Block polymer for inkjet ink

Abstract

To provide a block polymer for aqueous inkjet ink, which exhibits superior ejection stability from an inkjet head during printing on packaging or label materials, while demonstrating superior rub resistance and water resistance.SOLUTION: An inkjet ink block polymer comprises a hydrophilic unit (b-1) and a hydrophobic unit (b-2). The block polymer has a number average molecular weight of 8,000 to 50,000 and has an average particle diameter of 30 to 150 nm. The hydrophilic unit (b-1) includes a structural unit represented by the following formula.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a block polymer for inkjet ink, an aqueous inkjet ink using the same, and a printed matter thereof.

Background Art

[0002] An inkjet printing method, which is a type of digital printing method, forms an image or characters (hereinafter collectively referred to as "printed matter") on a printing medium by flying and landing minute droplets of ink from an inkjet head onto a base material as the printing medium. Compared with other digital printing methods, it is excellent in terms of the size and cost of the printing apparatus, the running cost during printing, the ease of full-colorization, etc., and in recent years, it has been increasingly used also in industrial printing applications.

[0003] Inks used in the inkjet printing method cover a wide range, such as oil-based, solvent-based, active energy ray-curable, and water-based. Heretofore, solvent-based and active energy ray-curable inks have been used in industrial printing applications. However, in recent years, due to considerations and responses regarding environmental and human hazards, the demand for water-based inks (also referred to as aqueous inks) has been increasing.

[0004] By the way, base materials used for package packaging of daily necessities, label materials, etc. require the formation of printed matter having characteristics that can withstand actual use with respect to hardly permeable base materials such as art paper and coated paper, and non-permeable base materials such as polyolefin and polyethylene terephthalate (PET) film, from the viewpoints of their cosmetic properties, protection of the contents, and long-term information display.

[0005] When printing on hardly permeable base materials and non-permeable base materials used for package packaging and label materials, since the ink droplets after landing hardly penetrate into the base material, drying due to penetration does not occur, and problems such as color mixing bleeding and color unevenness occur, and the printed image quality is impaired.

[0006] Regarding the problem of impaired printing quality, pretreatment liquids are known. Generally, as pretreatment liquids for aqueous inkjet inks, there are those that form a layer (ink receiving layer) that absorbs the liquid components in the aqueous inkjet ink and improves the drying property (see Patent Documents 1 and 2), and those that form a layer (ink aggregation layer) that intentionally aggregates the solid components contained in the aqueous inkjet ink, such as colorants and resins, to prevent bleeding between droplets and color unevenness and improve the printing quality (see Patent Documents 3 and 4). Two types are known.

[0007] As printing methods for these pretreatment liquids, gravure coating method, flexographic roll coating method, kiss coating method, spray coating method, curtain coating method, blade coating method, reverse roll coating method, etc. are usually used, and the pretreatment liquid is applied to the entire surface of the substrate. This is because it can cope with various images printed by inkjet printing and is cost-effective.

[0008] However, in the portions where the inkjet ink image is not printed (also referred to as non-image portions), the application of the pretreatment liquid is unnecessary, and only the consumption amount of the pretreatment liquid increases. In addition, there is a need to accommodate different printing methods, one for printing the pretreatment liquid and the other for printing the image by the inkjet method, in one device, resulting in problems such as the enlargement of the printing device and the increase in running costs.

[0009] Regarding this problem, studies have been conducted on pretreatment liquids printed by the inkjet method. Most of them are the formation of an ink aggregation layer that intentionally aggregates the solid components contained in the inkjet ink to prevent bleeding between droplets and color unevenness, and are cationic materials that have an aggregating effect on anionic colorants and pigment dispersions (see Patent Documents 5 to 7).

[0010] However, printed matter using aqueous ink has problems such as low resistance of the coating film to liquids such as water and alcohol, rubbing off of the ink coating film, and bleeding of images. In particular, for printed matter used in package packaging, label materials, etc., strong water resistance, alcohol resistance, and abrasion resistance are required not only for the ink layer forming the image part but also for the coating film layer of the pretreatment liquid. This is because even if the coating film of the ink layer is strong, if the pretreatment layer existing between the base material and the ink layer is fragile, the ink layer will peel off together with the pretreatment layer.

[0011] On the other hand, emulsion resin particles for aqueous inkjet ink that have good water resistance and abrasion resistance and can form a tough coating film have been studied (see Patent Documents 8 to 9). Similarly, emulsion resin particles have also been studied for inkjet ink having a pretreatment liquid function for improving printing image quality (see Patent Document 10). However, while emulsion resin particles are excellent in water resistance, they are insoluble in water, so they tend to deposit on the nozzle surface of the inkjet head, resulting in a problem of reducing the ejection stability. Furthermore, if the ink adheres to the nozzle, the nozzle will be blocked and ejection will become impossible. In particular, in the one-pass printing inkjet printing method (also referred to as the "line printing method", hereinafter abbreviated as the "one-pass printing method"), just one nozzle being blocked will cause large image defects.

[0012] As described above, in printing on package packaging and label materials by the inkjet method, an aqueous inkjet ink that has excellent ejection stability, water resistance and abrasion resistance suitable for packaging materials, and also has a pretreatment liquid function for improving printing image quality has not been found so far.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Patent Document 10

Summary of the Invention

Problems to be Solved by the Invention

[0014] The present invention has been made to solve the above problems, and an object thereof is to provide an inkjet ink block polymer, an aqueous inkjet ink, and a printed matter that are excellent in ejection stability from the nozzles of an inkjet head even in printing on a hardly permeable substrate or a non-permeable substrate used for package packaging or label materials, and further excellent in water resistance and abrasion resistance.

[0015] As a result of intensive studies by the present inventors, it has been found that the above problems can be solved by an inkjet block polymer having the following configuration.

[0016] That is, the present inventors A block polymer for an inkjet ink having a hydrophilic unit (b-1) and a hydrophobic unit (b-2), wherein the block polymer has a number average molecular weight of 8,000 to 50,000 and an average particle diameter of 30 to 150 nm, and the hydrophilic unit (b-1) contains a structural unit represented by the formula (1). The present invention relates to a block polymer for an inkjet ink. Formula (1) [Chemical formula] (In formula (1), R 1 represents a hydrogen atom or a methyl group, Z represents an oxygen atom, -NH-, or -OCH2CH(OH)-, and R 2 , R 3 , R 4 each independently represents an alkyl group having 1 to 8 carbon atoms, X - represents a monovalent anion, and n represents an integer of 1 to 6.)

[0017] The present invention also relates to a block polymer for an inkjet ink, wherein the hydrophobic unit (b-2) contains a structural unit having a cyclic structure.

[0018] The present invention also relates to a block polymer for an inkjet ink, which contains 1 to 40% by mass of the structural unit represented by the formula (1) based on the total mass% of the block polymer for an inkjet ink.

[0019] The present invention also relates to an inkjet ink containing the block polymer for an inkjet ink, a polyvalent metal salt and / or a water-soluble cationic resin, and substantially free of a colorant.

