JP6183028B2 - Inkjet recording method - Google Patents

Description

  The present invention relates to an ink jet recording method.

  In addition to ink-absorbing recording media such as paper and cloth, one of the inkjet inks for industrial use; coated paper for printing with the surface of the paper coated with resin or clay, or the surface of which is coated with a resin layer Ink-jet inks that can be directly printed on recording media having low ink absorbability such as those; and recording media having no ink absorbability such as resin films have been studied.

  Examples of such an ink-jet ink include a solvent-based ink-jet ink using an organic solvent as a vehicle and an ultraviolet curable ink-jet ink mainly composed of a photopolymerizable monomer. The solvent-based ink-jet ink has a problem that there are many VOCs because most of the solvent components are scattered in the atmosphere when the solvent is dried. Also, there are concerns about odors and safety effects on workers, and facilities such as sufficient ventilation are required for use. On the other hand, an ultraviolet curable ink-jet ink is cured immediately after printing, and thus has a VOC close to zero, but may have a skin sensitization property depending on the monomer used. In addition, since it is necessary to incorporate an expensive ultraviolet irradiation light source into the ink jet printer, there is a limit to the fields that can be used.

  In view of this situation, water-based ink-jet ink (water-based ink) that has a small environmental burden and has been widely used in household specifications has been studied. In particular, in addition to recording media having ink absorptivity such as cloth and paper, various water-based inks that can be printed on recording media having low ink absorptivity or not having ink absorptivity (for example, patent documents). 1-3). For example, Patent Document 3 proposes an aqueous inkjet ink containing a pigment, a specific acrylic resin as an ink-soluble resin, and an organic solvent.

  By the way, as a recording medium, polyolefin films such as polypropylene and polyethylene are used in a wide range of applications because they are inexpensive and have high strength. However, it is known that a film such as polypropylene or polyethylene has a particularly low surface energy among polyolefin-based films and has a low ink absorbability, so that it is difficult for ink to adhere thereto.

  On the other hand, an aqueous ink containing a polypropylene resin emulsion as a binder resin has been proposed (for example, Patent Document 4). In the field of paints, for example, chlorinated polypropylene, chlorinated polypropylene-modified acrylic resins, or paints containing acrylic resins having a structure derived from cyclohexyl acrylate are proposed as binder resins (see, for example, Patent Documents 5 and 6). ).

JP 2010-89370 A JP 2009-226664 A JP 2011-144303 A JP 2010-116459 A JP 2007-308528 A JP 2004-196990 A

  However, the binder resins disclosed in Patent Documents 5 and 6 have a problem that even if they are dispersed in a solvent such as toluene or ethyl acetate, they are not suitable for water-based inks because they are difficult to disperse in water. In addition, the water-based ink containing the binder resin disclosed in Patent Document 4 has a problem of low ejection stability and storage stability and low long-term reliability.

  As described above, there is a demand for a water-based inkjet ink that can form an image on a hardly-adherent plastic film such as a polyolefin-based film and has good ejection stability and storage stability.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a water-based inkjet ink that can form an image on a hardly-adhesive plastic film such as a polyolefin-based film and has good ejection stability.

[1] Inkjet including a step of ejecting a water-based inkjet ink onto a polyolefin film having a wetting tension of 30 mN / m or more and less than 40 mN / m, and a step of heating and drying the water-based inkjet ink ejected on the film. In the recording method, the water-based inkjet ink includes a coloring material, a fixing resin, water, and a water-soluble organic solvent, and the fixing resin has a (meth) acrylic acid ester having an alicyclic hydrocarbon group. An inkjet recording method comprising a (meth) acrylic resin containing a structural unit derived from 10% by mass or more and less than 50% by mass.
[2] The inkjet recording method according to [1], wherein the content of the (meth) acrylic resin is 3% by mass or more and less than 10% by mass with respect to the entire water-based inkjet ink.
[3] The color material is a pigment, and the water-based inkjet ink further includes a dispersion resin in which the pigment is dispersed, and the dispersion resin is a block copolymer including a hydrophobic block and a hydrophilic block. The inkjet recording method according to [1] or [2].
[4] The inkjet recording method according to [3], wherein the block copolymer is a block copolymer obtained by a living radical polymerization method.
[5] The water-soluble organic solvent contains at least one organic solvent in which the sum ΣSP of the hydrogen bond term and the polar term of the solubility parameter is 8 MPa ^1/2 or more and 18 MPa ^1/2 or less, [1] to [4] Any one of the inkjet recording methods.
[6] The inkjet recording method according to any one of [1] to [5], wherein the (meth) acrylic acid ester having an alicyclic hydrocarbon group includes a (meth) acrylic acid ester having a cyclohexyl group.

  According to the present invention, it is possible to obtain a water-based inkjet ink that can form an image on a hardly-adherent plastic film such as a polyolefin-based film and has good ejection stability.

It is a figure which shows an example of a structure of the principal part of the inkjet recording device of a single pass recording system. It is a figure which shows an example of the head unit which arranged the nozzle alternately. It is a figure which shows an example of the head unit which arranged the head alternately. It is a figure which shows an example of a structure of the principal part of the inkjet recording device of a scan recording system.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. As a result of intensive investigations in view of the above problems, the present inventors have incorporated a “(meth) acrylic resin having an alicyclic hydrocarbon group” into an aqueous inkjet ink without impairing ejection stability. The present invention has found that an environment-friendly water-based ink-jet ink can also form a high-definition and excellent scratch-resistant image even on a recording medium of difficult-to-adhere plastic such as polypropylene and polyethylene. It came to.

  The reason why the problems of the present invention can be solved by using the above-described ink-jet ink is not clear, but is estimated as follows.

In conventional water-based inks, sufficient adhesion to a recording medium such as a polyolefin film cannot be obtained. 1) The landed ink droplets are difficult to get wet on the surface of the recording medium. 2) Ink film and recording after drying It is considered that the affinity with the medium surface is low. On the other hand, in the present invention, the ink film after drying contains “(meth) acrylic resin having (hydrophobic) alicyclic hydrocarbon group”, so that the (meth) acrylic resin and polar It is thought that the affinity with a low polyolefin film is increased. As a result, it is considered that a strong interaction occurs between the ink film and the polyolefin-based film, and the ink adhesion can be improved. In addition, by adding a water-soluble solvent (ΣSP is an organic solvent having a surface tension of 8 MPa ^1/2 or more and 18 MPa ^1/2 or less) having a low surface tension to the ink, the wettability to a polyolefin film having a low surface energy is improved. It is considered that the ink adhesion can be further enhanced.

  In addition, water-based inks containing a conventional (meth) acrylic resin that does not have an alicyclic hydrocarbon group accumulate ink droplets little by little around the nozzle holes on the nozzle plate surface after long-term use. It was easy to cause a defect. On the other hand, in the present invention, since the ink contains “(meth) acrylic resin having an alicyclic hydrocarbon group”, ink droplets hardly accumulate around the nozzle holes on the nozzle plate surface. It was found that high discharge stability can be obtained. This is because the “(meth) acrylic resin having an alicyclic hydrocarbon group” is a layer made of a water repellent having a bulky alicyclic hydrocarbon group having a bulky substituent applied to the nozzle plate surface. It is thought that this is because a three-dimensional repulsive action is generated against the nozzle hole and hardly adsorbs to the nozzle hole periphery.

