JP2011094082A - Inkjet ink and recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide inkjet ink which allows an image printed therewith on a non-absorbent recording medium to have high abrasion resistance, high adhesion properties, high gloss and high quality and allows an inkjet head to have high jetting property and excellent recoverability after maintenance and to provide an inkjet recording method using the inkjet ink. <P>SOLUTION: The water-based inkjet ink contains, at least, water, a pigment, a resin, a water-soluble organic solvent and a silicone-based or fluorine-based surfactant. The resin contains a copolymer resin synthesized from a monomer containing, at least, methyl methacrylate, an acid monomer, alkyl acrylate having a 2-4C alkyl group and alkyl acrylate having a 6-12C alkyl group. The copolymer resin has 50-120 mg-KOH/g acid value, 30-110°C glass transition temperature (Tg) and 20,000-80,000 weight-average molecular weight (Mw). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an inkjet ink and an inkjet recording method, and more particularly to an aqueous inkjet ink and an inkjet recording method that can be recorded on a non-absorbable recording medium.

  Ink that can be directly printed on non-absorbent media such as a vinyl chloride sheet has been developed as an inkjet ink for industrial use. Examples of these inks include a solvent ink using an organic solvent as a vehicle, and a UV ink mainly containing a polymerizable monomer. Since the solvent ink dries the solvent and evaporates it into the atmosphere, there is a problem that many VOCs have become a social problem in recent years. Workers are also concerned about odors and safety impacts, and facilities such as sufficient ventilation are required. Since UV ink is cured immediately after printing, VOC is close to zero. However, depending on the monomers used, many have a skin sensitization problem, and it is used because of the limitation of incorporating an expensive UV light source into the printer. There are limitations in the field. Furthermore, when printing was performed on a glossy sheet or the like, the glossiness was remarkably impaired at the portion where the ink was adhered, and a high-quality image could not be obtained.

  Against this backdrop, the development of inks that can be printed directly on non-water-absorbing recording media with water-based inks that have a low environmental impact and have been widely used in homes, etc. Yes.

  Patent Document 1 proposes a water-based ink containing a solvent compatible with water selected from the group consisting of glycol and glycol ether, and further has a hydrophobic main chain and a nonionic hydrophilic side. Inks have been proposed that contain a graft copolymer binder that has a chain and is soluble in an aqueous vehicle containing water and a water-soluble organic solvent, but insoluble in water. However, as a result of investigations by the present inventors, in the method of Patent Document 1, ink mixing occurs in which ink dots landed adjacently on a non-absorbent recording medium are combined, and a solid image portion having a uniform intermediate density is obtained. The image quality was inadequate, for example, dots were gathered to create a mottled pattern, or color bleed (a phenomenon in which ink was mixed and blurred at the color boundary portion) during multicolor printing. Further, the durability of the obtained image was insufficient. Furthermore, in the method of Patent Document 1, an ejection failure occurs when the inkjet head is continuously used. In order to recover the light emission, generally, maintenance is performed at a certain frequency, but the recovery by the maintenance is not satisfactory.

  Patent Document 2 describes that a styrene-acrylic acid copolymer is added to the ink. However, the copolymerizable polymer containing styrene has a characteristic that the glossiness of the image is high, but the image printed directly on a hydrophobic substrate or the like has poor abrasion resistance and adhesiveness.

  As commercially available water-soluble resins, copolymers of styrene and α-methylstyrene and acid monomers such as acrylic acid are commercially available. When these are used in inkjet inks, high gloss can be obtained, but abrasion resistance and adhesion are very poor. The reason for this is not clear, but the adhesion of styrene to the base material is poor, or the coating film is too hard and lacks flexibility. It is estimated.

  On the other hand, an all-acrylic type that uses methyl methacrylate in place of styrene and does not contain a styrene component is also commercially available. However, these types that do not contain styrene have a problem that image gloss tends to decrease.

  Patent Document 3 discloses that a water-soluble acrylic resin not containing styrene is added to ink. By using the resin-coated pigment as the pigment dispersion, a certain degree of high image durability (scratch property) is obtained even when directly printed on a vinyl chloride substrate. However, the market demands resistance to even stronger friction, which is not sufficient for such strong friction.

  Furthermore, some of the commercially available resins have a remarkable injection failure with an inkjet head, and in particular, a resin having a high scratch resistance tends to be an injection failure, and a resin that satisfies both high image durability and good injection properties at the same time. The current situation is not found.

JP 2000-44858 A JP 2006-249393 A JP 2008-208153 A

  The present invention has been made in view of the above problems, and its purpose is to form an image printed on a non-absorbent recording medium with high abrasion resistance and high adhesiveness, and with high gloss and high image quality. In addition, an object of the present invention is to provide an ink jet ink excellent in high ejection properties and recoverability by maintenance, and an ink jet recording method using the same.

  The above object of the present invention is achieved by the following means.

  1. In an aqueous inkjet ink containing at least water, a pigment, a resin, a water-soluble organic solvent, and a silicone-based or fluorine-based surfactant, the resin has at least methyl methacrylate, an acid monomer, and an alkyl group having 2 to 4 carbon atoms. And a copolymer resin synthesized from a monomer containing an alkyl acrylate having an alkyl group having 6 to 12 carbon atoms, and the copolymer resin has an acid value of 50 mgKOH / g or more and 120 mgKOH. / G or less, a glass transition temperature (Tg) of 30 ° C. to 110 ° C., and a weight average molecular weight (Mw) of 20,000 to 80,000.

