Aqueous white ink for inkjet recording

Abstract

To provide a water-based white ink for ink-jet recording, that has excellent discharge stability during ink-jet recording and can provide recorded matter having excellent whiteness, adhesion to a substrate, scratch resistance, and water resistance even when recording is performed on a recording medium with low liquid absorption.SOLUTION: Provided is a water-based white ink for ink-jet recording, comprising titanium oxide, two polyurethane resins A and B having different glass transition temperatures, where the polyurethane resin A has a glass transition temperature of 40-95°C, the polyurethane resin B has a glass transition temperature of 5-20°C, a mass ratio of the polyurethane A to the polyurethane B, (A / B), is 0.4-3, and a content of titanium oxide in the ink is 3-14 mass%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous white ink for inkjet recording.

Background Art

[0002] The inkjet recording method is a recording method in which ink droplets are directly ejected from very fine nozzles onto a recording medium and adhered to obtain a printed matter on which characters and images are recorded. Different from the conventional recording methods, since it is a recording method that does not use a plate, it is expected to have a wide range of application fields as on-demand printing that can handle small quantities and multiple varieties. In particular, in recent years, there has been an increasing demand for printing on low-absorbency recording media such as coated paper and resin films that are not white paper, rather than on conventional white paper. In the case of printing on a non-white recording medium, white ink is used for the purpose of expressing white or enhancing visibility. As a pigment used in white ink, titanium oxide, an inorganic pigment with high hiding power, is widely used. On the other hand, when printing is performed by an inkjet recording method on a low-absorbency recording medium such as a resin film, since the absorption of the liquid component is slow or not absorbed, it takes time for the ink to dry, and problems such as poor fixability to the recording medium and poor rub resistance of the printed matter are known.

[0003] For example, Patent Document 1 discloses a white ink composition that contains a white coloring material and a fixing resin, and gives a high-quality image that is excellent in whiteness and scratch resistance while suppressing the stickiness of the image surface and suppressing bleeding with color ink. The fixing resin contains a urethane resin and a styrene-acrylic resin in a mass ratio of 10:1 or more.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the white ink composition of Patent Document 1 had low ejection stability during inkjet recording, and the water resistance and adhesion to the substrate of the obtained printed matter were also insufficient. An object of the present invention is to provide an aqueous white ink for inkjet recording that is excellent in ejection stability during inkjet recording and can obtain a recorded matter excellent in whiteness, substrate adhesion, rubbing resistance, and water resistance even when recording is performed on a low-absorbency recording medium.

Means for Solving the Problems

[0006] The present inventors have found that the above problems can be solved by using two types of polyurethane resins having different glass transition temperatures in a specific mass ratio as the fixing resin for titanium oxide, which is a white pigment. That is, the present invention includes titanium oxide and two types of polyurethane resins A and B having different glass transition temperatures, the glass transition temperature of the polyurethane resin A is 40°C or higher and 95°C or lower, the glass transition temperature of the polyurethane resin B is 5°C or higher and 20°C or lower, the mass ratio of the polyurethane resin A to the polyurethane resin B (polyurethane resin A / polyurethane resin B) is 0.4 or higher and 3 or lower, the titanium oxide content in the ink is 3% by mass or higher and 14% by mass or lower, and provides an aqueous white ink for inkjet recording.

Advantages of the Invention

[0007] According to the present invention, it is possible to provide an aqueous white ink for inkjet recording that is excellent in ejection stability during inkjet recording and can obtain a recorded matter excellent in whiteness, substrate adhesion, rubbing resistance, and water resistance even when recording is performed on a low-absorbency recording medium.

Embodiments for Carrying Out the Invention

[0008] [Aqueous White Ink for Inkjet Recording] The aqueous ink for inkjet recording of the present invention (hereinafter also referred to as "the ink of the present invention") contains titanium oxide and two kinds of polyurethane resins A and B having different glass transition temperatures. The glass transition temperature of the polyurethane resin A is 40°C or higher and 95°C or lower. The glass transition temperature of the polyurethane resin B is 5°C or higher and 20°C or lower. The mass ratio of the polyurethane resin A to the polyurethane resin B (polyurethane resin A / polyurethane resin B) is 0.4 or higher and 3 or lower. The titanium oxide content in the ink is 3% by mass or higher and 14% by mass or lower. In this specification, "aqueous" means that water occupies the largest proportion by mass in the medium in which titanium oxide is dispersed. Also, "recording" is a concept including printing and typing for recording characters and images, and "recorded matter" is a concept including printed matter and typed matter on which characters and images are recorded. "Low liquid absorbency" is a concept including low liquid absorbency and non-liquid absorbency, and means that the water absorption of the recording medium at 100 msec of the contact time between the recording medium and pure water is 0 g / m 2 or more and 10 g / m 2 or less.

[0009] According to the present invention, excellent discharge stability during inkjet recording can be achieved, and even when recording is performed on a low liquid absorbency recording medium, a recorded matter excellent in whiteness, substrate adhesion, scratch resistance, and water resistance can be obtained. The reason is not necessarily clear, but it is considered as follows. In the ink of the present invention, a polyurethane resin A with a high glass transition temperature (Tg) of 40°C or higher and 95°C or lower (hereinafter also referred to as "high-Tg polyurethane resin A") and a polyurethane resin B with a low Tg of 5°C or higher and 20°C or lower (hereinafter also referred to as "low-Tg polyurethane resin B") are considered to independently exist in a mass ratio (A / B) range of 0.4 or higher and 3 or lower. Therefore, when the ink is ejected, it is considered that the particles of the high-Tg polyurethane resin A and the particles of the low-Tg polyurethane resin B do not interfere with each other and do not adversely affect the ejection stability. Furthermore, even when the ink lands on the recording medium and an ink coating film is formed, it is considered that they independently maintain their structures.

[0010] More specifically, a crystal structure exists in the high-Tg polyurethane resin A, and it is considered that this crystal structure is formed by strong attractive forces acting between specific molecular groups. However, the attractive forces between these crystal structures act beyond the sites composed of the low-Tg polyurethane resin B (existing independently of the high-Tg polyurethane resin A) in the ink coating film. That is, it is considered that the strong cohesive force resulting from the segments constituting the crystal structure of the high-Tg polyurethane resin A in the ink coating film acts beyond the components constituting the low-Tg polyurethane resin B. In other words, it is considered that there is a force that attracts the high-Tg polyurethane resin A to each other. Due to the specific configuration of the ink coating film in which the resins A and B exist independently in the ink coating film and there is a force that attracts the high-Tg polyurethane resin A to each other, the excellent adhesion derived from the low-Tg polyurethane resin B is not impaired. Therefore, the whiteness and substrate adhesion of the recorded matter are improved. Also, the elastic modulus of the entire ink coating film increases due to the force that attracts the high-Tg polyurethane resin A to each other, so the abrasion resistance increases. Furthermore, it is considered that the water resistance is improved because the diffusion of water is also suppressed.

[0011] <Titanium Oxide> Titanium oxide is contained as a white pigment in the ink of the present invention. The crystal structures of titanium oxide include rutile type (tetragonal), anatase type (tetragonal), and brookite type (orthorhombic). From the viewpoints of crystal stability, hiding power, and availability, rutile type titanium oxide is preferred. As for titanium oxide, untreated titanium oxide can be used, but from the viewpoint of obtaining good dispersibility, surface-treated titanium oxide is preferred. Examples of the surface treatment of titanium oxide include surface treatment with inorganic substances, surface treatment with organic substances such as titanium coupling agents, silane coupling agents, and silicone oils. Among them, surface treatment with inorganic substances is preferred.