1. Water-based inkjet ink The water-based inkjet ink used in the present invention contains a color material, a fixing resin, a water-soluble organic solvent, and water.

Fixing Resin The fixing resin includes a (meth) acrylic resin having an alicyclic hydrocarbon group. An alicyclic hydrocarbon group is an alicyclic hydrocarbon group having 5 to 10 carbon atoms; examples thereof include a cyclopentyl group, a cyclohexyl group, a cycloheptanyl group, a cyclooctyl group, a cyclodecanyl group, and an isobornyl group. A cycloalkyl group; a cyclopentadienyl group, a cyclopentenyl group and the like are included, and a cyclohexyl group is preferable.

  The (meth) acrylic resin having an alicyclic hydrocarbon group includes a certain amount of structural units derived from a (meth) acrylic acid ester having an alicyclic hydrocarbon group at the ester site. That is, the (meth) acrylic resin can be a copolymer of a (meth) acrylic acid ester having an alicyclic hydrocarbon group and another monomer copolymerizable therewith.

Examples of (meth) acrylic acid esters having an alicyclic hydrocarbon group include
Cyclohexyl methacrylate, cyclohexyl acrylate, dicyclopentenyl acrylate, dicyclopentenyloxyethyl acrylate, dicyclopentanyl acrylate, dicyclopentenyloxyethyl methacrylate, dicyclopentenyloxyethyl methacrylate, And monofunctional (meth) acrylic acid esters such as dicyclopentanyl methacrylate;
Bifunctional (meth) acrylic acid esters such as cyclohexane dimethanol diacrylate, cyclohexane dimethanol dimethacrylate, dimethylol tricyclodecane diacrylate and dimethylol tricyclodecane dimethacrylate are included. The (meth) acrylic acid ester monomer having an alicyclic hydrocarbon group may be one type or a combination of two or more types.

  Among these, from the viewpoint of good adhesion to a polyolefin film, a (meth) acrylic acid ester monomer containing a cyclohexyl group is preferable, and cyclohexyl acrylate or cyclohexyl methacrylate is more preferable.

  Other monomers copolymerizable with (meth) acrylic acid ester having an alicyclic hydrocarbon group include (meth) acrylic acid ester having no alicyclic hydrocarbon group, unsaturated acid, aromatic vinyl compound, etc. It is possible.

  Examples of (meth) acrylic acid ester having no alicyclic hydrocarbon group include (meth) acrylic acid alkyl ester. The number of carbon atoms in the alkyl of the (meth) acrylic acid alkyl ester is preferably 1 to 12, and more preferably 1 to 8. Examples of the (meth) acrylic acid alkyl ester include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and the like.

  (Meth) acrylic acid ester which does not have an alicyclic hydrocarbon group may be one kind, or may combine two or more kinds. Preferred examples of combinations of (meth) acrylic acid esters not having two or more types of alicyclic hydrocarbon groups include methyl methacrylate, alkyl acrylate (alkyl having 1 to 12 carbon atoms), and methacryl Combinations of acid alkyl esters (alkyl having 2 to 12 carbon atoms) are included.

  Examples of the unsaturated acid include α, β-unsaturated acids such as acrylic acid and methacrylic acid; unsaturated group-containing dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid.

  At least a part of the acidic groups of the unsaturated acid is preferably neutralized with a base from the viewpoint of increasing the solubility in an aqueous solvent (a mixture of a water-soluble organic solvent and water). Examples of the base to be neutralized include alkali metal or alkaline earth metal hydroxides (for example, NaOH, KOH, etc.); amines (for example, alkanolamine, alkylamine, etc.); ammonia and the like. Among them, the resin neutralized with at least one of ammonia and amines is such that at least one of ammonia and amines evaporates from the ink after fixing on the recording medium together with the aqueous solvent. The solubility of the removed resin is reduced. A cured ink film containing such a resin is preferable because it has water resistance. Of these, amines are preferable, and specific examples thereof include triethylamine, 2-dimethylaminoethanol, 2-di-n-butylaminoethanol, methyldiethanolamine, 2-amino-2-methyl-1-propanol, and diethanolamine. , Triethanolamine, 2-methylaminoethanol and the like.

  Examples of the aromatic vinyl compound include styrene and α-methylstyrene.

  The content ratio of the structural unit derived from the (meth) acrylic acid ester having an alicyclic hydrocarbon group in the (meth) acrylic resin having an alicyclic hydrocarbon group is 10 mass with respect to all the structural units constituting the resin. % Or more and less than 50% by mass, more preferably 10% by mass or more and less than 30% by mass. By setting the content ratio of the structural unit derived from the (meth) acrylic acid ester having an alicyclic hydrocarbon group to a certain level or more, the adhesion to the polyolefin film can be sufficiently increased, and the discharge stability can be easily obtained. By making the content rate of the structural unit derived from the (meth) acrylic acid ester having an alicyclic hydrocarbon group below a certain level, it is difficult to impair the dispersibility in water. The other copolymerizable monomer may be one kind or a combination of two or more kinds.

  The acid value of the (meth) acrylic resin having an alicyclic hydrocarbon group is preferably 50 to 300 mgKOH / g, and more preferably 50 to 130 mgKOH / g. When the acid value of the resin is 50 mgKOH / g or more, sufficient solubility in water can be easily obtained, and the resin can be sufficiently dissolved in an aqueous solvent. On the other hand, when the acid value of the resin is 300 mgKOH / g or less, the ink film does not become too soft, and thus it is difficult to impair the abrasion resistance.

  The acid value of the resin refers to the number of milligrams of potassium hydroxide required to neutralize the acid contained in 1 g of the resin; measured by acid value measurement and hydrolysis acid value measurement (total acid value measurement) of JIS K 0070. can do.

  Although the content of the neutralizing base depends on the acid value and content of the resin, it is set so that the number of chemical equivalents is 0.5 to 5 times the number of chemical equivalents of acidic groups contained in the resin. It is preferable. By making the content of the neutralizing base 0.5 times or more with respect to the number of chemical equivalents of the acidic groups contained in the resin, the effect of improving the dispersibility of the (meth) acrylic resin can be sufficiently obtained. On the other hand, when the content of the neutralizing base is 5 times or less the number of chemical equivalents of acidic groups contained in the resin, it is possible to suppress a decrease in water resistance, discoloration, odor and the like of the ink film.

  The (meth) acrylic resin having an alicyclic hydrocarbon group is not particularly limited as long as it can be dissolved or dispersed in an aqueous solvent, and may be a water-soluble resin or aqueous dispersed polymer fine particles. Especially, since the solubility with respect to an aqueous solvent and stability are high, it is more preferable that the (meth) acrylic resin which has an alicyclic hydrocarbon group is a water-soluble resin.

The weight average molecular weight (Mw) of the (meth) acrylic resin having an alicyclic hydrocarbon group is preferably 2.0 × 10 ^{4 to} 8.0 × 10 ⁴ , and 2.5 × 10 ^{4 to} 7. More preferably, it is 0 × 10 ⁴ . When the weight average molecular weight is 2.0 × 10 ⁴ or more, the fixing ability of the ink can be increased to a certain level, so that sufficient abrasion resistance is easily obtained. On the other hand, when the weight average molecular weight (Mw) is 8.0 × 10 ⁴ or more, a decrease in ejection stability from the nozzle due to an increase in the viscosity of the ink can be suppressed.

