JP5928027B2 - Water-based ink for inkjet recording - Google Patents

Description

  INDUSTRIAL APPLICABILITY The present invention is an ink jet recording water-based ink that is excellent in printability for a highly hydrophobic and difficult-to-absorbent substrate, has little change in surface tension of the ink even after long-term storage, and printability such as wettability does not deteriorate over time. It is about.

  Conventionally, in order to form an image on a hard-to-absorb substrate using an ink jet ink 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, there has been a demand for inks that have little impact on the environment and are safe for workers. Water-based inks have been developed not only for indoor applications such as homes and offices, but also for inkjet ink printers for industrial applications such as outdoor billboards. Has been promoted.

  The drying mechanism of water-based inks is classified into penetration and evaporation after the ink has landed on the substrate, but the contribution of penetration is very large, and hydrophobic properties such as polyvinyl chloride sheets used for industrial applications. Since the poorly absorbable base material having high properties permeates slowly, there is a problem in that in the case of multicolor printing, the ink is mixed to form a clear image and the printing speed cannot be increased.

  As water-based inks for ink jets, as in Patent Documents 1 and 2, the development of inks for exclusive paper applications such as plain paper and photographic paper has long been made. However, it has been impossible to obtain a printed matter having sufficient print quality for a hard-to-absorbable printing base material used for industrial applications and the like, and it 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 hard-to-absorb base material, and that the ink does not easily penetrate into the base material and the dots are blurred.

  As a water-based ink that forms an image on a hardly-absorbable substrate, the ink is landed on a hardly-absorbable substrate such as a polyvinyl chloride sheet by using a specific water-soluble organic solvent or copolymer resin, and then dried. Patent Document 3 mentions that an excellent image in which bleeding is suppressed by the thickening effect of the ink at the time can be obtained. However, since the wettability with respect to the base material is insufficient, there is a problem that white spots or the like occur in the printed portion. In addition, the stability of the silicon-based surfactant used is poor, and after storage for a long period of time, the surface tension of the ink changes, and printability such as wettability deteriorates with time.

  Patent Document 4 describes that printing quality such as glossiness and sharpness can be improved by using two or more polysiloxane surfactants having different HLB values. However, even though excellent print quality was obtained for an absorbent substrate having an ink-receiving layer such as photographic paper, wettability was poor for difficult-to-absorbent substrates, and excellent print quality could not be achieved. . In addition, as in Patent Document 3, there is a problem that the stability of the silicon surfactant used is poor and the surface tension of the ink changes with time.

  Furthermore, 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, it can maintain excellent print quality for paper-based absorbent base materials such as plain paper, but it is difficult to absorb highly hydrophobic base materials such as polyvinyl chloride sheets. Has insufficient wettability, so that excellent print quality could not be obtained.

Japanese Patent No. 4764562 Japanese Patent No. 3994734 JP 2009-235322 A Japanese Patent No. 4138593 Japanese Patent No. 3858793

  The object of the present invention is excellent in printability for a highly hydrophobic hardly-absorbable substrate, and has little change in the surface tension of ink even after long-term storage, and the printability such as wettability does not deteriorate over 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 two kinds of water-based pigments, water-soluble organic solvents, binder resins, and silicon-based surfactants. It is a silicon-based surfactant represented by the formula (1), and at least one kind is a silicon-based surfactant represented by the general formula (3), which is represented by the general formulas (1) and (3). The present invention relates to a water-based ink for ink-jet recording, wherein the total content of the silicon-based surfactant satisfies the relationship of the general formula (5).
(However, water-based ink for ink-jet recording is for UV-curable ink-jet recording.
Except when )
General formula (1)

(Wherein R _1, R ₂ is an alkylene group having 1 to 6 carbon atoms, X _1, X ₂ is a polyether (polyoxyalkylene) group represented by the general formula (2).)
General formula (2)

(Wherein 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. EO, P
The order of O may be random. In the formula, a represents an integer of 10 to 80. )
General formula (3)

(In the formula, R ₄ and R ₅ are alkyl groups having 1 to 6 carbon atoms, and X ₃ is a polyether (polyoxyalkylene) group represented by the general formula (4).)
General formula (4)

(Wherein, R ₆ is an alkylene group having 1 to 6 carbon atoms, R ₇ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, EO is an ethylene oxide group, PO is propylene oxide groups , F is an integer of 1 or more, g is an integer of 0 or more, and f + g is an integer of 1 or more, and the order of EO and PO may be random, where d and e are 1 or more. D + e represents an integer of 3 to 50.)