[0020] The present invention also relates to a printed matter obtained by printing an inkjet ink containing the block polymer for an inkjet ink on a substrate. [Advantages of the Invention]

[0021] The block polymer for inkjet ink of the present invention enables the provision of an aqueous inkjet ink that is excellent in ejection stability from the nozzles of an inkjet head and further has excellent water resistance and abrasion resistance.

Mode for Carrying Out the Invention

[0022] Preferred embodiments will be given below to describe the block polymer for inkjet ink of the present invention. Hereinafter, the "block polymer for inkjet ink" may be referred to as the "block polymer", and the "aqueous inkjet ink" may be referred to as the "aqueous ink" or the "ink".

[0023] <Block Polymer> A block polymer is a copolymer composed of two or more types of monomers, and is a polymer in which two or more polymer units having different copolymerization compositions are bonded in one polymer chain, and is also called a block copolymer or a block copolymer. Block polymers have methods of chemically bonding each polymer unit and methods of polymerizing other monomers at the ends of one polymer unit. Unlike a random copolymer (also called a random polymer), a block polymer has the properties of each polymer unit.

[0024] The block polymer of the present invention has a hydrophilic unit (b-1) and a hydrophobic unit (b-2). The hydrophilic unit has a high affinity for water and is dissolved in water, while the hydrophobic unit is not dissolved in water. Therefore, in water, micelles with a particulate nature are formed. This is because polymer units with greatly different solubilities, namely hydrophilicity and hydrophobicity, cause repulsion between the hydrophilic-hydrophobic units and phase-separate in micro regions. From this, by having a hydrophobic unit, the hydrophobic units of a plurality of polymers aggregate and maintain a particulate state, so that the viscosity of the resin dispersion is suppressed, the viscous change of the resin dispersion is small, and it is considered that the ejection stability of the inkjet ink using the block polymer is improved. Furthermore, the water resistance and rub resistance of the ink coating film after printing are improved. Also, by having a hydrophilic unit, the hydrophilic unit dissolved in water covers the hydrophobic unit, and the dispersion stability in water becomes good. Furthermore, by having solubility in water, nozzle clogging of the inkjet head is suppressed. However, the above is based on scientific considerations, and the present invention is not limited only to the said action.

[0025] The polymerization method of the block polymer can be carried out by polymerization using the living radical polymerization method, which is a known polymerization method. Examples of the living radical polymerization method include nitroxide-mediated polymerization, atom transfer polymerization, reversible addition-fragmentation chain transfer polymerization, organic tellurium-mediated polymerization, iodine transfer polymerization, and the like. It is preferable to use the reversible addition-fragmentation chain transfer polymerization method (also referred to as RAFT polymerization) for the block polymer of the present invention.

[0026] Reversible addition-fragmentation chain transfer polymerization is a type of reversible deactivation radical polymerization and is one of the methods that can impart livingness to radical polymerization. In living polymerization, the polymerization reaction starts in all polymer chains from the initial stage of the reaction, the polymer chains grow at the same reaction rate, and polymerization proceeds. Therefore, there are no irreversible chain transfer or termination reactions, and a polymer with a narrow molecular weight distribution (PDI = weight average molecular weight / number average molecular weight) can be obtained. Also, by adding more monomers to the polymerization reaction system, the polymer chains can be extended. Utilizing this, multiple blocks with different properties can be connected, and AB diblock polymers, ABA or ABC triblock polymers, etc. can be obtained.

[0027] The number average molecular weight (Mn) of the block polymer of the present invention is 8,000 to 50,000. Preferably it is 10,000 to 30,000, and more preferably 12,000 to 20,000. By setting the number average molecular weight to 8,000 or more, the water resistance and abrasion resistance of the coating film after printing are excellent, and the alcohol resistance is also excellent. By setting it to 50,000 or less, good ejection stability can be obtained.

[0028] The number average molecular weight of the block polymer in the present invention can be measured by conventional methods. In the present invention, it was measured using GPC (manufactured by Tosoh Corporation, HLC-8120GPC) equipped with a TSKgel column (manufactured by Tosoh Corporation) and an RI detector, and calcium nitrate solution was used as the eluent. For both, PEG (polyethylene glycol) and PEO (polyethylene oxide), which are water-soluble molecular weight standard polymers, were used to create the calibration curve.

[0029] In addition, the block polymer obtained by living radical polymerization can provide a polymer with a narrower molecular weight distribution compared to the random polymer obtained by conventional radical polymerization. The more uniform the molecular weight distribution of the block polymer, the stronger the phase separation in the micro region, and the stronger the characteristics of each polymer unit with different solubilities can be expressed. The molecular weight distribution of the block polymer of the present invention is preferably 1.6 or less, more preferably 1.5 or less. By setting it to 1.6 or less, the characteristics of each polymer unit are easily expressed, and good ejection stability and dispersion stability can be obtained.

[0030] The block polymer of the present invention has an average particle size in the range of 30 to 150 nm, more preferably 40 to 120 nm. The average particle size in the present invention was measured by a particle distribution measurement method using dynamic light scattering with a NanoTrac UPA-EX150 manufactured by Microtrac Bell Corporation, and the 50% volume average particle size (D50) was used as the average particle size. In addition, polymer samples with a small average particle size that were impossible to measure were judged to be water-soluble resins because they did not maintain a particulate state. If the water solubility is strong and the particulate state is not expressed, not only the water resistance of the printed coating film will be inferior, but also the viscosity of the dispersion liquid will increase and the ejection stability will decrease. By setting the average particle size to 30 nm or more, the ejection stability is excellent, and furthermore, the resistance of the ink coating film is good. By setting it to 150 nm or less, the storage stability of the inkjet ink is excellent.

[0031] Subsequently, each component constituting the block polymer for inkjet ink of the present invention will be described in detail below.

[0032] <Hydrophilic unit (b-1)> The block polymer of the present invention includes, as a structural unit, a structural unit represented by the formula (1) in the hydrophilic unit (b-1). Formula (1)

Chemical formula

[0033] In formula (1), R 1 , R 2 , and R 3 being a methyl group and Z being an oxygen atom are preferred from the viewpoint of the ejection stability of the inkjet ink.

[0034] As a method for introducing the structural unit represented by formula (1) into the hydrophilic unit (b-1), there are a method of copolymerizing using a vinyl monomer containing a cationic group, and a method of obtaining a block polymer having a tertiary amino group by copolymerizing a vinyl monomer having a tertiary amino group as a monomer component and then reacting with an onium saltifying agent to quaternize ammonium chloride. In the present invention, either polymerization method can be selected.

