JP2012087261A - Inkjet ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet ink which has good preservability, can be ejected stably also after a long term preservation, has high durability of images printed on various types of non-absorbing media, and can be well recovered by maintenance.SOLUTION: The inkjet ink includes a water-soluble resin, a water-insoluble resin, a pigment and water, wherein the acid value of the water-soluble resin is ≥50 and <70; and the acid value of the water-insoluble resin is ≥60 and <90.

Description

  The present invention relates to an inkjet ink, and more particularly to an aqueous inkjet ink.

  It has been proposed to add various resins to the aqueous pigment inkjet ink as a pigment dispersant or as a binder resin.

  Aqueous pigment inkjet inks have been proposed for printing on non-absorbent media in addition to conventional printing on inkjet paper.

  As a result of the study by the present inventors, it is important to control the wettability to the recording medium and the ink-jet ink viscosity in order to obtain a high-quality print that does not generate from the liquid when printing on the non-absorbent medium. Has come to understand.

  Based on this finding, the present inventors have found that adding a specific water-soluble resin to an inkjet ink is effective in obtaining a high-quality print that does not occur from the liquid (for example, see Patent Document 1). .

  In addition, the present inventors can use inkjet pigments coated with a water-insoluble resin to print on non-absorbent media with high image quality, high image durability, inkjet ink storage stability and injection stability. An ink was proposed (for example, see Patent Document 2).

  However, when used for outdoor exhibitions for a long period of time, the image may be wiped with dry cloth, water, a detergent, an alcohol aqueous solution, or the like. At this time, stronger image durability is required so that the image cannot be taken. In addition, there is a need for stability that allows ink jet ink to be ejected more stably after long-term storage.

  Moreover, although the inkjet ink containing the water-soluble resin of acid values 60-80 is disclosed (for example, refer patent document 3), there is no description of combined use with water-insoluble resin. In particular, there is no description specifying the acid value of the water-insoluble resin.

WO2008 / 105289 JP 2008-208153 A JP 2010-47660 A

  An object of the present invention is to provide an ink-jet ink that has good storage stability and can be stably ejected even after long-term storage. Images printed on various non-absorbent media have high durability, and are based on maintenance. An object of the present invention is to provide an ink-jet ink having good recovery.

  The above object of the present invention can be achieved by the following configuration.

  1. An ink-jet ink containing a water-soluble resin, a water-insoluble resin, a pigment, and water, wherein the water-soluble resin has an acid value of 50 or more and less than 70, and the water-insoluble resin has an acid value of 60 or more and less than 90. An inkjet ink characterized by

  2. 2. The ink-jet ink as described in 1 above, wherein the acid value of the water-soluble resin is smaller than the acid value of the water-insoluble resin.

  3. The water-soluble resin is an acrylic copolymer with an aromatic group-containing monomer, and the content derived from the aromatic group-containing monomer is less than 20% by mass of the entire water-soluble resin. The inkjet ink according to 1 or 2 above.

  4). 4. The ink-jet ink as described in any one of 1 to 3, wherein the water-soluble resin is an acrylic copolymer having a weight average molecular weight of 20,000 or more and less than 100,000.

  5). The water-insoluble resin is an acrylic copolymer with an aromatic group-containing monomer, and the content derived from the aromatic group-containing monomer is 35% by mass or more and less than 80% by mass of the entire water-insoluble resin. The inkjet ink according to any one of 1 to 4, wherein the inkjet ink is characterized in that

  6). 6. The inkjet ink according to any one of 1 to 5, wherein at least a part of the water-insoluble resin covers the pigment.

  7). The ink-jet ink according to any one of 1 to 6, wherein the content of the water-insoluble resin is less than the content of the pigment, and the content of the water-soluble resin is greater than the content of the pigment. .

  According to the present invention, an ink-jet ink having good storage stability and capable of being stably ejected even after long-term storage is provided, images printed on various non-absorbent media have high durability, and maintenance is required. An ink-jet ink with good recovery can be provided.

  The best mode for carrying out the present invention will be described in detail below, but the present invention is not limited thereto.

(Water-soluble resin and water-insoluble resin of the present invention)
In the present invention, the water-soluble resin means a resin having a solubility in ion exchange water of 10% by mass or more, and the water-insoluble resin means a resin having a solubility in ion exchange water of less than 2% by mass. The solubility can be determined as the concentration at which a transparent aqueous solution is obtained without stirring in the range of 25 ° C. to 50 ° C. for 1 day.

  The present invention provides an ink-jet ink which has good storage stability and can be stably ejected even after long-term storage by using a water-soluble resin having a specific acid value together with a water-insoluble resin having a specific acid value. It was possible to provide an inkjet ink that was provided and printed on various non-absorbent media having high durability and good recovery by maintenance.

  By adding a water-soluble resin to the ink, it is possible to suppress image quality deterioration due to the liquid or the like, and it is possible to print on various non-absorbent media. At the same time, the water-soluble resin functions as a pigment binder and improves image durability. Although the addition of a water-soluble resin improves the image durability, the image may be peeled off when a strong load is applied and the image is wiped with a dry cloth or water, a detergent, an alcohol aqueous solution or the like. In Patent Document 2, an improvement in image durability is achieved by bringing a water-insoluble resin into ink by using a pigment coated with a water-insoluble resin. However, if a strong load is applied and the image is wiped with a dry cloth or water, a detergent, or an alcohol aqueous solution, the image may be peeled off, which is still insufficient. The present invention uses a water-soluble resin having a specific acid value and a water-soluble resin having an acid value of 50 or more and less than 70, thereby preventing image quality deterioration due to the liquid and improving durability even when a heavy load is applied. I found out. Furthermore, by using a water-soluble resin having an acid value of 50 or more and less than 70 and a water-insoluble resin having an acid value of 60 or more and less than 90, sufficient durability can be obtained even when a heavy load is applied. It came to.

