JP2013189598A - Aqueous ink for inkjet recording - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous ink for inkjet recording that excels in a quick drying property and fixability capable of image formation to a variety of poorly absorbable substrates, in which change of a surface tension is reduced even if ink is stored for a long term, and that can maintain excellent print quality.SOLUTION: An aqueous ink for inkjet recording at least includes: water; a pigment; a water-dispersible resin fine particle as a binder resin; a water-soluble organic solvent; and a silicon-based surfactant shown by a specific structural formula, wherein at least one of (poly)propylene glycol alkyl ethers having a boiling point of at most 180°C is included as the water-soluble organic solvent, and a content of the (poly)propylene glycol alkyl ethers is at most 15 wt.% in a composition of the aqueous ink.

Description

  The present invention is excellent in quick-drying and fixability capable of forming an image on various difficult-to-absorbent substrates, and can maintain excellent printing quality with little change in surface tension even when the ink is stored for a long period of time. It relates to ink.

  Along with the development of general household PCs and on-demand printing, various printers for small lots have appeared. Among them, inkjet printing is the most widespread and has been developed and commercialized in a wide range of fields. In addition, improvement of inkjet technology is expected to be used as an output device for digital printing.

  Conventionally, in order to form an image on a hardly absorbent substrate using an ink jet printer, an ink having good drying properties has been demanded. In particular, polyvinyl chloride sheets used for industrial applications are difficult to absorb ink, and high productivity is required. Therefore, inks having quick drying properties such as solvent inks and UV curable inks are often used. . However, solvent inks are concerned that the odor and harmfulness of solvents that volatilize during drying may affect the environment, and many UV inks have strong irritating properties or odors depending on the monomers used. There was a problem for the workers who handle ink.

In recent years, water-based inks have been developed as inks that have little environmental impact and are highly safe for workers. In addition, since water-based inks have a low environmental impact, they are expected to be used in all indoor and outdoor applications. To expand the versatility of inkjet printers, only general paper-based absorbent base materials such as plain paper and special paper can be used. However, there has been a demand for water-based inks that can form images by direct drawing on various hardly-absorbent substrates used in industrial applications.
It is generally known that fine droplets ejected by inkjet are landed on a substrate and then dried by permeation or volatilization. Hard-absorbent substrates such as polyvinyl chloride sheets that are used for industrial applications are difficult to permeate ink, so when multi-color printing is performed, the inks are mixed to form a clear image, and the printing speed can be increased. There was no problem.

  As ink-jet water-based inks, water-based inks have been conventionally developed as printing substrates for special papers that are easy to absorb inks such as plain paper and photographic paper. (See, for example, Patent Documents 1, 2, and 3) However, even for these hard-to-absorbable printing base materials used in industrial applications, even if these inks were used, sufficient print quality was obtained A printed matter could not be obtained and could not be used practically. This is due to the fact that water-based inks are difficult to wet and spread with respect to a hardly-absorbing substrate, and the penetration of the ink into the substrate hardly occurs and the dots are fused and spread.

  Patent Document 4 describes an ink using a water-soluble resin having a specific structure, a silicon-based or a fluorine-based surfactant as a water-based ink capable of forming an image on a hardly-absorbable substrate such as a polyvinyl chloride sheet. Yes. However, the water-soluble resin has poor film formability, and the drying property of the ink is not sufficient to form an image on a hardly absorbent substrate. In addition, the stability of the silicon surfactant used is poor, and there is a problem that the surface tension of the ink increases with time and the wettability decreases. Furthermore, the fluorosurfactant has poor water repellency with respect to the ink jet nozzle surface and is difficult to use in practice.

  Patent Document 5 describes that, by using a surfactant having a specific structure, it is possible to suppress changes in surface tension over time and deterioration in print quality after long-term storage. However, because the surface tension of the ink is high, even if it can maintain excellent print quality for paper-based absorbent substrates such as plain paper, it has wettability for poorly absorbent substrates such as polyvinyl chloride sheets. Insufficient print quality was not obtained.

Japanese Patent No. 3994734 Japanese Patent No. 4595281 JP 2008-247951 A JP 2011-094082 A Japanese Patent No. 3858793

  An object of the present invention is an ink jet recording which is excellent in quick-drying property and fixability capable of forming an image on various hardly-absorbable substrates, and can maintain excellent printing quality with little change in surface tension even when the ink is stored for a long period of time. It is to provide a water-based ink.

The above object of the present invention is achieved by the following configurations.
That is, the present invention relates to a water-based ink for ink jet recording comprising at least water, a pigment, water-dispersible resin fine particles as a binder resin, a water-soluble organic solvent, and a silicon-based surfactant represented by the general formula (1). 1 type or more of (poly) propylene glycol alkyl ethers whose boiling point is 180 degrees C or less as a water-soluble organic solvent, and content of the said (poly) propylene glycol alkyl ethers in the said water-based ink composition is 15 weight% or less The present invention relates to a water-based ink for inkjet recording.
General formula (1)

(In the formula, R ₁ and R ₂ are alkyl groups having 1 to 6 carbon atoms, and X ₁ and X ₂ are polyether (polyoxyalkylene) groups represented by the general formula (2).)
General formula (2)

(In the formula, R ₃ is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or a (meth) acryl group, EO is an ethylene oxide group, PO is a propylene oxide group, and b is an integer of 1 or more. , C is an integer greater than or equal to 0, and b + c is an integer greater than or equal to 1. The order of EO and PO may be random, where a represents an integer of 10 to 80.)

