraviolet absorption rate is used,
Alternatively, the larger one is used in a limited amount. Generally, carbon black is used as a coloring material for black,
Since it has strong ultraviolet absorption, it is preferable to use as little as possible.

Specifically, for example, titanium black is preferable, and titanium black is specifically formed by subjecting titanium oxide to nitriding reduction treatment with ammonia gas.
(NaCl type) black fine powder. It is preferable as a black colorant for UV curing because it absorbs ultraviolet rays in the visible region less than carbon black.

In order to match the color tone with the process color black, other dyes or pigments may be added.

In addition to this, as a preferable color material, there is a method of reproducing in a plurality of colors. That is, in the case of an aqueous inkjet ink using a water-soluble dye without using carbon black, black is reproduced by color mixing, but a similar method can be adopted.

In any case, in accordance with the gist of the present invention, 30
It is desirable to select a coloring material so that absorption at 0 to 400 nm can be suppressed. Known dyes and pigments can be used as such a coloring material, but from the viewpoint of UV curability and light resistance, the coloring material is preferably a pigment or a microencapsulated dye.

As a preferable pigment for color tone adjustment and reproduction without using carbon black, yellow pigments include
C. I Pigment Yellow-1,3,1
2, 13, 14, 17, 81, 83, 87, 95, 10
9, 42, 74, 128, 185, and C.I. I Pig
ment Orange-16, 36, 38, and magenta system, C.I. I Pigment Red-5, 22,
38,48: 1,48: 2,48: 4,49: 1,5
3: 1, 57: 1, 63: 1, 144, 146, 18
5,101,2,12,9,122,184,188,
In the cyan system, C.I. I Pigment Violet
-19, 23, and C.I. I Pigment Blue
-15: 1, 15: 3, 15: 4, 18, 60, 27,
29, C.I. I Pigment Green-7,3
There are 6, etc.

Coloring agents (pigments) other than those described above can be used without particular limitation, but the amount to be added must be determined depending on the desired concentration and the color developability after dispersion. % Is preferred.

For dispersion of the coloring material, a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer,
A pearl mill, a wet jet mill, a paint shaker, etc. can be used.

It is also possible to add a dispersant when dispersing the pigment. A polymer dispersant is preferably used as the dispersant. As the polymer dispersant, for example, Ave
The Solsperse series manufactured by Cia is mentioned.

Further, it is possible to use synergists corresponding to various pigments as the dispersion aid.

These dispersants and dispersion aids are used in Pigment 1
It is preferable to add 1 to 50 parts by mass to 00 parts by mass. The dispersion medium is a solvent or a polymerizable compound, but the radiation-curable ink used in the present invention is preferably solvent-free because it reacts and cures immediately after landing of the ink.
If the solvent remains in the cured image, problems of solvent resistance deterioration and residual solvent VOC occur. Therefore, it is preferable in view of dispersion suitability that the dispersion medium is not a solvent but a polymerizable compound, in which a monomer having a low viscosity is selected.

The dispersion has an average particle diameter of the pigment of 0.08 to
0.5 μm is preferable, and the maximum particle size is 0.3 to
The thickness is preferably 10 μm, more preferably 0.3.
Selection of pigment, dispersant, and dispersion medium such that
Set dispersion and filtration conditions.

The particle size of the pigment can be measured by a light scattering method. Here, the average particle size means the average of the histogram (D
50).

By controlling the particle size of the pigment, clogging of the head nozzle can be suppressed, and the ink storage stability, ink transparency and curing sensitivity can be maintained. The color material is preferably added in an amount of 1 to 10% by mass of the entire ink.

As described above, it is preferable to use titanium black or a non-carbon black black coloring material using a plurality of colors in the present invention, but it is preferable to mainly use titanium black to add black by adding a small amount of coloring material. It is more preferable because it can be reproduced. When the number of color materials is increased, it becomes difficult to maintain the solubility or dispersibility, the storage stability of the ink, and the low viscosity for ensuring the ink ejectability.

