Titanium dioxide dispersion

Abstract

To provide a titanium oxide dispersion that has high antifoamability, comprises reduced coarse particles, has excellent sedimentation stability, and expresses excellent coating properties when used as ink raw material.SOLUTION: A titanium oxide dispersion comprises rutile titanium oxide (A), a dispersant (B), and water. In the rutile titanium oxide (A), the total amount of aluminum and silicon elements is 3.4 pts.mass or less relative to 100 pts.mass of titanium element. The dispersant (B) has an acid value of 300 mgKOH / g or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a titanium oxide dispersion. The titanium oxide dispersion of the present invention can be particularly preferably used as an ink raw material for inkjet.

Background Art

[0002] Inks are roughly classified into two types: organic solvent-based inks in which an organic solvent is used as the main component of the solvent, and aqueous inks in which water is used as the main component of the solvent. Since organic solvent-based inks are inferior in safety to the human body and generate odors based on organic solvents, in recent years, aqueous inks using an aqueous solvent have been attracting attention. Furthermore, in recent years, inkjet recording devices, which are digital printing methods that do not require plate making to cope with printing of multiple varieties in small lots, have come to be used. Rutile-type titanium oxide, which is an inorganic pigment, is often used as a colorant for white ink for aqueous inkjet. A titanium oxide dispersion (also referred to as a titanium oxide paste or a titanium oxide slurry) containing rutile-type titanium oxide at a high concentration is prepared, and a method of manufacturing white ink by mixing a water-soluble organic solvent, a resin dispersion liquid, an additive, water, etc. into the titanium oxide dispersion has been adopted.

[0003] In white ink for aqueous inkjet, the ink viscosity is low, and the specific gravity of rutile-type titanium oxide is large, so it is easy to sediment, and a redispersion process such as circulation, oscillation, and stirring during use is required. At that time, bubbles are likely to occur and may have an adverse effect on the ejection head, so high defoaming properties are required for the ink itself. For example, Patent Document 1 shows that in an aqueous ink containing rutile-type titanium oxide and a polymer dispersant, a water-based white ink excellent in defoaming properties in which foaming during redispersion hardly occurs can be obtained by using a high acid value dispersant containing 72% by mass or more of a constituent component derived from an anionic group-containing monomer. For example, Patent Document 2 describes an aqueous pigment dispersion containing titanium dioxide, a resin containing anionic groups, a water-soluble organic solvent, and a basic compound, wherein the titanium dioxide is surface-treated with alumina and silica, and then further surface-treated with a silane coupling agent, and the ratio of the amount of alumina treatment to the total amount of surface treatment by alumina and silica is 35% by mass or more and 80% by mass or less, and it is stated that this aqueous pigment dispersion can provide a white aqueous pigment dispersion that is less prone to settling and has excellent display stability. In this way, much research has been conducted on water-based white inks and titanium dioxide dispersions that stabilize the dispersion state of rutile-type titanium dioxide and have good sedimentation stability. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 6881836 [Patent Document 2] Japanese Patent Publication No. 2011-225867 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Rutile-type titanium dioxide, used as a white pigment, has a high specific gravity and is prone to settling. Therefore, when using titanium dioxide dispersions as ink raw materials, a redispersion operation was necessary to homogenize the internal solid content concentration through shaking or stirring. However, due to the foaming properties caused by the dispersant, a surfactant, contained in the titanium dioxide dispersion, it was difficult to sufficiently homogenize the internal solid content concentration during the redispersion operation. Furthermore, bubbles generated during the redispersion operation were entrained in the ink, causing problems when used as ink. In addition, even after redispersion, there was a tendency for hard sediment (so-called hard cake formation) to occur, resulting in an inability to homogenize the internal solid content concentration. Patent Document 1 describes an aqueous white ink and its raw material, a titanium dioxide dispersion, which is an invention relating to a type of dispersant with low foaming properties. However, because the mass ratio of various elements to the titanium element in the rutile-type titanium dioxide used is not optimized, the above-mentioned hard cake formation is likely to occur, and even if excessive redispersion is possible due to the low foaming properties, there is a problem in that the internal solid content concentration cannot be made uniform.

[0006] Although the titanium dioxide dispersion described in Patent Document 2 has been shown to have excellent settling stability, it has been found to have high manufacturing costs for titanium dioxide, a tendency to foam, and issues with ink drying during printing. The inventors considered that the adsorption behavior of the dispersant to the titanium oxide surface is important for maintaining good dispersion stability, and therefore, the balance between the acid value of the dispersant and the acid-base content on the titanium oxide surface is crucial. Generally, metal oxide coatings are applied to adjust the acid-base content on the titanium oxide surface. It is known that alumina treatment increases the base content, and silica treatment decreases it. When using a dispersant with an acid value of 300 mg KOH / g or higher, which can suppress the increase in electrolyte content, the balance of silicon and aluminum elements contained in titanium oxide in order to achieve the optimal surface acid-base content for titanium oxide that exhibits good properties has not been studied before. The object of the present invention is to provide a titanium oxide dispersion that has high foam-suppressing properties, low coarse particle content, excellent sedimentation stability, and exhibits excellent coating film properties when used as an ink raw material. [Means for solving the problem]

[0007] In view of the above-mentioned problems, the inventors conducted research and found that a titanium dioxide dispersion containing rutile-type titanium dioxide (A), a dispersant (B), and water, wherein the total amount of aluminum and silicon elements per 100 parts by mass of titanium element in the rutile-type titanium dioxide (A) is 3.4 parts by mass or less, and the acid value of the dispersant (B) is 300 mgKOH / g or more, has high anti-foaming properties, few coarse particles, excellent settling stability, and excellent coating film properties when used as an ink raw material, thus completing the present invention. [Effects of the Invention]

[0008] The present invention provides a titanium dioxide dispersion that has high foam-suppressing properties, low levels of coarse particles, excellent settling stability, and excellent coating film properties when used as an ink raw material. [Modes for carrying out the invention]

[0009] A titanium dioxide dispersion comprising rutile-type titanium dioxide (A), a dispersant (B), and water, characterized in that the rutile-type titanium dioxide (A) has a total amount of aluminum and silicon elements of 3.4 parts by mass or less per 100 parts by mass of titanium, and the acid value of the dispersant (B) is 300 mgKOH / g or more.

