JP2011225867A - Method for producing aqueous pigment dispersion - Google Patents

Abstract

Disclosed is a white aqueous pigment dispersion for inkjet recording, which has good color developability and concealability, little sedimentation, excellent dispersibility and long-term dispersion stability, and a method for producing the same.
An aqueous pigment dispersion containing titanium oxide, an anionic group-containing resin, a water-soluble organic solvent, and a basic compound, and a specific surface treatment using silica and alumina and a silane coupling agent By using the surface treatment with, a very excellent dispersion stability effect and sedimentation suppressing effect can be obtained. The titanium oxide is further surface-treated with a silane coupling agent after the surface treatment with alumina and silica, and the ratio of the alumina treatment amount is 35% by mass or more and less than 80% by mass in the total surface treatment amount with the alumina and silica. It is.
[Selection figure] None

Description

  The present invention relates to a method for producing an aqueous pigment dispersion having good dispersion stability using titanium oxide as a colorant.

In recent years, inkjet recording methods have been widely used for office and industrial purposes.
As the ink used, water-based ink that has little environmental impact and no problem in odor is already widely used for office use. However, from the viewpoint of safety and cost, industrial ink is more solvent-based than UV-based ink. However, water-based inks are desired and conversion to water-based ink is progressing.
In particular, industrial inks are required to have high durability and light resistance in terms of use environment, and use of pigments as colorants is required. In recent years, the use of colorants from dyes to pigments has also been promoted for office use.
Ink-jet printing inks are expected to expand not only to printing on white paper under the ground, but also to printing on fabrics and fibers with a lot of black and dark colors, or transparent films and colored plastics. Therefore, there is a strong demand for water-based white inks for both office and industrial use. However, some of these ink-jet white inks are commercially available in solvent and UV systems, but water-based ink-jet white inks that are difficult to produce and stabilize over time are not yet in practical use. It is.
White ink for inkjet recording is particularly important as industrial marking ink, and titanium oxide is used as a white pigment because of its good concealment and low cost. However, since titanium oxide used as a colorant has a large specific gravity, it easily settles and has been conventionally difficult to stably disperse. In particular, when used as a water-based ink, it has been difficult to ensure good stability while maintaining high concealability and color developability.

In order to stably disperse titanium oxide as a colorant, various attempts have been made focusing on the surface treatment. For example, Patent Document 1 describes that a paint dispersion, which is a white pigment composition in which titanium oxide is dispersed and dispersed with an alcohol solvent, is obtained, but mention is made of water-based pigment compositions and aqueous paints. There is no description of silane coupling treatment to titanium oxide. Further, in Patent Document 2, there is a description that a titanium oxide having a hydrophilic surface is hydrophobized with an organosilane compound in order to knead it into a plastic. However, there is no mention of an aqueous method, and how As to whether titanium oxide is suitable, surface treatment such as alumina treatment and silica treatment of titanium oxide is not described. Patent Document 3 describes an oily white ink for ink-jet recording, which is an oil-based paint using a polysiloxane containing no alkyl group as a silane coupling agent, although there is a description regarding the surface treatment of titanium oxide. Only water-based ink is not described. Further, Patent Document 4 mentions silane coupling treatment / aqueous coating of titanium oxide, but there is a description of the ratio of alumina treatment: silica treatment of titanium oxide surface and a combination with a suitable coupling agent. No. Moreover, since the primary particle diameter of titanium oxide is 1 to 130 nm and titanium oxide having a very small particle diameter is used, the hiding property is inferior.
As described above, the conventional methods have not yet achieved excellent dispersion stability over a long period of time by securing good dispersibility, concealability and non-sedimentability of titanium oxide in an aqueous medium.

JP-A-6-107964 JP 2007-254757 A JP 2004-263181 A JP 2009-0697968 A

An object of the present invention is to provide a white aqueous pigment dispersion for inkjet recording, which has good color developability and concealability, little sedimentation, excellent dispersibility and long-term dispersion stability, and a method for producing the same. is there.
Furthermore, an object of the present invention is to provide a white aqueous ink for ink-jet recording capable of forming a fine image excellent in concealing property because it has the above characteristics and good dischargeability.

In order to secure good dispersibility of titanium oxide in an aqueous medium, the inventors adsorbed a resin having an anionic group on the surface of titanium oxide in the same manner as a normal organic pigment. We thought to do this by coating the pigment and using the steric hindrance effect of the adsorbing resin and the electrostatic repulsion of the anionic group. For this reason, when we focused on the surface treatment of the surface of titanium oxide, the dispersion was extremely excellent by combining specific surface treatment with silica and alumina and surface treatment with a silane coupling agent. It has been found that a stability effect and a sedimentation suppressing effect can be obtained.
That is, the present invention is an aqueous pigment dispersion containing titanium oxide, a resin containing an anionic group, a water-soluble organic solvent, and a basic compound, wherein the titanium oxide is further treated with silane after surface treatment with alumina and silica. Provided is an aqueous pigment dispersion which is surface-treated with a coupling agent and has a ratio of alumina treatment amount of 35% by mass or more and 80% by mass or less of the total surface treatment amount by alumina and silica. .
The present invention also provides an inkjet recording ink containing the aqueous pigment dispersion.
Further, the present invention is a titanium oxide surface-treated in advance with alumina and silica, wherein the alumina present together with the titanium oxide is 35% by mass or more, 80% based on the total amount of alumina and silica present together with the titanium oxide. Surface treatment step for surface treatment with a silane coupling agent, titanium oxide surface-treated with the silane coupling agent, a resin containing an anionic group, a water-soluble organic solvent, And a kneading step of kneading a mixture containing a basic compound to produce a solid kneaded product, and a dispersion step of dispersing the solid kneaded material in an aqueous medium. provide.