  In addition, the present inventors have found that the water-soluble resin suppresses the liquid and improves the image durability, but deteriorates the pigment dispersion stability in the ink. At this time, it was found that the water-soluble resin having an acid value of 50 or more and less than 70 used in the present invention improves the pigment dispersion stability over the water-soluble resin having an acid value of 70 or more. Furthermore, it has been found that the constitution of the present invention using a water-insoluble resin having an acid value of 60 or more and less than 90 in combination significantly improves the present invention. As described above, by using a water-soluble resin having an acid value of 50 or more and less than 70 and a water-insoluble resin having an acid value of 60 or more and less than 90, for the first time in image durability and pigment storage stability in ink. A sufficient level of improvement could be achieved.

  Furthermore, the ink added with the resin is likely to be clogged or bent due to the solidification of the resin at the nozzle. Further, at this time, even if maintenance work such as cleaning of the head surface or flushing is performed, it is often not completely recovered. When a water-soluble resin having an acid value of 50 or more and less than 70 and a water-insoluble resin having an acid value of 60 or more and less than 90 are used in combination, a sufficient amount of resin for image durability is added to the ink. Regardless, it can be improved by maintenance work such as cleaning the head surface and flushing.

  The details of the effects of the present invention are unknown, but are estimated as follows.

  By adding a water-soluble resin to the ink, it is considered that the deterioration of the image quality due to the liquid or the like can be suppressed because the ink is thickened at the time of drying immediately after landing on the medium and the liquid is prevented. At this time, the water-soluble resin in the ink needs to have a polymer chain spread to form a network. At this time, the amount of acidic groups, that is, the acid value greatly affects, and if the acid value is 50 or more, the network configuration is sufficient. I think it is possible. When the acid value is less than 50, the resin network does not spread sufficiently and cannot contribute to prevention than the liquid. On the other hand, in order for the water-soluble resin to improve the image durability, it is necessary to effectively adsorb the hydrophobic portion of the resin to a non-absorbent medium, a pigment or the like by a hydrophobic bond or the like. When the acid value is 70 or more, the resin is relatively stable in the ink, and the hydrophobic bond is not sufficiently formed.

  On the other hand, the water-insoluble resin is in some form dispersed in the ink. When a water-soluble resin coexists, it is very important to design an ink in consideration of the interaction between the water-insoluble resin and the water-soluble resin. When the acid value of the water-insoluble resin is 90 or more, the dispersion stability of the resin itself is high. However, in the case of coexisting with the water-soluble resin, the ink storability is insufficient due to the interaction with the acidic group of the water-soluble resin. When the acid value is less than 60, the dispersibility of the water-insoluble resin is insufficient, and the storage stability in the ink is not good.

  From the above, it is considered that the effect of the present invention is manifested only when the combination is unique such that the acid value of the water-soluble resin is 50 or more and less than 70 and the acid value of the water-insoluble resin is 60 or more and less than 90.

  In particular, it has been found that when the acid value of the water-soluble resin is smaller than the acid value of the water-insoluble resin, the image durability, the ink storage stability, and the prevention effect are greater than the liquid.

  As described above, the acid value of the water-soluble resin is mainly determined from the viewpoint of ink thickening and image durability, and the acid value of the water-insoluble resin is determined in terms of dispersion stability, particularly dispersion in the presence of the water-soluble resin. Since a preferable range is determined from the viewpoint of stability, it is considered that the excellent effect of the present invention is achieved.

(Water-soluble resin)
The water-soluble resin according to the present invention is a water-soluble resin having a solubility in ion-exchanged water of 10% by mass or more by containing a necessary amount of nonionic or ionic components in the resin. Examples of nonionic components include polyethylene oxide and polyamide. The ionic component includes an anionic component and a cation component. Examples of the anionic component include neutralized products of polycarboxylic acid and polysulfonic acid. Among these, neutralized products of polyacrylic acid, polymethacrylic acid, and polymaleic acid are preferable.

  Acrylic resin can copolymerize various monomers arbitrarily, so water-soluble resin can be synthesized by copolymerizing acidic component monomer in the required amount for dissolution in water according to the composition of other copolymerization monomers. Can be preferred. Examples of the acid component monomer at this time include acrylic acid, methacrylic acid, maleic acid, itaconic acid, and styrene sulfonic acid. Water-solubilization can be adjusted by copolymerizing an acid component monomer and neutralizing all or part of the portion corresponding to the acid component monomer with an alkali. As the neutralizing base, alkali metal-containing bases such as sodium hydroxide and potassium hydroxide, and amines (for example, ammonia, alkanolamine, alkylamine and the like) can be used.

  In order to make it water-soluble, the molecular weight is preferably less than 100,000.

  As the water-soluble resin, an acrylic copolymer resin can be preferably used. That is, a water-soluble acrylic copolymer resin having an acid value of 50 or more and less than 70 can be preferably used. Among them, a resin having an acid value adjusted to 50 or more and less than 70 using at least acrylic acid or methacrylic acid as a copolymerization monomer is preferable. In this case, the acid groups in the resin are adjusted for water solubilization by neutralizing all or part of them with an alkali. As a copolymerizable monomer other than acrylic acid or methacrylic acid, various acrylic acid esters and methacrylic acid esters can be used, which is preferable. For example, it is preferable to use an alkyl acrylate having 2 to 8 carbon atoms or an alkyl methacrylate having 2 to 8 carbon atoms, and an alkyl acrylate having 2 to 8 carbon atoms. Esters include ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, n-hexyl acrylate, cyclo-hexyl acrylate, octyl acrylate, acrylic acid 2-ethylhexyl etc. are mentioned.

  Examples of the alkyl methacrylate having 2 to 8 carbon atoms in the alkyl group include ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, and n-hexyl methacrylate. , Cyclo-hexyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate and the like.

