JP7451633B2 - Water-based ink, ink cartridge, inkjet recording method, titanium oxide particle dispersion, titanium oxide particle dispersion manufacturing method, and water-based ink manufacturing method - Google Patents

Description

The present invention relates to an aqueous ink, an ink cartridge, an inkjet recording method, a dispersion of titanium oxide particles, a method for producing a dispersion of titanium oxide particles, and a method for producing an aqueous ink.

2. Description of the Related Art In recent years, inkjet recording devices have become widely used when outputting advertisements and exhibits using recording media such as paper and resin films. For example, in order to express clear color images even on transparent recording media, white ink is used in addition to black or basic color ink (hereinafter sometimes referred to collectively as color ink). . Specifically, white ink is applied in advance to a portion of a transparent recording medium that includes an area where an image is to be recorded to perform a base treatment, and then color ink is applied from above, or each ink is applied in the reverse order ( A so-called back print) recording method is used.

Titanium oxide is widely used as a coloring material for white ink because it is low cost and has excellent properties required for white ink, such as whiteness and opacity. On the other hand, a dispersant is required to stably disperse titanium oxide in aqueous ink. Dispersants exist by repeatedly adsorbing and desorbing from titanium oxide, so when environmental changes such as temperature occur, it becomes difficult for the dispersant that has been desorbed to adsorb to titanium oxide again. This may lead to loss of dispersion stability. Even if we assume the temperature during the ink transportation process and the various locations where the inkjet recording device is placed, we maintain a stable state of titanium oxide dispersion so that the ink ejection stability is not affected. It is necessary to

Until now, methods for stably dispersing titanium oxide while maintaining ink ejection stability have been studied. For example, after surface-treating titanium oxide with silica, the surface is further treated with a silane coupling agent, and dried, resulting in a dry titanium dioxide product in which a portion of the silane coupling agent is covalently bonded to the surface of the titanium oxide particles. A manufacturing method has been proposed (see Patent Document 1). Furthermore, an ink containing titanium oxide surface-treated with alumina, a monovalent metal salt, and alumina fine particles has been proposed (see Patent Document 2). Furthermore, an ink containing titanium oxide surface-treated with alumina and silica and then surface-treated with a silane coupling agent, a resin containing an anionic group, a water-soluble organic solvent, and a basic compound has been proposed. (See Patent Document 3).

Special table 2017-521348 publication International Publication No. 2018/190848 JP2011-225867A

The present inventors investigated the ejection stability of ink using the water-based ink prepared using dry titanium dioxide proposed in Patent Document 1, and the water-based ink proposed in Patent Document 2 and Patent Document 3. did. As a result, it was found that the discharge stability was insufficient and there was room for improvement compared to the current situation where performance is required even in severe environmental changes.

Therefore, an object of the present inventors is to provide an aqueous inkjet ink containing titanium oxide that has excellent ejection stability, an ink cartridge using the aqueous ink, and an inkjet recording method. Another object of the present invention is to provide a method for producing a dispersion of titanium oxide particles that can be used to produce an aqueous inkjet ink with excellent ejection stability, and a dispersion of titanium oxide particles obtained by the production method. An object of the present invention is to provide a method for producing an aqueous ink using a liquid.

The above object is achieved by the present invention as follows. That is, the aqueous ink according to the present invention is an inkjet aqueous ink containing titanium oxide particles and a dispersant for the titanium oxide particles, wherein at least a portion of the surface of the titanium oxide particles is composed of alumina and silica. The titanium oxide is coated with titanium oxide, and the proportion (mass%) of the alumina in the titanium oxide particles is 0.50 times or more and 1.00 times or less relative to the proportion (mass%) of the silica. The dispersant for the titanium oxide particles is a compound represented by the following general formula (1).

(In general formula (1), R ₁ , R ₂ , and R ₃ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. _{R 4} is each independently a hydrogen atom or an alkyl group having 2 to 4 carbon atoms. It is an alkylene group. X is a single bond or an alkylene group having 1 to 6 carbon atoms. n is 6 to 24; a is 1 to 3; b is 0 to 2; )

According to the present invention, it is possible to provide an aqueous inkjet ink containing titanium oxide that has excellent ejection stability, an ink cartridge using the aqueous ink, and an inkjet recording method. Further, according to the present invention, there is provided a method for producing a dispersion of titanium oxide particles that can be used for producing an aqueous inkjet ink having excellent ejection stability, and a dispersion of titanium oxide particles obtained by the above production method. A method for producing the aqueous ink used can be provided.

1 is a cross-sectional view schematically showing an embodiment of an ink cartridge of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram schematically showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, in which (a) is a perspective view of the main part of the inkjet recording apparatus, and (b) is a perspective view of a head cartridge.

Hereinafter, the present invention will be further explained in detail by citing preferred embodiments. In the present invention, when a compound is a salt, the salt is dissociated into ions and exists in the ink, but for convenience, it is expressed as "containing a salt." Titanium oxide and titanium oxide particles are sometimes simply referred to as "pigments." Furthermore, water-based ink for inkjet is sometimes simply referred to as "ink." Physical property values are values at room temperature (25° C.) unless otherwise specified.

Inorganic oxides such as titanium oxide react with water molecules constituting the aqueous medium in the aqueous ink to generate hydroxy groups (hereinafter sometimes referred to as "surface hydroxy groups") on their surfaces. For this reason, water-based inks for inkjet use are surface-treated with inorganic oxides such as alumina and silica in order to utilize the generated surface hydroxyl groups and further improve the storage stability of the ink. It is commonly used. The surface hydroxy groups of titanium oxide particles have properties unique to the inorganic oxide corresponding to the inorganic compound used for surface treatment, and the isoelectric point, which is an indicator of acid strength, differs depending on the type of inorganic compound. Therefore, although titanium oxide itself is an inorganic oxide, the surface of titanium oxide particles exhibits the properties of an inorganic oxide corresponding to the inorganic compound used for surface treatment, and the surface charge of titanium oxide particles is It strongly depends on the pH of the surface treatment agent, the type of surface treatment agent, and the amount of surface treatment agent used.

The present inventors have studied how to improve the ejection stability of ink by changing the components contained in the ink. A dispersant is required to stably disperse titanium oxide. On the other hand, it has been found that using a dispersant with high affinity for titanium oxide allows for stable dispersion, but affects the ejection stability of the ink. Although titanium oxide has a certain degree of dispersion stability due to charge repulsion due to surface hydroxyl groups, it is difficult to maintain a stable dispersed state over a long period of time. Therefore, in general, the storage stability of the ink is improved by coating titanium oxide with silica or alumina, and the dispersion state is kept stable by combining a dispersant suitable for the surface condition of the titanium oxide particles. ing.

As a result of studies conducted by the present inventors, as described in Patent Document 1, if titanium oxide is coated with silica only, even if a dispersant with low affinity for titanium oxide such as a silane coupling agent is used. , sufficient ink ejection stability could not be obtained. On the other hand, as described in Patent Document 2, when titanium oxide is coated with alumina only, even if a dispersant with low affinity for titanium oxide particles such as a silane coupling agent is used, the titanium oxide particles Sufficient dispersion stability could not be obtained. Furthermore, it has been found that when a dispersant with high affinity for titanium oxide particles is used in an attempt to improve the dispersion stability of titanium oxide particles, the ejection stability of the ink may be affected. Furthermore, as in Patent Document 3, it was found that titanium oxide particles that were surface-treated with alumina and silica and then surface-treated with a silane coupling agent showed the same tendency as above. .

Under these circumstances, we investigated how to obtain a balance between the dispersion stability of titanium oxide particles and the ejection stability of ink by adjusting the amount of coating of alumina and silica on the surface of titanium oxide particles. We then investigated a dispersant suitable for such titanium oxide particles. As a result, by dispersing titanium oxide particles whose surfaces are at least partially coated with alumina and silica in a specific ratio with a specific compound, ink can be ejected without impairing the dispersion stability of the titanium oxide particles. We have found that stability can be improved. That is, the ink and pigment dispersion of the present invention have the following characteristics. First, the proportion (mass%) of aluminum element in titanium oxide particles obtained by inductively coupled plasma emission spectrometry is 0.57 times or more and 1.13 times or less relative to the proportion (mass%) of silicon element. Certain titanium oxide particles are used. That is, titanium oxide particles are used in which the proportion of alumina (mass %) in the titanium oxide particles is 0.50 times or more and 1.00 times or less relative to the proportion of silica (mass %). Further, as a dispersant for dispersing titanium oxide particles, a compound represented by the general formula (1) described below is used. The inventors of the present invention conjecture the mechanism by which the ink ejection stability is improved by the above configuration as follows.