[0010] <Titanium Oxide> The titanium dioxide dispersion of this disclosure contains titanium dioxide. The titanium dioxide disclosed herein has three crystalline forms: anatase, rutile, and bluekite. From the viewpoint of opacity, it is preferable to use rutile titanium dioxide (A). The content of rutile-type titanium oxide (A) in 100 parts by mass of titanium oxide of the present disclosure is preferably 80 parts by mass or more, more preferably 90 parts by mass or more, even more preferably 95 parts by mass or more, and particularly preferably 100 parts by mass. The primary particle size of titanium dioxide in this disclosure is preferably 0.1 μm or larger, more preferably 0.15 μm or larger, even more preferably 0.2 μm or larger, preferably 1 μm or smaller, even more preferably 0.4 μm or smaller, and even more preferably 0.3 μm or smaller. The primary particle size of titanium dioxide can be measured by scanning electron microscopy or transmission electron microscopy. The titanium oxide of this disclosure comprises at least one element, either aluminum or silicon.

[0011] The titanium oxide of this disclosure preferably contains 0.2 parts by mass or more, more preferably 0.35 parts by mass or more, even more preferably 0.5 parts by mass or more, 3.4 parts by mass or less, more preferably 3.2 parts by mass or less, and even more preferably 3.0 parts by mass or less, per 100 parts by mass of titanium oxide. The titanium oxide of this disclosure preferably contains 0.007 parts by mass or more, more preferably 0.0085 parts by mass or more, even more preferably 0.01 parts by mass or more, preferably 2.0 parts by mass or less, more preferably 1.8 parts by mass or less, and even more preferably 1.6 parts by mass or less, with a silicon content of 0.007 parts by mass or more per 100 parts by mass of titanium oxide. The titanium oxide of this disclosure preferably has a total amount of aluminum and silicon elements of 3.4 parts by mass or less per 100 parts by mass of titanium, may be 3.3 parts by mass or less, or 3.2 parts by mass or less.

[0012] The amounts of silicon and aluminum contained in the titanium oxide of this disclosure can be measured using X-ray fluorescence. A quantitative analysis method using X-ray fluorescence has been established using a calibration curve with standard samples. The rutile-type titanium oxide (A) of this disclosure also contains at least one element, either aluminum or silicon, and preferably the content of aluminum and silicon, and the total amount of aluminum and silicon per 100 parts by mass of titanium, are the same as those of titanium oxide. Examples of the rutile-type titanium oxide (A) of the present disclosure include JR-403, JR-405, JR-600A, JR-701 (manufactured by Teika Corporation), CR-50, CR-58, CR-60, GTR-100 (manufactured by Ishihara Sangyo Co., Ltd.), R-5N, R-650 (manufactured by Sakai Chemical Industry Co., Ltd.), and the like.

[0013] The titanium oxide of the present disclosure is preferably surface-treated, and examples of the surface treatment method include using aluminum oxide, silicon dioxide, zinc oxide, a silane coupling agent, a polyhydric alcohol, an amine, etc. From the viewpoint of productivity, the surface treatment method using aluminum oxide, silicon dioxide, or zinc oxide is preferable, and it is preferable that the surface treatment is performed using at least aluminum oxide and silicon dioxide.

[0014] If the content of titanium oxide in 100 parts by mass of the titanium oxide dispersion of the present disclosure is too low, the productivity will decrease, and when preparing an aqueous white ink using the titanium oxide dispersion as a raw material, it will be difficult to blend a sufficient water-dispersible resin as a binder, resulting in a decrease in various physical properties such as the scratch resistance of the coating film. If it is too high, the viscosity will increase, making it difficult to perform dispersion treatment such as in a bead mill. From these viewpoints, 20 parts by mass or more is preferable, 30 parts by mass or more is more preferable, 40 parts by mass or more is even more preferable, 70 parts by mass or less is preferable, 65 parts by mass or less is more preferable, and 60 parts by mass or less is even more preferable.

[0015] <Dispersant> The titanium oxide dispersion of the present disclosure contains a dispersant (B) (hereinafter also referred to as a dispersant). The acid value of the dispersant of the present disclosure is preferably 300 mgKOH / g or more, more preferably 450 mgKOH / g or more, and even more preferably 650 mgKOH / g or more. The upper limit is not particularly limited and may be 1000 mgKOH / g or less, 900 mgKOH / g or less, or 800 mgKOH / g or less.

[0016] From the viewpoint of dispersion stability, the pH of the dispersant of the present disclosure is preferably a dispersant of 6 to 11. The dispersant of this disclosure may be a polymer having anionic groups. The anionic groups contained in the dispersant of this disclosure are preferably carboxyl groups, sulfo groups, and phosphate groups, with carboxyl groups being more preferred.

[0017] The dispersant used in the present invention is not particularly limited as long as its acid value is 300 mgKOH / g or higher, but examples include acrylic polymers, styrene-acrylic polymers, maleic acid polymers, styrene-maleic acid polymers, α-olefin-maleic acid polymers, urethane polymers, ester polymers, sulfonic acid polymers, phosphate polymers, etc. Among these, acrylic polymers and styrene-acrylic polymers are preferable from the viewpoint of dispersion stability.

