HK1116820B - Ink composition and printing method using the same - Google Patents

Description

Ink composition and printing method using the same

Technical Field

The present invention relates to a novel ink composition which can form a printed surface having a metallic luster by, for example, printing by an inkjet method; and a printing method using the same.

Background

In recent years, printing by the so-called inkjet method has been used in a wide range of fields from output printing of personal computers to printing of large printed matters such as commercials. In ink-jet printing, an ink pattern composed of a multi-color ink composition of three colors, cyan, magenta, and yellow, which are three primary colors, or four or more colors, which are basic colors, is superimposed on a printing medium such as paper, and a full-color image is expressed by color mixture of the respective colors.

However, there is a problem that metallic luster cannot be expressed in printing by the inkjet method due to the above expression method. Therefore, recently, various ink compositions using minute metal particles as colorants have been proposed in order to express metallic luster.

For example, in (1) japanese patent laid-open publication JP 11-323223, a (1999), an ink composition is disclosed in which a metal deposition film laminated on a resin film is finely pulverized by stretching the resin film to produce sheet-like metal particles, and the metal particles are dispersed as a colorant in a dispersion medium. Further, in (2) japanese patent laid-open publication JP 11-343436, a (1999), an ink composition is disclosed in which a laminate of 2 or more layers of a metal deposition film and a resin layer is pulverized in the same manner, and particles having a multilayer structure produced are dispersed in a dispersion medium as a colorant. Further, in (3) Japanese patent laid-open publication JP 2000-017208, A, there is disclosed an ink composition in which any of the above metal particles is dispersed as a colorant in a dispersion medium in a state of being encapsulated in a microcapsule.

However, the metal particles in the form of flakes used in the ink composition described in the above-mentioned document (1) are large, and the thickness is about 0.08 to 0.12 μm and the maximum length is about 0.8 to 2 μm at the level of the examples, and it is understood from the above-mentioned production method that the particles are flat and irregular and have non-uniform shapes and sizes among the particles.

Further, the particles having a multilayer structure used in the ink composition described in the document (2) are larger, and have a thickness of about 0.75 to 1.1 μm and a maximum length of about 3.8 to 4.0 μm at the level of examples, and are flat and irregular particles having non-uniform shapes and sizes among the particles. The microcapsules used in the ink composition described in the document (3) are particles having a diameter of about 5 to 70 μm.

Therefore, these particles are insufficient in dispersion stability in an aqueous dispersion medium such as water which is commonly used in ink compositions for ink jet printers for personal computers, and may be separated or precipitated during the period from the production to the actual use by the end user, thereby causing a problem that the particles cannot be used.

In addition, in recent years, the quality of images printed by the ink jet method has been rapidly improved, and in order to achieve high image quality, it is necessary to miniaturize the droplets of the ink composition discharged from a head of a printer as much as possible, and therefore the diameter of the nozzle tends to be miniaturized. However, the above-mentioned particles which are large, flat, and irregular and have non-uniform shapes and sizes among the particles cannot sufficiently cope with the miniaturization, and there is a problem that clogging of the nozzle is likely to occur.

Further, even when printing is performed using a conventional ink composition containing large-sized particles as described above, the granular feeling of each particle on the printing surface is conspicuous, and it is difficult to express a smooth and good metallic gloss such as a surface of a metal block, a metal foil, or a continuous metal film.

Therefore, the inventors have proposed the use of a metal colloid as a colorant for expressing a metallic luster (Japanese patent laid-open publication JP, 2003-306625, A).

For example, the aqueous metal colloid can be produced by mixing an aqueous solution containing metal ions with a reducing agent, or by spraying an aqueous solution containing metal ions to bring the aqueous solution into contact with a hydrogen flame, or the like, thereby reducing and precipitating the metal in the aqueous solution.

Since the metal particles contained in the metal colloid uniformly undergo the above-mentioned reduction reaction in the system, the particle diameters of the metal particles are uniform, and the particle size distribution is narrow. In addition, the shapes of the metal particles contained in the metal colloid are also substantially uniform in a spherical shape. Further, by adjusting the reaction conditions, the particle size of the metal particles can be made smaller than that of conventional particles. In addition, since the metal particles contained in the metal colloid are precipitated and generated by a reduction reaction or the like in water as described above, the surface thereof has hydrophilicity, and thus the metal particles are excellent in dispersion stability in an aqueous dispersion medium such as water.

As the metal colloid, various metal particle materials can be used which match the color tone of the metallic luster to be expressed, and the like. In particular, since silver particles have a brighter color tone than other metal particles, an ink composition using a metal colloid containing silver particles, i.e., a silver colloid, as a colorant is suitable for expressing metallic luster. However, a printed surface formed using an ink composition containing silver colloids has a problem that discoloration occurs in a relatively short period of time, although the printed surface has good metallic luster immediately after printing.

If a colloid of a noble metal such as platinum is used, the noble metal is more stable than silver, and therefore, the printed surface can be prevented from discoloring in a short time. In addition, as the colorant, if a colloid of gold among noble metals is used, gold color with luster can be expressed, and the printed surface can be prevented from discoloring in a short time. However, since noble metals are more expensive than silver, there is a problem in that the cost of the ink composition is significantly increased.

Disclosure of Invention

The present invention has an object to provide a novel ink composition which can prevent a printed surface from discoloring in a relatively short time and can maintain a good metallic luster of the printed surface for a longer time than at present, even though a silver colloid which is less expensive than noble metals and is easily discolored is used as a colorant.

Another object of the present invention is to provide a printing method for expressing various colors such as glossy gold using the ink composition.

The ink composition of the present invention for achieving the above object is characterized by containing a silver colloid and a discoloration inhibitor for preventing silver discoloration.