Polymerizable Compound (Polymerizable Monomer) and Initiator The ink jet recording ink of the present invention is characterized by containing a polymerizable monomer (hereinafter, also simply referred to as a monomer) and an initiator. As the type of polymerization, any of ordinary radical-polymerization type, curing system utilizing photoacid / base generator, and photoinduced alternating copolymerization can be used. These photo-curing systems are described in detail in "Photo-curing technology" -Selection of resin / initiator and measurement / evaluation of compounding conditions and curing degree- (issued by Technical Information Institute), and they can be used as they are. is there.

Generally, a radical polymerization system and a cationic polymerization system are often used, but a photo-induced alternating copolymerization type which does not require an initiator can also be used. It is also possible to use a hybrid type in which these are combined.

The cationic polymerization system is superior in performance without polymerization inhibition by oxygen, but has a low reaction rate and high cost. In the case of cationic polymerization system, in order to increase the reaction speed,
The combined use of an epoxy compound and an oxetane compound is preferred.
Radical polymerization systems are most widely used in inks such as the present invention. The following are preferred embodiments for the radical polymerization system.

Various acrylate monomers can be used as the polymerizable monomer. For example, isoamyl acrylate, stearyl acrylate, lauryl acrylate, octyl acrylate, decyl acrylate, isoamyl still acrylate, isostearyl acrylate, 2-ethylhexyl-diglycol acrylate,
2-hydroxybutyl acrylate, 2-acryloyloxyethyl hexahydrophthalic acid, butoxyethyl acrylate, ethoxydiethylene glycol acrylate, methoxydiethylene glycol acrylate, methoxypolyethylene glycol acrylate, methoxypropylene glycol acrylate, phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, isobor Nyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-
Acryloyloxyethyl succinic acid, 2-acryloyloxyethyl phthalic acid, 2-acryloyloxyethyl-2-hydroxyethyl-phthalic acid, lactone-modified flexible acrylate, monofunctional monomer such as t-butylcyclohexyl acrylate, tri Ethylene glycol diacrylate,
Tetraethylene glycol diacrylate, polyethylene glycol diacrylate, tripropylene glycol diacrylate, polypropylene glycol diacrylate, 1,4 butanediol diacrylate, 1,6
Hexanediol diacrylate, 1,9 nonanediol diacrylate, neopentyl glycol diacrylate, dimethylol-tricyclodecane diacrylate, EO (ethylene oxide) adduct of bisphenol A, PO (propylene oxide) adduct of bisphenol A Bifunctional monomers such as diacrylate, hydroxypivalic acid neopentyl glycol diacrylate, polytetramethylene glycol diacrylate, trimethylolpropane triacrylate, E
O-modified trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, ditrimethylolpropane tetraacrylate, glycerin propoxytriacrylate, cowprolactone modified trimethylolpropane triacrylate, pentaerythritol ethoxytetraacrylate , Trifunctional or higher polyfunctional monomers such as caprolactam-modified dipentaerythritol hexaacrylate.

Besides, polymerizable oligomers can be blended in the same manner as the monomers. As the polymerizable oligomer,
Epoxy acrylate, aliphatic urethane acrylate,
Aromatic urethane acrylates, polyester acrylates, linear acrylic oligomers and the like can be mentioned.

Further, the methacrylate of the above acrylate compound can be used in combination. Among the methacrylates, methoxypolyethyleneglycolmethacrylate, methoxytriethyleneglycolmethacrylate, phenoxyethylmethacrylate, cyclohexylmethacrylate, tetraethyleneglycoldimatacrylate, polyethyleneglycoldiacrylate, etc. have relatively high sensitivity, and also have adhesiveness to the substrate. It is preferable because it can be improved.

Further, in the present invention, it is particularly preferable that at least two kinds of polymerizable monomers are selected from monofunctional, bifunctional, and trifunctional or higher functional polyfunctional monomers.

