JP5098387B2 - Ink for inkjet recording - Google Patents

Description

  The present invention relates to a novel ink for ink-jet recording (hereinafter also referred to as ink-jet ink or simply ink) that is excellent in ejection stability and can provide high-quality printing on a non-water-absorbing recording medium.

  In recent years, the progress of ink-jet related technologies has been remarkable, and in combination with the improvement of technologies related to printers, inks or dedicated ink-jet recording media, the image quality obtained has been called photographic image quality.

  On the other hand, there has been an increasing demand for printing on recording media other than printable plain paper and inkjet dedicated paper, such as coated paper or art paper, which is the main printing paper, and resin sheets such as polyvinyl chloride (vinyl chloride) sheets. .

  As an inkjet ink for industrial use, an ink capable of directly printing on a non-absorbent medium such as a vinyl chloride sheet has been recently developed. Examples of these inks include solvent inks using an organic solvent as a vehicle and UV inks containing a polymerizable monomer as a main component.

  However, the solvent ink has a problem that there are many VOCs (volatile organic compounds), which have become a social problem in recent years, because the solvent is dried and evaporated to the atmosphere. There is a concern about safety and safety effects, and facilities such as adequate ventilation are required.

  Since UV ink is cured immediately after printing, VOC is close to zero. However, depending on the monomer used, there are many problems with skin sensitization, and there are restrictions on incorporating expensive UV light sources into the printer. Also can not be used. Further, when printing is performed on a glossy sheet or the like, there is a problem that glossiness is remarkably impaired.

  Against this background, water-based inks that use water as the main solvent, which has been widely used in the home, and the like, have been developed that can print directly on non-water-absorbing recording media. Yes.

Examples of inks for water-absorbing recording media include ethylene oxide adduct of alkylamine or polyoxyethylene lauryl ether (C ₁₂ H ₂₅ O (CH ₂ CH ₂ ) _n OH n ≦ 9) as surfactant and dipropylene as solvent An ink containing glycol, a colorant, and water has been proposed (see Patent Document 1). However, there is a problem that the absorption speed for art printing paper, coated paper such as coated paper is slow.

Further, as an example of ink for a non-water-absorbing recording medium (plastic film), an ink composed of a cyclic amide compound (or a cyclic ether compound), a thermoplastic resin, a colorant, and a main solvent has been proposed (see Patent Document 2). . Although this ink further contains a surfactant (acetylene glycol-based compound) and / or a low surface tension organic solvent (diethylene glycol butyl ether or triethylene glycol butyl ether), the printability on the recording medium is improved. There are problems with image quality and ink ejection stability.
Japanese Patent No. 3858736 JP 2006-282822 A

  Accordingly, an object of the present invention is to provide an ink for ink jet recording having a low foaming property and stable ejection. Furthermore, another object of the present invention is to provide an ink for ink jet recording capable of printing with high image quality on any recording medium from a water absorbing recording medium to a non-water absorbing recording medium.

  As a result of intensive studies on the above problems, the present inventors have used an inkjet recording ink containing a specific surfactant, pigment, water, and a specific organic solvent, so that bubbles can be produced even at higher printing speeds. The inventors have found that high-quality printing can be obtained on both the water-absorbing recording medium and the non-water-absorbing recording medium at the same time, and the present invention has been achieved.

That is, the above object of the present invention is achieved by the following configuration.
1.
An inkjet recording ink containing 1,2-hexanediol as a surfactant, a pigment, water, and an organic solvent represented by the following general formula (1):
An ink for ink jet recording, wherein the general formula (1) satisfies the condition (A), (B), (C) or (D).

General formula (1) R (OCH ₂ CH ₂ ) _n OH
[Wherein, R represents an alkyl group, n to display the repeating unit of oxyethylene unit]
(A) R is C ₁₀ H ₂₁ and n is 4,5
(B) R is C ₁₁ H ₂₃ and n is 4-6
(C) R is C ₁₂ H _25, n is 4-7
(D) R is C ₁₃ H _27, n is 5-7
2.
2. The inkjet recording ink according to item 1, wherein the general formula (1) of the surfactant satisfies the condition (B), (C), or (D).
3.
2. The inkjet recording ink according to item 1, wherein the general formula (1) of the surfactant satisfies the condition (C).
4 .
4. The ink for inkjet recording according to any one of 1 to 3 above, which is used for printing by heating a non-water-absorbing recording medium.
5 .
5. The ink for ink jet recording according to any one of 1 to 4 above, which contains a fixing resin.
6 .
6. The ink for ink jet recording according to 5 above, wherein the fixing resin is an ink-soluble resin, has a carboxyl group or a sulfo group as an acidic group, and has an acid value of 80 or more and less than 300.