[0035] The pretreatment liquid for improving the printing image quality by aggregation uses aggregating agents such as polyvalent metal salts and water-soluble cationic resins in order to impart a function of aggregating the solid components contained in the ink. In an aqueous solution, these are dissolved as cationic metal ions and cationic resins. This is because the solid components in the ink that form the image, mainly the pigment dispersion and the binder resin, are designed to be anionic, and when they come into contact, they aggregate, resulting in excellent printing image quality. Inkjet inks having the pretreatment liquid function require a material design that can stably exist with a cationic aggregating agent. Since the hydrophilic unit (b-1) of the block polymer of the present invention exhibits cationicity by including the structural unit of formula (1), it can stably exist without aggregating with the cationic aggregating agent, and the ejection stability and storage stability of the inkjet ink are improved. In the case of a hydrophilic unit exhibiting anionic properties obtained by polymerizing and neutralizing a block polymer from a monomer containing an acid group such as a carboxyl group, aggregation with the aggregating agent progresses, and the ejection stability and storage stability decrease.

[0036] The structural unit represented by formula (1) is preferably contained in an amount of 1 to 40% by mass, more preferably 5 to 30% by mass, based on the total mass% of the block polymer for inkjet. By setting it to 1% by mass or more, the storage stability of the inkjet ink is improved, and by setting it to 40% by mass or less, the ejection stability is excellent and the water resistance of the coating film after printing is good. Further, it is preferable that the entire amount of the structural unit represented by formula (1) is contained in the hydrophilic unit.

[0037] As the vinyl monomer containing a cationic group for introducing the structural unit represented by the formula (1) into the hydrophilic unit (b-1), a quaternary ammonium salt type monomer is preferable. For example, alkyl (meth)acrylate quaternary ammonium salts such as (meth)acryloyloxyethyltrimethylammonium chloride, (meth)acryloyloxyethyltriethylammonium chloride, (meth)acryloyloxyethyldimethylbenzylammonium chloride, (meth)acryloyloxyethylmethylmorpholinoammonium chloride, 2-hydroxy-3-(meth)acryloyloxypropyltrimethylammonium chloride, (meth)acryloylaminopropyltrimethylammonium chloride, (meth)acryloylaminoethyldimethylbenzylammonium chloride, and alkyl (meth)acryloylamide quaternary ammonium salts such as (meth)acryloylaminoethyltriethylammonium chloride can be mentioned, but it is not particularly limited to these. These can be used alone or in combination of two or more.

[0038] When introducing the structural unit represented by the formula (1) into the hydrophilic unit (b-1) from a vinyl monomer having a tertiary amino group, the vinyl monomer having a tertiary amino group to be used is, for example, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dipropylaminoethyl (meth)acrylate, diisopropylaminoethyl (meth)acrylate, dibutylaminoethyl (meth)acrylate, diisobutylaminoethyl (meth)acrylate, dit-butylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylamide, diethylaminopropyl (meth)acrylamide, dipropylaminopropyl (meth)acrylamide, diisopropylaminopropyl (meth)acrylamide, dibutylaminopropyl (meth)acrylamide, diisobutylaminopropyl (meth)acrylamide, dit-butylaminopropyl (meth)acrylamide, etc., which are (meth)acrylic acid esters or (meth)acrylamides having a dialkylamino group, but it is not particularly limited to these. These can be used alone or in combination of two or more.

[0039] When reacting an onium chlorinating agent with a tertiary amino group to perform ammonium chlorination, examples of the onium chlorinating agent used include alkyl halides such as chloromethane, chloroethane, chloropropane, chlorobutane, bromomethane, bromoethane, bromopropane, bromobutane, iodomethane, iodoethane, iodopropane, iodobutane, benzyl chloride, benzyl bromide, etc., alkyl sulfates such as dimethyl sulfate, diethyl sulfate, or dipropyl sulfate, and sulfonic acid esters such as methyl p-toluenesulfonate, methyl benzenesulfonate, etc. However, it is not particularly limited to these. These can be used alone or in combination of two or more. A part or all of the tertiary amino group can be ammonium chlorinated.

[0040] Other vinyl monomers constituting the hydrophilic unit (b-1) include, as hydrophilic monomers, hydroxyl group-containing vinyl monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, glycerol mono(meth)acrylate, 4-hydroxyvinylbenzene, 1-ethynyl-1-cyclohexanol, allyl alcohol, etc., and amide group-containing vinyl monomers such as (meth)acrylamide, N-methoxymethyl-(meth)acrylamide, N-ethoxymethyl-(meth)acrylamide, N-propoxymethyl-(meth)acrylamide, N-butoxymethyl-(meth)acrylamide, N,N-di(methoxymethyl)acrylamide, N-ethoxymethyl-N-methoxymethylmethacrylamide, N,N-di(ethoxymethyl)acrylamide, N-ethoxymethyl-N-propoxymethylmethacrylamide, N,N-di(propoxymethyl)acrylamide, N,N-di(butoxymethyl)acrylamide, N-butoxymethyl-N-(methoxymethyl)methacrylamide, N,N-dimethylaminopropylacrylamide, N,N-diethylaminopropylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, etc.

[0041] Furthermore, examples of the hydrophobic monomer include vinyl monomers containing a linear or branched alkyl group such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, heptyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, etc., vinyl monomers containing an alicyclic alkyl group such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, etc., and aromatic vinyl monomers such as styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, vinylnaphthalene, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxytetraethylene glycol (meth)acrylate, phenoxyhexaethylene glycol (meth)acrylate, phenyl (meth)acrylate, etc.

[0042] The hydrophilic unit (b-1) is not particularly limited as long as it is a unit exhibiting hydrophilicity, but the content of the structural unit derived from the hydrophilic monomer is preferably 60% by mass or more, more preferably 80% by mass or more.

[0043] <Hydrophobic unit (b-2)> Examples of the vinyl monomer constituting the hydrophobic unit include the above-described vinyl monomers containing a linear or branched alkyl group, vinyl monomers containing an alicyclic alkyl group, aromatic vinyl monomers, vinyl monomers containing a hydroxyl group, and vinyl monomers containing an amide group, but are not particularly limited thereto. These can be used alone or in combination of two or more. For the hydrophobic unit (b-2), the content of the structural unit derived from the hydrophobic monomer is preferably 60% by mass or more, more preferably 80% by mass or more.

[0044] More preferable vinyl monomers constituting the hydrophobic unit are monomers having a cyclic structure, preferably including alicyclic alkyl group-containing vinyl monomers and aromatic vinyl monomers. By having a cyclic structure, the water resistance and abrasion resistance of the ink coating film after printing are improved, and the alcohol resistance is also excellent. In addition, it strengthens the repulsion with the hydrophilic unit in water, promotes phase separation in the micro region, maintains the particulate state, and improves the ejection stability. The vinyl monomer having a cyclic structure constituting the hydrophobic unit is preferably contained in an amount of 5 to 50% by mass based on the total mass of the block polymer for inkjet ink.

[0045] The mass ratio of the hydrophilic unit (b-1) to the hydrophobic unit (b-2) is preferably 10:90 to 70:30. More preferably, it is 20:80 to 50:50. When the mass ratio of the hydrophilic unit is 10 or more, the storage stability is improved, and when it is 70 or less, the ejection stability and the water resistance and abrasion resistance of the coating film after printing are improved.

