JP2007023297A - Ink composition containing stimuli-responsive polymer, and image-forming method using the ink composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stimuli-responsive composition that contains a polymer, a solvent and a substance having a predetermined function. <P>SOLUTION: The stimuli-responsive composition contains the polymer, the solvent and the substance having the predetermined function. One embodiment of the composition contains a block polymer, the solvent and the substance having the predetermined function. Preferably, the solvent in the composition is water, and the polymer in the composition has a polyvinyl ether structure. The superior dispersion stability of the composition is provided in the present invention. The ink composition containing the composition, the image-forming method and the image-forming apparatus using the ink composition, and the recording medium having the composition are also provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink composition and an image forming method using the same. In particular, the ink composition of the present invention is an ink composition comprising a stimulus-responsive polymer, an aqueous solvent, and at least one of a pigment and a dye, and the stimulus-responsive polymer is present in a micelle state in the ink composition. About things.

  Conventionally, color materials such as ink having a colorant as a granular solid are well known. In recent years, digital printing technology has made great progress. This digital printing technology includes what is called inkjet technology, and in recent years, its presence as an image forming technology in offices, homes and the like has been increasingly increased.

  Ink jet technology is a direct recording method among digital printing technologies, and has the major features of compactness and low power consumption. In addition, the image quality is rapidly increasing due to the miniaturization of nozzles. An example of the ink jet technology is a method in which ink supplied from an ink tank is heated by a heater in a nozzle to evaporate and foam, and the ink is discharged to form an image on a recording medium. Another example is a method of ejecting ink from a nozzle by vibrating a piezo element. Ink used in these methods usually uses an aqueous dye solution, so that bleeding occurs when colors are superimposed, or a phenomenon called feathering appears in the fiber direction of the paper at the recording location on the recording medium. was there. The use of pigment-dispersed inks for the purpose of improving these has been studied (for example, US Pat. No. 5,085,698 (Patent Document 1)).

US Pat. No. 5,085,698 Japanese Patent Laid-Open No. 11-080221 JP-A-11-322942 JP-A-11-322866 Japanese Patent Publication No.61-7948 JP-A-3-237426 JP-A-8-82809 JP-A-64-63185 JP-A-8-216392 U.S. Pat. No. 4,723,129 U.S. Pat. No. 4,740,796 US Pat. No. 4,463,359 U.S. Pat. No. 4,345,262 U.S. Pat. No. 4,313,124 U.S. Pat. No. 4,558,333 U.S. Pat. No. 4,459,600 JP 59-123670 A JP 59-138461 A H. J. et al. Schneider, U.S. Pat. No. 30,062,892 (1962)

Although various improvements have been made regarding the ink composition, many improvements are still desired. In addition to the above-described improvement of bleeding and feathering, it is desirable that the ink composition has an increased amount of polymer in the ink composition to ensure fixability and have a low viscosity. Particularly in ink jet applications, it is desired that the ink has a low viscosity.
Accordingly, an object of the present invention is to provide an ink composition as described above.

  The above problems are solved by the present invention described below.

  The ink composition of the present invention comprises a block polymer having a hydrophilic part and a hydrophobic part, an aqueous solvent, and at least one of a pigment and a dye, and the block polymer is dispersed in a micelle form in the solvent. In the ink composition, the block segment that exhibits hydrophilicity when dispersed responds to a stimulus, and the block segment changes from hydrophilic to hydrophobic, thereby compatibilizing the block polymer. It has a stimulus response block that allows it to metastasize.

In the present invention, the block polymer preferably has a function of dispersing the pigment.
The block polymer in the ink composition is amphiphilic having a hydrophilic portion and a hydrophobic component, and an aqueous solvent is used as the solvent. At this time, micelles are formed by the block polymer, and the pigment is well dispersed. In addition, since most of the block polymer does not dissolve in the molecule and is dispersed in a micelle state, the ink composition of the present invention can realize a relatively low viscosity.

  Moreover, it is preferable that the said block polymer has a polyvinyl ether structure in the said hydrophilic part and hydrophobic part. This block polymer preferably has an oxyalkylene structure in at least a part of the side chains.

In the present invention, the polyvinyl ether structure has a repeating unit structure of the following formula (1).
^{_{- (CH 2 -CH (OR 1}} )) - (1)
[Wherein R ¹ is a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms, or — (CH (R ² ) —CH (R ³ ) —O) ₁ —R ⁴ or — (CH ₂ ) _m -(O) _n -R ^{4 is} selected. l and m are each independently selected from an integer of 1 to 12, and n is 0 or 1. R ² and R ³ are each independently H or CH ₃ . R ⁴ is H, a linear, branched or cyclic alkyl group having 1 to 6 carbon atoms, Ph, Pyr, Ph-Ph, Ph-Pyr, —CHO, —CH ₂ CHO, —CO—CH═CH ₂ , When —CO—C (CH ₃ ) ═CH ₂ , CH ₂ COOR ⁵ and R ⁴ is other than hydrogen, the hydrogen on the carbon atom is a linear or branched alkyl group having 1 to 4 carbon atoms or F , Cl, Br, and carbon in the aromatic ring can be substituted with nitrogen, respectively. R ⁵ is H or an alkyl group having 1 to 5 carbon atoms. ]

  The stimulus response block changes from hydrophobic to hydrophilic at a certain temperature or lower.

  The ink composition of the present invention can further contain a surfactant.

  The present invention includes an image forming method characterized in that an image is formed by applying the above-described ink composition onto a recording medium.

  In this image forming method, it is preferable that the recording medium includes a substance that gives a stimulus to the block polymer.

  In the image forming method of the present invention, the substance that gives irritation to the ink composition may be a substance that contains a crosslinking agent that crosslinks the block polymer contained in the ink composition.

  According to the present invention, in addition to improving bleeding and feathering, the amount of polymer in the ink composition can be increased to ensure fixability, and an ink composition having a low viscosity can be provided. In particular, by providing a stimulus response block in the hydrophilic segment of an amphiphilic block polymer (stimulus response block polymer), the recording medium such as on a paper surface has abundant stimulus response segments and can exhibit high fixability. . In the ink composition of the present invention, since the stimulus-responsive block polymer forms a micelle state, the viscosity can be kept low even with a high amount of polymer, and the ink composition can have good ejection performance.

  As a result of intensive studies on the background art and problems, the present inventors have completed the present invention.