  According to the present invention, it is possible to provide an ink for ink jet recording that has less foaming property and is stable in ejection. If the ink is used, high-quality printing can be performed not only on a water-absorbing recording medium but also on a non-water-absorbing recording medium.

  Hereinafter, the present invention will be described in detail.

  The ink of the present invention is a polyoxyethylene monoalkyl which is a nonionic surfactant represented by the general formula (1) and satisfying the condition (A), (B), (C) or (D). It contains an ether and an organic solvent selected from glycol ethers or 1,2-alkanediols. Although the interpretation of this combined effect has not yet been clarified, it will be explained in turn.

(Surfactant)
The carbon number of the alkyl group of the polyoxyethylene monoalkyl ether used in the present invention is a relatively small range of 10 to 13, and the number of moles of the ethyleneoxy moiety is any of 4 to 7 depending on the carbon number of the alkyl group. This is essential in order to remarkably exhibit both ink ejection stability and high-quality printing on a water-absorbing medium and a non-water-absorbing medium. By using polyoxyethylene monoalkyl ether having a relatively small volume as the surfactant, it becomes easy to arrange the surfactant at the nozzle end of the inkjet device and to form a molecular film, and to prevent ink drying.

  Also, low molecular weight polyoxyethylene monoalkyl ethers are easier to move than high molecular weight ones. For this reason, it is considered that the ink easily moves in accordance with the movement of ink discharge, can cope with foaming at the nozzle tip during discharge, and contributes to discharge stability.

  When the carbon number of the alkyl group of the polyoxyethylene monoalkyl ether is less than 10, it becomes relatively hydrophilic, for reducing the defoaming effect due to a decrease in wettability to a non-water-absorbing medium and a decrease in the adsorptivity to bubbles. It is not preferable. On the other hand, when the carbon number of the alkyl group exceeds 13, compatibility with the ink decreases, the bulk of the molecule increases, movement in the ink becomes difficult, and the defoaming effect corresponding to the ejection operation It will be difficult to show.

  Furthermore, in order to improve the ejection stability due to the defoaming effect, it is preferable to limit the structure of the polyoxyethylene monoalkyl ether. Most preferred is when the alkyl group has a structure with 12 carbon atoms and 4 to 7 ethylene oxide sites (condition (C)). This structure is considered to be most suitable for both the viewpoint of hydrophobicity and the bulkiness that allows easy movement in the ink.

  As such a surfactant, for example, polyoxyethylene lauryl ether Emulgen (registered trademark) 104P, 105, 106 and the like can be obtained. Other polyoxyethylene monoalkyl ethers can be synthesized by Williamson synthesis and purified by distillation and recrystallization.

  The addition amount of polyoxyethylene monoalkyl ether is preferably 0.1 to 1.5% by mass with respect to the total ink amount, and the effects of the present invention can be remarkably exhibited within this range.

(Organic solvent)
The organic solvent used in combination with the polyoxyethylene monoalkyl ether of the present invention is a water-miscible solvent selected from glycol ether or 1,2-alkanediol.

  There are two reasons why the above-mentioned solvent is selected from many organic solvents used in ink-jet inks: it is relatively hydrophobic among water-miscible solvents and promotes solubilization of the surfactant. That is, since it is a relatively hydrophobic class, it exhibits sufficient wettability not only for water-absorbing recording media but also for non-water-absorbing recording media, can suppress the occurrence of beading, and can achieve high image quality. These are structurally similar to the ethyleneoxy moiety of the polyoxyethylene monoalkyl ether, which is the nonionic surfactant of the present invention, so that the surfactant is easily soluble, and the surfactant It is thought that the defoaming effect brought about by this is easily manifested.

  Specifically, as glycol ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, tripropylene glycol A monomethyl ether etc. are mentioned. Examples of the 1,2-alkanediol include 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-heptanediol, and the like.

  The structure of the organic solvent is preferably limited. Most preferred are diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and 1,2-hexanediol. The structure having this structure is particularly preferable from the viewpoint of the effect of the present invention on the water-based ink.