  2. 2. The ink-jet ink as described in 1 above, wherein the acid monomer is acrylic acid or methacrylic acid.

  3. The mass ratio of the alkyl alkyl ester having 6 to 12 carbon atoms in the alkyl group is 5% or more and 20% or less with respect to the total mass of the monomer that is a synthetic raw material of the copolymer resin. The inkjet ink according to 1 or 2.

  4). The mass ratio of the alkyl alkyl ester having 2 to 4 carbon atoms of the alkyl group is 5% or more and 40% or less with respect to the total mass of the monomer that is a synthetic raw material of the copolymer resin. The inkjet ink of any one of 1-3.

  5. The mass of the alkyl alkyl ester having 6 to 12 carbon atoms in the alkyl group and the alkyl alkyl ester having 2 to 4 carbon atoms in the alkyl group with respect to the total mass of the monomer that is a synthetic raw material for the copolymer resin. 5. The inkjet ink as described in any one of 1 to 4 above, wherein the total is 10% or more and 50% or less.

  6). The inkjet ink according to any one of 1 to 5, wherein a mass ratio of the copolymer resin to the pigment contained in the ink is 1 to 15 times.

  7). The ammonia containing a chemical equivalent of 0.8 times or more and less than 3 times the chemical equivalent of the acid group of the copolymer resin or a water-soluble amine having a boiling point of 100 ° C. or more and less than 200 ° C. The inkjet ink of any one of 1-6.

  8). Using the inkjet ink according to any one of 1 to 7, printing is performed on a non-absorbing recording medium heated to 35 ° C. or more and less than 60 ° C., and the printed non-absorbing recording medium is 50 ° C. or more to 90 ° C. A recording method comprising heating and drying at less than

  According to the present invention, an image printed on a non-absorbent recording medium has high abrasion resistance and high adhesiveness, forms a high-gloss, high-quality image, and has high injection properties and excellent recoverability due to maintenance. An ink jet ink and an ink jet recording method using the ink can be provided.

  The present invention is described in detail below.

  The inventors of the present invention are highly glossy with respect to water-based pigment inks, such as PVC sheets used for signing applications, various resin substrates, and paper substrates that are slow to absorb such as printing paper. In addition to the formation of highly reliable images, investigations were repeated for the purpose of improving injection properties and maintainability.

(Non-absorbent recording medium)
The non-absorbable recording medium absorbs water to some extent like a recording medium made of a hydrophobic resin that hardly absorbs water such as polyvinyl chloride, PET, polypropylene, polyethylene, polycarbonate, or a printing paper such as coated paper, but absorbs water to some extent. This is a recording medium that is slow and has a problem that the water-based ink does not dry out in the printing process of normal ink jet printing under normal temperature and humidity conditions.

(Copolymer resin)
The copolymer resin functions as a binder for a pigment that is a colorant, has adhesiveness with a non-absorbent recording medium such as vinyl chloride, and has a function of improving the abrasion resistance of the coating film.

  In addition, the copolymer resin is required to have a function of forming an image having high gloss and high optical density. For this reason, the copolymer resin itself has high transparency in the coating film, and the pigment or pigment dispersion resin. It must also be compatible with

  As described above, in order to obtain a high-quality and highly durable printed image on various non-absorbing recording media including a vinyl chloride sheet, it is necessary to have ink wettability with respect to the non-absorbing recording medium. The higher the image quality and image durability, the higher the ink that gets wet with the recording medium. Therefore, it is preferable that the resin added to the ink does not deteriorate the wettability of the ink with respect to the non-absorbent recording medium.

  In addition, the injection characteristics must not be deteriorated by adding resin to the ink, and even if the injection performance deteriorates due to continuous printing or continuous pause, the initial injection state can be quickly restored by maintenance work. is necessary.

  There are several mechanisms for the deterioration of ink ejection properties. If ink droplets or dust adhere to the vicinity of the ejection nozzle of an inkjet head, the nozzle opening becomes dirty, the direction of the ejected ink droplet is bent, or the ejection amount is reduced. And troubles such as no longer discharging. Further, when the adhered ink covers the entire nozzle opening, ink droplets cannot be ejected. In order to avoid such troubles, an ink repellent treatment such as coating the periphery of the nozzle opening with a fluorine-based resin is performed to prevent ink droplets from adhering to the vicinity of the ejection nozzle.

  Accordingly, the resin added to the ink must be one that does not wet the ink with respect to the ink repellent treatment around the nozzle opening.

  As described above, it is necessary to add the resin to the ink sufficiently for many purposes. In particular, it is easy to wet the non-absorbent recording medium, and the ink repellent treatment around the nozzle opening. Therefore, it is necessary to design and select a resin having a conflicting function of not getting wet.

  As a result of detailed investigations on various resins, the inventors of the present invention have found that two or more alkyl acrylates having 2 to 4 and 6 to 12 carbon atoms in an alkyl group, particularly an acrylic copolymer resin having a low acid value. It has been found that an ink added with a resin obtained by copolymerizing an ester has good abrasion resistance and good ink repellency with respect to the ink repellency treatment around the nozzle opening of the ink jet head.

  As is well known, an acrylic resin can be freely selected and designed from a wide variety of monomers, is easily polymerized, and can be produced at a low cost. In particular, as described above, an acrylic resin having a high degree of design freedom is suitable for meeting many requirements required when added to ink.

