JP2007262272A - Ink composition and inkjet-recording method by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink composition recording on a recording medium of which recording surface is a plastic film, excellent in close adhesion, scratch resistance and weatherproof property such as waterproof property. <P>SOLUTION: This ink composition contains at least a lactic acid ester compound, a thermoplastic resin, a pigment, a cyclic amide compound, a surfactant, a low surface tension organic solvent and water, and is suitable for printing on the recording medium of which recording surface is the plastic film. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ink composition, and more particularly, to an ink composition suitably used for a recording medium whose recording surface is a plastic film. The present invention also relates to an ink jet recording method using such an ink composition.

  The ink jet recording method is a printing method in which printing is performed by causing droplets of an ink composition to fly and adhere to a recording surface of a recording medium. This method has a feature that high-resolution and high-quality images can be printed at high speed. Printing using the ink jet recording method is employed not only for general consumer printers used in offices, but also for industrial printers having a printing width exceeding 1 m. As the recording medium, a hydrophobic recording medium such as a plastic film is also used in addition to general paper.

  In addition to the features of the ink jet recording method, the reason why the ink jet recording method is employed in industrial printers is that an inexpensive print can be obtained even with a small number of production parts. Banners), wall coverings, interior decoration materials, etc. Since recording media and printing used for indoor and outdoor signage, etc., require strength, the recording medium is made of a plastic film as a recording medium or a medium coated with a plastic film on a substrate and is weather-resistant, such as pigment. In many cases, printing is performed with ink using an agent.

  In the case of performing ink jet recording using a plastic film made of plastic such as vinyl chloride as a recording medium, conventionally, an ink containing a curable monomer such as solvent-based ink, UV curable ink, or two-component curable ink has been used. It was used. However, the solvent-based ink has a solvent odor and may contain harmful components in the solvent volatile components. Even in a UV curable ink or a two-component curable ink, the curable monomer to be used may contain harmful components. In addition, when ink-jet recording is performed with a conventional water-based ink on a recording medium whose recording surface is not subjected to surface treatment exclusively for ink-jet recording, the recorded matter has weather resistance such as adhesion, scratch resistance, and water resistance. Was not enough.

  For example, as an aqueous pigment ink-jet ink composition that is directly printed on a hydrophobic recording medium, an ink composition including a specific graft copolymer binder has been proposed. (Japanese Patent Laid-Open No. 2000-44858 (Patent Document 1)) In this method, since the ink does not permeate the recording medium and the binder is fixed on the surface of the recording medium, UV curable ink, two-component curable ink, etc. There is a problem that adhesion to a recording medium is small as compared with the monomer curable type.

  On the other hand, for example, JP-A-2002-103785 (Patent Document 2) discloses that lactam or lactone can be used as a carrier medium substance in an ink composition for inkjet recording. (For example, claim 12 of the same document). However, here lactams and lactones are merely examples of solvents for dissolving the colorant of the ink composition, and printing on a recording medium whose recording surface is a plastic film is performed. Not suggested.

  For this reason, an ink jet recording method using an aqueous pigment ink is desired which can obtain a plastic recorded matter having excellent durability, particularly recording adhesion, scratch resistance, and water resistance such as water resistance.

JP 2000-44858 A JP 2002-103785 A

  As a result of repeated research on water-based inks for ink jet recording having sufficient weather resistance when ink jet recording is performed on a recording medium whose recording surface is a plastic film, the inventor has a specific composition containing a specific solvent. It was found that by using the recording material, the recording quality of the formed recording material and the adhesion between the recording medium and the ink composition can be improved, and the weather resistance of the recording material can be greatly improved. As a solvent to be used, a lactic acid ester compound that is miscible with water or slightly soluble in water and has volatility was more effective in achieving the above improvement. The present invention is based on these findings.

  Accordingly, an object of the present invention is to provide an ink composition suitable for ink jet recording, and suitable for printing on a recording medium whose recording surface is a plastic film. Another object of the present invention is to provide an ink jet recording method using such an ink composition.

  The ink composition according to the present invention comprises at least a lactic acid ester compound, a thermoplastic resin, a pigment, a cyclic amide compound, a surfactant, a low surface tension organic solvent, and water.

  The ink jet recording method according to the present invention preferably performs printing by ejecting droplets of an ink composition onto a recording medium having a recording surface made of a plastic film and attaching the droplets to the recording surface. The product is an ink composition according to the present invention.

<Ink composition>
As described above, the ink composition according to the present invention comprises at least a lactic acid ester compound, a thermoplastic resin, a pigment, a cyclic amide compound, a surfactant, a low surface tension organic solvent, and water.

  The ink composition according to the present invention is suitably used for printing on a recording medium whose recording surface is a plastic film.

  As a recording medium whose recording surface is a plastic film, in addition to the recording medium itself being a plastic film, a conventional recording medium substrate such as paper or fabric is plastic-coated, In addition, a product obtained by adhering a plastic film is also included. Here, the plastic is not particularly limited as long as it can be dissolved or swollen by a lactic acid ester compound, and examples thereof include vinyl chloride, polycarbonate, polystyrene, and polyurethane. The ink composition according to the present invention can be used for printing on both a plastic film not subjected to a surface treatment for inkjet printing and a plastic film subjected to a surface treatment for inkjet printing.

