JP7083036B2 - Inkjet Pigment Dispersant, Inkjet Aqueous Pigment Dispersion, Inkjet Aqueous Ink Composition, and Image Forming Method - Google Patents

Description

The present invention relates to an inkjet pigment dispersant, an inkjet aqueous pigment dispersion, an inkjet aqueous ink composition, and an image forming method.

As an image recording method for forming an image on a recording medium such as paper based on an image data signal, there are recording methods such as an electrophotographic method, a sublimation type and a molten type thermal transfer method, and an inkjet method.

Since the inkjet recording method does not require a printing plate and ejects ink only to the image forming portion to form an image directly on the recording medium, the ink can be used efficiently and the running cost is low. Further, in the inkjet recording method, the printing device is relatively low in cost as compared with the conventional printing machine, can be miniaturized, and has less noise. As described above, the inkjet recording method has various advantages over other image recording methods.

Dyes have been used as coloring materials in water-based inks of inkjet printers. However, in the water-based ink using a dye, bleeding of an image is likely to occur, and there are restrictions on improvement of light resistance and water resistance. In order to overcome these drawbacks, water-based inks using pigments as coloring materials have been used in recent years. In water-based inks using pigments, it is necessary to stably disperse the pigments in an aqueous medium. Therefore, the water-based ink and the pigment dispersion as a raw material thereof use a pigment dispersant to improve the dispersibility and dispersion stability of the pigment. As this pigment dispersant, a polymer having both a structural portion having adsorptivity to a pigment (pigment adsorptive portion) and a structural portion having a high affinity with an aqueous medium (aqueous medium affinity portion) is used.

There are many reports on pigment dispersants. For example, Patent Document 1 describes a pigment dispersant containing a polyurethane having a specific structure, which has a structure derived from a vinyl polymer in the side chain and has an acid value of 20 to 80. In Patent Document 1, by using this pigment dispersant as a pigment dispersant for an inkjet recording water-based ink, the obtained ink can be made excellent in pigment dispersibility and ejection stability, and also. It is described that the scratch resistance of the formed printed matter is also enhanced.

Further, Patent Document 2 describes a hydrophobic polymer diol obtained by polymerizing a styrene-based monomer and / or a (meth) acrylic-based monomer in the presence of a chain transfer agent containing one mercapto group and two hydroxyl groups. Acrylic-urethane resin containing a carboxyl group having a structure in which a hydrophilic polymer diol obtained by polymerizing (meth) acrylic acid in the presence of the above chain transfer agent and an organic diisocyanate are reacted is described. .. According to Patent Document 2, by using this resin for preparing a water-based ink for inkjet recording containing a pigment and a basic substance, the obtained water-based ink has excellent storage stability even when stored at high temperature for a long time. However, it is said that the colored image can be excellent in color development.

International Publication No. 2017/169840 Japanese Unexamined Patent Publication No. 2005-239847

In the inkjet recording method, a white recording medium such as a paper medium is generally used, and in order to form an image portion on the recording medium, usually three colors of red, blue and yellow or black is added thereto. Four colors of ink are used. However, in recent years, there has been an increasing demand for forming an image on this recording medium using a colored recording medium. In this case, as the ink, a white ink is also used in addition to the above-mentioned colored ink. Further, when an image is formed on a transparent or light-colored recording medium, white ink is applied in advance to a region on the recording medium to which colored ink is applied (so-called white ink) to enhance the sharpness of the formed image. Is done. The white ink applied to such a colored recording medium or a transparent or light color recording medium is required to have high hiding power.

A metal oxide is generally used as a white pigment which is a coloring material for white ink. In order to realize high hiding power with the white pigment made of this metal oxide, it is necessary to increase the particle size of the white pigment to some extent. However, white pigments made of metal oxides tend to have a large specific gravity as a whole, and white inks in which white pigments having a large particle size are dispersed tend to cause the pigments to settle easily, and once the pigments have settled, they are redispersed. There is a problem that it is difficult.

As a result of studies on conventional pigment dispersants including the pigment dispersants described in the above patent documents, the present inventors have made advanced demands in recent years even if these pigment dispersants are applied as pigment dispersants in white inks. The storage stability (dispersion stability) cannot be fully satisfied, and when this white ink is actually ejected by the inkjet method, the ejection rate when the white ink is ejected, left for a while, and then ejected again. It has been found that it tends to be inferior to (nozzle neglect-recoverability).

Therefore, the present invention sufficiently enhances the dispersibility of the pigment in an aqueous medium and disperses the pigment with excellent storage stability even when applied to a pigment having a larger particle size or a pigment having a higher specific gravity. To provide a pigment dispersant for inkjet, which can provide a substance and a water-based ink composition, and can sufficiently enhance the neglect-recoverability of a nozzle when the water-based ink composition is applied to an inkjet recording method. Make it an issue. Another object of the present invention is to provide an inkjet water-based pigment dispersion and an inkjet water-based ink composition in which a pigment is dispersed in an aqueous medium by the action of the pigment dispersant. Further, it is an object of the present invention to provide an image forming method using this water-based ink composition for inkjet.

上記式（１）及び（２）中、Ｒ^１ａ及びＲ^１ｂは水素原子又は炭素数１～４のアルキル基を示す。Ａ^１は－Ｏ－又は－ＮＲ^Ａ－を示す。Ｒ^Ａは水素原子または置換基を示す。Ｌ^１ａ及びＬ^１ｂは芳香族基、ベンジル基又は炭素数４以上のアルキル基を示す。

〔２〕

上記ポリマーの酸価が９０ｍｇＫＯＨ／ｇ以上２００ｍｇＫＯＨ／ｇ以下である、〔１〕記載のインクジェット用顔料分散剤。

〔３〕

上記ポリマー中に占める上記ポリビニル化合物構造部の割合が７０質量％以下である、〔１〕又は〔２〕記載のインクジェット用顔料分散剤。

〔４〕

上記ポリウレタン構造部が、下記式（３）、下記式（４）、及び下記式（５）で表される構成成分の少なくとも１種を含有する、〔１〕～〔３〕のいずれか記載のインクジェット用顔料分散剤。

上記式（３）、（４）、及び（５）中に示された環構造は芳香族環又は脂肪族環を示す。Ｌ^３～Ｌ^５は単結合又は２価の連結基を示す。Ｘ^３、Ｘ^４及びＸ^５は－Ｏ－＊、－ＮＨＣＯ－＊を示し、＊はポリマー中に組み込まれるための連結部位を示す。Ｒ^３～Ｒ^５は置換基を示す。ｎは０以上の整数である。Ａ^５は－Ｎ＝又は－ＣＨ＝を示す。Ｚは単結合又は２価の連結基を示す。Ｌ^３～Ｌ^５及びＺが２価の連結基の場合、この２価の連結基はウレタン結合を有さず、かつ環構造を有しない。

〔５〕

上記ポリマーがポリビニル化合物構造部にカルボキシ基を有する、〔１〕～〔４〕のいずれか記載のインクジェット用顔料分散剤。

〔６〕

白色顔料の分散剤として用いる、〔１〕～〔５〕のいずれか記載のインクジェット用顔料分散剤。

〔７〕

上記白色顔料が酸化チタンである、〔６〕記載のインクジェット用顔料分散剤。

〔８〕

上記酸化チタンがシリカ、アルミナ及び有機物の少なくとも１種により表面処理されている、〔７〕記載のインクジェット用顔料分散剤。

〔９〕

〔１〕～〔８〕のいずれか記載のインクジェット用顔料分散剤と、顔料と、水性媒体とを含有するインクジェット用水性顔料分散物。

〔１０〕

〔１〕～〔８〕のいずれか記載のインクジェット用顔料分散剤と、顔料と、水性媒体とを含有するインクジェット用水性インク組成物。

〔１１〕

〔１０〕記載のインクジェット用水性インク組成物を、インクジェット方式により記録媒体上に付与することを含む、画像形成方法。

That is, the above-mentioned problems of the present invention have been solved by the following means.

[1]

An inkjet pigment dispersant containing a polymer having a polyvinyl compound structure and a polyurethane structure.

In the polyvinyl compound structure, the total content of the constituents represented by the following formula (1) or the following formula (2) is 30% by mass or less, and the acid value of the polymer exceeds 80 mgKOH / g. Pigment dispersant for.

In the above formulas (1) and (2), R ^1a and R ^1b represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. A ¹ indicates -O- or -NR ^A- . ^RA indicates a hydrogen atom or a substituent. L ^1a and L ^1b represent an aromatic group, a benzyl group, or an alkyl group having 4 or more carbon atoms.