[0012] Examples of the method for surface treatment of titanium oxide with inorganic substances include treating with one or more selected from alumina (Al 2 O 3 ), silica (SiO 2 ), zinc oxide (ZnO), zirconia (ZrO 2 ), magnesium oxide (MgO), and the like. Since titanium oxide has the property of decomposing organic substances due to its photocatalytic activity, from the viewpoints of suppressing photocatalytic activity and improving the wetting of titanium oxide during dispersion, it is preferable to perform surface treatment on the surface of titanium oxide particles with alumina or the like. Further, from the viewpoints of adjusting the acid-base state on the surface of titanium oxide particles and improving durability, it is preferable to perform surface treatment in combination with silica. From the above viewpoints, it is more preferable to treat titanium oxide with one or more selected from alumina, silica, zinc oxide, and zirconia, and it is still more preferable to treat with one or more selected from alumina and silica. The powder of surface-treated titanium oxide can also suppress sintering between particles and improve the fluidity and dispersibility of secondary particles by firing at 800 to 1000 °C.

[0013] The particle shape of titanium oxide includes granular, acicular, etc. and is not particularly limited. However, from the viewpoint of whiteness, the average primary particle diameter is preferably 50 nm or more, more preferably 100 nm or more, still more preferably 150 nm or more, in terms of the arithmetic mean of the major axis of the primary particles, and preferably 450 nm or less, more preferably 400 nm or less, still more preferably 350 nm or less. The average primary particle diameter of titanium oxide is measured by the method described in the examples. Examples of commercially available rutile-type titanium dioxide include the product names: Typepeck R, CR, PF series manufactured by Ishihara Sangyo Co., Ltd., the product names: R series manufactured by Sakai Chemical Industry Co., Ltd., the product names: JR, MT series manufactured by Teika Co., Ltd., the product names: KURONOS KR series manufactured by Titanium Industry Co., Ltd., the product names: TR series manufactured by Fuji Titanium Industry Co., Ltd., and the like.

[0014] It is preferable that the titanium oxide used in the ink of the present invention is kept in a dispersed state in the ink with a polymer dispersant. As the form of existence of titanium oxide and the polymer dispersant in the ink of the present invention, it is preferable that they are polymer particles containing titanium oxide (hereinafter, also referred to as "pigment-containing polymer particles"). Pigment-containing polymer particles mean particles in which the polymer dispersant contains titanium oxide, particles in which a part of titanium oxide is exposed on the surface of particles composed of the polymer dispersant and titanium oxide, particles in which the polymer dispersant is adsorbed on a part of titanium oxide, and mixtures thereof. Among these, particles in which the polymer dispersant contains titanium oxide are more preferable.

[0015] 〔Pigment-containing polymer particles〕 The polymer dispersant (hereinafter, also referred to as "polymer a") constituting the pigment-containing polymer particles is not particularly limited as long as it has at least the ability to disperse titanium oxide. Examples of polymer a include vinyl resins obtained by addition polymerization of vinyl monomers, polyester resins, polyurethane resins, and the like. Among these, from the viewpoints of the dispersion stability and storage stability of titanium oxide, vinyl resins are preferable. Polymer a may be a suitably synthesized one or a commercially available product. The pigment-containing polymer particles may be pigment-containing crosslinked polymer particles crosslinked with a crosslinking agent as needed.

[0016] 〔Polymer a〕 When polymer a is a vinyl resin, polymer a preferably contains a structural unit derived from (a-1) an ionic monomer, and may further contain a structural unit derived from (a-2) a hydrophobic monomer and / or (a-3) a nonionic monomer.

[0017] [[(a-1) Ionic monomer]] (a-1) As the ionic monomer, an anionic monomer is preferable, and examples thereof include carboxylic acid monomers and sulfonic acid monomers, and carboxylic acid monomers are more preferable. Examples of the carboxylic acid monomer include (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, and fumaric acid, and preferably (meth) acrylic acid. “(Meth) acrylic acid” means at least one selected from acrylic acid and methacrylic acid.

[0018] [[(a-2) Hydrophobic monomer]] The “hydrophobicity” of the (a-2) hydrophobic monomer means that when the monomer is dissolved until saturated in 100 g of ion-exchanged water at 25° C., the dissolved amount is less than 10 g. Specific examples of the (a-2) hydrophobic monomer include those described in paragraphs

[0020] to

[0022] of JP-A-2018-83938. Among these, alkyl (meth) acrylates having an alkyl group having 1 to 18 carbon atoms, particularly 1 to 10 carbon atoms, aromatic group-containing monomers having an aromatic group having 6 to 22 carbon atoms, macromonomers having a polymerizable functional group at one end, etc. are preferable, and one or more selected from styrene, α-methylstyrene, and benzyl (meth) acrylate are more preferable.

[0019] [[(a-3) Nonionic monomer]] (a-3) The nonionic monomer is a monomer having a high affinity for water or a water-soluble organic solvent, and is, for example, a monomer containing a hydroxyl group or a polyalkylene glycol chain. Specific examples of the component (a-3) include those described in paragraph

[0018] of JP-A-2018-83938. Among these, one or more selected from methoxypolyethylene glycol (n = 1 to 30) (meth)acrylate and polypropylene glycol (n = 2 to 30) (meth)acrylate are preferable. The above monomer components can be used alone or in admixture of two or more thereof.

[0020] (Content of each constitutional unit in the vinyl resin) The content of the constitutional units derived from the components (a-1) to (a-3) in the vinyl resin is as follows from the viewpoint of improving ejection stability, substrate adhesion, scratch resistance, etc. The content of the component (a-1) is preferably 10% by mass or more, more preferably 20% by mass or more, still more preferably 30% by mass or more, and is preferably 100% by mass or less. When the components (a-2) and (a-3) are contained, their contents are preferably 2% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, and are preferably 40% by mass or less, more preferably 30% by mass or less, still more preferably 20% by mass or less.

[0021] (Production of polymer a) Polymer a can be produced by homopolymerizing the above monomer components or copolymerizing a monomer mixture by a known method. As the polymerization method, a solution polymerization method is preferable. There is no limitation on the solvent used in the solution polymerization method, but polar solvents such as water, aliphatic alcohols, ketones, ethers, and esters are preferable, and water and ketones such as MEK are more preferable. In the polymerization, polymerization initiators such as persulfates and water-soluble azo compounds, and polymerization chain transfer agents such as mercaptans can be used. The polymerization temperature varies depending on the types of the polymerization initiator, monomer, solvent, etc. used, but is preferably 30 to 95°C, more preferably 50 to 80°C. The vinyl resin is preferably neutralized with a neutralizing agent as described later.

[0022] From the viewpoint of improving discharge stability, substrate adhesion, abrasion resistance, etc., the weight-average molecular weight of polymer a is preferably 2000 or more, more preferably 3000 or more, still more preferably 4000 or more, and preferably 50,000 or less, more preferably 20,000 or less, still more preferably 10,000 or less. The weight-average molecular weight of the polymer is measured by the method described in the examples. From the viewpoint of dispersion stability, etc., the acid value of polymer a is preferably 100 mgKOH / g or more, more preferably 200 mgKOH / g or more, still more preferably 300 mgKOH / g or more, and preferably 1000 mgKOH / g or less, more preferably 900 mgKOH / g or less, still more preferably 800 mgKOH / g or less.

[0023] 〔Production of pigment-containing polymer particles〕 The pigment-containing polymer particles can be efficiently produced by a method having the following step 1 as a pigment aqueous dispersion. Step 1: A step of subjecting a pigment mixture containing titanium oxide, polymer a, and water to a dispersion treatment to obtain an aqueous dispersion of pigment-containing polymer particles (hereinafter also referred to as "pigment aqueous dispersion").