The (poly) propylene glycol alkyl ether is at least one selected from propylene glycol mono (alkyl having 1 to 4 carbons) ether and (di) propylene glycol di (alkyl having 1 carbon). The above-mentioned water-based ink for ink-jet recording is characterized by the above.
The present invention also relates to an ink set of four or more colors including the cyan ink, magenta ink, yellow ink, and black ink.
Furthermore, the present invention relates to an ink jet recording method in which ink droplets are ejected and adhered onto a printing substrate to perform printing, wherein the water-based ink is used as the ink.

  According to the present invention, ink jet recording is excellent in quick-drying and fixability capable of forming an image on various hardly-absorbable substrates, and can maintain excellent print quality with little change in surface tension even when the ink is stored for a long period of time. It is possible to provide a water-based ink for use.

The water-based ink for ink-jet recording of the present invention will be described below with preferred embodiments.
(Non-absorbable substrate)
The hardly absorbent substrate used in the present invention is a recording medium that hardly absorbs water or has a low absorption speed. For example, the drying rate is slow enough to form images, such as polycarbonate, polyvinyl chloride, polystyrene, foamed polystyrene, PMMA, polypropylene, polyethylene, PET, and other plastic substrates and art paper, coated paper such as coated paper. The base material which is hard to obtain is mentioned.
The water-based ink for ink-jet recording of the present invention is capable of forming an image on the hardly-absorbable substrate as described above, and contains at least water, a pigment, a binder resin, a water-soluble organic solvent, and a silicon surfactant. It is characterized by that.

First, the silicon-based surfactant characterizing the present invention will be described.
(Silicon surfactant)
In general, when printing is performed on a hardly absorbent substrate as described above, it is important that the ink has sufficient wettability on the substrate. This is because, after the ink has landed on the base material, it spreads out sufficiently so that the surface area of the dot increases, and it is possible to promote drying by penetration and evaporation and fix the dot on the base material. It is.
When the wettability of the ink on the printing substrate is insufficient, the ink filling in the printing portion is poor, and problems such as white spots occur. In order to solve such a problem, it is essential to improve the wettability of the ink on the printing substrate.

In general, the wettability of ink on a printing substrate depends on the surface tension of the ink and the surface tension of the printing substrate. When the surface tension of the ink is higher than the surface tension of the printing substrate, poor wetting occurs, the ink filling in the printing part is poor, and problems such as white spots occur. That is, in order to ensure sufficient wettability on the printing substrate, the surface tension of the ink needs to be sufficiently lower than the surface tension of the printing substrate. Moreover, since the above-mentioned hardly absorbable base material has low surface tension of the base material itself and it is not easy to wet the base material surface, it is important to keep the surface tension of the ink sufficiently low.
In particular, since water molecules are strongly bonded to each other by hydrogen bonds, the surface tension is extremely high among the solvents. very difficult.

In order to adjust the surface tension of the ink, a surfactant is generally used, and various surfactants such as silicon-based, fluorine-based, and acetylene-based are widely known.
Of these, silicon surfactants are often used for the purpose of sufficiently reducing the surface tension of the ink, and are effective surfactants for adjusting the surface tension.

 The silicon-based surfactant is a surfactant having a polysiloxane skeleton, and its characteristics are derived from the structure of the polysiloxane. In general, it is known that the ability to lower the surface tension is controlled by the length of the main chain formed of siloxane units (—Si—O—). The shorter the siloxane main chain, the better the compatibility in the ink and the lower the surface tension. Further, when the siloxane main chain becomes longer and the molecular weight increases, the compatibility in the ink becomes worse and the surface tension is not lowered so much.

 In addition, when controlling the compatibility of silicon in accordance with the application, it is possible to organically modify a site corresponding to a side chain or a terminal of the siloxane unit (—Si—O—). By organically modifying these, it is possible to obtain a silicon-based compound having an affinity for the raw materials used for the solvent and ink. Various organic modifications such as polyether, polyester, and aralkyl having a benzene ring are possible. It is also possible to introduce reactive groups such as epoxy and acrylic groups.

 When used in water-based inks, it is necessary to make the silicon surfactant itself highly polar. Generally, polyether modification using polyethylene oxide or polypropylene oxide is used. Since the silicon portion is hydrophobic, the polyether portion is oriented in water.

 However, when used in water-based inks, depending on the structure of the above-mentioned silicon surfactant, the surface tension increases after the ink has been stored for a long time, and the wettability on the base material often deteriorates over time. Occur. In particular, when using a silicon-based surfactant that has high compatibility with the raw materials used for the solvent and ink, it is possible to sufficiently reduce the surface tension of the ink, but the surface tension after the ink has been stored for a long period of time. Rises remarkably and the wettability decreases with time. Although the cause of this is not clear, the higher the compatibility, the more the surfactant is adsorbed on the interface of insoluble substances such as pigments and resin particles dispersed in water during long-term storage. This is considered to be caused by a decrease in the amount of the surfactant that was oriented at the gas-liquid interface in contact with the ink or the interface with the printing substrate.