[2]

The inkjet pigment dispersant according to [1], wherein the acid value of the polymer is 90 mgKOH / g or more and 200 mgKOH / g or less.

[3]

The pigment dispersant for inkjet according to [1] or [2], wherein the proportion of the polyvinyl compound structural portion in the polymer is 70% by mass or less.

[4]

The description of any of [1] to [3], wherein the polyurethane structure contains at least one of the constituents represented by the following formula (3), the following formula (4), and the following formula (5). Inkjet pigment dispersant.

The ring structure shown in the above formulas (3), (4), and (5) represents an aromatic ring or an aliphatic ring. L ³ to L ⁵ indicate a single bond or a divalent linking group. X ³ , X ⁴ and X ⁵ indicate -O- *, -NHCO- *, and * indicates a linking site for incorporation into the polymer. R ³ to R ⁵ indicate substituents. n is an integer of 0 or more. ^A5 indicates -N = or -CH =. Z represents a single bond or a divalent linking group. When L ³ to L ⁵ and Z are divalent linking groups, the divalent linking group does not have a urethane bond and does not have a ring structure.

[5]

The inkjet pigment dispersant according to any one of [1] to [4], wherein the polymer has a carboxy group in the polyvinyl compound structure.

[6]

The inkjet pigment dispersant according to any one of [1] to [5], which is used as a dispersant for white pigments.

[7]

The inkjet pigment dispersant according to [6], wherein the white pigment is titanium oxide.

[8]

The inkjet pigment dispersant according to [7], wherein the titanium oxide is surface-treated with at least one of silica, alumina and an organic substance.

[9]

An inkjet pigment dispersion containing the inkjet pigment dispersant according to any one of [1] to [8], a pigment, and an aqueous medium.

[10]

An inkjet water-based ink composition containing the inkjet pigment dispersant according to any one of [1] to [8], a pigment, and an aqueous medium.

[11]

[10] An image forming method comprising applying the water-based ink composition for inkjet according to [10] onto a recording medium by an inkjet method.

As used herein, the polyvinyl compound structural part means a structural part formed of a polymer obtained by polymerizing a compound having a vinyl group. As used herein, the term "vinyl group" is used in a broader sense than usual. That is, it is used to include all groups having a carbon-carbon double bond. As an example, in addition to "CH ₂ = CH-", "CH ₂ = CR ^B- " (RB is a substituent) is also included in the vinyl ^group in the present specification.

In the present specification, unless otherwise specified, when there are a plurality of substituents, linking groups, repeating units, etc. (hereinafter referred to as substituents, etc.) indicated by a specific reference numeral, or a plurality of substituents, etc. are simultaneously or selected. When defined uniformly, the substituents and the like may be the same or different from each other. This also applies to the regulation of the number of substituents and the like.

In the present specification, the numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value.

The inkjet pigment dispersant of the present invention sufficiently enhances the dispersibility of the pigment in an aqueous medium and has storage stability even when applied to a pigment having a larger particle size or a pigment having a higher specific gravity. It is possible to provide an excellent water-based pigment dispersion and a water-based ink composition. Further, the water-based inkjet pigment dispersion and the water-based ink composition for inkjet of the present invention are excellent in dispersion stability of the pigment due to the action of the above-mentioned water-based inkjet pigment dispersant, and are excellent in storage stability. Further, the water-based ink composition for inkjet of the present invention can sufficiently enhance the neglect-recoverability of the nozzle in the inkjet recording method. Further, according to the image forming method of the present invention, a high-precision image can be repeatedly and stably formed by an inkjet method.

Preferred embodiments of the inkjet pigment dispersant, the inkjet aqueous pigment dispersion, the inkjet aqueous ink composition, and the image forming method of the present invention will be described in order.

[Inkjet pigment dispersant]

The inkjet pigment dispersant of the present invention (hereinafter, also referred to as “dispersant of the present invention”) includes a polymer having a polyvinyl compound structure portion and a polyurethane structure portion. The content of the constituent component represented by the following formula (1) or (2) in the polyvinyl compound structure constituting this polymer is 30% by mass or less, and the acid value of the polymer exceeds 80 mgKOH / g.

In the polymer constituting the dispersant of the present invention (hereinafter, also referred to as “polymer of the present invention”), the polyurethane structural portion preferably functions as an adsorptive structural portion for pigments, and the polyvinyl compound structural portion is an aqueous medium. It is preferable that the structure functions as a structure having a high affinity with the above.

In the formulas (1) and (2), R ^1a and R ^1b represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. When the number of carbon atoms of this alkyl group is 3 or 4, it may be linear or have a branch.

R ^1a and R ^1b are preferably hydrogen atoms or methyl.

A ¹ indicates -O- or -NR ^A- . ^RA indicates a hydrogen atom or a substituent. When ^RA is a substituent, examples of the substituent include a substituent that can be taken as R ² described later.

L ^1a and L ^1b represent an aromatic group, a benzyl group, or an alkyl group having 4 or more carbon atoms. Of these, the alkyl group having 4 or more carbon atoms may contain at least one of —O—, —S— and ^−NR2- in the carbon chain, and such a structure is also defined in the present invention as “carbon”. It is included in "alkyl groups of several 4 or more". Here, R ² indicates a hydrogen atom or a substituent, and when R ² contains a carbon atom, this carbon atom is not included in the carbon number of the "alkyl group having 4 or more carbon atoms".

Further, the alkyl group having 4 or more carbon atoms which can be taken as L ^1a and L ^1b may have a substituent. Examples of this substituent include aromatic groups. When an alkyl group having 4 or more carbon atoms which can be taken as L ^1a and L ^1b has a substituent, the carbon atom of this substituent shall not be included in the carbon number of the "alkyl group having 4 or more carbon atoms". ..

Alkyl groups having 4 or more carbon atoms that can be taken as L ^1a and L ^1b usually have 20 or less carbon atoms.

When R ² is a substituent, this substituent is, for example, a hydrocarbon group. The number of carbon atoms of this hydrocarbon group is preferably, for example, 1 to 20, and may be 1 to 12, or may be 1 to 8. When R ² is a hydrocarbon group, it may be a cyclic group or a chain group. This hydrocarbon group is, for example, an alkyl group. This alkyl group may be linear or may have a branch.

It is more preferable that the constituents represented by the formulas (1) and (2) do not have a dissociative group. The dissociative group means a group having a hydrogen atom and the hydrogen atom dissociating by the action of a base. Specific examples of the dissociative group include a phenolic hydroxyl group, a mercapto group, a carboxy group, a phosphonyl group, a phosphoryl group, a sulfo group, and a borate group.

The content of the constituent component represented by the above formula (1) or (2) in the polyvinyl compound structure constituting the polymer of the present invention is 30% by mass or less, preferably 25% by mass or less, preferably 20% by mass. The following is more preferable. Further, the content of the constituent component represented by the above formula (1) or (2) in the polyvinyl compound structural part constituting the polymer of the present invention is more preferably 15% by mass or less, further more preferably 10% by mass or less. It is preferable that 5% by mass or less is particularly preferable, and the component represented by the above formula (1) or (2) is not contained in the polyvinyl compound structural part, that is, 0% by mass is most preferable.

As described above, by setting the content of the constituent component represented by the above formula (1) or (2) in the polyvinyl compound structure portion to a certain amount or less, the hydrophobicity having a high affinity with the pigment in the polyvinyl compound structure portion. The proportion of the sex structure can be suppressed, and the polyvinyl compound structure portion can be effectively functioned as an aqueous medium affinity portion.

The acid value of the polymer of the present invention exceeds 80 mgKOH / g. By using a polymer having such an acid value, charge repulsion between the portions having an acidic group works effectively in a state where the polymer is adsorbed on the surface of the pigment, and the dispersibility of the pigment can be further enhanced. The acid value of the polymer of the present invention is preferably 90 mgKOH / g or more and 200 mgKOH / g or less.

Since the polymer of the present invention is used as a pigment dispersant by increasing the solubility in an aqueous medium and effectively eliciting the charge repulsion of the acidic group of the polymer in the aqueous medium, the acidic group of the polymer is usually used. Is used as an alkali-neutralized salt. That is, in the present invention, the "pigment dispersant for inkjet containing a polymer having a polyvinyl compound structure and a polyurethane structure" means that the "pigment dispersant for inkjet" has a "polyvinyl compound structure and a polyurethane structure". It means that it is composed of a polymer in which the acidic group of "polymer" is neutralized into a salt state.