  The glass transition temperature (Tg) of the (meth) acrylic resin having an alicyclic hydrocarbon group is preferably 30 to 100 ° C. When Tg is 30 ° C. or higher, an image having sufficient abrasion resistance is easily obtained, and there is little possibility of blocking. On the other hand, when Tg is 100 ° C. or lower, it is considered that the ink film after drying does not become too hard and brittle, and it is difficult to impair the abrasion resistance.

  The content of the (meth) acrylic resin having an alicyclic hydrocarbon group is preferably 3 to 10% by mass, and more preferably 5 to 10% by mass with respect to the entire ink. When the content of the resin is 3% by mass or more, a color material such as a pigment is easily attached on the recording medium. On the other hand, when the content of the fixing resin is 10% by mass or less, it is easy to suppress a decrease in ejection stability due to an increase in ink viscosity.

  The fixing resin may further include other resins than the (meth) acrylic resin having the alicyclic hydrocarbon group, if necessary. Examples of such other resins include (meth) acrylic resins having no alicyclic hydrocarbon group, polyurethane resins, polyamide resins, polyester resins, polyolefin resins, and the like.

Colorant The colorant can be a pigment or a dye. A pigment is preferable from the viewpoint of enhancing the abrasion resistance of the obtained image.

  The pigment may be a known inorganic pigment, organic pigment, carbon black, or the like. Of these, carbon black and organic pigments are preferred from the viewpoints of good color development, low specific gravity, and difficulty in sedimentation during dispersion.

  Examples of carbon black include furnace black, lamp black, acetylene black, channel black and the like (CI Pigment Black 7). 2300, 900, MCF88, no. 20B, no. 33, no. 40, no. 45, no. 52, MA7, MA8, MA100, no. 2200B, etc. (all trade names, manufactured by Mitsubishi Chemical Corporation), color black FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Pretex 35, U, V, 140U, Special Black 6, 5, 4A 4, 250, etc. (all trade names, manufactured by Degussa), Conductex SC, Raven 1255, 5750, 5250, 5000, 3500, 1255, 700, etc. (all trade names, manufactured by Columbia Carbon Co., Ltd.), Regar 400R, 330R, 660R, mogul L, Monarch 700, 800, 880, 900, 1000, 1100, 1300, 1400, Elftex 12, etc. (all trade names, manufactured by Cabot Corporation).

  Examples of organic pigments include quinacridone pigments, quinacridone quinone pigments, dioxazine pigments, phthalocyanine pigments, anthrapyrimidine pigments, anthanthrone pigments, indanthrone pigments, flavanthrone pigments, perylene pigments, diene pigments. Ketopyrrolopyrrole pigments, perinone pigments, quinophthalone pigments, anthraquinone pigments, thioindigo pigments, benzimidazolone pigments, isoindolinone pigments, azomethine pigments and azo pigments are included.

Specific examples of the organic pigment include the following.
Examples of pigments used in cyan ink include C.I. I. Pigment blue 1, 2, 3, 15: 3, 15: 4, 15:34, 16, 22, 60, etc .; C.I. I. Bat blue 4, 60 and the like, preferably C.I. I. Pigment Blue 15: 3, 15: 4, and 60.

  Examples of pigments used in magenta ink include C.I. I. Pigment Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 112, 122, 123, 168, 184, 202, C.I. I. Pigment violet 19 and the like, preferably C.I. I. Pigment red 122, 202, 209, and C.I. I. Pigment Violet 19.

  Examples of pigments used in yellow ink include C.I. I. Pigment Yellow 1, 2, 3, 12, 13, 14C, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 128, 129, 138, 150, 151, 154, 155, 180, 185, etc., preferably C.I. I. Pigment Yellow 74, 109, 110, 128, and 138.

  The pigment content can be about 0.5% to 20% by mass, preferably about 1% to 10% by mass, based on the total ink.

  In order to stably disperse the pigment, the pigment is preferably contained in the ink as a pigment dispersion. The pigment dispersion may be a pigment dispersion in which a pigment is dispersed with a dispersion resin; it may be a capsule pigment in which the pigment is coated with a water-insoluble resin; Alternatively, a dispersible self-dispersing pigment may be used.

  In the present invention, since the fixing resin includes the (meth) acrylic resin having the above-described highly hydrophobic alicyclic hydrocarbon group, it tends to interact with the pigment fine particles and tends to make it difficult to disperse the pigment fine particles. Therefore, in order to facilitate the stable dispersion of the pigment fine particles in the aqueous solvent, the pigment fine particles are preferably dispersed with the dispersion resin.

Dispersion resin The dispersion resin is preferably a block copolymer containing a hydrophobic block composed of a hydrophobic monomer and a hydrophilic block composed of a hydrophilic monomer. The hydrophobic block of such a block copolymer is likely to interact with the pigment; the hydrophilic block is likely to interact with the aqueous solvent, so that the pigment is easily dispersed in the aqueous solvent.

  The block copolymer containing a hydrophobic block and a hydrophilic block is preferably a block copolymer obtained by a living radical polymerization method. Compared to ordinary block copolymers, block copolymers obtained by the living radical polymerization method have a main chain portion that is precisely divided into hydrophobic blocks and hydrophilic blocks, and hydrophobic blocks or hydrophilic groups. Since the base portions tend to be densely present, the characteristics of each block are easily developed. As a result, it is expected to prevent the formation of a bridge structure between the pigment particles and the fixing resin or between the pigment particles because of its excellent adsorptivity to the pigment particles and its steric hindrance effect. In the present invention, since the fixing resin contains the (meth) acrylic resin having the alicyclic hydrocarbon group, the hydrophobicity is relatively high, and it is more important to improve the dispersibility and discharge stability of the pigment particles. . Also from such a viewpoint, the dispersion resin is preferably a block copolymer obtained by a living radical polymerization method.

  Specifically, the living radical polymerization method is an atom transfer radical polymerization method (ATRP method, SHIJIE DING et al. Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 42, 5794-5801 (2004)), nitroxide method. (NMP method, Chemical Review (2001) 101, p3661), reversible addition-cleavage chain transfer polymerization method (RAFT method, Japanese translations of PCT publication No. 2000-515181), and other special publications 2008-527130 This can be done with reference to the described method.

  Examples of hydrophobic monomers constituting the hydrophobic block include benzyl methacrylate, butyl methacrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, lauryl methacrylate, stearyl methacrylate, phenyl methacrylate, phenoxy Ethyl methacrylate, methacrylonitrile, glycidyl methacrylate, p-tolyl methacrylate, sorbyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, lauryl acrylate, stearyl acrylate, phenyl acrylate Les , Phenoxyethyl acrylate, acrylonitrile, glycidyl acrylate, p-tolyl acrylate, sorbyl acrylate, styrene, α-methyl styrene, substituted styrene, N-alkyl acrylamide, N-alkyl methacrylamide, vinyl acetate, vinyl butyrate, and benzoic acid Vinyl etc. are included.

  Examples of hydrophilic monomers constituting the hydrophilic block include methacrylic acid, acrylic acid, maleic acid, maleic acid monoester, itaconic acid, itaconic acid monoester, crotonic acid, crotonic acid monoester, N, N-dimethylamino. Ethyl methacrylate, N, N-diethylaminoethyl methacrylate, N, N-dimethylaminoethyl acrylate, N, N-diethylaminoethyl acrylate, t-butylaminoethyl methacrylate, t-butylaminoethyl acrylate, vinylpyridine, N-vinylpyridine, And 2-acrylamido-2-propanesulfonic acid and the like. However, the hydrophobic monomer and the hydrophilic monomer constituting the dispersion resin are not limited to these; the dispersion resin is a block including a hydrophobic block and a hydrophilic block obtained by a living radical polymerization method. A preferred embodiment is a copolymer.