  Commercially available acrylic resins include water-dispersed acrylic emulsions and water-soluble resins. The emulsion type generally has a merit that the molecular weight is larger than that of the water-soluble one and has a merit that it is easy to increase the strength of the film produced by the resin, but the dried film does not dissolve in water. Therefore, once dried on the head or the like, it cannot be dissolved and removed, and must be physically rubbed off, and is often difficult to maintain. Therefore, the copolymer resin is preferably a water-soluble resin.

  The copolymer resin after neutralization to be described later is preferably dissolved by 5% or more in water at 25 ° C., more preferably 10% or more.

  As the monomer to be copolymerized constituting the copolymer resin, at least two kinds of alkyl acrylate ester having 2 to 4 carbon atoms in the alkyl group and alkyl acrylate ester having 6 to 12 carbon atoms in the alkyl group are included. The present inventors have found that it is necessary to achieve both the rub resistance and adhesiveness of the resin and the ink repellency for the ink repellency treatment of the inkjet head.

  As a result of the study by the present inventors, in order to ensure sufficient abrasion resistance and adhesion to the non-absorbent recording medium of the resin, at least a monomer having 6 or more carbon atoms in the alkyl group of the alkyl acrylate is copolymerized. In addition, it has been found that, when the copolymerization ratio of the alkyl acrylate ester is increased regardless of the number of carbon atoms of the alkyl group, the abrasion resistance and adhesion tend to increase. This is probably because the higher the hydrophobicity of the resin, the higher the abrasion resistance and adhesion to the non-absorbent recording medium.

  On the other hand, the ink repellency with respect to the ink repellency treatment of the inkjet head tends to be better when the copolymerization ratio of the acrylic acid alkyl ester is lower. When the acrylic acid alkyl ester is copolymerized, it is preferable that the alkyl group has 12 or less carbon atoms because the influence of deterioration on the ink repellency is small. Particularly preferred is an alkyl acrylate ester having 2 to 4 carbon atoms in the alkyl group.

  Therefore, in order to achieve both rub resistance, adhesiveness and ink repellency, the alkyl group carbon number is 6 to 12, while copolymerizing an alkyl acrylate ester having a good ink repellency. It has been found that it is only necessary to increase the copolymerization ratio as the total amount of the alkyl acrylate to increase the abrasion resistance and the adhesiveness by copolymerizing 2-4 alkyl acrylates.

  Specific examples of the alkyl ester having 2 to 4 carbon atoms in the alkyl group include ethyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, and the like.

  Specific examples of the alkyl acrylate ester having 6 to 12 carbon atoms in the alkyl group include n-hexyl acrylate, cyclohexyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, and the like.

  It is essential to copolymerize an alkyl alkyl ester having 6 to 12 carbon atoms in the alkyl group, but the mass ratio of the alkyl alkyl ester having 6 to 12 carbon atoms in the alkyl group to the mass of all monomers of the resin is It is preferably 5% or more and 20% or less. 5% by mass or more is preferable from the viewpoint of abrasion resistance and adhesiveness, and 20% by mass or less is preferable from the viewpoint of ink repellency with respect to the ink repellent treatment of the inkjet head. More preferably, it is 5 mass% or more and 10 mass% or less.

  Although it is also essential to copolymerize an alkyl acrylate ester having 2 to 4 carbon atoms in the alkyl group, the alkyl acrylate ester having 2 to 4 carbon atoms in the alkyl group with respect to the mass of all monomers of the copolymer resin is essential. The mass ratio is preferably 5% or more and 40% or less, and more preferably 5% or more and 20% or less.

  The total mass of the alkyl alkyl ester having 2 to 4 carbon atoms in the alkyl group and the alkyl ester having 6 to 12 carbon atoms in the alkyl group with respect to the mass of all monomers constituting the copolymer resin is 10% or more. 50% or less, preferably 10% or more and 30% or less.

  Methyl methacrylate is preferably added in an amount of 15 to 85% by mass, more preferably 40 to 80% by mass, based on the total amount of monomers as raw materials for the copolymer resin.

  Examples of the acid monomer include acrylic acid, methacrylic acid, itaconic acid, maleic acid, and maleic acid half ester. Of these, acrylic acid and methacrylic acid are preferable because of high injection stability and good maintainability.

  As the monomer copolymerized with the copolymer resin, in addition to the above alkyl acrylates, methyl methacrylate, and acid monomers, methacrylic acid esters and styrene are used as long as they do not impair rubbing resistance, ink repellency, and maintainability. Other monomers may be included.

  The copolymer resin has an acid value of 50 mgKOH / g or more and 120 mgKOH / g or less.

  The present inventors have examined various resins in detail, and as a result, there is a close relationship between the acid value of the copolymer resin and the abrasion resistance and adhesiveness, and the lower the acid value of the copolymer resin, the better the resistance. It was found that the rubbing property and adhesiveness were improved. In this regard, the present inventors have a high acid value of the copolymer resin, the hydrophilicity of the resin is high, the affinity with the hydrophobic base material is low, and the resin and the base material are difficult to adhere, Conversely, if the acid value is low, the resin becomes hydrophobic, and the affinity with the hydrophobic base material is increased, so that the resin and the base material are favorably bonded.