Further, the acid value of the polymer of the present invention described above is not measured in the state where the acidic group is in the salt state, but is measured in the form where the acidic group has a hydrogen atom (acid value before neutralization). For example, the acid value of the polymer of the present invention can be measured in a state where the pH of the solution of the polymer is acidified to pH 5 or less with a 0.1 M HCl aqueous solution.

The acid value of the polymer is calculated according to JIS K0070 and converted as 1 mmol / g = 56.1 mgKOH / g.

The polymer of the present invention preferably has a polyvinyl compound structure having an acidic group. With such a structure, the polyurethane structure can be used as a pigment-adsorbing group, and the polyvinyl compound structure can be used as an aqueous medium-affinitive part to more effectively separate the functions. As a result, in addition to the charge repulsion of the polyvinyl compound structure part, the polyvinyl compound structure part easily extends into the aqueous medium, and the steric repulsion of the polyvinyl compound structure part also works effectively to enhance the dispersibility of the pigment more effectively. Can be done.

In the present invention, the acidic group is a substituent having a dissociative proton and has a pKa of 11 or less. The pKa of the acidic group is J. Phys. Chem. It can be obtained according to the "SMD / M05-2X / 6-31G ^* " method described in A2011, 115, 6641-6645. Examples of the acidic group include groups exhibiting acidity such as a carboxy group, a phosphonyl group, a phosphoryl group, a sulfo group, and a borate group, and a carboxy group is preferable.

The polyurethane structure preferably has no acidic group, more preferably no dissociative group.

The ratio of the polyvinyl compound structure portion in the polymer of the present invention can be appropriately set as long as the effect of the present invention is not impaired. From the viewpoint of further enhancing the dispersibility of the pigment, the proportion of the polyvinyl compound structural portion in the polymer is preferably 70% by mass or less, and more preferably 65% by mass or less. From the same viewpoint, the proportion of the polyvinyl compound structural portion in the polymer is preferably 20% by mass or more, more preferably 30% by mass or more, further preferably 35% by mass or more, and particularly preferably 40% by mass or more.

The polyurethane structural portion constituting the polymer of the present invention preferably contains at least one of the constituent components represented by any of the following formulas (3) to (5).

The ring structure shown in the formulas (3) to (5) represents an aromatic ring or an aliphatic ring. These rings are monocyclic. The aromatic ring may be an aromatic hydrocarbon ring or an aromatic heterocycle, and an aromatic hydrocarbon ring is preferable. The number of ring-constituting atoms of the ring structure shown in the formulas (3) to (5) is preferably 3 to 10, more preferably 4 to 8, further preferably 5 or 6, and particularly preferably 6.

L ³ to L ⁵ indicate a single bond or a divalent linking group. When L ³ to L ⁵ are divalent linking groups, the divalent linking group does not have a urethane bond. Further, L ³ to L ⁵ do not have a ring structure. The divalent linking group that can be taken as L ³ to L ⁵ can be, for example, a divalent linking group having a molecular weight of 10 to 300. The divalent linking group that can be taken as L ³ to L ⁵ is preferably an alkylene group. This alkylene group may be linear or branched. The alkylene group preferably has 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, and even more preferably 1 to 3 carbon atoms.

X ³ , X ⁴ and X ⁵ indicate -O- *, -NHCO- *, and * indicates a linking site for incorporation into the polymer. That is, X ³ , X ⁴ and X ⁵ are groups that form part of the urethane bond.

R ³ to R ⁵ indicate a substituent, and n is an integer of 0 or more. The upper limit of n is the maximum number of substituents that the ring-constituting atom of the ring structure can have. The substituent that can be taken as R ³ to R ⁵ is preferably an alkyl group, an alkoxy group, an alkenyl group, or an alkynyl group.

When the substituents that can be taken as R ³ to R ⁵ have a carbon chain, the carbon chain may contain at least one of —O—, —S— and ^—NR2- in the carbon chain. R ² is synonymous with R ² described above.

The alkyl group and alkoxy group that can be taken as R ³ to R ⁵ have preferably 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, still more preferably 1 to 3 carbon atoms, and even more preferably methyl.

The alkenyl group and alkynyl group that can be obtained as R ³ to R ⁵ preferably have 2 to 10 carbon atoms, more preferably 2 to 6 carbon atoms, and even more preferably 2 to 3 carbon atoms.

n is preferably 0 to 8, more preferably 0 to 6, further preferably 0 to 4, and particularly preferably 0 to 3.

^A5 indicates -N = or -CH =.

The constituents represented by any of the formulas (3) to (5) preferably have no acidic group, and more preferably no dissociative group.

Z represents a single bond or a divalent linking group. When Z is a divalent linking group, this divalent linking group does not have a urethane bond. Further, Z does not have a ring structure. As the divalent linking group that can be taken as Z, for example, a divalent linking group having a molecular weight of 10 to 300 can be adopted. The divalent linking group that can be taken as Z is preferably an alkylene group. This alkylene group may be linear or branched. The alkylene group preferably has 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, and even more preferably 1 to 3 carbon atoms.

In the polyurethane structure constituting the polymer of the present invention, the total content of the constituents represented by any of the above formulas (3) to (5) is preferably 30% by mass or more, more preferably 50% by mass or more. It is preferable, and more preferably 70% by mass or more.

Further, it is also preferable that all of the polyurethane structural parts are composed of the constituent components represented by any of the above formulas (3) to (5). That is, it is also preferable that all of the diisocyanate component and the diol component constituting the polyurethane structure are components represented by any of the above formulas (3) to (5).

In the polymer of the present invention, the content of the polyurethane structure is preferably 30% by mass or more, more preferably 35% by mass or more, from the viewpoint of further enhancing the dispersibility of the pigment. From the same viewpoint, the content of the polyurethane structure in the polymer of the present invention is preferably 80% by mass or less, more preferably 70% by mass or less, further preferably 65% by mass or less, and particularly preferably 60% by mass or less.

The polymer of the present invention may have at least one polyvinyl compound structure and one polyurethane structure in one polymer molecule. It is also preferable to have a plurality of polyvinyl compound structural parts or a plurality of polyurethane structural parts in one molecule of the polymer, and it is also possible to have a plurality of both structural parts.

In the polymer of the present invention, the arrangement of the polyvinyl compound structure portion and the polyurethane structure portion is not particularly limited as long as the effect of the present invention is not impaired. For example, (a) a block copolymer composed of a polyvinyl compound structure part and a polyurethane structure part can be used. Further, (b) a graft polymer in which one of the polyvinyl compound structure and the polyurethane structure (X) is bonded to the other structure (Y) as a graft chain can also be used. Further, another X may be bound to the graft chain of (c) and (b), or the X bound to the graft chain may be bound to another Y.

In the present invention, the term "graft polymer" broadly means a form in which one structural part (X) is bonded to the other structural part (Y) as a graft chain, and another chain is bonded to this graft chain. , Even if a crosslinked structure is formed via the graft chain, it is included in the "graft polymer". Therefore, for example, the above (c) is a graft polymer.

When a plurality of polyvinyl compound structures are contained in one molecule of the polymer, the plurality of polyvinyl compound structures may have the same structure or different structures. Further, when a plurality of polyurethane structures are provided in one molecule of the polymer, the plurality of polyurethane structures may have the same structure or different structures. From the viewpoint of ease of synthesis, it is preferable that the plurality of polyvinyl compound structural parts have the same structure as each other, and the plurality of polyurethane structural parts also have the same structure as each other.

Here, "the same structure as each other" means that (i) the types of constituents, (ii) the molar ratio of the constituents, and (iii) the arrangement of the constituents (random or block) are all the same. ..

In the polymer of the present invention, the weight average molecular weight (Mw) of the polyvinyl compound structure can be, for example, 1000 to 20000. Further, the Mw of the polyurethane structure portion can be, for example, 3000 to 30,000.

In the present specification, the weight average molecular weight (Mw) means a value measured by gel permeation chromatography (GPC) unless otherwise specified.

For the measurement by gel permeation chromatography (GPC), HLC (registered trademark) -8020GPC (Tosoh Corporation) was used as the measuring device, and TSKgel (registered trademark) Super Multipore HZ-H (4.6 mm ID ×) was used as the column. Use 3 bottles of 15 cm, Tosoh Corporation, and use THF (tetrahydrofuran) as the eluent. The measurement conditions are a sample concentration of 0.45% by mass, a flow velocity of 0.35 ml / min, a sample injection amount of 10 μl, and a measurement temperature of 40 ° C., using an RI detector.

The calibration curve is "Standard sample TSK standard, polystyrene": "F-40", "F-20", "F-4", "F-1", "A-5000", "A" of Tosoh Corporation. It is made from 8 samples of "-2500", "A-1000", and "n-propylbenzene".