In order to improve the stability of the surface tension of water-based ink during long-term storage, the present inventors have examined the relationship between the structure of the silicon-based surfactant and the temporal change of the surface tension, and are represented by the general formula (1). It has been found that by using a silicon-based surfactant, the change in surface tension of the water-based ink over time is suppressed, and the wettability on the substrate does not decrease with time.
General formula (1)

(In the formula, R ₁ and R ₂ are alkyl groups having 1 to 6 carbon atoms, and X ₁ and X ₂ are polyether (polyoxyalkylene) groups represented by the general formula (2).)
General formula (2)

(In the formula, R ₃ is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or a (meth) acryl group, EO is an ethylene oxide group, PO is a propylene oxide group, and b is an integer of 1 or more. , C is an integer greater than or equal to 0, and b + c is an integer greater than or equal to 1. The order of EO and PO may be random, where a represents an integer of 10 to 80.)
Although it is not clear why the surface tension and wettability can be suppressed over time, the compatibility with the solvent and other materials used can be controlled by using the silicon surfactant represented by the general formula (1). It is presumed that the adsorption of the surfactant to the interface of pigments and resin fine particles dispersed in water is suppressed.

Furthermore, it became clear by examination of the present inventors that excellent wettability is exhibited on a hardly absorbent substrate by using the silicon surfactant represented by the general formula (1).
The silicon-based surfactant represented by the general formula (1) is an integer of a = 10 or more and 80 or less from the viewpoint of reducing the compatibility with an aqueous solvent and reducing the temporal change in surface tension and wettability. Preferably there is.

 Specific examples of commercially available silicon surfactants represented by the above general formula (1) include BY16-201 and SF8427 manufactured by Toray Dow Corning, BYK-333, BYK-UV3500 manufactured by BYK Chemie, and Evonik. Degussa's TEGO GLIDE 410, TEGO GLIDE 432, TEGO GLIDE 435, TEGO GLIDE 440, TEGO GLIDE 450, and the like can be used alone or in combination. Moreover, it is not limited to the said commercial item.

The content of the silicon-based surfactant used in the present invention has excellent wettability on a hardly absorbable substrate, and is 0.1 to 0.1 from the viewpoint of reducing changes in surface tension after long-term storage. It is preferably 2% by weight, and more preferably 0.5 to 2% by weight. If the content exceeds 2% by weight, the viscosity stability of the ink may be impaired.
By using the above-mentioned silicon-based surfactant used in the present invention, not only has excellent wettability on a highly hydrophobic hardly-absorbable substrate, but also sufficiently ensures the stability of the surface tension of the ink. it can.

 If the surface tension rises after long-term storage, the wettability with respect to the printing substrate is lowered, leading to problems such as white spots in the printing portion. Also, if the surface tension of the ink is different before and after long-term storage, the ink flows due to the difference in height of the surface tension, causing problems such as color mixing and bleeding between colors. Since the replacement time of the ink mounted on the printer varies depending on the use frequency of each color, it is preferable that the surface tension between the colors of the new and old inks is always stable and there is no difference in height.

 As the stability of the surface tension required for actual use in long-term storage of ink, the surface tension change rate of the ink represented by the following general formula (3) is less than 5% in the accelerated aging test at 50 ° C. for 6 weeks. It is preferable.

General formula (3)
Surface tension change rate (%) = (Surface tension difference before and after aging test) / (Surface tension before aging test)

When the surface tension change rate of the above-mentioned ink is 5% or more, white spots in the printed portion and bleeding between colors occur after long-term storage, and excellent print quality cannot be obtained, which is not preferable.
As described above, by using the silicon-based surfactant represented by the general formula (1), it is possible to maintain excellent wettability on a hardly absorbent substrate even after the ink has been stored for a long time. It was confirmed by the examination of those. However, even if the ink has excellent wettability, if the dryness of the water-soluble organic solvent used is poor, the dots do not dry sufficiently on the hard-to-absorbent substrate, the dots are connected, and bleeding and white A new problem has been discovered that omissions occur.

(Water-soluble organic solvent)
In order to improve the drying property of the ink while maintaining the wettability on the hardly absorbent substrate, the present inventors have intensively studied the influence of various water-soluble organic solvents on the image formation on the hardly absorbent substrate. went. As a result, the use of at least one (poly) propylene glycol alkyl ether having a boiling point of 180 ° C. or lower as the water-soluble organic solvent improves the drying and fixing properties of the ink and provides excellent printability. I found out. Furthermore, by using together with the silicon-based surfactant of the present invention, it has been found that excellent print quality can be maintained even after long-term storage, and the present invention has been achieved.
Although the reason why excellent printability can be obtained is not clear, the following is presumed. In (poly) propylene glycol alkyl ethers, the solvent itself is excellent in solubility and exhibits good permeability to a hardly absorbable substrate. Further, it is suitable for promoting the film formation of resin fine particles in the drying process and enhancing the dot fixing property on the hardly absorbent substrate. Further, the present inventors have found that (poly) propylene glycol alkyl ethers have good compatibility with the silicon surfactant used in the present invention and have excellent wettability on a hardly absorbable substrate. It was confirmed by examination. Furthermore, it is considered that by having a boiling point in a suitable range, the volatility of the solvent itself is increased, thereby contributing to the improvement of the drying property of the ink. For the reasons described above, it is considered that the ink has sufficient wettability and drying property on the hardly-absorbable substrate, and excellent printability with few white spots in the printed portion and less blur between dots can be obtained.