  The acid value of the copolymer resin is also related to the water solubility of the resin, the ink ejection properties, and the maintainability. If the acid value is high, the water solubility of the resin is high and the ink is easily dissolved. It is easy to dissolve and remove when dried, and the physical scraping force can be reduced, facilitating maintenance. On the contrary, the acid value of the copolymer resin also affects the gloss, and when the acid value is low, the gloss tends to be improved.

  From the above, the acid value of the copolymer resin is preferably 50 mgKOH / g or more and 120 mgKOH / g or less, more preferably 50 mgKOH / g or more and 100 mgKOH / g or less.

  The copolymer resin has a glass transition temperature (Tg) of 30 ° C. or higher and 110 ° C. or lower. When Tg is 30 ° C. or higher, the abrasion resistance is high and blocking does not occur. Further, when Tg is 110 ° C. or less, the abrasion resistance is good. This is thought to be because the film after drying maintains flexibility without being brittle at room temperature. In addition, Tg of this copolymer resin can be adjusted with the kind and composition ratio of the monomer to be copolymerized.

  The copolymer resin has a weight average molecular weight (Mw) of 20,000 or more and less than 80,000. This is because if the weight average molecular weight is 20,000 or more, the rubbing resistance is good, and if it is less than 80,000, the ink ejection properties and maintenance properties are excellent. The weight average molecular weight of the copolymer resin is more preferably 25,000 or more and 70,000 or less.

  The weight average molecular weight of the copolymer resin can be adjusted by reaction conditions such as the monomer concentration and the amount of the initiator at the time of polymerization.For example, the weight average molecular weight can be increased by increasing the monomer concentration, The weight average molecular weight can be reduced by increasing the amount.

  The copolymer resin may be added before the pigment is dispersed or may be added after the pigment is dispersed, but is preferably added after the pigment is dispersed.

  The copolymer resin is preferably added in an amount of 1% by mass to 15% by mass in the ink. More preferably, it is 3 mass% to 10 mass%.

  The copolymer resin provides good image abrasion resistance, adhesion and gloss when the mass ratio to the pigment solid content is 1 or more, and ink ejection and maintenance when the mass ratio is 15 or less. It is preferable because the properties are not impaired. More preferably, the mass ratio is 1 to 10 times.

  Resins other than the copolymer resin can be used together with the inkjet ink of the present invention. A preferable content of the copolymer resin with respect to the total resin contained in the ink is 50% by mass or more and 100% by mass or less.

(Neutralization of copolymer resin)
The copolymer resin is preferably used by neutralizing all or part of the portion corresponding to the acid monomer with a base. As the neutralizing base, an alkali metal-containing base (for example, NaOH, KOH, etc.), an amine (for example, alkanolamine, alkylamine, etc.) or ammonia is preferably used.

  In particular, neutralization with ammonia or amines having a boiling point of 100 ° C. or higher and 200 ° C. or lower is preferable in order to dissolve the copolymer resin in the ink or improve image durability. -Dimethylaminoethanol, 2-amino-2-methylpropanol and the like are particularly preferable in terms of injection stability.

  If the addition amount of the neutralizing base is too small, the effect of neutralization of the copolymer resin cannot be obtained, and if it is too large, there are problems such as water resistance, discoloration, and odor of the image. A chemical equivalent of 0.8 times or more and less than 3 times is preferable.

  Next, the configuration other than the copolymer resin will be described in detail.

(Pigment)
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.

  Preferred specific organic pigments are exemplified below.

  Examples of pigments for magenta or red include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.

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

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

(Pigment dispersion)
The pigment is processed in various ways to maintain a stable dispersion state in water-based ink, and a pigment dispersion is produced.

  The dispersion is not particularly limited as long as it can be stably dispersed in an aqueous system. A pigment dispersion dispersed with a polymer dispersion resin, a capsule pigment coated with a water-insoluble resin, and a dispersion surface can be used without modifying the pigment surface. It can be selected from dispersible self-dispersing pigments and the like.

  When a pigment dispersion dispersed with a polymer dispersion resin is used, a water-soluble resin can be used. As the water-soluble resin, styrene-acrylic acid-acrylic acid alkyl ester copolymer, styrene-acrylic acid copolymer, styrene-maleic acid copolymer, styrene-maleic acid-acrylic acid alkyl ester copolymer are preferably used. Styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid alkyl ester copolymer, styrene-maleic acid half ester copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer It is a water-soluble resin such as.

  Further, as the pigment dispersion resin, the copolymer resin may be used for dispersion.

  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 method for dispersing the pigment.

  It is also preferable to use a centrifuge or a filter for the purpose of removing the coarse particles of the pigment dispersion.

  Further, a capsule pigment coated with a water-insoluble resin may be used as the pigment. The water-insoluble resin is a resin that is insoluble in water in a weakly acidic to weakly basic range, and is preferably a resin having a solubility of 2% or less in an aqueous solution having a pH of 4 to 10.

  The water-insoluble resin is preferably acrylic, styrene-acrylic, acrylonitrile-acrylic, vinyl acetate, vinyl acetate-acrylic, vinyl acetate-vinyl chloride, polyurethane, silicone-acrylic, acrylic silicon, Listed are polyester resins and epoxy resins.

  As the molecular weight of the dispersion resin or the water-insoluble resin, those having an average molecular weight of 3000 to 500,000 can be used, and those having a molecular weight of 7000 to 200,000 are more preferable.

  The dispersion resin or the water-insoluble resin preferably has a Tg of about -30 ° C to 100 ° C, more preferably about -10 ° C to 80 ° C.