  The aqueous pigment dispersion of the present invention uses a specific surface treatment using silica or alumina and a surface treatment using a silane coupling agent. Since titanium oxide has a hydroxyl group on the surface and is hydrophilic, when dispersing, coating, or encapsulating with a resin, it is preferable to make the surface oleophilic by silane coupling treatment.

  When the silane coupling treatment is performed, if the titanium oxide surface is treated in advance with a specific AL / Si ratio, the subsequent silane coupling treatment and the coating of the dispersion resin having an anionic group can proceed well. And titanium oxide suitable for dispersion in water can be obtained. In general, the surface treatment of titanium oxide is generally carried out with alumina in order to suppress the photocatalytic properties of titanium oxide, but more importantly, alumina is used for the purpose of controlling the acidity and basicity of the surface. In addition, it is often surface treated with silica.

  When titanium oxide treated with alumina and silica is coated with a dispersion resin having an anionic group and dispersed in an aqueous dispersion to obtain an aqueous dispersion, if too much alumina is present, hydrophilicity of the titanium oxide surface is obtained. Therefore, the hydrophilic group on the surface of titanium oxide that cannot be completely covered with the silane coupling agent remains. For this reason, the adsorption of the dispersing resin having an anionic group, which normally adsorbs the hydrophobic group toward the pigment surface and adsorbs to the hydrophobic portion of the titanium oxide, is hindered. When a surface treatment with silica, which is less hydrophilic than alumina, is used in combination, the adsorption of the dispersing resin proceeds more easily. On the other hand, if the amount of alumina is too small, the silica portion having the characteristics as an acidic oxide repels the anionic group portion in the dispersion resin having an anionic group, making the resin difficult to adsorb, and the stability of the dispersion liquid.・ It will be inferior to non-sedimentation. For this reason, a suitable AL / Si ratio range is considered to exist.

  Thus, the amount of resin adsorption increases by further subjecting titanium oxide treated at a suitable AL / Si ratio to silane coupling treatment. Therefore, a white aqueous pigment dispersion in which titanium oxide is difficult to settle can be obtained by steric hindrance due to the adsorbing resin and electrostatic repulsion in water due to the anionic group of the resin.

  The ink for inkjet recording that can be prepared by adding a known organic solvent, surfactant, antioxidant, antifungal agent, anti-adhesive agent, pH adjusting agent, etc. to the aqueous pigment dispersion of the present invention has a concealing property. It is excellent in non-sedimentation and stability over time, and can be very usefully used for printing on recording media such as paper, cloth, fiber, transparent film, and colored plastic by various ink jet devices.

  In the method for producing an aqueous pigment dispersion of the present invention, the surface treatment is performed in which the alumina present together with titanium oxide is 35% by mass or more and 80% by mass or less based on the total amount of alumina and silica present together with the titanium oxide. Titanium oxide is used, and titanium oxide produced through a surface treatment process for further surface treatment with a silane coupling agent is used for this. Therefore, the resin is well adsorbed on the titanium oxide surface and can be easily coated. An aqueous white dispersion having excellent dispersion stability can be obtained through a dispersion step of dispersing a mixture containing a resin containing an anionic group, a water-soluble organic solvent, and a basic compound.

The aqueous pigment dispersion of the present invention has no adverse effect of concealment deterioration due to the use of titanium oxide having a fine particle size, and has a large amount of resin adsorption, so that titanium oxide is difficult to settle due to electrostatic repulsion in an aqueous medium. . For this reason, it is a white aqueous pigment dispersion excellent in stability over time, and similarly has good characteristics as a water-based ink for inkjet recording.
Furthermore, the method for producing an aqueous pigment dispersion of the present invention further includes a step of subjecting titanium oxide that has been surface-treated with a specific amount of alumina and silica to a surface treatment with a silane coupling agent. Since an anionic group-containing resin is favorably adsorbed on titanium, an aqueous pigment dispersion having extremely good dispersion stability can be produced.

  Hereinafter, the aqueous pigment dispersion of the present invention, the production method thereof, and the ink for inkjet recording will be described in more detail. First, various raw materials used in the present invention and the blending ranges thereof will be described in detail, and then a method for producing the aqueous pigment dispersion of the present invention using them will be described.