General formula (5)
5 <(A / B) × 100
(A = total content of silicon surfactants represented by the general formulas (1) and (3), B = total content of insoluble substances excluding the silicon surfactants)

  The present invention also relates to a water-based ink for ink jet recording, comprising at least one selected from alkanediols and glycol ethers as the water-soluble organic solvent.

The present invention also relates to a water-based ink for inkjet recording, wherein the alkanediol is an alkanediol having 3 to 6 carbon atoms.
The present invention also relates to a water-based ink for ink jet recording, wherein the glycol ether is a (poly) alkylene glycol mono (or di) alkyl ether.

Moreover, an ink set comprising the water-based ink for inkjet recording according to the invention ,
In addition, the present invention relates to an ink set of four or more colors including cyan ink, magenta ink, yellow ink, and black ink.
Furthermore, it is related with the printed matter formed by printing with the water-based ink for inkjet recording of the said invention.

  According to the present invention, ink jet recording is excellent in printability to a highly hydrophobic hardly-absorbable substrate and has little change in surface tension of ink even after long-term storage, and printability such as wettability does not deteriorate over time. It becomes possible to provide water-based ink.

The water-based ink for ink-jet recording of the present invention will be described below with preferred embodiments.
The water-based ink for ink-jet recording of the present invention is characterized by containing two or more types of silicon surfactants having the above structure. First, the silicon-based surfactant characterizing the present invention will be described.

  Generally, when printing is performed on a highly hydrophobic hardly-absorbable substrate, it is important that the ink has sufficient wettability on the substrate. This is because, after the ink has landed on the base material, the ink surface is sufficiently wet and spread, so that the surface area of the dots is increased, and drying by penetration and evaporation can be promoted. By having sufficient wettability, the ink can be sufficiently dried and fixed on the substrate.

  When ink spreading on the printing substrate is insufficient, ink filling in the printing portion is poor, and problems such as white spots occur. In addition, since the ink is not sufficiently spread, the ink is not sufficiently dried, and the dots are fused to each other on the substrate, resulting in problems such as color mixing and bleeding between colors. 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 spread on the printing substrate, the surface tension of the ink needs to be sufficiently lower than the surface tension of the printing substrate. In addition, since a highly hydrophobic hardly absorbent substrate such as a polyvinyl chloride sheet has a low surface tension and it is not easy to wet the surface of the substrate, it is important to keep the surface tension of the ink sufficiently low.
In particular, since water molecules are strongly bound to each other by hydrogen bonding, water has extremely high surface tension, making it very difficult to ensure sufficient wettability of water-based ink on a highly hydrophobic substrate. .

In order to adjust the surface tension of the ink, it is common to use a surfactant. Of these, a silicon-based surfactant is often used for the purpose of sufficiently reducing the surface tension of the ink. It is an effective surfactant for adjusting the viscosity.

  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-based surfactant, there is often a problem that the surface tension increases after long-term storage of the ink and the wettability on the substrate decreases with 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. 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 thought 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 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, it is possible to suppress a change in the surface tension of the water-based ink with time and to suppress a decrease in wettability on the substrate over 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, compatibility with solvents and other materials used can be controlled by using the silicon-based surfactant represented by the general formula (1). It is presumed that the adsorption of the surfactant to the interface of the pigment, the water-dispersible resin fine particles and the like is suppressed.

  Furthermore, the silicon-based surfactant represented by the general formula (1) is used in combination with the silicon-based surfactant represented by the following general formula (3), thereby using each surfactant alone. According to the study by the present inventors, the wettability with respect to a highly hydrophobic difficult-to-absorbent substrate such as a polyvinyl chloride sheet is greatly improved, and excellent printability with less white spots can be obtained in the printed part. It became clear.

General formula (3)

(In the formula, R ₄ and R ₅ are alkyl groups having 1 to 6 carbon atoms, and X ₃ is a polyether (polyoxyalkylene) group represented by the general formula (4).)
General formula (4)

(Wherein R ₆ is an alkyl group having 1 to 6 carbon atoms, R ₇ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, EO is an ethylene oxide group, PO is a propylene oxide group, f is an integer of 1 or more, g is an integer of 0 or more, and f + g is an integer of 1 or more, and the order of EO and PO may be random, where d and e are 1 or more. (It is an integer, and d + e represents an integer of 3 to 50.)