  That is, the present invention relates to an ink comprising a block polymer having a hydrophilic part and a hydrophobic part, an aqueous solvent, and at least one of a pigment and a dye, wherein the block polymer is dispersed in a micelle form in the solvent. The block polymer is a composition in which a block segment that exhibits hydrophilicity at the time of dispersion responds to a stimulus, and the block segment changes from hydrophilic to hydrophobic, thereby causing the block polymer to undergo a phase transition. An ink composition having a response block. In particular, in the present invention, the block polymer contained in the composition is preferably a polymer containing a polyvinyl ether structure.

  The ink composition of the present invention contains a granular solid such as a pigment, a dye, and the like. Moreover, the composition of this invention contains a solvent. Although the solvent contained in the composition of this invention is not specifically limited, The medium which can melt | dissolve, suspend, and disperse | distribute the component contained in a composition is meant. In the composition of the present invention, water and an aqueous solvent can be preferably used. Examples of the aqueous solvent include, for example, polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, glycerin, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether. And polyhydric alcohol ethers such as diethylene glycol monoethyl ether and diethylene glycol monobutyl ether, and nitrogen-containing solvents such as N-methyl-2-pyrrolidone, substituted pyrrolidone and triethanolamine. In addition, monohydric alcohols such as methanol, ethanol and isopropyl alcohol can also be used for the purpose of speeding up drying with paper.

  The ink composition of the present invention has a characteristic that the characteristic changes in response to various stimuli. When the composition of the present invention is used as a pigment-dispersed ink material, the composition has high pigment dispersion stability, improved bleeding and feathering when adhered to a recording medium, and excellent fixability. It can be used as a pigment-dispersed ink material. Therefore, the composition as the pigment-dispersed ink material of the present invention can be used as an image forming material with high image quality, low energy consumption, and high speed. In the present invention, the pigment at this time may be a dye.

  The composition of the present invention changes its state (characteristic) in response to various stimuli. For example, the state change can include a phase change from a sol state to a gel state, a phase change from a solution state to a solid state, a chemical structure change, and the like. In the present invention, the stimulus is a change in temperature, application of an electric field, exposure to light (electromagnetic waves) such as ultraviolet rays, visible light, and infrared rays, change in pH of the composition, addition of chemical substances, change in concentration of the composition. And so on. As used herein, the term “stimulus responsiveness” means that the composition of the present invention changes its properties in response to the above stimuli. That is, the stimulus responsiveness means that this stimulus (environmental change) is caused by applying stimulus to the composition, such as exposure to electromagnetic waves, electric field application, temperature change, pH change, chemical substance addition, composition concentration change, etc. It means that the shape and physical properties of the composition change remarkably according to the above. In the present invention, the stimulus-responsive function is realized by the block polymer included in the composition. In the ink composition of the present invention, as a change in properties, the composition causes a phase change (for example, a change from sol to gel) by stimulation, thereby improving the fixability to a recording medium. In the present invention, preferable stimulus responsiveness includes responsiveness shown below. The first is with respect to the temperature change, and the range of the temperature change is the range over the phase transition temperature of the composition. Furthermore, in the composition of the present invention, the stimulus responsiveness is to exposure to electromagnetic waves, and the wavelength range of electromagnetic waves is preferably 100 to 800 nm. Moreover, in the composition of this invention, irritation | stimulation responsiveness is with respect to the pH change of a composition, and it is preferable that the range of pH change is the range of pH3 to pH12. Furthermore, the stimulus responsiveness of the present invention includes changes to the concentration of the composition. An example of this irritation is when the concentration of the composition changes as the solvent of the composition evaporates or is absorbed, or by changing the concentration of dissolved polymer in the composition. it can. In such stimulation, the concentration change is preferably in a range before and after the concentration at which the composition causes a phase transition. In the present invention, at least two kinds of these stimuli may be combined.

  The composition of the present invention contains a pigment or dye and is suitable for use as an ink material using water or a solvent as a solvent. By using the composition of the present invention, it is possible to improve various properties including the fixing property of the ink material.

  The reason why the composition of the present invention is preferably used as an ink is that the polymer used can favorably disperse the pigment and the dye in the solvent. At this time, a polymer having an affinity for the solvent used is used. Particularly in the present invention, the polymer is preferably a copolymer, particularly a block polymer.

  In addition, the block polymer contained in the composition of the present invention can substantially retain the characteristics of the repeating unit structure of each block or unit and exhibit the characteristics in a coexisting form. In particular, the block or unit portion having stimulus responsiveness functions effectively, and can exhibit its functionality more efficiently than random polymers. The block polymers used in the present invention are conventionally known, such as acrylic, methacrylic block polymers, polystyrene and other addition polymerization or condensation polymerization block polymers, and block polymers having polyoxyethylene and polyoxyalkylene blocks. The block polymer can also be used. In a preferred embodiment of the present invention, a block polymer containing a polyvinyl ether structure described below is preferably used.

  The block polymer used in the present invention may have two or more different hydrophilic blocks. Here, “different” means a different chemical structure, means that the monomer structure or the branched structure of the polymer chain is different, and only the molecular chain length of a single repeating unit in the polymer chain is different. It does not mean the state that is. The composition is denatured when at least one hydrophilic block of the two or more different types of these blocks responds to a stimulus, for example, changes from hydrophilic to hydrophobic. On the contrary, the composition may be denatured by the block that showed hydrophobicity under certain conditions responding to the stimulus and changing to a hydrophilic block. A preferable example of the stimulus response of such a block polymer is a block polymer in which the polymer contained in the composition of the present invention has a plurality of blocks, and two or more of the plurality of blocks are hydrophilic blocks (in the present invention, Means a block that remains hydrophilic or can become hydrophilic upon stimulation, at least one of which is stimuli responsive and at least one of the other is always under the conditions of use. This is the case when it is hydrophilic. In such a composition, when the stimulus-responsive block is hydrophobic under certain conditions and is applied in a state of being dispersed in a low-viscous micelle state, the stimulus-responsive block becomes hydrophilic. It is denatured and the polymer is associated, for example, so that it is denatured from a low viscosity dispersion state to a high viscosity polymer solution state. In this way, certain stimuli change the properties of the composition of the present invention.