  The addition amount of these organic solvents is preferably 5 to 20% by mass with respect to the total ink amount. More preferably, it is 5-15 mass%, and the effect of this invention can be exhibited notably in this range.

  Hereinafter, materials used for the ink of the present invention in addition to the surfactant and the organic solvent will be specifically described.

(Pigment and dispersion resin)
The pigment used in the present invention is not particularly limited as long as it can be stably dispersed in an aqueous system. A pigment dispersion dispersed with a dispersion resin, a capsule pigment coated with a water-insoluble resin, a dispersion without modifying the pigment surface and using a dispersion resin. It can be selected from possible self-dispersing pigments and the like. When the ink storage stability is particularly important, it is preferable to select a capsule pigment coated with a water-insoluble resin.

  When a pigment dispersion dispersed by a dispersion resin is used, a water-soluble one can be used as the dispersion resin, and styrene-acrylic acid-acrylic acid alkyl ester copolymers and styrene are preferably used as the water-soluble resin. -Acrylic acid copolymer, styrene-maleic 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.

  Various methods such as a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, and a paint shaker can be used as a pigment dispersion method.

  For the purpose of removing the coarse particles of the pigment dispersion of the present invention, it is preferable to use a centrifugal separator or a filter.

  When capsule capsules coated with a water-insoluble resin are used, the water-insoluble resin is a resin that is insoluble in water in a weakly acidic to weakly basic range, and preferably has a solubility in an aqueous solution having a pH of 4 to 10. Less than 2% resin.

  Such resins include acrylic, styrene-acrylic, acrylonitrile-acrylic, vinyl acetate, vinyl acetate-acrylic, vinyl acetate-vinyl chloride, polyurethane, silicon-acrylic, acrylic silicon, polyester Examples thereof include epoxy resins and epoxy resins.

  Further, as the dispersion resin of the present invention, a resin produced using both a hydrophobic monomer and a hydrophilic monomer as polymerization components can be used. As this hydrophobic monomer, acrylic acid ester (butyl acrylate, acrylic acid-2-ethylhexyl, acrylic acid-2-hydroxyethyl, etc.), methacrylic acid ester (ethyl methacrylate, butyl methacrylate, glycidyl methacrylate, etc.), Examples include styrene. Examples of the hydrophilic monomer include acrylic acid, methacrylic acid, acrylamide and the like, and those having an acidic group such as acrylic acid can preferably be those neutralized with a base after polymerization.

  As the molecular weight of the resin, those having an average molecular weight of 3,000 to 500,000 can be used. Preferably, a thing of 7,000-200,000 can be used.

  A resin having a glass transition temperature (Tg) of about −30 to 100 ° C. can be used. Preferably it is about -10-80 degreeC.

  As the polymerization method, solution polymerization or emulsion polymerization can be used. The polymerization may be separately synthesized with the pigment in advance, or may be performed by supplying a monomer into the system in which the pigment is dispersed.

  Various known methods can be used as a method for coating the pigment with the resin. Preferably, in addition to the phase-emulsification method and the acid precipitation method, the pigment is dispersed using a polymerizable surfactant. It is preferable to select from a method in which a monomer is supplied to the substrate and coating is performed while polymerizing.

  As a more preferable method, a water-insoluble resin is dissolved in an organic solvent such as methyl ethyl ketone, and after partially or completely neutralizing acidic groups in the resin with a base, a pigment and ion-exchanged water are added and dispersed. A production method in which an organic solvent is removed and water is added as necessary is preferable.

  The ratio (mass) of the pigment and the resin can be selected in the range of 100/40 to 100/150 as the pigment / resin ratio. Particularly, the range of 100/60 to 100/110 has good image durability, ejection stability and ink storage stability.

  The average particle diameter of the pigment particles coated with the water-insoluble resin is preferably about 80 to 150 nm from the viewpoints of ink storage stability and color developability.

  Further, as the self-dispersing pigment, commercially available products that have been surface-treated can be used, and examples thereof include CABO-JET200, CABO-JET300 (both manufactured by Cabot Corporation), and Bonjet CW1 (manufactured by Orient Chemical Industries). .