  Examples of commercially available block copolymers obtained by living radical polymerization include EFKA4585 (BASF), EFKA7701 (BASF), BYK2012 (BYK), BYK2015 (BYK), etc. It is.

  The dispersion resin may further include other dispersion resins. The other dispersion resin is preferably a water-soluble resin; examples of such water-soluble resins include styrene-acrylic acid-acrylic acid alkyl ester copolymers, styrene-acrylic acid copolymers, styrene-maleic resins. Acid copolymer, styrene-maleic acid-alkyl acrylate copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-alkyl acrylate copolymer, styrene-maleic acid half ester copolymer, vinyl Naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer, and the like are included. The water-soluble resin may be a water-soluble resin that can be used as a fixing resin.

  The water-insoluble resin in the capsule pigment is a resin that is insoluble in water in a weakly acidic to weakly basic range. Specifically, a resin having a solubility in an aqueous solution having a pH of 4 to 10 is 2% or less. Examples of water-insoluble resins include acrylic resins, styrene-acrylic resins, acrylonitrile-acrylic resins, vinyl acetate resins, vinyl acetate-acrylic resins, vinyl acetate-vinyl chloride resins, polyurethane resins, silicon- Examples include acrylic resins, acrylic silicon resins, polyester resins, and epoxy resins. The average particle diameter of the capsule pigment is preferably about 80 to 200 nm from the viewpoints of ink storage stability, color developability, and the like.

  The capsule pigment can be produced by a known method. For example, a water-insoluble resin is dissolved in an organic solvent (for example, methyl ethyl ketone), and a base component is further added to partially or completely neutralize acidic groups contained in the water-insoluble resin. A pigment and ion-exchanged water are added to the obtained solution and mixed and dispersed. Thereafter, the organic solvent is removed from the obtained solution, and ion-exchanged water is further added as necessary to prepare a capsule pigment. Alternatively, there is a method in which a monomer is added to a solution in which a pigment and a polymerizable surfactant are dispersed and a polymerization reaction is performed to coat the pigment with a resin.

The weight average molecular weight (Mw) of the dispersion resin and the water-insoluble resin is preferably 3.0 × 10 ^{3 to} 5.0 × 10 ⁵ , more preferably 7.0 × 10 ^{3 to} 2.0 × 10 ⁵ . is there.

  The acid value and amine value of the dispersion resin are each preferably 0 to 100 mgKOH / g, and more preferably 7 to 50 mgKOH / g. If the acid value or amine value of the resin is above a certain level, sufficient solubility in water can be easily obtained, and the pigment can be sufficiently dispersed in an aqueous solvent. The acid value and amine value of the dispersion resin can be measured by potentiometric titration.

  Specifically, the acid value of the dispersion resin means the number of mg of KOH required to neutralize 1 g of the solid content of the dispersion resin, and can be measured by the method described in JIS K0070. The amine value of the dispersion resin means the number of mg of KOH equivalent to the amount of HCl required to neutralize 1 g of the solid content of the dispersion resin, and can be measured by the method described in JIS K7237.

  The glass transition temperature (Tg) of the dispersion resin and the water-insoluble resin is preferably about −30 to 100 ° C., more preferably about −10 to 80 ° C.

  The mass ratio of the pigment to the dispersion resin is preferably 100/150 to 100/30 for the pigment / dispersion resin. When the dispersion resin is above a certain level, the pigment is easily dispersed well even in the case of the ink containing the (meth) acrylic resin having the alicyclic hydrocarbon group. If the dispersion resin is below a certain level, there is no possibility that the viscosity will increase too much. From the viewpoint of enhancing the durability of the image, the ejection stability of the ink, and the storage stability, it is more preferably 100/100 to 100/40.

  The pigment can be dispersed by, for example, a ball mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet jet mill, paint shaker, or the like. From the viewpoint of removing the coarse particles of the pigment dispersion and making the particle size distribution of the pigment fine particles uniform, the pigment dispersion is subjected to a centrifugal separation process or a filtration process using a filter before being added to the ink. Also good.

  The self-dispersing pigment may be a commercial product. Examples of commercially available self-dispersing pigments include CABO-JET200, CABO-JET300 (manufactured by Cabot Corp.), Bonjet CW1 (manufactured by Orient Chemical Industries Ltd.), and the like.

Water-soluble organic solvent-soluble organic solvents, the sum ΣSP polarity section and hydrogen bond in the dissolution parameters, ^{8 MPa 1/2} or ^{18 MPa 1/2} or less, the range preferably of ^{8 MPa 1/2} or ^{15 MPa 1/2} or less It is preferable to contain at least one organic solvent. Since such organic solvents have low surface tension, they make the ink easy to wet even on recording media with low surface energy; specifically, non-water-absorbing or low-water-absorbing recording media such as polyolefin-based films. Ink adhesion can be improved.

The solubility parameter (SP) is a value generally used as an indicator of solubility and derived from the cohesive energy of molecules. In addition, in the Hansen parameter obtained by dividing the solubility parameter into the contribution terms of the dispersion component, the polar component, and the hydrogen bond component, the hydrogen bond component is represented by a hydrogen bond term (σh), and the polar component is represented by a polar term (σp). Is (MPa) ^1/2 .

  For example, there is a detailed description in Polymer HandBook (Second Edition) Chapter IV, Solubility Parameter Value, and the hydrogen bond term (σh) and the polar term (σp) of the organic solvent used in the present invention are the above Polymer HandBook (SequionE). Chapter VII p. 686 Table. The value calculated using the energy contribution term for the atomic group described in 4 was used. Further, the sum ΣSP of the polar term and the hydrogen bond term in the solubility parameter (hereinafter sometimes simply referred to as ΣSP) is the sum of the polar term (σp) and the hydrogen bond term (σh) defined in the Hansen parameter described above. It can be calculated by ΣSP = δp + δh.

Examples of organic solvents having ΣSP of 8 MPa ^1/2 or more and 18 MPa ^1/2 or less include propylene glycol monopropyl ether, 3-butoxy-N, N-dimethylpropionamide, propylene glycol monobutyl ether, diethylene glycol monobutyl ether, dipropylene glycol Monomethyl ether, triethylene glycol monobutyl ether, ethylene glycol diacetate, ethylene glycol monoethyl ether acetate, dipropylene glycol monoethyl ether, 1-octanol, dipropylene glycol monopropyl ether, 3-methoxy-N, N-dimethylpropionamide , Tetraethylene glycol dimethyl ether, cyclohexanone, diethylene glycol diethyl ether, dipropylene glycol Examples include coal dimethyl ether, tripropylene glycol monomethyl ether, and tripropylene glycol dimethyl ether. Among them, since the likely increase the wettability to the recording medium, dipropylene glycol monopropyl ether (ΣSP ^{= 14.3MPa} 1/2), 3- butoxy -N, N-dimethyl propionamide (.SIGMA.SP = 13.8 MPa ^{1 / 2} ), dipropylene glycol monomethyl ether (ΣSP = 16.2 MPa ^1/2 ) and the like are preferable.

  Examples of other organic solvents include 1,2-alkanediols and alcohols. Examples of 1,2-alkanediols include 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-heptanediol, and the like. Examples of alcohols include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol and the like.