As the titanium oxide, known rutile type / anatase type titanium dioxide can be used, but rutile type titanium dioxide is preferably used. As an average particle diameter of the titanium oxide used by this invention, it is preferable to use a 100-500 nm thing, and it is more preferable to use a 150-400 nm thing. When the average particle size is 100 nm or less, non-sedimentation and dispersion stability in an aqueous medium are more easily realized, but the whiteness and hiding properties are inferior and the practicality as an original white ink is lowered. When the particle size is 500 nm or more, there is no problem in terms of whiteness and hiding properties, but it is very easy to settle and it is difficult to obtain a stable dispersion in an aqueous medium. In addition, since the size and weight adversely affect the ink ejection properties, it is extremely difficult to use as ink for ink jet recording. For these reasons, the practical particle size is more preferably 200 to 300 nm.
In addition, the average particle diameter of the titanium oxide as a raw material shall have taken the average by measuring 20 particle diameters with an electron micrograph.
Further, since titanium oxide generally has organic substance decomposability due to photocatalytic properties, it is not suitable to directly disperse and coat with resin. In order to seal this photocatalytic property, it is common to coat the surface with an inorganic substance and perform surface treatment with alumina. Furthermore, in order to adjust the acid / base state of the surface of titanium oxide, surface treatment is also performed using silica together. Further, alumina is mainly used to improve the wettability of titanium oxide at the time of dispersion, and silica is mainly used mainly to improve the durability of the printed matter.
As the surface treatment method of titanium oxide, aqueous treatment, gas phase treatment, etc. are performed. For the above reasons, alumina and silica are generally used as the surface treatment agent. Are untreated, treated with alumina, and treated with alumina / silica. As for the pigments treated with alumina / silica, varieties having a higher silica treatment amount than the alumina treatment amount and varieties having a larger alumina treatment amount than the silica treatment amount are commercially available.
The surface treatment of the titanium oxide used in the present invention is based on the relationship with the resin having an anionic group adsorbed on the surface of the titanium oxide after the surface treatment. The ratio of 35 mass% or more and 80 mass% or less is used.
The amount of these inorganic substances for treating titanium oxide is not necessarily limited, but is generally 30 parts or less with respect to 100 parts of titanium oxide.

When the surface of titanium oxide is ideographically treated with alumina, or alumina and silica, if the alumina is too much, its strong hydrophilicity cannot be completely removed. As a result, the adsorption of the resin having an anionic group used in the present invention, which is usually adsorbed to the pigment by the hydrophobic portion with the anionic group outside, is inhibited from being performed on the titanium oxide surface. Furthermore, alumina exists in the form of Al-OH on the surface of titanium oxide. If the amount of alumina treated is too large, a large amount of silane coupling agent is required to be adsorbed on this OH. The problem is likely to occur. On the other hand, if the alumina treatment amount is too small and the silica treatment amount ratio is too large, the properties as an acidic pigment become strong, so the titanium oxide surface repels the anionic group portion of the resin having an anionic group, and the titanium oxide surface It becomes difficult to adsorb. Therefore, the range of the ratio of the treatment amount with practical alumina to the sum of the treatment amounts of alumina and silica is 35 to 80% by mass. 35-65% by mass
Is more preferable, and 35-50 mass% is still more preferable.

  Titanium oxide subjected to such surface treatment is commercially available from manufacturers of titanium oxide such as Ishihara Sangyo Co., Ltd. and Teika Co., Ltd., and there are untreated, alumina-treated, and alumina / silica-treated ones. As for the pigments treated with alumina / silica, varieties with a higher silica treatment amount compared to the alumina treatment amount and varieties with a higher alumina treatment amount than the silica treatment amount are commercially available, and the treatment amount with alumina is in the above ratio. Titanium oxide that falls within the range is also available.

The mass ratio of alumina and silica used for the surface treatment of the present invention can be estimated from the amount of alumina and silica present together with titanium oxide on the surface of titanium oxide. The abundance ratio of alumina and silica can be confirmed by analyzing and comparing the amount of alumina or silica adsorbed on the titanium oxide surface by fluorescent X-rays or ESCA. In particular, measurement with fluorescent X-rays is simple and accurate. Silica and alumina may exist on the surface of titanium oxide, and some of them may exist as free particles, and the total amount can be measured by measuring with fluorescent X-rays. As for the quantitative method using fluorescent X-rays, an analytical method using a calibration curve using standard data has been established.
Therefore, the mass ratio of alumina and silica present on the surface of commercially available titanium oxide can be confirmed by measurement with fluorescent X-rays, and titanium oxides having various mass ratios can be used.

The silane coupling agent used in the present invention has a hydrolyzable group that reacts with a hydroxyl group present on the surface of titanium oxide treated with alumina or alumina and silica, and an organic functional group. General formula (1)