  Another example is that the composition of the present invention is an aqueous composition and the polymer is a block polymer as described above, and is hydrophilic under conditions where there is a stimuli-responsive block of the block polymer. A composition. In such an aqueous composition, a stimulus is applied from a state in which the polymer is dissolved in the aqueous solution, the stimulus-responsive block is denatured to be hydrophobic, and the composition gels while forming a micelle state, so that the composition is highly drastic. Viscosify.

  As a further example, there is one using a block polymer composed of three types of blocks: a hydrophobic block A, a stimulus-responsive block B, and a hydrophilic block C. In this example, stimulus-responsive block B behaves as a hydrophobic micelle-dispersed condition in which AB is a core under water-dispersing conditions, and stimulation is applied to make B hydrophilic and change to micelle having A as a core. The interaction between micelles changes and gels, and the viscosity increases drastically.

  As described above, when two or more different hydrophilic blocks are used in the present invention, it is possible to express a very preferable stimulus responsiveness particularly when water is used as a solvent.

  In addition, from the viewpoint of molecular design as described above, the block polymer block form is AB type, ABA type, ABC type, ABCD type (where D is a block having a structure different from A, B, C). And may be hydrophilic or hydrophobic.) ABCA type is preferably used.

  A preferred embodiment of the ink composition of the present invention is an aqueous dispersion (ink composition) containing at least one of a block polymer containing a polyvinyl ether structure, water and a particulate solid (pigment) and a dye having stimuli responsiveness. is there. Preferably, the ink composition of the present invention is an ink composition that is used as a color material whose characteristics change by stimulation. In the ink composition of this embodiment, the dispersion stability of the particulate solid (for example, pigment) becomes high, bleeding and feathering are improved, and furthermore, a pigment-dispersed ink material having excellent fixability can be provided. Therefore, the ink composition of the present invention can be used as an image forming material with high image quality, low energy consumption, and high speed.

  In the present specification, the particulate solid means a compound in a solid state, and in a preferred embodiment means a particulate solid substance such as a pigment.

  The ink composition of the present invention contains a block polymer having a polyvinyl ether structure, water, and a granular solid, particularly as a block polymer, so that it is excellent in dispersion stability of the granular solid (eg, pigment) and responds to external stimuli. Thus, the characteristic can be changed to improve color bleeding and feathering. Therefore, the ink composition of the present invention exhibits excellent image fixability. Therefore, it is also suitably used as ink for inkjet printers.

  Hereinafter, the ink composition of the present invention will be described in detail. Further, a description will be given taking a pigment as an example of a granular solid. However, the present invention is not limited to this.

  First, the polyvinyl ether characteristically used in the present invention will be described. The block polymer material containing the polyvinyl ether structure used in the dispersion is characterized by high pigment dispersion stability, improved bleeding and feathering, and excellent fixability, which are the characteristics of the ink composition of the present invention. The place by is big. As described above, the stimulus responsiveness in the present invention means that the dispersion is stimulated by exposure to electromagnetic waves, electric field application, temperature change, pH change, chemical substance addition, composition concentration change, etc. It means that the shape and physical properties of the aqueous dispersion are remarkably changed in response to this stimulus (environmental change). Stimulus responsiveness can be imparted by a block polymer containing a polyvinyl ether structure. In the ink composition of the present invention, the block polymer preferably exhibits a function in terms of dispersion stability of pigments and the like. Accordingly, the polyvinyl ether preferably has a so-called amphiphilic structure having both a hydrophilic portion and a hydrophobic portion. Specifically, a polymer in which a hydrophilic monomer and a hydrophobic monomer are copolymerized can be given as a preferred example. Such a polymer having a polyvinyl ether structure has a soft characteristic that the polyvinyl ether structure generally has a low glass transition point. More preferable dispersion characteristics.

A number of methods for synthesizing a polymer containing a polyvinyl ether structure have been reported (for example, JP-A-11-080221 (Patent Document 2), but a method using cationic living polymerization by Aoshima et al. (JP-A-11-322942 (Patent Document)). 3), Japanese Patent Laid-Open No. 11-322866 (Patent Document 4)) By synthesizing the polymer by cation living polymerization, the block polymer is synthesized with the same length (molecular weight). In addition, various functional groups can be introduced into the side chain of polyvinyl ether, and the cationic polymerization method can also be carried out by HI / I ₂ system, HCl / SnCl ₄ system, or the like.

  The block polymer containing the polyvinyl ether structure used in the present invention can impart dispersibility of a particulate solid such as a pigment to the composition by adding it.

  There is no particular limitation on the stimulus applied to the ink composition containing the block polymer containing the polyvinyl ether structure, water, and particulate solid, but preferably exposure to electromagnetic waves as described above, electric field application, temperature change, Examples include pH change, chemical substance addition, ink composition concentration change, and electron beam irradiation. Even more preferably, exposure to electromagnetic waves, temperature change, pH change, and ink composition concentration change are included. In this specification, exposure to electromagnetic waves refers to exposing the ink composition to light such as ultraviolet rays, visible rays, and infrared rays.

  Below, typical things among the above-mentioned irritation | stimulation are demonstrated and the block polymer containing the polyvinyl ether structure which responds to such irritation | stimulation is illustrated.

  With respect to the stimulus response due to temperature change, for example, changes in ink composition due to solubility, thermal polymerization, polarity change, phase transition (sol-gel transition, liquid crystal) and the like can be mentioned. The range of the temperature change is preferably a range extending around the phase transition temperature of a block polymer containing a polyvinyl ether structure and a granular solid such as water or a pigment, and further a temperature range extending around a critical gelation temperature. Is more preferable. For example, poly (2-methoxyethyl vinyl ether), alkoxy vinyl ether derivatives such as poly (2-ethoxyethyl vinyl ether), etc., or copolymers mainly composed of these polymer compounds are used as polyvinyl ether structures that respond to stimuli due to temperature changes. Can be mentioned. In particular, in a block copolymer made of poly ((2-methoxyethyl vinyl ether) -b- (2-ethoxyethyl vinyl ether)), a sudden viscosity change occurs at 20 ° C. when the block copolymer is used. Here, b of poly ((2-methoxyethyl vinyl ether) -b- (2-ethoxyethyl vinyl ether)) is an abbreviation meaning a block polymer.