[0024] When polymer a has an acid group, at least a part of the acid group is preferably neutralized using a neutralizing agent. It is considered that this increases the charge repulsive force generated after neutralization, suppresses the aggregation of titanium oxide particles in the aqueous ink, and improves the dispersion stability. When neutralizing, it is preferable to neutralize so that the pH becomes 7 or more and 11 or less. Examples of the neutralizing agent include bases such as sodium hydroxide, potassium hydroxide, ammonia, and various amines, and sodium hydroxide and ammonia are preferable. Also, polymer a may be neutralized in advance. From the viewpoint of improving dispersion stability, the equivalent amount of the neutralizing agent used is preferably 10 mol% or more, more preferably 20 mol% or more, and preferably 150 mol% or less, more preferably 100 mol% or less. Here, when the equivalent amount of the neutralizing agent used is based on the polymer a before neutralization being defined as "polymer a'", it can be determined by the following formula. Equivalent amount of neutralizing agent used (mol%) = [{mass of neutralizing agent added (g) / equivalent of neutralizing agent} / [{acid value of polymer a' (mg KOH / g) × mass of polymer (B) (g)} / (56 × 1,000)]] × 100

[0025] The dispersion treatment in Step 1 is preferably carried out by first performing preliminary dispersion if necessary and then performing main dispersion. Examples of the disperser used for the main dispersion include kneaders such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers, media-type dispersers such as paint shakers and bead mills. Among these, from the perspective of reducing the particle size of the pigment, it is preferable to use a high-pressure homogenizer or a bead mill. When an organic solvent is included in Step 1, the organic solvent can be removed by a known method. It is preferable that the organic solvent in the obtained pigment aqueous dispersion is substantially removed, but it may remain as long as the object of the present invention is not impaired. Also, for the purpose of removing coarse particles and the like, it is preferable to further centrifuge the obtained aqueous dispersion and then filter the liquid layer portion to obtain a pigment aqueous dispersion.

[0026] The non-volatile component concentration (solid content concentration) of the obtained pigment aqueous dispersion is preferably 10% by mass or more, more preferably 20% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass or less, from the perspective of improving the dispersion stability of the pigment aqueous dispersion. The solid content concentration is measured by the method described in the examples. The content of titanium oxide in the pigment aqueous dispersion is preferably 10% by mass or more, more preferably 20% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass or less, from the perspective of dispersion stability. The average particle size of the pigment-containing polymer particles is preferably 50 nm or more, more preferably 100 nm or more, and preferably 400 nm or less, more preferably 350 nm or less, from the perspective of dispersion stability. The average particle diameter of the pigment-containing polymer particles is measured by the method described in the examples.

[0027] <Polyurethane resin> The polyurethane resin acts as a fixing agent for fixing the ink of the present invention as ink droplets on a recording medium by an inkjet recording method. In the ink of the present invention, from the viewpoint of improving the substrate adhesion, rubbing resistance, water resistance, etc. to a low-absorbency recording medium, two types of polyurethane resins A and B having different glass transition temperatures are contained. The glass transition temperature of the polyurethane resin A is 40°C or higher and 95°C or lower, and the glass transition temperature of the polyurethane resin B is 5°C or higher and 20°C or lower. The polyurethane resin can be obtained by subjecting a polyol and a polyisocyanate to a polyaddition reaction by a known method. The glass transition temperature of the polyurethane resin can be adjusted by the molecular weight of the polyurethane resin, the combination of the polyol and the polyisocyanate of the polyurethane resin, etc.

[0028] (Polyol) The polyol is not particularly limited as long as it is a compound having two or more hydroxy groups in one molecule, and one or more selected from polyester polyols, polycarbonate polyols, polyether polyols, etc. are preferable. That is, the polyurethane resin is preferably one or more selected from (i) polyester-based polyurethane resins, (ii) polycarbonate-based polyurethane resins, and (iii) polyether-based polyurethane resins.

[0029] (i) Polyester-based polyurethane resin The polyester-based polyurethane resin can be obtained by subjecting a polyester polyol and a polyisocyanate to a polyaddition reaction. The polyester polyol as a raw material can be obtained by condensing a diol and a dicarboxylic acid. As the diol, one or more selected from diols having 2 to 10 carbon atoms such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4 - butanediol, 3 - methyl - 1,5 - pentanediol, cyclohexanediol are preferred. As the dicarboxylic acid, one or more selected from aliphatic dibasic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, brassilic acid, and aromatic dibasic acids such as isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid are preferred.

[0030] (ii) Polycarbonate - based polyurethane resin As the polycarbonate - based polyurethane resin, a polyurethane resin containing structural units derived from one or more polyols (a) selected from aliphatic polyols having 2 to 12 carbon atoms, alicyclic polyols, aromatic polyols, polycarbonate polyols, polyalkylene carbonate diols containing 1 to 1000 repeating units, polyethylene ether carbonate diols containing 1 to 1000 repeating units, and combinations thereof, and structural units derived from polyisocyanate is preferred.

[0031] (iii) Polyether - based polyurethane resin The polyether - based polyurethane resin can be obtained by polyaddition reaction of a polyether polyol and a polyisocyanate. As the polyether polyol as a raw material, polyether diols obtained by polymerizing 2 to 45 molecules, preferably 10 to 40 molecules of alkylene glycols such as ethylene glycol, propylene glycol, butylene glycol, tetramethylene glycol; polymers obtained by ring - opening polymerization of cyclic ether compounds such as tetrahydrofuran, epichlorohydrin alone or in combination of two or more are preferred.

[0032] (Polyisocyanate) Examples of the polyisocyanate that is a component of the polyurethane resin include one or more selected from aliphatic diisocyanates, aliphatic diisocyanates having a cyclic structure, aliphatic diisocyanates having an aromatic ring, aromatic diisocyanates, and modified products of these diisocyanates (such as carbodiimide, uretdione, and uretoimine-containing modified products). As the aliphatic diisocyanate, one or more selected from tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, etc. are preferable. As the aliphatic diisocyanate having a cyclic structure, one or more selected from 1,3-cyclohexylene diisocyanate, 1,4-cyclohexylene diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane 4,4'-diisocyanate, etc. are preferable. As the aliphatic diisocyanate having an aromatic ring, one or more selected from xylylene diisocyanate, tetramethylxylylene diisocyanate, etc. are preferable. As the aromatic diisocyanate, one or more selected from tolylene diisocyanate, phenylene diisocyanate, diphenylmethane diisocyanate, etc. are preferable.

[0033] Among these, from the viewpoint of improving the substrate adhesion, abrasion resistance, water resistance, etc. to the low liquid absorption recording medium, one or more selected from the aliphatic diisocyanate having a cyclic structure and the aromatic diisocyanate are preferable, and one or more selected from isophorone diisocyanate, dicyclohexylmethane 4,4'-diisocyanate, tolylene diisocyanates such as 2,4-TDI and 2,6-TDI are more preferable. The above polyol and polyisocyanate can be used alone or in combination of two or more of the compounds contained in each component, respectively.

[0034] (Production of polyurethane resin) In the polyaddition reaction of the polyurethane resin, it is preferable to use a polymerization catalyst such as an aliphatic amine compound or an organotin compound. Examples of the reaction solvent include acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, ethyl acetate, toluene, xylene, etc., and acetone, methyl ethyl ketone, ethyl acetate, etc. are preferable. In the polyaddition reaction, a chain extender may be used in combination as necessary. By using a chain extender, the molecular weight can be increased. Examples of the chain extender include polyols, polyamines, etc., and polyamines are preferable. Specific examples of the polyamine include aliphatic diamines such as ethylenediamine, propylenediamine, hexamethylenediamine, alicyclic diamines such as isophoronediamine, alkyl aromatic diamines such as xylylenediamine, hydrazine, etc. Among these, aliphatic diamines are preferable, and ethylenediamine is more preferable.