The total content of the water-soluble organic solvent is preferably in the range of 5.0% by mass to 40% by mass with respect to the entire ink. Among them, the content of the organic solvent having ΣSP of 8 MPa ^1/2 or more and 18 MPa ^1/2 or less is 30% by mass or more with respect to the total content of the water-soluble organic solvent, or 5.0% by mass or more with respect to the whole ink Of these, the larger one is preferable.

  The total amount of water and the water-soluble organic solvent is preferably adjusted so that the viscosity of the ink falls within the range described below, and can be, for example, about 60 to 95% by mass with respect to the entire ink.

  The water-based inkjet ink may further contain other components as necessary. Examples of other components include surfactants, preservatives, antifungal agents, rust preventives, antifoaming agents, viscosity modifiers, penetrants, pH adjusters, drying inhibitors (eg urea, thiourea, ethylene urea) Etc.) are included.

  The surfactant can easily spread the water-based ink on the recording medium. The surfactant is not particularly limited, but it can easily spread the ink even on a non-water-absorbing recording medium (for example, polyolefin film) or a low water-absorbing recording medium (for example, printing paper). An agent or a fluorosurfactant is preferred. By including a silicon-based surfactant or a fluorine-based surfactant in the ink, the dot diameter of the landed ink droplet can be greatly increased, and a high-quality image with high density and no unevenness can be formed.

  Preferred examples of the silicon-based surfactant include a polyether-modified polysiloxane compound. Examples of commercially available products include KF-351A and KF-642 manufactured by Shin-Etsu Chemical Co., Ltd., BYK331 and BYK333 manufactured by Big Chemie. , BYK345, BYK347, BYK348, and the like.

  The fluorine-based surfactant may be a compound in which at least a part of hydrogen atoms bonded to the carbon atoms constituting the hydrophobic group is substituted with a fluorine atom in a normal surfactant. Of these, a fluorosurfactant having a perfluoroalkyl group is preferred.

  Examples of commercially available fluorosurfactants include DIC's product name: Megafac F, Asahi Glass Co., Ltd. Product name: Surflon, Minnesota Mining & Manufacturing Company Name: Fluorad FC, manufactured by Imperial Chemical Industry, Inc. Product name: Monflor, manufactured by EI Dupont Nemeras & Company, Inc. Product name: Zonyls, Farbevelke Hoechst : Licobet VPF, Neos Co., Ltd. Trade name: Footagent, Big Chemie Co., Ltd. Trade name: BYK340 (surface conditioner, fluorine-modified polymer) and the like.

  The content of the surfactant is preferably adjusted so that the surface tension of the ink is 15 mN / m or more and less than 35 mN / m so that the ink is wet and spread on the recording medium. Specifically, the content is preferably 0.01% by mass or more and less than 2.0% by mass with respect to the entire ink.

  The antiseptic and the antifungal agent have a function of maintaining the storage stability of the ink for a long period of time. The preservative and the antifungal agent are not particularly limited, and for example, aromatic halogen compounds (for example, Preventol CMK), methylene dithiocyanate, halogen-containing nitrogen sulfur compounds, 1,2-benzisothiazolin-3-one (for example, PROXEL) GXL).

Ink physical properties In the present invention, the water-based inkjet ink has a viscosity at 25 ° C. in the range of 1 mPa · s or more and less than 50 mPa · s from the viewpoint of obtaining good ejection stability, and preferably 3 to 20 mPa · s. A range is more preferable. The viscosity of the ink can be measured by adjusting the ink temperature to 25 ° C. and using a vibration viscometer (Viscomate VM-1L, manufactured by CBC Materials).

  The surface tension of the water-based inkjet ink of the present invention at 25 ° C. is preferably 15 mN / m or more and less than 35 mN / m in order to make the ink easily spread even on a low water-absorbing or non-water-absorbing recording medium. More preferably, it is 20-30 mN / m. The surface tension of the ink can be measured by a platinum plate method at 25 ° C. using a surface tension meter CBVP-Z manufactured by Kyowa Interface Science.

  The difference between the surface tension of the water-based inkjet ink at 25 ° C. and the surface tension of the recording medium at 25 ° C. is preferably 20 mN / m or less, and more preferably 10 mN / m or less.

2. Inkjet recording method The inkjet recording method of the present invention includes 1) a step of discharging a water-based inkjet ink onto a recording medium; and 2) a step of heating and drying the aqueous inkjet ink discharged onto the recording medium. The water-based inkjet ink can be the above-described water-based inkjet ink.

  The recording medium can be a recording medium having water absorption, a recording medium having low water absorption, or a recording medium having no water absorption.

  Examples of the recording medium having water absorption include plain paper, fabric, inkjet exclusive paper, inkjet glossy paper, cardboard, and wood. Examples of recording media with low water absorption include coated paper such as printing paper; examples of commercially available products include Ricoh Business Cogross 100 (manufactured by Ricoh Co., Ltd.), OK Top Coat +, OK Kanto +, SA Kanofuji + (Oji Paper Co., Ltd.) etc. are included.

  Examples of the recording medium having no water absorption include a resin substrate, a metal substrate, a glass substrate, and the like, and preferably a resin substrate made of a hydrophobic resin. Examples of the substrate made of a hydrophobic resin include a polyolefin film, a polystyrene film, a vinyl chloride film, a polyethylene terephthalate (PET) film, and the like. Especially, since the above-mentioned water-based inkjet ink can adhere favorably, a polyolefin-type film is preferable and it is more preferable that it is a polyethylene or a polypropylene film.

  The polyolefin film may be surface-treated or not surface-treated. By using the water-based ink-jet ink described above, it is possible to satisfactorily fix even a polyolefin film that has not been surface-treated.

  The wetting tension of the polyolefin film is preferably 30 mN / m or more and less than 40 mN / m, and more preferably 30 mN / m or more and 35 mN / m or less.

  The wetting tension of the film can be measured according to JIS K 6768: 1999 “Plastic-film and sheet-wetting tension test method”. That is, a tension checker pen (manufactured by Kasuga Denki Co., Ltd.) according to JIS K 6768: 1999 is prepared as a test liquid mixture having different wetting tensions. And these mixed liquids for a test are dripped and apply | coated to the surface of a film test piece, the state of the center part of the liquid film when 2 second passes is visually observed, and wetting is determined. The numerical value of the surface tension of the mixed solution determined to be able to wet the surface of the test piece accurately in 2 seconds is defined as the wet tension of the test piece.

  Ink jet ink can be discharged using an ink jet recording apparatus as will be described later.

  The recording medium is preferably heated so that the surface temperature of the recording medium is 40 ° C. or higher and 60 ° C. or lower. When the surface temperature of the recording medium is 40 ° C. or higher, drying of the ink can be promoted, and adhesion to the recording medium can be improved. If the surface temperature of the recording medium is 60 ° C. or less, the ink can be sufficiently leveled. The heating of the recording medium may be performed before recording, may be performed after recording, or a combination thereof.

  The heating method is not particularly limited, and there are a method of heating the back surface of the recording medium, a method of heating the surface with infrared rays or the like immediately before the recording medium is conveyed under the head, and the like. The heating means is not particularly limited, and may be an infrared heater, heating wire, UV lamp, gas, hot air dryer or the like, preferably a heating wire, infrared heater or the like.