  When the recording surface of the ink composition according to the present invention is printed on a recording medium that is a plastic film, the lactic acid ester compound, which is a component capable of dissolving the material component of the medium such as plastic, dissolves the recording surface, and at the same time, the ink composition Since the product contains a resin component that can be cured to form a film, when the volatile component in the ink evaporates, the resin component in the ink composition is cured to form a film. At this time, a mixed layer of the melted plastic on the recording surface and the resin formed into a film is formed, and the plastic and the resin film on which the mixed layer is not formed are firmly bonded via the mixed layer. For this reason, there is almost no rubbing of the ink film due to external force or water permeation into the interface between the ink film and the recording surface, and a recorded matter having excellent weather resistance such as adhesion, scratch resistance, and water resistance can be formed. it can.

  In the ink composition according to the present invention, since the lactic acid ester compound, which is a component capable of dissolving plastic and the like, is diluted with water, the liquid contact member constituting the printer is hardly destroyed or damaged.

  Since the ink composition of the present invention has a low surface tension by including a surfactant, even if it is a water-based ink, it does not aggregate on the surface of a recording medium that does not have water absorbability, such as a plastic film, and is recorded. It spreads evenly on the surface and good recording quality is obtained.

<Lactic acid ester compound>
The ink composition according to the present invention comprises a lactic acid ester compound. In the ink jet recording, fine droplets of a liquid ink composition are attached to a recording medium, and moisture of the droplets is evaporated or permeated into the recording medium and dried to perform recording. Since the lactic acid ester compound in the ink composition has a lower vapor pressure than water, it evaporates more slowly than water. When moisture of the ink composition printed at the time of recording evaporates, the component of the lactic acid ester compound becomes high in the printed portion. The lactic acid ester compound in the ink composition according to the present invention has a property of dissolving plastic, and in the ink adhering to the recording surface, when the concentration of the lactic acid ester compound is high, the plastic constituting the recording surface is dissolved. The action to do is enhanced.

  The reason why the lactic acid ester compound is used as the component for dissolving the plastic in the ink composition of the present invention is as follows. 1) It is water soluble. 2) The 100% concentration of lactic acid ester compound dissolves or swells the plastic, but the aqueous solution below the concentration added to the ink composition does not destroy the ink contact parts of the printer. 3) Below the concentration added to the ink composition, the dispersed components such as the pigment dispersion, the pigment dispersant, and the resin emulsion are not aggregated. 4) The vapor pressure is below water. In the present invention, when the plastic soaked in the solvent is deformed, it is determined that it has dissolved or swollen.

  Examples of the lactic acid ester compound used in the ink composition of the present invention include methyl lactate, ethyl lactate, butyl lactate, amyl lactate, hexyl lactate and the like, preferably ethyl lactate and butyl lactate. Two or more kinds of these lactic acid ester compounds may be mixed and used. Even if the content of the lactic acid ester compound is 1% or less with respect to the total amount of the ink composition, it has a limited effect, but preferably 1.0 to 25.0% by weight, more preferably 2 with respect to the total amount of the ink composition. 0.0 to 15.0% by weight.

<Thermoplastic resin>
The ink composition according to the present invention comprises a thermoplastic resin. The thermoplastic resin includes an amorphous part that is not crystallized or cross-linked, and the amorphous part has a characteristic that its shape changes due to melting by heating or dissolution in a specific solvent. When the molten or dissolved thermoplastic resin is solidified again, the amorphous parts are welded together to form a strong resin layer.

  Since the thermoplastic resin in the ink composition of the present invention is dissolved in the lactic acid ester compound in the ink composition, the thermoplastic resin is dissolved and solidified in the course of drying of the ink composition of the present invention. The resins or the thermoplastic resin and the plastic film are welded to form a strong film of the thermoplastic resin on the surface of the plastic film.

  As the thermoplastic resin that can be used in the present invention, in addition to water-soluble resins, water-insoluble resins can also be used. As the resin soluble in water, a resin dispersant used to disperse the pigment can be preferably used. Moreover, it is preferable that the resin insoluble in water is added to the ink composition in the form of a resin emulsion. Here, the resin emulsion is composed of water as a continuous phase and a resin component as a dispersed phase.

  According to a preferred embodiment of the present invention, the thermoplastic resin component is preferably a polymer having both a hydrophilic portion and a hydrophobic portion. When a resin emulsion is used, the particle diameter is not particularly limited as long as the emulsion is formed, but is preferably about 150 nm or less, more preferably about 5 to 100 nm.