  The next stimulus response is exposure to electromagnetic waves. The wavelength range of this electromagnetic wave is more preferably 100 to 800 nm. Examples of the response to stimulation by exposure to electromagnetic waves include solubility, photopolymerization and photochromism, photoisomerization, photodimerization, phase transition (sol-gel transition, liquid crystal) and the like. Examples of the polyvinyl ether structure that responds to the stimulus include vinyl ether derivatives having a polymerizable functional group such as poly (2-vinyloxyethyl methacrylate) or a copolymer mainly composed of these polymer compounds. .

  With respect to the stimulus response due to pH change, it is more preferable that the ink composition responds in the pH range of 3-12. Examples of the response to stimulation by pH change include solubility, hydrogen bond and coordination bond, polarity change, phase transition (sol-gel transition, liquid crystal) and the like. The structure of the polymer containing the polyvinyl ether structure contained in the dispersion that responds to such a stimulus is, for example, an alkoxy vinyl ether derivative such as poly (2-methoxyethyl vinyl ether) or poly (2-ethoxyethyl vinyl ether) and polymethacrylic acid. Examples thereof include copolymers and polymer blends with polycarboxylic acids.

  As a further example, stimulation due to a change in the concentration of the ink composition may be mentioned. Examples of the stimulation include a case where the concentration of the ink composition is changed by evaporating or absorbing water of the ink composition or by changing the concentration of the polymer dissolved in the ink composition. . Regarding this stimulation, a concentration change in a range over the phase transition concentration of the ink composition is preferable, and a concentration change before and after the critical gelation concentration is more preferable. Stimulation by changing the solution concentration includes responsiveness such as hydrogen bonding, hydrophobic interaction, and phase transition (sol-gel transition, liquid crystal). As an example, the main component is an alkoxy vinyl ether derivative such as poly (2-methoxyethyl vinyl ether) or poly (2-ethoxyethyl vinyl ether), an aryloxy vinyl ether derivative such as poly (2-phenoxyethyl vinyl ether), or a polymer compound thereof. And a copolymer.

  Furthermore, it is also possible to combine two or more types of stimuli among these stimuli.

  A block polymer containing a polyvinyl ether structure in an ink composition containing a polyvinyl ether structure, water and a granular solid having stimuli responsiveness is a co-polymer comprising two or more vinyl ethers in order to optimize the physical properties of the polymer. Polymers are preferred. The copolymer is a block polymer in order to maximize the stimulus response of each monomer component constituting the polymer.

  The function of stimuli responsiveness can be achieved by the block polymer itself containing a polyvinyl ether structure, but in the present invention, it can be used in combination with other polymers in order to enhance the function. As an example, giving stimulus responsiveness to a polymer other than a block polymer containing a polyvinyl ether structure and imparting other functions (for example, dispersion stability) to the block polymer containing a polyvinyl ether structure.

  Examples of other polymers having stimulus responsiveness include the following, but the present invention is not limited thereto.

  As a first example, there can be mentioned a polymer which changes the composition of the dispersion when heated by application of heat and causes a phase transition. Specific examples of this polymer include poly (meth) acrylamide, poly-N-alkyl-substituted (meth) acrylamide such as poly-N-isopropyl (meth) acrylamide, polyN-vinylisobutyramide, poly (meth) acrylic acid or the like. Metal salt, poly-2-hydroxyethyl (meth) acrylate, poly-N- (meth) acrylic piperidine, poly (2-ethyloxazoline), polyvinyl alcohol or a partially saponified product thereof, polyethylene oxide, polyethylene oxide and polypropylene oxide Copolymer, poly (ethylene glycol monomethacrylate), poly (ethylene glycol monoacrylate), substituted cellulose such as methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, etc. Conductors, etc., or these polymeric compounds include copolymers or polymer blends as a main component.

  As a second example, there is one in which a polymer structure is changed by a photoreaction by exposure to electromagnetic waves, and the composition of the ink composition is changed to cause a phase transition. Specific examples of this polymer include polymer compounds having groups such as photochromic groups. Specifically, poly N-alkyl substitutions such as poly (meth) acrylamides and poly-N-isopropyl (meth) acrylamides having groups such as triphenylmethane derivatives, spiropyran derivatives and spirooxazine derivatives that are ion cleaved by light. Various types such as a (meth) acrylamide type and an N-vinylisobutyramide type may be mentioned.

  As a third example, there is a polymer in which the composition of the ink composition changes due to a change in pH value and causes a phase transition. Specific examples of this polymer include poly (meth) acrylic acid or a metal salt thereof, polyvinyl sulfonic acid, polyvinyl benzene sulfonic acid, poly (meth) acrylamide alkyl sulfonic acid, polymaleic acid or a metal salt thereof, or a polymer compound thereof. Copolymer obtained by using as a main component a monomer component, polyvinyl alcohol-polyacrylic acid complex or metal salt thereof, poly (ethylene glycol monomethacrylate), metal salt of carboxymethyl cellulose, metal salt of carboxyethyl cellulose, etc. Or the copolymer and polymer blend which have these polymer compounds as a main component are mentioned.

  A fourth example is a polymer that causes a phase transition by changing the concentration of dissolved polymer in the ink composition. Specific examples of this polymer include aqueous solutions of polymer compounds such as poly (meth) acrylamide, poly N-alkyl-substituted (meth) acrylamide, polyvinyl methyl ether, and polymethacrylic acid having a lower critical solution temperature (LCST) (Japanese Patent Publication No. 61). No. 7948 (Patent Document 5), JP-A-3-237426 (Patent Document 6), JP-A-8-82809 (Patent Document 7)), polyvinyl alcohol, polyvinyl alcohol-polyacrylic acid complex or Examples thereof include inorganic polymers such as metal salt poly (ethylene glycol monomethacrylate) and alkoxysiloxane, and copolymers and polymer blends mainly composed of these polymer compounds.

  The structure of the block polymer containing the polyvinyl ether structure in the ink composition containing the block polymer containing the polyvinyl ether structure, water and particulate solid having stimuli responsiveness is a copolymer composed of vinyl ether and another polymer. Also good. The copolymer is a block polymer in order to maximize the stimulus response of each monomer component constituting the polymer.

  In the ink composition of the present invention, a block polymer is preferably used. The block polymer substantially retains the respective characteristics based on the repeating unit structure of each block or unit, and can exhibit the characteristics in a coexisting form. In the block polymer, it is considered that the block or unit portion having stimulus response functions effectively, and the functionality can be exhibited better than the random polymer. Furthermore, in this invention, it is thought that the block polymer used can disperse | distribute a granular solid favorably with respect to an aqueous solvent. At this time, a part of the polymer has affinity for the aqueous solvent to be used. Further, in the case of a block polymer having a polyvinyl ether structure, as described above, AB, ABA, ABC or ABCD (where D is a block having a structure different from A, B and C, and may be hydrophilic or hydrophobic). Etc.) and various block forms are possible, and it is preferable to have two or more different hydrophilic blocks.

