JP5590791B2 - Inkjet ink - Google Patents

Description

  The present invention relates to an inkjet ink.

  Conventional ink jet inks are required to satisfy a high level of weather resistance and water resistance, and pigments have been used as coloring materials in order to achieve them. Since pigments are in the form of particles unlike dyes, it is required to stably disperse pigments in ink. Examples of a method for stably dispersing the pigment in the aqueous medium include a method using a dispersant, for example, a resin dispersant. By using the above-described technique, that is, a resin-dispersed pigment, the pigment can maintain a stable dispersion state in an aqueous medium. Another technique for dispersing the pigment is a method of chemically modifying the surface of the pigment. Such a pigment is called a self-dispersing pigment, and the pigment can be stably dispersed in an aqueous medium without using a dispersant. As another technique, a method using a pigment in which a dispersible resin having a hydrophilic group is chemically bonded to the surface of pigment particles has been proposed (see Patent Document 1). An ink containing a self-dispersing pigment has reliability such as long-term storage stability and ejection stability of the ink, and can form an image showing excellent scratch resistance against rubbing after printing.

As described above, studies using pigments have been actively conducted. However, pigments generally have low gloss, and inks containing pigments are particularly useful for recording media with high surface smoothness (hereinafter also referred to as glossy paper). When applied, the glossiness of the area where the ink was applied could be impaired. In order to solve such a decrease in glossiness, a method has been proposed in which a nonionic surfactant having a copolymer portion of propylene oxide and ethylene oxide is added as a brightener in a pigment ink (Patent Document 2). reference).
JP 2004-83743 A JP 2005-82663 A

  However, according to the method described in Patent Document 2, an image having a gloss level that satisfies the present inventors could not be obtained.

  Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide an ink jet ink that can form an image having excellent glossiness on glossy paper without impairing reliability such as ejection stability. To do.

The present invention is a polymer-bonded self-dispersion Pigments, an inkjet ink containing 及 beauty water, the polymer-bonded self-dispersion pigment is chemically bonded directly or through another atomic group to the surface of the pigment The functional group is reacted with a polymer having an acid value of 80 mgKOH / g or more and 250 mgKOH / g or less, and the ink further has a structure represented by the following formula (1), and Contains a surfactant having a cloud point of 35 ° C. or lower, and the content b (% by mass) of the polymer bonded to the pigment with respect to the content a (% by mass) of the surfactant in the ink. the ratio b / a of an ink jet ink, characterized in der Rukoto 0.15 to 6.0.

(In the formula (1), PO is propylene Oki side group, EO is an ethylene oxide side groups, R is an alkyl chain having 7 to 14 carbon atoms, m is an integer of 2 to 15, n Is an integer of 2 to 15, and m / n is 1 or more.)

  By using the present invention, an inkjet ink having excellent ejection stability can be provided. In addition, it is possible to provide an ink-jet ink that can form an image having both excellent glossiness and color developability on glossy paper.

  It is presumed that the ink jet ink of the present invention can form an image having excellent gloss on glossy paper by the following mechanism.

  The surfactant used in the present invention is highly hydrophobic with a cloud point of 35 ° C. or lower. This is because it has a hydrophobic functional group such as a propylene oxide chain and an alkyl chain at a plurality of locations. As a result, the hydrophobic interaction with the hydrophobic portion of the copolymer of the polymer-bonded self-dispersing pigment can be strengthened. As a result, the hydrophilic part of the copolymer and the surfactant can be promoted to be exposed to the aqueous medium side. In addition, the polymer-bonded self-dispersing pigment is one in which the pigment and the copolymer are firmly bonded to each other, and therefore, the removal of the copolymer from the pigment surface can be reduced. Therefore, the hydrophilic group directed to the aqueous medium side can efficiently promote the dispersion of the pigment, and the aggregation rate of the copolymer when ink droplets are applied to the surface of the recording medium can be reduced. As a result, the unevenness between dots when a plurality of ink dots are applied on the recording medium is reduced and smoothed, so that excellent glossiness can be exhibited on glossy paper.

  Hereinafter, each component used in the inkjet ink of the present invention will be described in detail.

<Surfactant>
The surfactant that can be used in the inkjet ink of the present invention is a surfactant having a cloud point of 35 ° C. or lower and a structure represented by the formula (1).

(In the formula (1), PO is propylene Oki side group, EO is an ethylene oxide side groups, R is an alkyl chain having 7 to 14 carbon atoms, m is an integer of 2 to 15, n Is an integer of 2 to 15, and m / n is 1 or more.)