The ink or pigment dispersion liquid contains a compound represented by general formula (1) as a dispersant for dispersing titanium oxide particles. Some of the compounds represented by general formula (1) are known as silane coupling agents. In general formula (1), OR ₁ each independently represents a hydroxy group or an alkoxy group having 1 to 4 carbon atoms. A portion of OR ₁ bonded to the silicon atom can be hydrolyzed in an aqueous medium to form a silanol group, and a portion of the silanol group can dissociate into ions. Therefore, "weak affinity" is exhibited due to the formation of hydrogen bonds between the surface hydroxyl groups of the titanium oxide particles and the silanol groups of the compound represented by general formula (1). Furthermore, a part of the surface hydroxyl group of the titanium oxide particle and the silanol group of the compound represented by the general formula (1) can form a covalently bonded state due to a dehydration reaction. In other words, the hydroxyl group on the surface of the titanium oxide particle and the silanol group in the compound represented by the general formula (1) exhibit affinity through hydrogen bonds and covalent bonds, and repeat desorption and adsorption to form a bond near the titanium oxide particle. A compound represented by general formula (1) can be present. If OR ₁ is an alkoxy group having more than 4 carbon atoms, it will be difficult to hydrolyze it to form a silanol group. As a result, affinity with the surface hydroxyl group of the titanium oxide particles cannot be obtained, the titanium oxide particles cannot be stably dispersed, and the ejection stability of the ink cannot be obtained.

In addition to the structure capable of forming a silanol group as described above, the compound represented by general formula (1) has an alkylene oxide group having 2 to 4 carbon atoms as a repeating unit via X serving as a linking group. It has a structure having n pieces ((OR ₄ ) _n in general formula (1)). n represents the number (average value) of alkylene oxide groups that are repeating units, and is from 6 to 24. Hereinafter, the above structure will also be referred to as an alkylene oxide chain. Since the alkylene oxide chain has hydrophilicity, it stretches appropriately in an aqueous medium and exhibits repulsive force due to steric hindrance. Therefore, when the compound represented by the general formula (1) exists near the titanium oxide particles, the titanium oxide particles can be stably dispersed.

Titanium oxide particles surface-treated with silica only have an affinity with the dispersant, which is also a silicon-containing compound, as described above. Therefore, the dispersant tends to be present in excess near the titanium oxide particles, and the surface characteristics of the titanium oxide particles are dominated by the characteristics possessed by the dispersant. In a state where an excessive amount of dispersant is repeatedly adsorbed and desorbed, the energy applied when ink is ejected is consumed to desorb the excess dispersant. Therefore, the ink ejection speed decreases, and the ink ejection stability becomes insufficient.

Titanium oxide particles surface-treated with alumina only have a weak affinity with the dispersant, which is a compound containing silicon, and it is difficult to allow the dispersant to exist near the titanium oxide particles. Therefore, as mentioned above, although the repulsive force of the electric double layer obtained by ionizing some of the surface hydroxyl groups of titanium oxide particles can be obtained, if environmental changes such as long-term storage or temperature changes occur, titanium oxide Unable to maintain stable dispersion of particles.

The titanium oxide particles contained in the ink and pigment dispersion of the present invention are titanium oxide coated with alumina and silica. The proportion (mass %) of the aluminum element obtained by inductively coupled plasma emission spectrometry in the titanium oxide particles is 0.57 times or more and 1.13 times or less relative to the proportion (mass %) of the silicon element. In other words, the proportion of alumina (mass%) in titanium oxide particles, which is calculated by converting the obtained value of each element to its oxide, is the mass ratio to the proportion of silica (mass%), which is 0. .50 times or more and 1.00 times or less. When the proportion (mass %) of the alumina is within the above range, not only can the titanium oxide particles be stably dispersed, but also the ejection stability of the ink is not affected. This is because since the alumina is coated at a specific ratio, the amount of dispersant present near the titanium oxide particles can be controlled within a range that provides dispersion stability. If the mass ratio is less than 0.50 times, the ratio of silica to alumina will be too large. Therefore, the affinity with the compound represented by the general formula (1) becomes high, and an excessive amount of the compound is adsorbed on the titanium oxide particles, as in the case where the titanium oxide particles are coated only with silica. become a state. As a result, ink ejection stability cannot be achieved. If the mass ratio is more than 1.00 times, the ratio of silica to alumina is too small, so that sufficient affinity with the compound represented by formula (1) cannot be obtained, and titanium oxide particles are Cannot be stably dispersed. Therefore, ink ejection stability cannot be obtained.

In the present invention, titanium oxide particles whose surfaces are coated with alumina and silica are dispersed with a compound represented by general formula (1), so that the compound has the above-mentioned affinity to form titanium oxide particles. It can exist widely in the surrounding area. Therefore, titanium oxide particles can be stably dispersed. Furthermore, since the titanium oxide particles are coated with alumina and silica at a predetermined ratio, adsorption of excess of the compound can be suppressed. Therefore, the energy for desorption of the excess compound used during discharge does not increase, and a decrease in the discharge speed can be suppressed. By satisfying these configurations, ink ejection stability can be improved.

<Water-based ink, method for manufacturing water-based ink>
The ink of the present invention is an aqueous inkjet ink containing titanium oxide particles coated with a specific inorganic oxide and a specific compound for dispersing the titanium oxide particles. This ink is preferably a white ink because titanium oxide is a white pigment. Further, the ink of the present invention does not need to be a so-called "curable ink". Therefore, the ink of the present invention does not need to contain compounds such as polymerizable monomers that can be polymerized by application of external energy such as heat or light. Hereinafter, the components constituting the ink of the present invention, the physical properties of the ink, the manufacturing method, etc. will be explained in detail.

(color material)
The ink contains titanium oxide particles, which are surface-treated with a specific inorganic oxide, as a coloring material (pigment). That is, the ink contains titanium oxide particles whose surfaces are coated with a specific inorganic oxide. The content (mass%) of titanium oxide particles in the ink is preferably 0.10% by mass or more and 20.00% by mass or less, based on the total mass of the ink. Further, the content (mass%) of titanium oxide particles in the ink is more preferably 1.00% by mass or more and 20.00% by mass or less, based on the total mass of the ink. Among these, the content (mass%) of titanium oxide particles in the ink is particularly preferably 1.00% by mass or more and 15.00% by mass or less, based on the total mass of the ink.

Titanium oxide is a white pigment, and exists in three crystal forms: rutile type, anatase type, and brookite type. Among these, rutile-type titanium oxide is preferred. Industrial methods for producing titanium oxide include a sulfuric acid method and a chlorine method, and the titanium oxide used in the present invention may be produced by either method.

The volume-based cumulative 50% particle diameter (hereinafter also referred to as average particle diameter) of the titanium oxide particles is preferably 200 nm or more and 500 nm or less. Among these, it is more preferable that the volume-based cumulative 50% particle diameter of the titanium oxide particles is 200 nm or more and 400 nm or less. The volume-based cumulative 50% particle diameter (D ₅₀ ) of titanium oxide particles is the particle diameter that is 50% cumulative from the small particle diameter side, based on the total volume of the measured particles in the particle diameter integration curve. It is. The _D50 of the titanium oxide particles can be measured, for example, under the following conditions: Set Zero: 30 seconds, number of measurements: 3 times, measurement time: 180 seconds, shape: non-spherical, and refractive index: 2.60. As the particle size distribution measuring device, a particle size analyzer using a dynamic light scattering method can be used. Of course, the measurement conditions are not limited to the above.

Titanium oxide that has been surface-treated with alumina and silica is used. Surface treatment is expected to suppress photocatalytic activity and improve dispersibility. In this specification, "alumina" is a general term for aluminum oxides such as aluminum oxide. Furthermore, in this specification, "silica" is a general term for silicon dioxide or a substance composed of silicon dioxide. Most of the alumina and silica coating titanium oxide are present in the form of silicon dioxide and aluminum oxide.

The proportion (mass%) of titanium oxide in the titanium oxide particles is preferably 90.00% by mass or more based on the total mass of the titanium oxide particles. Further, the proportion (mass%) of titanium oxide in the titanium oxide particles is preferably 98.50% by mass or less based on the total mass of the titanium oxide particles. The proportion (mass %) of alumina in the titanium oxide particles is required to be 0.50 times or more and 1.00 times or less relative to the proportion (mass %) of silica. When the mass ratio is less than 0.50 times or more than 1.00 times, ink ejection stability cannot be obtained. Further, the proportion of silica (% by mass) in the titanium oxide particles is preferably 1.00% by mass or more and 4.00% by mass or less, based on the total mass of the titanium oxide particles. If the proportion (mass%) of the silica is less than 1.00% by mass, sufficient affinity with the compound represented by the general formula (1) will not be obtained, and sufficient ejection stability of the ink will not be obtained. There may be no. When the proportion (mass%) of the silica is more than 4.00% by mass, the amount of the compound represented by general formula (1) adsorbed to the titanium oxide particles is suppressed even if the surface is treated with alumina. Therefore, sufficient ink ejection stability may not be obtained. The proportion (mass%) of alumina in the titanium oxide particles is preferably 0.50% by mass or more and 4.00% by mass or less, based on the total mass of the titanium oxide particles.