The reason why the printed surface formed of the ink composition using the silver colloid as the colorant discolors in a short time is that the silver particles react with a sulfur gas (sulfur gas) in the air (sulfurization reaction), and a black silver sulfide coating film is formed on the surface thereof. In contrast, when the anti-tarnish agent is contained in the ink composition as described above, the progress of the sulfidation reaction on the surface of the silver particles after printing and the formation of a silver sulfide coating film accompanying the progress can be suppressed by the action of the anti-tarnish agent.

Therefore, according to the ink composition of the present invention, although a silver colloid which is liable to change color is used as a colorant, the color change of the printing surface can be prevented in a relatively short time, and the printing surface can be maintained with good metallic luster for a longer time than hitherto. Further, since a large amount of the discoloration inhibitor also functions as a binder for the silver particles, the fixation of the silver particles to the printing object can be improved. Further, since silver is less expensive than a noble metal such as platinum, the cost of the ink composition can be reduced.

As the silver colloid, it is preferable to use a median particle diameter d obtained by a laser diffraction scattering method₅₀Colloid with a particle size of 0.04 μm or less. If an ink composition containing such fine silver particles is used, the discoloration prevention effect of the antitarnish agent against silver can be made more effective. In addition, the fixing property of the silver particles to the print medium can be improved.

For example, when printing the ink composition on the surface of a porous printing object such as paper, the following is considered. I.e. the median particle diameter d₅₀Silver particles larger than the above range may not completely sink into a plurality of pores present on the surface of the printed object to be printed but slightly float, and therefore, the fixation to the printed object may be insufficient. Further, since most of the other components containing the antitarnish agent are absorbed into the pores, the wide range of the surface of the silver particles, particularly the upper surface side of the print, is not covered with the antitarnish agent and is exposed, and thus discoloration may easily occur.

In contrast, the median particle diameter d₅₀The fine silver particles satisfying the above range can be present in a state of being more sunken in the plurality of pores present on the surface of the object to be printed than in the above case on the surface of the object to be printed, and thus the fixability to the object to be printed can be improved. In this state, the surface of the silver particles can be covered with the discoloration inhibitor in a wider range than in the above case, and therefore discoloration thereof can be more effectively prevented.

On the other hand, when consideringThe ink composition is printed on a surface of a non-porous object to be printed such as a plastic film as follows. I.e. the median particle diameter d₅₀Silver particles larger than the above range are present on the surface of the printed object to be printed in a state of being clearly protruded from the surface. In addition, in an ink composition suitable for printing on such a non-porous printing object, a binder resin is usually added, and a coating film for binding and fixing silver particles is formed on the surface of the printing object from the binder resin, and the median particle diameter d is as described above₅₀The larger silver particles are formed in a state of protruding significantly from the coating film. In this case, the fixation of the silver particles to the print medium may be insufficient.

In addition, most of the other components containing the antitarnish agent are present only in the vicinity of the surface of the printing object. As with the cover film. Therefore, the silver particles are exposed to the outside without being covered with the discoloration inhibitor, particularly over a wide area on the upper surface side of the printing, and may be easily discolored.

In contrast, the median particle diameter d₅₀The fine silver particles satisfying the above range can be formed on the surface of the printed object to be printed so that the amount of projection from the surface is smaller than the above range, and therefore, particularly when a coating film is formed on the surface of the printed object, most of the silver particles can be covered with the coating film. This can improve the fixing property to the print medium. In addition, in this state, the surface of the silver particles can be covered with the discoloration inhibitor in a wider range than in the above case, and therefore discoloration thereof can be more effectively prevented.

The amount of the silver colloid to be added is preferably 1 to 20% by weight, in terms of the proportion of the silver particles contained in the silver colloid to the total amount of the ink composition. If the amount of the silver colloid added is less than this range, a printed surface having good metallic luster may not be formed. On the other hand, if the amount of addition exceeds this range, the solid content concentration in the ink composition becomes too high, and therefore, particularly when used in an ink jet printer, the ejection stability from the nozzles provided in the head of the printer is lowered, and there is a possibility that good printing cannot be performed.

The addition amount of the anti-discoloration agent is preferably 0.02 to 2 wt% of the total amount of the ink composition. If the amount of the antitarnish agent is less than this range, the antitarnish agent may not sufficiently exhibit the effect of preventing the discoloration of silver and the effect of improving the fixability of silver particles. On the other hand, if the amount exceeds this range, the viscosity of the ink composition increases, and when the ink composition is used in an ink jet printer, the ejection stability from nozzles provided in a head may be lowered, or the storage stability of the ink composition may be lowered because the anti-tarnish agent is likely to precipitate.

When an aqueous dispersion medium is used as the dispersion medium, it is preferable to use at least one compound selected from the group consisting of 2-mercaptobenzothiazole and salts thereof as the antitarnish agent. These compounds have water solubility, and therefore, the storage stability of the ink composition can be improved.

In addition, when an organic solvent is used as the dispersion medium, it is preferable to use at least one compound selected from the group consisting of 2-mercaptobenzothiazole and octadecanethiol, which are excellent in the ability to prevent silver discoloration, as the discoloration inhibitor.

The printing method of the present invention is characterized by printing with the silver colloid-containing ink composition of the present invention and then overprinting the colored transparent ink.

When inks such as yellow and orange are printed on a printing surface having a metallic luster printed by using the ink composition of the present invention in an overlapping manner, the luster of the ink can be reproduced without using gold. When inks of other colors are overprinted, it is also possible to reproduce a metallic luster similar to that of the surface of other metals such as iron, nickel, titanium, and copper, or to express metallic luster of various colors which is not actually present. Further, since the ink composition of the base layer contains a discoloration inhibitor for preventing the discoloration of silver, these metallic colors can be maintained for a long time.

The ink composition containing silver colloid and the colored transparent ink are preferably printed by superposition printing using an ink jet system. If the two inks are printed in a superimposed manner by the ink jet method, the time and labor for the superimposed printing can be omitted. Further, by using an ink jet printer capable of printing a full color image or the like by superimposing a multicolor ink pattern as described above, it is possible to print a colored transparent ink on the printing surface on which the ink composition containing a silver colloid is printed, with high accuracy of 1440dpi (dot per inch) or more, for example, and to improve the accuracy of the superimposed printing.