  In order to accelerate the drying of the ink and enhance the durability of the image, it is preferable to further heat the ink film dried on the recording medium at a temperature of 55 ° C. or higher and lower than 100 ° C.

  As described above, the water-based inkjet ink of the present invention includes “(meth) acrylic resin having a certain number of alicyclic hydrocarbon groups” as a fixing resin. Since the (meth) acrylic resin has a bulky alicyclic hydrocarbon group, it tends to cause a steric repulsion effect on a layer made of a water repellent having a bulky substituent applied to the nozzle plate surface, It is difficult to adhere to the periphery of the nozzle hole. Therefore, even when ink is ejected for a long time, nozzle clogging is unlikely to occur and high ejection stability can be achieved.

  Further, the ink film discharged onto the recording medium is dried by heating and solidified. Since the (meth) acrylic resin contained in the ink film after heat drying has high hydrophobicity derived from an alicyclic hydrocarbon group, it can have high adhesion to a polyolefin film as a recording medium. . Therefore, it is possible to form a high-definition and excellent scratch-resistant image even on a hard-to-adhere recording medium such as a polyolefin film.

  The ink jet recording apparatus used in the ink jet recording method of the present invention includes a single pass recording method and a scan recording method. A single-pass recording method is preferable from the viewpoint of high-speed recording, although it may be selected according to the required image resolution and recording speed.

  FIG. 1 is a diagram illustrating an example of a configuration of a main part of a single-pass recording type inkjet recording apparatus. As shown in FIG. 1, the inkjet recording apparatus 10 includes a head unit 11 that accommodates a plurality of heads 111 to 114, and a heating unit 13 that covers the entire width of the recording medium 12 and that is disposed on the upstream side of the head unit 11. And a heating unit (not shown) that is disposed on the downstream side of the head unit 11 and heats the back surface of the recording medium 12.

  The head unit 11 is fixedly arranged so as to cover the entire width of the recording medium 12, and includes a plurality of heads 111 to 114 provided for each color. The heads 111 to 114 may be an on-demand type or a continuous type. Discharge methods include electro-mechanical conversion methods (eg, single cavity type, double cavity type, bender type, piston type, shear mode type, shared wall type, etc.), electro-thermal conversion methods (eg, thermal ink jet type, Bubble jet (registered trademark) type or the like. In particular, it is preferable to use a piezo ink jet recording head having a nozzle diameter of 30 μm or less.

  The nozzle holes 15 of the heads 111 and 112 or the heads 113 and 114 are arranged alternately (see FIG. 2). When increasing the printing width, a line head unit in which the heads are arranged alternately may be used (see FIG. 3).

  The heating means 13 is an infrared heater or the like disposed on the upstream side of the head unit 11 in the conveyance direction of the recording medium 12, and can preheat the recording medium 12 before recording.

  The ink jet recording apparatus 10 may have a coating roller 14 as necessary. The application roller 14 is arranged on the upstream side in the transport direction of the recording medium 12 of the head unit 11 so that the processing liquid can be applied to the recording medium 12.

  In the single-pass inkjet recording apparatus 10, the surface of the recording medium 12 is heated in advance by the heating unit 13. You may apply | coat a process liquid on the recording medium 12 as needed. Then, the recording medium 12 is transported to the head unit 11, and ink is ejected from the heads 111 to 114 of the head unit 11 to adhere (land) on the recording medium 12. Then, the back surface of the recording medium 12 is heated by a heating means (not shown), and the ink droplets attached on the recording medium 12 are heated and dried.

  FIG. 4 is a diagram illustrating an example of a configuration of a main part of the scan recording type inkjet recording apparatus 40. As shown in FIG. 4, the ink jet recording apparatus 40 includes a head unit 41 that is narrower than the entire width of the recording medium 12 and accommodates a plurality of heads 411 to 415, and the head unit 41 in the width direction of the recording medium 12. It has a guide part 42 for moving, and a heating means 43 for heating the back surface of the recording medium of the head unit 41.

  In the scan recording type inkjet recording apparatus 40, the head unit 41 ejects ink from the heads 411 to 415 accommodated in the head unit 41 while moving in the width direction of the recording medium 12 along the guide portion 42. After the head unit 41 has completely moved in the width direction of the recording medium 12 (for each pass), the recording medium 12 is fed by the conveyance roller 45. Then, the back surface of the recording medium 12 is heated by the heating unit 43 to dry the ink droplets.

  In the following, the invention will be described in more detail with reference to examples. These examples do not limit the scope of the present invention.

1. Ink materials 1) Fixing resin (Synthesis of fixing resin P-1)
50 parts of methyl ethyl ketone was added to a flask equipped with a dropping funnel, a nitrogen introducer, a reflux condenser, a thermometer and a stirring device, and heated to 75 ° C. while bubbling nitrogen. To this were added monomer (9 parts methacrylic acid, 67 parts methyl methacrylate, 9 parts ethyl acrylate and 15 parts cyclohexyl acrylate), 50 parts methyl ethyl ketone, initiator (AIBN: 2,2'-azobisisobutyro). A mixture of 0.5 part of nitrile) was dropped from the dropping funnel over 3 hours. After the dropwise addition, the mixture was further heated under reflux for 6 hours. The resulting solution was allowed to cool and then heated under reduced pressure to distill off methyl ethyl ketone to obtain a copolymer.

  On the other hand, a solution was prepared by dissolving dimethylaminoethanol corresponding to 1.05 mol of acrylic acid added as a monomer in 450 parts of ion-exchanged water. The copolymer was dissolved in this solution and further adjusted with ion exchange water to obtain a solution (resin solution) of fixing resin P-1 having a solid content concentration of 20% by mass.

(Synthesis of fixing resins P-2 to P-7)
Fixing resins P-2 to P-7 were synthesized in the same manner except that the monomer composition was changed as shown in Table 1 in the synthesis of the fixing resin P-1. Further, the weight average molecular weight of the fixing resin was appropriately adjusted depending on the initiator amount and the polymerization conditions.

  The acid value, glass transition temperature (Tg) and weight average molecular weight of the obtained fixing resin were measured according to the following methods.

(Measurement of acid value)
The acid value was measured by the method defined in JIS K0070. That is, the resin solution was dried and solidified to obtain a resin. 10 g of the obtained resin was weighed into a 300 ml Erlenmeyer flask, and about 50 ml of a mixed solvent of ethanol: benzene = 1: 2 was added to dissolve the resin. Subsequently, this solution was titrated with a 0.1 mol / L potassium hydroxide ethanol solution standardized in advance using a phenolphthalein indicator. And the acid value (mgKOH / g) was calculated | required by the following formula (1) from the quantity of the potassium hydroxide ethanol solution used for titration.

  If the resin does not dissolve in about 50 ml of a mixed solvent of ethanol: benzene = 1: 2, use either 50 ml of ethanol or about 50 ml of a mixed solvent of ethanol / pure water = 1: 1. Titration was performed.