  The cloud point here is a temperature at which the surfactant associates innumerably due to a decrease in the affinity of the hydrophilic group of the nonionic surfactant with water and phase-separates from the solvent. Therefore, in the present invention, a low cloud point means that the hydrophobicity of the surfactant is high.

  Specific examples of the surfactant described above include FINESURF 7085 (manufactured by Aoki Yushi Co., Ltd.), Softanol EP5035 (manufactured by Nippon Shokubai Co., Ltd.), and New Pole PE-61, 62, 71 (manufactured by Sanyo Chemical Co., Ltd.). Moreover, as long as it has the physical property shown above, you may use the surfactant newly created for this invention separately.

  In the present invention, as described above, the cloud point of the surfactant is 35 ° C. or lower, but preferably 25 ° C. or lower. In the present invention, the lower limit of the cloud point is not particularly limited, but is preferably 0 ° C. or higher.

  The surfactant of the present invention preferably has a weight average molecular weight of 100 or more and 4000 or less. By setting the weight average molecular weight of the surfactant within the range shown above, the interaction between the polymer-bonded self-dispersing pigment and the surfactant can be made more effective.

<Color material>
The present invention uses, as a colorant, a polymer-bonded self-dispersing pigment that enhances the dispersibility of the pigment itself and that can be dispersed without using a dispersant or the like. The coloring material of the present invention, that is, the polymer-bonded self-dispersing pigment, is covalently bonded to the pigment, a functional group that is chemically bonded to the surface of the pigment directly or through another atomic group, and the functional group. It refers to a copolymer. By using the polymer-bonded self-dispersing pigment, the copolymer efficiently contributes to the dispersion of the pigment, so that the glossiness can be improved. In the present invention, since the above-described surfactant is used, the dispersibility of the pigment due to the contribution of the surfactant can also be improved efficiently.

  Hereinafter, each component used in the polymer-bonded self-dispersing pigment of the present invention will be described in detail.

(Pigment)
As the base pigment of the polymer-bonded self-dispersing pigment that can be used in the present invention, any of known inorganic pigments and organic pigments can be used.

  As the inorganic pigment used in the black ink, carbon black can be preferably used. For example, any of furnace black, lamp black, acetylene black, and channel black can be used. Specifically, for example, Ray-Van 7000, 5750, 5250, 5000ULTRA, 3500, 2000, 1500, 1250, 1200, 1190ULTRA-11, 1170, 1255 (above Colombia), Black Pearls L, Legal, 400R, 300R 660R, Mowgle L, Monak 700, 800, 880, 900, 1000, 1100, 1300, 1400, 2000, Vulcan XC-72R (above, manufactured by Cabot Corporation), Color Black FW1, FW2, FW2V, FW18, FW200, S150 , S160, S170, Printex 35, U, V, 140U, 140V, Special Black 6, 5, 4, 4A (above, manufactured by Degussa), No. 25, no. 33, no. 40, no. 47, no. 52, no. 900 No. 2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical Corporation) and the like. Further, the material is not limited to carbon black, and magnetic fine particles such as magnetite and ferrite, titanium black, and the like may be used as a black pigment. Furthermore, carbon black newly prepared for the present invention can also be used.

  Specific examples of the organic pigment include insoluble azo pigments such as toluidine red, toluidine maroon, Hansa yellow, benzine yellow, and pyrazolone red, soluble azo pigments such as ritole red, heliobordeaux, pigment scarlet, and permanent red 2B, Derivatives from vat dyes such as alizarin, indanthrone, thioindigo maroon, phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green, quinacridone pigments such as quinacridone red and quinacridone magenta, perylene pigments such as perylene red and perylene scarlet, Isoindolinone pigments such as isoindolinone yellow and isoindolino orange, and benzimidazolone yellow, benzimidazolone orange and benzimidazolone red Imidazolone pigments, pyranthrone pigments such as pyranthrone red, pyranthrone orange, thioindigo pigments, condensed azo pigments, thioindigo pigments, diketopyrrolopyrrole pigments, flavanthrone yellow, acylamide yellow, quinophthalone yellow, nickel azo Yellow, copper azomethine yellow, perinone orange, anthrone orange, dianslaquinonyl red, dioxazine violet and the like.