[0035] The polyurethane resin is preferably used as an aqueous dispersion in which water-insoluble polyurethane resin particles containing no pigment are dispersed in an aqueous medium, and may contain a dispersant such as a surfactant as necessary. The polyurethane resin may have a crosslinked structure. Examples of the method for forming a crosslinked structure include a method of synthesizing polyurethane using a monomer having a functionality of 3 or more, and a method of reacting a linear polyurethane obtained using a bifunctional monomer with a crosslinking agent having a functionality of 3 or more that reacts with the terminal isocyanate group or hydroxy group.

[0036] [Polyurethane Resin A] The glass transition temperature of the polyurethane resin A is 40 °C or higher, preferably 45 °C or higher, more preferably 50 °C or higher, still more preferably 55 °C or higher, even more preferably 60 °C or higher, and 95 °C or lower, preferably 90 °C or lower, more preferably 85 °C or lower, still more preferably 82 °C or lower, even more preferably 80 °C or lower. The glass transition temperature of the polyurethane resin A is measured by the method described in the examples. Polyurethane resin A has a structural unit a derived from one or more selected from aliphatic diisocyanates and aromatic diisocyanates having a cyclic structure, and the content of the structural unit a is 15% by mass or more in all the structural units of polyurethane resin A.

[0037] As the polyurethane resin A, one or more selected from polyester-based polyurethane resin A-1 and polycarbonate-based polyurethane resin A-2 are preferable. Polyurethane resin A has a structural unit a derived from one or more selected from aromatic diisocyanates and aliphatic diisocyanates having a cyclic structure, and the content of the structural unit a is 15% by mass or more in all the structural units of polyurethane resin A.

[0038] (Polyester-based polyurethane resin A-1) As the polyester-based polyurethane resin A-1, among the above-mentioned (i) polyester-based polyurethane resins, a polyurethane resin containing a structural unit derived from a polyester polyol obtained by condensing ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 3-methyl-1,5-pentanediol, cyclohexanediol and a dicarboxylic acid and a structural unit derived from a polyisocyanate (b) is preferable. Among these, the polyester-based polyurethane resin A-1 is preferably a polyurethane resin containing a structural unit derived from a polyester polyol obtained by condensing ethylene glycol, propylene glycol, 1,4-butanediol, 3-methyl-1,5-pentanediol, cyclohexanediol and a structural unit derived from an aromatic diisocyanate, and more preferably a polyurethane resin containing a structural unit derived from a polyester polyol obtained by condensing ethylene glycol, propylene glycol, 1,4-butanediol, 3-methyl-1,5-pentanediol, cyclohexanediol and adipic acid and / or terephthalic acid and a structural unit derived from tolylene diisocyanate (TDI).

[0039] In the polyester-based polyurethane resin A-1, the content of the structural unit derived from polyisocyanate, preferably the content of aromatic diisocyanate, is preferably 15% by mass or more, more preferably 17% by mass or more, still more preferably 19% by mass or more, and preferably 50% by mass or less, more preferably 45% by mass or less, still more preferably 40% by mass or less, based on all the structural units of the polyester-based polyurethane resin A-1.

[0040] (Polycarbonate-based polyurethane resin A-2) As the polycarbonate-based polyurethane resin A-2, among the above-mentioned (ii) polycarbonate-based polyurethane resins, a polyurethane resin containing a structural unit derived from a polycarbonate polyol having a lower polyol structure and a structural unit derived from polyisocyanate is preferred. Specific examples of the lower polyol include one or more selected from aliphatic diols such as ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, heptanediol, octanediol, nonanediol, decanediol, dodecanediol; alicyclic diols such as cyclohexanediol, hydrogenated xylylene glycol; aromatic diols such as xylylene glycol, and combinations thereof.

[0041] Among these, the polycarbonate-based polyurethane resin A-2 is preferably a polycarbonate-based polyurethane resin containing a structural unit derived from a polycarbonate polyol having a structure derived from an aliphatic diol and a structural unit derived from an aliphatic diisocyanate having a cyclic structure. A polyurethane resin containing a structural unit derived from a polycarbonate polyol having a structure derived from an aliphatic diol having 4 to 9 carbon atoms such as 1,4-butanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, heptanediol, octanediol, nonanediol, etc., and a structural unit derived from dicyclohexylmethane 4,4'-diisocyanate is preferred. A polyurethane resin containing a structural unit derived from a polycarbonate polyol having a structure derived from 1,6-hexanediol and a structural unit derived from dicyclohexylmethane-4,4'-diisocyanate is more preferred.

[0042] In the polycarbonate-based polyurethane resin A-2, the content of the structural unit derived from polyisocyanate, preferably the content of the aliphatic diisocyanate having a cyclic structure, is preferably 15% by mass or more, more preferably 18% by mass or more, still more preferably 20% by mass or more in all the structural units of the polycarbonate-based polyurethane resin A-2, and is preferably 50% by mass or less, more preferably 40% by mass or less, still more preferably 30% by mass or less.

[0043] From the viewpoint of improving the discharge stability, scratch resistance, etc., the weight average molecular weight of the polyurethane resin A is preferably 100,000 or more, more preferably 200,000 or more, still more preferably 300,000 or more, and is preferably 3,000,000 or less, more preferably 2,000,000 or less, still more preferably 1,000,000 or less. From the viewpoint of improving the discharge stability, scratch resistance, etc., the acid value of the polyurethane resin A is preferably 2 mgKOH / g or more, more preferably 4 mgKOH / g or more, still more preferably 6 mgKOH / g or more, and is preferably 80 mgKOH / g or less, more preferably 40 mgKOH / g or less, still more preferably 30 mgKOH / g or less. The weight average molecular weight and acid value of the polymer are measured by the method described in the examples.

[0044] In terms of improving ejection stability, substrate adhesion to the printing medium, scratch resistance, etc., the average particle size of the particles of polyurethane resin A in the dispersion is preferably 10 nm or more, more preferably 20 nm or more, still more preferably 30 nm or more, and preferably 300 nm or less, more preferably 200 nm or less, still more preferably 150 nm or less. The average particle size of the polyurethane resin particles is measured by the method described in the examples.

[0045] Examples of commercially available products of the dispersion of polyurethane resin A include Superflex 830HS (polyester type) manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., Superflex 820 (polyester type) manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., NeoRez R-940 (polyester type) manufactured by DSM Coating Resins, NeoRez R-4000 (polycarbonate type) manufactured by DSM Coating Resins, etc.

[0046] [Polyurethane resin B] The glass transition temperature of polyurethane resin B is 20°C or lower, preferably 18°C or lower, more preferably 16°C or lower, and 5°C or higher, preferably 7°C or higher, more preferably 9°C or higher, still more preferably 10°C or higher. Polyurethane resin B contains a structural unit b derived from an aliphatic diisocyanate having a cyclic structure, and the content of the structural unit b is preferably 15% by mass or more in all the structural units of polyurethane resin B.

[0047] As the polyurethane resin B, a polyether-based polyurethane resin B-1 is preferred. (Polyether-based polyurethane resin B-1) As the polyether-based polyurethane resin B-1, among the above-mentioned (iii) polyether-based polyurethane resins, polyether diols obtained by polymerizing 2 to 45 molecules, preferably 10 to 40 molecules of alkylene glycols such as ethylene glycol, propylene glycol, butylene glycol, and tetramethylene glycol; structural units derived from polymers obtained by ring-opening polymerization of cyclic ether compounds such as tetrahydrofuran and epichlorohydrin alone or in combination of two or more, and polyurethane resins containing structural units derived from polyisocyanates are preferred.