  In addition, styrene derivatives such as styrene and methylstyrene and aromatic group-containing monomers such as benzyl (meth) acrylate can be copolymerized. In this case, the copolymerization ratio of the aromatic group-containing monomer is less than 20% by mass. It is preferable to make it. More preferably, the content derived from the aromatic group-containing monomer is less than 5% by mass of the entire water-soluble resin, and most preferably is substantially not contained or less than 1% by mass.

  On the other hand, the aromatic group has an effect of improving the image gloss, but the prevention effect is smaller than that of the liquid, and the adhesiveness to the non-absorbing medium is also disadvantageous. On the other hand, (meth) acrylic acid alkyl ester and the copolymer of the acid component were found to be particularly advantageous in the prevention effect and adhesiveness to non-absorbent media than the liquid.

  In the most preferable embodiment, acrylic acid or methacrylic acid is used as a copolymerization monomer, the acid value is adjusted to 50 or more and less than 70, and the alkyl group has 2 to 8 carbon atoms and alkyl group alkyl ester or alkyl group carbon. The total amount of alkyl esters of 2 to 8 methacrylic acid is 5% or more and less than 30%, and the remainder is methyl methacrylate. The acidic groups derived from acrylic acid or methacrylic acid are all or partly neutralized with alkali. What was neutralized completely is still more preferable. The water-soluble acrylic resin according to the present invention is preferably synthesized by solution polymerization.

  The Tg of the water-soluble resin of the present invention is preferably 50 ° C. or more and less than 100 ° C. from the viewpoint of image durability. The weight average molecular weight of the water-soluble resin is preferably from 20,000 to less than 100,000 from the viewpoints of image durability, ink storage stability, and maintenance recoverability.

(Water-insoluble resin)
The water-insoluble resin of the present invention has a solubility in ion exchange water of less than 2% by mass, and preferably has a solubility in ion exchange water of less than 1% by mass. Contrary to the water-soluble resin, the water-insoluble resin is a resin whose solubility in ion-exchanged water is adjusted to less than 2% by mass so that the resin does not contain nonions or ionic components more than necessary. The nonionic or ionic component mentioned here has the same meaning as described for the water-soluble resin.

  In the present invention, an acrylic copolymer resin can be preferably used as the water-insoluble resin. That is, a water-soluble acrylic copolymer resin having an acid value of 60 or more and less than 90 can be preferably used. Among them, a resin having an acid value adjusted to 60 or more and less than 90 using at least acrylic acid or methacrylic acid as a copolymerization monomer is preferable. In this case, the acid groups in the resin are adjusted for water solubilization by neutralizing all or part of them with an alkali. As a copolymerizable monomer other than acrylic acid or methacrylic acid, various acrylic acid esters and methacrylic acid esters can be used, which is preferable. For example, it is preferable to use an alkyl acrylate having 2 to 8 carbon atoms or an alkyl methacrylate having 2 to 8 carbon atoms, and an alkyl acrylate having 2 to 8 carbon atoms. Esters include ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, n-hexyl acrylate, cyclo-hexyl acrylate, octyl acrylate, acrylic acid 2-ethylhexyl etc. are mentioned.

  Examples of the alkyl methacrylate having 2 to 8 carbon atoms in the alkyl group include ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, and n-hexyl methacrylate. , Cyclo-hexyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate and the like.

  In addition, styrene derivatives such as styrene and methylstyrene, and aromatic group-containing monomers such as benzyl (meth) acrylate can be copolymerized.

  Among these, it is particularly preferable in terms of ink stability to use an acrylic ester or a methacrylic ester that can constitute a repeating unit represented by the following general formula 1.

  More preferably, the aromatic compound-containing monomer of the general formula 1 is particularly preferably contained in the polymer compound in a total amount of 30% by mass to 80% by mass.

General formula 1
_{- (CH 2 -CR 1 (L} 1 -L 2 -Ar)) -
In the formula, R ₁ represents a hydrogen atom or a methyl group, L ₁ represents —COO—, —CONH—, —OCO—, —NHCO—, L ₂ represents a divalent linking group, and Ar represents an aromatic ring. To express.

Specific examples of the divalent linking group represented by L ₂ include an alkylene group (1-10 carbon atoms), an alkenylene group, (1-10 carbon atoms), —CO—, —NR ₂ — (R ₂ is hydrogen). alkyl group atoms or carbon atoms 1~6), - O -, - S -, - SO -, - SO 2 - linking group selected from the preferred. Two or more of the divalent linking groups may be combined. Particularly preferred linking groups are methylene, ethylene, propylene, oxyethylene, oxyethoxyethylene groups.

  As the aromatic ring represented by Ar, a monovalent group derived from a phenyl group, a condensed ring type aromatic ring compound, a heterocyclic compound in which an aromatic ring is condensed, or a compound in which two or more benzenes are linked is preferably used. It is done.

  As specific examples, monovalent groups derived from benzene, naphthalene, biphenyl, triphenylmethane, phthalimide, acridone, fluorene, anthracene, phenanthrene, diphenylmethane, or carbazole are preferable. Ar may have a substituent.

  Examples of the substituent include an alkyl group, an alkoxyl group, an alkylcarbonyl group, an alkylcarbonyloxy group, an alkyloxycarbonyloxy group, a halogen group, and a cyano group.

  As the water-insoluble resin of the present invention, it is particularly preferable to use acrylic acid or methacrylic acid as at least a copolymerization monomer to adjust the acid value to 60 or more and less than 90, and to use an aromatic group-containing monomer of 35% or more and less than 80%. The remainder is obtained by using another copolymerization monomer. The acidic group derived from acrylic acid or methacrylic acid is more preferably a neutralized group obtained by neutralizing all or part of the acidic group with an alkali. At this time, the aromatic group-containing monomer is most preferably a monomer represented by the general formula 1.

  The water-insoluble resin of the present invention can be synthesized by solution polymerization or emulsion polymerization. The weight average molecular weight of the water-insoluble resin is preferably 20,000 or more and less than 200,000, and the weight average molecular weight is preferably controlled by a solution polymerization method.