  The mass ratio of the pigment to the dispersion resin or the water-insoluble resin can be selected preferably in the range of 100/150 or more and 100/30 or less in the pigment / resin ratio. Particularly, the image durability, injection stability, and ink storage stability are in the range of 100/100 or more and 100/40 or less.

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

  Various known methods can be used as a method of coating the pigment with the water-insoluble resin. Preferably, the water-insoluble resin is dissolved in an organic solvent such as methyl ethyl ketone, and the acidic groups in the resin are partially categorized with a base. Preferably, after neutralization or complete neutralization, a pigment and ion-exchanged water are added and dispersed, and then the organic solvent is removed, and water is added if necessary for adjustment. Alternatively, a method in which a pigment is dispersed using a polymerizable surfactant, a monomer is supplied thereto, and coating is performed while polymerization is also preferable.

  In addition, as the self-dispersing pigment, a surface-treated commercial product can be used, and preferable self-dispersing pigments include, for example, CABO-JET200, CABO-JET300 (manufactured by Cabot Corporation), Bonjet CW1 (Orient Chemical Co., Ltd.) Manufactured).

(Water-soluble organic solvent)
It is preferable to add a low surface tension water-soluble organic solvent to the ink of the present invention.

  Addition of water-soluble organic solvent with low surface tension further suppresses ink mixing on recording media made of various hydrophobic resins such as soft PVC sheets and paper substrates that absorb slowly such as printing paper. This is because a high-quality printed image can be obtained. Water-soluble organic solvents with low surface tension have the effect of improving the wettability of ink with respect to vinyl chloride, etc. In addition, when the above copolymer resin is used, the viscosity of the ink increases as the moisture in the ink dries. This is thought to be due to the effect of

  In particular, it is preferable to add glycol ethers or 1,2-alkanediols. Specifically, it is preferable to use a water-soluble organic solvent having the following low surface tension.

  Examples of glycol ethers include 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, dipropylene glycol propyl ether, And propylene glycol monomethyl ether.

  Examples of 1,2-alkanediols include 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-heptanediol, and the like.

  It is also preferable to add a solvent that can dissolve, soften, or swell recording media such as vinyl chloride. This is preferable because the adhesion between the vinyl chloride and the copolymer resin is further improved, and the adhesion and abrasion resistance of the image are improved.

  Examples of such solvents include cyclic solvents containing nitrogen or sulfur atoms, cyclic ester solvents, lactic acid esters, alkylene glycol diethers, alkylene glycol monoether monoesters, and dimethyl sulfoxide.

  Preferable specific examples of the cyclic solvent containing a nitrogen atom include a cyclic amide compound, preferably a 5- to 7-membered ring, such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone. 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, methylcaprolactam, 2-azacyclooctanone and the like.

  Preferable specific examples of the cyclic solvent containing sulfur atoms are preferably cyclic 5- to 7-membered rings, such as sulfolane.

  Preferable specific examples of the cyclic ester solvent include γ-butyrolactone and ε-caprolactone, and examples of the lactic acid ester include butyl lactate and ethyl lactate.

  A preferred specific example of the alkylene glycol diether is diethylene glycol diethyl ether.

  Preferable specific examples of the alkylene glycol monoether monoester include diethylene glycol monoethyl monoacetate.

  In addition, alcohols (eg, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol), polyhydric alcohols (eg, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol) , Dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol), amines (eg, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine) , Morpholine, N-ethylmorpholine, ethylenediamine, diethylenedia , Triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine), amides (for example, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, etc.), etc. It is done.

(Surfactant)
Next, the silicone-based or fluorine-based surfactant will be described.

  By adding a silicone-based or fluorine-based surfactant, it is possible to further suppress ink mixing on recording media composed of various hydrophobic resins including vinyl chloride sheets and recording media that absorb slowly such as printing paper. And high-quality printed images can be obtained. The surfactant is particularly preferably used in combination with the low surface tension water-soluble organic solvent.

  The silicone surfactant is preferably a polyether-modified polysiloxane compound, and examples thereof include KF-351A and KF-642 manufactured by Shin-Etsu Chemical Co., and BYK345, BYK347, and BYK348 manufactured by Big Chemie.

  The fluorine-based surfactant means a compound in which a part or all of the fluorine-based surfactant is substituted with fluorine in place of hydrogen bonded to carbon of a hydrophobic group of a normal surfactant. Of these, those having a perfluoroalkyl group in the molecule are preferred.

  Among the fluorosurfactants, a certain type is a trade name of Megafac F from DIC Corporation and a trade name of Surflon from Asahi Glass Co., Minnesota Mining and Manufacture. The product name is Fluorad FC from Ring Company, the product name is Monflor from Imperial Chemical Industry, and the product name is Zonyls from EI DuPont Nemeras and Company. The product is also commercially available under the name and the product name Licobet VPF from the company Farbeberke Hoechst.

  The fluorine-based surfactant is classified into an anionic type, a cationic type, and a nonionic type depending on the kind of the hydrophilic group, and a nonionic type is preferable.

  Preferable specific examples of the nonionic fluorosurfactant include Megafax 144D manufactured by DIC Corporation, Surflon S-141 and 145 manufactured by Asahi Glass Co., Ltd., and amphoteric fluorosurfactants. Examples of the agent include Surflon S-131 and 132 manufactured by Asahi Glass Co., Ltd.

  The silicone-based or fluorine-based surfactant can be used in combination with the following activator.