[0048] Among these, polyurethane resins containing structural units derived from one or more polyols selected from polyethylene glycol, polypropylene glycol, and polytetramethylene glycol and structural units derived from aliphatic diisocyanates having a cyclic structure are preferred, and polyurethane resins containing structural units derived from polytetramethylene glycol and structural units derived from isophorone diisocyanate are preferred. In the polyether-based polyurethane resin B-1, the content of the structural units derived from polyisocyanates, preferably the content of the structural units derived from aliphatic diisocyanates having a cyclic structure, is preferably 15% by mass or more, more preferably 18% by mass or more, still more preferably 20% by mass or more in all the structural units of the polyether-based polyurethane resin B, and is preferably 65% by mass or less, more preferably 60% by mass or less, still more preferably 55% by mass or less.

[0049] From the viewpoint of improving substrate adhesion, abrasion resistance, etc., the weight average molecular weight of the polyurethane resin B is preferably 10,000 or more, more preferably 20,000 or more, still more preferably 30,000 or more, and is preferably 120,000 or less, more preferably 100,000 or less, still more preferably 80,000 or less. The weight average molecular weight of the polymer is measured by the method described in the examples. The acid value of polyurethane resin B is preferably 1 mgKOH / g or more, more preferably 2 mgKOH / g or more, still more preferably 3 mgKOH / g or more, and preferably 60 mgKOH / g or less, more preferably 40 mgKOH / g or less, still more preferably 20 mgKOH / g or less, from the viewpoints of improving the adhesion of the base material to the printing medium, scratch resistance, etc. The acid value of the polymer is measured by the method described in the examples.

[0050] The average particle size in the dispersion of the particles of polyurethane resin B is preferably 10 nm or more, more preferably 20 nm or more, still more preferably 40 nm or more, and preferably 300 nm or less, more preferably 200 nm or less, still more preferably 150 nm or less, from the viewpoints of improving ejection stability, adhesion of the base material to the printing medium, scratch resistance, etc. The average particle size of the polymer particles is measured by the method described in the examples.

[0051] Examples of commercially available products of the dispersion of polyurethane resin B include those manufactured by DSM Coating Resins, trade names: NeoRez R-600, NeoRez R-966 (polyether type), etc.

[0052] <Water-soluble organic solvent> From the viewpoint of improving the adhesion of the base material, etc., the ink of the present invention preferably contains a water-soluble organic solvent having a boiling point of 100°C or more and 300°C or less. The water-soluble organic solvent may be liquid or solid at normal temperature (25°C). The water-soluble organic solvent refers to an organic solvent whose dissolution amount is 10 mL or more when the organic solvent is dissolved in 100 mL of water at 25°C. The boiling point of the water-soluble organic solvent is preferably 110°C or more, more preferably 115°C or more, still more preferably 118°C or more, and preferably 300°C or less, more preferably 298°C or less, still more preferably 295°C or less, from the viewpoint of improving the adhesion of the base material, etc. Here, the boiling point refers to the standard boiling point (boiling point under 1 atm), and when using two or more water-soluble organic solvents, it is the weighted average value weighted by the content (% by mass) of each water-soluble organic solvent.

[0053] Examples of the water-soluble organic solvent include glycol ethers, polyhydric alcohols, nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, and alkanolamines. Among these, one or more selected from glycol ethers and polyhydric alcohols are more preferable. As the glycol ether, alkylene glycol monoalkyl ether and alkylene glycol dialkyl ether are preferable, and alkylene glycol monoalkyl ether is more preferable. The number of carbon atoms of the alkyl group of the glycol ether is 1 or more, preferably 2 or more, more preferably 3 or more, and preferably 6 or less, more preferably 5 or less, still more preferably 4 or less. The alkyl group may be linear or branched.

[0054] Preferable examples of the alkylene glycol monoalkyl ether include ethylene glycol monoisopropyl ether, ethylene glycol monopropyl ether, diethylene glycol monomethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monoisobutyl ether, diethylene glycol monobutyl ether, etc. Among them, one or more selected from ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether, and diethylene glycol monoisobutyl ether are preferable, and diethylene glycol monoisobutyl ether is more preferable.

[0055] As the polyhydric alcohol, one or more selected from alkanediols having 2 to 6 carbon atoms such as propylene glycol, diethylene glycol, 1,2-hexanediol, glycerin, and polypropylene glycol having a molecular weight of 500 to 1000 are preferable, and propylene glycol is more preferable. In the present invention, an organic solvent other than a water-soluble organic solvent having a boiling point of 100°C or higher and 300°C or lower may be contained as long as the effects of the present invention are not impaired. Examples of other organic solvents include monohydric alcohols such as ethanol, isopropyl alcohol, and n-propyl alcohol.

[0056] <Surfactant> From the viewpoint of improving whiteness and the like, the ink of the present invention preferably contains a surfactant. As the surfactant, a nonionic surfactant is preferable. From the viewpoint of improving whiteness and the like, one or more selected from acetylene glycol-based surfactants and silicone-based surfactants are more preferable, and it is even more preferable to use an acetylene glycol-based surfactant and a silicone-based surfactant in combination.

[0057] (Acetylene glycol-based surfactant) Examples of acetylene glycol-based surfactants include acetylene-based diols such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyne-3-ol, and 2,4-dimethyl-5-hexyne-3-ol, and ethylene oxide adducts thereof. The sum (n) of the average number of moles of added ethylene oxide groups (EO) of the ethylene oxide adduct is preferably 0 or more, and preferably 20 or less, more preferably 10 or less. The HLB (hydrophilic-lipophilic balance) value of the acetylene glycol-based surfactant is preferably 1 or more, more preferably 2 or more, still more preferably 3 or more from the viewpoint of solubility in the aqueous ink, and preferably 6 or less, more preferably 5 or less, still more preferably 4 or less from the viewpoint of enhancing the adhesion of the coating film formed by the ink. Examples of commercially available products of acetylene glycol-based surfactants include the "Surfinol" series manufactured by Nissin Chemical Industry Co., Ltd., the "Olfin" series, and the "Acetylenol" series manufactured by Kawaken Fine Chemical Co., Ltd.

[0058] (Silicone surfactant) Examples of silicone surfactants include dimethylpolysiloxane, polyether-modified silicone, amino-modified silicone, carboxy-modified silicone, etc. From the same perspective as above, polyether-modified silicone is preferred. From the perspective of solubility in aqueous ink, the HLB (hydrophilic-lipophilic balance) value of the polyether-modified silicone surfactant is preferably 8 or more, more preferably 10 or more, and still more preferably 13 or more. The HLB value can be determined by the Griffin method. Specific examples of polyether-modified silicone surfactants include the KF series manufactured by Shin-Etsu Chemical Co., Ltd., the Silface SAG series manufactured by Nichi-Shin Chemical Industry Co., Ltd., the BYK series manufactured by BYK-Chemie Japan Co., Ltd., etc. Among these, the KF series manufactured by Shin-Etsu Chemical Co., Ltd. is preferred.

[0059] [Manufacture of aqueous ink] The ink of the present invention can be obtained by mixing an aqueous dispersion of pigment-containing polymer particles containing titanium oxide, polyurethane resin A, polyurethane resin B, and, if necessary, an organic solvent, water, and various additives such as a humectant, wetting agent, penetrant, surfactant, viscosity modifier, defoaming agent, preservative, antifungal agent, and rust inhibitor commonly used in inks.

[0060] [Content of each component of aqueous ink] The content of each component in the ink of the present invention is as follows from the perspective of improving the ejection stability, whiteness of the recording medium, substrate adhesion, scratch resistance, and water resistance of the ink of the present invention.