The monofunctional monomer has a large effect of reducing the shrinkage rate at the time of curing, has a low viscosity, and can easily obtain the ejection stability at the time of ink jet recording. The bifunctional monomer is particularly preferable because it has an appropriate sensitivity and excellent adhesion to various substrates.
A trifunctional or higher polyfunctional monomer provides sensitivity and film strength after curing. By using two or more of these three types, and more preferably three types in combination, it is possible to balance the adhesion to the support, image durability, and high sensitivity.

It is preferable that the monofunctional monomer is contained in an amount of 5 to 40% by mass, the bifunctional monomer is contained in an amount of 5 to 70% by mass, and the polyfunctional monomer is contained in an amount of 5 to 30% by mass.

The difference between the maximum value and the minimum value of the solubility parameter (SP value) of the monomers to be used in combination is preferably 1 or more because the adhesion to various substrates can be obtained. More preferably, it is 1.5 or more. The upper limit is 2.5.

As the initiator, conventionally known aryl alkyl ketone, oxime ketone, acylphosphine oxide, acylphosphonate, S-phenyl thiobenzoate, titanocene, aromatic ketone, thioxanthone, benzyl and quinone derivatives, ketocoumarins and the like. An initiator can be used.

Among them, acyl phosphine oxide and acyl phosphonate have high sensitivity and their absorption is reduced by photocleavage of the initiator. Therefore, internal curing in an ink image having a thickness of 5 to 15 μm per color as in the ink jet system is performed. Especially effective for.

Specifically, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethyl-pentylphosphine oxide and the like are preferable.

In addition, in consideration of high sensitivity, safety and odor, 1-hydroxy-cyclohexyl-phenyl-
Ketone, 2-methyl-1 [4- (methylthio) phenyl] -2-morpholinopropan-1-one, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 2-benzyl-2. -Dimethylamino-1- (4-morpholinophenyl) -butanone-1 is preferably used.

In the combination considering oxygen polymerization inhibition and sensitivity, 2-benzyl-2-dimethylamino-1- (4-
Morpholinophenyl) -butanone-1 in combination with 1-hydroxy-cyclohexyl-phenyl-ketone,
A combination of 1-hydroxy-cyclohexyl-phenyl-ketone and benzophenone, 2-methyl-1 [4-
(Methylthio) phenyl] -2-morpholinopropane-
1-one or 2-methyl-1 [4- (methylthio) phenyl] -2-morpholinopropan-1-one in combination with diethylthioxanthone or isopropylthioxanthone, benzophenone and an acrylic acid derivative having a tertiary amino group And the addition of tertiary amines are effective.

The preferred amount of the initiator added is 1 to 10% by mass, preferably 1 to 6% by mass, based on the whole ink. In the present invention, the irradiation is preferably divided into two stages by changing the absorption wavelength or concentration of the coloring material, and it is particularly preferable to use two or more kinds of initiators together.

Other components In order to improve the storage stability of the ink, a polymerization inhibitor of 200 to 200 is added.
It is preferable to add 20,000 ppm. As the polymerization inhibitor, hydroquinone, p-methoxyphenol, t-butylcatechol, pyrogallol, hydroquinone monomethyl ether and the like can be used. Further, it is preferable to contain a hindered phenol-based compound or a hindered amine-based compound because storage stability can be maintained without lowering curing sensitivity. Moreover, in order to suppress the thermal polymerization caused by heating, it is effective to add a hindered phenol having an unsaturated bond (for example, Sumilizer GS manufactured by Sumitomo Chemical Co., Ltd.).

Since it is preferable that the ultraviolet curable ink is heated to lower its viscosity and then ejected, it is preferable to add a polymerization inhibitor in order to prevent head clogging due to thermal polymerization. Such a polymerization inhibitor is effective even in an environment in which oxygen does not exist, and is also effective in an environment in which a high share is taken such as pigment dispersion.

In addition to these, a surfactant, a leveling additive, a matting agent, a polyester resin for adjusting the physical properties of the film, a polyurethane resin, a vinyl resin, if necessary.
Acrylic resins, rubber resins, and waxes can be added. As the surfactant, a fluorine-based compound or a silicone-based compound can be used. However, since the surfactant itself does not crosslink, a harmful effect due to bleed-out may occur after image formation. In such a case, it is preferable to use a copolymerizable monomer having a surface active effect together. For example, silicone-modified (meth) acrylate, fluorinated (meth) acrylate, and the like. A specific example is WO
99/29787 and WO99 / 29788.