  For example, anionic surfactants such as dialkyl sulfosuccinates, alkyl naphthalene sulfonates, fatty acid salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, polyoxyethylene / polyoxypropylene blocks Nonionic surfactants such as copolymers, and cationic surfactants such as alkylamine salts and quaternary ammonium salts. In particular, an anionic surfactant and a nonionic surfactant can be preferably used.

(Heating of recording medium)
By using the water-based ink of the present invention, it is possible to print on the non-absorbent recording medium with high image quality without ink mixing, and to form an image with high gloss, high abrasion resistance and adhesiveness.

  In order to form images with higher image quality and higher abrasion resistance and adhesion, and to be able to cope with higher printing conditions, the recording medium is heated to a temperature of 35 ° C. or higher and 60 ° C. or lower. It is preferable to print while. When the temperature is 35 ° C. or higher, the heating effect is sufficiently exhibited, and when the temperature is 60 ° C. or lower, the flatness of the vinyl chloride recording medium is good, and the ink on the head is difficult to dry and the injection stability is good.

  In addition, after printing with heating, the combined use of drying by heating at 50 ° C. or more and less than 90 ° C. promotes drying by heating after printing, and the copolymer resin and the non-absorbent recording medium It is more preferable for improving the adhesiveness.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

Example 1
(Synthesis of copolymer resin)
(Synthesis of copolymer resin P-1 of the present invention)
186 parts of 2-propanol was placed in a flask equipped with a dropping funnel, a reflux tube, a nitrogen introduction tube, a thermometer, and a stirring device, and the mixture was heated to reflux while bubbling nitrogen. A monomer solution in which 0.5 part of initiator (AIBN) was dissolved in a mixed liquid of 70 parts of methyl methacrylate, 10 parts of ethyl acrylate, 10 parts of 2-ethylhexyl acrylate, and 10 parts of methacrylic acid was added from a dropping funnel. It was added dropwise over time. After dropping, the mixture was further heated and refluxed for 5 hours and then allowed to cool, and 2-propanol was distilled off under reduced pressure to obtain a copolymer resin P-1.

(Synthesis of copolymer resins P-2 to P-27)
Similarly to the synthesis of copolymer resin P-1, copolymer resins P-2 to P-27 were synthesized at the monomer composition ratios shown in Table 1. The weight average molecular weight (Mw) of the copolymer resin was adjusted by changing the amount of the initiator.

  The Tg and weight average molecular weight (Mw) of the copolymer resin were measured by the following methods.

(Measurement of Tg)
The Tg of the copolymer resin was measured by DSC in a nitrogen stream. The DSC measurement conditions were measured when the temperature was raised from −30 to 100 ° C. or from 0 to 130 ° C. at 10 ° C./min, and after cooling, the temperature was raised again. Tg was calculated | required from the measured value when it heated up again.

(Measurement of weight average molecular weight)
The weight average molecular weight (Mw) of the copolymer resin was measured by GPC. The measurement conditions are shown below.

Column: Tosoh TSKgel G40000 + 2500 + 2000HXL, 40 ° C.
Eluent: THF 1.0 (ml / min)
Injection volume: 100 μl
Detection: RI
Calibration curve: standard polystyrene.

(Synthesis of copolymer resin P-28 (monomer composition ratio is the same as ink-soluble resin R-2 described in Patent Document 3))
As a monomer, except that a mixed liquid of 40 parts of butyl acrylate, 5 parts of 2-hydroxyethyl methacrylate, 30 parts of styrene and 25 parts of acrylic acid was used and the weight average molecular weight was adjusted to 8000 by changing the amount of the initiator, Copolymer resin P-28 was synthesized in the same manner as copolymer resin P-1.

(Synthesis of copolymer resin P-29 (monomer composition ratio is the same as binder polymer 1 described in Patent Document 1))
A copolymer resin P-29 was synthesized in the same manner as the copolymer resin P-1, except that a mixed liquid of 30 parts of methoxypolyethylene glycol methacrylate, 10 parts of styrene, and 60 parts of methyl methacrylate was used as the monomer.

(Preparation of aqueous solution of copolymer resin)
To 10 parts of the copolymer resin P-1, 39.35 parts of ion-exchanged water and 0.65 part of 28% ammonia water as a neutralizing base were added, and the mixture was heated and stirred at 70 ° C. to dissolve the resin. Of 20% aqueous solution of copolymer resin P-1. The amount of ammonia is an amount corresponding to a number of chemical equivalents of 1.05 times the number of chemical equivalents of acid groups of copolymer resin P-1.

  Subsequently, P-2 to P-29 were used in place of the copolymer resin P-1, and the neutralized base in Table 2 was used in place of ammonia, as in the aqueous solution of the copolymer resin P-1. Then, aqueous solutions of copolymer resins P-2 to P-29 were prepared.

  The copolymer resin P-26 could not be used for the subsequent ink preparation because the resin did not dissolve in the aqueous ammonia solution and the solution became cloudy.

  Table 1 shows the Tg, acid value, and weight average molecular weight (Mw) of the copolymer resin. In Table 1, a monomer is described with an abbreviation, but the relationship between the abbreviation of the monomer and the compound name is as follows.