As the colored transparent ink, it is preferable to use one containing a dye as a colorant or having a median particle diameter d obtained by a laser diffraction scattering method₅₀An ink containing a pigment having a particle size of 0.12 μm or less. Since the dye is dissolved in the ink at a molecular level, good metallic luster without granular feel can be expressed. Further, since the pigment is generally opaque particles, when the particle diameter is large, the granular feeling is noticeable and good metallic luster may not be expressed, however, if the median particle diameter d obtained by the laser diffraction scattering method is used₅₀When the particle size of the pigment is 0.12 μm or less, the particles cannot be visually confirmed, and therefore, a good metallic luster without a granular feeling can be substantially expressed as in the case of using a dye.

As the colored transparent ink, an ink containing an aqueous dispersion medium as a dispersion medium is preferably used. The ink containing an aqueous dispersion medium as a dispersion medium does not corrode a printing surface formed by printing an ink composition containing a silver colloid unlike an ink containing an organic solvent as a dispersion medium, and therefore, it is possible to prevent deterioration or loss of metallic luster of the printing surface caused by overprinting of a colored transparent ink.

Detailed Description

The present invention will be explained below.

Ink composition

The ink composition of the present invention is characterized by containing a silver colloid and a discoloration inhibitor for preventing silver discoloration, as described above. As the ink composition, there are: an aqueous ink composition using an aqueous dispersion medium such as water as a dispersion medium, which is suitable for use in printing on a porous printing object such as paper, for example, in an ink jet printer for personal computers; for example, in printing of large printed matters such as commercial advertisements, an organic solvent-based ink composition using an organic solvent as a dispersion medium is suitable for use in printing on non-porous print targets such as plastics, glass, and metals.

< silver colloid >

As the silver colloid, a material in which fine silver particles are colloidally dispersed in a dispersion medium can be used. The particle diameter of the silver particles is determined by the median diameter d obtained by the laser diffraction scattering method as described above₅₀It is preferably 0.04 μm or less. The reason for this is as described above. In addition, when the fixation of the silver particles to the printing medium is further improved while the discoloration prevention effect of the discoloration inhibitor is further improved, the median diameter d of the silver particles is increased₅₀Within the above range, the particle size is particularly preferably 0.03 μm or less. Further, the median diameter d of the silver particles₅₀The lower limit of (b) is not particularly limited, and particles in a minimum range that can be produced technically can be used.

The aqueous silver colloid suitable for the aqueous ink composition can be produced by reducing an aqueous solution containing silver ions, for example, an aqueous silver nitrate solution, and precipitating silver particles in the aqueous solution, as described above.

For example, when a silver nitrate aqueous solution is added to a mixed solution of an iron (II) sulfate aqueous solution and a citric acid aqueous solution, a dark blue precipitate can be obtained. In this case, the precipitate is filtered, washed with distilled water, and then poured with distilled water, whereby an aqueous silver colloid having good dispersion stability of silver particles can be produced.

The aqueous silver colloid can be produced, for example, by spraying an aqueous solution containing silver ions and bringing the solution into contact with a hydrogen flame to reduce and precipitate the silver ions, as described in Japanese patent laid-open publication No. JP 07-173511A (1995).

When a silver colloid is produced by these production methods, the dispersion stability of the silver particles can be further improved if a surfactant or a hydrophilic protective colloid is added to the aqueous solution at any time before and after the reduction reaction.

As the hydrophilic protective colloid, for example, gelatin, albumin, gum arabic, egg albumin acid, and a substance corresponding to an aqueous dispersion medium such as water among high molecular weight pigment dispersants described in Japanese patent laid-open publication JP 11-80647(1999), are preferable. Specific examples of the hydrophilic protective colloid include Solsperse20000 and 27000, tradename Disper BYK 180, 184 and 190, manufactured by BYK CHEMIE, tradename Polymer 451, manufactured by EFKA chemical, FLOWLEN DOPA-17, manufactured by Kyoeisha chemical Co., Ltd.

The organic solvent-based silver colloid suitable for the organic solvent-based ink composition can be produced, for example, by separating silver particles from the aqueous silver colloid produced by the above-described production method and dispersing the silver particles in an organic solvent that is the same as or compatible with the organic solvent used in the ink composition. In this case, it is also preferable to maintain the dispersion stability of the silver particles in the organic solvent by adding the hydrophilic protective colloid.

More specifically, at any point in the process of producing an aqueous silver colloid before removing water from the silver colloid and separating silver particles, a hydrophilic protective colloid is added and then water is removed, whereby the surfaces of the silver particles are covered with the hydrophilic protective colloid. Thereafter, the silver particles can be dispersed in an organic solvent that is the same as or compatible with the organic solvent used in the ink composition, thereby producing an organic solvent-based silver colloid.

The organic solvent-based silver colloid can be produced by the method described in, for example, Japanese patent application laid-open No. 11-319538. Namely, an aqueous phase composed of an aqueous solution containing silver ions; and an organic solvent such as an organic solvent-soluble high-molecular-weight pigment dispersant added to an organic solvent not mixed with water as needed, and the reducing agent is added under stirring to precipitate silver particles and transfer the silver particles from the aqueous phase to the organic solvent phase, and then the aqueous phase is removed to produce an organic solvent-based silver colloid.

Further, the organic solvent-based silver colloid can be produced, for example, as described in Japanese patent application laid-open No. 11-80647 by reducing an organic solvent solution containing silver ions and, if necessary, an organic solvent-soluble high-molecular-weight pigment dispersant or the like to precipitate silver particles in the solution.