[0018] The amount of monomers derived from anionic monomers contained in the polymer having anionic groups of this disclosure is preferably 50 parts by mass or more, and more preferably 70 parts by mass or more, per 100 parts by mass of the dispersant.

[0019] Specific examples of the dispersants described herein include commercially available products such as polyacrylic acid neutralization products from Wako Pure Chemical Industries, Ltd., special polycarboxylic acid neutralization products such as Poise 520 and 530 from Kao Corporation, water-soluble acrylic acid such as Aron 6012 from Toagosei Co., Ltd., and the Aqualic series from Nippon Shokubai Co., Ltd.

[0020] The amount of dispersant per 100 parts by mass of titanium dioxide in this disclosure is 2% by mass or more from the viewpoint of dispersion stability, preferably 2.2 parts by mass or more, more preferably 2.5% by mass or more, and even more preferably 2.8% by mass or more. From the viewpoint of anti-foaming properties and the physical properties of the coating film after ink formation, it is preferably 12% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less.

[0021] If the titanium dioxide content in 100 parts by mass of the titanium dioxide dispersion of this disclosure is too low, productivity will decrease, and if it is too high, viscosity will increase, making dispersion processing such as bead milling difficult. From these viewpoints, 20 parts by mass or more is preferred, 30 parts by mass or more is more preferred, 40 parts by mass or more is even more preferred, 80 parts by mass or less is preferred, 70 parts by mass or less is more preferred, and 60 parts by mass or less is even more preferred.

[0022] <Water> The titanium dioxide dispersion of this disclosure contains water. From the viewpoint of safety during titanium dioxide dispersion production, the water content in 100 parts by mass of the liquid phase component of the titanium dioxide dispersion of this disclosure is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The titanium dioxide dispersion of this disclosure may contain water-soluble organic solvents other than water. Ethylene glycol and propylene glycol are preferred as water-soluble organic solvents. The boiling point of the above water-soluble organic solvent is preferably 240°C or lower, more preferably 220°C or lower, and even more preferably 200°C or lower, from the viewpoint of the drying properties of the ink when the ink is prepared using titanium dioxide dispersion as a raw material.

[0023] From the viewpoint of safety when used as a water-based ink and the drying properties of the ink, the amount of water-soluble organic solvent having a lactam ring structure is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 2 parts by mass or less per 100 parts by mass of titanium dioxide dispersion, and may not be included at all. Examples of water-soluble organic solvents having a lactam ring structure include 2-pyrrolidone, N-methylpyrrolidone, and N-ethylpyrrolidone. The boiling point of the above water-soluble organic solvent is preferably 240°C or lower, more preferably 220°C or lower, and even more preferably 200°C or lower, from the viewpoint of the drying properties of the ink when the ink is prepared using titanium dioxide dispersion as a raw material.

[0024] From the viewpoint of safety during titanium dioxide dispersion production, the water content in 100 parts by mass of the liquid phase component of the titanium dioxide dispersion of this disclosure is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0025] <Other additives> Other additives that can be added as appropriate include defoamers, plasticizers, leveling agents, fungicides, rust inhibitors, matting agents, flame retardants, thixotropes, tackifiers, thickeners, lubricants, antistatic agents, surfactants, reaction retarders, antioxidants, UV absorbers, hydrolysis inhibitors, weather stabilizers, and anti-tack agents. The proportions of each additive are selected as appropriate depending on the purpose and application.

[0026] Examples of defoaming agents in this disclosure include silicone-based defoaming agents, polyether-based defoaming agents, fatty acid ester-based defoaming agents, and acetylene glycol-based defoaming agents. Among these, silicone-based defoaming agents and acetylene glycol-based defoaming agents are preferred because they have excellent ability to properly maintain surface tension and interfacial tension and hardly generate foam. The amount of the defoaming agent per 100 parts by mass of the titanium oxide dispersion of this disclosure is preferably 0.001 parts by mass or more, more preferably 0.01 parts by mass or more, and still preferably 0.05 parts by mass or more, from the viewpoint of suppressing foam formation, preferably 0.5 parts by mass or less, more preferably 0.4 parts by mass or less, and still preferably 0.3 parts by mass or less.

[0027] <Properties of titanium oxide dispersions> The pH of the titanium dioxide dispersion of this disclosure is preferably 5 to 10, more preferably 6 to 9, and even more preferably 7 to 8, from the viewpoint of dispersion stability. If the viscosity of the titanium dioxide dispersion in this disclosure is too high, the efficiency of dispersion processing such as bead mills will decrease, and when used as a raw material for water-based white ink, the viscosity of the water-based white ink will increase, reducing printability. If the viscosity is too low, there is a concern that the settling rate of titanium dioxide, which has a high specific gravity, will increase, leading to the formation of hard cake. From these viewpoints, the viscosity of the titanium dioxide dispersion is preferably 1 to 200 mPa·s or less, more preferably 2 to 100 mPa·s or more, more preferably 5 to 50 mPa·s or more, and more preferably 10 to 20 mPa·s or more. The viscosity of the titanium oxide dispersion of this disclosure at 25°C can be measured by known methods, specifically using a B-type viscometer or an E-type viscometer.

[0028] With respect to the titanium dioxide-containing particles (C) in the titanium dioxide dispersion of this disclosure, when the particle diameter representing 99% of the cumulative particle size distribution from the finest particle side on a volume basis is defined as the D99 particle diameter, the preferred upper limit of the D99 particle diameter is preferably 800 nm or less, more preferably 750 nm or less, and even more preferably 700 nm or less, from the viewpoint of the sedimentation stability of the titanium dioxide dispersion and the ejection stability when used as an inkjet-based white ink. The preferred lower limit of the D99 particle diameter is preferably 300 nm or more, more preferably 350 nm or more, and even more preferably 400 nm or more, from the viewpoint of preventing over-dispersion and thickening caused by the shedding of surface-treated metal oxides due to excessive bead milling.