（１）
（式中、（Ｒ1）（Ｒ２）（Ｒ３）及び（Ｒ４）はそれぞれ独立に、水素原子、アルコキシ基、ヒドロキシ基、クロル基、有機基のいずれかであり、少なくとも１つはアルコキシ基、ヒドロキシ基、クロル基のいずれかであり、かつ、少なくとも１つは有機基である。
ａ，ｂ，ｃ及びｄは０〜３の整数であり、かつ、ａ＋ｂ＋ｃ＋ｄ＝４である。）
の構造を有する有機ケイ素化合物である。
これらシランカップリング剤は加水分解基の加水分解によってシラノールを生じ、シラノール同士が縮合してシロキサン結合となりオリゴマーを形成する。一方、無機化合物の酸化表面あるいは水酸基とも同様のメカニズムで反応し、無機物表面にある水酸基との水素結合を介して無機物表面に移行し、脱水縮合反応を経てポリシロキサン結合を形成する。これら反応は並行して進行し、ポリシロキサン結合を有するオリゴマー、ポリマーによる被覆、すなわちオルガノポリシロキサン被覆を無機物表面に形成する。
具体的な化合物としては、ビニルトリクロルシラン、ビニルトリエトキシシラン、ビニルトリエトキシシラン、ビニルトリス（２−メトキシエトキシ）シラン、ビニルメチルジメトキシシラン等のビニルシラン、３−メタクリロキシプロピルトリエトキシシラン、３−メタクリロキシプロピルトリメトキシシラン等のメタクリルシラン、２−（３，４−エポキシシクロヘキシル）エチルトリメトキシシラン、３−グリシドキシプロピルトリメトキシシラン、３−グリシドキシプロピルトリエトキシシラン等のエポキシシラン、３−メルカプトプロピルトリメトキシシラン、３−メルカプトプロピルトリエトキシシラン等のメルカプトシラン、３−オクタノイルチオ−１−プロピルトリエトキシシラン等のサルファーシラン、３−アミノプロピルトリエトキシシラン、３−アミノプロピルトリメトキシシラン、Ｎ−（２−アミノエチル）−３−アミノプロピルトリメトキシシラン、Ｎ−（２−アミノエチル）−３−アミノプロピルメチルジメトキシシラン、３−（Ｎ−フェニル）アミノプロピルトリメトキシシラン等のアミノシラン、３−ウレイドプロピルトリエトキシシラン等のウレイドシラン、３−イソシアネートプロピルトリエトキシシラン、３−イソシアネートプロピルトリメトキシシラン等のイソシアネートシラン等をあげることができる。

(1)
(In the formula, (R 1) (R 2) (R 3) and (R 4) are each independently any one of a hydrogen atom, an alkoxy group, a hydroxy group, a chloro group, and an organic group, at least one of which is an alkoxy group, a hydroxy group And at least one is an organic group.
a, b, c, and d are integers of 0 to 3, and a + b + c + d = 4. )
An organosilicon compound having the structure:
These silane coupling agents produce silanols by hydrolysis of hydrolyzable groups, and the silanols condense to form siloxane bonds to form oligomers. On the other hand, it reacts with the oxidized surface or hydroxyl group of the inorganic compound by the same mechanism, moves to the inorganic surface through hydrogen bonds with the hydroxyl group on the inorganic surface, and forms a polysiloxane bond through a dehydration condensation reaction. These reactions proceed in parallel to form an oligomer or polymer coating having a polysiloxane bond, that is, an organopolysiloxane coating on the inorganic surface.
Specific compounds include vinyltrichlorosilane, vinyltriethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxy) silane, vinylmethyldimethoxysilane and other vinylsilanes, 3-methacryloxypropyltriethoxysilane, 3-methacrylic Methoxysilanes such as loxypropyltrimethoxysilane, epoxy silanes such as 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3 -Mercaptosilanes such as mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane; Sulfur silanes such as 3-octanoylthio-1-propyltriethoxysilane; Triethoxysilane, 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane, 3- (N Examples include aminosilanes such as -phenyl) aminopropyltrimethoxysilane, ureidosilanes such as 3-ureidopropyltriethoxysilane, and isocyanate silanes such as 3-isocyanatopropyltriethoxysilane and 3-isocyanatopropyltrimethoxysilane.

In the general formula (1), at least one of (R1) (R2) (R3) and (R4) is a chloro group, a methoxy group, or an ethoxy group, and (R1) (R2) (R3) and ( At least one of R4) is preferably a vinyl group.
These silane coupling agents may be used alone or in combination of two or more.
As the silane coupling agent used in the present invention, it has good adsorptivity to the hydrophobic portion of the resin having an anionic group, and as described later, the water-soluble resin for dispersing, coating and encapsulating titanium oxide Since those containing many St monomers are preferable, among these organic functional groups, a vinyl group having a strong affinity for St is particularly preferable. For this reason, particularly when the resin having an anionic group is a styrene acrylic resin, vinyl silane considered to have good adsorptivity to a hydrophobic portion made of a styrene monomer is preferable, and among these, vinyl triethoxysilane or vinyl trimethoxysilane is preferable. More preferred is vinyltriethoxysilane, which is superior in terms of storage stability and safety from the viewpoint of the environment.

  To treat alumina oxide or titanium oxide treated with alumina and silica with a silane coupling agent, for example, mix titanium oxide and silane coupling agent in water, heat and stir, and then volatilize the water completely. You can do it. The amount of the silane coupling agent used is generally about 0.05 to 20%. Since titanium oxide has a relatively small specific surface area, the effect can be exhibited at about 1 to 10%.

  Examples of the resin having an anionic group used in the present invention include acrylic, polyester, epoxy, urethane, and copolymers having a polar group such as a carboxyl group and a sulfone group. Considering that the better adsorption to the organic functional group of the ring agent is preferable, a resin having a styrene moiety in the monomer component is preferable, and the acid value and the glass transition point can be easily controlled. To styrene acrylic acid resin is preferable.