  In addition, a polymer other than a block polymer containing a polyvinyl ether structure in an ink composition containing a block polymer containing a polyvinyl ether structure, water, and a granular solid having stimuli responsiveness (for example, the polymer having the above-described stimuli responsiveness). It is also possible to impart or improve stimulus responsiveness by adding.

  The molecular structure of the repeating unit of the block polymer containing a polyvinyl ether structure in the ink composition having the above-described stimulus responsiveness is not particularly limited, but a polymer represented by the following general formula (1) is preferable.

^{_{- (CH 2 -CH (OR 1}} )) - (1)

R ¹ is a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms, phenyl (Ph), pyridyl (Pyr), Ph-Ph, Ph-Pyr, or — (CH (R ² ) —CH ( R ³ ) —O) ₁ —R ⁴ or — (CH ₂ ) _m — (O) _n —R ⁴ , wherein the hydrogen in the aromatic ring is a linear or branched alkyl group having 1 to 4 carbon atoms; Carbon in the aromatic ring can be substituted for nitrogen. l is selected from an integer of 1 to 18, m is selected from an integer of 1 to 36, and n is 0 or 1. R ² and R ³ are each independently H or CH ₃ . R ⁴ is H, a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms, Ph, Pyr, Ph-Ph, Ph-Pyr, —CHO, —CH ₂ CHO, —CO—CH═CH ₂ , When —CO—C (CH ₃ ) ═CH ₂ , CH ₂ COOR ⁵ and R ⁴ is other than hydrogen, the hydrogen on the carbon atom is a linear or branched alkyl group having 1 to 4 carbon atoms or F , Cl, Br, and carbon in the aromatic ring can be substituted with nitrogen, respectively. R ⁵ is H or an alkyl group having 1 to 5 carbon atoms.

Preferably, R ¹ is a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms, or — (CH (R ² ) —CH (R ³ ) —O) ₁ —R ⁴ or — (CH ₂ ). _m— (O) _n —R ^{4 is} selected. l and m are each independently selected from an integer of 1 to 12, and n is 0 or 1. R ² and R ³ are each independently H or CH ₃ . R ⁴ is H, a linear, branched or cyclic alkyl group having 1 to 6 carbon atoms, Ph, Pyr, Ph-Ph, Ph-Pyr, —CHO, —CH ₂ CHO, —CO—CH═CH ₂ , When —CO—C (CH ₃ ) ═CH ₂ , CH ₂ COOR ⁵ and R ⁴ is other than hydrogen, the hydrogen on the carbon atom is a linear or branched alkyl group having 1 to 4 carbon atoms or F , Cl, Br, and carbon in the aromatic ring can be substituted with nitrogen, respectively. R ⁵ is H or an alkyl group having 1 to 5 carbon atoms.

  In the present invention, a linear or branched alkyl group means methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl, tert-butyl, pentyl, n-hexyl, heptyl, octyl, nonyl, decyl. , Undecyl, dodecyl, octadecyl and the like. The cyclic alkyl group includes cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclooctyl and the like. When hydrogen on a carbon atom is substituted, the substitution may be at one location or multiple locations.

  Preferably, the polymer represented by the following general formula (2) is preferable as the repeating unit molecular structure of the block polymer containing the polyvinyl ether structure in the ink composition having stimulus responsiveness described above.

^{_{- (CH 2 -CH (OR 6}} )) - (2)

R ⁶ represents a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms, Ph, Pyr, Ph-Ph, Ph-Pyr, or — (CH ₂ —CH ₂ —O) ₁ —R ⁷ or — (CH ₂ ) _m — (O) _n —R ⁷ , wherein hydrogen in the aromatic ring is substituted with a linear or branched alkyl group having 1 to 4 carbon atoms, and carbon in the aromatic ring is substituted with nitrogen. be able to. l is selected from an integer of 1 to 18, m is selected from an integer of 1 to 36, and n is 0 or 1. R ⁷ is H, a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms, Ph, Pyr, Ph-Ph, Ph-Pyr, —CHO, —CH ₂ CHO, —CO—CH═CH _2. , —CO—C (CH ₃ ) ═CH ₂ , CH ₂ COOR ⁸ , and when R ⁷ is other than hydrogen, the hydrogen on the carbon atom is a linear or branched alkyl group having 1 to 4 carbon atoms or F, Cl, Br, and carbon in the aromatic ring can be substituted with nitrogen, respectively. R ⁸ is H or an alkyl group having 1 to 5 carbon atoms.

Preferably, R ⁶ is a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms, Ph, Pyr, Ph-Ph, Ph-Pyr, or — (CH ₂ —CH ₂ —O) 1 —R ^7. Or — (CH ₂ ) _m — (O) _n —R ⁷ , wherein the hydrogen in the aromatic ring is a linear or branched alkyl group having 1 to 4 carbon atoms, and the carbon in the aromatic ring is nitrogen and Can be replaced. l is selected from an integer of 1 to 18, m is selected from an integer of 1 to 36, and is 0 or 1. R ⁷ is H, a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms, Ph, Pyr, Ph-Ph, Ph-Pyr, —CHO, —CO—CH═CH ₂ , —CO—C ( CH ₃ ) ═CH ₂ and when R ⁷ is other than hydrogen, the hydrogen on the carbon atom is a straight or branched alkyl group having 1 to 4 carbon atoms or F, Cl, Br, and in the aromatic ring Each of the carbons can be replaced with nitrogen.

  More preferably, the structure of the vinyl ether monomer is specified below as the repeating unit molecular structure of the block polymer containing the polyvinyl ether structure in the ink composition having stimuli responsiveness described above. The polyvinyl ether structure used in the present invention is described below. Is not limited to these.

  In the present invention, a block polymer comprising a vinyl ether structure having stimuli responsiveness and composed of these vinyl ether monomers can be suitably used. The polymer that can be used in the present invention is not limited to a block polymer including a polyvinyl ether structure having a stimulus responsiveness composed of the above-mentioned vinyl ether monomer. Examples of the block polymer that are preferable include those specified below, but the polymer used in the present invention is not limited thereto.