Examples of the organic solvent-soluble high-molecular-weight pigment dispersant used in these methods include those soluble in the organic solvent used among the high-molecular-weight pigment dispersants corresponding to the above-mentioned aqueous dispersion media, and further include, for example, trade names Solsperse 24000, 26000, 28000, manufactured by BYK Chemie, trade names DisperbyK 161, 162, 163, 170, 182, manufactured by EFKA Chemical, trade name Polymer401, manufactured by Corongian Chemical Co., Ltd., FLOEN DOPA-22, trade names AJISPER PB711, PA111, manufactured by Piromonette, and the like.

The amount of the silver colloid added to the ink composition is preferably 1 to 20% by weight, as represented by the content ratio of the silver particles contained in the silver colloid to the total amount of the ink composition. The reason for this is as described above. In addition, if the concentration of the solid content in the ink composition is limited, particularly if the ink composition is used in ink jet printing, the discharge stability is further improved and a printed surface having a more favorable metallic luster is formed, the amount of the silver colloid is within the above range, and more preferably 3 to 15% by weight.

Further, in the ink composition, 1 or 2 or more kinds of metal colloids containing fine particles of other metals may be used in combination within a range not impairing the good metallic luster due to the silver particles. As the other metal colloid, for example, an aqueous or organic solvent colloid in which fine metal particles made of various metals such as gold, ruthenium, rhodium, palladium, osmium, iridium, platinum, copper, aluminum, zinc, tin, nickel, cobalt, and iron are dispersed in a colloidal state can be used. When the silver colloid is used in combination with 1 or 2 or more other metal colloids, the amount of each colloid added to the ink composition may be adjusted so that the total amount of metal particles contained in each colloid falls within the above range.

< discoloration inhibitor >

As the discoloration inhibitor, various conventionally known discoloration inhibitors capable of inhibiting the above-mentioned silver sulfurization reaction can be used. Examples of the antitarnish agent include 2-mercaptobenzothiazole or salts thereof (sodium salt, zinc salt, cyclohexylammonium salt, etc.), 2-heptadecylimidazole, mercaptoacetatyltetralin amine (2-mercapto-N-2-naphthylacetamide), and octadecanethiol [ CH ] for example₃(CH₂)₁₇SH]And alkyl mercaptans in which the alkyl group has about 12 to 20 carbon atoms.

However, since most of the antitarnish agent is water-insoluble or hardly soluble, when the ink composition is an aqueous system, it is preferable to use 2-mercaptobenzothiazole or a salt thereof having water solubility as described above, and among them, a salt of 2-mercaptobenzothiazole, particularly a sodium salt, is more preferable because of excellent water solubility. On the other hand, when the ink composition is an organic solvent system, any antitarnish agent may be used, but 2-mercaptobenzothiazole or octadecanethiol is preferable if the performance of preventing the discoloration of silver is particularly considered.

The amount of the antitarnish agent added is preferably 0.02 to 2 wt% based on the total amount of the ink composition. The reason for this is as described above. Further, if it is considered that the viscosity increase of the ink composition is suppressed, the ejection stability from the nozzles provided in the head of the ink jet printer is further improved; or the precipitation of the antitarnish agent is inhibited, and the storage stability of the ink composition is further improved; or further improving the effect of preventing the discoloration of silver by the discoloration inhibitor and the effect of improving the fixability of silver particles, the amount of the discoloration inhibitor is in the above range, and particularly preferably 0.2 to 1.5% by weight.

< Dispersion Medium >

As the aqueous dispersion medium for the ink composition which constitutes an aqueous system together with the above-mentioned two components, water can be mainly used, and a medium in which a small amount of a water-soluble organic solvent for adjusting, for example, the drying property of the ink, the permeability to a porous printing object, the wettability to a non-porous printing object, and the like are added to water as a main component may be used.

As the organic solvent used for the organic solvent-based ink composition, 1 or 2 or more kinds of arbitrary organic solvents having a function of improving wettability to the aforementioned non-porous object to be printed such as plastic, glass, or metal are preferably used.

Examples of the organic solvent include monohydric alcohols such as methanol, ethanol, 1-propanol, isopropanol, sec-butanol, and tert-butanol; glycol ethers such as ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether, etc., or derivatives thereof; propylene glycol ethers such as propylene glycol monomethyl ether and propylene glycol monomethyl ether acetate, and derivatives thereof; 2-3-membered alcohols such as propylene glycol, diethylene glycol, and glycerin; aromatic hydrocarbons such as benzene, toluene, and xylene; n-paraffinic hydrocarbon; iso-paraffinic hydrocarbons; dimethyl sulfoxide; n-methyl-2-pyrrolidone, methyl ethyl ketone, cyclohexanone, isophorone, and the like.

As the organic solvent that can be added to water in the aqueous ink composition, any solvent having excellent water solubility among the above may be used. In the ink composition of the present invention, in addition to the above-mentioned components, a binder resin, a dispersant, and other conventionally known components may be added.

< Binder resin >

The binder resin is a substance that fixes silver particles or the like to the surface of the object to be printed, and in the aqueous ink composition, for example, a water-soluble binder resin such as a cellulose resin, a polyamide resin, polyvinylpyrrolidone, a water-soluble acrylic resin, or a water-soluble oxazoline group-containing polymer is preferably used, and among these, a water-soluble oxazoline group-containing polymer is most preferable in view of improving the metallic gloss of the printed surface.

In the organic solvent-based ink composition using an organic solvent as a dispersion medium without using water, the binder resin is not limited to a water-soluble resin, and various resins soluble in the organic solvent used as a dispersion medium can be used. In particular, in view of improving the metallic luster of the printed surface, it is preferable to use 1 or 2 or more kinds of vinyl chloride-vinyl acetate copolymer, vinyl alcohol-modified product thereof, hydroxyalkyl acrylate-modified product thereof, and the like as the binder resin.

The weight average molecular weight Mw of the binder resin is preferably 5,000 or more in view of improving the fixability of the silver particles. When the molecular weight is too large, the binder resin is likely to precipitate or precipitate, and the ejection of the ink composition may become unstable. In addition, when the ink composition is stored, precipitation or precipitation may occur. Therefore, the weight average molecular weight Mw of the binder resin is in the above range, and particularly preferably 50,000 or less, and further preferably about 10,000 to 40,000 in consideration of these characteristics.