  As the resin, the same resin component as the resin emulsion conventionally used in the ink composition for ink jet recording can be used. Specific examples of the resin component include acrylic polymers such as polyacrylate esters or copolymers thereof, polymethacrylate esters or copolymers thereof, polyacrylonitrile or copolymers thereof, polycyanoacrylates, and polyacrylamides. , Polyacrylic acid, or polymethacrylic acid; polyolefin polymers such as polyethylene, polypropylene, polybutene, polyisobutylene, polystyrene, or copolymers thereof, petroleum resins, coumarone-indene resins, or terpene resins; vinyl acetate vinyl Alcohol-based polymers such as polyvinyl acetate or copolymers thereof, polyvinyl alcohol, polyvinyl acetal, or polyvinyl ether; halogen-containing polymers such as polyvinyl chloride or copolymers thereof , Polyvinylidene chloride, fluororesin, or fluororubber; nitrogen-containing vinyl polymer such as polyvinyl carbazole, polyvinyl pyrrolidone or copolymer thereof, polyvinyl pyridine or polyvinyl imidazole; diene polymer such as polybutadiene or copolymer thereof A polymer, polychloroprene, or polyisoprene (butyl rubber); or other ring-opening polymerization resin, condensation polymerization resin, natural polymer resin, or the like can be used.

  If the resin is obtained in the form of an emulsion, it can be prepared by mixing the resin particles in water, optionally with a surfactant. For example, an emulsion of an acrylic resin or a styrene-acrylic acid copolymer resin is composed of a (meth) acrylic ester resin or a styrene- (meth) acrylic ester resin, and optionally a (meth) acrylic resin, It can be obtained by mixing the active agent with water. The mixing ratio of the resin component and the surfactant is usually preferably about 50: 1 to 5: 1. When the amount of the surfactant used is less than the above range, it is difficult to form an emulsion, and when the amount exceeds the above range, the water resistance of the ink tends to decrease or the adhesion tends to deteriorate. Absent.

  The surfactant used in the preparation of the resin emulsion is not particularly limited, but preferred examples include anionic surfactants (for example, sodium dodecylbenzansulfonate, sodium laurylate, ammonium salt of polyoxyethylene alkyl ether sulfate, etc.) ), Nonionic surfactant (for example, polyoxyethylene alkyl ether, polyoxyethylene alkyl ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene alkylphenyl ether, polyoxyethylene alkylamine, polyoxyethylene alkylamide, etc.) These can be used as a mixture of two or more.

  The resin emulsion can also be obtained by emulsion polymerization of the above resin component monomers in water in the presence of a polymerization catalyst and an emulsifier. A polymerization initiator, an emulsifier, and a molecular weight modifier used in the emulsion polymerization can be used according to a conventional method.

  As the polymerization initiator, those used for normal radical polymerization are used, for example, potassium persulfate, ammonium persulfate, hydrogen peroxide, azobisisobutyronitrile, benzoyl peroxide, dibutyl peroxide, Examples include peracetic acid, cumene hydroperoxide, t-butyl hydroxy peroxide, paramentane hydroxy peroxide, and the like. When the polymerization reaction is performed in water, a water-soluble polymerization initiator is preferable. Examples of the emulsifier include sodium lauryl sulfate, those generally used as an anionic surfactant, nonionic surfactant or amphoteric surfactant, and mixtures thereof. These can be used in combination of two or more.

  The ratio of the resin and water as the dispersed phase component is preferably 60 to 400 parts by weight, more preferably 100 to 200 parts by weight of water with respect to 100 parts by weight of the resin.

  When a resin emulsion is used as the resin, a known resin emulsion can be used. For example, Japanese Patent Publication No. 62-1426, Japanese Patent Laid-Open No. 3-56573, Japanese Patent Laid-Open No. 3-79678, Japanese Patent Laid-Open No. 3-160068, Alternatively, the resin emulsion described in JP-A-4-18462 can be used as it is. Commercially available resin emulsions can also be used. For example, Microgel E-1002, E-5002 (styrene-acrylic resin emulsion; manufactured by Nippon Paint Co., Ltd.), Boncoat 4001 (acrylic resin emulsion; Dainippon) Ink Chemical Co., Ltd.), Boncoat 5454 (styrene-acrylic resin emulsion; Dainippon Ink and Chemicals Co., Ltd.), SAE1014 (styrene-acrylic resin emulsion; manufactured by Nippon Zeon Co., Ltd.), or Cybinol SK-200 ( Acrylic resin emulsion (manufactured by Seiden Chemical Co., Ltd.).

  In the present invention, the resin may be mixed as a fine particle powder with other components in the ink composition. However, after the resin fine particles are dispersed in an aqueous medium to form a resin emulsion, the other components of the ink composition are used. It is more preferable to mix with.

  From the viewpoint of long-term storage stability and ejection stability of the ink composition, the resin fine particles preferably used in the present invention have a particle size in the range of 5 to 400 nm, more preferably in the range of 50 to 200 nm.

  The resin is preferably included in the range of 0.1 to 15.0% by weight in terms of solid content, and more preferably in the range of 0.5 to 10.0% by weight, based on the total amount of the ink composition. preferable. If the resin component is too small in the ink composition, the ink film formed on the recording surface may become thin, and the adhesion to the recording surface may be insufficient. If the resin component is too much, the dispersion of the resin may become unstable during storage of the ink composition, or the resin component may agglomerate and solidify due to the slight evaporation of water, making it impossible to form a uniform film.