[0029] With respect to the titanium dioxide-containing particles (C) in the titanium dioxide dispersion of this disclosure, when the particle diameter at which 50% of the cumulative particle size distribution from the finest particle side is taken as the D50 particle diameter, if the D50 particle diameter is too large, it will cause nozzle clogging when used as an inkjet ink raw material, and if it is too small, it will reduce the opacity when used as an inkjet ink raw material. From these viewpoints, the upper limit of the D50 particle diameter is preferably 500 nm or less, more preferably 450 nm or less, and even more preferably 380 nm or less, and the lower limit of D50 is preferably 150 nm or more, more preferably 200 nm or more, and even more preferably 250 nm or more.

[0030] The particle size distribution in the titanium oxide dispersion of this disclosure can be measured by known methods, specifically by dynamic scattering or Coulter counter methods, or by particle size distribution measurement methods compliant with ISO 13319, etc. Regarding the titanium dioxide particles (C) in the titanium dioxide dispersion of this disclosure, if the particle concentration of particles with a diameter of 1.0 μm or larger is too high, it will cause nozzle clogging when used as a raw material for inkjet inks, and if it is too small, the productivity of the titanium dioxide dispersion will decrease. From these perspectives, 1 × 10 6 ~200×10 6 It is preferable that the concentration is μm³ / ml, which is 3 × 10 6 ~100×10 6 μm 3 It is more preferable that it be / ml, which is 5 × 10 6 ~50×10 6 A concentration of μm³ / ml is even more preferable. The concentration of particles with a diameter of 1.0 μm or larger in the titanium dioxide dispersion of this disclosure can be measured by known methods, specifically by the Coulter counter method or the like.

[0031] The amount of non-volatile components in the titanium oxide dispersion of this disclosure is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and particularly preferably 50% by mass or more, from the viewpoint of opacity and processing efficiency when used in printed materials. Furthermore, from the viewpoint of suppressing the viscosity of the titanium oxide dispersion, it is preferably 80% by mass or less, and more preferably 70% by mass or less. The non-volatile components of the titanium dioxide dispersion in this disclosure are, from the total mass of the titanium dioxide dispersion, water and various additives. Alternatively, the mass may be calculated by excluding the mass of volatile components contained in the additive, or by weighing 1 g of titanium dioxide dispersion, drying it in a hot air dryer at 150°C for 1 hour, and considering the resulting residue as non-volatile content, the formula is: [Non-volatile content (mass%) in titanium dioxide dispersion] = ([Mass of residue] ÷ [1g of titanium dioxide dispersion]) × 100 It may also be calculated based on this.

[0032] <Method for producing titanium dioxide dispersion> The titanium dioxide dispersion of this disclosure can be dispersed using titanium dioxide, a dispersant, and water by known methods. Dispersion methods may include using dispersion devices with media such as ball mills, sand mills, or bead mills, or using media-less dispersion devices. A particularly effective dispersion method involves performing the dispersion at a high pigment concentration of approximately twice the target pigment concentration, and then diluting the dispersion to the target pigment concentration with a dispersion medium before withdrawal. At high pigment concentrations, the ratio of pigment to dispersant polymer increases, leading to increased contact between the dispersant polymer and pigment, and is expected to promote the adsorption of the dispersant polymer to the pigment. In a dispersion device using media, zirconia beads are preferred as the dispersion medium from the viewpoint of dispersibility and dispersion efficiency. Furthermore, two or more of these dispersion methods may be used in combination.

[0033] A dispersion apparatus using a bead mill is preferred as the dispersion method for the titanium oxide dispersion according to this disclosure. The material of the bead mill is preferably a ceramic such as zirconia or titania, a polymer material such as polyethylene or nylon, or a metal, with zirconia being preferred from the viewpoint of wear resistance. The bead diameter for the bead mill is preferably 0.01 mm or larger, more preferably 0.05 mm or larger, even more preferably 0.07 mm or larger, preferably 1 mm or smaller, more preferably 0.5 mm or smaller, and even more preferably 0.2 mm or smaller.

[0034] The titanium oxide dispersion method of this disclosure may be a circulation method or a multi-pass method. A circulation method may involve installing a tank and a media-type disperser, forming a circulation system with piping, and circulating the dispersion. A multi-pass method may involve installing a mother tank, a receiving tank, and a media-type disperser, returning the dispersion from the receiving tank to the mother tank, or installing two tanks and a media-type disperser and passing the dispersion in a catch-and-throw manner. However, a circulation method is preferred from the viewpoint of simplicity of the equipment. Media-type dispersers may be installed in the required number of units arranged in series. The preferred circulation method of this disclosure is a circulation method in which a titanium dioxide dispersion containing titanium dioxide, a dispersant, and water is repeatedly circulated to a media disperser.

[0035] <Water-based white ink using titanium dioxide dispersion> If the amount of rutile-type titanium dioxide contained in the aqueous white ink using the titanium dioxide dispersion of this disclosure as a raw material is too low, the opacity decreases, and if it is too high, the ink viscosity increases and the printability decreases. From these viewpoints, the amount of rutile-type titanium dioxide contained in 100 parts by mass of aqueous white ink is preferably 1 to 25 parts by mass, more preferably 3 to 20 parts by mass, and even more preferably 6 to 12 parts by mass.