That is, the present invention is characterized in that it contains at least one (poly) propylene glycol alkyl ether having a boiling point of 180 ° C. or lower as a water-soluble organic solvent in addition to the above-mentioned silicon-based surfactant.
The (poly) propylene glycol alkyl ethers used in the present invention preferably have a boiling point of 180 ° C. or less from the viewpoint of having quick drying properties and obtaining excellent print quality on a hardly absorbent substrate. More preferably, it is 160 degrees C or less, Especially preferably, it is 140 degrees C or less.

Examples of (poly) propylene glycol alkyl ethers having a boiling point of 180 ° C. or lower include propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol dimethyl ether, dipropylene glycol dimethyl ether and the like. Can be used alone or in combination.
Examples of (poly) propylene glycol alkyl ethers having a boiling point of 160 ° C. or lower include propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol dimethyl ether and the like.
Examples of (poly) propylene glycol alkyl ethers having a boiling point of 140 ° C. or lower include propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol dimethyl ether and the like.

 When the boiling point of the above (poly) propylene glycol alkyl ethers exceeds 180 ° C., the drying property on the hardly absorbable substrate becomes insufficient, the dots are easily fused, and mixed color bleeding, white spots, etc. are likely to occur. Therefore, it is not preferable.

 The content of the (poly) propylene glycol alkyl ethers used in the present invention in the ink composition is 15% by weight or less. Preferably it is 1 to 15 weight%, More preferably, it is 5 to 15 weight%. If the content exceeds 15% by weight, film formation of resin fine particles is promoted in the drying process, and the dots may be dried before spreading sufficiently on the substrate, and white spots may occur in the printed portion. In addition, the viscosity stability of the ink may be impaired.

In addition, a water-soluble organic solvent other than those described above can be used alone or in combination within a suitable content range that does not reduce the effect of the present invention.
For example, alkanediols can be contained as water-soluble organic solvents other than those described above. Alkanediols are excellent in moisture retention and can ensure stable ejection on an inkjet nozzle.

 Examples of alkanediols include 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, and 1,2-butanediol. 1,3-butanediol, 3-methyl-1,3-butanediol, 1,2-pentanediol, 2-methyl-2,4-pentanediol, 1,2-hexanediol and the like alone or Multiple can be used.

 The content of the alkanediol in the ink composition is 11% by weight or more from the viewpoint of ensuring stable ejection on an inkjet nozzle and obtaining drying properties for image formation on a hardly absorbent substrate. It is preferably less than 25% by weight, more preferably 11% by weight or more and less than 20% by weight. When the content is 25% by weight or more, there is a possibility that the drying property is lowered and the image quality is impaired.

Furthermore, a water-soluble nitrogen-containing solvent can be added for the purpose of improving the permeability to the hardly absorbable substrate.
Nitrogen-containing solvents include 2-pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, 3-methyl-2-oxazolidinone, 3-ethyl-2-oxazolidinone, N, N-dimethyl-β-methoxypropionamide, N , N-dimethyl-β-ethoxypropionamide, N, N-dimethyl-β-butoxypropionamide, N, N-dimethyl-β-pentoxypropionamide, N, N-dimethyl-β-hexoxypropionamide, N , N-dimethyl-β-heptoxypropionamide, N, N-dimethyl-β-2-ethylhexoxypropionamide, N, N-dimethyl-β-octoxypropionamide, N, N-diethyl-β-butoxy Propionamide, N, N-diethyl-β-pentoxypropionamide, N, N-diethyl-β- Examples include hexoxypropionamide, N, N-diethyl-β-heptoxypropionamide, N, N-diethyl-β-octoxypropionamide, and the like.

(Binder resin)
In the water-based inkjet ink of the present invention, a binder resin can be used in order to enhance dot fixability on a hardly absorbable substrate and film resistance of printed matter. In the present invention, it is preferable to use water-dispersible resin fine particles as the binder resin. Water-soluble resin and water-dispersible resin fine particles are widely known as water-based ink binder resins. Generally, water-dispersible resin fine particles have a higher molecular weight than water-soluble resins and realize high resistance. Can do. Further, since the water-dispersible resin fine particles can lower the viscosity of the ink and a larger amount of resin can be blended in the ink, it can be said that the water-dispersible resin fine particles are suitable for increasing the resistance of the ink-jet ink. Examples of the resin fine particles include acrylic, urethane, styrene butadiene, vinyl chloride, and polyolefin.