  As the pigment that can be used in the present invention, conventionally known organic and inorganic pigments can be used. For example, azo pigments such as azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perylene pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc. Examples include cyclic pigments, dye lakes such as basic dye lakes, and acid dye lakes, organic pigments such as nitro pigments, nitroso pigments, aniline black, and daylight fluorescent pigments, and inorganic pigments such as carbon black.

  Specific organic pigments are exemplified below.

  Examples of pigments for magenta or red include C.I. I. Pigment Red 2, 3, 5, 6, 7, 15, 16, 48: 1, 53: 1, 57: 1, 122, 123, 139, 144, 149, 166, 178, 222 and the like.

  Examples of the orange or yellow pigment include C.I. I. Pigment orange 31, 43, C.I. I. Pigment Yellow 12, 13, 14, 15, 17, 74, 93, 94, 128, 138 and the like.

  Examples of green or cyan pigments include C.I. I. Pigment blue 15, 15: 2, 15: 3, 16, 60, C.I. I. Pigment Green 7 etc.

(Fixing resin)
Fixing resins that exhibit high image fastness by increasing ink coating strength include ink-soluble resins having a hydrophobic monomer as a polymerization component and dispersion resins.

  As the ink-soluble resin, a resin that is stably dissolved in the ink but is provided with water resistance after drying on the recording medium is preferable.

  As such a fixing resin, a resin having a hydrophobic component and a hydrophilic component in a certain balance is designed and used. In this case, as the hydrophilic component, either an ionic component or a nonionic component may be used, but an ionic component is more preferable, and an anionic component is more preferable. In particular, those which are rendered water-soluble by neutralizing anionic substances with a volatile base component are preferred.

  In particular, at least one of the ink-soluble resins has a carboxyl group or a sulfonic acid group as an acidic group, and a resin having an acid value of 80 or more and less than 300 is preferable in view of the effects of the present invention.

  Examples of such a fixing resin include acrylic resins, styrene-acrylic resins, acrylonitrile-acrylic resins, vinyl acetate-acrylic resins, polyurethane resins, and polyester resins.

  As the resin of the present invention, a resin containing a hydrophobic monomer and a hydrophilic monomer can be used.

  Examples of hydrophobic monomers include acrylic acid esters (such as n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate), methacrylic acid esters (such as ethyl methacrylate, butyl methacrylate, glycidyl methacrylate), styrene. Etc.

  Examples of the hydrophilic monomer include acrylic acid, methacrylic acid, acrylamide and the like, and those having an acidic group such as acrylic acid can preferably be those neutralized with a base after polymerization.

  As the molecular weight of the fixing resin, those having an average molecular weight of 3,000 to 30,000 can be used. Preferably, 7,000 to 20,000 can be used.

  A resin having a Tg of about −30 to 100 ° C. can be used. Preferably, about -10 degreeC-80 degreeC can be used.

  As the acid value of the resin, those having about 90 to 300 can be particularly preferably used. An acid value of 80 to 300 is preferable for improving ink ejection stability and image durability, particularly water resistance. As the polymerization method, it is preferable to use solution polymerization.

  The acidic group derived from the acidic monomer of the resin is preferably neutralized partially or completely with a base component. As the neutralizing base in this case, alkali metal-containing bases such as sodium hydroxide and potassium, and amines (ammonia, alkanolamine, alkylamine, etc.) can be used. In particular, neutralization with amines having a boiling point of less than 200 ° C. is preferable from the viewpoint of improving image durability.

  In order to obtain the object of the present invention, the amount of these resins added is preferably 2 to 10% by mass with respect to the total ink amount. More preferably, it is 3-6 mass%. The ink of the present invention preferably contains 2 to 10% by mass of an ink-soluble resin as a solid content.

  Next, the aqueous dispersion type polymer fine particles according to the present invention will be described.

  As the polymer fine particles, a dispersion polymerized in an aqueous system may be used as it is or may be treated, or a polymer polymerized in a solvent system may be dispersed in an aqueous system. Select from acrylic, urethane, styrene, vinyl acetate, vinylidene chloride, vinyl chloride, styrene-butadiene, styrene-acrylonitrile, polybutadiene, polyethylene, poly-i-butylene, polyester, etc. I can do it.