  In the present invention, an organic pigment represented by a color index (CI) number can also be used. Specifically, C.I. I. Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 97, 109, 110, 117, 120, 125, 128, 137, 138, 147, 148, 150, 151, 153, 154, 166, 168, 180, 185, C.I. I. Pigment orange 16, 36, 43, 51, 55, 59, 61, 71, C.I. I. Pigment Red 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 175, 176, 177, 180, 192, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240, 254, 255, 272, C.I. I. Pigment violet 19, 23, 29, 30, 37, 40, 50, C.I. I. Pigment blue 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64, C.I. I. Pigment green 7, 36, C.I. I. Pigment brown 23, 25, 26, and the like.

(Functional group chemically bonded to the pigment)
In the present invention, in order to obtain a polymer-bonded self-dispersing pigment, it is required to introduce a functional group chemically bonded to the surface of the above-described inorganic pigment or organic pigment directly or via another atomic group. Since the functional group is for constituting an organic group containing a reaction product with the copolymer described later, the type of the functional group is appropriately selected depending on the reactivity with the functional group possessed by the copolymer. can do.

  The functional group chemically bonded to the surface of the pigment is preferably one that forms a bond that does not cause hydrolysis such as an amide bond in the reaction with the copolymer. For example, when the functional group and the copolymer are bonded by an amide bond, it is preferable that the functional group is an amino group and the copolymer has a carboxyl group. Further, when the functional group is a carboxyl group and the copolymer has an amino group, it is preferable for forming an amide bond.

  The functional group may be chemically bonded to the surface of the pigment directly or through another atomic group. When the molecular weight of the copolymer that reacts with the functional group is relatively large, the copolymer In order to avoid mutual steric hindrance, it is preferable to introduce a functional group to the surface of the pigment via another atomic group. Here, the other atomic group is not particularly limited as long as it is a polyvalent element or organic group, but from the viewpoint of reducing the steric hindrance by controlling the distance of the functional group from the surface of the pigment. For example, a divalent organic residue is preferable. Examples of the divalent organic residue include an alkylene group and an arylene group (phenylene group). More specifically, the aminophenyl (2-sulfoethyl) sulfone group is introduced to the surface of the pigment by reacting the pigment with aminophenyl (2-sulfoethyl) sulfone, and then the amino group and amino group of pentaethylenehexamine are introduced. By reacting with a phenyl (2-sulfoethyl) sulfone group, an amino group as a functional group can be introduced. In this case, it can also be said that the amino group is chemically bonded to the surface of the pigment through an atomic group containing a phenyl (2-sulfoethyl) group.

(Copolymer)
In the present invention, the copolymer covalently bonded to the functional group described above has an acid value of 80 mgKOH / g or more and 250 mgKOH / g or less. In the present invention, the copolymer is not particularly problematic as long as it is covalently bonded to the above functional group and satisfies the above acid value.

  Specific monomer units for forming the copolymer are not particularly limited, and styrene, styrene derivatives, vinyl naphthalene, vinyl naphthalene derivatives, aliphatic alcohol esters of α, β-ethylenically unsaturated carboxylic acid, acrylic acid, Appropriately selected from acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives, vinyl acetate, vinylpyrrolidone, acrylamide, and derivatives thereof to satisfy the physical properties of the present invention. However, in view of the physical properties of the copolymer in the present invention, at least one of the monomer units forming the copolymer is required to be a hydrophilic monomer unit having an acid value. Further, the arrangement of the monomer units in the copolymer is not particularly limited, and may be any of a block copolymer, a random copolymer, and a graft copolymer.

  When the acid value of the copolymer is less than 80 mgKOH / g, the long-term storage stability and ejection stability of the ink are lowered. On the other hand, when the acid value of the copolymer exceeds 250 mgKOH / g, sufficient gloss improvement effect cannot be obtained when the surfactant described above is added. If the acid value is too high, the hydrophobic portion on the surface of the polymer-bonded self-dispersing pigment is reduced, and it is considered that the surfactant cannot be sufficiently adsorbed.

  The weight average molecular weight (Mw) of the above-mentioned copolymer is preferably in the range of 1,000 to 20,000, preferably in the range of 3,000 to 20,000. More preferable.

<Inkjet ink>
The ink-jet ink of the present invention may further contain a copolymer that is present free in the ink. Such a copolymer preferably has an acid value of 80 mgKOH / g or more in order to improve the long-term storage stability and ejection stability of the ink. Moreover, it is preferable that an acid value is 200 mgKOH / g or less from a viewpoint of controlling the permeability | transmittance of resin.

  The content of the polymer-bonded self-dispersing pigment in the inkjet ink of the present invention is preferably 0.5% by mass or more based on the total mass of the ink from the viewpoint of obtaining a sufficient image density. Moreover, although it does not specifically limit as an upper limit, Even if it adds more than 15 mass%, since the coloring effect beyond it is hard to be acquired, it is preferable that it is 15 mass% or less. The content of the polymer-bonded self-dispersing pigment is more preferably 1% by mass to 10% by mass with respect to the total mass of the ink.