MMA: methyl methacrylate EA: ethyl acrylate n-BA: n-butyl acrylate i-BA: i-butyl acrylate n-HA: n-hexyl acrylate c-HA: cyclohexyl acrylate EHA: 2-acrylic acid 2- Ethylhexyl LA: Lauryl acrylate SA: Stearyl acrylate MAA: Methacrylic acid AA: Acrylic acid (Preparation of black pigment dispersion)
As a pigment dispersant, 8 parts of DISPERBYK-190 (manufactured by Big Chemie) was added to 72 parts of ion-exchanged water, and 5 parts of dipropylene glycol propyl ether was mixed therein. 15 parts of carbon black was added to this solution and premixed, and then dispersed using a sand grinder filled with 50% by volume of 0.5 mm zirconia beads to obtain a black pigment dispersion having a pigment solid content of 15%. .

(Preparation of ink K-1)
40 parts of aqueous solution of copolymer resin P-1 with 24.5 parts of ion-exchanged water, 5 parts of dipropylene glycol propyl ether, 10 parts of 1,3-dimethyl-2-imidazolidinone, KF which is a silicone surfactant -351A (Shin-Etsu Chemical Co., Ltd.) 0.5 part was added and stirred. Next, 20 parts of the black pigment dispersion was added thereto and stirred, and then filtered through a 0.8 μm filter to obtain a black ink K-1.

(Preparation of inks K-2 to K-25 and K-27 to K-29)
In ink K-1, the aqueous solution of the copolymer resin P-1 was changed to the aqueous solution of the copolymer resins P-2 to P-25 and P-27 to P-29, and the content of the copolymer resin, the organic solvent, Ink K-2 to K-25 and K-27 to K-29 were prepared by changing the mass ratio of the surfactant and the copolymer resin / pigment as shown in Table 2. In Table 2, the content of the copolymer resin and the content of the organic solvent represent the content (% by mass) relative to the ink.

  In Table 2, the neutralizing base, the organic solvent, and the surfactant are described in abbreviations. The abbreviations will be described below.

(Neutralizing base)
DMAE: N, N-dimethylaminoethanol AMP: 2-amino-2-methylpropanol.

(Organic solvent)
DPGPE: Dipropylene glycol propyl ether DEGBE: Diethylene glycol monobutyl ether HDO: 1,2-hexanediol DMI: 1,3-dimethyl-2-imidazolidinone.

(Surfactant)
Si-1: Silicone surfactant KF-351A (manufactured by Shin-Etsu Chemical Co., Ltd.)
Si-2: Silicone-based surfactant BYK-347 (manufactured by Big Chemie)
F: Fluorosurfactant FC-430 (manufactured by 3M).

  Each ink prepared as described above was evaluated according to the following method. In addition, the surface tension measured by the plate method for each ink was in the range of 25 to 30 mN / m.

(Image formation)
Each black ink was loaded into one of the heads of an on-demand type ink jet printer equipped with four rows of piezo heads having a nozzle diameter of 28 μm, a driving frequency of 18 kHz, a nozzle number of 512, a minimum droplet amount of 12 pl, and a nozzle density of 180 dpi.

  In addition, the printer can arbitrarily heat the recording medium from the back side (the side opposite to the side facing the head) using a contact heater, and the head storage position has an ink emptying position and a blade wipe type maintenance unit. The head cleaning can be performed at any frequency.

  Subsequently, a solid image of 100% Duty of 10 cm × 10 cm was printed at a printing resolution of 720 dpi × 720 dpi on a soft vinyl chloride sheet for a solvent inkjet printer as a recording medium.

  During printing on a polyvinyl chloride recording medium, the recording medium was heated from the back side and controlled with a heater so that the surface temperature of the recording medium during image recording 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 printing, the recording medium was dried at 60 ° C. for 5 minutes to obtain a recorded image.

(Evaluation of ink and recorded image)
(Abrasion resistance)
The recorded image was rubbed with dry cotton (Kanakin No. 3) under a load of 400 g, and scratch resistance was evaluated according to the following criteria.

A: The image does not change even after rubbing 50 times or more. ○: Some scratches remain after rubbing 50 times, but the image density is not affected and there is no practical problem. Δ: The image density is changed between 21 to 50 times. Although it is reduced, it is a practical level. X: The image density is lowered during rubbing 20 times or less, and there is a problem in practical use.

(Adhesive evaluation)
3 cm of cellophane tape was attached to the recorded image, and the image surface after peeling was observed.

◎: No change at all ○: Slight trace remains but no problem for practical use △: Part of the image is slightly peeled off and the density is partially reduced, but is at a practical level ×: Most of the image Peel off and the white background of the substrate is visible, which is problematic in practice.

(Evaluation of gloss)
The 20 ° glossiness of the recorded image was measured.

A: 20 ° glossiness is greater than 100% B: 20 ° glossiness is 81% to 100%
Δ: Glossiness at 20 ° is 60% to 80%
X: 20 degree glossiness is less than 60%.

(Ejection evaluation)
Evaluation images were continuously printed 10 times under the conditions of 25 ° C. and 25% relative humidity, and the 10th image was observed.

◎: No image defect is observed. ○: Slight fading is observed in the image writing portion (2 mm or less). △: Image defect (streaks due to ink ejection failure) is slightly observed. X: Image defect due to ink ejection failure. Can be seen quite a bit.

(Maintenance)
An evaluation image was printed under the conditions of 25 ° C. and a relative humidity of 25%, and then left for 30 minutes without capping the head. Thereafter, immediately after performing maintenance with a blade wipe type maintenance unit, an evaluation image was printed under conditions of 25 ° C. and a relative humidity of 25%, and this image was observed.