[0061] (Content of titanium oxide) The content of titanium oxide in the ink of the present invention is 3% by mass or more, preferably 4% by mass or more, more preferably 5% by mass or more, still more preferably 6% by mass or more, and 14% by mass or less, preferably 13% by mass or less, more preferably 12% by mass or less, still more preferably 11% by mass or less. The content of the pigment-containing polymer particles in the ink of the present invention is preferably 2% by mass or more, more preferably 4% by mass or more, still more preferably 6% by mass or more, and is preferably 20% by mass or less, more preferably 18% by mass or less, still more preferably 15% by mass or less.

[0062] (Content of polyurethane resin A) The content of polyurethane resin A in the ink of the present invention is preferably 0.5% by mass or more, more preferably 0.8% by mass or more, still more preferably 1% by mass or more, and is preferably 6% by mass or less, more preferably 5% by mass or less, still more preferably 4% by mass or less. (Content of polyurethane resin B) The content of polyurethane resin B in the ink of the present invention is preferably 0.5% by mass or more, more preferably 0.8% by mass or more, still more preferably 1% by mass or more, and is preferably 6% by mass or less, more preferably 5% by mass or less, still more preferably 4% by mass or less. The mass ratio of polyurethane resin A to polyurethane resin B (polyurethane resin A / polyurethane resin B) in the ink of the present invention is 0.4 or more, preferably 0.5 or more, more preferably 0.6 or more, still more preferably 0.62 or more, and is 3 or less, preferably 2 or less, more preferably 1.8 or less, still more preferably 1.6 or less.

[0063] (Content of water-soluble organic solvent) The content of the water-soluble organic solvent in the ink of the present invention is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and is preferably 45% by mass or less, more preferably 40% by mass or less, still more preferably 35% by mass or less. The content of water in the ink of the present invention is preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 45% by mass or more, and is preferably 80% by mass or less, more preferably 70% by mass or less, still more preferably 60% by mass or less.

[0064] <Physical properties of aqueous ink> From the viewpoint of improving ejection stability and image density, the viscosity of the ink of the present invention at 32°C is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, still more preferably 5 mPa·s or more, and preferably 12 mPa·s or less, more preferably 9 mPa·s or less, still more preferably 7 mPa·s or less. The viscosity of the aqueous ink can be measured using an E-type viscometer. From the viewpoint of improving storage stability and image density, the pH of the ink of the present invention is preferably 7.0 or more, more preferably 7.2 or more, still more preferably 7.5 or more. Also, from the viewpoints of member resistance and skin irritation, the pH is preferably 11 or less, more preferably 10 or less, still more preferably 9.5 or less. The pH of the aqueous ink can be measured by a conventional method.

[0065] The ink of the present invention can be loaded into a known inkjet recording apparatus such as a piezo type, and ejected as ink droplets onto a recording medium to record an image or the like. The ink of the present invention can obtain a recording having excellent image fastness even in inkjet recording on a low liquid-absorbing recording medium. Examples of the low liquid-absorbing recording medium include low liquid-absorbing coated paper, art paper, and non-liquid-absorbing resin films. Examples of the coated paper include general-purpose glossy paper, multicolor form gloss paper, and the like. Examples of the resin film include transparent synthetic resin films, such as films of polyester, polyvinyl chloride, polyolefin, nylon, and the like. These films may be biaxially stretched, uniaxially stretched, or unstretched films. Among these, polyester films and stretched polypropylene films are preferred, and corona discharge-treated polyethylene terephthalate (PET) films, corona discharge-treated biaxially stretched polypropylene (OPP) films, and the like are more preferred.

Examples

[0066] In the following production examples, examples, and comparative examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The measurement methods for each physical property and the like are as follows.

[0067] (1) Measurement of the weight-average molecular weight (Mw) of the polymer Using a solution prepared by dissolving phosphoric acid and lithium bromide in N,N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively, as the eluent, gel permeation chromatography [GPC apparatus (HLC-8320GPC) manufactured by Tosoh Corporation, columns (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolum Super AW-H) manufactured by Tosoh Corporation, flow rate: 0.5 mL / min] was used to measure with a monodisperse polystyrene kit [PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A-500), manufactured by Tosoh Corporation] of known molecular weight as the standard substance. The measurement sample was prepared by mixing 0.1 g of the polymer with 10 mL of the above eluent in a glass vial, stirring at 25 °C for 10 hours with a magnetic stirrer, and filtering with a syringe filter (DISMIC-13HP, made of PTFE, 0.2 μm, manufactured by Advantec Co., Ltd.).

[0068] (2) Measurement of the average primary particle diameter of titanium oxide The average primary particle diameter of titanium oxide was measured by using a transmission electron microscope "JEM-2100" (manufactured by JEOL Ltd.), extracting 500 titanium oxide primary particles by image analysis, measuring their particle diameters, and calculating the average to obtain the arithmetic mean particle diameter. When the titanium oxide has a major axis and a minor axis, the major axis was used for the calculation.

[0069] (3) Measurement of the average particle diameter of pigment-containing polymer particles and polyurethane resin particles Cumulant analysis was performed using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.) to measure the average particle diameter. The concentration of the particles to be measured was 5×10 -3A dispersion diluted with water to a weight percentage (in terms of solid content concentration) was used. The measurement conditions were a temperature of 25 °C, an angle of 90° between the incident light and the detector, and 100 integration times. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent, and the resulting cumulant average particle size was taken as the average particle size of the pigment-containing polymer particles and polyurethane particles.

[0070] (4) Measurement of solid content concentration Using an infrared moisture meter "FD-230" (manufactured by Kett Scientific Co., Ltd.), 5 g of the measurement sample was dried under the conditions of a drying temperature of 150 °C and a measurement mode of 96 (monitoring time 2.5 minutes / variation width 0.05%). Then, the moisture (%) of the measurement sample was measured, and the solid content concentration was calculated using the following formula. Solid content concentration (%) = 100 - moisture (%) of the measurement sample

[0071] (5) Measurement of acid value of polymer The resin was dissolved in a titration solvent obtained by mixing toluene and acetone (2:1) in an automatic potentiometric titrator (manufactured by Kyoto Electronics Industry Co., Ltd., motor burette, model number: APB-610), and titrated with a 0.1 N potassium hydroxide / ethanol solution by potentiometric titration. The inflection point on the titration curve was taken as the end point. The acid value (mgKOH / g) was calculated from the titration volume up to the end point of the potassium hydroxide solution.

[0072] (6) Calculation of glass transition temperature (Tg) of polyurethane resin Using a differential scanning calorimeter (manufactured by Perkin Elmer, "Pyris 6 DSC"), 5 mg of the sample was weighed into an aluminum pan, heated to 150 °C, and then cooled from that temperature to -30 °C at a cooling rate of 20 °C / min. Next, the sample was heated at a heating rate of 10 °C / min. The temperature at the intersection of the extension of the baseline below the maximum peak temperature of the endotherm and the tangent showing the maximum slope from the rising part of the peak to the apex of the peak was taken as the glass transition temperature (Tg). Note that for the aqueous dispersion, a sample obtained by freeze-drying the aqueous dispersion at -10 °C for 9 hours using a freeze-dryer (manufactured by Tokyo Rika Kikai Co., Ltd., "FDU-2100") was used.