As a method for measuring the proportion of alumina and silica in titanium oxide particles, that is, the amount of alumina and silica covered, for example, quantitative analysis of aluminum and silicon elements by inductively coupled plasma (ICP) emission spectrometry can be mentioned. In this case, it can be calculated by assuming that all the atoms covering the surface are oxides and converting the obtained values of aluminum and silicon into their oxides, that is, alumina and silica. The proportion (mass %) of the aluminum element obtained by inductively coupled plasma emission spectrometry in the titanium oxide particles is 0.57 times or more and 1.13 times or less relative to the proportion (mass %) of the silicon element. When converting this value into its oxides, that is, alumina and silica, the proportion of alumina (mass%) in the titanium oxide particles is 0.50 times or more 1. 00 times or less.

Examples of surface treatment methods for titanium oxide include wet treatment and dry treatment. For example, it is possible to perform surface treatment by dispersing titanium oxide in a liquid medium and then reacting it with a surface treatment agent such as sodium aluminate or sodium silicate, and by changing the ratio of these surface treatment agents as appropriate. It can also be adjusted to the characteristics of In addition to alumina and silica, inorganic oxides such as zinc oxide and zirconia, and organic substances such as polyols can be used for the surface treatment, as long as the effects of the present invention are not impaired.

The ink may contain pigments other than titanium oxide as long as the effects of the present invention are not impaired. In this case, ink of a color other than white ink may be used. The content (mass%) of other pigments in the ink is preferably 0.10% by mass or more and 5.00% by mass or less, and 0.10% by mass or more and 1.00% by mass, based on the total mass of the ink. % or less is more preferable.

(Compound represented by general formula (1))
The ink contains a compound represented by the following general formula (1) as a dispersant for dispersing titanium oxide particles. The content (mass%) of the compound represented by general formula (1) in the ink is preferably 0.01% by mass or more and 1.00% by mass or less, and 0.02% by mass or less, based on the total mass of the ink. It is more preferable that the amount is not less than 0.50% by mass and not more than 0.50% by mass.

(In general formula (1), R ₁ , R ₂ , and R ₃ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. _{R 4} is each independently a hydrogen atom or an alkyl group having 2 to 4 carbon atoms. It is an alkylene group. X is a single bond or an alkylene group having 1 to 6 carbon atoms. n is 6 to 24; a is 1 to 3; b is 0 to 2; )

In general formula (1), R ₁ , R ₂ and R ₃ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Examples of the alkyl group having 1 to 4 carbon atoms include methyl group, ethyl group, n-propyl group, i-propyl group, and n-butyl group. Among these, a methyl group is preferred from the viewpoint of ease of hydrolysis. If R ₁ , R ₂ , and R ₃ are each an alkyl group having more than 4 carbon atoms, it becomes difficult to hydrolyze to form a silanol group, and affinity with titanium oxide particles cannot be obtained. Therefore, titanium oxide particles cannot be stably dispersed, and ink ejection stability cannot be obtained. a representing the number of R ₁ O is 1 to 3, b representing the number of R ₂ is 0 to 2, and a+b=3. Among these, it is preferable that a is 3 and b is 0, that is, all three substituents on the silicon atom are R ₁ O.

In the general formula (1), each R ₄ independently represents an alkylene group having 2 to 4 carbon atoms. Examples of the alkylene group having 2 to 4 carbon atoms include ethylene group, n-propylene group, i-propylene group, and n-butylene group. Among these, ethylene group is preferred. The number of OR ₄ , that is, n (average value) representing the number of alkylene oxide groups is 6 to 24. When n is less than 6, the length of the alkylene oxide chain is too short, so that sufficient repulsive force due to steric hindrance cannot be obtained, and ink ejection stability cannot be obtained. When n is more than 24, the alkylene oxide chain is too long, resulting in increased hydrophilicity and easy release into the aqueous medium. Therefore, sufficient affinity with the surface hydroxyl groups of titanium oxide particles cannot be obtained, making it impossible to suppress aggregation of titanium oxide particles. Therefore, titanium oxide particles cannot be stably dispersed, and ink ejection stability cannot be obtained.

In the general formula (1), X is a single bond or an alkylene group having 1 to 6 carbon atoms. When X is a single bond, it means that the silicon atom and OR ₄ are directly bonded. Examples of the alkylene group having 1 to 6 carbon atoms include methylene group, ethylene group, n-propylene group, i-propylene group, n-butylene group, n-pentylene group, and n-hexylene group. Among them, n-propylene group is preferred. If X is an alkylene group having more than 6 carbon atoms, the hydrophobicity of the compound represented by general formula (1) will become too high, making it impossible to stably disperse titanium oxide particles, resulting in poor ink ejection stability. is not obtained.

The compound represented by the general formula (1), which is a dispersant for titanium oxide particles, is preferably a compound represented by the following general formula (2). Since the compound represented by the general formula (2) has three _OR1s bonded to the silicon atom, a portion thereof is hydrolyzed in an aqueous medium to form three hydroxy groups bonded to the silicon atom. It is possible to increase the portion having affinity with titanium oxide particles. Further, the compound represented by the following general formula (2) has a repeating structure of ethylene oxide groups. Therefore, the ethylene oxide chain is appropriately extended in the aqueous medium, and a repulsive force due to steric hindrance can be obtained.

(In general formula (2), R ₁ and R ₃ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. m is 8 to 24.)

The content (mass%) of the compound represented by general formula (1) in the ink should be 0.002 times or more and 0.10 times or less relative to the content (mass%) of titanium oxide particles. is preferred. When the mass ratio is less than 0.002 times, the effect of stably dispersing titanium oxide particles becomes weak, and sufficient ink ejection stability may not be obtained. If the mass ratio is more than 0.10 times, the proportion of the compound represented by the general formula (1) becomes too high, leading to intermolecular condensation (self-condensation) of the compound represented by the general formula (1). ) is likely to occur. Therefore, the compound represented by the general formula (1) is consumed without acting as a dispersant, and the effect of stably dispersing titanium oxide particles is weak, resulting in insufficient ink ejection stability. be.

The compound represented by the general formula (1) forms a hydrogen bond with the surface hydroxyl group of the titanium oxide particles, and it is thought that a part of the hydrogen bond forms a covalent bond through a dehydration reaction. However, in the present invention, the compound represented by general formula (1) can disperse titanium oxide particles without forming a covalent bond with the titanium oxide particles. In other words, the amount of the compound represented by the general formula (1) covalently bonded to the titanium oxide particles is very small and can be ignored. Therefore, the content of the titanium oxide particles does not include the covalently bonded compound represented by the general formula (1). As a result of studies conducted by the present inventors, it was found that when the amount of the compound represented by the general formula (1) covalently bonded to titanium oxide particles is too large, the ejection stability of the ink decreases. Possible reasons for this are as follows. In general, in a liquid medium with a high dielectric constant such as water, electrostatic attraction is less likely to work, so titanium oxide particles move freely without being affected by the surrounding environment. However, when the compound represented by general formula (1) is covalently bonded to titanium oxide particles, the hydrophilic part (OR ₄ part) of the structure of general formula (1) forms a hydrogen bond with a water molecule, As a result, the movement of titanium oxide particles may be affected. Therefore, in a situation where the liquid is deformed by instantaneous pressure, such as during inkjet ejection, the above-mentioned characteristics appear as differences in ejection characteristics. Therefore, the amount (mass%) of the compound represented by general formula (1) covalently bonded to the titanium oxide particles is 0.001 times or less relative to the content (mass%) of the titanium oxide particles. It is preferable that If the mass ratio is more than 0.001 times, sufficient ink ejection stability may not be obtained. The mass ratio may be 0.000 times. The amount of the compound represented by the general formula (1) covalently bonded to the titanium oxide particles can be calculated by thermogravimetric analysis or the like.

(resin)
The ink can contain a resin. Examples of the resin include acrylic resin, urethane resin, and urea resin. Among these, acrylic resins are preferred. The content (mass%) of the resin in the ink is preferably 1.00% by mass or more and 25.00% by mass or less, and 3.00% by mass or more and 15.00% by mass or less, based on the total mass of the ink. It is more preferable that Among these, the content is particularly preferably 5.00% by mass or more and 15.00% by mass or less.

The resin can be included in the ink for purposes of improving various properties of recorded images, such as scratch resistance and hiding properties. Examples of the form of the resin include block copolymers, random copolymers, graft copolymers, and combinations thereof. Further, the resin may be a water-soluble resin that can be dissolved in an aqueous medium, or may be resin particles that are dispersed in an aqueous medium. The resin particles do not need to contain coloring material.