[0046] Examples of the RAFT agent (chain transfer agent) used in the reversible addition-fragmentation chain transfer polymerization method include diester-based, trithiocarbonate-based, dithiocarbamate-based, and xanthate-based agents. Among these, trithiocarbonate-based and diester-based RAFT agents, which are highly active and have good reactivity with alkyl group-containing vinyl monomers such as (meth)acrylates, aromatic vinyl monomers, amide group-containing vinyl monomers, and aromatic vinyl monomers, are preferred. Specifically, examples include methyl 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoate, S,S-dibenzyl trithiocarbonate, trithiocarbonic acid bis{4-[ethyl-(2-acetyloxyethyl)carbamoyl]benzyl}, benzyl 4-methoxybenzodithioate, 2-cyanopropan-2-yl benzodithioate, and the like. The mass of the RAFT agent used in the polymerization can be calculated from the molecular weight of the RAFT agent, the molecular weights and composition ratios of the respective vinyl monomers to be polymerized, and the number average molecular weight of the desired block polymer.

[0047] In addition, as the polymerization initiator necessary for radical generation at the initial stage of polymerization, known ones can be used. From the viewpoints of polymerizability and molecular weight control, azo compounds are preferable, and it is preferable to use 0.2 to 0.8 mol with respect to 1 mol of the RAFT agent. Examples of the azo compound include, but are not particularly limited to, 2,2'-azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(isobutyric acid)dimethyl, etc.

[0048] In addition, the total amount of the block polymer of the present invention is preferably 3% by mass or more and 30% by mass or less with respect to the total amount of the inkjet ink. By setting it to 3% by mass or more, the resistance after printing becomes good, and by setting it to 30% by mass or less, excellent ejection performance can be obtained. More preferably, it is 5% by mass or more and 20% by mass or less.

[0049] <Inkjet ink> Next, the inkjet ink constituting the present invention will be described. The inkjet ink of the present invention contains a block polymer for inkjet ink, water, a polyvalent metal salt and / or a water-soluble cationic resin. Since the inkjet ink of the present invention is an aqueous inkjet ink having a pretreatment function for improving the printing image quality, colorants such as yellow, magenta, cyan, black, and white, which are necessary for forming the image portion, are not substantially contained.

[0050] <Flocculant> For the purpose of aggregating and thickening the inkjet ink containing the colorant for forming the image portion to obtain an excellent image, the inkjet ink of the present invention contains a flocculant. The flocculant is at least one or more selected from the group consisting of polyvalent metal salts and water-soluble cationic resins. These may be used alone or in combination of two or more.

[0051] The polyvalent metal salt is not particularly limited as long as it is composed of a metal ion and an anion that binds to the metal ion. Among them, it is preferable that the polyvalent metal salt contains a divalent metal salt because it can instantaneously interact with the pigment to suppress bleeding and color mixing and obtain a clear image. Particularly, calcium ions or magnesium ions are preferable. Metal salts include inorganic metal salts and organic metal salts.

[0052] Specific examples of inorganic metal salts include aluminum chloride, polyaluminum chloride (PAC), calcium chloride, magnesium chloride, aluminum chloride, calcium bromide, magnesium bromide, aluminum nitrate, calcium nitrate, magnesium nitrate, aluminum sulfate, magnesium sulfate, calcium carbonate, and magnesium carbonate, but are not limited thereto. Among these inorganic metal salts, it is preferable to select calcium nitrate from the viewpoints of hygroscopicity and the aggregation / thickening effect of the inkjet ink.

[0053] Specific examples of organic metal salts include aluminum salts, calcium salts, magnesium salts, nickel salts, and zinc salts of organic acids such as pantothenic acid, propionic acid, ascorbic acid, acetic acid, and lactic acid, but are not limited thereto. Among these metal salts of organic acids, it is preferable to select calcium salts of lactic acid and / or acetic acid from the viewpoints of hygroscopicity and the aggregation / thickening effect of the inkjet ink.

[0054] In the inkjet ink of the present invention, the content of the polyvalent metal salt is preferably 0.25 to 8.0% by mass, more preferably 0.75 to 5% by mass as metal ions based on the total amount of the inkjet ink. By setting the content of metal ions within the above range, the wettability of the inkjet ink to the substrate can be ensured.

[0055] When a water-soluble cationic resin is selected as the flocculant, it can be arbitrarily used as long as it reduces the dispersion function of the pigment in the ink printed after printing the inkjet ink of the present invention and has suitable solubility and diffusibility. As an index related to suitable solubility, the solubility in 100 mL of water at 25°C can be used. That is, a water-soluble cationic resin having a solubility in 100 mL of water at 25°C of 5 g / 100 mL or more is preferably used in the inkjet ink of the present embodiment.

[0056] Hereinafter, the evaluation and judgment method of the solubility of the water-soluble cationic resin will be described in detail. The sample is prepared by thoroughly mixing 5 g of the water-soluble cationic resin and 100 mL of water. When the water-soluble cationic resin can only be obtained in the form of an aqueous solution, such as a commercially available product, water is added or volatilized and removed so that the solid content is 5 g with respect to 100 mL of water to obtain a sample. Then, for the sample left standing at 25°C for 24 hours, if the 50% volume average particle diameter is not measured, it is determined that the solubility of the water-soluble cationic resin in 100 mL of water at 25°C is 5 g / 100 mL or more. The above 50% volume average particle diameter can be measured by, for example, a particle size distribution measuring instrument (NanoTrack UPA-EX150 manufactured by Microtrac Bell).

[0057] Examples of the cationic group contained in the water-soluble cationic resin include, but are not limited to, an amino group, an ammonium group, an amide group, and a -NHCONH2 group.

[0058] As materials used for introducing the above cationic groups into the water-soluble cationic resin, for example, amine compounds such as vinylamine, allylamine, methyldiallylamine, ethyleneimine, etc.; amide compounds such as acrylamide, vinylformamide, vinylacetamide, etc.; cyanamide compounds such as dicyandiamide; epihalohydrin compounds such as epifluorohydrin, epichlorohydrin, methylepichlorohydrin, epibromohydrin, epi-iodohydrin, etc.; cyclic vinyl compounds such as vinylpyrrolidone, vinylcaprolactam, vinylimidazole, etc.; amidine compounds; pyridinium salt compounds; imidazolium salt compounds, etc. can be mentioned.

[0059] When using a water-soluble cationic resin as a flocculant, it is preferable that the water-soluble cationic resin is a compound containing one or more structural units selected from the group consisting of a mono(meth)acrylamine structural unit, a mono(meth)acrylammonium chloride structural unit, a diallylamine structural unit, a diallylammonium structural unit, and an epihalohydrin structural unit. All of the above water-soluble cationic resins are strong electrolytes, have good dissolution stability of the water-soluble cationic resin in the inkjet ink, and are excellent in the ability to reduce the dispersion of pigments in the inkjet ink for forming an image. As the above water-soluble cationic resin, those synthesized by known synthesis methods may be used, or commercially available products may be used.