<Pigment>
The ink composition according to the present invention comprises a pigment. As the pigment, any pigment conventionally used in an aqueous ink jet recording ink composition can be used, and examples thereof include organic pigments and inorganic pigments. The pigment is a resin-dispersed pigment dispersed with a dispersant such as a water-soluble resin or a surfactant, or a surface-treated pigment that has a hydrophilic group introduced into the pigment surface and can be dispersed or dissolved in an aqueous medium without the use of a dispersant. Can be added to the ink composition. The pigment dispersant resin can be used as a thermoplastic resin as described above. Two or more kinds of pigments may be used in combination.

  As the inorganic pigment, titanium oxide and iron oxide, or carbon black produced by a known method such as a contact method, a furnace method, or a thermal method can be used.

  Examples of organic pigments include azo pigments (for example, azo lakes, insoluble azo pigments, condensed azo pigments, or chelate azo pigments), polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, verinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, A thioindigo pigment, an isoindolinone pigment, or a quinophthalone pigment), a dye chelate (for example, a basic dye chelate or an acid dye chelate), a nitro pigment, a nitroso pigment, or aniline black can be used. Of these pigments, it is preferable to use a pigment having good affinity with water.

  More specifically, as a pigment for black ink, for example, carbon black (CI pigment black 7) such as furnace black, lamp black, acetylene black, or channel black, or copper oxide, iron oxide ( CI pigment black 11), metals such as titanium oxide, and organic pigments such as aniline black (CI pigment black 1).

  Specific examples of suitable carbon black include carbon black manufactured by Mitsubishi Chemical Corporation, No. 2300, 900, MCF88, no. 20B, no. 33, no. 40, no. 45, no. 52, MA7, MA8, MA100, No2200B and the like. Degussa carbon blacks include Color Black FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Pretex 35, U, V, 140U, Special Black 6, 5, 4A, 4, 250, etc. It is done. Examples of carbon black manufactured by Columbia Carbon include Conductex SC, Raven 1255, 5750, 5250, 5000, 3500, 1255, 700, and the like. Examples of the carbon black manufactured by Cabot include Regal 400R, 330R, 660R, Mogul L, Monarch 700, 800, 880, 900, 1000, 1100, 1300, 1400, Elftex 12 and the like manufactured by Cabot.

  Examples of color ink pigments include C.I. I. Pigment Yellow 1 (Fast Yellow G), 3, 12 (Disazo Yellow AAA), 13, 14, 17, 23, 24, 34, 35, 37, 42 (Yellow Iron Oxide), 53, 55, 74, 81, 83 (Disazo Yellow HR), 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 138, 153, 154; I. Pigment Red 1, 2, 3, 5, 17, 22 (Brilliant First Scarlet), 23, 31, 38, 48: 2 (Permanent Red 2B (Ba)), 48: 2 (Permanent Red 2B (Ca)), 48 : 3 (Permanent Red 2B (Sr)), 48: 4 (Permanent Red 2B (Mn)), 49: 1, 52: 2, 53: 1, 57: 1 (Brilliant Carmine 6B), 60: 1, 63: 1, 63: 2, 64: 1, 81 (Rhodamine 6G rake), 83, 88, 92, 101 (Bengara), 104, 105, 106, 108 (Cadmium red), 112, 114, 122 (Quinacridone magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 185, 190, 193, 209, 2 9; or C. I. Pigment Blue 1, 2, 15 (phthalocyanine blue R), 15: 1, 15: 2, 15: 3 (phthalocyanine blue G), 15: 4, 15: 6 (phthalocyanine blue E), 16, 17: 1, 56 , 60, 63; and the like.

  The particle diameter of the pigment is not particularly limited, but the average particle diameter is preferably 25 μm or less, more preferably 1 μm or less. By using a pigment having an average particle diameter of 25 μm or less, the occurrence of clogging can be suppressed, and further sufficient ejection stability can be realized.

  The content of the pigment is preferably 0.5 to 15.0% by weight, more preferably 1.0 to 10.0% by weight, based on the entire ink composition.

  When the above pigment is used, it is preferable to add a dispersant to the ink so that the pigment is completely dispersed in an aqueous medium. As the dispersant used here, for example, a polymer dispersant and a surfactant can be used.

  Preferred examples of the polymer dispersant include synthetic polymers, such as polyvinyl alcohols, polyvinyl pyrrolidones, polyacrylic acid, acrylic acid-acrylonitrile copolymer, potassium acrylate-acrylonitrile copolymer, vinyl acetate- Acrylic resins such as acrylic acid ester copolymers, acrylic acid-acrylic acid ester copolymers, styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, styrene-methacrylic acid-acrylic acid ester copolymers, Styrene-acrylic resins such as styrene-α-methylstyrene-acrylic acid copolymer, styrene-α-methylstyrene-acrylic acid-acrylic acid ester copolymer, styrene-maleic acid copolymer, styrene-maleic anhydride copolymer Polymer, vinylnaphthalene-acrylic acid copolymer, vinyl Nylnaphthalene-maleic acid copolymer, vinyl acetate-ethylene copolymer, vinyl acetate-fatty acid vinyl ethylene copolymer, vinyl acetate-maleic acid ester copolymer, vinyl acetate-crotonic acid copolymer, vinyl acetate- Examples thereof include vinyl acetate copolymers such as acrylic acid copolymers and salts thereof. Among these, a copolymer of a monomer having a hydrophobic group and a monomer having a hydrophilic group, and a polymer comprising a monomer having both a hydrophobic group and a hydrophilic group in the molecular structure are preferable. The coalescence may be either a random copolymer or a block copolymer. Examples of the salt include diethylamine, ammonia, ethylamine, triethylamine, propylamine, isopropylamine, dipropylamine, butylamine, isobutylamine, triethanolamine, diethanolamine, aminomethylpropanol, morpholine, and the like. These compounds for forming a salt may be at least the neutralization equivalent of a dispersant composed of an organic substance before forming a salt. These copolymers preferably have a weight average molecular weight of 1000 to 50000, more preferably 3000 to 10,000.