  As the physical properties of the ink, it is preferable that there is no shear dependency on the viscosity. From this viewpoint, as a dispersion form of the polymer fine particles, an emulsifier such as an active agent is made as low as possible, or a soap-free dispersed polymer particle using no emulsifier Is preferred. A preferred aqueous dispersion polymer fine particle is a self-dispersion dispersion of a copolymer obtained by polymerizing unsaturated vinyl having a carboxyl group as at least a monomer component. For example, an acrylic monomer such as ethyl acrylate alone or an acrylic monomer After a dispersion obtained by emulsion polymerization or suspension polymerization of acrylic acid or maleic acid as a carboxylic acid monomer in a composition comprising an ethylenically unsaturated monomer that can be copolymerized with an alkali, particles are swelled by alkali shearing and then mechanically sheared. Is an acrylic hydrosol obtained by dividing Among acrylic hydrosols, it is preferable to contain styrene in the monomer composition from the viewpoint of increasing the refractive index of the resin and obtaining high glossiness.

  The alkali is an amine such as ammonia, triethylamine, 2-dimethylaminoethanol, 2-butylaminoethanol, methyldiethanolamine, 2-amino-2-methyl-1-propanol, diethanolamine, triethanolamine, or 2-methylaminoethanol. Ammonia, 2-amino-2-methyl-1-propanol, and 2-methylaminoethanol are particularly preferable in terms of dispersion stability of the aqueous dispersion polymer fine particles.

  As the acrylic hydrosol, Jonkrill (registered trademark) manufactured by Johnson Polymer is commercially available.

  The aqueous dispersion type polymer fine particles preferably have a Tg of 35 ° C. or higher in order to increase the scratch resistance of the image, and more preferably 49 ° C. or higher. The upper limit of Tg is not particularly limited, but if it is less than about 100 ° C., a flexible ink film can be obtained and image cracking failure due to bending of the printed matter can be prevented.

  The acid value of the aqueous dispersion polymer fine particles is preferably 44 or more, more preferably 60 or more, from the viewpoint of obtaining good redispersion / solubility of the ink dry film. The upper limit of the acid value is not particularly limited, but is preferably less than 110 from the viewpoint of easily obtaining a more stable dispersion.

  The average particle size of the water-dispersed polymer fine particles is preferably 300 nm or less, more preferably 130 nm or less, from the viewpoint that the head nozzle is not clogged and a good gloss is obtained. The lower limit of the average particle diameter is preferably 30 nm or more from the viewpoint of the production stability of the fine particles. The average particle diameter of the water-dispersed polymer fine particles can be easily measured using a commercially available measuring apparatus using a light scattering method or a laser Doppler method. In addition, the dispersion of aqueous dispersion polymer fine particles can be freeze-dried, and the average particle diameter can be converted from the particles observed with a transmission electron microscope.

  The content of the water-dispersible polymer fine particles is preferably 0.7 to 6% by mass, and good fixability (abrasion resistance, alcohol resistance) and long-term storage stability of the ink are easily obtained in this range. More preferably, it is 1-3 mass%.

(recoding media)
The recording medium that can be used for ink jet recording using the ink according to the present invention may be a water-absorbing recording medium or a non-water-absorbing recording medium. The water-absorbing recording medium mentioned here is plain paper (copy paper, plain paper for printing, etc.), corrugated cardboard, wood, printing paper, coated paper, art paper, ink jet dedicated paper, ink jet gloss, which is a slightly water absorbent recording medium. Including paper. On the other hand, the non-water-absorbing recording medium includes a polymer sheet, board (soft vinyl chloride, hard vinyl chloride, acrylic plate, polyolefin plate, etc.), glass, tile, rubber, synthetic paper and the like.

  In particular, when ink-jet recording is performed on a non-water-absorbing recording medium or a slightly water-absorbing recording medium, the ink of the present invention can obtain a recorded image with much higher image quality than when a conventional ink is used. This is considered to be because the use of the nonionic surfactant and the organic solvent according to the present invention provides sufficient wettability to these recording media and can suppress the occurrence of beading.

(Heating during recording)
In the present invention, it is preferable to print by heating the recording medium. By heating the recording medium, the drying and thickening speed of the ink is remarkably improved, and high image quality can be obtained. Also, the durability of the image is improved. This is particularly effective when a non-water-absorbing recording medium or a slightly water-absorbing recording medium is used as the recording medium.

  As a further requirement for high-quality printing, it is important to prevent deterioration in image quality due to ink mixing such as beading and color bleeding. For this purpose, rapid thickening after ink landing by the fixing resin and lowering of fluidity are effective, and particularly effective for ink for printing by heating the medium as in the present invention.