The content of the binder resin is preferably 0.3 to 5.0 wt%, more preferably 0.5 to 3.0 wt%, based on the total amount of the ink composition. If the content ratio is less than this range, the effect of improving the fixability of the silver particles may become insufficient. If the amount of the organic solvent is more than this range, a good metallic luster may not be imparted to the printing surface, and the solid content concentration in the ink composition may be too high, so that the ink ejection stability may be lowered and good printing may not be performed particularly when the ink composition is used for printing by an ink jet method.

< other additives >

Examples of the other additives include a surface tension adjusting agent, a wetting agent, a fungicide, and a bactericide.

As the surface tension adjusting agent, a nonionic surfactant is mainly used. In order to prevent foaming of the ink composition and bleeding of the printing, the amount of the surface tension adjusting agent to be added should be as small as possible, and specifically, the content ratio with respect to the total amount of the ink composition is preferably 0.1% by weight or less, particularly preferably 0.05% by weight or less, and if possible, it is not added. In addition, in order to adjust the wettability of the aqueous ink composition to a non-porous printing object, a surface tension adjusting agent such as a fluorine-based surfactant or a silicon-based surfactant may be added.

The wetting agent is a material added for suppressing drying of the ink and preventing clogging of the ink in a nozzle or the like provided in a head of a printer, and is preferably 2-or 3-membered alcohol, 2-pyrrolidone or a derivative thereof, for example.

Examples of the 2-membered alcohol include 1, 5-pentanediol, propylene glycol, and diethylene glycol, and examples of the 3-membered alcohol include glycerin and trimethylolpropane. Examples of the 2-pyrrolidone and derivatives thereof include 2-pyrrolidone and N-methyl-2-pyrrolidone. The humectant may be used in 1 or more than 2 kinds. The content ratio of the wetting agent is preferably 2 to 30% by weight based on the total amount of the ink composition. When 2 or more kinds of wetting agents are used in combination, the total amount thereof is set to the above range.

In addition, various dyes, pigments, and the like may be used in combination as a colorant together with silver particles derived from a silver colloid. In this case, for example, the gloss of cash can be reproduced without using gold, or metallic gloss of various colors which is not actually present can be expressed. In addition, the amount of silver particles derived from silver colloid may be made smaller than that of a colorant such as a dye as a main component. In this case, although the metallic luster reproduced on the surface of the metal foil or the like cannot be obtained, a so-called metallic painting state can be reproduced.

< method for producing ink composition >

The ink composition of the present invention can be produced by blending the above components so as to have a predetermined content ratio. The procedure for blending is not particularly limited, but particularly since 2-mercaptobenzothiazole or its sodium salt is a basic substance, if the ink composition itself is not kept basic, the temporarily dissolved substance is likely to precipitate, and the stability thereof may be lowered.

This phenomenon occurs in both aqueous and organic solvent-based ink compositions, but is particularly significant in aqueous systems. Therefore, in the case of using an alkaline antitarnish agent such as 2-mercaptobenzothiazole or its sodium salt in an aqueous ink composition, it is preferable to add an alkaline substance before adding a component (e.g., glycerin or Olfine E1010) having a tendency to change the ink composition to acidity in order to improve the dispersion stability of the ink composition, and to always keep the ink composition alkaline from the start to the end of production.

More specifically, the pH of the ink composition from the start to the end of production is preferably 9.5 to 12.5, and particularly preferably 9.9 to 12.2. When the pH of the ink composition is less than this range, as described above, in particular, a basic substance such as 2-mercaptobenzothiazole or a sodium salt thereof is likely to precipitate, and the stability of the ink composition may be lowered, whereas when the pH exceeds this range, there is a possibility that the pH affects a member or the like which the ink composition of the ink jet printer contacts.

As the alkaline substance, ammonia, organic amine, caustic alkali, and the like are preferable. Among them, examples of the organic amine include 1 or 2 or more species such as monoethanolamine, diethanolamine, triethanolamine, ethylmonoethanolamine, ethyldiethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, mono-1-propanolamine, 2-amino-2-methyl-1-propanol, and derivatives thereof, and among them, 2-amino-2-methyl-1-propanol is particularly preferable.

The ink composition of the present invention thus produced can be suitably used particularly for printing by an ink jet system. Examples of printers using an ink jet system include so-called on-demand ink jet printers such as a thermal ink jet system and a piezoelectric system; and a so-called continuous ink jet printer that forms droplets of ink while circulating the ink and performs printing. The ink composition of the present invention can be used as various inks for marker pens, ballpoint pens, and the like.

Printing method

The printing method of the present invention is characterized by printing with the silver colloid-containing ink composition of the present invention and then overprinting the colored transparent ink.

As a method of overprinting two inks, various printing methods can be employed, but a method of overprinting two inks by an inkjet method is particularly preferable. Thus, the time and labor for the overprinting can be saved. Further, by using an ink jet printer capable of printing a full-color image or the like by superimposing a plurality of color ink patterns, it is possible to print colored transparent inks with a high accuracy of, for example, 1440dpi (dot per inch) or more on the printing surface on which the ink composition containing silver colloid is printed, and it is possible to improve the accuracy of the superimposition printing.

Specifically, when the head of the printer forms a full-color image or the like, the ink cartridge connected to the nozzle that ejects the ink first is filled with the silver colloid-containing ink composition of the present invention, and the ink cartridge connected to the nozzle that ejects the ink later is filled with the colored transparent ink having a color tone that matches the metallic gloss to be expressed.

In addition, a plurality of ink cartridges connected to the nozzles may be filled with colored transparent inks having different color tones, and the colored transparent inks may be selected by printing an ink composition containing silver colloid and then overprinting the printed ink composition in accordance with the metallic luster to be expressed; or printing an ink composition containing silver colloid and then printing colored transparent ink with more than 2 colors in an overlapped mode.