  The Tg of the water-insoluble resin of the present invention is preferably 50 ° C. or more and less than 100 ° C. from the viewpoint of image durability and ink storage stability.

  A method for adding the water-insoluble resin to the ink is not limited. The water-insoluble resin may be dispersed in the ink or may be coated with a pigment.

  The water-insoluble resin of the present invention has a pigment dispersion function and is preferably added to the ink as a pigment dispersant. In this case, if the structure derived from the aromatic group-containing monomer is 35% or more and less than 80% of the entire water-insoluble resin as the adsorbing group to the pigment, it is preferable because the ink storage stability is further improved. It is considered that the hydrophobic part such as the structure derived from the aromatic group-containing monomer of the water-insoluble resin is preferably adsorbed on the pigment surface in order to improve the ink storage stability.

  In terms of image gloss, the aromatic group-containing monomer-derived structure is preferably 35% or more and less than 80% of the entire water-insoluble resin. Furthermore, when the aromatic group-containing monomer-derived structure is 35% or more and less than 80% of the entire water-insoluble resin, the effect of improving solvent resistance and detergent resistance, which is a problem when using a water-soluble resin, is preferable. .

  As described above, the water-insoluble resin preferably has a pigment dispersion function, and it is particularly preferable from the viewpoint of ink storage stability that at least a part of the water-insoluble resin is coated with the pigment. It can be seen that at least a part of the water-insoluble resin is coated with the pigment by separating the pigment particles and observing them with an electron microscope.

  Various known methods can be used to coat the pigment with the water-insoluble resin. Preferably, in addition to the phase inversion emulsification method and the acid precipitation method, the pigment is dispersed using a polymerizable surfactant. However, it is preferable to select from a method in which a monomer is supplied thereto and coating is performed while polymerizing.

  As a more preferred method, the water-insoluble resin is dissolved in an organic solvent such as methyl ethyl ketone, and after partially or completely neutralizing the acidic groups in the resin with a base, the pigment and ion-exchanged water are added and dispersed. Thereafter, a production method in which the organic solvent is removed and the mixture is prepared by adding water as necessary is preferable.

(Content of water-soluble resin and water-insoluble resin in ink)
The content of the water-soluble resin in the ink is preferably higher than that of the pigment from the viewpoint of prevention and abrasion resistance than the liquid.

  In the case of dark ink, the pigment concentration can be preferably used in the range of 2% to 7%. In this case, the water-soluble resin is preferably used in the range of 4% to 10%.

  In terms of the ratio of the pigment to the water-soluble resin, it is preferably used in the range of 1.2 times to less than 2 times that of the pigment.

  In the case of a light color ink, the pigment concentration can be preferably used in the range of 0.3% to 1.5%. In this case, the water-soluble resin can be used in the range of 1% to 10%.

  In terms of the ratio of pigment to water-soluble resin, it is preferably used in the range of 2 times to less than 10 times the pigment.

  Less water-insoluble resin than pigment is more preferable from the viewpoints of ink storage stability and ejection stability.

  In terms of the ratio of the pigment to the water-insoluble resin, it is preferably used in the range of 0.2 times or more and less than 1 time of the pigment.

  Hereinafter, additives that can be preferably used in the inkjet ink of the present invention will be described.

(Organic pigment)
As the pigment that can be used in the present invention, conventionally known organic and inorganic pigments can be used. For example, azo pigments such as azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perylene pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc. Examples include cyclic pigments, dye lakes such as basic dye lakes, and acid dye lakes, organic pigments such as nitro pigments, nitroso pigments, aniline black, and daylight fluorescent pigments, and inorganic pigments such as carbon black.

  Specific organic pigments are exemplified below.

  Examples of pigments for magenta or red include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.

  Examples of the orange or yellow pigment include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 128, C.I. I. Pigment Yellow 138, Pigment Yellow 150, Pigment Yellow 155, and the like.

  Examples of pigments for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.

(Inorganic pigment)
As the inorganic pigment, a white pigment can be preferably used. The white pigment is not particularly limited as long as it makes the ink composition white, and usually white pigments used in this field can be used. As such a white pigment, for example, a white inorganic pigment, a white organic pigment, or white hollow polymer fine particles can be used. Examples of white inorganic pigments include alkaline earth metal sulfates such as barium sulfate, alkaline earth metal carbonates such as calcium carbonate, silicas such as finely divided silicic acid, and synthetic silicates, calcium silicate, alumina, alumina Hydrates, titanium oxide, zinc oxide, talc, clay and the like can be mentioned. In particular, titanium oxide is known as a white pigment having favorable concealability, colorability, and dispersed particle size.

  Examples of white organic pigments include organic compound salts disclosed in JP-A No. 11-129613 and alkylene bismelamine derivatives disclosed in JP-A Nos. 11-14365 and 2001-234093. Specific examples of white organic pigments include Shigenox OWP, Shigenox OWPL, Shigenox FWP, Shigenox FWG, Shigenox UL, and Shigenox U (all of these are trade names manufactured by Hackol Chemical).

  Examples of the white hollow polymer fine particles include fine particles showing thermoplasticity substantially made of an organic polymer disclosed in US Pat. No. 4,089,800.

  In the present invention, the white pigments described above may be used alone or in combination.

(Distribution method, preliminary dispersion method)
As a method for dispersing the pigment, various dispersing means such as a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, and a paint shaker can be used.

  In the present invention, it is also preferable to use a centrifugal separator or a filter for the purpose of removing coarse particles of the pigment dispersion.

  In the present invention, a part or all of the water-insoluble resin can be used as a pigment dispersant. By using a water-insoluble resin as a dispersant, a pigment dispersion in which a water-insoluble resin called a capsule pigment is dispersed in a state where the pigment is coated can be produced.