In this specification, "the resin is water-soluble" means that when the resin is neutralized with an alkali equivalent to the acid value, it does not form particles whose particle size can be measured by dynamic light scattering. means present in an aqueous medium. Whether or not a resin is water-soluble can be determined according to the method shown below. First, a liquid (resin solid content: 10% by mass) containing a resin neutralized with an alkali equivalent to an acid value (sodium hydroxide, potassium hydroxide, etc.) is prepared. Next, the prepared liquid is diluted 10 times (by volume) with pure water to prepare a sample solution. When the particle size of the resin in the sample solution is measured by dynamic light scattering and no particles having the same particle size are detected, it can be determined that the resin is water-soluble. The measurement conditions at this time can be, for example, Set Zero: 30 seconds, number of measurements: 3 times, and measurement time: 180 seconds. As the particle size distribution measuring device, a particle size analyzer using a dynamic light scattering method (for example, trade name "UPA-EX150", manufactured by Nikkiso Co., Ltd.) or the like can be used. Of course, the particle size distribution measuring device and measurement conditions used are not limited to those described above.

The acid value of the water-soluble resin is preferably 80 mgKOH/g or more and 250 mgKOH/g or less, more preferably 100 mgKOH/g or more and 200 mgKOH/g or less. When using resin particles, the acid value thereof is preferably 0 mgKOH/g or more and 50 mgKOH/g or less. The weight average molecular weight of the resin is preferably 1,000 or more and 30,000 or less, more preferably 5,000 or more and 15,000 or less. The weight average molecular weight of the resin is a polystyrene equivalent value measured by gel permeation chromatography (GPC).

(aqueous medium)
The ink is an aqueous ink containing water as an aqueous medium. The ink can contain an aqueous medium that is water or a mixed solvent of water and a water-soluble organic solvent. As water, it is preferable to use deionized water (ion-exchanged water). The water content (mass%) in the ink is preferably 50.00% by mass or more and 95.00% by mass or less, based on the total mass of the ink.

The water-soluble organic solvent is not particularly limited as long as it is water-soluble (preferably one that dissolves in water at 25° C. in any proportion). Specifically, monohydric or polyhydric alcohols, alkylene glycols, glycol ethers, nitrogen-containing polar compounds, sulfur-containing polar compounds, etc. can be used. The content (mass%) of the water-soluble organic solvent in the ink is preferably 3.00% by mass or more and 50.00% by mass or less, and 10.00% by mass or more and 40.00% by mass, based on the total mass of the ink. It is more preferable that it is less than % by mass. If the content (mass %) of the water-soluble organic solvent is less than 3.00 mass %, the ink will stick within the inkjet recording device, and sufficient sticking resistance may not be obtained. If the content (mass %) of the water-soluble organic solvent exceeds 50.00 mass %, ink supply failure may occur.

(Other additives)
In addition to the above additives, the ink may contain surfactants, pH adjusters, rust preventives, preservatives, antifungal agents, antioxidants, reduction inhibitors, evaporation promoters, and chelating agents, as necessary. Various additives such as agents can be included. Among these, it is preferable that the ink contains a surfactant. The content (mass%) of the surfactant in the ink is preferably 0.10% by mass or more and 5.00% by mass or less, and 0.10% by mass or more and 2.00% by mass, based on the total mass of the ink. % or less is more preferable. Examples of the surfactant include anionic surfactants, cationic surfactants, and nonionic surfactants. Among these, nonionic surfactants are preferred because they have a low affinity with titanium oxide particles and are effective in small amounts because they are used to adjust various physical properties of ink.

(Physical properties of ink)
Since the ink is an ink to be applied to an inkjet method, it is preferable to appropriately control its physical properties. The surface tension of the ink at 25° C. is preferably 10 mN/m or more and 60 mN/m or less, more preferably 20 mN/m or more and 40 mN/m or less. The surface tension of the ink can be adjusted by appropriately determining the type and content of the surfactant in the ink. Further, the viscosity of the ink at 25° C. is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the ink at 25° C. is preferably 7.0 or more and 9.0 or less. If the pH of the ink is within the above range, the generation of silanol groups by hydrolysis of the compound represented by general formula (1) will proceed, so that the weak titanium oxide particles and the compound represented by general formula (1) will be Affinity is effectively demonstrated. The pH of the ink can be measured with a general pH meter equipped with a glass electrode or the like.

(Ink manufacturing method)
The ink manufacturing method of the present invention includes a step of mixing a titanium oxide particle dispersion and other ink components. As the dispersion of titanium oxide particles, a dispersion of titanium oxide particles manufactured by a manufacturing method described below is used. Other ink components include water, water-soluble organic solvents, resins, and the above-mentioned "other additives" that are further added. The ink may be manufactured by, for example, adding a dispersion of titanium oxide particles and other ink components to a suitable container and stirring the mixture. Conditions such as stirring speed, temperature, and time can be appropriately set according to desired conditions. Other known manufacturing processes may be combined.

<Method for producing a dispersion of titanium oxide particles>
The method for producing a dispersion of titanium oxide particles of the present invention is for use in producing an aqueous inkjet ink. The method includes a step (first step) of reacting a predetermined treatment agent on the surface of titanium oxide to prepare titanium oxide particles whose surfaces are coated with alumina and silica. After the first step, there is a dispersion step (second step) in which the titanium oxide particles are dispersed in a liquid medium using a compound represented by general formula (1) for dispersing the titanium oxide particles. Each step will be explained in detail below.

(1st step)
The first step is to prepare titanium oxide particles whose surfaces are coated with alumina and silica. As the titanium oxide particles, particles coated with alumina and silica in advance may be used, or particles obtained by subjecting untreated titanium oxide to a coating treatment may be used. Examples of coating treatment methods include wet treatment and dry treatment. Among these, wet processing is preferred because it allows uniform surface treatment. Specifically, a method may be mentioned in which a surface treatment agent is added to a dispersion of titanium oxide, which is a raw material. Examples of the surface treatment agent include sodium aluminate and sodium silicate. The surface treatment conditions may be general ones. Furthermore, titanium oxide particles that have been coated with alumina and silica may be further coated to adjust various properties of the titanium oxide particles.

The surface-treated titanium oxide (titanium oxide particles) may be in a dry state after the first step, or may be in a state contained in a liquid medium such as water. In order to facilitate handling in the subsequent second step, it is preferable to keep the titanium oxide particles contained in the liquid medium. It is preferable to set the concentration of titanium oxide particles in the liquid medium from the viewpoint of efficiency of the second step and ease of handling. Specifically, the content (mass%) of titanium oxide particles in the liquid containing titanium oxide particles is preferably 20.00% by mass or more and 60.00% by mass or less, based on the total mass of the liquid.

(Second process)
The second step is a dispersion step in which titanium oxide particles are dispersed in a liquid medium using a compound represented by general formula (1) for dispersing titanium oxide particles. A pH adjuster and various additives may be used as necessary. In the second step, titanium oxide particles are dispersed using a compound represented by general formula (1) as a dispersant by applying a shearing force necessary to obtain a desired particle size distribution. In the second step, a known dispersion method such as media dispersion or medialess dispersion can be used. Examples of dispersing machines using media dispersion include paint shakers, bead mills, sand mills, ball mills, and roll mills. Examples of dispersion machines that perform medialess dispersion include ultrasonic homogenizers and high-pressure homogenizers. The second step may be performed using a combination of two or more types of dispersers described above.

The dispersion of titanium oxide particles obtained in the second step is stored for a certain period of time as required, and then used for preparing an aqueous inkjet ink. From this point of view, it is preferable to set the concentration of titanium oxide particles in the dispersion. Specifically, the content (mass%) of titanium oxide particles in the titanium oxide particle dispersion is preferably 20.00% by mass or more and 60.00% by mass or less, based on the total mass of the dispersion. .

The temperature in the second step can be set arbitrarily. Since the second step is performed in an aqueous liquid medium, the temperature is preferably 0°C or more and 100°C or less, and from the viewpoint of heat generation during the process and reliability of the media when using a media dispersion method, it is 10°C or more. More preferably, the temperature is 40°C or lower. The time for the second step may be adjusted depending on the equipment used, the concentration of the dispersion, etc., and can be set arbitrarily as long as the titanium oxide particles are not overdispersed. For example, when performing the dispersion step at 25° C. with a paint shaker using 0.5 mm zirconia beads, the time is preferably 10 hours or more and 20 hours or less.

Further, a preliminary dispersion step may be performed in order to mix components containing titanium oxide particles and wet them with a liquid medium to facilitate dispersion. In the preliminary dispersion step, the dispersion method and apparatus described above as those that can be used in the second step can be used.