  Furthermore, it is preferable that the number of repeating units of polyvinyl ether (x, y, z in the above (II-a) to (II-e) is independently 1 or more and 10,000 or less, and the total Is more preferably 10 or more and 40,000 or less (in the above (II-a) to (II-e) (x + y + z)).

  In the present invention, the polymer preferably has an oxyalkylene structure in at least a part of the side chains.

  Next, other components of the ink composition of the present invention will be described.

[water]
The water contained in the ink composition of the present invention is preferably ion-exchanged water, pure water, or ultrapure water from which metal ions have been removed.

[Aqueous solvent]
Examples of the aqueous solvent include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, glycerin and other polyhydric alcohols, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol. Polyhydric alcohol ethers such as monoethyl ether and diethylene glycol monobutyl ether, nitrogen-containing solvents such as N-methyl-2-pyrrolidone, substituted pyrrolidone, and triethanolamine can be used. In addition, monohydric alcohols such as methanol, ethanol and isopropyl alcohol can be used for the purpose of accelerating the drying of the ink composition on the recording medium.

  The water and aqueous solvent content in the ink composition of the present invention is preferably in the range of 20 to 95% by weight with respect to the total weight of the ink composition. More preferably, it is the range of 30 to 90 weight%.

[Granular solid]
The particulate solid useful in the present invention can be a pigment. The granular solid used in the ink composition of the present invention is preferably 0.1 to 50% by weight based on the weight of the ink composition.

  In the case of the ink which is a preferred embodiment of the ink composition of the present invention, a pigment is usually used as the granular solid. Specific examples of the pigment and dye of the ink of the present invention are shown below.

The pigment may be either an organic pigment or an inorganic pigment, and the pigment used in the ink is preferably a black pigment and three primary color pigments of cyan, magenta, and yellow. Color pigments other than those described above, colorless or light color pigments, metallic luster pigments, and the like may be used. In addition, a newly synthesized pigment may be used for the present invention.
Examples of commercially available pigments for black, cyan, magenta, and yellow are shown below.

  Black pigments include Raven1060, Raven1080, Raven1170, Raven1200, Raven1250, Raven1255, Raven1500, Raven2000, Raven3500, Raven5250, Raven5750, Raven7000, Raven5000, Raven5000, Raven5000, Raven5000, Raven5000, Raven5000, Raven5000, Raven5000, Raven5000U. MOGUL-L, Regal 400R, Regal 660R, Regal 330R, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1300, Monarch 1400 (above, manufactured by Cabot), Color Black F 1, Color Black FW2, Color Black FW200, Color Black 18, Color Black S160, Color Black S170, Special Black 4P, Special Black 4A, Special BlackP No. 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical Co., Ltd.) and the like can be mentioned, but are not limited thereto.

  Examples of cyan pigments include C.I. I. Pigment Blue-1, C.I. I. Pigment Blue-2, C.I. I. Pigment Blue-3, 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-15: 4, C.I. I. Pigment Blue-16, C.I. I. Pigment Blue-22, C.I. I. Pigment Blue-60 etc. are mentioned, but it is not limited to these.

  Examples of magenta pigments include C.I. I. Pigment Red-5, C.I. I. Pigment Red-7, C.I. I. Pigment Red-12, C.I. I. Pigment Red-48, C.I. I. Pigment Red-48: 1, C.I. I. Pigment Red-57, C.I. I. Pigment Red-112, C.I. I. Pigment Red-122, C.I. I. Pigment Red-123, C.I. I. Pigment Red-146, C.I. I. Pigment Red-168, C.I. I. Pigment Red-184, C.I. I. Pigment Red-202, C.I. I. Pigment Red-207 and the like, but are not limited thereto.

  Examples of yellow pigments include C.I. I. Pigment Yellow-12, C.I. I. Pigment Yellow-13, C.I. I. Pigment Yellow-14, C.I. I. Pigment Yellow-16, C.I. I. Pigment Yellow-17, C.I. I. Pigment Yellow-74, C.I. I. Pigment Yellow-83, C.I. I. Pigment Yellow-93, C.I. I. Pigment Yellow-95, C.I. I. Pigment Yellow-97, C.I. I. Pigment Yellow-98, C.I. I. Pigment Yellow-114, C.I. I. Pigment Yellow-128, C.I. I. Pigment Yellow-129, C.I. I. Pigment Yellow-151, C.I. I. Pigment Yellow-154 and the like, but are not limited thereto.

  In the ink composition of the present invention, a pigment that is self-dispersible in water can also be used. Examples of water-dispersible pigments include those using a steric hindrance effect in which a polymer is adsorbed on the pigment surface and those using electrostatic repulsion, and commercially available products include CAB-0-JET200, CAB- Examples thereof include 0-JET300 (manufactured by Cabot Corporation), Microjet Black CW-1 (manufactured by Orient Chemical Co., Ltd.), and the like.

  The pigment used in the ink composition of the present invention is preferably 0.1 to 50% by weight based on the weight of the ink composition. When the amount of the pigment is less than 0.1% by weight, a sufficient image density cannot be obtained, and when it exceeds 50% by weight, the fixability of the image may be deteriorated. A more preferable range is from 0.5 wt% to 30 wt%.

  In addition, the dye that can be used in the ink composition of the present invention may be a known dye, such as a direct dye, an acid dye, a basic dye, a reactive dye, a water-soluble dye for food coloring as described below, or Insoluble pigments of disperse dyes can be used.