[0036] The aqueous white ink using the titanium dioxide dispersion of this disclosure contains a binder resin. In the aqueous white ink using the titanium dioxide dispersion of this disclosure as a raw material, the amount of binder resin relative to rutile-type titanium dioxide (mass of rutile-type titanium dioxide / mass of non-volatile content of the binder resin) is important. If it is too low, the opacity decreases; if it is too high, the abrasion resistance and gloss of the coating film decrease. From these viewpoints, a ratio of 2 / 10 to 6 / 1 is preferred, 5 / 10 to 2 / 1 is more preferred, and 6 / 10 to 1 / 1 is even more preferred.

[0037] The non-volatile content of the binder resin may be determined by referring to the value listed in the catalog, or by calculating it as the mass excluding the volatile components contained in the binder resin and various additives. Alternatively, 1 g of a water-dispersible resin containing the binder resin may be weighed, dried in a hot air dryer at 110°C for 1 hour, and the resulting residue may be used as the non-volatile content, using the formula: [Non-volatile content (mass%) in water-dispersible resins] = ([Mass of residue] ÷ [1g of water-dispersible resin]) × 100 It may also be calculated based on this.

[0038] The type of water-dispersible resin contained as a binder resin in the water-based white ink using the titanium dioxide dispersion of this disclosure as a raw material is not particularly limited, but from the viewpoint of improving the abrasion resistance of the coating film and adhesion to the substrate, acrylic resin, styrene-acrylic resin, and urethane resin are preferred. Among these, acrylic resin is preferred from the viewpoint of improving adhesion to poorly absorbent substrates such as plastics, and more preferably, from the viewpoint of obtaining good adhesion to poorly adhering olefin substrates such as biaxially oriented polypropylene (OPP) without primer printing, it is preferable that the water-dispersible resin contains a polymer having structural units derived from cyclic aliphatic group-containing monomers.

[0039] The water-dispersible resin disclosed herein may be a single-layer resin emulsion particle or a resin emulsion particle having multiple layers.

[0040] The cyclic aliphatic group-containing monomers of this disclosure are preferably monomers having a carbon-carbon double bond, and include (meth)acrylate monomers having a cyclic aliphatic hydrocarbon group. The (meth)acrylate monomer having a cyclic aliphatic hydrocarbon group is preferably a compound having a monovalent cyclic aliphatic hydrocarbon group and a monovalent (meth)acrylate group, where the monovalent cyclic aliphatic hydrocarbon group and the monovalent (meth)acrylate group are directly bonded. Examples of cyclic aliphatic hydrocarbon groups include monocyclic groups, polycyclic groups, and cross-linked ring groups. The number of carbon atoms in the cyclic aliphatic hydrocarbon group is preferably 4 to 20. The cyclic aliphatic hydrocarbon group is preferably a cyclic aliphatic group having 4 to 20 carbon atoms, particularly 5 to 12 carbon atoms. The number of carbon atoms in the cyclic aliphatic hydrocarbon group is preferably 15 or less, for example, 10 or less. It is preferable that the carbon atoms in the ring of the cyclic aliphatic hydrocarbon group are directly bonded to the ester group in the (meth)acrylate group. Specific examples of cyclic aliphatic hydrocarbon groups are cyclohexyl group, t-butylcyclohexyl group, isobornyl group, dicyclopentanyl group, and dicyclopentenyl group. The (meth)acrylate group is either an acrylate group or a methacrylate group, but a methacrylate group is preferred.

[0041] Specific examples of monomers having a cyclic aliphatic hydrocarbon group include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentenyl (meth)acrylate. Cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate are preferred, and cyclohexyl (meth)acrylate and isobornyl (meth)acrylate are more preferred. These cyclic aliphatic group-containing monomers can be used individually or in combination of several types.

[0042] The content of structural units derived from monomers having cyclic aliphatic hydrocarbon groups in 100 parts by mass of the polymer having structural units derived from cyclic aliphatic group-containing monomers of the present disclosure may be 30 parts by mass or more, preferably 35 parts by mass or more, more preferably 40 parts by mass or more, even more preferably 45 parts by mass or more, and may be 95 parts by mass or less, preferably 90 parts by mass or less, and more preferably 85 parts by mass or less.

[0043] When a water-dispersible resin containing a polymer having structural units derived from a cyclic aliphatic group-containing monomer is used as the binder resin of the present disclosure, the content of structural units derived from a monomer having a cyclic aliphatic hydrocarbon group in 100 parts by mass of the water-dispersible resin may be 30 parts by mass or more, preferably 35 parts by mass or more, more preferably 40 parts by mass or more, even more preferably 45 parts by mass or more, may be 95 parts by mass or less, preferably 90 parts by mass or less, and more preferably 85 parts by mass or less.

[0044] The polymer having structural units derived from cyclic aliphatic group-containing monomers according to this disclosure may also have structural units derived from monomers other than those derived from cyclic aliphatic group-containing monomers. Other monomer-derived structural units are not limited to structural units formed by polymerization of the other monomers described below, but may also include structural units formed by post-reactions after polymerization, for example.

[0045] Other monomers include monofunctional monomers and polyfunctional monomers. Monofunctional monomers and polyfunctional monomers may be used individually or in combination. Examples of monofunctional monomers include (meth)acrylic acid esters having linear alkyl groups, (meth)acrylic acid esters having branched alkyl groups, acid group-containing monomers, hydroxyl group-containing (meth)acrylates, oxo group-containing monomers, fluorine atom-containing monomers, nitrogen atom-containing monomers, epoxy group-containing monomers, alkoxyalkyl (meth)acrylates, silane group-containing monomers, carbonyl group-containing monomers, aziridinyl group-containing monomers, styrene monomers, aralkyl (meth)acrylates, and addition-polymerizable oxazolines, but are not limited to these examples.