By increasing the glass transition temperature (Tg) of the water-dispersible resin fine particles, it is possible to improve resistance such as abrasion resistance and chemical resistance, preferably in the range of 50 to 100 ° C., more preferably Is in the range of 75 ° C to 90 ° C. When the temperature is lower than 50 ° C., sufficient resistance cannot be obtained, and printing may be peeled off from the printed matter in practice. When the temperature is higher than 100 ° C., the coating film becomes very hard, and cracking and cracking may occur on the printed surface when the printed material is bent.
In addition, the water-dispersible resin fine particles not only increase the coating film resistance of the printed matter, but also quickly form a film after the droplets have landed, thereby suppressing the bleeding between dots and being excellent without bleeding between colors. Print quality can be obtained.
The content of the water-dispersible resin fine particles as described above in the ink composition is preferably in the range of 3 to 20% by weight based on the total weight of the ink in terms of nonvolatile content.

(water)
As water contained in the water-based inkjet ink of the present invention, it is preferable to use ion-exchanged water (deionized water) instead of general water containing various ions.
The content of water that can be used in the present invention is in the range of 20 to 80% by weight of the total weight of the ink.

(Pigment)
As the pigment contained in the aqueous pigment ink of the present invention, conventionally known pigments can be used.
Examples of cyan pigments that can be used in the present invention include C.I. I. Pigment Blue 1, 2, 3, 15: 3, 15: 4, 16, 22, C.I. I. Vat Blue 4, 6 etc. are mentioned.
Examples of magenta pigments that can be used in the present invention include C.I. I. Pigment Red 5, 7, 12, 22, 23, 31, 48 (Ca), 48 (Mn), 49, 52, 53, 57 (Ca), 57: 1, 112, 122; quinacridone solid solution, 146, 147, 150 238, 269, C.I. I. Pigment Violet 19 etc. are mentioned.
Examples of yellow pigments that can be used in the present invention include C.I. I. Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 94, 95, 109, 110, 117, 120, 125, 128, 137, 138, 139, 147, 148, 150, 151 , 154, 155, 166, 168, 180, 185, 213 and the like.

Examples of the black pigment that can be used in the present invention include carbon black (CI Pigment Black 7) produced by the furnace method and the channel method. For example, these carbon blacks have a primary particle diameter of 11 to 40 mμm (nm), a specific surface area by the BET method of 50 to 400 m ² / g, a volatile content of 0.5 to 10% by weight, and a pH value of 2 to 2. Those having characteristics such as 10 are preferred. The following are mentioned as a commercial item which has such a characteristic. For example,
No. 33, 40, 45, 52, 900, 2200B, 2300, MA7, MA8, MCF88 (manufactured by Mitsubishi Chemical), RAVEN1255 (manufactured by Colombia), REGAL330R, 400R, 660R, MOGUL L (manufactured by Cabot), Nipex 160IQ , Nexex 170IQ, Nipex 75, Printex 85, Printex 95, Printex 90, Printex 35, Printex U (manufactured by Degussa) and the like, and any of them can be preferably used.

In the present invention, the pigment is not limited to the above-described pigments, and can be used as an ink set in which other pigments are combined with special colors such as orange, green, and white and clear that does not contain pigments.
The content of the pigment that can be used in the present invention is in the range of 0.1 to 10% by weight in the ink composition.

(Pigment dispersion resin)
As the pigment dispersion resin contained in the aqueous pigment ink of the present invention, conventionally known ones can be used, but (meth) acrylic acid copolymers are generally used. This is because charge repulsion occurs between pigments in an aqueous solvent due to charge repulsion when the (meth) acrylic acid copolymer adsorbed on the pigment surface is ionized, and a stable pigment dispersion state can be maintained. Conceivable.
In the present invention, not only a single color ink but also an ink set of four or more colors combining cyan, magenta, yellow and black inks can be used. The composition of each color ink is not particularly limited, but it is preferable that all components other than the pigment have the same composition. By using the same composition, the drying speed at the time of printing and the wetting spread on the substrate can be made uniform in all colors, and the printing quality can be improved.

(Other ingredients)
In addition to the above-described components, the ink of the present invention can be appropriately added with additives such as an antifoaming agent and an antiseptic agent in order to obtain an ink having desired physical properties as required. As an example of the amount of these additives, 0.01 to 10% by weight, preferably 0.2 to 5% by weight, is suitable based on the total weight of the ink.

(Ink preparation method)
Examples of the method for preparing the ink of the present invention comprising the components described above include the following methods, but the present invention is not limited to these. First, a pigment is added to an aqueous medium in which at least a pigment dispersion resin and water are mixed, and after mixing and stirring, dispersion processing is performed using a dispersion means described later, and centrifugation is performed as necessary. To obtain a desired pigment dispersion. Next, if necessary, a water-soluble organic solvent or an appropriately selected additive component as listed above is added to this pigment dispersion, and the mixture is stirred and filtered as necessary to obtain the ink of the present invention. And

 In the ink preparation method of the present invention, as described above, a pigment dispersion obtained by carrying out a dispersion treatment is used for ink preparation, but before the dispersion treatment carried out during the preparation of the pigment dispersion. It is effective to perform premixing. That is, premixing may be performed by adding a pigment to an aqueous medium in which at least a pigment dispersion resin and water are mixed. Such a premixing operation is preferable because it improves wettability of the pigment surface and promotes adsorption of the dispersant to the pigment surface.