For example, water-soluble dyes include C.I. I. Direct black, -17, -19, -22, -32, -38, -51, -62, -71, -108, -146, -154;
C. I. Direct yellow, -12, -24, -26, -44, -86, -87, -98, -100, -130, -142;
C. I. Direct red, -1, -4, -13, -17, -23, -28, 31, -62, -79, -81, -83, -89, -227, -240, -242, -243 ;
C. I. Direct blue, -6, -22, -25, -71, -78, -86, -90, -106, -199;
C. I. Direct orange, −34, −39, −44, −46, −60;
C. I. Direct violet, -47, -48;
C. I. Direct brown, -109;
C. I. Direct green, direct dyes such as -59,
C. I. Acid Black, −2, −7, −24, −26, −31, −52, −63, −112, −118, −168, −172, −208;
C. I. Acid Yellow, -11, -17, -23, -25, -29, -42, -49, -61, -71;
C. I. Acid Red, -1, -6, -8, -32, -37, -51, -52, -80, -85, -87, -92, -94, -115, -180, -254, -256 , -289, -315, -317;
C. I. Acid Blue, −9, −22, −40, −59, −93, −102, −104, −113, −117, −120, −167, −229, −234, −254;
C. I. Acid Orange, -7, -19;
C. I. Acid violet, acid dyes such as -49,
C. I. Reactive Black, -1, -5, -8, -13, -14, -23, 31, 34, -39;
C. I. Reactive Yellow, -2, -3, -13, -15, -17, -18, -23, -24, -37, -42, -57, -58, -64, -75, -76,- 77, -79, -81, -84, -85, -87, -88, -91, -92, -93, -95, -102, -111, -115, -116, -130, -131, -132, -133, -135, -137, -139, -140, -142, -143, -144, -145, -146, -147, -148, -151, -162, -163;
C. I. Reactive Red, -3, -13, -16, -21, -22, -23, -24, -29, 31, 333, 35, 455, -49, -55, -63,- 85, -106, -109, -111, -112, -113, -114, -118, -126, -128, -130, -131, -141, -151, -170, -171, -174, -176, -177, -183, -184, -186, -187, -188, -190, -193, -194, -195, -196, -200, -201, -202, -204, -206 , -218, -221;
C. I. Reactive blue, -2, -3, -5, -8, -10, -13, -14, -15, -18, -19, -21, -25, -27, -28, -38,- 39, −40, −41, −49, −52, −63, −71, −72, −74, −75, −77, −78, −79, −89, −100, −101, −104, -105, -119, -122, -147, -158, -160, -162, -166, -169, -170, -171, -172, -173, -174, -176, -179, -184 , -190, -191, -194, -195, -198, -204, -211, -216, -217;
C. I. Reactive orange, -5, -7, -11, -12, -13, -15, -16, -35, -45, -46, -56, -62, -70, -72, -74,- 82, -84, -87, -91, -92, -93, -95, -97, -99;
C. I. Reactive violet, -1, -4, -5, -6, -22, -24, -33, -36, -38;
C. I. Reactive Green, -5, -8, -12, -15, -19, -23;
C. I. Reactive dyes such as reactive brown, -2, -7, -8, -9, -11, -16, -17, -18, -21, -24, -26, 31, -32, -33;
C. I. Basic black, -2;
C. I. Basic Red, -1, -2, -9, -12, -13, -14, -27;
C. I. Basic blue, -1, -3, -5, -7, -9, -24, -25, -26, -28, -29;
C. I. Basic violet, -7, -14, -27;
C. I. Food black, -1, -2, etc. are mentioned.

  These examples of the color material are particularly preferable for the ink composition of the present invention, but the color material used in the ink composition of the present invention is not particularly limited to the color material. .

  The dye used in the ink composition of the present invention is preferably 0.1 to 50% by weight with respect to the weight of the ink composition. When the amount of the dye is less than 0.1% by weight, a sufficient image density cannot be obtained, and when it exceeds 50% by weight, the fixability of the image may be deteriorated. A more preferable range is from 0.5 wt% to 30 wt%.

  In the present invention, pigments and dyes may be used in combination.

[Additive]
Various additives and auxiliaries can be added to the ink composition of the present invention as necessary.

  One additive of the ink composition is a dispersion stabilizer that stably disperses a pigment in a solvent. The ink composition of the present invention has a function of dispersing a particulate solid such as a pigment with a block polymer containing a polyvinyl ether structure, but when the dispersion is insufficient, other dispersion stabilizers are added. It may be added.

  As another dispersion stabilizer, it is possible to use a resin or a surfactant having both hydrophilic and hydrophobic portions.

  Examples of the resin having both hydrophilic and hydrophobic parts include a copolymer of a hydrophilic monomer and a hydrophobic monomer. Hydrophilic monomers include acrylic acid, methacrylic acid, maleic acid, fumaric acid, or the above carboxylic acid monoesters, vinyl sulfonic acid, styrene sulfonic acid, vinyl alcohol, acrylamide, methacryloxyethyl phosphate, etc. Styrene derivatives such as styrene and α-methylstyrene, vinylcyclohexane, vinylnaphthalene derivatives, acrylic acid esters, and methacrylic acid esters. Copolymers having various configurations such as random, block, and graft copolymers can be used. Of course, both hydrophilic and hydrophobic monomers are not limited to those shown above.

  As the surfactant, an anionic, nonionic, cationic or amphoteric surfactant can be used.

  Anionic activators include fatty acid salts, alkyl sulfate esters, alkyl aryl sulfonates, alkyl diaryl ether disulfonates, dialkyl sulfosuccinates, alkyl phosphates, naphthalene sulfonate formalin condensates, polyoxyethylene alkyls. Examples thereof include phosphate ester salts and glycerol borate fatty acid esters.

  Nonionic activators include polyoxyethylene alkyl ether, polyoxyethyleneoxypropylene block copolymer, sorbitan fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene alkylamine, fluorine-based, silicon-based, etc. It is done.

  Examples of the cationic activator include alkylamine salts, quaternary ammonium salts, alkylpyridinium salts, alkylimidazolium salts and the like.

  Examples of amphoteric activators include alkyl betaines, alkyl amine oxides, phosphadyl cholines and the like. Similarly, the surfactant is not limited to the above.

  Furthermore, the ink composition of the present invention may contain a composition containing an additive (crosslinking agent) having a function of crosslinking with the block polymer in the ink composition containing the block polymer. Such a composition is preferably used as the ink composition of the present invention.

  The composition containing the cross-linking agent is provided, for example, as a composition separate from the ink composition of the present invention, and can be in contact with the composition when necessary. Specifically, for example, in the case of ink jet ink, an ink tank containing the ink composition of the present invention and an ink tank containing a composition containing a crosslinking agent are prepared, and each composition is recorded separately. For example, it may be ejected and brought into contact with a medium. In addition to this, a composition containing a cross-linking agent is provided in advance on a recording medium, and the ink composition of the present invention is ejected and brought into contact therewith.

  Furthermore, an aqueous solvent can be added to the ink composition of the present invention as necessary. In particular, when used in an inkjet ink, the aqueous solvent is used to prevent drying at the nozzle portion of the ink and solidification of the ink, and can be used alone or in combination. As the aqueous solvent, those described above are applied as they are. In the case of ink, the content is 0.1 to 60% by weight, preferably 1 to 25% by weight, based on the total weight of the ink.