Formula (1)
A = (B × f × 5.611) / S
(In the formula, A is the acid value of the resin (mgKOH / g), B is the amount (ml) of 0.1 mol / L potassium hydroxide ethanol solution used for titration, and f is 0.1 mol / liter potassium hydroxide ethanol solution. Factor, S is the mass of resin (g), 5.611 is 1/10 of the formula weight of potassium hydroxide (56.11 / 10))

(Measurement of glass transition temperature (Tg))
Tg was measured by the following procedure using a DSC-7 differential scanning calorimeter (Perkin Elmer) and a TAC7 / DX thermal analyzer controller (Perkin Elmer).
1) First, 10.00 mg of fixing resin was precisely weighed to two digits after the decimal point, sealed in an aluminum pan (KITNO.0219-0041), and set in a DSC-7 sample holder. The reference used an empty aluminum pan.
2) Heat-cool-heat temperature control was then performed at a measurement temperature of 0 to 130 ° C., a temperature increase rate of 10 ° C./min, and a temperature decrease rate of 10 ° C./min. Tg was measured under a nitrogen stream condition.
3) Then, in the second Heat data, an extension of the baseline before the rise of the first endothermic peak and a tangent line indicating the maximum slope between the rise portion of the first peak and the peak apex are drawn, The intersection was defined as the glass transition temperature (Tg).

(Measurement of weight average molecular weight)
The weight average molecular weight was measured using gel permeation chromatography. The measurement conditions were as follows.
(Measurement condition)
Solvent: Tetrahydrofuran Column: Tosoh TSKgel G4000 + 2500 + 2000HXL
Column temperature: 40 ° C
Injection volume: 100 μl
Detector: RI Model 504 (GL Science Co., Ltd.)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0 ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Co., Ltd.) Mw = 100000 to 500 samples were used. Thirteen samples were used at approximately equal intervals.

Table 1 shows the compositions and physical properties of the fixing resins P-1 to P-7.

2) Dispersing resin EFKA-4585 (manufactured by BASF): acrylic gradient block copolymer synthesized by living radical polymerization (acid value = 20 mgKOH)
BYK-2012 (manufactured by BASF): comb-type acrylic block copolymer synthesized by living radical polymerization method (amine value = 7 mgKOH / g, acid value = 7 mgKOH / g)
BYK-2015 (manufactured by BASF): Comb type acrylic block copolymer synthesized by living radical polymerization method (acid value = 10 mgKOH / g)
EFKA-4550 (manufactured by BASF): acrylic random copolymer (amine value = 30 mgKOH)
The acid value of each dispersion resin was measured by the method described in JIS K0070; the amine value was measured by the method described in JIS K7237.

2. Ink Preparation and Image Formation (Example 1)
Preparation of pigment dispersion To 62 parts by mass of ion-exchanged water, 20 parts by mass of EFKA-4550 (solid content 50%, manufactured by BASF) and 3 parts by mass of triethylene glycol monobutyl ether were added as a dispersion resin. To this solution, C.I. I. 15 parts by weight of Pigment Blue 15: 3 was added and premixed, and then dispersed using a sand grinder filled with 50% by volume of 0.5 mm zirconia beads to obtain a cyan pigment dispersion having a pigment solid content of 15% by weight. Obtained.

Preparation of ink Cyan pigment dispersion is 4.0% by mass (solid content concentration), fixing resin P-1 is 5.0% by mass (solid content concentration), dipropylene glycol monomethyl ether (ΣSP is 16.2 MPa ^{1 / 2} ) is 10.0% by mass, 1,2-hexanediol (ΣSP is 23.6 MPa ^1/2 ) is 8.0% by mass, dipropylene glycol monopropyl ether (ΣSP is 14.3 MPa ^1/2 organic solvent) was 5.0% by mass, and polyether-modified polydimethylsiloxane (BYK-333 manufactured by BYK-Chemie) as the silicon surfactant was 0.1% by mass. Exchanged water was further added, and each component was mixed so that it might become 100 mass%. The obtained solution was filtered with a 5 μm filter to obtain cyan ink C-1.

  As a result of measuring the viscosity and surface tension of the obtained cyan ink C-1 by the following method, the viscosity was in the range of 5 to 15 mPa · s; the surface tension was in the range of 20 to 30 mN / m.

(viscosity)
The viscosity of the ink was measured by adjusting the ink temperature to 25 ° C. and using a vibration viscometer (Viscomate VM-1L, manufactured by CBC Materials).

(Measurement of surface tension)
As for the surface tension of the ink, the surface tension at 25 ° C. was measured by a platinum plate method using a surface tension meter CBVP-Z manufactured by Kyowa Interface Science.

Image formation The prepared cyan ink C-1 was piezo-type with a nozzle diameter of 28 μm, a drive frequency of 10 kHz, a nozzle number of 512, a minimum droplet amount of 14 pl, and a nozzle density of 360 dpi (dpi represents the number of dots per 2.54 cm). The ink jet head of a scanning ink jet printer equipped with the head was loaded.

  In the ink jet printer, the recording medium can be arbitrarily heated from the back surface (the surface opposite to the surface facing the head) by a contact heater. In addition, an ink emptying position and a blade wipe type maintenance unit are provided at the head storage position so that the head can be cleaned at an arbitrary frequency.

Then, using an inkjet printer, a rectangular solid image of 10 cm × 10 cm is printed on each of the following recording media at a printing resolution of 720 dpi × 720 dpi in increments of 10% Duty from 10% Duty to 100% Duty. Respectively.
Recording medium A: Untreated polypropylene film (FP, manufactured by Futamura Chemical Co., Ltd.): Wetting tension 30 mN / m
Recording medium B: Surface-treated polyethylene film (LL-MTNAS, manufactured by Futamura Chemical Co., Ltd.): Wetting tension 36 mN / m
Recording medium C: Surface-treated polypropylene film (Santox OP-PA30, manufactured by Suntox): Wetting tension 38 mN / m

  The measurement of the wetting tension of the film was performed according to JIS K 6768: 1999 “Plastic-film and sheet-wetting tension test method”. That is, a tension checker pen (manufactured by Kasuga Denki Co., Ltd.) in accordance with JIS K 6768: 1999 was prepared as a test mixture having different wetting tensions. These test mixed liquids were dropped and applied on the surface of the film test piece, and the state of the central part of the liquid film at the time when 2 seconds passed was visually observed to determine wetting. And the numerical value of the surface tension of the liquid mixture determined to be able to wet the surface of the test piece accurately in 2 seconds was defined as the wetting tension of the test piece.

  During image formation, the back surface of the recording medium was heated with a heater so that the surface temperature of the recording medium was 50 ° C. The surface temperature of the recording medium was measured using a non-contact thermometer (IT-530N type, manufactured by Horiba, Ltd.). The distance between the nozzle surface and the recording medium was set to 1.5 mm. After the image formation, the recording medium was quickly left on a hot plate at 60 ° C. to dry the image.

(Density unevenness tolerance)
The uniformity of the image surface (density unevenness of the ink application part) of the formed 100% duty solid image part was visually observed, and the density unevenness resistance was evaluated according to the following criteria.
◎: Solid image is uniform and no unevenness is observed ○: Density unevenness in the solid image is inconspicuous, but there are scattered areas with extremely weak shading unevenness at the boundary between the solid image and the unprinted portion Δ: Density unevenness is observed in the solid image portion, and it is not recognized as a uniform solid image. ×: Occurrence of repellency and mottle is recognized in the entire image by visual observation, and many shades of a size in mm are generated. .
In the above-mentioned evaluation rank, it was judged that ○ or more was practically preferable.

(Abrasion resistance)
The image surface of the formed 100% duty solid image portion was rubbed 30 times with a dry cotton (Kanakin No. 3) under a load of 200 g. Then, the obtained image was visually observed, and the abrasion resistance was evaluated according to the following criteria.
◎: No image change is observed ○: Color transfer to the cloth is slightly observed, but no image change is observed △: Image change is slightly recognized ×: White line-shaped scratches or image peeling In the above-mentioned evaluation ranks that were recognized, it was judged that a value of ○ or more was practically preferable.