It is also effective to add an extremely small amount of an organic solvent in order to improve the adhesion to the recording medium after UV curing.
In this case, it is possible to add it within a range that does not cause problems of solvent resistance and VOC, but it is preferable not to use it as much as possible. If necessary, the addition amount is preferably 0.1 to 5% by mass, more preferably 0.1 to 3% by mass.

Further, due to the light-shielding effect of the ink coloring material, as a means for preventing sensitivity deterioration, it is also possible to combine a cationically polymerizable monomer having a long initiator life with an initiator to form a radical / cation hybrid type curable ink. is there.

Ink preparation conditions In the present invention, the transmission density at 360 nm when an ink adhesion amount corresponding to the solid density is applied to the substrate by selecting the above-mentioned coloring materials and adjusting the compounding ratio appropriately. , As follows. (1) The transmission density corresponding to the components excluding the initiator is 1.30.
Or less, more preferably 1.20 or less. If it exceeds 1.30, the photocurability is deteriorated, and bleeding due to uncuring occurs particularly in bidirectional printing. The lower limit is not particularly limited, but will be 0.30 or more for practical use. (2) The initiator component and the permeation density corresponding to the initiator component are preferably 0.15 or more, more preferably 0.25 or more.
If it is less than 0.15, sufficient curability cannot be obtained. There is no particular upper limit, but in practice it will be 0.60 or less.

Here, the component corresponding to the initiator refers to the initiator and the initiation aid. When the monomer is a photo-induced type such as maleimide which does not require an initiator, it means a component corresponding to the monomer.

The amount of ink adhered to the solid portion of the black ink is ^{2 to 20} g / m ² , more preferably ^{2 to} 10 g.
/ M ² . If it is larger than 20 g / m ² , the internal curability will be deteriorated. On the other hand, if it is less than 2 g / m ² , there is a problem in the maximum image density.

By setting in this way, it is possible to obtain the adhesion to the substrate even when using a UV light source of relatively low illuminance. This is not only for black single color, but also for yellow, magenta, cyan, other orange, green,
A particularly remarkable effect is obtained when mixed with red, blue, white and the like. That is, in the mixed color, the UV transmissivity inside is further deteriorated, so that it is effective to use the ink of the present invention. In addition, the maximum amount of adhering color including black is 6 to 60 g / m ² , more preferably 6
Is about 30 g / m ² .

It should be noted that it is preferable to appropriately select the order of ejecting the black ink when the colors are mixed, depending on the quality of the image to be obtained and the transparency of other colors. When the adhesion to the substrate is of the highest importance, it is preferable to eject the black ink first and then eject the other color inks. When the sharpness of characters due to black is given the highest priority, black ink is ejected last.

In the ink of the present invention, U of black ink is used.
Since the V transparency is high, it is particularly effective for improving the internal curability of the black ink in the latter ejection method in which characters are most important and in the bidirectional printing in which speed is important.

In another preferred embodiment, the water content of the ink is preferably 0.02 to 2.0% by mass, and further, the monomer heating before adding the initiator, reduced pressure, calcium carbonate, etc. It is preferable that the dehydration treatment used and the ink supply system of the printer be a closed system so as not to come into contact with the air outside the system, from the viewpoint of more exerting the effect of the present invention. In particular, dehydration under reduced pressure is more preferable because it can be effectively performed without applying excessive heat to the ink.

In addition, the water content of the ink is 0.02 to 2.
When the content is 0% by mass, the adhesion to the support is improved, the image durability after formation, especially the water resistance is improved, and the long-term storage stability of the ink, especially the storage stability of the ink retained in the nozzle is improved. However, it is possible to prevent clogging of the nozzle for a long period of time. More preferably 0.02-1.5 mass%
Is.