The styrene acrylic resin having an anionic group contains a styrene monomer as a constituent monomer and a monomer having a radical polymerizable double bond and containing an anionic group. A known compound can be used as the styrene monomer. For example, alkyl styrene such as styrene, α-methyl styrene, β-methyl styrene, 2,4-dimethyl styrene, α-ethyl styrene, α-butyl styrene, α-hexyl styrene, 4-fluorostyrene, 3-chlorostyrene, There are halogenated styrenes such as 3-bromostyrene, 3-nitrostyrene, 4-methoxystyrene, vinyltoluene and the like.
The use ratio of the styrene monomer as a constituent component of the styrene acrylic resin is preferably 20 to 90% by mass, more preferably 30 to 90% by mass, and 50 to 90% by mass with respect to all monomer components. %, More preferably 60 to 90% by mass, still more preferably 70 to 90% by mass. When the use ratio of the styrene monomer is less than 20% by mass, the affinity of the styrene acrylic acid resin having an anionic group to the surface-treated titanium oxide becomes insufficient, and the dispersion stability of the aqueous pigment dispersion is reduced. There is a tendency to decrease. In addition, the recording characteristics of the water-based ink for ink jet recording obtained from the aqueous pigment dispersion tend to deteriorate, the image recording density tends to decrease, and the water resistance tends to decrease. When the amount is less than 30% by mass, the same tendency is recognized although not as much as when the amount is less than 20% by mass. When the amount of the styrene monomer is within the above range, the styrene acrylic acid resin having an anionic group is easily adsorbed on the surface of the titanium oxide that has become hydrophobic by the surface treatment. In addition, since a monomer having an anionic group such as acrylic acid or methacrylic acid can be sufficiently used as a constituent component, the dispersibility of the styrene acrylic resin in an aqueous medium can be maintained well, and the dispersion of the pigment in the aqueous pigment dispersion liquid can be maintained. And dispersion stability can be improved. Furthermore, the printing stability when used as a water-based ink for inkjet recording is improved. On the other hand, when the use ratio of the styrene monomer exceeds 90% by mass, the constituent ratio of the monomer having an anionic group is extremely small, and thus the dispersibility in an aqueous medium tends to be insufficient. There is a tendency for the dispersibility and dispersion stability when ink is produced to decrease.

Examples of the anionic group of the monomer having a radical polymerizable double bond and an anionic group to be copolymerized with the styrenic monomer include a carboxyl group, a sulfone group, and a phospho group. In view of the availability of raw material monomers, the price, etc., an anionic group-containing monomer containing a carboxyl group or a sulfone group is preferable, and the coexistence range of the electrical neutral state and the anionic state can be controlled widely. An anionic group-containing monomer having a carboxyl group is preferable, and an unsaturated aliphatic carboxylic acid monomer is particularly preferable among them.
Known compounds can be used as the unsaturated aliphatic carboxylic acid monomer. For example, acrylic acid, methacrylic acid, α-ethylacrylic acid, crotonic acid, α-methylcrotonic acid, α-ethylcrotonic acid, isocrotonic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, Etc. Among them, it is preferable to use acrylic acid and methacrylic acid, and it is particularly preferable to use both in combination. By using acrylic acid and methacrylic acid together, the copolymerizability at the time of resin synthesis is improved, the uniformity of the resin is improved, and when the pigment is dispersed with the resin, the composition of the dispersant is non-uniform. It is considered that the decrease in stability considered to be caused is suppressed.

  Therefore, as the constituent monomer of the styrene acrylic resin having an anionic group used in the present invention, it is preferable to use three kinds of monomers, styrene monomer, acrylic acid, and methacrylic acid. The total sum is more preferably 95% by mass or more based on the total monomer components.

  The styrene acrylic resin having an anionic group used in the present invention preferably has a resin acid value of 50 to 250 mgKOH / g in order to obtain stable water dispersibility by neutralization with a basic compound. If it is less than 50 mgKOH / g, the dispersibility and solubility in an aqueous medium are extremely poor, and there is a possibility that the aqueous dispersion or aqueous solution may not be formed, or precipitation may occur in the liquid. On the other hand, if it exceeds 250 mgKOH / g, the resin component eluted in the aqueous medium will increase and the amount of resin adsorbed on titanium oxide will decrease, the viscosity of the dispersion will increase, the pigment particle size and the resin itself There may be adverse effects such as deterioration of stability, yellowing of the resin, and brittleness of the resin coating film. For these reasons, the acid value range is more preferably 75 to 200 mgKOH / g, and still more preferably 100 to 200 mgKOH / g.

  The weight average molecular weight of the styrene acrylic copolymer (b) having an anionic group used in the present invention is preferably in the range of 5,000 to 40,000, and in the range of 7,500 to 30,000. More preferably. Especially, it is especially preferable that it exists in the range of 10,000-25,000. When the weight average molecular weight is less than 5,000, long-term storage stability tends to deteriorate when an aqueous pigment dispersion for inkjet recording of the pigment (a) is produced, and sedimentation occurs due to aggregation of the pigment or the like. There is. When the weight average molecular weight of the styrene acrylic copolymer (b) having an anionic group exceeds 40,000, the viscosity of the aqueous ink for inkjet recording prepared from the aqueous pigment dispersion for inkjet recording using this increases. Therefore, the ink ejection stability tends to become unstable. Here, the weight average molecular weight is a value in terms of polystyrene measured by a GPC (gel permeation / chromatography) method.