  The silicon-based surfactant represented by the general formula (3) has a good compatibility with an aqueous solvent and is often used for the purpose of adjusting the surface tension of the ink. It is an effective surfactant for lowering. However, when one or more silicon-based surfactants represented by the general formula (3) are used, the surface tension of the ink may change over time in the presence of insoluble substances such as pigments and water-dispersible resin fine particles. There arises a problem that the wettability with respect to the base material decreases with time.

  Even when the silicon-based surfactant represented by the general formula (3) is used, by using it together with the silicon-based surfactant represented by the general formula (1), the change in surface tension is reduced. The inventors have clarified that excellent wettability can be maintained on a highly hydrophobic difficult-to-absorbent substrate, leading to the present invention.

  Further, from the viewpoint of having excellent wettability with respect to a highly hydrophobic hardly-absorbing substrate such as a polyvinyl chloride sheet, and reducing changes with time such as the surface tension and wettability of the ink, the above general formula (1 ) And (3), the total content of the silicon surfactants preferably satisfies the relationship of the general formula (5).

General formula (5)
5 <(A / B) × 100
(A = total content of silicon surfactants represented by the general formulas (1) and (3), B = total content of insoluble substances excluding the silicon surfactants)

  The insoluble substance described in the general formula (5) is a solid substance having low solubility in water-based ink. Examples thereof include solid substances such as pigments and water-dispersible resin fine particles. Moreover, content represents the weight part in an ink composition.

  By satisfying the relationship of the general formula (5), even after the ink has been stored for a long period of time, the change in surface tension can be suppressed and the printing quality can be maintained. By satisfying the above formula, even if the surfactant is adsorbed to the interface of insoluble substances such as pigments and water-dispersible resin fine particles to some extent, the gas-liquid in contact with the ink due to the presence of excess surfactant. This is because it is possible to compensate for the orientation to the interface or the substrate interface, and to suppress the change in surface tension and the decrease in wettability with respect to the substrate. When the relationship of the general formula (5) is not satisfied, the wettability with respect to the hardly absorbent substrate is poor, and excellent printability cannot be obtained. Further, the surface tension and wettability of the ink change with time, which is not preferable.

  Furthermore, the total content of the silicon-based surfactant represented by the above general formula (5) from the viewpoint of improving the wettability on the hardly-absorbable substrate and reducing the temporal change in surface tension and wettability is , 8 <(A / B) × 100 is more preferable.

  The ratio of the silicon-based surfactant represented by the general formulas (1) and (3) is not particularly limited, but is represented by the general formula (1) from the viewpoint of reducing the change in the surface tension of the ink. It is preferable that the weight ratio of the content of the silicon surfactant and the silicon surfactant represented by the above general formula (3) is 1: 1 to 10: 1. If the weight ratio is less than 1: 1, the effect of the present invention of reducing the change in the surface tension of the ink may be reduced.

  Further, the total content of the silicon-based surfactants represented by the above general formulas (1) and (3) is 0.5% by weight or more from the viewpoint of ensuring sufficient wettability on the hardly absorbent substrate. It is preferable that it is below wt%. If the content exceeds 2% by weight, the viscosity stability of the ink may be impaired.

The silicon surfactant represented by the general formula (1) is an integer of 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. Examples include, but are not limited to, TEGO Glide 410, TEGO Glide 432, TEGO Glide 435, TEGO Glide 440, and TEGO Glide 450 manufactured by Degussa.

The silicon surfactant represented by the general formula (3) improves the compatibility with an aqueous solvent, and d + e is an integer of 3 or more and 50 or less from the viewpoint of sufficiently reducing the surface tension of the ink. preferable.
Specific examples of commercially available silicon-based surfactants represented by the above general formula (3) include SF8428, FZ-2162, 8032 ADDITIVE, SH3749, FZ-77, L7001, L-, manufactured by Toray Dow Corning. 7002, FZ-2104, FZ-2110, FZ-2123, SH8400, SH3773M, BYK-345, BYK-346, BYK-347, BYK-348 manufactured by BYK Chemie, TEGO WET 250, TEGO WET 260 manufactured by Evonik Degussa , TEGO WET 270, TEGO WET 280, KF-351A, KF-352A, KF-353L, KF-354L, KF-355A, KF-615A, KF-640, KF-642, KF-643, manufactured by Shin-Etsu Chemical Co., Ltd. But is limited to these Is not something

  By using two or more kinds of the above-mentioned silicon-based surfactants used in the present invention, not only has excellent wettability on a highly hydrophobic difficult-to-absorbent substrate, but also sufficiently stabilizes the surface tension of the ink. Can be secured.