Next, the pigment to which the dispersant of the present invention is applied will be described.

<Pigment>

As the pigment to which the dispersant of the present invention is applied, ordinary organic pigments or inorganic pigments can be used.

Examples of the organic pigment include an azo pigment, a polycyclic pigment, a dye chelate, a nitro pigment, a nitroso pigment, and an aniline black. Among these, azo pigments or polycyclic pigments are preferable.

Examples of the azo pigment include azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments.

Examples of the polycyclic pigment include phthalocyanine pigment, perylene pigment, perinone pigment, anthraquinone pigment, quinacridone pigment, dioxazine pigment, indigo pigment, thioindigo pigment, isoindolinone pigment, and quinophthalone pigment.

Examples of the dye chelate include a basic dye type chelate and an acid dye type chelate.

Examples of the inorganic pigment include titanium oxide, iron oxide, zinc oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, carbon black and the like. Among these, titanium oxide and carbon black are preferable.

The amount of DBP absorbed by the carbon black pigment is not particularly limited, but is preferably 30 ml / 100 g or more and 200 ml / 100 g or less, and more preferably 50 ml / 100 g or more and 150 ml / 100 g or less, from the viewpoint of color tone and print density. .. The amount of DBP absorbed is measured by the JIS K6221 A method.

The BET specific surface area of the carbon black pigment is not particularly limited, but is preferably 30 m ² / g or more and 450 m ² / g or less, and 200 m ² / g or more and 400 m ² / g, from the viewpoint of print concentration and storage stability. The following is more preferable.

Examples of the carbon black pigment include those produced by a known method such as a contact method, a furnace method, and a thermal method.

具体例としては例えば、Ｒａｖｅｎ１２５０、Ｒａｖｅｎ１２００、Ｒａｖｅｎ１１９０ ＵＬＴＲＡ、Ｒａｖｅｎ１１７０、Ｒａｖｅｎ１２５５、Ｒａｖｅｎ１０８０ＵＬＴＲＡ、Ｒａｖｅｎ１０６０ＵＬＴＲＡ、Ｒａｖｅｎ１０４０、Ｒａｖｅｎ１０３５、Ｒａｖｅｎ１０２０、Ｒａｖｅｎ１０００、Ｒａｖｅｎ９００、Ｒａｖｅｎ８９０、Ｒａｖｅｎ８５０、Ｒａｖｅｎ７８０ＵＬＴＲＡ、Ｒａｖｅｎ８６０Ｕｌｔｒａ、Ｒａｖｅｎ５２０、Ｒａｖｅｎ５００、Ｒａｖｅｎ４５０、Ｒａｖｅｎ４６０、Ｒａｖｅｎ４１５、Ｒａｖｅｎ１４ , Conductex 7055 Ultra (above, Colombian Carbon), Regal400R, Regal330R, Regal660R, Mogul L, Black Pearls L, Regal99, Regal350, MONARCH280, MONARCH120, MONARCH120, MONARCH120, MONARCH120, MONARCH120 Ｐｒｉｎｔｅｘ３５、Ｐｒｉｎｔｅｘ Ｕ、Ｐｒｉｎｔｅｘ Ｖ、Ｐｒｉｎｔｅｘ１４０Ｕ、Ｐｒｉｎｔｅｘ１４０Ｖ、Ｐｒｉｎｔｅｘ３００、Ｐｒｉｎｔｅｘ２５、Ｐｒｉｎｔｅｘ２００、ＰｒｉｎｔｅｘＡ、ＰｒｉｎｔｅｘＧ、Ｓｐｅｃｉａｌ Ｂｌａｃｋ ５、Ｓｐｅｃｉａｌ Ｂｌａｃｋ ４Ａ、Ｓｐｅｃｉａｌ Ｂｌａｃｋ４、Ｓｐｅｃｉａｌ Ｂｌａｃｋ５５０、Ｓｐｅｃｉａｌ Ｂｌａｃｋ ３５０、Ｓｐｅｃｉａｌ Ｂｌａｃｋ２５０、Ｓｐｅｃｉａｌ Ｂｌａｃｋ１００、ＮＥＲＯＸ３５００、ＮＥＲＯＸ１０００、 NEROX2500 (above, manufactured by Evonik Degussa), No. 10, No. 20, No. 25, No. 33, No. 40, No. 45, No. 47, No. 52, No. 85, No. 95, No. 260, MA7, MA8, MA11, MA77, MA100, MA220, MA230, MA600 (all manufactured by Mitsubishi Chemical Corporation) and the like can be mentioned. However, it is not limited to these.

Further, specific examples of the pigment that can be used in the present invention include the pigments described in paragraphs 0142 to 0145 of JP-A-2007-170571.

The particle size of the organic pigment and carbon black is preferably 10 to 200 nm, more preferably 80 to 150 nm, still more preferably 90 to 120 nm. Here, the particle size of the pigment means the volume average particle size.

By setting the particle size of the organic pigment and carbon black to 200 nm or less, the color reproducibility when used in an aqueous ink composition can be improved. Further, by setting the particle size of the pigment in the pigment dispersion to 10 nm or more, the light resistance when used in an aqueous ink composition can be improved.

The particle size of the inorganic pigment, particularly the inorganic pigment used in the white ink, is preferably 150 to 400 nm, more preferably 200 to 300 nm.

By setting the particle size of the inorganic pigment used in the white ink to 150 nm or more, the concealing property when used in an aqueous ink composition can be improved.

The dispersant of the present invention is particularly suitable as a dispersant for white pigments (titanium oxide, barium sulfate, zinc oxide, etc.) in an aqueous medium. Generally, a white pigment having a relatively large particle size is used in order to improve hiding power and the like, and the specific gravity tends to be large. Therefore, white pigments generally tend to be inferior in dispersion stability. Even when the dispersant of the present invention is applied to such a white pigment, the dispersion stability of the pigment can be effectively enhanced.

The white pigment to which the dispersant of the present invention is applied is more preferably titanium oxide. The particle shape of titanium oxide is not particularly limited, and may be any shape such as granular and needle-shaped.

The crystal structure of titanium oxide is not particularly limited, and may be any of rutile type (tetragonal crystal), anatase type (tetragonal crystal) and brookite type (orthorhombic crystal).

Titanium oxide can be produced by a vapor phase method or a liquid phase method.

Titanium oxide is preferably surface-treated from the viewpoint of obtaining good dispersibility. The surface treatment may be such that at least a part or all of the particles have been treated. The surface treatment of titanium oxide is not particularly limited, and for example, surface treatment with at least one inorganic substance such as alumina, silica, zinc oxide, zirconia and magnesium oxide, titanium coupling agent, silane coupling agent, silicone oil and the like. Surface treatment with organic substances in the above can be mentioned. From the viewpoint of improving the hiding power, the titanium oxide used as the white pigment is preferably titanium oxide surface-treated with at least one of silica, alumina and an organic substance.

[Aqueous pigment dispersion for inkjet]

The aqueous pigment dispersion for inkjet of the present invention (hereinafter, also referred to as “dispersion of the present invention”) contains the dispersant of the present invention, a pigment, and an aqueous medium.

The dispersion of the present invention may further contain other components as needed. Examples of other components include water-soluble resins, water-dispersible resins, surfactants, pH adjusters, inorganic salts, organic salts and the like.

Each component constituting the dispersion of the present invention will be described in detail.

<Aqueous medium>

The aqueous medium used for the dispersion of the present invention (hereinafter referred to as aqueous medium (a)) is water or a mixed solution of water and a water-soluble organic solvent.

The amount of water is not particularly limited, and the content of water in the dispersion of the present invention is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 20% by mass or more, and more preferably 30% by mass or more. Especially preferable. The upper limit of the water content is not particularly limited, but is preferably 95% by mass or less, more preferably 90% by mass or less in the dispersion of the present invention.

The water-soluble organic solvent that can be contained in the aqueous medium (a) preferably has a solubility in water of 5% by mass or more at 20 ° C. Examples of the water-soluble organic solvent include alcohol compounds, ketone compounds, ether compounds, amide compounds, ditryl compounds, and sulfone compounds.

Among these, alcohol compounds include, for example, ethanol, isopropanol, n-butanol, t-butanol, isobutanol, 1-methoxy-2-propanol, diacetone alcohol, diethylene glycol, ethylene glycol, dipropylene glycol, propylene glycol, and Glycerin can be mentioned.

Examples of the ketone compound include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone.

Examples of the ether compound include dibutyl ether, tetrahydrofuran, dioxane, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, and polyoxypropylene glyceryl ether.

Examples of the amide compound include dimethylformamide and diethylformamide.