The disperser used in the above-described pigment dispersion treatment may be any disperser that is generally used, and examples thereof include a ball mill, a roll mill, a sand mill, a bead mill, and a nanomizer. Among these, a bead mill is preferably used. Examples of such include a super mill, a sand grinder, an agitator mill, a glen mill, a dyno mill, a pearl mill, and a cobol mill (all are trade names).
Further, in the above-described pigment premixing and dispersion treatment, the pigment dispersion resin may be dissolved or dispersed only in water, or may be dissolved or dispersed in a mixed solvent of a water-soluble organic solvent and water. .

 Since the ink of the present invention is for inkjet recording, it is preferable to use a pigment having an optimum particle size distribution. That is, in order to allow ink containing pigment particles to be suitably used in the ink jet recording method, it is preferable to use a pigment having an optimum particle size distribution in view of demands such as nozzle clogging resistance. Examples of a method for obtaining a pigment having a desired particle size distribution include the following methods. Reduce the size of the grinding media of the disperser as mentioned above, increase the filling rate of the grinding media, increase the processing time, classify with a filter or centrifuge after grinding, etc. There are methods such as a combination of these methods.

(Recording method)
The recording method used in the present invention is an inkjet recording method in which printing is performed by adhering to a printing substrate, and an inkjet recording method using the above-described aqueous inkjet ink is provided.

 Hereinafter, the present invention will be described more specifically with reference to examples. In the examples, “part” represents “part by weight”, and “%” represents “% by weight”.

(Production example of pigment dispersion resin)
A reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer was charged with 93.4 parts of triethylene glycol monomethyl ether and replaced with nitrogen gas. The inside of the reaction vessel was heated to 110 ° C., and a mixture of 35.0 parts of lauryl methacrylate, 35.0 parts of styrene, 30.0 parts of acrylic acid, and 6.0 parts of V-601 (manufactured by Wako Pure Chemical Industries) was added for 2 hours. Over the course of the polymerization reaction. After completion of the dropwise addition, the mixture was further reacted at 110 ° C. for 3 hours, and then 0.6 part of V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the reaction was further continued at 110 ° C. for 1 hour to prepare a pigment dispersion resin 1 solution. Obtained. The weight average molecular weight of the pigment dispersion resin 1 was about 16000.
Further, after cooling to room temperature, 37.1 parts of dimethylaminoethanol was added for neutralization. This is the amount that neutralizes 100% of acrylic acid. Further, 200 parts of water was added to make it aqueous. 1 g of this was sampled, heated and dried at 180 ° C. for 20 minutes to measure the non-volatile content, and water was added so that the non-volatile content of the previously aqueous resin solution was 20%. As a result, an aqueous solution having a non-volatile content of 20% of the pigment dispersion resin 1 was obtained.

(Production example of water-dispersible resin fine particles)
A reaction vessel equipped with a stirrer, a thermometer, a dropping funnel, and a refluxing vessel was charged with 40 parts of ion exchange water and 0.2 part of Aqualon KH-10 (Daiichi Kogyo Seiyaku) as a surfactant. -10 parts of ethylhexyl acrylate, 57 parts of methyl methacrylate, 30 parts of styrene, 2 parts of dimethylacrylamide, 1 part of methacrylic acid, 53 parts of ion-exchanged water and 1.8 parts of Aqualon KH-10 (Daiichi Kogyo Seiyaku) as a surfactant An additional 1% of the pre-emulsion previously mixed with was added. After raising the internal temperature to 60 ° C. and sufficiently purging with nitrogen, 10 parts of a 5% aqueous solution of potassium persulfate and 20 parts of a 1% aqueous solution of anhydrous sodium bisulfite were added to initiate polymerization. After maintaining the reaction system at 60 ° C. for 5 minutes, the remaining pre-emulsion, 5% aqueous solution of potassium persulfate, and 1% aqueous solution of anhydrous sodium bisulfite were maintained for 1.5 hours while maintaining the internal temperature at 60 ° C. The mixture was added dropwise and stirring was continued for 2 hours. After confirming that the conversion rate exceeded 98% by solid content measurement, the temperature was cooled to 30 ° C. Diethylaminoethanol was added to adjust the pH to 8.5, and the non-volatile content was adjusted to 40% with ion exchange water to obtain a resin fine particle water dispersion. The obtained resin fine particle water dispersion was designated as water dispersible resin fine particles 1. The calculated glass transition temperature of the water-dispersible resin fine particles 1 is 80 ° C.