[pH adjuster]
In the second step, it is preferable to use a pH adjuster in order to control the state of the surface hydroxyl groups of the titanium oxide particles. The pH adjuster may be an acidic compound or a basic compound. Among these, basic compounds are preferred because they can keep the surface hydroxyl groups of the titanium oxide particles anionic. When the liquid medium is alkaline, some of the surface hydroxyl groups of the titanium oxide particles are ionized, an electric double layer is formed, and dispersion stability can be obtained due to charge repulsion. Examples of the basic compound include ammonia; organic ammonium compounds; and alkali metal hydroxides such as potassium hydroxide and sodium hydroxide. Among these, potassium hydroxide is preferred, considering that it is carried into the ink from the produced dispersion. The pH of the liquid medium in the second step, which is adjusted using a pH adjuster, is preferably 7.0 or more and 12.5 or less. If the pH is over 12.5, the silica coating the surface of the titanium oxide particles may dissolve. The pH adjuster may be added continuously at any timing to maintain the pH of the liquid medium within the above range.

[Liquid medium]
The second step is carried out in a liquid medium, preferably an aqueous liquid medium. As the aqueous liquid medium, it is possible to use only water or an aqueous medium using water as the main solvent in combination with a protic or aprotic organic solvent. The aqueous medium is a mixed solvent of water and an organic solvent. As the organic solvent, it is preferable to use one that is miscible or soluble in water in any proportion. Among these, it is preferable to use a homogeneous mixed solvent containing 50% by mass or more of water as the aqueous medium. As water, it is preferable to use ion exchange water or pure water.

A protic organic solvent is an organic solvent having a hydrogen atom (acidic hydrogen atom) bonded to oxygen or nitrogen. Furthermore, the aprotic organic solvent is an organic solvent that does not have acidic hydrogen atoms. Examples of organic solvents include alcohols; alkylene glycols; polyalkylene glycols; glycol ethers; glycol ether esters; carboxylic acid amides; ketones; keto alcohols; cyclic ethers; nitrogen-containing compounds; Examples include sulfur compounds.

(post-processing)
The produced dispersion of titanium oxide particles is preferably subjected to a general post-treatment method such as purification, and then used for producing an aqueous ink for inkjet use. When only water is used as the liquid medium without using an organic solvent, the obtained dispersion can be used as is for preparing ink, or it can be used after washing and adjusting the content of titanium oxide particles. can also be used as the final dispersion. When a liquid medium containing an organic solvent is used, the organic solvent can be removed. As a method for removing the organic solvent, for example, there is a method of adding water while removing the organic solvent by reducing pressure or heating using an evaporator or the like to obtain an aqueous dispersion of titanium oxide particles. Furthermore, there is also a method of repeatedly adding water after removing the organic solvent by ultrafiltration or the like. In particular, when creating a dispersion of titanium oxide particles dispersed in an aqueous medium, the surface hydroxyl groups of the titanium oxide particles are ionically dissociated to maintain a more stable dispersion state due to the repulsive force caused by electrostatic repulsion. be able to. Therefore, it is preferable to make the dispersion alkaline by adding a pH adjuster or the like as necessary.

<Ink cartridge>
The ink cartridge of the present invention includes ink and an ink storage portion that stores the ink. The ink contained in this ink storage portion is the water-based ink (white ink) of the present invention described above. FIG. 1 is a cross-sectional view schematically showing an embodiment of an ink cartridge of the present invention. As shown in FIG. 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge serves as an ink storage section for storing ink. The ink storage section includes an ink storage chamber 14 and an absorbent storage chamber 16, which communicate with each other via a communication port 18. Further, the absorbent storage chamber 16 communicates with the ink supply port 12 . The ink storage chamber 14 stores liquid ink 20, and the absorbent storage chamber 16 stores absorbers 22 and 24 that hold the ink in an impregnated state. The ink storage section may have a configuration in which the entire amount of ink contained therein is retained by an absorber without having an ink storage chamber that stores liquid ink. Further, the ink accommodating portion may have a form that does not include an absorber and stores the entire amount of ink in a liquid state. Furthermore, the ink cartridge may be configured to include an ink storage section and a recording head.

<Inkjet recording method>
The inkjet recording method of the present invention is a method of recording an image on a recording medium by ejecting the aqueous ink of the present invention described above from an inkjet recording head. Examples of methods for ejecting ink include a method of applying mechanical energy to the ink and a method of applying thermal energy to the ink. In the present invention, it is particularly preferable to adopt a method of ejecting ink by applying thermal energy to the ink. Other than using the ink of the present invention, the steps of the inkjet recording method may be those known in the art. For example, when recording an image using white ink, a general inkjet recording method can be applied as is. In addition, when using white ink as a base treatment for color ink, color ink (black, cyan, magenta, yellow, etc.) is applied so as to overlap at least a portion of the area to which the white ink has been applied. Just record it. It can also be used for back printing in which white ink is applied so as to overlap at least a portion of the area to which color ink has been applied. The recording medium is not particularly limited, but since the aqueous ink of the present invention can be used as a white ink, it is preferable to use a transparent or colored recording medium. Further, the recording medium may be a poorly absorbent medium (non-absorbent medium) such as a resin film that has low absorbency for liquid media.

FIG. 2 is a diagram schematically showing an example of an inkjet recording device used in the inkjet recording method of the present invention, in which (a) is a perspective view of the main part of the inkjet recording device, and (b) is a perspective view of a head cartridge. It is. The inkjet recording apparatus is provided with a conveying means (not shown) for conveying the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 includes recording heads 38 and 40, and is configured such that an ink cartridge 42 is set therein. While the head cartridge 36 is transported in the main scanning direction along the carriage shaft 34, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, an image is recorded on the recording medium 32 by conveying the recording medium 32 in the sub-scanning direction by a conveying means (not shown).

Multi-pass printing is preferable, in which ink is applied to a unit area of a printing medium by dividing the printing head and the printing medium into multiple relative scans. In particular, it is preferable to apply white ink and color ink to a unit area using different relative scans. This lengthens the time it takes for each ink to come into contact with each other, making it easier to suppress mixing. The unit area can be set as any area such as one pixel or one band.

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples in any way unless it exceeds the gist thereof. Regarding component amounts, "parts" and "%" are based on mass unless otherwise specified. Further, a dispersion of titanium oxide particles will be referred to as a "pigment dispersion".

<Preparation of titanium oxide>
Commercially available titanium oxide particles that had been surface-treated in advance and titanium oxide particles prepared by surface-treating untreated titanium oxide were used. The volume-based cumulative 50% particle diameter (D ₅₀ ) of the titanium oxide particles was measured using a dynamic light scattering particle size analyzer (trade name "Nanotrac Wave II-EX150", manufactured by Microtrac Bell). Table 1 shows the properties of the titanium oxide particles. In Table 1, TITANIX: JR, JR-403, JR-800, JR-806, JR-805, JR-301, JR-405, and JR-600A are trade names of rutile-type titanium oxide manufactured by Teika. . Further, TITONE: R-62N and R-7E are trade names of rutile-type titanium oxide manufactured by Sakai Chemical Industries. Typeke: PFC-208, R-780-2, PFC-211, and R-780 are trade names of rutile-type titanium oxide manufactured by Ishihara Sangyo.

(Measurement of coating amount of alumina and silica)
The proportion of alumina and silica in the titanium oxide particles, that is, the amount of coverage of alumina and silica, was measured as follows. Using a liquid prepared by adding titanium oxide particles to nitric acid as a sample, quantitative analysis of aluminum and silicon elements was performed using an inductively coupled plasma (ICP) emission spectrometer. At this time, assuming that all the atoms covering the surface were oxides, the obtained values of aluminum and silicon were converted to their oxides, that is, alumina and silica, to calculate the mass ratio.

(Titanium oxide particles 1 to 8)
Titanium oxide particles 1 to 8 were produced by surface treatment of titanium oxide by a wet method. In surface treatment using the wet method, untreated titanium oxide is brought into contact with a surface treatment agent (sodium aluminate, sodium silicate, etc.), and by adjusting the amount and ratio of the surface treatment agent used, arbitrary Surface treatment was applied to the ratio.

Specifically, 300 parts of rutile-type titanium oxide (trade name "TITANIX JR", manufactured by Teika), which has not been subjected to surface treatment, and 700 parts of pure water were mixed using a homogenizer. Then, the temperature was raised to 90° C. while stirring, and potassium hydroxide (pH adjuster) was added to adjust the pH to 10.5. Next, sodium silicate was added and dilute sulfuric acid (pH adjuster) was added over about 1 hour to adjust the pH to 5.0. The reaction continued for about 1 hour. Thereafter, sodium aluminate was added little by little at 90°C. At this time, in order to maintain the pH, dilute sulfuric acid was used in combination to maintain the pH between 6.0 and 8.0. After the addition of sodium aluminate, the reaction was continued for about 1 hour to obtain a dispersion. After cooling the dispersion liquid to 25°C, it is purified by repeating sedimentation using a centrifuge and redispersion in ion-exchanged water, and then dried at 120°C to perform surface treatment on at least one of alumina and silica. Each titanium oxide particle was obtained. Table 1 shows the characteristics of titanium oxide particles 1 to 8.