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

(General formula (6))
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 ink described above is 5% or more, it is not preferable because white spots and bleeding between colors occur after long-term storage, and excellent print quality cannot be obtained.

  The water-based ink for ink jet recording of the present invention comprises at least water, a pigment, a water-soluble organic solvent, and a binder resin in addition to the silicon surfactant described above. Each component contained will be described.

<Water>
As water contained in the water-based ink for ink jet recording 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 (Mitsubishi Chemical), RAVEN1255 (Colombia), REGAL330R, 400R, 660R, MOGUL L (Cabot), Nexex 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.

  The present invention is not limited to the above-described pigments, and can be used as an ink set in which other pigments are used and a special color such as orange, green, white, etc., and clear that does not contain pigments are combined.

  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 water-based 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 desirable 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.

<Binder resin>
Furthermore, the water base ink for inkjet recording of the present invention can use a binder resin in order to increase the coating film resistance of the printed matter. The binder resin preferably contains water-dispersible resin fine particles. Water-soluble resins and fine resin particles are generally known as binder resins for water-based inks. In general, resin fine particles have a higher molecular weight than water-soluble resins, and can achieve high resistance. In addition, the resin fine particles can lower the viscosity of the ink, and a larger amount of resin can be blended in the ink. Therefore, it can be said that the resin fine particles are suitable for increasing the resistance of the inkjet 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 aqueous resin fine particles, it is possible to improve resistance such as abrasion resistance and chemical resistance, preferably 50 to 120 ° C, more preferably 80 to 100 ° C. Range. 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 120 ° 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-based 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 and dry it to suppress the blur between dots, and there is little color mixing or blur between colors. Excellent print quality can be obtained.
The content of the aqueous resin fine particles as described above in the ink is in the range of 3 to 20% by weight of the total weight of the ink in terms of solid content.

<Water-soluble organic solvent>

  Moreover, the water-based ink of the present invention can contain a water-soluble organic solvent. Those having good compatibility with the silicon surfactant having the above structure can be suitably used. From the viewpoint of obtaining excellent printing quality, it is preferable to include at least one selected from alkanediols and glycol ethers as the water-soluble organic solvent.

Alkanediols are less effective for drying because of the low permeability of the solvent itself, but are used for the purpose of improving the wettability with respect to hardly-absorbing substrates and the viscosity stability of the ink. Since the permeability of the solvent itself is low, it is easy to stay on the base material, and it is possible to improve the wettability by allowing time for the silicon-based surfactant to sufficiently align on the base material surface. In addition, since the solubility of the solvent itself is low, there is little influence on the pigment dispersion, and sufficient viscosity stability can be obtained even when stored for a long period of time.
Specific examples of alkanediols include 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,2-pentanediol, and 1,5-pentanediol. 1,2-hexanediol, 1,6-hexanediol, 2-methyl-2,4-pentanediol and the like. Among alkanediols, 1,2-alkanediol having 3 to 6 carbon atoms such as 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, and 1,2-hexanediol is used. preferable.

  The content of the alkanediols that can be used in the present invention in the ink composition is preferably 10% by weight or more and 30% by weight or less from the viewpoint of having excellent printability on a hardly absorbent substrate. When the content is less than 10% by weight, the wettability of the ink becomes insufficient, and white spots or the like may occur. On the other hand, if the content exceeds 30% by weight, the drying property of the ink is deteriorated on the hardly absorbing substrate, and dots may be easily connected, and the excellent printability may not be obtained.

  Glycol ethers have permeability to substrates that are difficult to absorb ink, such as polyvinyl chloride sheets, and are used for the purpose of improving the drying properties of the ink. Among these, by using (poly) alkylene glycol mono (or di) alkyl ether, it becomes possible to suppress fusion of dots on a hardly-absorbable substrate.

  Examples of the alkylene glycol monoalkyl ether include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monopentyl ether, diethylene glycol monohexyl ether, triethylene Glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl Ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, 3-methoxy-1-butanol, 3-methoxy-3-methylbutanol, etc. It is done.