The basic compound contained in the aqueous pigment dispersion of the present invention neutralizes the anionic group of the resin having an anionic group and improves the dispersibility of the copolymer. As a result, the dispersion state of the titanium oxide particles coated with the resin in the dispersion becomes more stable, and the dispersion stability and long-term storage stability are also improved.
As the basic compound to be used, either an inorganic basic compound or an organic basic compound can be used, but an inorganic basic compound is more preferable because alkali strength can be easily adjusted. More preferred are metal hydroxides.

As the water-soluble organic solvent used in the present invention, known and conventional solvents suitable for inkjet water-based inks can be used. For example, polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, glycerol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene Polyhydric alcohol alkyl ethers such as glycol monomethyl ether and propylene glycol monoethyl ether, polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether; N-methyl-2-pyrrolidone, N-hydroxyethyl -2-pyrrolidone, 1,3-dimethyl Nitrogen-containing heterocyclic compounds such as Louisimidazolidinone, ε-caprolactam, γ-butyrolactone; amides such as formamide, N-methylformamide, N, N-dimethylformamide; monoethanolamine, diethanolamine, triethanolamine, mono Examples thereof include amines such as ethylamine, diethylamine and triethylamine, sulfur-containing compounds such as dimethyl sulfoxide, sulfolane and thiodiethanol, propylene carbonate, and ethylene carbonate.
These water-soluble organic solvents can be used alone or in combination of two or more. Moreover, water can also be used together as appropriate. In particular, when a water-soluble organic solvent having a boiling point of 170 ° C. or higher, more preferably 200 ° C. or higher is used, these water-soluble organic solvents are less likely to be volatilized during the production of the aqueous pigment dispersion. Dispersion can proceed while the solid content ratio of the dispersion is kept constant.

  Examples of organic solvents that can be used in combination with water include monohydric alcohols such as methanol, ethanol, and isopropyl alcohol, polyhydric alcohols such as glycerin and diglycerin, and glycols such as ethylene glycol, propylene glycol, and hexylene glycol. Organic solvents such as ketones such as acetone and methyl ethyl ketone, and ethers such as diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol, and triethylene glycol monobutyl ether can be used.

  In order to obtain an aqueous pigment dispersion by dispersing silane-coupled titanium oxide in an anionic group-containing resin, a water-soluble organic solvent, a basic compound, and water, a known kneader / disperser is used. Can be used. For example, after kneading all these materials in a high-concentration solid state with various known kneading groups such as a kneader, the product in the kneading step can be diluted. Further, it can be obtained by directly dispersing a mixed solution obtained by mixing all these materials with various known dispersers such as a bead mill. Further, the above kneader / disperser may be used in combination. Among these, the production through the kneading step is preferable in that the resin is easily adsorbed stably on the pigment surface, and therefore the production time of the aqueous pigment dispersion is short and the production efficiency is improved.

  In order to prepare the aqueous pigment dispersion of the present invention using the above raw materials, titanium oxide that has been surface-treated with alumina and silica in advance, and the treatment amount with alumina is 35 to 80% by mass of the total treatment amount of alumina and silica. In contrast, a surface treatment step of surface treatment with a silane coupling agent is performed, and the titanium oxide surface-treated with the silane coupling agent, a resin containing an anionic group, a water-soluble organic solvent, and a basic compound are contained. The mixture is dispersed by dispersing in an aqueous medium.

  The aqueous ink for inkjet recording of the present invention can be prepared and prepared by a conventional method using an aqueous pigment dispersion. Basically, for example, the aqueous pigment dispersion obtained as described above can be further diluted with an aqueous medium. When preparing an aqueous ink for inkjet recording using the aqueous pigment dispersion for inkjet recording of the present invention, coarse components generated or mixed in the process do not cause nozzle clogging or other deterioration of image characteristics. In addition, before or after the ink preparation, a process for further removing coarse particles by centrifugal separation or filtration treatment to reduce the number of coarse particles may be used. In order to prepare an ink jet recording ink from an aqueous pigment dispersion, the material to be further added is not particularly limited, and is a known organic solvent, surfactant, antioxidant, antifungal agent, anti-adhesive agent, A pH adjusting agent, etc. can be added. In the ink composition, it is preferable to add a wetting agent to the aqueous medium for diluting the aqueous pigment dispersion because it contributes to prevention of drying, viscosity adjustment, and concentration adjustment. In addition, it is preferable that a water-soluble organic solvent exhibiting permeability to the recording medium is blended to impart permeability to the ink composition. In the ink composition, the permeability is a characteristic necessary for adjusting the penetrability of the ink composition into the recording medium and the dot diameter on the recording medium.

  The water-based ink for ink-jet recording thus produced can be suitably used for various ink-jet printers as ink for ink-jet recording. Applicable ink jet methods are not particularly limited, but are on-demand types such as a continuous injection type such as a charge control type and a spray type, a piezo type, a thermal type and an electrostatic suction type, and well-known types. It can be illustrated. The water-based ink for ink jet recording of the present application enables extremely stable ink ejection when applied to these various ink jet methods, and can be suitably used particularly for thermal jet ink jet recording.