As the colored transparent ink used in the above-mentioned printing method, it is preferable to use a dye as a colorant or a medium particle diameter d obtained by a laser diffraction scattering method₅₀An ink containing a pigment having a particle size of 0.12 μm or less. The reason for this is as described above. The median particle diameter d of the pigment obtained by a laser diffraction scattering method₅₀Within the above range, the particle diameter is preferably 0.10 μm or less, and particularly preferably 0.06 μm or less.

As the dye, various dyes can be used so as to match a desired color tone, but as described later, it is preferable that the water-based ink using an aqueous dispersion medium be used as the colored transparent ink, and a water-soluble dye can be used as the water-based ink.

Examples of the water-soluble dye include 1 or 2 or more kinds of acridine dye, nigrosine dye, anthraquinone dye, azine dye, azomethine dye, benzoquinone dye, naphthoquinone dye, indigoid dye, indophenol dye, indoaniline dye, indamine dye, leuco dye, naphthalimide dye, nigrosine dye, indacene dye, nitro dye, nitroso dye, oxazine dye, dioxazine dye, oxidation dye, phthalocyanine dye, polymethine dye, quinophthalone dye, triacrylmethane dye, diacryloylmethane dye, thiazine dye, thiazole dye, xanthine dye, cyano dye, and the like.

In the case where the colored transparent ink is an organic solvent system, various dyes soluble in the organic solvent used may be used.

As the pigment, any inorganic pigment and/or organic pigment that is generally used in ink jet ink compositions can be used.

Then, examples of the inorganic pigment include metal compounds such as titanium oxide and iron oxide; or 1 or 2 or more kinds of carbon black produced by a known method such as a contact method, a furnace method, a pyrolysis method, or the like. Examples of the organic pigment include 1 or 2 or more kinds of azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, and the like), polycyclic pigments (for example, phthalocyanine pigments, perillene (ベリレン) pigments, belinone (ベリノン) pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindoline pigments, quinophthalone pigments, and the like), dye chelates (for example, basic dye chelates, acidic dye chelates, and the like), nitro pigments, nitroso pigments, aniline black, and the like.

Specific examples of the pigment include c.i. pigment yellow 74, 109, 110 and 138; c.i. pigment red 122, 202, 209 as magenta pigment; the blue-green pigment is C.I. pigment blue 15:3, 60; c.i. pigment black 7 as a black pigment; orange pigments include c.i. pigment orange 36 and 43, and green pigments include c.i. pigment green 7 and 36.

Depending on the color tone of the ink, 1 or 2 or more kinds of dyes and pigments may be used. In addition, a dye and a pigment may be used in combination.

The colored transparent ink is preferably an aqueous system using an aqueous dispersion medium as a dispersion medium. The reason for this is as described above. As the aqueous dispersion medium constituting the aqueous ink, water is mainly used, and a medium containing water as a main component and, if necessary, a small amount of a water-soluble organic solvent added thereto for adjusting, for example, drying properties of the ink, permeability to a porous printing object, wettability to a non-porous printing object, and the like can be used.

The colored transparent ink may be an organic solvent system using an organic solvent as a dispersion medium, and 1 or 2 or more kinds of organic solvents may be used as the organic solvent from among the various organic solvents exemplified above. As the organic solvent that can be added to water in the aqueous ink, any solvent having excellent water solubility among the above-mentioned organic solvents can be used. The colored transparent ink may contain, in addition to the above components, the binder resin and the dispersant as exemplified above, and may contain various components known in the art.

Examples

Hereinafter, the present invention will be described in further detail based on examples.

Example 1

As the silver colloid, a particle size measuring apparatus of laser diffraction scattering method type (Microtrac UPA manufactured by Nikkiso Co., Ltd.) was used]Measured median particle diameter d₅₀An aqueous silver colloid A (silver particles contained at a concentration of 30 wt%) of 0.0168 μm. In addition, as the antitarnish agent, sodium salt of 2-mercaptobenzothiazole was used. The silver colloid and the discoloration inhibitor were mixed with the following components, stirred, mixed, and filtered using a 0.8 μm membrane filter to prepare an aqueous ink composition. The content ratio of the silver particles to the total amount of the ink composition was 3.0 wt%.

The compounding order is that firstly, the sodium salt of 2-mercaptobenzothiazole is dissolved in ultrapure water, then 2-amino-2-methyl-1-propanol is added and stirred, then glycerin, diethylene glycol monobutyl ether, water soluble oxazoline, Olfine E1010 and Proxel XL-2 are added and stirred, and finally, aqueous silver colloid A is added and stirred.

The pH at the time of stirring (referred to as "process 1") when the sodium salt of 2-mercaptobenzothiazole and 2-amino-2-methyl-1-propanol were added to ultrapure water was measured, and the result was 12.10. The pH at the time of stirring (referred to as "process 2") when all the components were added was measured, and the result was 10.52. Thus, based on the results, it was confirmed that the addition of 2-amino-2-methyl-1-propanol maintained the pH of the ink composition in the range of 9.5 to 12.5 from the start to the end of production. HV-40 of Toyo electric wave industry (strain) was used for pH measurement.

(ingredient) (parts by weight)

Silver colloid A10.0

Anti-tarnish agent

Sodium salt of 2-mercaptobenzothiazole 0.5

Wetting agent

Glycerol 23.2

Germicide

Proxel XL-2 (manufactured by Avecia) 0.2

Dispersing media

Diethylene glycol monobutyl ether 10.0

Ultrapure Water 52.6

Basic substance

2-amino-2-methyl-1-propanol 0.5

Adhesive resin

Water-soluble oxazoline group-containing Polymer 2.0

[ (product name of Japan catalyst System: EPOCROS WS-700]

Surface tension adjusting agent

Ethylene oxide adduct of acetylene glycol 1.0

[ product name of Olfine E1010 manufactured by Nissan chemical industry Co., Ltd ]

Example 2

An aqueous ink composition was produced in the same manner as in example 1, except that 0.2 parts by weight of 2-mercaptobenzothiazole was used as the discoloration inhibitor and the amount of ultrapure water was changed to 52.9 parts by weight.