As a means for adjusting the water content of the ink to 0.02 to 2.0% by mass, the acid value of the polymerizable monomer is set to 0.
It is preferably 00001 to 1.0 mg / g (KOH), but other means include a heating treatment, a dehydration treatment, and a printer internal There is a means for adjusting the dehydration rate by shutting off the outside air in the liquid supply system.

The ink is used so that the dots are appropriately leveled on the substrate after landing, and in order to obtain adhesion.
It is preferable that the viscosity at 25 ° C. is 6 to 80 mPa · s and the surface tension is 20 to 35 mN / m. Further, it is preferable from the viewpoint of stable ejection that the temperature is controlled by heating so that the viscosity of the ink when ejected is 6 to 20 mPa · s.

In the present invention, the viscosity at 25 ° C. is 6 to 80 mPa · s, and the surface tension is 20 to 35 mN / in order to improve the adhesion of a high-definition image using the above ink.
m, and the ink viscosity at the time of ejection is 6 to 20 mPa.
It is preferable to control the temperature by heating so as to obtain s, but the more important factor is the energy irradiation condition.

[2] Substrate The substrate used in the present invention is printing paper such as high-quality paper or coated paper, PET (polyethylene terephthalate), O
PS (stretched polystyrene), ONy (stretched nylon),
It can be applied to a wide range of base materials such as OPP (stretched polypropylene), PVC (vinyl chloride), various polyolefin films, acrylic resins, polycarbonates, phenol resins, glass and metals. OPP, P
Materials with high UV transparency, such as polyolefin films such as E, can be UV-cured from the substrate side, but other materials with low UV transparency, substrates with a transmission density at 360 nm of 0.2 or more. However, since the UV light is emitted only from the ink ejection side, the ink of the present invention is suitable.

Before the ink is ejected, the substrate is provided with a function of adjusting the surface energy of the substrate surface by any one of flame treatment, corona treatment, plasma treatment and liquid treatment, so that uniform dots can be obtained. It is possible to obtain the diameter,
It is preferable because the image quality is improved and the adhesion to the substrate can be improved. Above all, the plasma treatment is very effective because it does not generate ozone.

[3] Recording Method As an ink jet head used for ink ejection, various types such as a continuous type, a piezo type, and a thermal type can be used. However, the piezo type can cope with a wide range of liquid physical properties. It is particularly preferable because it does not cause the ink to burn or polymerize. For example, the structure described in EP-A-0277703 / 0278590 can be used.

Immediately after the ink is jetted and the ink is landed on the base material within a period of 1 to 1000 ms, 5 to 2000 mW /
It is preferable to irradiate the energy rays with an illuminance of cm ² .
If it is less than 1 ms, the distance between the head and the light source is too short, which causes problems such as unwanted energy irradiation to the head. Further, when the time is 1000 ms or more, the image quality deteriorates due to ink bleeding in multiple colors. At a low illuminance of less than 5 mW / cm ^2, problems may occur such that oxygen inhibits polymerization and ink curing is delayed, causing bleeding. 2000m
If W / cm ² or more, the base material is deformed by the heat source of the light source, the light source cost is increased, and the light source size is large, which causes inconvenience in improving the apparatus size and the recording speed.

As the light source, any ultraviolet light source can be used. For example, a high pressure mercury lamp, a low pressure mercury lamp, a cold cathode tube, a black light, an ultraviolet LED, an ultraviolet laser, a flash light and the like can be mentioned. Among these, a UV light having a relatively long wavelength type as an ultraviolet light component having a main wavelength of 300 to 400 nm, particularly a UV-A light source, is not easily affected by light scattering and is preferable for obtaining internal curability.

Incidentally, it is also possible to cure by using two kinds of light sources having different light sources and different illuminances.

[0086]

EXAMPLES The present invention will be specifically described below with reference to examples, but the embodiments of the present invention are not limited thereto. Incidentally, the stated addition amount ratio is a mass ratio unless otherwise specified.