[0060] <Water-soluble organic solvent> The inkjet ink of the present invention can use a water-soluble organic solvent. The water-soluble organic solvent is not particularly limited, and known ones can be arbitrarily used. However, from the viewpoints of the dispersion stability of the block polymer, the solubility of the aggregating agent, the ejection stability of the inkjet ink, and the wettability to the substrate, it preferably contains a glycol ether-based solvent and / or an alkyl polyol-based solvent. In particular, the boiling point of the water-soluble organic solvent under 1 atm is preferably 100°C or higher and lower than 240°C. By setting it to 100°C or higher, the dispersion stability, ejection stability, and moisture retention of the inkjet ink are improved. By setting it lower than 240°C, the drying property of the inkjet ink, the water resistance, and the rubbing resistance of the printed matter are improved. The water-soluble organic solvent may be used alone or in combination of two or more.

[0061] Incidentally, the boiling point under 1 atm can be measured by using a thermal analyzer such as DSC (differential scanning calorimetry).

[0062] The total amount of the water-soluble organic solvent is preferably 3% by mass or more and 40% by mass or less based on the total amount of the inkjet ink. Further, from the viewpoint of ensuring the ejection stability from the inkjet head, the water resistance, and the rubbing resistance, it is more preferably 5% by mass or more and 35% by mass, and particularly preferably 8% by mass or more and 30% by mass or less. By setting the total amount of the water-soluble organic solvent to 3% by mass or more, the moisture retention and ejection stability are excellent. By setting it to 40% by mass or less, the drying property is good, and a printed matter having good water resistance and rubbing resistance can be obtained.

[0063] Examples of alkyl polyol solvents that are suitably used as water-soluble organic solvents include 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-1,3-propanediol, 2-ethyl-2-methyl-1,3-propanediol, 3-methyl-1,3-butanediol, 3-methyl-1,5-pentanediol, 2-methyl-2-propyl-1,3-propanediol, 2-methylpentane-2,4-diol, 2-ethyl-1,3-hexanediol, diethylene glycol, and dipropylene glycol.

[0064] Examples of glycol ether solvents that are suitably used as water-soluble organic solvents include glycol monoalkyl ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, and tripropylene glycol monomethyl ether; and glycol dialkyl ethers such as diethylene glycol diethyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol butyl methyl ether, and tetraethylene glycol dimethyl ether.

[0065] <Surfactant> For the inkjet ink of the present invention, it is preferable to use a surfactant for the purpose of adjusting its surface tension, ensuring wettability on the substrate, and improving the printing image quality. On the other hand, if the surface tension is too low, the nozzle surface of the inkjet head will be wetted by the aqueous ink, impairing the ejection stability. Therefore, the selection of the type and amount of the surfactant is important. From the viewpoints of ensuring optimal wettability and achieving ejection stability, it is preferable to use surfactants such as siloxane-based, acetylene-based, acrylic-based, fluorine-based, polyoxyalkylene alkyl ether-based surfactants, etc., and it is particularly preferable to use siloxane-based and / or acetylene-based surfactants. As the addition amount of the surfactant, it is preferably 0.05% by mass or more and 5.0% by mass or less, more preferably 0.1% by mass or more and 3.0% by mass or less, based on the total amount of the aqueous ink. By setting it to 0.05% by mass or more, the function of the surfactant can be fully exerted, and by setting it to 5.0% by mass or less, the storage stability and ejection stability of the inkjet ink can be maintained at a suitable level.

[0066] <Other components> In addition to the above components, additives such as a pH adjuster, an antifoaming agent, a preservative, an infrared absorber, an ultraviolet absorber, a thickener, a wax additive, a crosslinking agent, etc. can be appropriately added as necessary. As an example of the addition amount of these additives, it is preferably 0.01% by mass or more and 10% by mass or less based on the total mass of the aqueous ink.

[0067] <Method for preparing ink> As a method for preparing the ink of the present invention, for example, a block polymer, a flocculant, water, and, if necessary, a surfactant, a water-soluble organic solvent, and appropriately selected additives as described above are added, stirred and mixed, and then filtered if necessary for adjustment. However, the method for adjusting the inkjet ink is not limited to the above.

[0068] <Printing method> The inkjet ink of the present invention is printed on a substrate by an inkjet printing method. At this time, it is preferably printed by a one-pass printing method (also referred to as a line printing method). The one-pass printing method has fewer scanning times than the multi-pass method in which the inkjet head is scanned multiple times, and can increase the printing speed. Therefore, it is suitable for industrial applications that require high printing speed. Also, it is suitable because a printed matter with high print quality can be obtained at a high recording resolution of 600 dpi or more. Note that the "recording resolution" is expressed in units of dpi (Dots Per Inch) and represents the number of inkjet ink droplets printed per inch. Also, the "recording resolution" in this specification refers to both the recording resolution in the conveyance direction of the substrate and the recording resolution in the direction perpendicular to the conveyance direction within the plane of the substrate (hereinafter referred to as the recording width direction).

[0069] When printing the inkjet ink by a one-pass printing method, the drop volume of the ink depends greatly on the performance of the inkjet head. However, in order to obtain a printed matter with excellent various resistances and print quality, it is preferably in the range of 0.6 to 60 pL. More preferably, it is 1 to 50 pL, and particularly preferably 1.4 to 40 pL. Also, in order to obtain a high-quality image, it is particularly preferable to use an inkjet head with a gradation specification that can change the drop volume.

[0070] <Substrate> The substrate on which the ink of the present invention is printed is not particularly limited, and known substrates can be arbitrarily used. Among them, from the viewpoints of package packaging and label materials, non-permeable substrates or semi-permeable substrates are preferable, and they can be preferably used particularly for non-permeable substrates.

[0071] Examples of non-permeable or hardly permeable substrates include plastic substrates such as polyvinyl chloride, polyethylene terephthalate (PET), polypropylene, polyethylene, nylon, polystyrene, and polyvinyl alcohol; coated paper substrates such as coated paper, art paper, and cast paper; metal substrates such as aluminum, iron, stainless steel, and titanium; and glass substrates.

[0072] The above substrates may have a smooth or uneven surface, and may be transparent, translucent, or opaque. Further, two or more of these recording media may be laminated together. Additionally, a release adhesive layer or the like may be provided on the side opposite the printing surface, or an adhesive layer or the like may be provided on the printing surface after printing. Also, the shape of the recording medium used in the inkjet recording method of the present invention may be in the form of a roll or a sheet.

[0073] In addition, in order to improve the wettability of the inkjet ink of the present invention, improve the printing image quality and drying property, and also improve the abrasion resistance and adhesion so that the surface of the printed matter becomes uniform, it is also preferable to perform a surface modification method such as corona treatment or plasma treatment on the non-permeable substrate or hardly permeable substrate exemplified above.

Examples

[0074] Hereinafter, the present invention will be specifically described with reference to examples and comparative examples. In the following description, "parts" and "%" represent "parts by mass" and "mass %", respectively, unless otherwise specified.