Since 2-mercaptobenzothiazole is less water-soluble than sodium salt, 2-mercaptobenzothiazole is first dissolved in diethylene glycol monobutyl ether, then 2-amino-2-methyl-1-propanol is added thereto and stirred (process 1), then glycerin, ultrapure water, water-soluble oxazoline, Olfine E1010 and Proxel XL-2 are added thereto and stirred, and finally, aqueous silver colloid a is added thereto and stirred (process 2).

The pH of Process 1 was measured and found to be 11.04. In addition, the pH of process 2 was measured, and the result was 9.98. Thus, based on the results, it was confirmed that the addition of 2-amino-2-methyl-1-propanol maintained the pH of the ink composition in the range of 9.5 to 12.5 from the start to the end of production.

Example 3

The same amount of the median diameter d measured by the above-mentioned laser diffraction/scattering method type particle size measuring apparatus was used except that silver colloid was used₅₀An aqueous ink composition was prepared in the same manner as in example 1, except that the aqueous silver colloid B was 0.0291 μm (the silver particle content was 30% by weight).

The pH of Process 1 was measured and found to be 12.12. In addition, the pH of process 2 was measured, and the result was 10.60. Thus, based on the results, it was confirmed that the addition of 2-amino-2-methyl-1-propanol maintained the pH of the ink composition in the range of 9.5 to 12.5 from the start to the end of production.

Example 4

The same amount of the median diameter d measured by the above-mentioned laser diffraction/scattering method type particle size measuring apparatus was used except that silver colloid was used₅₀An aqueous ink composition was prepared in the same manner as in example 1, except that the amount of the aqueous silver colloid C (the content of silver particles was 30 wt%) was 0.0377 μm.

The pH of Process 1 was measured and found to be 12.10. In addition, the pH of process 2 was measured, and the result was 10.52. Thus, based on the results, it was confirmed that the addition of 2-amino-2-methyl-1-propanol maintained the pH of the ink composition in the range of 9.5 to 12.5 from the start to the end of production.

Example 5

The same amount of the median diameter d measured by the above-mentioned laser diffraction/scattering method type particle size measuring apparatus was used except that silver colloid was used₅₀An aqueous ink composition was prepared in the same manner as in example 1, except that the aqueous silver colloid D (the silver particle content was 30% by weight) was 0.0511 μm.

The pH of Process 1 was measured and found to be 12.10. In addition, the pH of process 2 was measured, and the result was 10.54. Thus, based on the results, it was confirmed that the addition of 2-amino-2-methyl-1-propanol maintained the pH of the ink composition in the range of 9.5 to 12.5 from the start to the end of production.

Comparative example 1

An aqueous ink composition was produced in the same manner as in example 1, except that the antitarnish agent was not blended and the amount of ultrapure water was 53.1 parts by weight.

The ink compositions produced in the examples and comparative examples were used in a commercially available thermal inkjet printer [ Deskjet 970cxi manufactured by Hewlett Packard, Japan ], and full-page printing was performed on inkjet Photo-glossy paper as a porous printing object [ QP manufactured by Konica Minolta Photo Imaging, Ltd.) with the dot number of 2400 dpi.

Evaluation of discoloration resistance

After the printing surface of the full-size printing was left at room temperature for 1 week, the presence or absence of discoloration was evaluated by visual observation under the following criteria.

Very good: compared with the printing process, the printing process has no change and has beautiful metal luster.

O: although slight discoloration can be seen, there is no problem in terms of metallic luster.

And (delta): discoloration was more pronounced than that described above (∘), but within the permissible range.

X: obviously discolored and loses metallic luster.

Evaluation of fixability

The change in the state of the printed surface when it was subjected to continuous wiping 3 times while applying a load of 200gf (1.96N) to the printed surface using an eraser (trade name MONO manufactured by Tombow pencil, ltd.) was observed by visual observation, and the fixability of the silver particles was evaluated according to the following criteria.

Very good: even if the rubbing was performed 3 times, no change was observed on the printed surface.

O: when rubbed 3 times, some variation was visible on the printed side, but at a substantially unproblematic level.

And (delta): when rubbed 3 times, the change was visible on the printed surface, while brushing only 1 time was a substantially unproblematic level.

X: the change was evident only after 1 pass of the printing surface.

The results are shown in table 1 together with the measured values of pH in processes 1 and 2.

TABLE 1

As can be seen from the table, the printed surface formed by using the ink composition of comparative example 1 in which the discoloration inhibitor was not blended was poor in the fixation of the silver particles to the porous printing object, and was peeled off only by wiping 1 time, and the printed surface was significantly changed, and further the discoloration resistance was insufficient, and the printed surface was discolored by leaving for 1 week, and the metallic luster was lost. On the other hand, the printed surfaces formed using the ink compositions of examples 1 to 5 containing the antitarnish agent had better fixability of silver particles and were less likely to be discolored than those of comparative example 1.

Further, from the results of examples 1 and 2, it is understood that the sodium salt is more excellent in water solubility than 2-mercaptobenzothiazole, and can be incorporated in an ink composition in a larger amount, so that the effect of preventing discoloration of the printed surface can be improved. Further, from the results of examples 1, 3, 4 and 5, it is understood that the median diameter d of the silver particles in the silver colloid is set to be₅₀The smaller the size, the more the effect of preventing discoloration and the fixability to a print medium can be improved.