[0046] The aqueous white ink disclosed herein may contain water or other water-soluble organic solvents from the viewpoint of controlling ink viscosity, wetting spread on the recording medium to be printed, improving image quality, and ejection stability. Examples of water-soluble organic solvents include glycols such as propylene glycol, 1,3-propanediol, glycerin, dipropylene glycol, tripropylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol; monoethylene glycol ethers such as monoethylene glycol monomethyl ether, monoethylene glycol monoethyl ether, monoethylene glycol monopropyl ether, monoethylene glycol monoisopropyl ether, monoethylene glycol monobutyl ether, and monoethylene glycol monoisobutyl ether; monopropylene glycol monomethyl ether, monopropylene glycol monoethyl ether, monopropylene glycol monopropyl ether, monopropylene glycol monoisopropyl ether, and mono Monopropylene glycol ethers such as propylene glycol monobutyl ether and monopropylene glycol monoisobutyl ether; polyethylene glycol ethers such as polyethylene glycol monomethyl ether (moles of EO added = 2-10, preferably 2-4), polyethylene glycol monoethyl ether (moles of EO added = 2-10, preferably 2-4), polyethylene glycol monopropyl ether (moles of EO added = 2-10, preferably 2-4), polyethylene glycol monoisopropyl ether (moles of EO added = 2-10, preferably 2-4), polyethylene glycol monobutyl ether (moles of EO added = 2-10, preferably 2-4), and polyethylene glycol monoisobutyl ether (moles of EO added = 2-10, preferably 2-4);Examples of polypropylene glycol ethers include polypropylene glycol monomethyl ether (number of EO added moles = 2 to 10, preferably 2 to 4), polypropylene glycol monoethyl ether (number of EO added moles = 2 to 10, preferably 2 to 4), polypropylene glycol monopropyl ether (number of EO added moles = 2 to 10, preferably 2 to 4), polypropylene glycol monoisopropyl ether (number of EO added moles = 2 to 10, preferably 2 to 4), polypropylene glycol monobutyl ether (number of EO added moles = 2 to 10, preferably 2 to 4), and polypropylene glycol monoisobutyl ether. Among these, propylene glycol, diethylene glycol, triethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, tripropylene glycol monomethyl ether, monoethylene glycol monoisopropyl ether, and monopropylene glycol monopropyl ether are preferred. These organic solvents may be used individually or in combination of two or more types. ;

[0047] The amount of water-soluble organic solvent varies depending on the type and amount of colorants contained in the water-based white ink, and therefore cannot be determined in general terms. It is preferable to determine the amount appropriately according to the type and amount of colorants contained in the water-based white ink. For example, if the coloring agent contains a white pigment, the amount of organic solvent in 100g by mass of water-based white ink may be 5 parts by mass or more, preferably 8 parts by mass or more, more preferably 10 parts by mass or more, may be 50 parts by mass or less, preferably 45 parts by mass or less, and more preferably 40 parts by mass or less, from the viewpoint of controlling the wetting spread on the recording medium to be printed and improving image quality.

[0048] The aqueous white ink of this disclosure contains the aforementioned aqueous ink resin emulsion and colorant, but may also contain resins other than the aforementioned aqueous ink resin emulsion, water-soluble resins, water-dispersible resins, etc., as long as the objectives of the present invention are not hindered. Furthermore, the aqueous ink of the present invention may also contain appropriate amounts of additives such as surfactants, film-forming aids, ultraviolet absorbers, ultraviolet inhibitors, fillers, leveling agents, dispersants, thickeners, wetting agents, plasticizers, stabilizers, antioxidants, waxes, etc., as long as the objectives of the present invention are not hindered.

[0049] <Applications and substrates of the aqueous white ink using the titanium dioxide dispersion of this disclosure as a raw material> The aqueous white ink obtained as described above has excellent adhesion and scratch resistance, and can therefore be suitably used as an ink for various applications, such as water-based inkjet inks, flexographic printing inks, offset printing inks, lithograph printing inks, gravure printing inks, and screen printing inks, and is particularly suitable as a water-based inkjet ink.

[0050] The aqueous white ink of this disclosure can form prints or images having a predetermined pattern by ejecting aqueous ink onto a recording medium in a predetermined pattern using, for example, an inkjet recording device.

[0051] Examples of recording media include paper, paper laminated with resin films such as polyethylene, polypropylene, and polystyrene (such as coated paper), metal plates such as aluminum, zinc, and copper, resin films such as cellulose, polyethylene terephthalate, polystyrene, olefin resins, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyamide, nylon, and acrylic resins, paper with a metal coating, and resin films with a metal coating. Resin films are preferred as recording media for printing the aqueous ink of this disclosure, and among these, application to polyethylene terephthalate and olefin resins is preferred. Examples of olefin resins include polyethylene and polypropylene, with particular preference for application to polypropylene such as biaxially oriented polypropylene film (OPP) and unoriented polypropylene film (CPP).

[0052] The aqueous white ink of this disclosure is preferably formed on a resin film, and the embodiment thereof is a laminate having a printed layer formed from the aqueous ink on the resin film. The disclosed laminate may or may not have a primer layer between the resin film and the printed layer, but from a productivity standpoint it is preferable not to have one, and it is preferable to form the printed layer directly on the resin film. The disclosed laminate is laminated in the order of resin film and printed layer, and may or may not have a protective film (laminate layer) on the printed layer, but from a productivity standpoint it is preferable not to have one, and by using the aqueous ink of the disclosed, it is expected that a laminate with excellent adhesion to the substrate and good scratch resistance can be obtained even without a primer layer or protective film (laminate layer). [Examples]

[0053] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means "parts by mass" and "%" means "percent mass".