  Various known methods can be used to coat the pigment with the water-insoluble resin. Preferably, in addition to the phase inversion emulsification method and the acid precipitation method, the pigment is dispersed using a polymerizable surfactant. However, it is preferable to select from a method in which a monomer is supplied thereto and coating is performed while polymerizing.

  As a more preferred method, the water-insoluble resin is dissolved in an organic solvent such as methyl ethyl ketone, and after partially or completely neutralizing the acidic groups in the resin with a base, the pigment and ion-exchanged water are added and dispersed. After that, the organic solvent is removed, and it is prepared by adding water as necessary.

  The average particle diameter of the pigment after dispersion is preferably dispersed so as to be 50 nm or more and 300 nm or less. More preferably, it is 50 nm or more and 150 nm or less.

(Particle size measurement method)
The average particle diameter can be easily measured using a commercially available measuring device using a light scattering method or a laser Doppler method. Specifically, it is preferable to measure using a Zetasizer 1000 (manufactured by Malvern).

(Organic solvent)
The organic solvent used for the ink of the present invention will be described.

  It is preferable to add a low surface tension solvent to the ink of the present invention. A low surface tension solvent is a solvent whose surface tension is 25 mN / m or more and 35 mN / m or less. By adding a low surface tension solvent, it is possible to further suppress ink mixing even on various resin substrates such as vinyl chloride sheets and paper supports with slow ink absorption speed such as printing paper. Print image can be obtained. The low surface tension solvent has an effect of improving the wettability of the ink with respect to vinyl chloride or the like.

  In the present invention, it is preferable to add glycol ethers or alkanediols as the low surface tension solvent.

  An example of a low surface tension solvent suitable for the ink of the present invention is shown below. In addition, the numerical value in a parenthesis represents the surface tension (mN / m) of a solvent.

  Examples of glycol ethers include ethylene glycol monoethyl ether (28.2), ethylene glycol monobutyl ether (27.4), diethylene glycol monoethyl ether (31.8), diethylene glycol monobutyl ether (33.6), and triethylene. Examples include glycol monobutyl ether (32.1), propylene glycol monopropyl ether (25.9), dipropylene glycol monomethyl ether (28.8), and tripropylene glycol monomethyl ether (30.0).

  Moreover, as alkanediols, 1,2-alkanediol or 1,3-alkanediol is preferable. For example, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol (28.1), 1,2-heptanediol, 2-methyl-1,3-propanediol and the like can be mentioned.

  Further, by adding a solvent having an action capable of dissolving or softening or swelling a recording medium such as vinyl chloride, the adhesion between the vinyl chloride and the resin according to the present invention is further improved, and excellent image adhesion, It is preferable from the viewpoint of obtaining abrasion resistance.

  Examples of such solvents include cyclic solvents containing nitrogen or sulfur atoms, cyclic ester solvents, lactic acid esters, alkylene glycol diethers, alkylene glycol monoether monoesters, and dimethyl sulfoxide.

  The cyclic solvent containing a nitrogen atom is preferably a cyclic amide compound, particularly a 5- to 7-membered ring, such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone 1,3-dimethyl. Examples include imidazolidinone, 1,3-dimethyl-2-imidozolidinone, ε-caprolactam, methylcaprolactam, and 2-azacyclooctanone. As the cyclic solvent containing a nitrogen atom other than the cyclic amide, formylmorpholine, and as the cyclic solvent containing a sulfur atom, a cyclic amide compound is preferable, and a 5- to 7-membered ring is preferable, and examples thereof include sulfolane. Examples of the cyclic ester solvent include γ-butyrolactone and ε-caprolactone, and examples of the lactic acid ester include butyl lactate and ethyl lactate. Examples of the alkylene glycol diether include diethylene glycol diethyl ether. Examples of the alkylene glycol monoether monoester include diethylene glycol monoethyl monoacetate.

  In the present invention, from the viewpoint of ink ejection stability from the ink jet head, maintainability, and gloss of the formed image, as one of the solvents, a water-soluble alkanolamine is 0.30% by mass or more of the total mass of the ink, It is preferable to contain 2.0 mass% or less, More preferably, it is 0.3 mass% or more and 1.8 mass% or less. Examples of water-soluble alkanolamines that can be preferably applied to the present invention include N, N-dimethylaminoethanol, 2-amino-2-methylpropanol, and N-methylaminoethanol.

  In addition, alcohols (eg, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol), polyhydric alcohols (eg, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene) Glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol), amines (eg, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyl) Diethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenedi Amine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine), amides (for example, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, etc.), etc. It is done.

  In the present invention, the amount of the organic solvent used is preferably 10% by mass or more and 50% by mass or less of the total mass of the ink.

(Other ink additives)
[Surfactant]
As the surfactant of the ink of the present invention, it is preferable to add a silicone-based or fluorine-based surfactant.

  Addition of silicone-based or fluorine-based surfactants further suppresses ink mixing even on vinyl resin sheets and other resin substrates and paper supports with slow ink absorption speeds such as printing paper. And a high-quality printed image can be obtained. Further, it is particularly preferable to use in combination with a low surface tension solvent.

  The silicone surfactant is preferably a polyether-modified polysiloxane compound, and examples thereof include KF-351A and KF-642 manufactured by Shin-Etsu Chemical Co., and BYK345, BYK347, and BYK348 manufactured by Big Chemie.

  The fluorosurfactant means a compound in which a part or all of the fluorosurfactant is substituted with fluorine in place of hydrogen bonded to carbon of a hydrophobic group of a normal surfactant. Among these, those having a perfluoroalkyl group in the molecule are preferable.

  Among the fluorosurfactants, certain types are traded under the trade name Megafac F from Dainippon Ink & Chemicals, Inc., and surflon from Asahi Glass Co., Minnesota Mining and Under the trade name Fluorad FC from Manufacturing Company, under the trade name Monflor from Imperial Chemical Industry, and Zonyls from EI Dupont Nemeras & Company. It is commercially available under the trade name and also under the trade name Licobet VPF from Farbeberke Hoechst.