(Manufacture of pigment dispersion)
20 parts of the following pigment, 42.9 parts of an aqueous solution of the pigment dispersion resin 1 and 37.1 parts of water were charged into a mayonnaise bottle, predispersed with a disper, and filled with 1800 g of zirconia beads having a diameter of 0.5 mm as a dispersion medium. This dispersion was performed for 2 hours using a 0.6 L dyno mill to obtain a pigment dispersion. At this time, the ratio of the non-volatile content between the pigment and the pigment-dispersed resin 1 is pigment / dispersed resin (non-volatile) = 7/3. The pigment types used for preparing the pigment dispersion are shown below.
・ C. I. Pigment Blue 15: 3 (used to prepare cyan pigment dispersion)
・ C. I. Pigment Red 122 (used to prepare magenta pigment dispersion)
・ C. I. Pigment Yellow 120 (used to prepare yellow pigment dispersion)
・ C. I. Pigment Black 7 (used to prepare black pigment dispersion)

It shows below about the water-soluble organic solvent used by an Example and a comparative example.
<(Poly) propylene glycol alkyl ethers>
PGDME: Propylene glycol dimethyl ether (boiling point: 96 ° C.)
・ PGMME: Propylene glycol monomethyl ether (boiling point: 120 ° C.)
・ PGMPE: Propylene glycol monopropyl ether (boiling point: 150 ° C.)
DPGDME: Dipropylene glycol dimethyl ether (boiling point: 175 ° C.)
DPGMME: Dipropylene glycol monomethyl ether (boiling point: 189.6 ° C.)

<Water-soluble organic solvents other than the above>
・ 1,2-BD: 1,2-butanediol ・ 2-PY: 2-pyrrolidone ・ DEGDME: diethylene glycol dimethyl ether ・ DEGMBE: diethylene glycol monobutyl ether

The silicon-based surfactant used as an example is shown below.
<Silicon surfactant represented by the general formula (1)>
・ BYK-333 (by Big Chemie)
・ TEGO GLIDE 432 (Evonik Degussa)
The surfactant used as a comparative example is shown below.
<Silicon surfactant not having the structure of the general formula (1)>
・ BYK-347 (by Big Chemie)
・ KF-351A (manufactured by Shin-Etsu Chemical Co., Ltd.)
<Non-silicone surfactant (acetylene surfactant)>
・ Surfinol 465 (manufactured by Air Products Japan)

(Examples 1-16 and Comparative Examples 1-9)
Ink jet inks were prepared according to the compositions described in Tables 1 and 2. Specifically, the pigment dispersion prepared by the above method and other raw materials were charged into a mayonnaise bottle according to the composition described in Tables 1 and 2, and stirred and mixed with a high speed mixer. And it filtered with the membrane filter of 1 micrometer and 0.45 micrometer, and obtained the inkjet ink. The prepared four inks of cyan, magenta, yellow, and black were used as one ink set, and ink sets of Examples 1 to 16 and Comparative Examples 1 to 9 having different compositions were obtained. The following evaluation was performed using these ink sets.

The evaluation method of the prepared ink is shown below.
(Evaluation 1: Evaluation of viscosity stability)
The viscosities of the inks obtained in Examples 1 to 16 and Comparative Examples 1 to 9 were measured using an E-type viscometer (TVE-20L manufactured by Toki Sangyo Co., Ltd.) at 25 ° C. under the condition of a rotational speed of 50 rpm. The ink was stored in a thermostat at 50 ° C. and allowed to accelerate with time, and the change in ink viscosity before and after aging was evaluated. Evaluation criteria are as follows, and A and B evaluations are practical areas.
<Evaluation criteria>
A: Viscosity change rate after storage for 10 weeks is less than ± 5% B: Viscosity change rate after storage for 6 weeks is less than ± 5% C: Viscosity change rate after storage for 6 weeks is ± 5% or more
(Evaluation 2: Surface tension stability evaluation)
The surface tension values of the inks obtained in Examples 1 to 16 and Comparative Examples 1 to 9 were measured using CBVP-Z (manufactured by Kyowa Interface Science). This ink was stored in a thermostat at 50 ° C., accelerated with time, and the change in the surface tension of the ink before and after the time test was evaluated. The evaluation criteria are as follows.
A and B evaluations are practical areas.

<Evaluation criteria>
A: Change rate of surface tension after storage for 10 weeks is less than ± 5% B: Change rate of surface tension after storage for 6 weeks is less than ± 5% C: Change rate of surface tension after storage for 6 weeks is ± 5% or more
(Evaluation 3: Ink wettability evaluation)
The inks obtained in Examples 1 to 16 and Comparative Examples 1 to 9 were filled in an ink jet printer equipped with an ink jet head having a piezoelectric element in an environment of 25 ° C., and the following printing substrate was heated to 50 ° C. While performing solid printing at a printing rate of 100%, the degree of white spots on the printed matter was visually confirmed. In addition, this ink was stored in a thermostat at 50 ° C. and accelerated for 6 weeks, and the degree of white spot was evaluated before and after aging. The evaluation criteria are as follows, and AA, A, and B evaluations are practical areas.