  In the inkjet ink of the present invention, when the total mass of the surfactant is a and the total mass of the copolymer bonded to the functional group on the pigment surface is b, b / a is 0.15. It is preferably 6.0 or less from the viewpoint of improving glossiness and improving long-term storage stability. Further, b / a is more preferably 0.25 or more and 4.0 or less.

  In the inkjet ink of the present invention, the total mass of the copolymer bonded to the functional group on the surface of the pigment is a, the total mass of the free copolymer is c, and the polymer bond It is preferable that (da) / (c + a) when the total mass of the self-dispersing pigment is d is 1 / 0.5 or more from the viewpoint of improving the glossiness. Further, from the viewpoint of ejection stability, it is preferable to set it to 1/4 or less ((d−a) / (c + a) is a mass ratio between the pigment and the copolymer in the ink, and hence the P / B ratio is also referred to below. Say).

<Other ingredients>
In addition to the above components, a water-soluble organic solvent as an aqueous medium may be added to the inkjet ink of the present invention as necessary. Further, a penetrant, an antiseptic, an antifungal agent, or the like for assisting the permeability to the recording medium may be added.

  EXAMPLES The present invention will be specifically described with reference to examples and comparative examples. In the examples, “parts” or “%” are based on mass unless otherwise specified.

<Manufacture of pigment dispersion>
[Pigment dispersion 1]
500 g of carbon black (BP100: manufactured by Cabot Corporation), 45 g of aminophenyl (2-sulfoethyl) sulfone (APSES), and 900 g of ion-exchanged water were kept at 55 ° C. and stirred at 300 rpm for 20 minutes to obtain a dispersion. Next, after the dispersion was reacted with 25% by mass sodium nitrite, a dispersion A having a 15% by mass solid content concentration was obtained by performing centrifugation and purification treatment. While the dispersion A was vigorously stirred at room temperature, pentaethylenehexamine (PEHA) was added dropwise to the dispersion A. After the addition of PEHA, Dispersion A was stirred for 48 hours and purified to obtain Dispersion B having a solid content concentration of 10% by mass. Next, a 9.5 mass% aqueous solution of Resin 1 was prepared as a copolymer and stirred. The dispersion B was added dropwise to the stirring aqueous resin solution to obtain a mixture C. At this time, the resin 1 is a styrene-acrylic acid-butyl acrylate copolymer having an acid value of 100 mgKOH / g and a weight average molecular weight of 7,500. Thereafter, the mixture C was heat-dried at 150 ° C. for 15 hours to obtain an evaporated dry product. Next, the evaporated and dried product is dispersed in an aqueous NaOH solution adjusted to pH 9 and further adjusted to pH 10 by adding an aqueous NaOH solution, and further subjected to purification treatment and removal of coarse particles to contain a polymer-bound self-dispersing pigment. A pigment dispersion 1 was prepared. The pigment concentration in the pigment dispersion was 10% by mass, and the P / B ratio was 1 / 0.5.

[Pigment dispersion 2]
A pigment dispersion 2 for Example 3 was obtained in the same manner as in the pigment dispersion 1 except that the resin 2 was used instead of the resin 1. At this time, the resin 2 is a styrene-acrylic acid-butyl acrylate copolymer having an acid value of 220 mgKOH / g and a weight average molecular weight of 12,000. The pigment concentration in the pigment dispersion was 10% by mass, and the P / B ratio was 1 / 0.5.

[Pigment dispersion 3]
A pigment dispersion 3 was obtained in the same manner as in the pigment dispersion 1 except that the resin 3 was used in place of the resin 1. At this time, the resin 3 is a styrene-acrylic acid-butyl acrylate copolymer having an acid value of 300 mgKOH / g and a weight average molecular weight of 12,000. The pigment concentration in the pigment dispersion was 10% by mass, and the P / B ratio was 1 / 0.5.

[Pigment dispersion 4]
A pigment dispersion 4 was obtained in the same manner as in the pigment dispersion 1 except that it was used in Pigment Blue 15: 3 (manufactured by Clariant) instead of carbon black. The pigment concentration in the pigment dispersion was 10% by mass, and the P / B ratio was 1 / 0.5.

[Pigment dispersion 5]
A pigment dispersion 5 was obtained in the same manner as in the pigment dispersion 1 except that Pigment Red 122 (manufactured by Ciba Specialty Chemicals) was used instead of carbon black. The pigment concentration in the pigment dispersion was 10% by mass, and the P / B ratio was 1 / 0.5.