Example 6

As the silver colloid, a particle size measuring apparatus of laser diffraction scattering method type (Microtrac UPA manufactured by Nikkiso Co., Ltd.) was used]Measured median particle diameter d₅₀0.0172 μm silver colloid E of ethylene glycol monobutyl ether acetate (silver particle content concentration is 30 wt%). In addition, 2-mercaptobenzothiazole was used as an antitarnish agent. The silver colloid and the discoloration inhibitor were mixed with the following components, stirred, mixed, and filtered using a 0.8 μm membrane filter to prepare an organic solvent-based ink composition. The content ratio of the silver particles to the total amount of the ink composition was 3.0 wt%.

(ingredient) (parts by weight)

Silver colloid E10.0

Anti-tarnish agent

2-mercaptobenzothiazole 0.5

Adhesive resin

Vinyl alcohol modified vinyl chloride-vinyl acetate copolymer 0.4

[ VAGH manufactured by Dow Chemical Co., Ltd ]

Vinyl chloride-vinyl acetate copolymer

[ VAGH manufactured by Dow Chemical Co., Ltd ]

Dispersing media

N-methyl-2-pyrrolidone 10.0

Ethylene glycol monobutyl ether acetate 72.7

Cyclohexanone 4.3

Basic substance

2-amino-2-methyl-1-propanol 0.5

Example 7

An organic solvent-based ink composition was produced in the same manner as in example 6, except that octadecanethiol was used in the same amount as the anti-tarnish agent.

Comparative example 2

An organic solvent-based ink composition was produced in the same manner as in example 6, except that the antitarnish agent was not blended and the amount of ethylene glycol monobutyl ether acetate was 73.2 parts by weight.

The ink compositions produced in the examples and comparative examples were used in a commercially available piezoelectric inkjet printer (SOLJET PRO II, manufactured by ROland DG), and full-size printing was performed on a PET film as a non-porous object to be printed, with the dot number being 1440 dpi. Further, the above-mentioned evaluation of discoloration resistance was performed to evaluate the presence or absence of discoloration, and the evaluation of fixability was performed to evaluate the fixability of silver particles.

The results are shown in table 2.

TABLE 2

As is clear from the table, the printed surface formed by using the ink composition of comparative example 2 in which the antitarnish agent was not blended was slightly lower in the fixing property of the silver particles to the non-porous printing object than in examples 6 and 7, and the discoloration resistance was insufficient, and the printed surface was discolored by leaving for 1 week, and the metallic luster was lost. On the other hand, the printed surfaces formed by using the ink compositions of examples 6 and 7 containing the antitarnish agent had better fixing property of silver particles and were less likely to be discolored than those of comparative example 2.

Example 8

The ink composition produced in example 1 was used in a commercially available thermal inkjet printer [ Deskjet 970cxi manufactured by Hewlett Packard, Japan ], and full-page printing was performed on a porous print-receiving photographic glossy paper for inkjet [ QP manufactured by Konica Minolta Photoimaging, Inc. ] with the dot number of 2400 dpi. Then, full-size printing was performed by superimposing the ink on the full-size printing using a yellow ink (dye-based, aqueous ink) which was set in a standard manner on the ink jet printer, and the printed surface was observed, and as a result, the gloss of cash was reproduced without using gold.

Example 9

The ink composition produced in example 1 was used in a commercially available piezoelectric inkjet printer [ Colorio PX-V700 manufactured by Seiko Epson Ltd.)]In the photographic glossy paper for ink jet as a porous printing object [ Konica MinoQP manufactured by lta Photoimaging (Ltd.)]Then, full-page printing was performed with the dot number of 1440 dpi. Then, full-size printing was performed by superimposing the ink on the full-size printing using a yellow ink (pigment-based, aqueous ink) which was set in a standard manner on the ink jet printer, and the printed surface was observed, and as a result, the gloss of cash was reproduced without using gold. Then, a laser diffraction scattering particle size measuring apparatus [ MicrotracUPA manufactured by Nissan Co., Ltd. ]was used]The median particle diameter d of the pigment of the yellow ink was measured₅₀The thickness was 0.0535 μm.

Claims (9)

1. An ink composition comprising a silver colloid and a discoloration inhibitor for preventing discoloration of silver, wherein the discoloration inhibitor is at least one compound selected from the group consisting of 2-mercaptobenzothiazole and salts thereof, 2-heptadecylimidazole, mercaptoacetyltetralin amine, 2-mercapto-N-2-naphthylacetamide, and alkyl mercaptan having 12 to 20 carbon atoms in the alkyl group, and the content of the discoloration inhibitor is 0.02 to 2 wt% based on the total amount of the ink composition.

2. The ink set of claim 1The silver colloid is characterized in that the silver colloid has a median particle diameter d obtained by a laser diffraction scattering method₅₀Colloid with a particle size of 0.04 μm or less.

3. The ink composition according to claim 1 or 2, wherein the silver colloid is contained in a proportion of 1 to 20 wt% in terms of a content ratio of the silver particles contained in the silver colloid relative to the total amount of the ink composition.

4. The ink composition according to any one of claims 1 to 3, wherein an aqueous dispersion medium is used as the dispersion medium, and at least one compound selected from the group consisting of 2-mercaptobenzothiazole and salts thereof is used as the antitarnish agent.

5. The ink composition according to any one of claims 1 to 3, wherein an organic solvent is used as the dispersion medium, and at least one compound selected from the group consisting of 2-mercaptobenzothiazole and octadecanethiol is used as the antitarnish agent.

6. A printing method comprising printing using the silver colloid-containing ink composition according to any one of claims 1 to 5, and then overprinting the colored transparent ink.

7. The printing method according to claim 6, wherein the ink composition containing silver colloid and the transparent coloring ink are printed in a superimposed manner by an ink jet method.

8. A printing method according to claim 6 or 7, wherein a colored transparent ink containing a dye or a pigment having a median particle diameter d50 of 0.12 μm or less obtained by a laser diffraction scattering method as a colorant is used.

9. A printing method according to any one of claims 6 to 8, wherein a transparent and colored ink containing an aqueous dispersion medium as a dispersion medium is used.