(Titanium oxide particles 9 to 22)
Commercially available titanium oxide particles (including those whose surface had been previously subjected to alumina or silica treatment) were used as titanium oxide particles 9 to 22. Table 1 also shows the properties of titanium oxide particles 9 to 22. Some commercially available titanium oxide particles contain inorganic oxides such as zinc oxide and zirconia, and organic compounds such as polyols in addition to alumina and silica, but the proportion of these is at most 1. It was about .0%. Therefore, for convenience, the proportion T (%) of titanium oxide in the titanium oxide particles ("titanium oxide T (%)" in Table 1) is summarized.

<Preparation of compound represented by general formula (1)>
A compound represented by general formula (1) was synthesized by the following procedure. The synthesis conditions and structures of the compound synthesized as the compound represented by general formula (1) and the comparative compound are shown in Tables 2 and 3, respectively. The compound represented by general formula (1) can be synthesized by allylating and hydrosilylating a raw material (polyalkylene glycol monoalkyl ether, etc.).

(Compounds 1 to 13, comparative compound 14)
The raw materials, base, and solvent listed in Table 2 were placed in a three-necked flask equipped with a stirring bar and a nitrogen inlet tube, and the mixture was stirred at 25° C. for 30 minutes. As "sodium hydride", a paraffin dispersion of 60% sodium hydride was used, and the dispersion was used so that the amount of sodium hydride used was as shown in Table 2. Then, the bromide listed in Table 2 was added dropwise while stirring at 25°C, and after the completion of the addition, stirring was continued for 12 hours to obtain a solution containing the reactant. After filtering off unreacted sodium hydride and neutralized product (sodium bromide) from the solution containing the reactants, THF was removed under reduced pressure to obtain a concentrate. The concentrate was dissolved in 500 parts of pure water, and this aqueous solution was extracted three times with 200 mL of hexane, and then extracted with 200 mL of dichloromethane. The solvent containing the product was dried by adding magnesium sulfate and concentrated under reduced pressure to obtain each allylated compound (allylation step).

The allylated raw materials and silane compound listed in Table 2 were placed in a passivated dry round bottom flask equipped with a stirring bar and an argon inlet tube, and stirred at 85°C. Then, 0.54 parts of an aqueous isopropyl alcohol solution of 65 mmol/L chloroplatinic acid monohydrate was added, and the mixture was heated at 85° C. for 5 hours. After the reaction was completed, the mixture was allowed to cool to 25°C, and excess silane compound was removed under reduced pressure. The residue was purified by column chromatography using silica gel passivated with triethoxysilane as a carrier to obtain each compound (hydrosilylation step). For purification by column chromatography, an eluent of ethyl acetate/hexane/ethanol = 85/15/5 (by volume) was used.

(Comparative compound 15)
The raw materials and solvent listed in Table 2 were placed in a three-necked flask equipped with a stirring bar, a reflux condenser, and an argon inlet tube, and the raw materials were dissolved. The bromides listed in Table 2 were added dropwise at 80° C. over about 1 hour with stirring, and the mixture was refluxed for 30 minutes. After the reaction was completed, THF was removed under reduced pressure, and 300 parts of pure water and the bases listed in Table 2 were added. The resulting liquid containing the reaction product was allowed to cool to 25° C. and extracted twice with 200 mL of diethyl ether. The solvent containing the product was dried by adding magnesium sulfate and concentrated under reduced pressure to obtain the allylated compound. The hydrosilylation step was carried out in the same manner as for Compounds 1 to 13 and Comparative Compound 14 to obtain Comparative Compound 15.

(Comparative compound 16)
The raw materials listed in Table 2 and the solvent were placed in a three-necked flask equipped with a stirrer and a nitrogen introduction tube, and the raw materials were dissolved. The mixture was stirred at 55° C. for 3 hours, and after the reaction was completed, the solvent was removed under reduced pressure to obtain a concentrate. 100 parts of ethanol was added to the concentrate, filtered, and the residue was washed with ethanol to remove impurities. The liquid component was removed by reducing the pressure of the filtrate, and an allylated compound was obtained. The hydrosilylation step was carried out in the same manner as for Compounds 1 to 13 and Comparative Compound 14 to obtain Comparative Compound 16.

<Preparation of pigment dispersion>
A pigment dispersion was produced according to the following procedure. Table 4 shows the conditions for producing the pigment dispersion.

(Pigment dispersions 1-22, 27-29, 31-47, 50)
40.00 parts of titanium oxide particles of the type shown in Table 4, a dispersant of the type and usage amount (parts) shown in Table 4, and ion-exchanged water for a total of 100.00 parts of the ingredients were mixed, and using a homogenizer. Preliminary dispersion was performed. Thereafter, dispersion treatment was performed using 0.5 mm zirconia beads at 25° C. in a paint shaker for 12 hours. The zirconia beads were filtered and an appropriate amount of ion-exchanged water was added as needed to prepare each pigment dispersion having a titanium oxide particle content of 40.00%.

(Pigment dispersions 23-26, 30)
40.00 parts of titanium oxide particles of the type shown in Table 4, a dispersant of the type and usage amount (parts) shown in Table 4, and ion-exchanged water for a total of 100.00 parts of the ingredients were mixed, and using a homogenizer. Preliminary dispersion was performed. Thereafter, dispersion treatment was performed using 0.5 mm zirconia beads at 25° C. in a paint shaker for 12 hours. The zirconia beads were filtered and an appropriate amount of ion-exchanged water was added as needed to prepare each pigment dispersion. While stirring each of the prepared pigment dispersions, water was removed by drying with air at 35°C. After that, a dehydration condensation reaction between the silanol groups and the surface hydroxyl groups of the titanium oxide particles is promoted in an oven at 120°C, and a part of the compound represented by general formula (1) is covalently bonded to the surface hydroxyl groups of the titanium oxide particles. A powder of titanium oxide particles was obtained. By adjusting the heating time in an oven at 120°C, the "mass ratio (times) of covalently bonded compound" listed in Tables 5 to 9 was obtained. The powder of titanium oxide particles was redispersed with an appropriate amount of ion-exchanged water to prepare each pigment dispersion having a content of titanium oxide particles of 40.00%.

(Pigment dispersion liquid 48)
40.00 parts of titanium oxide particles of the types shown in Table 4 and 60.00 parts of ion-exchanged water were mixed and pre-dispersed using a homogenizer. Thereafter, a resin dispersant for dispersing titanium oxide particles (trade name: "Floren G700", acid value: 60 mgKOH/g, manufactured by Kyoeisha Chemical Co., Ltd.) was added to obtain a mixture. This mixture was subjected to a dispersion treatment for 12 hours using a paint shaker filled with 0.5 mm zirconia beads to prepare a pigment dispersion liquid 48 having a content of titanium oxide particles of 40.00%.

(Pigment dispersion liquid 49)
A pigment dispersion was prepared according to the method for preparing pigment 3k in Example 3 of Patent Document 1. Specifically, a pigment dispersion liquid was prepared in the same manner as the above pigment dispersion liquid 1 except that titanium oxide particles 4 and compound 4 were used instead of titanium oxide particles 1 and compound 5. The resulting pigment dispersion was dried by blowing air at 35° C. while stirring to remove moisture, and then dried in an oven at 105° C. for 4 hours and 15 minutes to obtain a powder of titanium oxide particles. The powder of titanium oxide particles was redispersed with an appropriate amount of ion-exchanged water to prepare a pigment dispersion liquid 49 containing 40.0% titanium oxide particles.

(Pigment dispersion liquid 51)
A pigment dispersion was prepared according to the method for preparing aqueous pigment dispersion A in Example 1 of Patent Document 3. Specifically, a pigment dispersion was prepared in the same manner as Pigment Dispersion 1 above, except that 1.2 parts of vinyltriethoxysilane (silane coupling agent) was used instead of Compound 5. The obtained pigment dispersion was heated to dryness to obtain a powder of titanium oxide particles that had been surface-treated with a silane coupling agent. 40.00 parts of powder of titanium oxide particles, 3.20 parts of styrene acrylic resin, and 56.80 parts of ion-exchanged water were mixed. The styrene acrylic resin was synthesized by a known method, and had a styrene/acrylic acid/methacrylic acid ratio of 77/10/13, and an acid value of 150 mg/KOH. Thereafter, dispersion treatment was performed again in the same manner as in Pigment Dispersion 1 to prepare Pigment Dispersion 51 having a titanium oxide particle content of 40.00% and a resin content of 3.20%.