[Pigment dispersion 6]
A pigment dispersion 6 was obtained in the same manner as in the pigment dispersion 1, except that Pigment Yellow 74 (manufactured by Clariant) was used instead of carbon black. The pigment concentration in the pigment dispersion was 10% by mass, and the P / B ratio was 1 / 0.5.

[Pigment dispersion 7]
A pigment dispersion 3 was obtained in the same manner as in the pigment dispersion 1 except that the resin 4 was used instead of the resin 1. At this time, the resin 4 is a styrene-acrylic acid-butyl acrylate copolymer having an acid value of 70 mgKOH / g and a weight average molecular weight of 12,000. The pigment concentration in the pigment dispersion was 10% by mass, and the P / B ratio was 1 / 0.5.

<Creation of water-based ink for inkjet recording>
Each component was mixed according to the formulation shown in Table 1, dissolved sufficiently by stirring, and then pressure-filtered with a micro filter (manufactured by Fuji Film Co., Ltd.) having a pore size of 1.5 μm. Produced. When the P / B ratio of the obtained ink, the total mass of the surfactant contained in the ink is a, and the total mass of the copolymer bonded to the polymer-bonded self-dispersing pigment contained in the ink is b Table 1 also shows b / a.

  Table 2 shows the structure and physical properties of the surfactant shown in Table 1.

<Evaluation of inkjet ink>
[Evaluation of glossiness and optical density]
The ink jet inks of Examples and Comparative Examples were packed in an ink cartridge for Canon BJF-900, and printing was performed on a recording medium at 100% duty using Canon BJF-900. Based on the obtained printed matter, the following physical properties were evaluated. At this time, Canon Super Photo Paper SP-101A4 was used as a recording medium.

(Glossy)
The obtained printed matter was naturally dried for 24 hours, and then the glossiness of the printed matter was measured using a image clarity analyzer DIAS (OEA, USA). The measurement results were evaluated according to the following criteria. The results are shown in Table 3.
(Double-circle): The glossiness improved very much compared with the ink which does not contain surfactant.
○: Glossiness was improved as compared with ink containing no surfactant.
(Triangle | delta): The improvement of glossiness was not seen compared with the ink which does not contain surfactant.
X: Glossiness decreased as compared with ink containing no surfactant.

(Optical density (OD))
The obtained printed matter was naturally dried for 24 hours, and the optical density of the printed matter was measured by Gretag Spectrolino (trade name: manufactured by Gretag). The measurement results were evaluated according to the following criteria. The results are shown in Table 3.
○: O.D. compared with ink containing no surfactant. D. The value has increased.
X: O.D. compared with ink containing no surfactant. D. The value did not change or decreased.

[Evaluation of ejection stability]
The solid print that contains the nozzle check pattern first is printed continuously on 3 sheets of A4 plain paper, left without printing for 2 hours, and then the solid print is continuously printed again 10 times. It was. The print disorder at that time and the presence or absence of non-ejection were visually evaluated. The results are shown in Table 3.
◎: No printing disorder and non-ejection ○: Slight printing disturbance but no non-ejection ×: Printing disorder and non-ejection

  As is apparent from the evaluation results shown in Table 3, the ink composition prepared in each example has glossiness, O.D. D. In both tests of discharge stability, high evaluation was obtained.

Claims (3)

An inkjet ink containing a polymer-bonded self-dispersion Pigment及 beauty water,
The polymer-bonded self-dispersing pigment reacts with a functional group chemically bonded to the pigment surface directly or via another atomic group and a polymer having an acid value of 80 mgKOH / g or more and 250 mgKOH / g or less. It is obtained by letting
Ink further comprises a structure of formula (1), and its cloud point contains a surfactant Ru der 35 ° C. or less,
The ratio b / a of the content b (mass%) of the polymer bonded to the pigment to the content a (mass%) of the surfactant in the ink is 0.15 or more and 6.0 or less. inkjet ink, characterized in Rukoto Oh.

(In the formula (1), PO is a propylene oxide group, EO is an ethylene oxide group, R is an alkyl chain having 7 to 14 carbon atoms, m is an integer of 2 to 15 and n is (It is an integer of 2 to 15, and m / n is 1 or more.)   The inkjet ink according to claim 1, wherein a cloud point of the surfactant is 25 ° C. or less. The inkjet ink according to claim 1, wherein the ratio b / a is 0.25 or more and 4.0 or less.