Example A pigment dispersion of each color was prepared with the following composition. K1 <Black pigment dispersion 1> Titanium black 50 parts by mass Polymer dispersant 10 parts by mass Tetraethylene glycol diacrylate 45 parts by mass K2 <Black pigment dispersion 2> Pigment black 7 (carbon black) 50 parts by mass Polymer dispersant 10 parts by mass Tetraethylene glycol diacrylate 45 parts by mass Y <Yellow pigment dispersion> Pigment Yellow 93 50 parts by mass Polymer dispersant 10 parts by mass Tetraethylene glycol diacrylate 40 parts by mass M <Magenta pigment dispersion> Pigment Violet 19 50 Parts by mass Polymer dispersant 10 parts by mass Tetraethylene glycol diacrylate 40 parts by mass C <Cyan pigment dispersion> Pigment Blue 15: 3 50 parts by mass Polymer dispersant 10 parts by mass Tetraethylene glycol diacrylate 40 Using the amounts portion of these pigment dispersions were prepared each color ink as shown in Table 1.

For the ink, all materials other than the pigment dispersion were blended, and after confirming that they were sufficiently dissolved, they were added little by little to the pigment dispersion under stirring. 0.8 μm
After performing filtration with the filter of No. 2, while heating and stirring at 50 ° C., the pressure was reduced to remove dissolved air and water to obtain an ink. The viscosity of the ink at 25 ° C. is 12 to 22 mPa · s, and the surface tension is 24 to 3
The average particle size of the pigment is 0 mN / m and 0.08 to 0.3 μm.

[0089]

[Table 1]

DPCA60: Nippon Kayaku, KAYARA
D DPCA (caprolactam-modified dipentaerythritol hexaacrylate) TEGDA: Osaka Organic product, biscoat # 335HP (tetraethylene glycol diacrylate) PO-A: Kyoeisha Chemical, light acrylate PO-A (phenoxyethyl acrylate) I369: Ciba Specialty・ Chemical, Irg
acure369 (2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1) I184: Ciba Specialty Chemicals Irg.
acure184 (1-hydroxy-cyclohexyl-
Phenylketone) These inks were applied onto a polypropylene film base with a wire bar so that the amount of ink adhered was 6 g / m ^2, and the transmission density at 360 nm was measured without UV curing. Also, ink from Irgacure 369 and I1
The transmission densities of the inks except 84 were measured in the same manner. The ink adhesion amount of 6 g / m ² corresponds to the ink adhesion amount of the solid image (maximum density image) of each color.

[0091]

[Table 2]

Next, recording was performed on a recording medium by an ink jet recording apparatus using a piezo type ink jet nozzle having a nozzle diameter of 23 μm and 128 nozzles.

The ink supply system consisted of an ink tank, a supply pipe, a front chamber ink tank immediately before the head, piping with a filter, and a piezo head, and heat insulation and heating were performed from the front chamber tank to the head portion. Temperature sensors were provided near the nozzles of the antechamber tank and the piezo head, respectively, and the temperature was controlled so that the nozzle portions were always at 60 ° C ± 2 ° C. Droplet size is about 7 pl, 720 x 720 dp
The driving frequency is 10 kHz so that the image can be ejected with a resolution of i (dpi means the number of dots per 2.54 cm).
Driven at z. The image was evaluated by recording a character image in cyan on magenta solid.

Evaluation was carried out with a four-color full-color printer equipped with four-color heads of Y, M, C, and K (K represents black, C represents cyan, M represents magenta, and Y represents yellow) on the head carriage. It was At both ends of the carriage, UV-A
By mounting a low-pressure mercury lamp that emits light and scanning the head, UV light can be emitted within 1000 ms after ink landing.

Sensitivity (exposure energy): exposure surface illuminance is 1
It was set to 000 mW / cm ² . The exposure energy is performed by changing the speed of the head carriage, and the integrated light amount applied to all inks is 50 to 600 mJ / cm 2.
^{It is} possible to adjust up to ^2, and the point where surface tackiness disappears is defined as the sensitivity.