  However, if an attempt is made to include a fixing resin in order to improve the ink fixing property to the recording medium, bubbles generated in the ink are stabilized when the head is ejected at a high frequency of 5 to 20 kHz. It becomes difficult to defoam. However, by using the nonionic surfactant and the organic solvent of the present invention, it is possible to remarkably suppress the deterioration of ejection stability caused by bubbles that appears remarkably in the resin-containing ink, and further, it is possible to obtain an image having good ink fixing properties. An ink composition can be provided.

  The heating temperature is preferably such that the recording surface temperature of the recording medium is 40 to 80 ° C., more preferably 40 to 60 ° C.

  As a heating method, there can be selected a method in which a heater is incorporated in the medium conveyance system or the platen member and heated from the lower side of the recording medium in a contact manner, or a method of heating in a non-contact manner from the lower side or the upper side by a lamp or the like.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. Unless otherwise specified, “%” in the examples represents “mass%”.

  Ink jet recording ink was prepared by the following procedure.

  First, Table 1 shows the structure of the surfactant polyethyleneoxymonoalkyl ether used for the preparation of the example ink and the comparative ink.

<Preparation of pigment dispersion>
As a pigment dispersant, styrene-acrylic acid copolymer (manufactured by Jonkrill Co., Ltd .: Jonkrill 678, Mw8,500, acid value 215) 3%, dimethylaminoethanol 1.3%, ion-exchanged water 80.7% was stirred. Mixed and dissolved. In this solution, C.I. I. After 15% of Pigment Blue 15: 3 was added and premixed, the mixture was dispersed using a sand grinder filled with 50% by volume of 0.5 mm zirconia beads to obtain a pigment dispersion having a solid content concentration of 15%.

<Preparation of ink>
[Ink of Example 101]
After adding 1.0% activator 12 to 10.0% diethylene glycol monobutyl ether (DEGBE), water was added and stirred. While continuing stirring, 5.0% of the pigment dispersion was added, and the mixture was filtered through a 5 μm filter. This is referred to as ink of Example 101.

[Inks of Examples 102 to 115 and Comparative Examples 101 to 112]
In the same manner as the ink of Example 101, inks having the compositions shown in Tables 2 and 3 were mixed and filtered through a 5 μm filter to obtain inks of Examples 102 to 115 and Comparative Examples 101 to 112.

[Ink of Example 201]
<Synthesis of ink-soluble resin>
50 g of methyl ethyl ketone (MEK) was placed in a flask equipped with a dropping funnel, a nitrogen introducing officer, a reflux condenser, a thermometer and a stirring device, and heated to 75 ° C. while nitrogen bubbling was performed. The mixture of the monomer of Table 4, MEK50g, and initiator (AIBN) 500mg was dripped there over 3 hours from the dropping funnel. After dropping, the mixture was further heated and refluxed for 6 hours. After allowing to cool, MEK was distilled off by heating under reduced pressure. In 450 ml of ion-exchanged water, dimethylaminoethanol corresponding to 1.05 mol of acrylic acid added as a monomer was dissolved, and the polymer residue was dissolved therein. A resin aqueous solution having a solid content concentration of 20% was obtained by adjusting with ion-exchanged water.

<Preparation of ink>
After adding 1.0% activator 12 to DEGBE 10.0%, water was added and stirred. While continuing the stirring, 5.0% of the pigment dispersion and 3.0% of the ink-soluble resin were added and filtered through a 5 μm filter. This is referred to as ink of Example 201.

[Inks of Examples 202 to 220 and Comparative Examples 201 to 212]
In the same manner as the ink of Example 201, inks having the compositions shown in Tables 5 and 6 were mixed and filtered through a 5 μm filter to obtain inks of Examples 202 to 220 and Comparative Examples 201 to 212.

<Evaluation of ink performance>
The following performance evaluation was performed using each ink produced as described above.

<Discharge stability>
Evaluation was carried out using a printing apparatus having a piezo-type head (720 dpi, appropriate amount of liquid 16 pl). Here, dpi is a resolution representing the number of dots per inch (1.54 cm). Each ink was introduced into one head, 10 images were continuously formed in A4 size, images were formed again at intervals of 60 minutes, and the obtained images were evaluated in 5 stages.