  Examples of nonionic fluorosurfactants include Megafax 144D manufactured by Dainippon Ink and Surflon S-141 and 145 manufactured by Asahi Glass Co., and amphoteric fluorosurfactants. Examples of the agent include Surflon S-131 and 132 manufactured by Asahi Glass Co., Ltd.

  The following surfactants can be used in combination with the silicone-based or fluorine-based surfactant.

  For example, anionic surfactants such as dialkylsulfosuccinates, alkylnaphthalenesulfonates, fatty acid salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, polyoxyethylene / polyoxypropylene blocks Nonionic surfactants such as copolymers, and cationic surfactants such as alkylamine salts and quaternary ammonium salts. In particular, an anionic surfactant and a nonionic surfactant can be preferably used.

  In the ink of the present invention, in addition to the above description, if necessary, the output stability, print head and ink cartridge compatibility, storage stability, image storage stability, and other various performance improvement objectives are known. Various additives such as polysaccharides, viscosity modifiers, specific resistance regulators, film forming agents, ultraviolet absorbers, antioxidants, anti-fading agents, antifungal agents, rust preventives, etc. may be appropriately selected and used. Examples thereof include liquid droplets such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicone oil, ultraviolet absorbers, anti-fading agents, and fluorescent whitening agents.

(Image forming method)
Next, the image forming method according to the present invention will be described.

  By using the water-based inkjet recording ink of the present invention, it is possible to print a high-quality image without ink mixing on a hydrophobic recording medium, and it is possible to form an image with high gloss, high abrasion resistance and adhesiveness.

  In the image forming method according to the present invention, in addition to using the ink of the present invention, an image with high image quality, high scratch resistance and high adhesion is formed, and it is possible to cope with printing conditions at higher speed. Therefore, it is preferable to print while heating the recording medium to a temperature of 35 ° C. or more and less than 55 ° C. By heating the recording medium to 35 ° C. or higher, the ink of the present invention can be efficiently cured. If the recording medium is 55 ° C. or lower, deformation due to thermal damage to the recording medium, for example, a vinyl chloride sheet or the like. In addition, it is possible to suppress a decrease in ejection stability by drying ink with an inkjet head.

  In addition, after printing and image formation while heating, the printed matter is heat-dried at a temperature of 45 ° C. or higher and lower than 90 ° C.

  While drying is accelerated by heating after printing, the adhesion between the resin according to the present invention and the substrate can be further improved.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

Example 1
<< Synthesis of Resin 1 >> Synthesis of Water-soluble Resin S-1 [Synthesis of Resin 1 (2-EHA / MMA / MAA): N, N-dimethylaminoethanol salt]
In a 500 ml four-necked flask, a mechanical stirrer, a nitrogen introducing tube, a condenser, and a dropping funnel were set, 185 g of isopropyl alcohol was added to the flask, and the mixture was heated to reflux while bubbling nitrogen gas. In a dropping funnel, 13 g of 2-ethylhexyl methacrylate, 79 g of methyl methacrylate, 8 g of methyl acrylate, and 0.5 g of azobisisobutyronitrile (AIBN) as an initiator were mixed and heated to reflux for about 2 hours. The solution was added dropwise. After the dropwise addition, the mixture was further heated under reflux for 6 hours, and 0.05 g of AIBN in isopropyl alcohol was further added dropwise over 15 minutes. Thereafter, the mixture was further heated to reflux for 5 hours.

  After allowing the reaction liquid to cool, the solvent isopropyl alcohol was distilled off under reduced pressure. To this residue, N, N-dimethylaminoethanol as an alkali neutralized base was added in a neutralized amount of 105% of acidic groups. The finished solid content concentration is about 15% by mass.

  The acid value, glass transition temperature, and weight average molecular weight of the resin 1 prepared above were measured according to the following methods.

Synthesis of water-insoluble resin IS-1 A four-head flask was provided with a nitrogen inlet tube, a condenser, a thermometer, and a dropping funnel. To the flask was added 230 g of methyl ethyl ketone, nitrogen gas was introduced, and the mixture was heated to reflux with stirring for 30 minutes. Meanwhile, 50 g of benzyl methacrylate, 42 g of methyl methacrylate, 8 g of methacrylic acid, and 0.45 g of AIBN were stirred and mixed at room temperature to dissolve. This monomer / initiator mixture was dropped from the dropping funnel over 2 hours. During the dropwise addition, heating under reflux was maintained. After completion of the dropwise addition, the mixture was further heated to reflux for 5 hours. The reaction solution was allowed to cool and then poured little by little into 2 kg of stirring hexane. The candy-like polymer gradually solidified. When fully solidified, a solid was obtained by filtration. The weight average molecular weight was 34,000.

<Measurement of acid value>
10 g of resin was weighed into a 300 ml Erlenmeyer flask, and about 50 ml of a mixed solvent of ethanol: benzene = 1: 2 was added to dissolve the resin. Next, using a phenolphthalein indicator, titration was performed with a 0.1 mol / l potassium hydroxide ethanol solution that had been standardized in advance. From the amount of the potassium hydroxide ethanol solution used for titration, the acid value was calculated using the following formula (1). (Mg KOH / g) was determined. For resins that do not dissolve in about 50 ml of a mixed solvent of ethanol: benzene = 1: 2, select either 50 ml of ethanol or about 50 ml of a mixed solvent of ethanol / pure water = 1: 1. The others were titrated by the same operation.

Formula (1)
A = (B × f × 5.611) / S
In the formula, A is the acid value of the resin (mgKOH / g), B is the amount of 0.1 mol / L potassium hydroxide ethanol solution used for titration (ml), and f is the 0.1 mol / liter potassium hydroxide ethanol solution. Factor, S is the mass of the resin (g), 5.611 is the formula weight of potassium hydroxide (56.11 / 10).

  The acid value of the resin 1 measured by the above method was 46 mgKOH / g.