Examples of the nitrile compound include acetonitrile.

Examples of the sulfone compound include dimethyl sulfoxide, dimethyl sulfone, and sulfolane.

The content of the water-soluble organic solvent is preferably 3 to 50% by mass, more preferably 4 to 45% by mass, still more preferably 5 to 40% by mass in the dispersion of the present invention.

The dispersion of the present invention may contain a water-soluble organic solvent alone or in combination of two or more. When the dispersion of the present invention uses two or more kinds of water-soluble organic solvents in combination, the above-mentioned content means the total content of the water-soluble organic solvents.

The content of the aqueous medium (a) in the dispersion of the present invention is preferably 20 to 90% by mass, more preferably 25 to 80% by mass, further preferably 30 to 75% by mass, and particularly preferably 35 to 70% by mass. preferable.

<Pigment>

The pigment contained in the dispersion of the present invention is the same as that described in the dispersant of the present invention.

The content of the pigment in the dispersion of the present invention can be, for example, 5 to 80% by mass, preferably 10 to 75% by mass, more preferably 20 to 70% by mass, still more preferably 25 to 65% by mass. ..

In the dispersion of the present invention, the ratio of the content of the pigment to the content of the dispersant of the present invention is not particularly limited as long as the pigment can be stably dispersed in the aqueous medium (a). Usually, the pigment: the dispersant of the present invention = 1: 0.01 to 1: 2 (mass ratio), and the pigment: the dispersant of the present invention = 1: 0.01 to 1: 1.5 (mass ratio). Pigment: dispersant of the present invention = 1: 0.02 to 1: 1 (mass ratio), and pigment: dispersant of the present invention = 1: 0.02 to 1: 1. It is more preferably 0.5 (mass ratio).

The viscosity of the dispersion of the present invention is usually 2 to 100 mPa · s, more preferably 3 to 50 mPa · s.

In this specification, the viscosity means a value measured at 25 ° C. using a viscometer. As the viscometer, for example, a VISCOMETER TV-22 type viscometer (manufactured by Toki Sangyo Co., Ltd.) can be used.

The pH of the dispersion of the present invention is preferably pH 6 to 11, more preferably pH 7 to 10, and even more preferably pH 7 to 9.

<Preparation of water-based pigment dispersion for inkjet>

The dispersion of the present invention can be obtained, for example, by mixing and treating at least the aqueous medium (a), the pigment, and the dispersion of the present invention to obtain the aqueous pigment dispersion of the present invention. This dispersion processing can be performed using various mixers. Examples of the mixer include ball mills, bead mills, planetary mixers, blade mixers, roll mills, kneaders, disc mills and the like.

The particle size of the organic pigment and carbon black dispersed in the dispersion of the present invention is preferably 80 to 120 nm, more preferably 90 to 110 nm. The particle size of the pigment in the dispersion of the present invention means the volume average particle size. The inorganic pigment dispersed in the dispersion of the present invention (for example, the particle size of titanium oxide used in white ink) is preferably 180 to 350 nm, more preferably 200 to 300 nm.

[Aqueous ink composition for inkjet]

The water-based ink composition for inkjet of the present invention (hereinafter, also referred to as “ink composition of the present invention”) may be the dispersion of the present invention itself, but is usually prepared using the dispersion of the present invention as a raw material. To. More specifically, it is preferable to prepare the ink composition of the present invention by mixing at least the dispersion of the present invention with an aqueous medium (hereinafter referred to as an aqueous medium (b)). The ink composition of the present invention contains, if necessary, a surfactant, a drying inhibitor (swelling agent), a coloring inhibitor, a penetration accelerator, an ultraviolet absorber, a preservative, a rust inhibitor, an antifoaming agent, and a viscosity. Additives such as regulators, pH regulators and chelating agents may be mixed. The mixing method is not particularly limited, and the commonly used mixing method can be appropriately selected to obtain the ink composition of the present invention.

The aqueous medium (b) has the same meaning as the aqueous medium (a), and the preferred embodiment is also the same. In the ink composition of the present invention, the content of the aqueous medium (total content of the aqueous mediums (a) and (b)) is preferably 10 to 99% by mass from the viewpoint of ink stability and ejection reliability. 30 to 80% by mass is more preferable, and 50 to 70% by mass is further preferable.

In the ink composition of the present invention, the pigment concentration is preferably 0.5 to 25% by mass, more preferably 1 to 15% by mass, from the viewpoint of image density.

The particle size of the organic pigment and carbon black dispersed in the ink composition of the present invention is preferably 80 to 120 nm, more preferably 90 to 110 nm. The particle size of the pigment in the ink composition means the volume average particle size. The particle size of titanium oxide used in the inorganic pigment dispersed in the ink composition of the present invention, particularly the white ink, is preferably 180 to 350 nm, more preferably 200 to 300 nm.

The above-mentioned surfactant that can be contained in the ink composition of the present invention can be used, for example, as a surface tension adjusting agent.

As the above-mentioned surfactant, a compound having a structure having both a hydrophilic part and a hydrophobic part in the molecule can be effectively used, and an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and a nonion can be effectively used. Both a sex surfactant and a betaine-based surfactant can be used.

In the present invention, a nonionic surfactant is preferable from the viewpoint of suppressing ink droplet interference, and an acetylene glycol derivative (acetylene glycol-based surfactant) is more preferable.

Examples of the acetylene glycol-based surfactant include 2,4,7,9-tetramethyl-5-decyne-4,7-diol and 2,4,7,9-tetramethyl-5-decyne-4, Examples thereof include an alkylene oxide adduct of 7-diol, and at least one selected from these is preferable. Examples of commercially available products of these compounds include E series such as Orfin E1010 manufactured by Nissin Chemical Industry Co., Ltd.

From the viewpoint of satisfactorily ejecting the ink composition by an inkjet method, the above-mentioned surfactant is preferably contained in an amount within a range in which the surface tension of the ink composition can be adjusted to 20 to 60 mN / m, and more preferably the ink. The surface tension of the composition is contained in an amount in a range that can be adjusted to 20 to 45 mN / m, more preferably 25 to 40 mN / m.

Surface tension is measured under conditions of 25 ° C. using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.) and an aqueous ink composition.

When the ink composition of the present invention contains a surfactant, the content of the surfactant is not particularly limited, but is preferably 0.1% by mass or more, more preferably 0.1 to 10% by mass in the aqueous ink composition. %, More preferably 0.2 to 3% by mass.

The viscosity of the ink composition of the present invention is not particularly limited, but the viscosity at 25 ° C. is preferably 1.2 mPa · s or more and 15.0 mPa · s or less, and more preferably 2 mPa · s or more and 13 mPa · s. It is less than s, and more preferably 2.5 mPa · s or more and less than 10 mPa · s.

The pH of the ink composition of the present invention is preferably pH 6 to 11 from the viewpoint of dispersion stability. In the case of the ink set described later, pH 7 to 10 is more preferable, and pH 7 to 9 is further preferable, because the ink composition is preferably aggregated at high speed by contact with a treatment agent containing an acidic compound or the like.

[Image formation method]

The image forming method of the present invention includes applying the ink composition of the present invention onto a recording medium by an inkjet method.

The image forming method of the present invention is preferably preferred.

The treatment agent application step of applying the treatment agent on the recording medium, and

The process includes an ink application step of applying the ink composition of the present invention containing a pigment onto a recording medium after the treatment agent application step by an inkjet method to form an image.

<Treatment agent>

The treatment agent contains an aggregation-inducing component (also referred to as "aggregation component" for short) that aggregates the ink composition by contacting with the ink composition of the present invention. Examples of the agglomerating component include a component selected from an acidic compound, a polyvalent metal salt and a cationic polymer, and the agglomerating component is preferably an acidic compound. The treatment agent may contain other components in addition to the agglomerating component, if necessary.

The treatment agent is usually in the form of an aqueous solution.

-Acid compound-

The acidic compound can agglomerate (immobilize) the ink composition by coming into contact with the ink composition on a recording medium, and functions as an immobilizing agent. For example, if the ink composition is dropped on the recording medium in a state where the treatment agent containing an acidic compound is applied to the recording medium (preferably coated paper), the ink composition can be aggregated and the ink composition can be aggregated. An object can be fixed on a recording medium.