[0073] Production Example 1 (Production of Aqueous Dispersion of Polyurethane Resin Particles A1) Into a four-necked flask equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen inlet tube, polyester polyol (P-2011) as a polyol component, Coronate T-80 as a diisocyanate component, and methyl ethyl ketone were added, and reacted at 75°C for 1 hour to obtain a MEK solution containing 30% prepolymer. Further, dimethylolpropionic acid, 1,4-butanediol, triethylamine, and methyl ethyl ketone were added, and reacted at 75°C for 1 hour to obtain a MEK solution containing 50% prepolymer. Next, this solution was cooled to 45°C, and subsequently, emulsified water and ethylenediamine were mixed. This emulsified dispersion was subjected to solvent removal by vacuum distillation at 50°C for 2 hours to obtain an aqueous dispersion of polyurethane resin particles A1 with a solid content concentration of 20%. The results are shown in Table 1.

[0074] Production Examples 2 to 5 (Production of Aqueous Dispersions of Polyurethane Resin Particles A2 to A3, B4 to B5) In Production Example 1, except that the conditions shown in Table 1 were changed, aqueous dispersions of polyurethane resin particles A2 to A3, B4 to B5 with a concentration of 20% were obtained in the same manner as in Production Example 1. The results are shown in Table 1.

[0075] Details of the raw materials used in Table 1 are as follows. *1: Polyester polyol composed of 3-methyl-1,5-pentanediol, terephthalic acid, and adipic acid Manufactured by Kuraray Co., Ltd., trade name: P-2011, molecular weight 2000, hydroxyl value 56.1 (mgKOH / g) *2: Polycarbonate polyol composed of 1,6-hexanediol Manufactured by Asahi Kasei Corporation, trade name: Duranol T-6002, molecular weight 2000, hydroxyl value 56.1 (mgKOH / g) *3: Polyether polyol composed of 1,4-butanediol Manufactured by Mitsubishi Chemical Corporation, trade name: PTMG1000, molecular weight 1000, hydroxyl value 112.2 (mgKOH / g) *4: 8:2 mixture of isomers of 2,4-TDI and 2,6-TDI Manufactured by Tosoh Corporation, Product Name: Coronate T-80 *5: Dicyclohexylmethane 4,4'-diisocyanate, manufactured by Tokyo Chemical Industry Co., Ltd. *6: Isophorone diisocyanate, manufactured by Tokyo Chemical Industry Co., Ltd. Note that dimethylolpropionic acid, 1,4-butanediol, triethylamine, and ethylenediamine are manufactured by Tokyo Chemical Industry Co., Ltd.

[0076]

Table 1

[0077] Production Example 6 (Production of Aqueous Dispersion of Pigment-Containing Polymer Particles) In a 5 L plastic container, 2500 g of a polyacrylic acid dispersant (manufactured by Toagosei Co., Ltd., Aron A-10SL, Mw: 5000, acid value: 735 mgKOH / g, solid content concentration: 40%) and 3.57 g of ion-exchanged water were added. The container was cooled in an ice bath, and while stirring the solution at 100 rpm, 1666.43 g of a 5N aqueous sodium hydroxide solution was slowly added for neutralization. Ion-exchanged water was added to the neutralized aqueous solution to adjust the solid content concentration to 20% to obtain a neutralized aqueous solution of the polyacrylic acid dispersant (degree of neutralization: 53 mol%, acid value: 735 mgKOH / g). In a 2 L plastic container, 33.0 g of the neutralized aqueous solution of the polyacrylic acid dispersant, 300 g of titanium oxide (manufactured by Ishihara Sangyo Co., Ltd., C.I. Pigment White 6, product name: Ty-Pake CR-80, rutile type, Al·Si treated, average primary particle diameter 250 nm), and 300 g of water were added. 1000 g of zirconia beads were added, and dispersion treatment was carried out for 8 hours on a desktop pot mill stand (manufactured by AS ONE Corporation). The zirconia beads were removed using a metal mesh, and the solid content concentration was adjusted with ion-exchanged water to obtain an aqueous dispersion of pigment-containing polymer particles (solid content concentration: 51%, titanium oxide: 50%, polyacrylic acid: 1%, average particle diameter 280 nm, pH: 7.6).

[0078] Example 1 (Production of Aqueous White Ink 1) 39.2 g of an aqueous dispersion of pigment-containing polymer particles obtained in Production Example 6 (solid content concentration: 51%), 30.0 g of an aqueous dispersion of polyurethane resin particles A1 obtained in Production Example 1 (solid content concentration: 20%, Tg: 68°C), 20.0 g of an aqueous dispersion of polyurethane resin particles B4 obtained in Production Example 4 (solid content concentration: 20%, Tg: 14°C), 6.0 g of diethylene glycol mono isobutyl ether (manufactured by Nippon Emulsifier Co., Ltd.), 54.0 g of propylene glycol, 6.0 g of an acetylene glycol-based surfactant (manufactured by Kawaken Fine Chemicals Co., Ltd., trade name: Surfynol 104PG50, 2,4,7,9-tetramethyl-5-decyne-4,7-diol (HLB: 3.0), propylene glycol solution with an active ingredient concentration of 50%), 0.6 g of a silicone-based surfactant (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: KF-6011, HLB: 14.5), 0.5 g of a silicone-based surfactant (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: KF-353A, HLB: 10), 2.4 g of 1N aqueous sodium hydroxide solution, and 41.3 g of ion-exchanged water were added and mixed. The resulting mixture was filtered through a membrane filter (manufactured by Sartorius, trade name: Mini Sartorius Syringe Filter, pore size: 5.0 μm, material: cellulose acetate) to obtain aqueous ink 1 (solid content concentration: 15.2%, titanium oxide: 10%, polymer: 5.2% (polyacrylic acid: 0.2%, polyurethane resin A: 3.0%, polyurethane resin B: 2.0%), pH: 8.4).

[0079] Examples 2 to 10, Comparative Examples 1 to 4 In Example 1, except that the conditions shown in Table 2 were changed, aqueous white inks 2 to 10 and 11 to 14 were obtained in the same manner as in Example 1.

[0080] Using the aqueous white inks 1 to 10 and 11 to 14 obtained in the above Examples and Comparative Examples, the ejection stability was evaluated by the method shown in [1] below. Also, printed matter was produced by the method shown in [2] below, and evaluations were performed by the methods shown in [3] to [6] below. The results are shown in Table 2. The amounts of each component in Table 2 are the amounts of the active ingredients (solid content). The details of the components shown in Table 2 are as follows.

[0081] <Polyurethane Resin A> (1) Polyester-based polyurethane resin particles A1, solid content concentration: 20%, Tg: 68 °C, Mw: 560,000, acid value: 26 mgKOH / g, average particle size: 53 nm · Polyol component: Polyester polyol composed of 3-methyl-1,5-pentanediol, adipic acid, and terephthalic acid · Aromatic diisocyanate component: Mixture of 2,4-tolylene diisocyanate / 2,6-tolylene diisocyanate, content in all constituent units: 36.2% (2) Polyester-based polyurethane resin particles A2, solid content concentration: 20%, Tg: 80 °C, Mw: 620,000, acid value: 12 mgKOH / g, average particle size: 127 nm · Polyol component: Polyester polyol composed of 3-methyl-1,5-pentanediol, adipic acid, and terephthalic acid · Aromatic diisocyanate component: Mixture of 2,4-TDI / 2,6-TDI, content in all constituent units: 18.3%

[0082] (3) Polycarbonate-based polyurethane resin particles A3, solid content concentration: 20%, Tg: 78 °C, Mw: 350,000, acid value: 12 mgKOH / g, average particle size: 96 nm · Polyol component: 1,6-hexanediol · Aliphatic diisocyanate component: Dicyclohexylmethane 4,4'-diisocyanate, content in all constituent units: 21.8%