Examples and comparative examples are shown below.
(Example 1) 3 parts of vinyltriethoxysilane was added to 100 parts of surface-treated titanium oxide having an alumina: silica = 2: 3 mass ratio of alumina and silica present together with titanium oxide, and then in a ball mill. After taking out by hydration, heating, and mixing treatment, the mixture was further heated to remove moisture to obtain silane-coupled titanium oxide. Subsequently, 100 parts of titanium oxide surface-treated with the obtained silane coupling agent was used to prepare a mixture with the following composition, put in a polyethylene container together with 450 parts of zirconia beads, and shaken with a paint conditioner for 3 hours to form an aqueous pigment Dispersion A was obtained.
When the mass ratio of alumina and silica present on the surface of the titanium oxide used was measured using a scanning X-ray fluorescence analyzer (manufactured by ZSX Primus Rigaku), the amount of alumina was 38 of the total amount of alumina and silica. It was mass%.
100 parts of titanium oxide treated with silane coupling agent Styrene acrylic resin A
(Acid number 150, weight average molecular weight 10,000
Styrene / acrylic acid / methacrylic acid = 77/10/13) 8 parts 2-Pyrrolidone 32 parts Potassium hydroxide aqueous solution (8N) 3.53 parts Pure water 106.47 parts (Example 2) Styrene acrylic of Example 1 The resin A was changed to a styrene acrylic resin B having an acid value of 150, a weight average molecular weight of 12,000, and styrene / methyl methacrylate / acrylic acid / methacrylic acid = 30/47/10/13. An aqueous pigment dispersion F was obtained.

(Comparative Example 1) Surface treatment with a silane coupling agent was not performed on 100 parts of surface-treated titanium oxide having a mass ratio of alumina and silica present with titanium oxide of AL: Si = 2: 3, Otherwise in the same manner as in Example 1, an aqueous pigment dispersion B was obtained.
(Comparative Example 2) In place of the surface-treated titanium oxide having a mass ratio of alumina and silica existing with titanium oxide of AL: Si = 2: 3, 100 parts of titanium oxide not surface-treated with AL or Si were used. An aqueous pigment dispersion C was obtained in the same manner as in Example 1 except for using.
Comparative Example 3 Oxidation with the same mass ratio of AL: Si = 1: 2 instead of surface-treated titanium oxide with a mass ratio of alumina and silica present with titanium oxide of AL: Si = 2: 3 An aqueous pigment dispersion D was obtained in the same manner as in Example 1 except that titanium was used. When the mass ratio of alumina and silica present on the surface of the used titanium oxide was measured in the same manner as in Example 1, the amount of alumina was 29% by mass of the total amount of alumina and silica.
(Comparative example 4) Instead of the surface-treated titanium oxide in which the mass ratio of alumina and silica present with titanium oxide is AL: Si = 2: 3, titanium oxide surface-treated with only alumina is used. In the same manner as in Example 1, an aqueous pigment dispersion E was obtained.

In addition, in order to check the particle size stability and non-sedimentability of the obtained dispersion, the particle size stability after 2 weeks at 60 ° C. and the tendency to settle after 2 weeks at room temperature were measured. Furthermore, the zeta potential and the scattered light reduction rate, which have a large effect on dispersion stability, were measured. The measurement method is shown below.
[Initial dispersion particle size and particle size stability]
The aqueous pigment dispersions prepared in Examples and Comparative Examples were diluted about 2000 times with pure water, and the volume average particle size at the time of preparation of the aqueous pigment dispersion was determined using Microtrac UPA-150 (manufactured by Nikkiso Co., Ltd.). This was measured and used as the initial dispersed particle size. The aqueous pigment dispersion is allowed to stand in a constant temperature layer at 60 ° C. for 2 weeks, then the volume average particle size is measured by the same method to calculate the rate of increase in particle size, and evaluation is performed according to the following evaluation criteria.
○: Increase in particle size is less than 20%
X: Particle size increase rate is 20% or more and less than 50%
XX: Particle size increase rate is 50% or more

[Sedimentation tendency]
The aqueous pigment dispersions prepared in Examples and Comparative Examples were placed in a glass bottle having a capacity of 10 ml, and after stored at 25 ° C. for 1 week, the tendency to settle to the bottom was visually evaluated according to the following criteria.
○: No sedimentation is observed
Δ: Slight settling is observed
X: It is clear that there is sedimentation
XX: Very much sedimentation

[Zeta potential]
The aqueous pigment dispersions prepared in Examples and Comparative Examples were diluted to a titanium oxide concentration of 1%, and DT1200 (manufactured by Nippon Luft Co., Ltd.) was used to measure the zeta potential of titanium oxide in the dispersion.
[Scattered light reduction rate]:
The aqueous pigment dispersions prepared in Examples and Comparative Examples were diluted with water to a titanium oxide concentration of 1% to prepare a dispersion sample, which was left at 25 ° C. and light scattering 2 cm below the liquid surface every 2 hours. The rate (%) was measured by Turbiscan Lab (manufactured by Formulaction), and the reduction rate of scattered light per unit time was determined. A smaller value indicates that light scattering by the titanium oxide particles does not decrease (titanium oxide does not settle).
Table 1 shows the measurement results of the aqueous pigment dispersions prepared in the above Examples and Comparative Examples.