Examples of acidic compounds include sulfuric acid, hydrochloric acid, nitrate, phosphoric acid, polyacrylic acid, acetic acid, glycolic acid, malonic acid, malic acid, maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid, citric acid and tartrate acid. , Lactic acid, sulfonic acid, orthoric acid, metaphosphate, pyrrolidone carboxylic acid, pyron carboxylic acid, pyrrol carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, coumarin acid, thiophene carboxylic acid, nicotinic acid, oxalic acid, acetic acid, benzoic acid Can be mentioned. From the viewpoint of both suppression of volatilization and solubility in a solvent, the acidic compound is preferably an acid having a molecular weight of 35 or more and 1000 or less, more preferably an acid having a molecular weight of 50 or more and 500 or less, and particularly preferably an acid having a molecular weight of 50 or more and 200 or less. Further, as pKa (in _H2O , 25 ° C.), an acid of -10 or more and 7 or less is preferable, an acid of 1 or more and 7 or less is more preferable, and an acid of 1 or more is more preferable, from the viewpoint of achieving both ink bleeding prevention and photocurability. Acids of 5 or less are particularly preferred.

pKa is a value calculated by Advanced Chemistry Development (ACD / Labs) Software V11.02 (1994-2014 ACD / Labs), or a literature value (for example, described in J. Phys. Chem. A 2011, 115, 6641-6645). Values can be used.

Among these, acidic compounds having high water solubility are preferable. Further, from the viewpoint of reacting with the ink composition to immobilize the entire ink, a trivalent or lower acidic compound is preferable, and a divalent or trivalent acidic compound is particularly preferable.

As the treatment agent, one type of acidic compound may be used alone, or two or more types may be used in combination.

When the treatment agent is an aqueous solution containing an acidic compound, the pH (25 ° C.) of the treatment agent is preferably 0.1 to 6.8, more preferably 0.1 to 6.0, and 0. It is more preferably 1.1 to 5.0.

When the treatment agent contains an acidic compound as an agglomerating component, the content of the acidic compound in the treatment agent is preferably 40% by mass or less, more preferably 15 to 40% by mass, still more preferably 15% by mass to 35% by mass. 20% by mass to 30% by mass is particularly preferable. By setting the content of the acidic compound in the treatment agent to 15 to 40% by mass, the components in the ink composition can be more efficiently immobilized.

When the treatment agent contains an acidic compound as an agglomerating component, the amount of the treatment agent applied to the recording medium is not particularly limited as long as it is sufficient to agglomerate the ink composition, but it is easy to immobilize the ink composition. From the viewpoint of the above, it is preferable to add the treatment agent so that the amount of the acidic compound applied is 0.5 g / m ² to 4.0 g / m ² , and 0.9 g / m ² to 3.75 g / m ² . It is preferable to add a treatment agent so as to be.

-Multivalent metal salt-

As the treatment agent, a form containing one or more of polyvalent metal salts as an agglomerating component is also preferable. By containing a polyvalent metal salt as a cohesive component, high-speed cohesiveness can be improved. Examples of the polyvalent metal salt include a salt of the second group of alkaline earth metals (for example, magnesium and calcium) in the periodic table, a salt of a transition metal of the third group of the periodic table (for example, lantern), and a salt of the thirteenth group of the periodic table. Salts of cations (eg, aluminum) from the genus, salts of lanthanides (eg, neodymium) can be mentioned. Suitable metal salts include carboxylates (such as formic acid, acetic acid and benzoate), nitrates, chlorides and thiocyanates. Among them, a calcium salt or magnesium salt of a carboxylic acid (aric acid, acetic acid, benzoate, etc.), a calcium salt or magnesium salt of nitrate, calcium chloride, magnesium chloride, and a calcium salt or magnesium salt of thiocyan acid are preferable.

When the treating agent contains a polyvalent metal salt as an agglomerating component, the content of the polyvalent metal salt in the treating agent is preferably 1 to 10% by mass, more preferably 1.5 to 7 from the viewpoint of the coagulation effect. It is by mass, more preferably in the range of 2 to 6% by mass.

-Cationic polymer-

Further, as the treatment agent, it is also preferable to contain one kind or two or more kinds of cationic polymers as an agglomerating component. The cationic polymer includes a homopolymer of a cationic monomer having a primary to tertiary amino group or a quaternary ammonium base as a cationic group, or a co-polymer of the cationic monomer and a non-cationic monomer. Those obtained as a polymer or a shrunk polymer are preferable. As the cationic polymer, either a water-soluble polymer or a water-dispersible latex particle may be used.

Preferred specific examples of the cationic polymer include poly (vinylpyridine) salt, polyalkylaminoethyl acrylate, polyalkylaminoethyl methacrylate, poly (vinylimidazole), polyethyleneimine, polybiguanide, polyguanide, or polyallylamine and its derivatives. Cationic polymers can be mentioned.

As the weight average molecular weight of the cationic polymer, it is preferable that the molecular weight is small from the viewpoint of the viscosity of the treating agent. When the treatment agent is applied to the recording medium by an inkjet method, the range is preferably 1,000 to 500,000, more preferably 1,500 to 200,000, and even more preferably 2,000 to 100,000. Is the range of. When the weight average molecular weight is 1000 or more, it is advantageous in terms of aggregation rate, and when it is 500,000 or less, it is advantageous in terms of discharge reliability. However, this does not apply when the treatment agent is applied to the recording medium by a method other than inkjet.

When the treating agent contains a cationic polymer as an aggregating component, the content of the cationic polymer in the treating agent is preferably 1 to 50% by mass, more preferably 2 to 30% by mass, from the viewpoint of the aggregating effect. , More preferably in the range of 2 to 20% by mass.

<Recording medium>

The recording medium is not particularly limited, and may be a penetrating recording medium which is a paper medium, or a low-permeability recording medium typified by coated paper (coated paper), and is non-penetrating of plastic, metal, glass and the like. It is also preferable that it is a recording medium. The water-based ink composition of the present invention can be quickly dried even when an image portion is formed on a low-permeability or non-permeable recording medium, and a desired image is formed at high speed and with high accuracy. be able to.

In the present invention, the "low permeability recording medium" means a recording medium having a water absorption coefficient Ka of 0.05 to 0.5 mL / m ² · ms ^1/2 . Further, in the present invention, the "impermeable recording medium" means a recording medium having a water absorption coefficient Ka of less than 0.05 mL / m ² · ms ^1/2 .

The water absorption coefficient Ka is synonymous with that described in JAPAN TAPPI Pulp and Paper Test Method No. 51: 2000 (Published by Japan Technical Association of the Pulp and Paper), and specifically, the automatic scanning liquid absorption meter KM500Win (Kumaya Riki). It is calculated from the difference in the amount of water transfer between the contact time of 100 ms and the contact time of 900 ms.

The non-permeable base material is not particularly limited, but a resin base material is preferable. The resin base material is not particularly limited, and examples thereof include a base material obtained by molding a thermoplastic resin into a sheet shape. The resin base material preferably contains polypropylene, polyethylene terephthalate, nylon, polyethylene, or polyimide.

The resin base material may be a transparent resin base material, a colored resin base material, or at least a part thereof may be subjected to metal vapor deposition treatment or the like.

The shape of the resin base material is not particularly limited. The resin base material is usually a sheet-shaped resin base material, and is more preferably a sheet-shaped resin base material on which rolls can be formed by winding from the viewpoint of productivity of the recording medium.

The thickness of the resin base material is preferably 10 μm to 200 μm, more preferably 10 μm to 100 μm.

The resin base material may be surface-treated from the viewpoint of improving the surface energy.

Examples of the surface treatment include, but are not limited to, corona treatment, plasma treatment, frame treatment, heat treatment, wear treatment, light irradiation treatment (UV treatment), and flame treatment.

The corona treatment can be performed using, for example, a corona master (manufactured by Shinko Electric Meter Co., Ltd., PS-10S) or the like.

The conditions for the corona treatment may be appropriately selected depending on the type of the resin base material, the composition of the ink, and the like. As an example, the following processing conditions can be mentioned.

-Processing voltage: 10 to 15.6 kV

-Processing speed: 30 to 100 mm / s

<Treatment agent application process>

In the treatment agent application step, the treatment agent is applied onto the recording medium. The treatment agent is usually applied on a recording medium in the form of an aqueous solution. A known liquid application method can be used without particular limitation for applying the treatment agent to the recording medium, and any method such as spray coating, coating with a coating roller, application by an inkjet method, or immersion can be selected. can.

Specifically, for example, a size press method typified by a horizontal size press method, a roll coater method, a calendar size press method, etc .; a size press method typified by an air knife coater method, etc .; a typified by an air knife coater method, etc. Knife coater method; Transfer roll coater method such as gate roll coater method, Direct roll coater method, Reverse roll coater method, Roll coater method represented by squeeze roll coater method; Bill blade coater method, Short duel coater method; Two Blade coater method represented by stream coater method; bar coater method represented by rod bar coater method; bar coater method represented by rod bar coater method; cast coater method; gravure coater method; curtain coater method; Die coater method; brush coater method; transfer method and the like can be mentioned.