(Calculation of mass ratio of compound represented by general formula (1) covalently bonded to titanium oxide particles)
The mass ratio of the compound represented by the general formula (1) covalently bonded to the surface hydroxyl group of the titanium oxide particles was measured as follows. First, each prepared pigment dispersion liquid is centrifuged using a centrifuge to sediment the solid content containing titanium oxide particles, the supernatant liquid component is removed, and water is added to the solid content to regenerate it. Dispersed. By repeating the above series of operations three times, the compound represented by general formula (1) that is not covalently bonded to the surface hydroxyl group of the titanium oxide particles is removed, and the compound represented by general formula (1) is covalently bonded to the surface hydroxyl group of the titanium oxide particles. Bonded titanium oxide particles were obtained. The mass ratio was calculated by quantitatively analyzing the titanium oxide particles using thermogravimetric analysis (TGA). In Tables 5 to 9, it is expressed as "mass ratio (times) of covalently bonded compound". Similar measurements were performed on inks containing each pigment dispersion, and it was found that the mass ratios did not change. However, when a compound that does not satisfy general formula (1) was used as a dispersant, the column of "mass ratio (times) of covalently bonded compound" was written as "0.000".

<Preparation of liquid containing alumina particles>
The liquid containing alumina particles was prepared with reference to the method for preparing ink 3 in Example 1 of Patent Document 2. Specifically, an alumina particle dispersion containing 10% of amphoteric alumina particles (trade name "Dispal 23N4-80", dispersed particle diameter 90 nm, manufactured by Sasol) was prepared. The pH of the alumina particle dispersion liquid is adjusted to 4.0 with a strong acid (1 mol/L hydrochloric acid), the alumina particle dispersion liquid is mixed with a propeller mixer until it becomes uniform, and the alumina particle dispersion liquid is pulverized using a bead mill. (Content of alumina particles: 10%) was obtained.

<Preparation of ink>
The types and amounts of each component shown in the upper row of Tables 5 to 9 were mixed and stirred. Viniblan 2685 (trade name) is the trade name of an acrylic emulsion (acrylic resin particle content: 30%) manufactured by Nissin Chemical Industry. Acetylenol E60 (trade name) is a nonionic surfactant manufactured by Kawaken Fine Chemicals. The ion exchange water containing potassium hydroxide is ion exchange water containing potassium hydroxide for adjusting the pH of each ink to the values listed in Tables 5 to 9. , the remaining amount was added. Thereafter, pressure filtration was performed using a membrane filter (manufactured by Sartorius) with a pore size of 5.0 μm to prepare each ink. The pH of each ink was measured using a pH meter (trade name "Portable pH Meter D-74", manufactured by Horiba, Ltd.).

<Evaluation>
The following items were evaluated for each ink obtained above. In the present invention, in the evaluation criteria for each item shown below, "A", "B", "C", "D", and "E" are considered to be acceptable levels, and "F" is defined as unacceptable level. . Since the inks of Comparative Examples 16 and 17 could not be ejected, the column for evaluation results of ink ejection stability was written as "unable to eject." Further, the evaluation of the ejection stability of the ink of Example 18 was "D", which is the same as that of Example 17, but Example 17 was superior. The evaluation results are shown in the lower rows of Tables 5 to 9. In Tables 5 to 9, the column "Mass ratio of covalently bonded compound (times)" indicates the amount (mass%) of the compound represented by general formula (1) covalently bonded to the surface of titanium oxide particles. ) is expressed as a mass ratio to the content (mass%) of titanium oxide particles.

(Discharge stability)
Each ink obtained above was placed in a sealed container and stored at 70°C for one week. If the pH of the ink rose above the pH before storage, potassium hydroxide was added to adjust the pH to the same pH as before storage. This operation is an accelerated condition that assumes long-term storage and environmental changes such as temperature. Thereafter, each ink was filled into an ink cartridge, and the cartridge was set in an inkjet recording apparatus (trade name: "PIXUS PRO-10S", manufactured by Canon) equipped with a recording head that ejects ink using thermal energy. Select any five ejection ports of the print head, eject ink continuously at a frequency of 50,000 shots/second, photograph the ejected ink droplets from the side, and use image processing to calculate the ejection speed of the ink droplets. did. The ejection speed of ink droplets after a predetermined time (1 minute, 3 hours) after starting continuous ejection was calculated. "Change in ejection speed" is based on the formula ("ink droplet ejection speed after 1 minute" - "ink droplet ejection speed after 3 hours")/("ink droplet ejection speed after 1 minute") Calculated for each outlet. The average of the "changes in ejection speed" for the five ejection ports was determined, the rate of change in ejection speed was calculated, and the ejection stability of the ink was evaluated according to the evaluation criteria shown below. The smaller the rate of change in ejection speed, the better the ink ejection stability. On the other hand, if, for example, an excessive amount of dispersant is adsorbed to the titanium oxide particles, the energy for ejection will be consumed to remove the excess adsorbed dispersant during ejection. , the ejection speed decreases and the rate of change in ejection speed increases.
A: The rate of change in discharge speed was 0.02 or less.
B: The rate of change in discharge speed was more than 0.02 and less than 0.05.
C: The rate of change in discharge speed was more than 0.05 and less than 0.08.
D: The rate of change in discharge speed was more than 0.08 and less than 0.10.
E: The rate of change in discharge speed was more than 0.10 and less than 0.20.
F: The rate of change in discharge speed exceeded 0.20.

The disclosure of this embodiment includes the following configuration and method.

[Configuration 1]
An aqueous inkjet ink containing titanium oxide particles and a dispersant for the titanium oxide particles,
The titanium oxide particles are titanium oxide whose surfaces are at least partially coated with alumina and silica,
The proportion (mass %) of the alumina in the titanium oxide particles is 0.50 times or more and 1.00 times or less relative to the proportion (mass %) of the silica,
An aqueous ink characterized in that the dispersant for the titanium oxide particles is a compound represented by the following general formula (1).

(In general formula (1), R ₁ , R ₂ , and R ₃ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. _{R 4} is each independently a hydrogen atom or an alkyl group having 2 to 4 carbon atoms. It is an alkylene group. X is a single bond or an alkylene group having 1 to 6 carbon atoms. n is 6 to 24; a is 1 to 3; b is 0 to 2; )

[Configuration 2]
The aqueous ink according to configuration 1, wherein the proportion (mass%) of the titanium oxide in the titanium oxide particles is 90.0% by mass or more based on the total mass of the titanium oxide particles.

[Configuration 3]
The aqueous ink according to configuration 1 or 2, wherein the proportion (mass%) of the titanium oxide in the titanium oxide particles is 98.5% by mass or less based on the total mass of the titanium oxide particles.

[Configuration 4]
In any one of configurations 1 to 3, the proportion (mass%) of the alumina in the titanium oxide particles is 0.50% by mass or more and 4.00% by mass or less, based on the total mass of the titanium oxide particles. Water-based ink as described.

[Configuration 5]
In any one of configurations 1 to 4, the proportion (mass%) of the silica in the titanium oxide particles is 1.00% by mass or more and 4.00% by mass or less, based on the total mass of the titanium oxide particles. Water-based ink as described.

[Configuration 6]
The aqueous ink according to any one of configurations 1 to 5, wherein the titanium oxide particles have a volume-based cumulative 50% particle diameter of 200 nm or more and 400 nm or less.

[Configuration 7]
7. The aqueous ink according to any one of configurations 1 to 6, wherein the content (mass%) of the titanium oxide particles is 1.00% by mass or more and 20.00% by mass or less, based on the total mass of the ink.

[Configuration 8]
The content (mass%) of the compound represented by the general formula (1) in the aqueous ink is 0.002 times or more 0.10 times the content (mass%) of the titanium oxide particles. 8. The aqueous ink according to any one of Structures 1 to 7, wherein the water-based ink is equal to or less than twice that of the previous structure.

[Configuration 9]
The amount (mass%) of the compound represented by the general formula (1) covalently bonded to the surface of the titanium oxide particles is 0.001 as a mass ratio to the content (mass%) of the titanium oxide particles. 9. The water-based ink according to any one of Structures 1 to 8, wherein the water-based ink is equal to or less than twice as much.

[Configuration 10]
The aqueous ink according to any one of Structures 1 to 9, wherein the compound represented by the general formula (1) is a compound represented by the following general formula (2).

(In general formula (2), R ₁ and R ₃ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. m is 8 to 24.)

[Configuration 11]
Any one of configurations 1 to 10, wherein the content (mass%) of the compound represented by the general formula (1) is 0.01% by mass or more and 1.00% by mass or less, based on the total mass of the ink. The water-based ink described in .

[Configuration 12]
Any one of configurations 1 to 11, wherein the content (mass%) of the compound represented by the general formula (1) is 0.02% by mass or more and 0.50% by mass or less, based on the total mass of the ink. The water-based ink described in .

[Configuration 13]
The aqueous ink according to any one of configurations 1 to 12, wherein the aqueous ink has a pH of 7.0 or more and 9.0 or less.

[Configuration 14]
An ink cartridge comprising ink and an ink accommodating portion accommodating the ink, the ink cartridge comprising:
An ink cartridge, wherein the ink is the water-based ink according to any one of Structures 1 to 13.

[Configuration 15]
An inkjet recording method that records an image on a recording medium by ejecting ink from an inkjet recording head, the method comprising:
An inkjet recording method, wherein the ink is the water-based ink according to any one of Structures 1 to 13.