[0075] <Synthesis Example of Block Polymer BP1> While introducing nitrogen gas into a reaction vessel equipped with a thermometer, a reflux condenser, a stirring device, a dropping funnel, and a gas inlet tube, 32 parts of methacrylate DMC-80, 5 parts of methyl methacrylate, 2.8 parts of methyl 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoate, and 33 parts of ethanol were charged, and the temperature was raised to 80 °C with stirring. After stirring for 15 minutes, 10 parts of ethanol and 0.2 part of 2,2'-azobisisobutyronitrile were mixed and added dropwise to the reaction solution over 6 hours. Further, after continuing the reaction at 80 °C for 1 hour, it was cooled to room temperature to obtain an ethanol solution containing the hydrophilic unit part of block polymer BP1.

[0076] To the obtained ethanol solution, 40 parts of benzyl methacrylate, 30 parts of methyl methacrylate, and 96 parts of ethanol were further added, and the temperature was raised to 80 °C again with stirring. After stirring for 15 minutes, 10 parts of ethanol and 0.5 part of 2,2'-azobisisobutyronitrile were mixed and added dropwise to the reaction solution over 6 hours. Further, the reaction was continued at 80 °C for 1 hour to obtain an ethanol solution containing a block polymer in which a hydrophobic unit part was bonded to the hydrophilic unit part. Subsequently, 165 parts of ion-exchanged water was added dropwise over 1 hour, the temperature was raised to 90 °C, and the total amount of ethanol was distilled off. After cooling to room temperature, further ion-exchanged water was added so that the resin solid content ratio became 30% to obtain an aqueous dispersion containing block polymer BP1.

[0077] The number average molecular weight (Mn) of the obtained block polymer BP1 was 15,400, and the molecular weight distribution (PDI) was 1.27. Also, the average particle diameter was 67 nm.

[0078] <Synthesis Examples of Block Polymers BP2 to 15 and BP31 to 33> Except for using the materials described in Table 1, 30% aqueous dispersions of block polymers BP2 to 15 and BP31 to 33 were obtained by the same operations as those for block polymer BP1.

[0079] <Synthesis Example of Block Polymer BP16> Into a reaction vessel equipped with a thermometer, a reflux condenser, a stirring device, a dropping funnel, and a gas inlet tube, while introducing nitrogen gas, 40 parts of benzyl methacrylate, 30 parts of methyl methacrylate, 2.8 parts of methyl 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoate, and 100 parts of ethanol were charged, and the temperature was raised to 80 °C with stirring. After stirring for 15 minutes, 10 parts of ethanol and 0.5 part of 2,2'-azobisisobutyronitrile were mixed and added dropwise to the reaction solution over 6 hours. Further, after continuing the reaction at 80 °C for 2 hours, it was cooled to room temperature to obtain an ethanol solution containing the hydrophobic unit part of block polymer BP16.

[0080] To the obtained ethanol solution, 32 parts of methacrylate DMC-80, 5 parts of methyl methacrylate, and 29 parts of ethanol were further added, and the temperature was raised to 80 °C again with stirring. After stirring for 15 minutes, 10 parts of ethanol and 0.2 part of 2,2'-azobisisobutyronitrile were mixed and added dropwise to the reaction solution over 6 hours. Further, the reaction was continued at 80 °C for 1 hour to obtain an ethanol solution containing a block polymer in which a hydrophilic unit part was bonded to the hydrophobic unit part. Subsequently, 165 parts of ion-exchanged water was added dropwise over 1 hour, the temperature was raised to 90 °C, and the total amount of ethanol was distilled off. After cooling to room temperature, further ion-exchanged water was added so that the resin solid content ratio became 30% to obtain an aqueous dispersion containing block polymer BP16.

[0081]

Table 1

[0082] <Synthesis Example of Block Polymer BP21> While introducing nitrogen gas into a reaction vessel equipped with a thermometer, a reflux condenser, a stirring device, a dropping funnel, and a gas inlet tube, 40 parts of methacrylate DMA, 5 parts of methyl methacrylate, 2.8 parts of methyl 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoate, and 63 parts of methyl ethyl ketone were charged, and the temperature was raised to 80 °C with stirring. After stirring for 15 minutes, 10 parts of methyl ethyl ketone and 0.3 part of 2,2'-azobisisobutyronitrile were mixed and added dropwise to the reaction solution over 6 hours. Further, after continuing the reaction at 80 °C for 1 hour, it was cooled to room temperature to obtain a methyl ethyl ketone solution containing a polymer having a tertiary amino group.

[0083] To the obtained methyl ethyl ketone solution, 30 parts of benzyl methacrylate, 25 parts of methyl methacrylate, and 74 parts of methyl ethyl ketone were further added, and the temperature was raised to 80 °C again with stirring. After stirring for 15 minutes, 10 parts of methyl ethyl ketone and 0.4 part of 2,2'-azobisisobutyronitrile were mixed and added dropwise to the reaction solution over 6 hours. Further, after continuing the reaction at 80 °C for 1 hour, it was cooled to room temperature to obtain a methyl ethyl ketone solution of a block polymer containing a unit part having a tertiary amino group and a hydrophobic unit part.

[0084] Subsequently, 19.3 parts of benzyl chloride was further added to the obtained methyl ethyl solution, the temperature was raised to 80 °C again, and after stirring for 6 hours, the tertiary amino group was quaternized with ammonium chloride to form a hydrophilic unit. Subsequently, 165 parts of ion-exchanged water was added dropwise over 1 hour, the temperature was raised to 90 °C, and the total amount of methyl ethyl ketone was distilled off. After cooling to room temperature, further ion-exchanged water was added so that the resin solid content ratio became 30% to obtain an aqueous dispersion containing block polymer BP21. The mass of benzyl chloride used was calculated from the molar amount required to quaternize 60% of the tertiary amino groups contained in one molecule of the polymer.

[0085] <Synthesis Examples of Block Polymers BP22 to 26 and BP34> Except for using the materials described in Table 2, 30% aqueous dispersions of block polymers BP22 to 26 and BP34 were obtained by the same operations as block polymer BP21.

[0086]

Table 2

[0087] <Synthesis Example of Polymer P35> 85 parts of isopropyl alcohol was charged into a reaction vessel equipped with a thermometer, a reflux condenser, a stirrer, two dropping funnels, and a gas inlet tube, and the temperature was raised to 80 °C while stirring and introducing nitrogen gas. Next, two dropping funnels were prepared. In one of them, 77 parts of methacrylate DMC-80, 10 parts of methacrylate DMA, 10 parts of methyl methacrylate, and 20 parts of styrene were dissolved in 150 parts of isopropyl alcohol and charged, and then dropped over 2 hours. In the other, 1.5 parts of 2,2'-azobis(isobutyric acid)dimethyl was dissolved in 7.5 parts of isopropyl alcohol and charged, and then dropped over 2 hours. After the dropping was completed, the reaction was carried out at 80 °C for 1 hour, and then 0.4 part of 2,2'-azobis(isobutyric acid)dimethyl was dissolved in 2 parts of isopropyl alcohol, charged into the reaction vessel, and the reaction was continued for another 1 hour and then terminated. Subsequently, 165 parts of ion-exchanged water was dropped over 1 hour, the temperature was raised to 95 °C, and the total amount of isopropyl alcohol was distilled off. After cooling to room temperature, more ion-exchanged water was added so that the resin solid content fraction became 30%, and an aqueous dispersion containing polymer P35, which is a random aggregate, was obtained.