From the above results, the surface of the titanium oxide is used so that the amount of alumina present with the titanium oxide exceeds 35% by mass of the total amount of alumina and silica present with the titanium oxide. % Of the silane coupling agent was further subjected to surface treatment, and a dispersion having an anionic group adsorbed on the pigment and dispersed in an aqueous medium (Example 1) had a particle size stability. Good and excellent non-sedimentation by visual inspection. This can be confirmed also by the measured value of the zeta potential, and this can also be confirmed by the scattered light reduction rate actually left at 25 ° C.
In Comparative Example 1 using the same alumina / silica-treated titanium oxide as used in Example 1 and not using the silane coupling agent, the resin was not sufficiently adsorbed on the pigment surface, This results in a decrease in diameter stability. Further, when titanium oxide not subjected to alumina / silica treatment is used, as shown in Comparative Example 2, even if the treatment with the silane coupling agent is performed, the adsorption of the coupling agent and the resin are not sufficiently performed. It can be seen that the particle size stability is poor and the sedimentation is large.
Furthermore, in Comparative Example 3 in which the alumina present together with titanium oxide was 35% by mass or less of the total amount of alumina and silica present together with titanium oxide, the acid content due to a large amount of Si and the resin in the resin as described above. Due to the repulsion of the anionic group, the adsorption of the resin to the titanium oxide surface does not proceed well and the particle size stability can be maintained, but the initial dispersed particle size increases and the non-sedimentation results. It is thought.
In Comparative Example 4 using titanium oxide surface-treated only with alumina, a certain amount of silane coupling agent adsorption and resin adsorption are performed, and particle size stability is good. However, since strong hydrophilicity by AL-OH remains, the progress of the adsorption of the resin is hindered, and it is considered that the precipitation has not been effectively suppressed.

  The white aqueous dispersion or ink according to the present invention is suitably used not only for printing on the underlying white paper, but also for printing for inkjet printing on cloth / fibers with a lot of black and dark colors, or transparent films / colored plastics, etc. Is done.

Claims (11)

An aqueous pigment dispersion containing titanium oxide, an anionic group-containing resin, a water-soluble organic solvent, and a basic compound, wherein the titanium oxide is surface-treated with a silane coupling agent after surface treatment with alumina and silica. An aqueous pigment dispersion, wherein the ratio of the amount of alumina treated is 35% by mass or more and 80% by mass or less of the total amount of the surface treated by alumina and silica. An aqueous pigment dispersion containing titanium oxide, an anionic group-containing resin, a water-soluble organic solvent, and a basic compound, wherein the titanium oxide surface is coated with alumina and silica, and is further coated with a silane coupling agent. The aqueous pigment dispersion characterized in that the alumina which is treated and coats the titanium oxide is 35% by mass or more and 80% by mass or less based on the total amount of alumina and silica coating the titanium oxide. The aqueous pigment dispersion according to claim 1 or 2, wherein the titanium oxide has an average particle size of 100 to 500 nm. The aqueous pigment dispersion according to any one of claims 1 to 3, wherein the silane coupling agent used for the surface treatment is 1 to 10% by mass of titanium oxide. The silane coupling agent has the following general formula (1) having a hydrolyzable group that reacts with a hydroxyl group and an organic functional group.

(1)
(In the formula, (R 1) (R 2) (R 3) and (R 4) are each independently any one of a hydrogen atom, an alkoxy group, a hydroxy group, a chloro group, and an organic group, at least one of which is an alkoxy group, a hydroxy group And at least one is an organic group.
a, b. c and d are integers of 0 to 3, and a + b + c + d = 4. )
The aqueous pigment dispersion according to any one of claims 1 to 4, which is an organosilicon compound having the following structure. In the general formula (1), at least one of (R1) (R2) (R3) and (R4) is a chloro group, a methoxy group, or an ethoxy group, and (R1) (R2) (R3) and ( The aqueous pigment dispersion according to claim 5, wherein at least one of R4) is a vinyl group. The aqueous pigment dispersion according to claim 5, wherein the silane coupling agent is one of vinyltrimethoxysilane and vinyltriethoxysilane. The resin having an anionic group is a styrene acrylic acid copolymer, and has an acid value of 50 to 250, a weight average molecular weight of 5000 to 40000, and a composition of 20% by mass or more based on the total amount of all constituent monomers. The aqueous pigment dispersion according to any one of claims 1 to 7, which contains a ratio of styrene monomer. A water-based ink for ink-jet recording, comprising the water-based pigment dispersion according to claim 1. Titanium oxide previously surface-treated with alumina and silica, and the alumina present together with the titanium oxide is 35% by mass or more and 80% by mass or less with respect to the total amount of alumina and silica present together with the titanium oxide. Surface treatment process for surface treatment with silane coupling agent for titanium oxide,
Dispersing step of dispersing a mixture containing titanium oxide surface-treated with the silane coupling agent, an anionic group-containing resin, a water-soluble organic solvent, and a basic compound, and an aqueous pigment dispersion Liquid manufacturing method. The resin having an anionic group is a styrene acrylic acid copolymer, and has an acid value of 75 to 200, a weight average molecular weight of 5000 to 40000, and a composition of 20% by mass or more based on the total amount of all constituent monomers. The method for producing an aqueous pigment dispersion according to claim 10, comprising a ratio of styrene monomers.