  Examples of the alkylene glycol dialkyl ether include diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol diethyl ether, tetraethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol methyl ethyl ether, tetra Ethylene glycol methyl ethyl ether, diethylene glycol butyl methyl ether, triethylene glycol butyl methyl ether, tetraethylene glycol butyl methyl ether, propylene glycol dimethyl ether, dipropylene glycol dimethyl ether, tripropylene glycol dimethyl Ether and the like.

It is more preferable to use alkylene glycol dialkyl ether among glycol ethers from the viewpoint of reducing color mixing and bleeding between colors by improving the permeability with respect to the hardly absorbent substrate and suppressing the connection between dots. .
The content of the glycol ethers that can be used in the present invention in the ink composition is preferably 15% by weight or less. If the content exceeds 15% by weight, the drying property of the ink is too high, and there is a possibility of impairing the wetting and spreading of the ink on the substrate.

  Moreover, in order to reduce the white spot of the printing part on a difficult absorption base material and to ensure the drying property which can suppress the bleeding between dots, it is especially preferable to use the said glycol ethers and alkanediol together.

  Furthermore, a water-soluble nitrogen-containing compound can also be added for the purpose of improving penetration and adhesion to a hardly-absorbable substrate such as a polyvinyl chloride sheet.

  Nitrogen-containing compounds 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 -Hexoxypropionamide, N, N-diethyl-β-heptoxypropionamide, N, N-diethyl-β-octoxypropionamide and the like.

  The total content of the water-soluble organic solvent used in the present invention in the ink composition is preferably in the range of 20 wt% to 40 wt%. When the total content of the water-soluble organic solvent is less than 20% by weight, the drying property of the ink is too good, and the effect of improving the wettability by the silicon surfactant of the present invention may be reduced. . When the amount is more than 40% by weight, the ink is difficult to dry on the hardly-absorbing substrate, dots are connected to each other, and there is a possibility that white spots, mixed color bleeding, and the like deteriorate. In addition, the storage stability of the ink may not be suitable for practical use.

<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 a desired physical property value as necessary. As an example of the amount of these additives, 0.01 to 10% by weight, preferably 0.01 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 solvent or an appropriately selected additive component as listed above is added to this pigment dispersion, followed by stirring, and if necessary, filtering to obtain the ink of the present invention. To do.

  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).

  Furthermore, in the pigment premixing and dispersion treatment described above, 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 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.

  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”.

<Example of pigment dispersion resin production>
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% in the pigment dispersion resin 1 was obtained.

<Preparation 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 component between the pigment and the pigment-dispersed resin 1 is pigment / dispersed resin (non-volatile component) = 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)

<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 measuring the non-volatile content, 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.

The silicon surfactants used as examples and comparative examples are shown below.
<Silicon surfactant represented by the general formula (1)>
・ BYK-333 (by Big Chemie)
・ BYK-UV3500 (by Big Chemie)
・ TEGO GLIDE 440 (Evonik Degussa)
<Silicon surfactant represented by the general formula (3)>
・ TEGO WET 260 (Evonik Degussa)
・ TEGO WET 270 (Evonik Degussa)
<Non-silicone surfactant>
・ Surfinol 465 (manufactured by Air Products Japan)

<Examples 1 to 22 and Comparative Examples 1 to 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 inks of four colors of cyan, magenta, yellow and black were used as one ink set, and ink sets of Examples 1 to 22 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: Viscosity stability evaluation>
The viscosities of the inks obtained in Examples 1 to 22 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. The evaluation criteria are as follows, and AA, A, and B evaluation are practical areas.
<Evaluation criteria>
AA: Change rate of viscosity after storage for 10 weeks is less than ± 5% A: Change rate of viscosity after storage for 8 weeks is less than ± 5% B: Change rate of viscosity after storage for 6 weeks is less than ± 5% C: Store for 6 weeks Later viscosity change rate is more than ± 5%

<Evaluation 2: Evaluation of surface tension stability>
The surface tension values of the inks obtained in Examples 1 to 22 and Comparative Examples 1 to 9 were measured using CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.). 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.
AA, A, and B evaluation are practical areas.
<Evaluation criteria>
AA: Change rate of surface tension after storage for 10 weeks is less than ± 5% A: Change rate of surface tension after storage for 8 weeks is less than ± 5% B: Change rate of surface tension after storage for 6 weeks is less than ± 5% C: Surface tension change rate after storage for 6 weeks ± 5% or more D: Surface tension change rate after storage for 4 weeks ± 5% or more