  Specific examples of surfactants as dispersants include sulfonic acids such as alkane sulfonates, α-olefin sulfonates, alkyl benzene sulfonates, alkyl naphthalene sulfonic acids, acylmethyl tauric acids, and dialkyl sulfosuccinic acids. Type, alkyl sulfate ester salt, sulfated oil, sulfated olefin, polyoxyethylene alkyl ether sulfate salt; carboxylic acid type such as fatty acid salt, alkyl sarcosine salt; alkyl phosphate ester salt, polyoxyethylene alkyl ether phosphorus Phosphoric acid ester types such as acid ester salts and monoglycerite phosphoric acid ester salts; anionic surfactants typified by, etc .; and pyridium types such as alkyl pyridium salts; amino acid types such as alkyl amino acid salts; Solids such as alkyldimethylbetaine Zwitterionic surfactants typified by, for example, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkyl amides, and other ethylene oxide addition types; glycerin alkyl esters Nonionic surfactants typified by polyol ester type such as sorbitan alkyl ester, sugar alkyl ester; polyether type such as polyhydric alcohol alkyl ether; alkanolamide type such as alkanolamine fatty acid amide; . The amount of these dispersants added is preferably about 1 to 50% by weight, more preferably 2 to 30% by weight based on the pigment.

  In a preferred embodiment of the present invention, a styrene- (meth) acrylic acid copolymer salt is used as a dispersant. The salt of a styrene- (meth) acrylic acid copolymer basically indicates that the structure contains at least a styrene skeleton and a (meth) acrylic acid salt skeleton, and the structure contains (meth) acrylic. It may have a skeleton derived from a monomer having another unsaturated group such as an acid ester skeleton. The salt of the styrene- (meth) acrylic acid copolymer may be a random copolymer or a block copolymer, and is produced by a known polymerization method such as radical copolymerization or group transfer polymerization. The acid value of the salt of the styrene- (meth) acrylic acid copolymer is preferably in the range of 50 to 300, more preferably in the range of 70 to 150. The molecular weight is preferably in the range of 1000 to 50000 in terms of weight average molecular weight, more preferably in the range of 1000 to 15000, and still more preferably in the range of 3000 to 10,000.

  Commercially available products can be used as the dispersant, and specific examples thereof include Johnson Polymer Co., Ltd., Jonkrill 68 (molecular weight 10,000, acid value 195), Jonkrill 680 (molecular weight 3900, acid value 215). ), Joncryl 682 (molecular weight 1600, acid value 235), Joncryl 550 (molecular weight 7500, acid value 200), Joncryl 555 (molecular weight 5000, acid value 200), Joncryl 586 (molecular weight 3100, acid value 105), Examples include Joncryl 683 (molecular weight 7300, acid value 150), B-36 (molecular weight 6800, acid value 250), and the like.

  Dispersion of the pigment by the dispersant is performed by mixing the pigment, the above-described dispersant, water, and a water-soluble organic solvent with a ball mill, sand mill, attritor, roll mill, agitator mill, Henschel mixer, colloid mill, ultrasonic homogenizer, jet mill, ang mill, etc. It is carried out with a suitable disperser.

  A surface-treated pigment that has been introduced with a hydrophilic group on the pigment surface and can be dispersed or dissolved in an aqueous medium without the use of a dispersant, has a functional group or a salt thereof as a hydrophilicity-imparting group, either directly or polyvalently. By introducing (chemically bonding) through the above-mentioned group, it is possible to disperse or dissolve in water without a dispersant, and the type and degree of the functional group or salt thereof to be introduced are aqueous. It may be appropriately determined in consideration of dispersion stability in the ink composition, color density, drying property on the entire surface of the ink jet head, and the like.

<Cyclic amide compound>
The ink composition according to the present invention comprises a cyclic amide compound. In consideration of ease of storage and application of the ink composition, the ink composition for ink jet recording contains a wetting agent. The purpose of adding the wetting agent is to aggregate the pigment component and the resin component by evaporation of moisture during storage. It is to prevent solidification, prevent clogging of nozzles of the inkjet head during inkjet application, and ensure ejection stability. As the wetting agent of the ink composition of the present invention, a cyclic amide compound that improves the solubility of the lactic acid ester compound is used.