<Measurement of glass transition temperature (Tg)>
Tg was measured using a DSC-7 differential scanning calorimeter (Perkin Elmer) and a TAC7 / DX thermal analyzer controller (Perkin Elmer).

  As a measurement procedure, 10.00 mg of Resin 1 is precisely weighed to two decimal places, sealed in an aluminum pan (KITNO.0219-0041), and set in a DSC-7 sample holder. The reference was an empty aluminum pan.

  The measurement conditions are 0-130 ° C, temperature increase rate 10 ° C / min, temperature decrease rate 10 ° C / min. Heat-cool-heat control is performed, and analysis is performed based on the data in 2nd Heat. went. The measurement was performed under a nitrogen stream condition.

  The glass transition temperature is obtained by drawing an extension of the baseline before the rise of the first endothermic peak and a tangent line indicating the maximum slope between the rising portion of the first peak and the peak apex, and the intersection is defined as the glass transition temperature. did.

  The glass transition temperature of the resin 1 measured by the above method was 79 ° C.

<Measurement of weight average molecular weight>
The weight average molecular weight was measured using gel permeation chromatography.

  The measurement conditions are as follows.

Solvent: Tetrahydrofuran Column: Tosoh TSKgel G4000 + 2500 + 2000HXL
Column temperature: 40 ° C
Injection volume: 100 μl
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 100000 to 500 samples were used. Thirteen samples are used at approximately equal intervals.

  The weight average molecular weight of the resin 1 measured by the above method was 35000.

  Similarly, water-soluble resins and water-insoluble resins shown in Tables 1 and 2 were respectively polymerized and produced.

In Tables 1 and 2, the abbreviations of the respective monomers are as follows: 2EHA: 2-ethylhexyl acrylate MMA: methyl methacrylate MAA: methacrylic acid n-BA: n-butyl acrylate BMA: butyl methacrylate St: styrene BzMA: benzyl methacrylate 2- PhOEtMA: 2-phenoxyethyl methacrylate Example 2
(Preparation of pigment dispersion)
30 g of each water-insoluble resin described in Table 3, 150 g of methyl ethyl ketone, sodium hydroxide for neutralizing 100% of the water-insoluble resin, 420 g of ion-exchanged water, and Pigment Blue 15: 3 (manufactured by FASTOGEN Blue GNKA-SD DIC) or As a Bk pigment, 50 g of carbon black (Mitsubishi # 950, manufactured by Mitsubishi Chemical) was premixed, charged into a 1 liter pot, and circulated with a desktop star mill miniature air (manufactured by Ashizawa), using zirconia YZT balls (0.5φ). ) Was used and dispersed at a filling rate of 80%. This dispersion was distilled using a rotary evaporator at a bath temperature of 45 ° C. for 60 minutes to distill off methyl ethyl ketone. Thereafter, the dispersion was stored at 60 ° C. for 1 day, returned to room temperature, and filtered through a 5 μm metal mesh filter. As a result, a dispersion having a pigment solid content concentration of 10% was obtained. Thus, a pigment dispersion in which the pigment was coated with the water-insoluble resin was produced.

  The average particle diameter was measured using a Zetasizer 1000 (manufactured by Malvern), and the results are shown in Table 3.

Example 3
(Preparation of inkjet ink)
Inks C1 to C28 and inks K1 to K4 were prepared according to the following formulation using combinations of the pigment dispersions described in Tables 4 and 5 (dispersed with the water-insoluble resin described in Table 3) and water-soluble resins.

Pigment dispersion with 3% pigment solid content Water-soluble resin 5%
1,2-hexanediol 6%
2-pyrrolidone 10%
Methylpropanediol 8%
Fluorine activator Footgent 100 0.6%
BYK Dynwet800 0.9%
The balance of ion-exchanged water (so that it becomes 100%)
The ink was filtered through a 1 μm filter.

  In Tables 4 and 5, for example, the ink C1 has the water-soluble resin as Comparative 1 shown in Table 1 and the pigment dispersion as C-1 shown in Table 3. Therefore, the water-insoluble resin is shown in Table 2. Represents comparison 5.

(Evaluation)
Evaluation from liquid The drawing devices EB-100 and XY-100 (manufactured by Konica Minolta IJ) are equipped with two piezo-type heads KM512M, and ink C1 is introduced into both heads, and cyan images on untreated PVC (METAMARK). Drawn.

  During printing, the stage was heated, and the vinyl chloride surface temperature was heated to 50 ° C. for printing. After printing, heating was performed at 50 ° C. for 5 minutes, and the ink amount was printed up to a maximum of 200% to evaluate where the liquid was generated.

5: Not generated from liquid even when ink amount is 200% 4: Generated from liquid for the first time when ink amount is 180% 3: Generated from liquid for the first time when ink amount is 160% 2: Generated from liquid for the first time when ink amount is 120% 1: Ink amount is 100% Similarly, the inks C2 to C25 shown in Table 4 were evaluated. In addition, the inks C26 to C28 and K1 to K4 in Table 5 were similarly evaluated.

Evaluation of storage stability The prepared ink was put in a sealed bottle, stored in a thermostat at 60 ° C. for 20 days, returned to room temperature, then measured for the average particle size, and the change from the average particle size immediately after preparation was evaluated.

5: Particle size variation is less than 3% 4: Particle size variation is 3% or more and less than 7% 3: Particle size variation is 7% or more and less than 10% 2: Particle size variation is 10% or more and less than 20% 1 : Particle size variation is 20% or more.

Evaluation of ejection stability Using a piezo-type head KM512M, the ink after storage was evaluated at an ejection frequency of 13.3 kHz and a droplet velocity of 6 m / sec. Environmental conditions: temperature 25 ° C. and relative humidity 50% RH. The injection state of each nozzle after 30-minute continuous injection evaluation was observed. 5: Stable injection without missing or bent at all nozzles (512 nozzles) 4: No missing at all nozzles (512 nozzles), but less than 1% nozzles 3: There is a slight bend in all nozzles (512 nozzles), but there is a slight bend in nozzles of 1% or more and less than 5%. 2: Missing occurs in nozzles of less than 5%. 1: 5% or more Missing occurred at the nozzle.