[0088] <Synthesis Example of Polymer P36> A 30% aqueous dispersion of polymer P36 was obtained by the same operation as that of polymer P35 except that the materials described in Table 3 were used.

[0089]

Table 3

[0090] The abbreviations described in Tables 1 to 3 are as follows. BM1448: Methyl 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoate manufactured by BORON MOLECULAR DMC-80: Methacrylate DMC manufactured by Sanyo Chemical Industries; Methacryloyloxyethyltrimethylammonium chloride (78% by mass aqueous solution) DMAEA-BQ: 2-(Dimethylamino)ethyl acrylate-benzyl chloride quaternary salt (75% by mass aqueous solution) manufactured by KJ Chemicals DMAPAA-Q: N-[3-(Dimethylamino)propyl]acrylamide-methyl chloride quaternary salt (75% by mass aqueous solution) manufactured by KJ Chemicals Cationic monomer MAQ: 3-Methacryloyl-2-hydroxypropyltrimethylammonium chloride (50% by mass aqueous solution) manufactured by Morin Chemical Industry Co., Ltd. DMA:: Methacrylate DMA manufactured by Sanyo Chemical Industries; 2-(Dimethylamino)ethyl methacrylate AIBN: 2,2'-Azobisisobutyronitrile V601: 2,2'-Azobis(isobutyric acid)dimethyl manufactured by Fujifilm Wako Pure Chemical Corporation

[0091] <Synthesis example of polymer P37> Into a reaction vessel equipped with a thermometer, a reflux condenser, a stirring device, two dropping funnels, and a gas inlet tube, 100 parts of an aqueous dispersion with a solid content fraction of 30% of polymer P35 and 40 parts of ion-exchanged water were charged, stirred, and heated to 88 °C while introducing nitrogen gas. Next, two dropping funnels were prepared. One was charged with 45 parts of methyl methacrylate and 25 parts of styrene and dropped over 2 hours. The other was charged with 12 parts of a 3% aqueous solution of 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)propionamide) and dropped over 2 hours. After completion of the dropping, the reaction was continued at 88 °C for 2 hours, then cooled to room temperature to terminate the reaction. Next, ion-exchanged water was added so that the resin solid content fraction became 30% to obtain an aqueous dispersion of core-shell type emulsion resin particles coated with polymer P35.

[0092] The physical properties of each resin obtained in the above synthesis example and the detailed structural units represented by formula (1) are as shown in Table 4.

[0093]

Table 4

[0094] Note that the 30% aqueous dispersion of block polymer BP33 and polymer P35 is a transparent liquid upon visual observation, and no average particle diameter was detected in the measurement using NanoTrac UPA-EX150 manufactured by Microtrac Bell Co., Ltd. Therefore, it was determined to be a water-soluble resin having no particle diameter.

[0095] <Production Example of Inkjet Ink PR1> 30 parts of an aqueous dispersion of block polymer BP-1 (resin solid content: 30%), 15 parts of a water-soluble cationic resin CP (resin solid content: 30%), 22 parts of 1,2-propanediol, 0.5 part of TegoWet280, 0.5 part of Surfynol 440, and 0.1 part of adipic acid dihydrazide were sequentially charged into a mixing container. Then, ion-exchanged water was added to adjust the total amount of the ink to 100 parts, and the mixture was stirred with a disper until it became sufficiently uniform. Thereafter, filtration was performed using a membrane filter with a pore size of 0.5 μm to prepare Ink PR1.

[0096] Note that the water-soluble cationic resin CP was synthesized in the same manner as the synthesis of the water-soluble cationic resin C-1 described in Patent Publication No. 2023-55183. The water-soluble cationic resin CP is a polymer of 50% by mass of methacryloyloxyethyltrimethylammonium chloride and 50% by mass of 2-(dimethylamino)ethyl methacrylate, having a number average molecular weight of 32,000 and a molecular weight distribution of 2.75.

[0097] <Production Examples of Inkjet Inks PR-2 to 18, 21 to 28, and 31 to 37> Inks PR2 to 18, 21 to 28, and PR31 to 37 were obtained by the same operations as those for Ink PR1, except that the materials listed in Table 5 were used. Further, the following Evaluations 1 to 6 were performed using these inkjet inks. The evaluation results are shown in Table 5.

[0098]

Table 5

[0099] The abbreviations described in Table 5 are as follows. TegoWet280: A siloxane surfactant manufactured by Evonik Surfynol 440: An acetylene diol surfactant manufactured by Shin-Etsu Chemical Co., Ltd.

[0100] <Preparation of Printed Matter> An inkjet head KJ4B-YH (manufactured by Kyocera, resolution 600 dpi, maximum drive frequency 40 kHz) was installed above a conveyor capable of transporting a printing substrate, and the aqueous inkjet ink prepared above was filled. Next, after fixing a film substrate on the conveyor, the conveyor was driven at 50 m / min, and when passing through the installation part of the inkjet head, the aqueous inkjet ink was ejected to perform the printing shown below. The drop volume during printing was 12 pL, and the printed matter was put into an air oven at 70°C and dried for 3 minutes.

[0101] The film substrate used was BWS854 (surface: PET clear film) manufactured by Avery Dennison.

[0102] <Evaluation 1: Initial Ejection Property> The evaluation of the initial ejection property was carried out by visually and using a loupe to check whether the starting part of 100% solid printing was printed under the above-described inkjet printer device and printing conditions. The evaluation criteria are as follows, and the ◎ and 〇 evaluations are in the practically usable range. ◎: No chipping was confirmed at the starting part even when visually and using a loupe. 〇: No chipping was visually observed, but chipping less than 1 mm was confirmed when checked with a loupe. △: Chipping of 1 mm or more and less than 5 mm was visually confirmed at the start. ×: Chipping of 5 mm or more was visually confirmed at the start.

[0103] <Evaluation 2: Standby Ejection Property> Solid printing with a printing rate of 100% was performed using the same printing conditions and the same base material as in Evaluation 1. After printing, the inkjet ejection device was allowed to standby for a certain period of time in an environment of 25°C, and then the nozzle check pattern was printed. The standby ejection performance was evaluated by visually checking whether nozzle clogging occurred. The evaluation criteria are as follows, and ◎ and 〇 evaluations are in the practical applicable range. ◎: Even after printing after a 2-hour standby, there was no nozzle clogging at all. 〇: Even after printing after a 1-hour standby, there was no nozzle clogging at all, but nozzle clogging occurred when printing after a 2-hour standby. △: When printing after a 1-hour standby, 1 to 9 nozzles were clogged. ×: When printing after a 1-hour standby, 10 or more nozzles were clogged.