  Preferable specific examples of the cyclic amide compound contained in the ink composition of the present invention include 2-pyrrolidone, N-methyl-2-pyrrolidone, and N-ethyl-2-pyrrolidone. You may use these in combination of 2 or more types. The content of the cyclic amide compound is, for example, 0.1 to 40.0% by weight, preferably 1.0 to 30.0% by weight, based on the total amount of the ink composition. By setting it as such a range, clogging prevention property or discharge stability can be ensured. When there is too much content, it may become a dry defect.

<Surfactant>
The ink composition according to the present invention comprises a surfactant. The aqueous solution is usually repelled on the surface of the hydrophobic material, but when a surfactant is added, the aqueous solution, that is, the ink composition can be uniformly applied to the surface of the hydrophobic material. The lactic acid ester compound in the uniformly applied ink composition dissolves only the desired area surface. Further, by uniformly applying the ink composition, the contained resin can be uniformly formed on the recording surface.

  Preferable specific examples of the polyether-modified polysiloxane compound contained as a surfactant in the ink composition of the present invention include compounds represented by the following general formula (I).

［式（Ｉ）中、Ｒ¹〜Ｒ⁷は、独立して、炭素数１〜６のアルキル基を表し、ｊおよびｋは、独立して１以上の整数を表し、ＥＯはエチレンオキシ基を表し、ＰＯはプロピレンオキシ基を表し、ｍおよびｎは０以上の整数を表すが、但しｍ＋ｎは１以上の整数を表し、ＥＯおよびＰＯは、[]内においてその順序は問わず、ランダムであってもブロックであってもよい。］

[In the formula (I), R ^{1 to} R ⁷ independently represent an alkyl group having 1 to 6 carbon atoms, j and k independently represent an integer of 1 or more, and EO represents an ethyleneoxy group. PO represents a propyleneoxy group, m and n represent an integer of 0 or more, provided that m + n represents an integer of 1 or more, and EO and PO are random regardless of the order in []. Or a block. ]

In formula (1), the alkyl group of R ^{1 to} R ⁷ is preferably a methyl group, and j and k are preferably 1 to 5, more preferably 1 to 4, and most preferably 1 or 2. M and n are preferably 1 to 5, and preferably m + n is 2 to 4. According to a preferred embodiment of the ink composition used in the recording method of the present invention, the compound of formula (I) preferably satisfies j = k = 1 to 3, preferably 1 or 2. As another preferred embodiment, as the compound of formula (I), R ^{1 to} R ⁷ all represent a methyl group, j represents 1, k represents 1, l represents 1, and m represents 1 or more. , Preferably 1 to 5, and n is preferably 0. The compounds represented by the general formula (I) are commercially available and can be used. For example, silicon surfactants BYK-347 and BYK-348 commercially available from Big Chemie Japan, Inc. can be used.

  Preferable specific examples of the acetylene glycol compound similarly included include compounds represented by the following general formula (II).

［式（II）中、ｍ＋ｎは０以上５０以下であり、Ｒ11、Ｒ12、Ｒ13、およびＲ14は独立してアルキル基を表す］

[In formula (II), m + n is 0 or more and 50 or less, and R11, R12, R13, and R14 independently represent an alkyl group]

  Among the compounds represented by the general formula (II), 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3 is particularly preferable. , 6-diol, or 3,5-dimethyl-1-hexyne-3ol. Commercially available products can also be used as the acetylene glycol compound represented by the general formula (II) and derivatives thereof, and specific examples thereof include Surfynol 104, 82, 465, 485, or TG (all of which are Air Products and Chemicals. Inc.), Orphin STG, Orphin E1010 (all trade names manufactured by Nisshin Chemical Co., Ltd.).

  The polyether-modified polysiloxane compound and the acetylene glycol compound may be used alone or in combination of two or more. The amount of addition of the polyether-modified polysiloxane compound and / or acetylene glycol compound surfactant as the surfactant in the ink composition used in the ink jet recording method of the present invention may be appropriately determined. The range of 0.01 to 5.0% by weight with respect to the product is preferable, and the range of 0.1 to 2.0% by weight is more preferable.

<Low surface tension organic solvent>
The ink composition according to the present invention comprises a low surface tension organic solvent. The low surface tension organic solvent used in the ink composition of the present invention is preferably at least one compound selected from alkanediol compounds or glycol ether compounds.

  The alkanediol compound is preferably a 1,2-alkanediol having 1 to 6 carbon atoms. From the viewpoint of pigment dispersion stability, 1,2-butanediol, 1,2-pentanediol and 1,2-hexane are preferred. Diol etc. are mentioned.

  Examples of glycol ether compounds include diethylene glycol mono (C 1-8 alkyl) ether, triethylene glycol mono (C 1-8 alkyl) ether, propylene glycol mono (C 1-6 alkyl) ether, dipropylene. A glycol mono (C1-C6 alkyl) ether can be mentioned, These can be used as a 1 type, or 2 or more types of mixture.