[0054] <Glass transition temperature of polymer components in water-dispersible resins> The glass transition temperature (Tg) of a polymer component is calculated using the glass transition temperature of the monomer homopolymer used in the monomer components constituting the polymer component, using the formula: 1 / Tg = Σ(Wm / Tgm) / 100 [In the formula, Wm represents the content (mass%) of monomer m in the monomer components constituting the polymer component, and Tgm represents the glass transition temperature (absolute temperature: K) of the monomer m homopolymer.] It was calculated based on Fox's formula, which is expressed as follows:

[0055] <Acid value derived from carboxyl groups of polymer components in water-dispersible resins> The acid value derived from the carboxyl groups of the resin emulsion particles was approximated by using the number of mg of potassium hydroxide required to neutralize the carboxyl groups present in 1 g of the monomer component used as the acid value. <Minimum film-forming temperature for polymer components in water-dispersible resins> The minimum film formation temperature is measured in accordance with JIS K6828-2:2003, and the measured value is shown.

[0056] <Average particle size of polymer components in water-dispersible resins> Using a multi-sample nanoparticle diameter measurement system [manufactured by Otsuka Electronics Co., Ltd., product name: nanoSAQLA], a particle size measurement device using dynamic light scattering at a measurement temperature of 25±0.5℃, the autocorrelation function was determined by photon correlation spectroscopy, and the average particle diameter (hydrodynamic diameter) was determined by cumulant analysis.

[0057] <Measurement of primary particle size of rutile-type titanium dioxide> This was calculated from scanning electron microscope observations. <Measurement of the mass amounts of each element contained in rutile-type titanium oxide> The elemental mass parts contained in rutile-type titanium oxide were measured using X-ray fluorescence (XRF) with a RIGAKU ZSX Primus II.

[0058] <Particle concentrations of titanium dioxide dispersion and aqueous white ink: D50, D99, and 1 μm or larger> The volume-based particle size was evaluated using the Multisizer 4e manufactured by Beckman Coulter, Inc.

[0059] [Production example 1] Water-dispersible resin 520 parts of deionized water were placed in a flask equipped with a dropping funnel, stirrer, nitrogen gas inlet tube, thermometer, and reflux condenser. A first-stage dropwise pre-emulsion was prepared in the dropping funnel, consisting of 163 parts of deionized water, 80 parts of a 25% aqueous solution of emulsifier [ADEKA Corporation, product name: Adekaryasorb SR-10], 322 parts of cyclohexyl methacrylate, 103 parts of 2-ethylhexyl acrylate, and 75 parts of 2-hydroxyethyl methacrylate. 74 parts of this pre-emulsion, representing 5% of the total monomer components, were added to the flask. The temperature was raised to 70°C while slowly blowing in nitrogen gas, and 30 parts of a 5% aqueous solution of ammonium persulfate were added to initiate polymerization. Subsequently, the remaining portion of the dropwise pre-emulsion was uniformly added dropwise to the flask over a period of 120 minutes.

[0060] After the dropwise dispensing was complete, the contents of the flask were maintained at 70°C for 60 minutes. Subsequently, a second-stage dropwise dispensing pre-emulsion consisting of 163 parts deionized water, 80 parts 25% aqueous solution of emulsifier [ADEKA Corporation, product name: Adeka Riasorb SR-10], 310 parts cyclohexyl methacrylate, 105 parts 2-ethylhexyl acrylate, 75 parts 2-hydroxyethyl methacrylate, and 10 parts 4-(meth)acryloyloxy-1,2,2,6,6-pentamethylpiperidine [ADEKA Corporation, product name: Adeka Stab LA-82], along with 30 parts 5% aqueous solution of ammonium persulfate, was uniformly added to the flask over 120 minutes.

[0061] After the dropwise addition was complete, the contents of the flask were maintained at 70°C for 60 minutes, and the pH was adjusted to 8 by adding 25% aqueous ammonia to complete the polymerization. After the resulting reaction solution was cooled to room temperature, an aqueous dispersion was prepared by filtering through a 300-mesh wire mesh. The obtained aqueous dispersion contained the polymer, which was a resin emulsion consisting of emulsion particles with a two-layer structure having an inner layer and an outer layer. The non-volatile content in this aqueous dispersion was 50%, the acid value derived from the carboxyl groups of the polymer was 0 mgKOH / g, the glass transition temperature of the inner layer resin constituting the resin emulsion particles contained in the emulsion was 32°C, and the glass transition temperature of the outer layer resin was also 32°C. The minimum film thickening temperature was 40°C, and the average particle size was 150 nm.

[0062] <Influence of Rutile-type Titanium Dioxide (Al+Si)> [Example 1] 39.96 parts of pure water, 4.94 parts of HL415-NH3 (a water-soluble polymer dispersant prepared by adjusting the pH of a polyacrylic acid aqueous solution Aquaric HL415 manufactured by Nippon Shokubai Co., Ltd. to 7.5 with a 25% ammonia aqueous solution manufactured by Wako Pure Chemical Industries, Ltd., acid value 750 mg KOH / g, molecular weight (MW) 11700, active ingredient concentration 39%) as a dispersant, 55.00 parts of titanium dioxide A (primary particle size 210-290 nm) as rutile-type titanium dioxide, and 0.10 parts of Orphine D10-PG (an acetylene-based surfactant manufactured by Nisshin Chemical Industry Co., Ltd.) as an antifoaming agent were added to a 250 mL plastic container. Subsequently, 100 g of 0.1 mm diameter zirconia beads were added as a dispersion medium. After sealing the plastic container and treating it with a paint shaker for 300 minutes, the zirconia beads were filtered by suction filtration using paper filter paper with a mesh size of 7 μm to obtain a titanium dioxide dispersion with a rutile-type titanium dioxide concentration of 55% by mass. Next, 24.5 parts of pure water, 15.0 parts of propylene glycol and 5.0 parts of tripropylene glycol monobutyl ether as water-soluble organic solvents, 20.0 parts of the above titanium dioxide dispersion, 35 parts of the water-dispersible resin obtained in Production Example 1 as a binder resin, and 0.5 parts of KF-6011 (manufactured by Shin-Etsu Chemical Co., Ltd.), PEG-11 methyl ether dimethicone (polyether-modified silicone surfactant) as a surfactant were mixed at 1000 rpm in a homodisper and filtered through a 3 μm filter [Advantec Co., Ltd., MCP-3-C10S] to obtain an aqueous white ink.