[0104] <Evaluation 3: Redissolvability> 0.3 g of ink was added to a small aluminum container with a capacity of 30 g and dried and solidified in a 35°C air oven for a predetermined time. In addition, when any of the inks were dried for 1 hour under the above conditions, they did not adhere to the fingertips when touched. Then, 10 g of ion-exchanged water was added and allowed to stand for 1 hour, and then whether the ink dissolved in the ion-exchanged water was visually observed to evaluate the redissolvability of the dried and solidified ink. The evaluation criteria are as follows, and ◎ and 〇 evaluations are in the practical applicable range. ◎: Even the ink dried and solidified in a 35°C air oven for 6 hours dissolved in the ion-exchanged water. 〇: The ink dried and solidified in a 35°C air oven for 6 hours did not dissolve in the ion-exchanged water, but the ink dried and solidified for 1 hour dissolved. △: The ink dried and solidified in a 35°C air oven for 1 hour did not dissolve in the ion-exchanged water, but the ink dried and solidified for 30 minutes dissolved. ×: Even the ink dried and solidified in a 35°C air oven for 30 minutes did not dissolve in the ion-exchanged water.

[0105] <Evaluation 4: Storage Stability> For each inkjet ink, the volume average particle size (D50) was measured using a NanoTrac UPA-EX150 manufactured by Microtrac Bell. This ink was placed in a sealed container, stored in a constant temperature machine at 70°C, and allowed to age for 2 weeks. Then, the volume average particle size was measured again using the above device, and the change in the volume average particle size of the ink before and after aging was calculated to evaluate the storage stability of the ink. The criteria are as follows, and ◎ and 〇 evaluations are in the practical application range. ◎: The change rate of the volume average particle size was less than ±15%. 〇: The change rate of the volume average particle size was 15% or more and less than 30%. △: The change rate of the volume average particle size was 30% or more and less than 45%. ×: The change rate of the volume average particle size after 2 weeks of storage was 45% or more.

[0106] <Evaluation 5: Rub resistance> Solid printing with a printing rate of 100% was performed. For the obtained printed matter, using a Kagaku Shinkou type friction fastness tester, with a cotton cloth (Kanakin No. 3), under the condition of a load of 200 g / cm 2 , 50 reciprocations, the printed surface was rubbed, and the rub resistance was evaluated from the ratio of the peeled area of the printed surface. The evaluation criteria are as follows, and ◎ and 〇 evaluations are in the practical application range. ◎: There is no peeling of the printed surface. 〇: The peeling of the printed surface is less than 20%. △: The peeling of the printed surface is 20% or more and less than 50%. ×: The peeling of the printed surface is 50% or more.

[0107] <Evaluation 6: Water resistance> Similar to Evaluation 5, solid printing with a printing rate of 100% was performed. For the obtained printed matter, the water resistance was evaluated by visually observing the state when rubbed with a cotton swab soaked in water. The evaluation criteria are as follows, and ◎ and 〇 evaluations are in the practical application range. ◎: Even when rubbed 20 times with a cotton swab soaked in water, there was no peeling of the printed matter or adhesion of the ink to the cotton swab. 〇: Even when rubbed 10 times with a cotton swab dipped in water, there was no peeling of the printed matter or adhesion of ink to the cotton swab. However, when rubbed 20 times, peeling of the printed matter and adhesion of ink to the cotton swab were observed. △: Even when rubbed 5 times with a cotton swab dipped in water, there was no peeling of the printed matter or adhesion of ink to the cotton swab. However, when rubbed 10 times, peeling of the printed matter and adhesion of ink to the cotton swab were observed. ×: When strongly rubbed 5 times with a cotton swab dipped in water, peeling of the printed matter and adhesion of ink to the cotton swab were observed.

[0108] In addition, since the inkjet ink of the present invention substantially does not contain a colorant, it was sometimes difficult to discriminate and grasp the results in the observation and evaluation of printed matter and ink. In this case, evaluation was performed using an ink in which 0.05 part of rhodamine B, a cationic dye, was added and dissolved with respect to 100 parts by mass of the inkjet ink.

[0109] Examples 1 to 18 and 21 to 28 have a hydrophilic unit (b-1) and a hydrophobic unit (b-2), a number average molecular weight of 8,000 to 50,000, and an average particle diameter of 30 to 150 nm. Since the hydrophilic unit (b-1) uses a block polymer containing a structural unit represented by the formula (1), inkjet inks and printed matters excellent in ejection performance, redissolution property, storage stability, water resistance, and abrasion resistance could be obtained.

[0110] In Comparative Example 31, since the number average molecular weight of the block polymer was less than 8,000, the abrasion resistance and water resistance were inferior. In Comparative Example 34, since the number average molecular weight exceeded 50,000, the ejection performance was inferior. In Comparative Example 32, since it did not contain the structural unit of the formula (1) and the average particle diameter exceeded 150 nm, the ejection performance, redissolution property, and storage stability were inferior. In Comparative Example 33, since the block polymer was a water-soluble resin having no particle diameter, the ejection performance, abrasion resistance, and water resistance were inferior.

[0111] Since Comparative Example 35 is a water-soluble resin having no randomly polymerized particle diameter, the ejection performance, water resistance, and abrasion resistance were poor. Since Comparative Example 36 is randomly polymerized resin particles, the ejection performance, redissolubility, and storage stability were poor. Comparative Example 37 is core-shell type emulsion particles in which a water-soluble resin coats a hydrophobic resin serving as a core, and since it is not a block polymer having a hydrophilic unit and a hydrophobic unit in one polymer molecule, the redissolubility and storage stability were poor.

Claims

1. A block polymer for inkjet ink having a hydrophilic unit (b-1) and a hydrophobic unit (b-2), wherein the block polymer has a number average molecular weight of 8,000 to 50,000 and an average particle diameter of 30 to 150 nm, and the hydrophilic unit (b-1) is characterized in that it contains a structural unit represented by formula (1). A block polymer for inkjet ink. Formula (1) 【Chemical 1】 (In formula (1), R １ represents a hydrogen atom or a methyl group, Z represents an oxygen atom, -NH-, or -OCH ２ CH(OH)-, R ２ , R ３ , R ４ each independently represents an alkyl group having 1 to 8 carbon atoms, X － represents a monovalent anion, and n represents an integer of 1 to 6.)

2. The block polymer for inkjet ink according to claim 1, wherein the hydrophobic unit (b-2) contains a structural unit having a cyclic structure.

3. The block polymer for inkjet ink according to claim 1, wherein the structural unit represented by the formula (1) is contained in an amount of 1 to 40% by mass based on the total mass of the block polymer for inkjet ink.

4. The block polymer for inkjet ink according to claim 1, wherein the mass ratio of the hydrophilic unit (b-1) to the hydrophobic unit (b-2) is 10:90 to 70:

30.

5. An inkjet ink comprising the block polymer for inkjet ink according to any one of claims 1 to 4, a polyvalent metal salt and / or a water-soluble cationic resin, and substantially free of a colorant.

6. A printed matter obtained by printing an inkjet ink containing the block polymer for inkjet ink according to any one of claims 1 to 4 on a substrate.

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