  Specifically, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-iso-propyl ether, ethylene glycol monobutyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl Ether, diethylene glycol mono-iso-propyl ether, diethylene glycol monobutyl ether, diethylene glycol mono-t-butyl ether, diethylene glycol monopentyl ether, diethylene glycol monohexyl ether, diethylene glycol monoheptyl ether, diethylene glycol monooctyl ether, triethylene glycol Cole monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, triethylene glycol monopentyl ether, triethylene glycol monohexyl ether, triethylene glycol monoheptyl ether, triethylene glycol monooctyl Tityl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol mono-iso-propyl ether, propylene glycol monobutyl ether, propylene glycol mono-t-butyl ether, propylene glycol monopentyl ether, propylene glycol Mono hex Ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol mono-iso-propyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monopentyl ether, dipropylene glycol monohexyl An ether etc. can be mentioned.

  The alkanediol compound or glycol ether compound can provide the ink composition with a complementary action between the action of the wetting agent and the action of the surfactant that uniformly applies the ink composition to the printing surface. The alkanediol compound or glycol ether compound can be added as appropriate, but it is preferably in the range of about 1 to 20% by weight, more preferably 3 to 15% by weight, based on the ink composition.

<Other ingredients>
In order to apply a water-soluble organic solvent containing a lactic acid ester compound thinly and uniformly to the surface of the recording medium, the solution is diluted with a solvent. As such a main solvent, water or a water-soluble organic solvent can be used. In the present invention, the solvent is preferably water from the viewpoint of safety. As water used here, pure water such as ion exchange water, ultrafiltration water, reverse osmosis water, distilled water, or ultrapure water is used for the purpose of reducing ionic impurities as much as possible. it can. Further, when water sterilized by ultraviolet irradiation or addition of hydrogen peroxide is used, it is preferable because generation of mold and bacteria can be prevented when the aqueous ink composition is stored for a long period of time.

  The ink composition of the present invention can achieve a desired effect by including the above-mentioned components, but if necessary, an antiseptic / antifungal agent, a pH adjuster, a dissolution aid, an antioxidant. And a clogging preventive agent for nozzles.

  Examples of the pH adjuster include potassium dihydrogen phosphate and disodium hydrogen phosphate. Examples of preservatives and fungicides include sodium benzoate, sodium pentachlorophenol, sodium 2-pyridinethiol-1-oxide, sodium sorbate, sodium dehydroacetate, 1,2-dibenzisothiazoline-3-one (Proxel CRL, Proxel BDN, Proxel GXL, Proxel XL-2, Proxel TN from ICI) and the like. Furthermore, examples of the dissolution aid or antioxidant include amines such as diethanolamine, triethanolamine, propanolamine, morpholine and their modified products, inorganic salts such as potassium hydroxide, sodium hydroxide, and lithium hydroxide. , Ammonium hydroxide, quaternary ammonium hydroxide (such as tetramethylammonium), carbonates such as potassium carbonate, sodium carbonate, lithium carbonate and other phosphates, ureas such as urea, thiourea and tetramethylurea, allophanates, Examples include L-ascorbic acid and salts thereof such as allophanates such as methyl allophanate, biurets such as biuret, dimethyl biuret, and tetramethyl biuret. Furthermore, urea, thiourea, ethylene urea or the like can be added for the purpose of preventing nozzle drying.

  Various physical properties of the ink composition according to the present invention can be appropriately controlled. According to a preferred embodiment of the present invention, the viscosity is preferably 25 mPa · sec or less, more preferably 10 mPa · sec or less (25 ° C.). is there. When the viscosity is within this range, the ink composition can be stably discharged from the ink discharge head. Further, the surface tension of the ink composition according to the present invention can be appropriately controlled, and the preferable surface tension is about 20 to 40 mN / m (25 ° C.), more preferably about 23 to 33 mN / m. .

<Manufacture of ink composition>
The ink composition of the present invention is prepared by mixing and dissolving (or dispersing) each of the above-described blending components individually or in any order in the form of a pigment dispersion or a resin emulsion, and then as necessary. It can be prepared by removing impurities by filtration.

In the ink composition according to the present invention, the amount of the lactic acid ester compound is such that the plastic on the recording surface can be dissolved; the viscosity and the surface tension that can be ejected by the ink jet recording head; The ink composition does not agglomerate or solidify at the nozzle; and further, the blending amount of each of the above components is appropriately set in consideration of the fact that the liquid contact member of the ink jet printer is not dissolved or destroyed. can do. Typical compositions for such ink compositions include, for example, the following:
0.5 to 15.0% by weight of pigment;
Resin 0.01-10.0 wt% (solid content);
Lactate compound 1.0 to 25.0 wt%;
Cyclic amide compound 0.1-40.0 wt%;
Surfactant 0.01-5.0% by weight;
Low surface tension organic solvent 1.0-20.0% by weight; and water balance.

<Recording method>
As described above, the ink jet recording method according to the present invention performs printing by ejecting ink composition droplets onto a recording surface and attaching them to the recording surface.

  In the ink composition of the present invention, the amount of ink applied to the recording surface can be appropriately changed according to the type of the recording medium and according to the reproducibility of the image.

  According to a preferred embodiment of the present invention, the ink jet recording method of the present invention includes either a heat printing step of attaching an ink composition to a heated recording medium, or a step of heating the recording medium to which the ink composition is attached. Or both heating steps.