Further, a method of controlling the coating amount by using a coating device provided with a liquid amount limiting member, such as the coating device described in Japanese Patent Application Laid-Open No. 10-230201, may be used.

The region to which the treatment agent is applied may be a full-scale application applied to the entire recording medium, or a partial application to a region to which the ink is applied in the ink application step. In the present invention, from the viewpoint of uniformly adjusting the amount of the treatment liquid applied, uniformly recording fine lines and fine image portions, and suppressing density unevenness such as image unevenness, a recording medium is applied by coating using a coating roller or the like. It is preferable to apply the entire surface to the entire image forming surface of the above.

As a method of controlling the amount of the treatment agent to be applied within the above range, for example, a method using an Anilox roller can be mentioned. Anilox rollers are rollers that have a pyramid-shaped, diagonal line, or hexagonal shape, etc., by processing the surface of the roller on which ceramic is sprayed with a laser. The treatment liquid enters the recessed portion on the surface of the roller, and when it comes into contact with the paper surface, it is transferred and coated with the coating amount controlled by the recess of the Anilox roller.

<Ink application process>

In the ink applying step, the ink composition is applied onto the recording medium by an inkjet method.

In the image formation by the inkjet method, the ink composition is ejected onto the recording medium by supplying energy to form an image portion. As a preferred inkjet recording method for the present invention, the method described in paragraphs 093 to 0105 of JP-A-2003-306623 can be applied.

The inkjet method is not particularly limited, and is a known method, for example, a charge control method for ejecting ink by using electrostatic attraction, a drop-on-demand method (pressure pulse method) using the vibration pressure of a piezo element, and the like. Either an acoustic inkjet method that converts an electric signal into an acoustic beam and irradiates the ink to eject the ink using radiation pressure, or a thermal inkjet method that heats the ink to form bubbles and uses the generated pressure. You may.

Further, the inkjet head used in the inkjet method may be an on-demand method or a continuous method. Further, the ink nozzle or the like used when recording by the above-mentioned inkjet method is not particularly limited, and can be appropriately selected depending on the purpose.

The inkjet method includes a method called photo ink, in which a large number of low-density inks are ejected in a small volume, a method in which multiple inks having substantially the same hue but different densities are used to improve image quality, and colorless and transparent inks. The method used is included.

In addition, as an inkjet method, a shuttle method that uses a short serial head and scans the head in the width direction of the recording medium for recording, and a line head in which recording elements are arranged over the entire side of the recording medium. There is a line method used. In the line method, the image can be recorded on the entire surface of the recording medium by scanning the recording medium in the direction orthogonal to the arrangement direction of the recording elements, and a transport system such as a carriage that scans the short head becomes unnecessary. Further, since the movement of the carriage and the complicated scanning control between the recording medium and the recording medium are not required and only the recording medium is moved, the recording speed can be increased as compared with the shuttle method.

The order of implementation of the treatment agent application step and the ink application step is not particularly limited, but from the viewpoint of image quality, it is preferable that the ink application step is performed after the treatment agent application step. That is, the ink applying step is preferably a step of applying the ink composition of the present invention on the recording medium to which the treatment agent is applied.

From the viewpoint of forming a high-definition print, the amount of droplets of the ink composition ejected by the inkjet method is preferably 1.5 to 8.0 pL, more preferably 1.5 to 5.0 pL. The amount of droplets of the ink composition to be ejected can be adjusted by appropriately adjusting the ejection conditions.

<Ink drying process>

The image forming method of the present invention may include, if necessary, an ink drying step of drying and removing a solvent (for example, water, the above-mentioned aqueous medium, etc.) in the ink composition applied onto the recording medium. .. The ink drying step is not particularly limited as long as at least a part of the ink solvent can be removed, and a commonly used method can be applied.

<Heat fixing process>

If necessary, the image forming method of the present invention preferably includes a heat fixing step after the ink drying step. By performing the heat fixing treatment, the image on the recording medium is fixed, and the resistance to scratching of the image can be further improved. As the heat fixing step, for example, the heat fixing step described in paragraphs <0112> to <0120> of JP2010-221415A can be adopted.

<Ink removal process>

The inkjet recording method of the present invention may include an ink removing step of removing, if necessary, an aqueous ink composition (for example, an ink solid solidified by drying) adhering to the inkjet recording head with a maintenance liquid. good. As for the details of the maintenance liquid and the ink removing step, the maintenance liquid and the ink removing step described in International Publication No. 2013/180074 can be preferably applied.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

[Preparation Example 1] Synthesis of Polymer P-1 and Preparation of Pigment Dispersant Containing Polymer P-1

Methyl ethyl ketone (265 g) was placed in a 1-liter three-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen gas introduction tube, and the temperature was raised to 80 ° C. under a nitrogen stream. There, a mixed solution consisting of V-601 (radical polymerization initiator, manufactured by Wako Pure Chemical Industries, Ltd.) (0.4 g) and methyl ethyl ketone (50 g), and methyl methacrylate (150 g), methacrylic acid (150 g), and 3- A monomer solution consisting of mercapto-1,2-propanediol (12.5 g) was added dropwise at a constant velocity so that the addition was completed in 4 hours. After the dropping of the monomer solution was completed, the mixture was further stirred for 6 hours to obtain a 50% by mass methyl ethyl ketone solution of polyvinyl compound V-1.

Subsequently, a methyl ethyl ketone solution (80 g, solid content 50% by mass) of the polyvinyl compound V-1 was placed in a three-necked flask equipped with a thermometer, a stirrer, a reflux condenser and a nitrogen introduction tube, and 1,4-benzenedi. Methanol (20.5 g), isophorone diisocyanate (39.5 g), and methyl ethyl ketone (25 g) were charged, and the temperature was raised to 70 ° C. by nitrogen air flow. Neostan U-600 (0.17 g) was added thereto, and the mixture was stirred for 8 hours. 2-Propanol (45 g) and methyl ethyl ketone (38 g) were added to the obtained reaction mixture, and the mixture was further stirred for 3 hours to form a polyurethane compound structure. A methyl ethyl ketone solution of polymer P-1 having a polyurethane structure was obtained. The acid value (acid value before neutralization) of this polymer P-1 was 99 mgKOH / g.

Next, 1-methoxy-2-propanol (100 g) and propylene glycol (100 g) were added to 200 g of a methyl ethyl ketone solution of the polymer P-1, and the mixture was sufficiently stirred. Then, after distilling off the methyl ethyl ketone, the mixture was heated to 70 ° C. and heated to 50% by mass. The carboxy group was neutralized by adding a% aqueous potassium hydroxide solution (16 g) and stirring for 2 hours to obtain a solution of the pigment dispersant P-1 containing the polymer P-1.

[Preparation Examples 2 to 14] Synthesis of polymers P-2 to P-14 and preparation of pigment dispersants containing polymers P-2 to P-14.

In the synthesis of the polymer P-1, the polymer P having a polyvinyl compound structure part and a polyurethane structure part is similar to the polymer P-1, except that the raw material used is changed to the one corresponding to the structure shown in the table below. -2 to P-14 were synthesized.

The obtained polymers P-2 to P-14 are subjected to neutralization treatment with potassium hydroxide in the same manner as described above, and the pigment dispersants P-2 to P-14 containing the polymers P-2 to P-14 are subjected to the same procedure. Solutions were obtained respectively.

[Comparative Preparation Examples 1 to 4] Synthesis of Polymers CP-1 to CP-4 and Preparation of Pigment Dispersant Containing Polymers CP-1 to CP-4

In the synthesis of the polymer P-1, the polymer CP having a polyvinyl compound structure part and a polyurethane structure part is similar to the polymer P-1, except that the raw material used is changed to the one corresponding to the structure shown in the table below. -1 to CP-4 were synthesized.

The obtained polymers CP-1-CP-4 were subjected to neutralization treatment with potassium hydroxide in the same manner as described above, and the pigment dispersants CP-1 to CP-4 containing the polymers CP-1 to CP-4 were subjected to the same procedure. Solutions were obtained respectively.

The Mw of the polymers P-1 to P-14 and the polymers CP-1 to CP-4 were all in the range of 5000 to 80000. Further, the Mw of the polyvinyl compounds used for the synthesis of the polymers P-1 to P-14 and the polymers CP-1 to CP-4 were all in the range of 1000 to 20000.

The numerical values attached to each component in the columns of "polyvinyl compound (PV)" and "polyurethane (PU)" in the above table indicate the mass ratio.