[0083] <Polyurethane Resin B> (4) Polyether-based polyurethane resin particles B4, solid content concentration: 20%, Tg: 14 °C, Mw: 60,000, acid value: 7 mgKOH / g, average particle size: 84 nm · Polyol component: Polytetramethylene glycol · Diisocyanate component: Isophorone diisocyanate, content in all constituent units: 20.5% (5) Polyether-based polyurethane resin particles B5, solid content concentration: 20%, Tg: 10 °C, Mw: 50,000, acid value: 9 mgKOH / g, average particle size: 136 nm · Polyol component: Polytetramethylene glycol · Diisocyanate component: Isophorone diisocyanate, content in all constituent units: 50.5% (Others: Acrylic resin) · Joncryl (J) PDX-7789, manufactured by BASF, Tg: 60 °C · Joncryl (J) PDX-7732, manufactured by BASF, Tg: 19 °C

[0084] 〔1〕Evaluation of ejection stability After filling the inkjet head (manufactured by Kyocera Corporation, KJ4B-1200) with ink, the head was left uncapped for 10 minutes, and then the ejection state of the ink when printing was started again was confirmed, and the ejection stability was evaluated according to the following evaluation criteria. The total number of all nozzles is 5312. (Evaluation criteria) ◎: The number of nozzles with chips is 1 / 16 or less of all nozzles. 〇: The number of nozzles with chips is more than 1 / 16 and 8 / 16 or less of all nozzles. △: The number of nozzles with chips is more than 8 / 16 and 12 / 16 or less of all nozzles. ×: The number of chips is more than 12 / 16 of all nozzles, but it can be recovered by maintenance. If the evaluation is 〇 or above, the ejection stability has no practical problem.

[0085] 〔2〕Production of printed matter The inkjet printer equipped with an inkjet head (manufactured by Kyocera Corporation, KJ4B-1200) was filled with the aqueous white ink obtained above, and solid images were printed on a polypropylene film (manufactured by Futamura Chemical Co., Ltd., FOR-AQ). The obtained printed matter was placed on a hot plate heated to 50 °C and dried by blowing warm air with a dryer for 1 minute. The obtained printed matter was placed in a dryer (DVS402, manufactured by Yamato Scientific Co., Ltd.) set at 60 °C and dried for 10 minutes to obtain the final printed matter.

[0086] 〔3〕Evaluation of whiteness The back side of the printed surface of the final printed product of the polypropylene film was overlapped on the predetermined black paper so that the back side faced upward, and the image density of black was measured using a colorimeter (SpectroEye, manufactured by GretagMacbeth), and the whiteness was evaluated according to the evaluation criteria shown below. The lower the image density of black, the higher the hiding property of the printed product, and this value is defined as the whiteness. The better the solid filling property of the white ink, the smaller the whiteness. (Evaluation Criteria) ◎: The whiteness is less than 0.4. 〇: The whiteness is 0.4 or more and less than 0.50. △: The whiteness is 0.5 or more and less than 0.80, which is insufficient. ×: The whiteness is 0.80 or more, which is a problem. If the evaluation is 〇 or more, the whiteness has no practical problem.

[0087] [4] Evaluation of Substrate Adhesion Using the final printed product of the polypropylene film, the evaluation was carried out by the cross-cut test method according to JIS K5400. That is, using a cutter knife, 11 cuts were made vertically and horizontally on the printed surface of the polypropylene film to reach the base material to create 100 cross-cuts. Cellophane tape (registered trademark) was strongly pressure-bonded to the cross-cut portion, and the end of the tape was peeled off at an angle of 120° all at once. The state of the printed surface was visually compared with the state before the test, and the substrate adhesion was evaluated according to the evaluation criteria shown below. (Evaluation Criteria) ◎: No peeling 〇: The peeling is less than 20% △: The peeling is 20% or more and less than 85% ×: The peeling is 85% or more If the evaluation is 〇 or more, the substrate adhesion has no practical problem.

[0088] [5] Evaluation of Rub Resistance For the final printed matter of the polypropylene film, while measuring the load on the fingertip during the rubbing test with a mass measuring instrument (manufactured by A&D Company, Ltd., GX-6100), a load of 300 g was applied with the tip of the index finger and rubbed, and after the printed surface was reciprocated 20 times, the surface state was visually confirmed, and the rub resistance was evaluated according to the evaluation criteria shown below. (Evaluation Criteria) ◎: No change can be visually confirmed at all. 〇: Ink peeling can be seen here and there in an area of 1 / 3 or less of the test section. △: Ink peeling can be seen here and there in an area wider than 1 / 3 and narrower than 2 / 3 of the test section. ×: Ink peeling areas can be seen here and there in an area wider than 2 / 3 of the test section, or all of it has peeled off. If the evaluation is 〇 or higher, the rub resistance has no practical problem.

[0089] 〔6〕Evaluation of Water Resistance The final printed matter of the polypropylene film was cut into test pieces of 4×15 cm, immersed in a screw tube manufactured by Maruemu Co., Ltd. containing ion-exchanged water, and left at room temperature for 24 hours. After leaving, the test piece of the final printed matter was taken out from the screw tube, clamped with a thumb and index finger with a load of 100 g using a mass measuring instrument (manufactured by A&D Company, Ltd., GX-6100), the printed surface was rubbed 15 times back and forth, the number of reciprocations when there was no change in the printed surface during the test was counted, and the water resistance was evaluated according to the evaluation criteria shown below. (Evaluation Criteria) ◎: No change can be visually confirmed even after 15 rubs. 〇: Ink peeling areas can be confirmed in an area of 2 / 5 or less of the test section after 2 to 14 rubs. △: Ink peeling areas can be confirmed in an area more than 2 / 5 and less than or equal to 4 / 5 of the test section after 2 to 14 rubs. ×: Ink peeling areas can be confirmed in an area wider than 4 / 5 of the test section after 1 rub, or all of it has peeled off. If the evaluation is 〇 or higher, the water resistance has no practical problem.

[0090]

Table 2

[0091] From Table 2, it can be seen that the water-based white inks 1 to 10 obtained in the examples are superior in ejection stability compared to the water-based white inks 11 to 14 obtained in the comparative examples, and can obtain inkjet prints excellent in whiteness, substrate adhesion, scratch resistance, and water resistance.

Claims

1. comprising titanium oxide and two polyurethane resins A and B having different glass transition temperatures, the glass transition temperature of the polyurethane resin A is 40°C or higher and 95°C or lower, the polyurethane resin A has a structural unit a derived from one or more selected from aromatic diisocyanates and aliphatic diisocyanates having a cyclic structure, and the content of the structural unit a is 15% by mass or more in all the structural units of the polyurethane resin A, the aromatic diisocyanate is tolylene diisocyanate, and the aliphatic diisocyanate having a cyclic structure is dicyclohexylmethane 4,4'-diisocyanate, the glass transition temperature of the polyurethane resin B is 5°C or higher and 20°C or lower, the mass ratio of the polyurethane resin A to the polyurethane resin B (polyurethane resin A / polyurethane resin B) is 0.4 or higher and 3 or lower, the titanium oxide content in the ink is 3% by mass or higher and 14% by mass or lower, an aqueous white ink for inkjet recording.

2. The aqueous white ink for inkjet recording according to claim 1, wherein the polyurethane resin B contains a structural unit b derived from an aliphatic diisocyanate having a cyclic structure, and the content of the structural unit b is 15% by mass or more in all the structural units of the polyurethane resin B.

3. The aqueous white ink for inkjet recording according to claim 2, wherein the aliphatic diisocyanate having a cyclic structure of the structural unit b contained in the polyurethane resin B is isophorone diisocyanate.

4. The aqueous white ink for inkjet recording according to any one of claims 1 to 3, wherein the content of the polyurethane resin A is 0.5% by mass or higher and 6% by mass or lower in the white ink.

5. The aqueous white ink for inkjet recording according to any one of claims 1 to 4, wherein the titanium oxide is polymer particles containing titanium oxide.

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