A: Image defect is not observed. O: Image defect (ink ejection failure) is very slightly observed. Δ: Image defect (ink ejection failure) is partially observed. X: Most of the image is not printed due to the defect.

(Evaluation of ink repellency)
As a member subjected to ink repellent treatment of an inkjet nozzle, an aqueous dispersion of tetrafluoroethylene / hexafluoropropylene copolymer (Neolon ND-1, manufactured by Daikin Industries, Ltd.) on a 75 μm-thick polyimide film is dried with a wire bar. Was prepared by applying, drying, and heat-treating to a thickness of 3 μm. The polyimide film that has been subjected to the ink repellent treatment is cut into 5 mm × 30 mm strips, the film pieces are dipped in the ink, then lifted with tweezers, and the ink is completely drained from the surface of the ink repellent treated surface immediately after the lifting. Was measured to evaluate ink repellency.

◎: The ink completely drains in less than 1 minute, and the ink repellency is good. ○: The ink runs out in less than 2 minutes and less than 2 minutes, and there is no problem with the ink repellency. △: More than 2 minutes and less than 3 minutes The ink runs out and is at a practical level. X: The ink remains on the surface even after 3 minutes or more, and there is a problem in practical use.

  The evaluation results are shown in Table 3.

  As is clear from the results shown in Table 3, the ink of the present invention has an ink ejection property, maintenance property, ink repellency, and abrasion resistance when an image is recorded on polyvinyl chloride as a recording medium, as compared with the comparative example. It can be seen that it is excellent in all properties of adhesiveness and gloss.

Example 2
(Preparation of pigment dispersion and ink)
In addition to carbon black, C.I. I. Pigment yellow 74, C.I. I. Pigment red 122, C.I. I. Pigment Blue 15: 3 was used to prepare black, yellow, magenta and cyan pigment dispersions in the same manner as in the preparation of the black pigment dispersion of Example 1.

  As shown in Table 4, using these pigment dispersions, the copolymer resin prepared in Example 1, a neutralizing base, an organic solvent, and a surfactant, the content of the copolymer resin with respect to the ink shown in Table 4 The ink set shown in Table 4 was obtained in the same manner as in Example 1 except that the mass ratio of the copolymer resin to the pigment was adjusted.

(Image formation)
These ink sets were loaded into the printer used in Example 1, and printed in the same manner as in Example 1 to obtain a 100% duty solid image of each color 10 cm × 10 cm.

(Evaluation of ink and recorded image)
The obtained evaluation image was evaluated in the same manner as in Example 1 for abrasion resistance, adhesiveness, and gloss. In addition, each ink was evaluated for ejection properties and ink repellency in the same manner as in Example 1.

  The evaluation results are shown in Table 5.

  As is apparent from the results shown in Table 5, the ink set comprising the ink of the present invention was compared with the comparative example in terms of abrasion resistance, adhesiveness, gloss, and ink ejection properties when an image was recorded on polyvinyl chloride. It turns out that it is excellent in all the characteristics of ink repellency.

Claims (8)

  In an aqueous inkjet ink containing at least water, a pigment, a resin, a water-soluble organic solvent, and a silicone-based or fluorine-based surfactant, the resin has at least methyl methacrylate, an acid monomer, and an alkyl group having 2 to 4 carbon atoms. And a copolymer resin synthesized from a monomer containing an alkyl acrylate having an alkyl group having 6 to 12 carbon atoms, and the copolymer resin has an acid value of 50 mgKOH / g or more and 120 mgKOH. / G or less, a glass transition temperature (Tg) of 30 ° C. to 110 ° C., and a weight average molecular weight (Mw) of 20,000 to 80,000.   The inkjet ink according to claim 1, wherein the acid monomer is acrylic acid or methacrylic acid.   The mass ratio of the alkyl alkyl ester having 6 to 12 carbon atoms in the alkyl group is 5% or more and 20% or less with respect to the total mass of the monomer that is a synthetic raw material of the copolymer resin. Item 3. The inkjet ink according to Item 1 or 2.   The mass ratio of the alkyl alkyl acrylate having 2 to 4 carbon atoms in the alkyl group is 5% to 40% with respect to the total mass of the monomer, which is a synthetic raw material for the copolymer resin. Item 4. The inkjet ink according to any one of Items 1 to 3.   The mass of the alkyl alkyl ester having 6 to 12 carbon atoms in the alkyl group and the alkyl alkyl ester having 2 to 4 carbon atoms in the alkyl group with respect to the total mass of the monomer that is a synthetic raw material for the copolymer resin. The total of is 10% or more and 50% or less, The inkjet ink according to any one of claims 1 to 4.   The inkjet ink according to claim 1, wherein a mass ratio of the copolymer resin to the pigment contained in the ink is 1 to 15 times.   A chemical equivalent of 0.8 times or more and less than 3 times the chemical equivalent of ammonia or a water-soluble amine having a boiling point of 100 ° C. or more and less than 200 ° C. with respect to the chemical equivalent of the acid group of the copolymer resin. Item 7. The inkjet ink according to any one of Items 1 to 6.   Printing is performed on a non-absorbent recording medium heated to 35 ° C. or higher and lower than 60 ° C. using the inkjet ink according to claim 1, and the printed non-absorbable recording medium is set to 50 ° C. or higher and 90 ° C. or higher. A recording method comprising heat drying at a temperature of less than ° C.