[Preparation of aqueous pigment dispersion]

Using a ready-mill model LSG-4U-08 (manufactured by IMEX), an aqueous pigment dispersion was prepared as follows.

In a container made of zirconia, 45 parts by mass of titanium oxide powder (PF690: manufactured by Ishihara Sangyo, volume average particle size 210 nm, alumina, silica and organic material treated product), and a 30% by mass solution of each pigment dispersant synthesized above 7.5. 47.5 parts by mass and 47.5 parts by mass of ultrapure water were added. Further, 400 parts by mass of 0.3 mmφ zirconia beads (TORAY made Trecerum beads) were added, and the mixture was lightly mixed with a spatula.

A zirconia container was set in the apparatus, and the dispersion treatment was performed at a rotation speed of 1000 rpm for 1.5 hours. After the dispersion treatment was completed, the beads were removed by filtration through a filter cloth. In this way, an aqueous pigment dispersion having a pigment concentration of 45% by mass was obtained by using any of the pigment dispersants P-1 to P-14 and CP-1 to CP-4 synthesized above as the pigment dispersant. The pH of the obtained aqueous pigment dispersion was 8.3.

[Test Example 1] Storage stability (dispersion stability) test

10 mL of the aqueous pigment dispersion obtained by the above method is packed in a sample bottle (size: 1.6 cmφ × height 10 cm), sealed, allowed to stand at room temperature (25 ° C) or 60 ° C for 1 week, and then aqueous. The dispersed state of the pigment dispersion was evaluated as follows.

Using a micropipettor, 300 μL was gently collected from the liquid level in the sample bottle so that the static state of the liquid in the sample bottle was not disturbed. The solid content mass of the collected liquid was measured, the dispersibility was calculated by the following formula, and the calculated value was applied to the following evaluation criteria to evaluate the storage stability.





Dispersity (%) = 100 × (solid content mass after standing for 1 week) / (solid content mass of aqueous pigment dispersion before standing)





<Storage stability evaluation criteria>

AA: Dispersibility is 90% or more

A: Dispersibility is 85% or more and less than 90%

B: Dispersibility is 80% or more and less than 85%

C: Dispersibility is 70% or more and less than 80%

D: Dispersibility is less than 70%

The results are shown in the table below.

[Preparation of water-based ink composition]

Each component is mixed with the following compounding ratio (unit: parts by mass), and the obtained mixed solution is filtered with a glass filter (GS-25) manufactured by ADVANTEC, and then a filter manufactured by Millipore (polyvinylidene fluoride film, pore diameter 5 μm). The water-based ink composition was prepared by filtering with. The pH of the obtained aqueous ink composition was 8.1.

<Mixing ratio of ink composition>

-Pigment dispersion prepared above: 20 parts by mass

Propylene glycol: 24 parts by mass

Orfin E1010 (surfactant manufactured by Nissin Chemical Industry Co., Ltd.): 0.5 parts by mass

-Ion-exchanged water: Amount of 100 parts by mass of the entire ink composition

[Test Example 2] Leaving in inkjet ejection-Recoverability test (1)

A fixed GELJET GX5000 printer head manufactured by Ricoh Co., Ltd. with a resolution of 1200 x 1200 dpi and a drop rate of 3.5 pL in a line system with a polyethylene terephthalate (PET) substrate (FE2001, thickness 12 μm, Futamura Chemical Co., Ltd.) ) A nozzle check pattern image was drawn on the top. After confirming that the filled ink was ejected from all 96 nozzles at the start of ejection, the environment of the recording head nozzle portion was maintained at 25 ° C. and a relative humidity of 50%, and left for 30 minutes. Then, one nozzle check pattern image same as the above was drawn again on another recording medium of the same type as the above (the image here is referred to as an “image sample after being left for 30 minutes”).

After leaving for 30 minutes, observe the nozzle omission (image omission) in the nozzle check pattern image with an optical microscope, calculate the ejection rate by the following formula, and apply the calculated value to the following evaluation criteria. Was evaluated.





Discharge rate (%) = 100 × (number of ejection nozzles when forming an image sample after leaving for 30 minutes) / (number of ejection nozzles when forming an initial image sample)





<Leaving-Recoverability Evaluation Criteria>

AA: Discharge rate is 95% or more

A: Discharge rate is 90% or more and less than 95%

B: Discharge rate is 85% or more and less than 90%

C: Discharge rate is 80% or more and less than 85%

D: Discharge rate is less than 80%

The results are shown in the table below.

[Test Example 3] Leaving in inkjet ejection-Recoverability test (2)

In the above [Test Example 2], after forming the initial image sample, the environment of the recording head nozzle portion was maintained at 25 ° C. and a relative humidity of 50%, and left for 15 hours in the same manner as in Test Example 2. In addition, the neglect-recoverability was evaluated by the same evaluation criteria.

The results are shown in the table below.

As shown in Table 2 above, when the acid value of the polymer constituting the pigment dispersant is lower than specified in the present invention, the aqueous pigment dispersion prepared using this pigment dispersant is inferior in dispersion stability. It became. In addition, the water-based ink prepared using this pigment dispersant was also inferior in the neglect-recoverability in image formation by the inkjet method (Comparative Examples 1 and 3). Further, even when a large amount of components exhibiting adsorptivity to the pigment are present in the polyvinyl compound structure, the aqueous pigment dispersion prepared by using this pigment dispersant is inferior in dispersion stability, and this pigment dispersant is used. The water-based ink prepared in the above was inferior in the neglect-recoverability in image formation by the inkjet method (Comparative Examples 2 and 4).

On the other hand, the water-based pigment dispersion prepared by using the pigment dispersant of the present invention has excellent dispersion stability, and by preparing a water-based ink using the pigment dispersant of the present invention, an image is formed by an inkjet method. It was found that the neglect-recovery property was also enhanced (Examples 1 to 14). That is, it was found that by using the pigment dispersant of the present invention, high-precision image formation can be stably formed by the inkjet method.

Claims (11)

An inkjet pigment dispersant containing a polymer having a polyvinyl compound structure and a polyurethane structure.
The total content of the constituents represented by the following formula (1) or the following formula (2) in the polyvinyl compound structural portion is 30% by mass or less, the polyvinyl compound structural portion has an acidic group, and the above. A pigment dispersant for inkjet in which the polyurethane structure has no acidic group and the acid value of the polymer exceeds 80 mgKOH / g.

In the formulas (1) and (2), R ^1a and R ^1b represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. A ¹ indicates -O- or -NR ^A- . ^RA indicates a hydrogen atom or a substituent. L ^1a and L ^1b represent an aromatic group, a benzyl group, or an alkyl group having 4 or more carbon atoms. The inkjet pigment dispersant according to claim 1, wherein the acid value of the polymer is 90 mgKOH / g or more and 200 mgKOH / g or less. The pigment dispersant for inkjet according to claim 1 or 2, wherein the proportion of the polyvinyl compound structural portion in the polymer is 70% by mass or less. The one according to any one of claims 1 to 3, wherein the polyurethane structure contains at least one of the constituents represented by the following formula (3), the following formula (4), and the following formula (5). Inkjet pigment dispersant.

The ring structure shown in the formulas (3), (4), and (5) represents an aromatic ring or an aliphatic ring. L ³ to L ⁵ indicate a single bond or a divalent linking group. X ³ , X ⁴ and X ⁵ indicate -O- *, -NHCO- *, and * indicates a linking site for incorporation into the polymer. R ³ to R ⁵ indicate substituents. n is an integer of 0 or more. ^A5 indicates -N = or -CH =. Z represents a single bond or a divalent linking group. When L ³ to L ⁵ and Z are divalent linking groups, the divalent linking group does not have a urethane bond and does not have a ring structure. The inkjet pigment dispersant according to any one of claims 1 to 4, wherein the polymer has a carboxy group in the polyvinyl compound structure. The inkjet pigment dispersant according to any one of claims 1 to 5, which is used as a dispersant for white pigments. The inkjet pigment dispersant according to claim 6, wherein the white pigment is titanium oxide. The inkjet pigment dispersant according to claim 7, wherein the titanium oxide is surface-treated with at least one of silica, alumina and an organic substance. An inkjet pigment dispersion containing the inkjet pigment dispersant according to any one of claims 1 to 8, the pigment, and an aqueous medium. An inkjet water-based ink composition containing the inkjet pigment dispersant according to any one of claims 1 to 8, the pigment, and an aqueous medium. An image forming method comprising applying the water-based ink composition for inkjet according to claim 10 onto a recording medium by an inkjet method.