<Evaluation 3: Ink wettability evaluation>
The inks obtained in Examples 1 to 22 and Comparative Examples 1 to 9 were filled into an ink jet printer equipped with an ink jet head having a piezoelectric element in an environment of 25 ° C., and a polyvinyl chloride sheet (MD-5 manufactured by Metamark Co., Ltd.). ) Was heated to 50 ° C. and solid printing was performed at a printing rate of 100%, and 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 4: Evaluation of ink color mixture>
About the ink obtained in Examples 1-22 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 time test The above ink was stored in a thermostat at 50 ° C. and accelerated for 6 weeks. The ink before and after the time test was printed as described above, and the degree of color mixture between colors was evaluated. 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: No dot fusion, no color mixing or bleeding between colors, and clear boundaries between colors.
A: There is a slight fusion of dots, but there is no color mixing or bleeding between colors, and the boundary between colors is clear. B: There is a slight fusion of dots, but there is a slight gap between colors. C: No color mixing or bleeding C: A slight color mixing or bleeding between colors is visually observed D: A color mixing or bleeding between colors is clearly visible

  Said evaluation result is shown in Table 3 about Examples 1-22. Comparative Examples 1-9 are shown in Table 4.

  In Examples 1 to 22, by using the silicon surfactant within the scope of the claims, the surface tension of the ink is changed even after being stored for a long period of time. There are few water-based inks for ink-jet recording in which printability does not deteriorate with time.

  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 that do not satisfy the relationship of the general formula (5), the stability of the ink surface tension was poor, and the printability deteriorated with time. In Comparative Examples 3 and 5 in which only the silicon-based surfactant represented by the general formula (1) is used, the surface tension stability is good, but the wettability with respect to the base material is insufficient, and thus excellent printability. Was not obtained. In Comparative Examples 4, 6, and 7 using only the silicon surfactant represented by the general formula (3), the stability of the surface tension of the ink was remarkably poor, and the printability deteriorated with time. Comparative Examples 8 and 9 which do not use any one of the silicon-based surfactants represented by the general formulas (1) and (3) have the least wettability, and white spots and mixed color bleeding are observed. It was bad.

Claims (6)

At least water, pigment, water-soluble organic solvent, binder resin and silicon surfactant 2
In the water-based ink for inkjet recording containing at least one species, at least one of the silicone surfactants is a silicone surfactant represented by the general formula (1), and at least one species is represented by the general formula (3). A silicon-based surfactant represented by the general formulas (1) and (
3. A water-based ink for ink-jet recording, wherein the total content of the silicon-based surfactant represented by 3) satisfies the relationship of the general formula (5).
(However, water-based ink for ink-jet recording is for UV-curable ink-jet recording.
Except when )
General formula (1)
(Wherein R _1, R ₂ is an alkylene group having 1 to 6 carbon atoms, X _1, X ₂ is a polyether (polyoxyalkylene) group represented by the general formula (2).)
General formula (2)

(Wherein 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. EO, P
The order of O may be random. In the formula, a represents an integer of 10 to 80. )
General formula (3)

(In the formula, R ₄ and R ₅ are alkyl groups having 1 to 6 carbon atoms, and X ₃ is a polyether (polyoxyalkylene) group represented by the general formula (4).)
General formula (4)

(Wherein, R ₆ is an alkylene group having 1 to 6 carbon atoms, R ₇ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, EO is an ethylene oxide group, PO is propylene oxide groups , F is an integer of 1 or more, g is an integer of 0 or more, and f + g is an integer of 1 or more, and the order of EO and PO may be random, where d and e are 1 or more. D + e represents an integer of 3 to 50.)
General formula (5)

5 <(A / B) × 100

(A = total content of silicon surfactants represented by the general formulas (1) and (3), B
= Total content of insoluble substances excluding the silicon-based surfactant) The water-based ink for ink-jet recording according to claim 1, wherein the water-soluble organic solvent contains at least one selected from alkanediols and glycol ethers. The water-based ink for inkjet recording according to claim 2 , wherein the alkanediol is a 1,2-alkanediol having 3 to 6 carbon atoms. The water-based ink for inkjet recording according to claim 2 or 3, wherein the glycol ether is a (poly) alkylene glycol mono (or di) alkyl ether. An ink set comprising the water-based ink for inkjet recording according to any one of claims 1 to 4,
In addition, an ink set of four or more colors including cyan ink, magenta ink, yellow ink, and black ink.   Printed matter formed by printing with the water-based ink for inkjet recording according to any one of claims 1 to 4.