1: Many image defects (improper ink ejection) are observed 2: Image defects are observed sparsely 3: There are almost no image defects, but lower-case depiction is deteriorated. Satellites were seen in the dots as a result of magnified observation. 4: There was no image defect, but there was very slight blurring in the image writing part (several mm). 5: No image defect was seen including the image writing part.

<Image evaluation for PVC>
Each ink was introduced into one head of the evaluation apparatus, and an image was created for evaluation. The creation conditions are as follows. The apparatus can arbitrarily heat the recording medium from below with a contact heater.

(conditions)
Printing resolution: 720 dpi x 720 dpi
Head transport speed: 200 mm / sec (bidirectional printing)
Recording medium: PVC sheet (manufactured by METAMARK: digital vinyl)
Medium heating temperature: printing surface temperature 50 ° C
Evaluation image: wedge image, character, white character Evaluation environment: 20 ° C. and 55% RH (relative humidity).

"image quality"
The presence / absence of image repellency, beading caused by ink mixing, and lowercase drawing performance were evaluated in 5 grades.

1: Local repellency is observed, beading is intense, lowercase letters cannot be drawn 2: No repellency is found, but beading is conspicuous, lowercase letters cannot be drawn 3: No cissing, but beading is very slightly seen Although it is possible to draw lowercase letters, it is somewhat unclear. 4: There is no repelling or beading, but lowercase drawing is possible, but the drawing of white characters is somewhat unclear. The drawing of white letters is also clear.

<Image evaluation for paper>
Three types of recording media (Glossy paper made by Oji Paper Co., Ltd .: SA Kanfuji, basis weight 128 g / m ² and Mitsubishi Paper Industries, Ltd .: two types of special rhodium art double-sided, basis weight 110 g / m ² , cast-coated paper Oji Paper Co., Ltd .: Mirror coat platinum, basis weight 110 g / m ² ), except that the evaluation image was a solid image of 10 cm × 10 cm, an image was created in exactly the same manner as the image evaluation for PVC, Three levels of image quality were evaluated. However, among the three types of glossy paper used, the judgment was made using the one with the worst evaluation result.

"image quality"
1: Spots appear on the entire surface, and the quality is outside the acceptable range for practical use. 2: Partial spots are observed, but are within the acceptable range for practical use.

  The results are summarized in Tables 2, 3 and 5, 6. In addition, the organic solvent abbreviations in the table are as follows, and the numerical values in the rows of pigment, resin, activator, and solvent all indicate g.

DEGBE: diethylene glycol monobutyl ether TEGBE: triethylene glycol monobutyl ether TPGME: tripropylene glycol monomethyl ether 1,2-HD: 1,2-hexanediol DEG: diethylene glycol DPG: dipropylene glycol As apparent from the results of the table, the present invention The ink jet ink is excellent in ejection stability, and gives a good image to not only a paper medium but also a non-absorbent medium such as a plastic film. It can also be seen that printing while heating the recording medium is effective for non-water-absorbing media.

Claims (6)

An inkjet recording ink containing 1,2-hexanediol as a surfactant, a pigment, water, and an organic solvent represented by the following general formula (1):
An ink for ink jet recording, wherein the general formula (1) satisfies the condition (A), (B), (C) or (D).
General formula (1) R (OCH ₂ CH ₂ ) _n OH
[Wherein, R represents an alkyl group, n to display the repeating unit of oxyethylene unit]
(A) R is C ₁₀ H ₂₁ and n is 4,5
(B) R is C ₁₁ H ₂₃ and n is 4-6
(C) R is C ₁₂ H _25, n is 4-7
(D) R is C ₁₃ H _27, n is 5-7   The ink for inkjet recording according to claim 1, wherein the general formula (1) of the surfactant satisfies the condition (B), (C), or (D).   The ink for inkjet recording according to claim 1, wherein the general formula (1) of the surfactant satisfies the condition (C). The ink for inkjet recording according to any one of claims 1 to 3 , wherein the ink is used for printing by heating a non-water-absorbing recording medium. The ink for inkjet recording according to any one of claims 1 to 4 , further comprising a fixing resin. 6. The ink for inkjet recording according to claim 5 , wherein the fixing resin is an ink-soluble resin, has a carboxyl group or a sulfo group as an acidic group, and has an acid value of 80 or more and less than 300.