<Evaluation criteria>
AA: The ink spreads sufficiently and no white spots are visually observed, and a uniform image is obtained with no density unevenness. A: The ink spreads appropriately and no white spots are visually observed. B: Ink spreads moderately and no white spots are visually observed C: Ink is not sufficiently spread, and white spots are slightly observed visually D: Insufficient ink spread and white spots clearly visible

<Evaluation substrate>
-Polyvinyl chloride sheet (PVC): MD-5 manufactured by Metamark
・ PET: Mitsubishi Plastics Diafoil
(Evaluation 4: Ink drying evaluation)
About the ink obtained in Examples 1-16 and Comparative Examples 1-9, it printed on the base material and printing conditions similar to evaluation 3. FIG. However, cyan, magenta, yellow, and black were printed adjacent to each other (the order of colors may be random), and the degree of color mixture between colors was evaluated.
1. Evaluation of color mixing of ink before time test The ink before the time test was printed as described above, and the degree of color mixing between colors was evaluated.
2. Evaluation of ink color mixture before and after the aging test The above ink was stored in a thermostat at 50 ° C. and accelerated for 6 weeks. The ink before and after the aging test was printed as described above, and the degree of color mixing between colors was visually observed. However, printing was performed so that the ink before the aging test and the ink after aging promotion were alternately adjacent. The degree of color mixture was observed visually, and the connection of dots was observed and evaluated with a loupe. The evaluation criteria are as follows, and AA, A, and B evaluations are practical areas.

<Evaluation criteria>
AA: There is no dot fusion, no color mixing or bleeding between colors, and each color has a clear boundary A: There is a slight dot fusion, but there is no color mixing or bleeding between colors visually B: The boundary of each color is clear B: There is a slight fusion of dots, but there is no color mixing or bleeding between colors C: There is a slight color mixing or bleeding between colors Object D: Visually visible color mixing and bleeding between colors

(Evaluation 5: Evaluation of ejection stability)
Solid printing of 1 m × 1 m solid printing was performed on PVC under the same conditions as in Evaluation 3, a nozzle check pattern was printed, the number of missing nozzles was counted, and the number was evaluated. In addition, for the ink in which omission was observed, the number of nozzle omissions after wiping the nozzle surface of the head (wiping with a rubber blade) was counted, and the returnability of the nozzles was also evaluated.
<Evaluation criteria>
◯: No nozzle missing △: Nozzle missing is less than 5 but nozzle missing recovers after wiping ×: Nozzle missing is 5 or more, and nozzle missing does not recover even after wiping

 Said evaluation result is shown in Table 3 about Examples 1-16. Comparative Examples 1-9 are shown in Table 4.

In Examples 1 to 16, by using the silicon surfactant and the water-soluble organic solvent within the scope of the claims, the change in surface tension with time was small, and excellent printing was performed on a hardly absorbent substrate before and after the time test. Quality is obtained.
On the other hand, in the comparative example which is outside the scope of the present invention, all the evaluation items are satisfied, and it is indicated that the ink cannot be made into a practical quality. In Comparative Examples 1 and 2 using a silicon surfactant that does not have the structure of the general formula (1), the surface tension of the ink changes with time, and the print quality also deteriorates with time. In Comparative Example 3 using a non-silicone surfactant, the wettability on the hardly absorbent substrate is poor, and excellent printability is not obtained. In Comparative Example 4 in which the content of the (poly) propylene glycol alkyl ethers is larger than the range of the present invention, white spots occur in the printed portion, and excellent print quality is not obtained. Further, Comparative Example 5 using (poly) propylene glycol alkyl ethers having a boiling point outside the scope of the present invention has poor drying properties and poor print quality such as mixed color bleeding on a hardly absorbent substrate. It was. In Comparative Examples 6 and 7 that do not contain any (poly) propylene glycol alkyl ethers, the wettability and drying properties on the base material are insufficient, so that excellent print quality is not obtained.

 Further, in Comparative Example 8 using a water-soluble resin as the binder resin, the wettability is good on the hardly absorbent substrate, but the resin film-forming property is poor, the dots are fused, and the color mixture between colors Bleeding occurred. Furthermore, in Comparative Example 9 containing no surfactant, the wettability on the hardly absorbent substrate was poor, white spots and mixed color bleeding were generated, and excellent printability could not be obtained.

Claims (4)

In a water-based ink for ink jet recording containing at least water, a pigment, a water-dispersible resin fine particle as a binder resin, a water-soluble organic solvent and a silicon surfactant represented by the general formula (1), the water-soluble organic solvent has a boiling point. Inkjet recording comprising at least one (poly) propylene glycol alkyl ether of 180 ° C. or less, wherein the content of the (poly) propylene glycol alkyl ether in the aqueous ink composition is 15% by weight or less. Water-based ink.
General formula (1)

(Wherein R ₁ and R ₂ are alkyl groups having 1 to 6 carbon atoms, and X ₁ and X ₂ are represented by the general formula (2).

(In the formula, R ₃ is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or a (meth) acryl group, EO is an ethylene oxide group, PO is a propylene oxide group, and b is an integer of 1 or more. , C is an integer greater than or equal to 0, and b + c is an integer greater than or equal to 1. The order of EO and PO may be random, where a represents an integer of 10 to 80.)   The (poly) propylene glycol alkyl ether is at least one selected from propylene glycol mono (alkyl having 1 to 4 carbons) ether and (di) propylene glycol di (alkyl having 1 carbon). The water-based ink for inkjet recording according to claim 1.   An ink set of four or more colors including the cyan ink, magenta ink, yellow ink, and black ink according to claim 1 or 2.   An ink jet recording method for performing printing by discharging ink droplets to adhere to a printing substrate, wherein the water-based ink according to any one of claims 1 to 3 is used as the ink. .