Image durability evaluation 1
A 100% cyan image or black 100% image prepared by evaluation from the above solution was subjected to a load of 900 g using cotton canakin No. 3 and rubbed back and forth to observe a decrease in image density.

5: 50 round trip and no defect 4: Less than 40 round trip image defect appears 3: 30 less round trip image defect occurs 2: Less than 20 round trip image defect appears 1: Less than 10 round trip image defect appears

Image durability evaluation 2
A 100% cyan image or 100% black image prepared from the above solution was moistened with 40% ethanol aqueous solution in cotton kanakin No. 3 and subjected to a load of 300 g, and rubbed back and forth to observe a decrease in image density.

No defect at 5:30 reciprocation 4: Image defect occurs at less than 20 reciprocation 3: Image defect occurs at less than 15 reciprocation 2: Image defect occurs at less than 10 reciprocation 1: Image defect occurs at less than 1: 5 reciprocation

Image durability evaluation 3
The 100% cyan or black 100% image prepared from the above solution is moistened with cotton canakin No. 3 diluted with an alkaline detergent in water, and the load is 200 g. saw.

No defect at 5:30 reciprocation 4: Image defect occurs at less than 20 reciprocation 3: Image defect occurs at less than 15 reciprocation 2: Image defect occurs at less than 10 reciprocation 1: Image defect occurs at less than 1: 5 reciprocation

Gloss Evaluation Using piezo-type head KM512M, drawing device EB-100, XY-100 (manufactured by Konica Minolta IJ), solid images (cyan and black) on untreated PVC (METAMARK) using the inks of Table 4 and Table 5. 100%). During printing, the stage was heated, and the vinyl chloride surface temperature was heated to 50 ° C. for printing. After printing, after heating for 5 minutes at 50 ° C., 20 ° gloss was measured.

5:50 or more 4:40 or more but less than 50 3:30 or more but less than 40 2:20 or more but less than 30 1:20 Maintenance recovery evaluation Piezotype head KM512M, drawing device EB-100, XY-100 (manufactured by Konica Minolta IJ) Was used to draw a solid image (cyan 100%) on untreated PVC (METAMARK) using the inks of Tables 4 and 5. During printing, the stage was heated, and the vinyl chloride surface temperature was heated to 50 ° C. for printing. After printing with 100% cyan and black, the head was not capped, and after waiting for a certain period of time, the head was cleaned with the following maintenance liquid, flushed, and then 100% cyan and black 100% were printed again. At this time, the room environment was 30 ° C. at 25 ° C.

  Maintenance liquid: N, N-dimethylaminoethanol 2%, dipropylene glycol monopropyl ether 7%, and the balance 100% with ion-exchanged water.

Even after waiting for 5: 1 hours, solid images could be drawn without missing or bent 4: After 30 minutes or more and less than 1 hour, solid images could be drawn without missing or bent 3: 10 minutes or more 30 After waiting less than a minute, there was no missing or bent, and a solid image could be drawn. 2: After waiting for 10 minutes, bending occurred, but there was no missing. 1: After waiting for 10 minutes, missing occurred and recovered. Not.

  The obtained results are shown in Table 6, Table 7, Table 8, and Table 9.

  In Table 6, Table 7, Table 8, and Table 9, for example, in the preservation table, the intersection of the comparison 1 and C-1 is the evaluation of the ink C1 and represents 1. The blank columns in Tables 8 and 9 are not evaluated because there is no corresponding ink.

  From the results shown in Tables 6 and 7, the inks C7 to C9, C12 to 14 and C17 to 19 of the present invention were compared with C1 to C6, C10, C11, C15, C16 and C20 to C25 for comparison. Provides ink-jet inks that have good storage stability and can be stably ejected even after long-term storage, images printed on various non-absorbent media have high durability, and recovery through maintenance is good I understood. In particular, it can be seen that an ink having a structure in which the acid value of the water-soluble resin is smaller than the acid value of the water-insoluble resin is more effective.

  From the results shown in Tables 8 and 9, the inks C26 to 28 and K1 to K4 of the present invention are ink-jet inks that have good storage stability and can be stably ejected even after long-term storage compared to the comparative ink. It was found that images provided and printed on various non-absorbent media have high durability and good recovery by maintenance.

Claims (7)

  An ink-jet ink containing a water-soluble resin, a water-insoluble resin, a pigment, and water, wherein the water-soluble resin has an acid value of 50 or more and less than 70, and the water-insoluble resin has an acid value of 60 or more and less than 90. An inkjet ink characterized by   The inkjet ink according to claim 1, wherein an acid value of the water-soluble resin is smaller than an acid value of the water-insoluble resin.   The water-soluble resin is an acrylic copolymer with an aromatic group-containing monomer, and the content derived from the aromatic group-containing monomer is less than 20% by mass of the entire water-soluble resin. The inkjet ink according to claim 1 or 2.   The inkjet ink according to any one of claims 1 to 3, wherein the water-soluble resin is an acrylic copolymer having a weight average molecular weight of 20,000 or more and less than 100,000.   The water-insoluble resin is an acrylic copolymer with an aromatic group-containing monomer, and the content derived from the aromatic group-containing monomer is 35% by mass or more and less than 80% by mass of the entire water-insoluble resin. The ink-jet ink according to any one of claims 1 to 4, wherein:   The inkjet ink according to any one of claims 1 to 5, wherein at least a part of the water-insoluble resin covers the pigment.   The inkjet according to any one of claims 1 to 6, wherein the content of the water-insoluble resin is less than the content of the pigment, and the content of the water-soluble resin is greater than the content of the pigment. ink.