[Configuration 16]
A dispersion of titanium oxide particles used for producing an aqueous inkjet ink, the dispersion containing titanium oxide particles and a dispersant for the titanium oxide particles,
The titanium oxide particles are titanium oxide whose surfaces are at least partially coated with alumina and silica,
The dispersant for the titanium oxide particles is a compound represented by the following general formula (1),
Titanium oxide particles, characterized in that the proportion (mass %) of the alumina in the titanium oxide particles is 0.50 times or more and 1.00 times or less relative to the proportion (mass %) of the silica. dispersion of.

(In general formula (1), R ₁ , R ₂ , and R ₃ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. _{R 4} is each independently a hydrogen atom or an alkyl group having 2 to 4 carbon atoms. It is an alkylene group. X is a single bond or an alkylene group having 1 to 6 carbon atoms. n is 6 to 24; a is 1 to 3; b is 0 to 2; )

[Configuration 17]
A method for producing a dispersion of titanium oxide particles for use in producing an aqueous inkjet ink, the method comprising:
providing titanium oxide particles whose surfaces are titanium oxide coated with alumina and silica, and
A dispersion step of dispersing the titanium oxide particles in a liquid medium using a compound represented by the following general formula (1) for dispersing the titanium oxide particles,
Titanium oxide particles, characterized in that the proportion (mass %) of the alumina in the titanium oxide particles is 0.50 times or more and 1.00 times or less relative to the proportion (mass %) of the silica. A method for producing a dispersion of

(In general formula (1), R ₁ , R ₂ , and R ₃ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. _{R 4} is each independently a hydrogen atom or an alkyl group having 2 to 4 carbon atoms. It is an alkylene group. X is a single bond or an alkylene group having 1 to 6 carbon atoms. n is 6 to 24; a is 1 to 3; b is 0 to 2; )

[Configuration 18]
A method for producing an aqueous ink for inkjet, the method comprising:
A method for producing an aqueous ink, comprising a step of mixing a dispersion of titanium oxide particles produced by the method for producing a dispersion of titanium oxide particles according to Structure 17 and other ink components.

[Configuration 19]
An aqueous inkjet ink containing titanium oxide particles and a dispersant for the titanium oxide particles,
The titanium oxide particles are titanium oxide whose surfaces are at least partially coated with alumina and silica,
The proportion (mass %) of aluminum element obtained by inductively coupled plasma emission spectrometry in the titanium oxide particles is 0.57 times or more and 1.13 times or less relative to the proportion (mass %) of silicon element. ,
An aqueous ink characterized in that the dispersant for the titanium oxide particles is a compound represented by the following general formula (1).

(In general formula (1), R ₁ , R ₂ , and R ₃ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. _{R 4} is each independently a hydrogen atom or an alkyl group having 2 to 4 carbon atoms. It is an alkylene group. X is a single bond or an alkylene group having 1 to 6 carbon atoms. n is 6 to 24; a is 1 to 3; b is 0 to 2; )

Claims (19)

An aqueous inkjet ink containing titanium oxide particles and a dispersant for the titanium oxide particles,
The titanium oxide particles are titanium oxide whose surfaces are at least partially coated with alumina and silica,
The proportion (mass %) of the alumina in the titanium oxide particles is 0.50 times or more and 1.00 times or less relative to the proportion (mass %) of the silica,
A water-based ink characterized in that the dispersant for the titanium oxide particles is a compound represented by the following general formula (1).

(In general formula (1), R ₁ , R ₂ , and R ₃ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. _{R 4} is each independently a hydrogen atom or an alkyl group having 2 to 4 carbon atoms. It is an alkylene group. ) The aqueous ink according to claim 1, wherein the proportion (mass%) of the titanium oxide in the titanium oxide particles is 90.0% by mass or more based on the total mass of the titanium oxide particles. The aqueous ink according to claim 1, wherein the proportion (mass%) of the titanium oxide in the titanium oxide particles is 98.5% by mass or less based on the total mass of the titanium oxide particles. The aqueous ink according to claim 1, wherein the proportion (mass%) of the alumina in the titanium oxide particles is from 0.50% by mass to 4.00% by mass, based on the total mass of the titanium oxide particles. The aqueous ink according to claim 1, wherein the proportion (mass%) of the silica in the titanium oxide particles is 1.00% by mass or more and 4.00% by mass or less, based on the total mass of the titanium oxide particles. The aqueous ink according to claim 1, wherein the titanium oxide particles have a volume-based cumulative 50% particle diameter of 200 nm or more and 400 nm or less. The aqueous ink according to claim 1, wherein the content (mass%) of the titanium oxide particles is 1.00% by mass or more and 20.00% by mass or less, based on the total mass of the ink. The content (mass%) of the compound represented by the general formula (1) in the aqueous ink is 0.002 times or more 0.10 times the content (mass%) of the titanium oxide particles. 2. The aqueous ink according to claim 1, wherein the water-based ink is less than or equal to twice as much. The amount (mass%) of the compound represented by the general formula (1) covalently bonded to the surface of the titanium oxide particles is 0.001 as a mass ratio to the content (mass%) of the titanium oxide particles. 2. The aqueous ink according to claim 1, wherein the water-based ink is less than or equal to twice as much. The aqueous ink according to claim 1, wherein the compound represented by the general formula (1) is a compound represented by the following general formula (2).

(In general formula (2), R ₁ and R ₃ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. m is 8 to 24.) The aqueous ink according to claim 1, wherein the content (mass%) of the compound represented by the general formula (1) is from 0.01% by mass to 1.00% by mass, based on the total mass of the ink. The aqueous ink according to claim 1, wherein the content (mass%) of the compound represented by the general formula (1) is from 0.02% by mass to 0.50% by mass, based on the total mass of the ink. The aqueous ink according to claim 1, wherein the aqueous ink has a pH of 7.0 or more and 9.0 or less. An ink cartridge comprising ink and an ink accommodating portion accommodating the ink, the ink cartridge comprising:
An ink cartridge, wherein the ink is an aqueous ink according to any one of claims 1 to 13. An inkjet recording method that records an image on a recording medium by ejecting ink from an inkjet recording head, the method comprising:
An inkjet recording method, wherein the ink is the aqueous ink according to any one of claims 1 to 13. A dispersion of titanium oxide particles used for producing an aqueous inkjet ink, the dispersion containing titanium oxide particles and a dispersant for the titanium oxide particles,
The titanium oxide particles are titanium oxide whose surfaces are at least partially coated with alumina and silica,
The dispersant for the titanium oxide particles is a compound represented by the following general formula (1),
Titanium oxide particles, characterized in that the proportion (mass %) of the alumina in the titanium oxide particles is 0.50 times or more and 1.00 times or less relative to the proportion (mass %) of the silica. dispersion of.

(In general formula (1), R ₁ , R ₂ , and R ₃ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. _{R 4} is each independently a hydrogen atom or an alkyl group having 2 to 4 carbon atoms. It is an alkylene group. X is a single bond or an alkylene group having 1 to 6 carbon atoms. n is 6 to 24; a is 1 to 3; b is 0 to 2; ) A method for producing a dispersion of titanium oxide particles for use in producing an aqueous inkjet ink, the method comprising:
providing titanium oxide particles whose surfaces are titanium oxide coated with alumina and silica, and
A dispersion step of dispersing the titanium oxide particles in a liquid medium using a compound represented by the following general formula (1) for dispersing the titanium oxide particles,
Titanium oxide particles, characterized in that the proportion (mass %) of the alumina in the titanium oxide particles is 0.50 times or more and 1.00 times or less relative to the proportion (mass %) of the silica. A method for producing a dispersion of.

(In general formula (1), R ₁ , R ₂ , and R ₃ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. _{R 4} is each independently a hydrogen atom or an alkyl group having 2 to 4 carbon atoms. It is an alkylene group. ) A method for producing an aqueous ink for inkjet, the method comprising:
A method for producing an aqueous ink, comprising the step of mixing a dispersion of titanium oxide particles produced by the method for producing a dispersion of titanium oxide particles according to claim 17, and other ink components. An aqueous inkjet ink containing titanium oxide particles and a dispersant for the titanium oxide particles,
The titanium oxide particles are titanium oxide whose surfaces are at least partially coated with alumina and silica,
The proportion (mass %) of aluminum element obtained by inductively coupled plasma emission spectrometry in the titanium oxide particles is 0.57 times or more and 1.13 times or less relative to the proportion (mass %) of silicon element. ,
An aqueous ink characterized in that the dispersant for the titanium oxide particles is a compound represented by the following general formula (1).

(In general formula (1), R ₁ , R ₂ , and R ₃ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. _{R 4} is each independently a hydrogen atom or an alkyl group having 2 to 4 carbon atoms. It is an alkylene group. X is a single bond or an alkylene group having 1 to 6 carbon atoms. n is 6 to 24; a is 1 to 3; b is 0 to 2; )

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