The arrangement of each color on the head carriage is as follows.
The test pieces were arranged as follows, and the test was conducted with three patterns of one-way printing only to the left, one-way printing only to the right, and bidirectional printing on the left and right. In right-to-left printing, black ink is ejected first, and then ink is deposited in the order of high UV absorption. The rightward direction is the opposite, and the Y ink that is ejected first is inside the K ink, so it is easily affected by light blocking. In both directions, since the case where K ink is the outermost layer is mixed, it is also easily affected by the light shielding by K ink.

← Lamp K C M Y lamp → In producing a color image, emission was limited so that one color was 100% and the maximum ink adhesion amount was 300%.

The support is OPS and has a surface wetting index of 46 m.
The plasma-treated product was used so as to have N / m.

Substrate adhesion: Y67%, M67%, C67
%, K100%, total 300% image part,
A tape peel test was performed. The recording surface side of each sample is cut into about 3 cm lengthwise and widthwise by a cutter, and about 3 cm is cut, Cellotape (R) is attached and rubbed with a claw 10 times, and then 1
It was peeled off in the 80 ° direction and evaluated.

: The image is not peeled. Δ: The image is partially peeled. X: The image is completely peeled. Table 3 shows the results of the recording sensitivity and the substrate adhesion in each ink set. Ink set A: K1, C, M, Y Ink set B: K2, C, M, Y Ink set C: K3, C, M, Y Ink set D: K4, C, M, Y (Comparative example) If the evaluation result is “Δ”, it is a practical property.

[0101]

[Table 3]

From Table 3, the ink set A in the present invention,
It can be seen that B and C have practical properties, but the ink set D has practical problems.

[0103]

According to the present invention, even if a UV light source suitable for an ink jet recording method is used, a substrate having a low UV transparency is used, and a light source of relatively low illuminance is used from the ink side, high density and high sensitivity can be obtained. It is possible to provide a black ink capable of forming an image having good adhesion to a substrate, and an image forming method using the black ink.

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Claims (12)

[Claims] 1. A black ink curable by irradiation with energy rays is jetted onto a substrate by an inkjet method,
Next, in an inkjet recording black ink that forms an image by irradiating an energy ray from the ink ejection surface side, the ink is composed of a coloring material that reproduces at least black and a photopolymerization initiator having a photosensitive wavelength in the ultraviolet region,
The transmission density corresponding to a solid image at 360 nm is 1.30 or less for the components excluding the photopolymerization initiator in the ink, and 0.15 or more for the photopolymerization initiator component in the ink. Black ink for inkjet recording. 2. The black ink for ink jet recording according to claim 1, which contains titanium black as a coloring material. 3. The black ink for inkjet recording according to claim 1, which contains at least two kinds of coloring materials. 4. A black ink curable by irradiation with energy rays is jetted onto a substrate by an inkjet method,
Next, in an image forming method for forming an image by irradiating an energy ray from the ink ejection surface side, the ink according to claim 1, 2 or 3 is used, and the ink adhesion amount in a solid image is determined by photopolymerization in the ink. An image forming method, characterized in that the ink is jetted and adhered to a substrate so that the transmission density at 360 nm excluding the initiator component is 1.30 or less and the photopolymerization initiator component in the ink is 0.15 or more. . 5. The image forming method according to claim 4, wherein an ink having a hue other than black is ejected onto the base material to form an image having a plurality of colors including black. 6. The image forming method according to claim 5, wherein the black ink is ejected last. 7. The image forming method according to claim 5, wherein the black ink is first ejected. 8. The image forming method according to claim 4, wherein a solid image of black ink has an ink adhesion amount of ² to 20 g / m ² . 9. The image forming method according to claim 5, wherein the maximum ink adhesion amount in a solid image of a plurality of colors is 6 to 60 g / m ² . 10. The image forming method according to claim 4, wherein the transmission density of the base material at 360 nm is 0.20 or more. 11. The image forming method according to claim 4, wherein ultraviolet light having a main wavelength of 300 to 400 nm is used as the energy ray. 12. The illuminance of energy rays is 5 to 2000.
It is mW / cm < ² >, The image forming method of any one of Claims 4-11 characterized by the above-mentioned.