  By heating the recording medium to which the ink composition is attached, dissolution of the plastic film on the recording surface is promoted when the ink composition is attached. By heating after the ink composition adheres, dissolution of the plastic film on the recording surface is promoted and evaporation of volatile components contained in the ink composition is also promoted. If the resin in the ink composition is a thermosetting resin, the adhesion between the recording surface and the formed resin film can be further strengthened.

  Here, a heating means can be performed in accordance with a conventional method, using a conventional heating means, for example, well-known heating apparatuses, such as an infrared type heating apparatus and a hot air heating apparatus. In the present invention, heating may be performed under any conditions so long as the recording surface can be dissolved and the resin contained in the ink composition can be cured to form a resin film. The solvent concentration, the type of resin particles, and the like can be set as appropriate. For example, in the case of heater heating or hot air drying, heating is performed at 25 to 90 ° C. (preferably 40 to 70 ° C.) for 1 minute to 1 day (preferably 2 minutes to 8 hours) including printing. It can be carried out.

<Example>
Hereinafter, the present invention will be described in detail according to the following examples, but the present invention is not limited thereto.

<Preparation of ink composition>
Ink compositions were prepared with the compositions shown in Tables 1 and 2, respectively. All compositions are weight percent.

<Evaluation test>
(Preparation of print sample)
Print samples were prepared using the ink compositions prepared as examples and comparative examples. Specifically, using an inkjet printer “PX-G920 (manufactured by Seiko Epson Corporation)” modified so that it can be heated during printing, 100% duty pattern and portrait image (Japanese standard) Association JIS X 9201-1995 compliant SCID data) was printed.

  Heating: Printing was performed by heating the recording medium to 50 ° C. prior to printing, followed by heating for 1 hour in an environment of 60 ° C. and 20% relative humidity.

  Recording medium: [1] Inkjet recording medium LLSP2000 (Surface vinyl chloride, manufactured by Sakurai Co., Ltd.) [2] Vinyl chloride film not subjected to inkjet recording treatment Scotch film (Sumitomo 3M Limited) )

(Sample evaluation)
Evaluation 1: Adhesive adhesive tape (Cello Tape (registered trademark) No. 252; manufactured by Sekisui Chemical Co., Ltd.) was applied to the printing part of the print sample, and the adhesive tape was peeled off after rubbing 2 to 3 times with a finger. . The printing state of the part was visually observed. The results were evaluated according to the following criteria.
○: There is no peeling of the ink (colorant) from the recording medium.
Δ: Part of the ink (colorant) peels from the recording medium.
X: The ink (colorant) largely peels from the recording medium.
Evaluation 2: Scratch resistance / scratch resistance Using a pencil having a hardness of 750 g using a 750 g load pencil scratch tester specified in JIS K-5600-5-4, the printed part was scratched, and whether or not the print was scraped by scratching. I investigated. The results were evaluated according to the following criteria.
◯: Printing cannot be scraped with an H hardness pencil.
Δ: Printing can be scraped with an H hardness pencil, but printing cannot be scraped with an HB hardness pencil.
X: Printing can be scraped off with an HB hardness pencil.
Evaluation 3: One drop of tap water was allowed to adhere to the printing portion of the water-resistant printing sample and left for 1 minute, and then the water drop was wiped off with a cotton cloth. The state of the printed part and cotton cloth after wiping off was visually observed. The results were evaluated according to the following criteria.
◯: There is no peeling of the ink (colorant) from the recording medium, and the cotton cloth is not colored.
X: A part of ink (coloring agent) peels from the recording medium, and the cotton cloth is colored.
The results were as shown in Table 3 below.

Claims (9)

  An ink composition comprising at least a lactic acid ester compound, a thermoplastic resin, a pigment, a cyclic amide compound, a surfactant, a low surface tension organic solvent, and water.   The ink composition according to claim 1, wherein the lactic acid ester compound is at least one compound selected from the group consisting of ethyl lactate, methyl lactate, butyl lactate, amyl lactate, and hexyl lactate.   The ink composition according to claim 1 or 2, wherein the cyclic amide compound is at least one compound selected from the group consisting of 2-pyrrolidone, N-methyl-2-pyrrolidone, and N-ethyl-2-pyrrolidone. object.   The ink composition according to any one of claims 1 to 3, wherein the surfactant is at least one compound selected from the group consisting of a polyether-modified polysiloxane compound and an acetylene glycol compound.   The ink composition according to any one of claims 1 to 4, wherein the low surface tension organic solvent is at least one compound selected from the group consisting of an alkanediol compound and a glycol ether compound.   The ink composition according to any one of claims 1 to 5, wherein the content of the lactic acid ester compound is 1.0 to 25.0 wt%.   An ink jet recording method for performing printing by discharging a droplet of an ink composition onto a recording surface and attaching the ink composition to the recording surface, wherein the ink composition is any one of claims 1 to 6. An ink-jet recording method, which is the ink composition according to the item.   8. The ink jet recording method according to claim 7, wherein the recording surface is a plastic film.   The ink jet recording method according to claim 7 or 8, further comprising a heating printing step of attaching the ink composition to the heated recording medium and / or a step of heating the recording medium to which the ink composition is attached.