(Adhesion)
The formed 100% duty solid image part was cut into 25 square grids and then peeled off with tape. The image obtained after peeling the tape was visually observed, and the adhesion was evaluated according to the following criteria.
A: Image change is not recognized at all O: Slight peeling is observed at the cut portion.
Δ: Peeling less than 5 squares is observed.
X: Peeling of 5 squares or more is recognized.
In the above-mentioned evaluation rank, it was judged that ○ or more was practically preferable.

(Discharge stability)
The above-mentioned image formation was continuously performed 10 times in an environment of 25 ° C. and a relative humidity of 50%. Thereafter, the 10th 100% duty image was visually observed, and the ejection stability was evaluated according to the following criteria.
◎: In the formed image, no image defect due to oblique emission or nozzle missing is observed at all. ○: In the formed image writing portion (several mm), slight fading is observed, but in practical use. The quality is acceptable. △: Obvious blurring is observed in the writing portion (several mm) of the formed image, which is a practical problem. ×: In the created image, due to oblique emission or nozzle missing. In the above-mentioned evaluation rank, it was judged that “◯” or more is preferable for practical use.

(Examples 2-5, Comparative Examples 1-2)
Cyan inks C-2 to C-7 were obtained in the same manner as in Example 1 except that the type of fixing resin was changed as shown in Table 2. As a result of measuring the viscosity and the surface tension of the cyan inks C-2 to C-7 in the same manner as in Example 1, the viscosities are all in the range of 5 to 15 mPa · s; the surface tensions are all in the range of 20 to 30 mN / s. m range. Then, image formation and evaluation were performed in the same manner as in Example 1.

Table 2 shows the evaluation results of Examples 1 to 5 and Comparative Examples 1 and 2.

  As shown in Table 2, the inks C-1 to C-5 of Examples 1 to 5 are polypropylene films and polyethylene films having a lower wetting tension than the inks C-6 to C-7 of Comparative Examples 1 and 2. It can be seen that a high-definition image can be formed without density unevenness. It can also be seen that the formed image has good abrasion resistance and adhesion.

  In particular, the inks of Examples 2 to 3 containing the fixing resin P-2 or P-3 having a high content of structural units derived from cyclohexyl (meth) acrylate were very excellent even for untreated polypropylene films. It turns out that adhesiveness is shown.

  It can also be seen that the inks C-1 to C-5 of Examples 1 to 5 have less density unevenness than the inks C-6 and C-7 of Comparative Examples 1 and 2. Since the inks of Examples 1 to 5 contain a highly hydrophobic fixing resin, it is considered that the inks are easily wetted with the polypropylene film. As a result, the ink droplets easily evaporate on the film, and the viscosity of the ink droplets easily increases accordingly. Even if the next droplet lands on the adjacent position of the ink droplet whose viscosity has increased in this way, it is presumed that the density unevenness has been reduced since the coalescence of the droplet does not easily occur.

(Example 6)
Ink Preparation Cyan ink C-8 was obtained in the same manner as in Example 1 except that the dispersion resin of cyan ink C-1 was changed as shown in Table 3 in the ink preparation of Example 1. The viscosity and surface tension of cyan ink C-8 were measured in the same manner as in Example 1. As a result, the viscosity was in the range of 5 to 15 mPa · s; the surface tension was in the range of 20 to 30 mN / m.

Image formation With cyan ink C-8, nozzle diameter 28 μm, drive frequency 10 kHz, nozzle number 512, minimum droplet amount 14 pl, nozzle density 360 dpi (dpi in the present invention represents the number of dots per 2.54 cm). It was loaded into the inkjet head of a single-pass inkjet printer equipped with a piezo-type head.

  In the ink jet printer, the recording medium can be arbitrarily heated from the back surface (the surface opposite to the surface facing the head) by a contact heater. The distance between the nozzle surface and the recording medium was set to 1.5 mm.

  Then, in the same manner as in Example 1, on each recording medium, a rectangular solid image of 5 cm × 5 cm in 10% duty increments with a print resolution of 360 dpi × 360 dpi on a piece basis. It formed by the direction 1Pass printing.

  During image formation, the back surface of the recording medium was heated with a heater so that the surface temperature of the recording medium was 50 ° C. The surface temperature of the recording medium was measured using a non-contact thermometer (IT-530N type, manufactured by Horiba, Ltd.). After the image formation, the recording medium was immediately placed on a hot plate at 60 ° C. to dry the image.

  In the same manner as in Example 1, image evaluation (rubbing resistance, adhesion) and ink ejection stability were evaluated.

(Examples 7 to 9, Comparative Example 3)
Cyan inks C-9 to C-11 were obtained in the same manner as in Example 6 except that the type of the dispersion resin was changed as shown in Table 3. The viscosity and surface tension of cyan inks C-9 to C-11 were measured in the same manner as in Example 6. As a result, the viscosities were all in the range of 5 to 15 mPa · s; the surface tensions were all 20 to 30 mN / s. m range. Then, image formation and evaluation were performed in the same manner as in Example 6.

Table 3 shows the evaluation results of Examples 6 to 9 and Comparative Example 3.

  As shown in Table 3, the inks of Examples 6 to 8 including a dispersion resin that is a block copolymer obtained by living radical polymerization are more effective than the ink of Example 9 including a dispersion resin that is not a block copolymer. In addition, it can be seen that even in single pass printing, the ejection stability is good, and the formed image has good abrasion resistance and adhesion.

  According to the present invention, it is possible to provide a water-based inkjet ink that can be printed on a hardly-adherent plastic film such as a polyolefin-based film and has good ejection stability.

DESCRIPTION OF SYMBOLS 10, 40 Inkjet recording device 11, 41 Head unit 12 Recording medium 13, 43 Heating means 14 Application roller 45 Conveyance roller 111-114, 411-415 Head

Claims (4)

A step of discharging a water-based inkjet ink to a polyolefin film having a wetting tension of 30 mN / m or more and less than 40 mN / m;
A step of heating and drying the water-based inkjet ink discharged on the film,
The water-based inkjet ink includes a pigment, a dispersion resin in which the pigment is dispersed , a fixing resin, water, and a water-soluble organic solvent.
The dispersion resin is an acrylic gradient block copolymer containing a hydrophobic block and a hydrophilic block, having an acid value of 0 mgKOH / g and an amine value of 7 to 50 mgKOH / g,
The inkjet recording method in which the fixing resin contains a (meth) acrylic resin containing a structural unit derived from a (meth) acrylic acid ester having an alicyclic hydrocarbon group in an amount of 10% by mass or more and less than 50% by mass.   The inkjet recording method according to claim 1, wherein the content of the (meth) acrylic resin is 3% by mass or more and less than 10% by mass with respect to the entire water-based inkjet ink. The inkjet recording according to claim 1 or 2 , wherein the water-soluble organic solvent contains at least one organic solvent having a hydrogen parameter of the solubility parameter and a sum of polar terms ΣSP of 8 MPa ^1/2 or more and 18 MPa ^1/2 or less. Method. The alicyclic hydrocarbon having a group (meth) acrylic acid ester, containing a cyclohexyl group containing (meth) acrylic acid ester, an ink jet recording method according to any one of claims 1-3.

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