[0063] [Examples 2-12, Comparative Examples 1-9] Titanium dioxide dispersions and aqueous white inks were prepared using the same method as in Example 1, except that the type of rutile-type titanium dioxide with a primary particle size of 210-280 nm and the type and amount of dispersant were changed according to Table 1. Table 1 shows the physical properties of titanium dioxide and the amount of dispersant added in Examples 1-12 and Comparative Examples 1-9.

[0064] [Table 1]

[0065] The abbreviations listed in Table 1 have the following meanings: HL415-NH3; A water-soluble polymer dispersant prepared by adjusting the pH of a polyacrylic acid aqueous solution Aquaric HL415 manufactured by Nippon Shokubai Co., Ltd. to pH 7.5 with a 25% ammonia aqueous solution manufactured by Wako Pure Chemical Industries, Ltd. Acid value 750 mg KOH / g, molecular weight (MW) 11700, active ingredient concentration 39%. BYK-190; manufactured by BYChemie Japan, a polyalkylene glycol group-containing acrylic water-soluble resin, acid value 10 mg KOH / g, active ingredient concentration 40%. HPD-196; BASF acrylic water-soluble polymer dispersant, acid value 200 mg KOH / g, molecular weight (MW) 9200, active ingredient concentration 36% Table 2 shows the evaluation results of the titanium dioxide dispersant and aqueous white ink obtained in Examples 1-12 and Comparative Examples 1-9.

[0066] <Evaluation Criteria> Settlement stability: After placing 50g of the sample in a 100cc plastic container and letting it stand at 50°C for 3 months, ○; When the container is gently shaken, the difference in non-volatile content between the supernatant liquid and the bottom of the container is less than 0.1%. △; When the container is gently shaken, the difference in non-volatile content between the supernatant liquid and the bottom of the container is between 0.1% and less than 1%. ×; Hard deposits (hard cake) have formed, and when the container is gently shaken, the difference in non-volatile content between the supernatant liquid and the bottom of the container is 1% or more. Foaming ability: When 50g of titanium dioxide dispersion was placed in a 100cc plastic container and shaken well for 5 minutes, the bubbles that were generated were 〇; Disappears within 2 seconds △; Disappears within 2 to 3 seconds ×; It takes more than 3 seconds to disappear. The bubbles that formed when 50g of water-based ink was placed in a 100cc plastic container and shaken well for 5 minutes were ○; Disappears within 20 seconds △; Disappears between 20 and 30 seconds ×; It takes more than 30 seconds to disappear.

[0067] Coating strength: A water-based white ink was applied to Futamura Chemical's OPP film (FOR-AQ) using a #3 bar coater and dried at 110°C for 2 minutes to obtain a white coating. When this coating was rubbed vigorously with a Kimwipe, ○; The white coating does not peel off at all. ×; The white coating peels off even slightly.

[0068] [Table 2]

[0069] Titanium oxide dispersions having the compositions of Examples 1 to 12, and water-based white inks using them as raw materials, were found to be of excellent quality in terms of excellent sedimentation stability, anti-foaming properties, and coating film strength. On the other hand, in comparative examples that fall outside the scope of the present invention, it was not possible to obtain a titanium dioxide dispersion of usable quality that satisfied all evaluation items, nor a water-based white ink using it as a raw material. From Tables 1 and 2, it was confirmed that the requirement that the total amount of aluminum and silicon elements per 100 parts by mass of titanium in rutile-type titanium oxide be 3.4 parts by mass or less is critically significant for titanium oxide dispersions and aqueous white inks to exhibit excellent settling stability.

Claims

1. A titanium dioxide dispersion comprising rutile-type titanium dioxide (A), a dispersant (B), and water, wherein the rutile-type titanium dioxide (A) has a total amount of aluminum and silicon elements of 3.4 parts by mass or less per 100 parts by mass of titanium, the acid value of the dispersant (B) is 650 mg KOH / g or more, the content of the dispersant (B) is 1 to 8 parts by mass per 100 parts by mass of rutile-type titanium dioxide (A), the dispersant (B) is a water-soluble polymer, and the content of rutile-type titanium dioxide (A) is 40 to 70 parts by mass per 100 parts by mass of the titanium dioxide dispersion.

2. The titanium dioxide dispersion according to claim 1, comprising an acetylene glycol-based defoaming agent or a silicone-based defoaming agent.

3. The titanium dioxide dispersion according to claim 1 or 2, wherein the D99 particle size of the particles (C) containing rutile-type titanium dioxide (A) is 800 nm or less.

4. The titanium dioxide dispersion according to claim 3, wherein the particles (C) have a particle size of 1.0 μm or larger and are 1 × 10⁶ to 200 × 10⁶ μm³ / ml or less.

5. A method for producing a titanium oxide dispersion according to any one of claims 1 to 4, which is prepared by bead milling with media with a diameter of 0.5 mm or less.

6. An ink using the titanium dioxide dispersion according to any one of Claims 1 to 4.

7. The ink according to claim 6, which is an inkjet ink.

8. A printed article obtained using the ink described in claim 6 or 7.

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