  Other additives include, for example, a pH adjuster for stabilizing the ink and the stability of the ink pipes in the recording apparatus, and penetrating that accelerates ink penetration into the recording medium and accelerates apparent drying. Agent, antifungal agent that prevents wrinkles in the ink, chelating agent that blocks metal ions in the ink and prevents the deposition of metal in the nozzle part and insoluble matter in the ink, Anti-foaming agent, antioxidant, anti-fungal agent, viscosity modifier, conductive agent, ultraviolet absorber, water-soluble dye, disperse dye for preventing the circulation and movement of recording liquid or generation of foam during recording liquid production And oil-soluble dyes.

  The specific contents of the inkjet ink (aqueous dispersion ink), which is a preferred embodiment of the ink of the present invention, are described below.

[Inkjet ink creation method]
As a method for preparing the ink-jet ink of the present invention, a pigment and a dispersion stabilizer are added to water and a water-soluble solvent, dispersed using a disperser, coarse particles are removed by centrifugation or the like, and then water is added. Or what adds a solvent, an additive, etc., performs stirring, mixing, and filtration can be mentioned as an example.

  Examples of the disperser include an ultrasonic homogenizer, a laboratory homogenizer, a colloid mill, a jet mill, and a ball mill, and these may be used alone or in combination.

  Even when a self-dispersing pigment is used, it can be prepared by the same operation as the above method.

[Image Forming Method and Image Forming Apparatus]
The aqueous dispersion ink in the present invention can be used in various image forming apparatuses such as various printing methods, ink jet methods, and electrophotographic methods, and can be drawn by an image forming method using this device.

When the aqueous dispersion ink is used as an inkjet ink, in the present invention, for example, it can be used in the following manner. The ink can be aggregated by the following stimuli (a) to (d).
(A) When used as an ink that responds to a temperature stimulus The ink jet ink of the present invention is compatible with the temperature stimulus due to the difference between the temperature of the ink in the ink tank and the temperature of the ink on the recording medium deposited by ejection. Changes occur and the thickening or insoluble components agglomerate rapidly.
(B) When used as ink that responds to electromagnetic wave stimulation: Ink in an ink tank that is a dark room and ink that is exposed to visible light by ejection or irradiated with electromagnetic waves by an electromagnetic wave irradiation unit provided in an ink jet recording apparatus Due to the difference, polymerization of the polymerized functional group of the polymer contained in the ink-jet ink of the present invention occurs, which leads to rapid thickening or aggregation of insoluble components.
(C) When used as ink that responds to stimulation due to pH change When the pH changes due to the influence of the recording medium, the pH of the ink in the ink tank differs from the pH of the ink attached to the recording medium. As a result, the inkjet ink of the present invention undergoes a phase change, and thickened or insoluble components aggregate.
(D) When ink-jet ink responding to stimulation due to density change is used The ink density in the ink tank and the water and aqueous solvent contained in the ejected ink are evaporated or absorbed by the recording medium. There is a difference between the ink density and the ink density, and the difference causes the ink-jet ink of the present invention to undergo a phase change to cause thickening or insoluble components to aggregate.

  By modifying the properties of these inks, it is possible to improve color bleeding and feathering, and to exhibit excellent fixing properties. The modification of the ink is not limited to the above-described thickening or aggregation of insoluble components.

  Various methods can be applied to the method of applying the stimulus. One preferred method is to mix or contact the stimulating composition with the previously described stimuli-responsive ink. For example, an ink jet method can be applied as a method of mixing the pH-responsive ink of (b) with a composition having a corresponding pH. As described in Japanese Patent Application Laid-Open No. 64-63185 (Patent Document 8), a stimulating composition can be driven over the entire surface of an image forming region by an ink jet head. As described in Japanese Patent Application Laid-Open No. 8-216392 (Patent Document 9), the amount of the composition that serves as a stimulus can be controlled to form a more excellent image.

  It is also possible to use the stimulating composition together with an ink containing a dye or a pigment. For example, ink that gives a stimulus to one of the cyan-magenta-yellow-black (CMYK) inks used in the color ink jet method is used, and ink that responds to the stimulus is used for any one of the CMYK inks. It is possible to improve. There are various combinations of CMYK for which stimulus-responsive ink is used, and for which other stimulus ink is used. In the present invention, any combination may be used. It is not intended to limit. Further, the kind of stimulating composition and stimulus response ink can be performed in all of the aforementioned stimulus response patterns, and is not particularly limited.

  In one embodiment of the present invention, the stimulating composition includes a composition containing an additive having a function of crosslinking with the block polymer in the ink composition containing the block polymer. That is, in a preferable embodiment of the image forming method of the present invention, the block is prepared as an ink composition containing a block polymer having a stimulus responsiveness, a solvent, and a substance having a predetermined function, and a composition that gives a stimulus to the composition. By bringing the polymer into contact with a composition containing a crosslinking additive (crosslinking agent), the ink composition is fixed on the recording medium and an excellent image is formed. As the substance having a predetermined function, a pigment is preferably used, and specific examples thereof include the aforementioned pigment group.

  The block polymer in the ink composition is amphiphilic having a hydrophilic portion and a hydrophobic portion, and water or an aqueous solvent is used as a solvent. In such a composition, micelles are formed by the block polymer and the pigment is well dispersed. In addition, a relatively low viscosity can be realized by dispersing the block polymer in a micelle state without dissolving the molecule. As the block polymer, the polymer group of the present invention described above can be used, but the block polymer having the polyvinyl ether structure described above is preferably used. In the present invention, such a composition is brought into contact with a composition containing a crosslinking agent capable of reacting or forming a complex with the block polymer portion, so that micelles take a network structure and the ink increases. Sticky and excellent fixability. Therefore, the image forming method using such a composition of the present invention is an image forming method having excellent fixability.

  When the ink composition for inkjet of the present invention is brought into contact with the composition containing the crosslinking agent, these compositions can be provided as separate compositions, for example. For example, the inkjet ink composition and the composition containing the crosslinking agent may be put in separate packages and used in contact with each other when necessary. As a specific drawing method, for example, in the case of inkjet ink, an ink tank containing the ink composition of the present invention and an ink tank containing a composition containing a crosslinking agent are prepared, and each composition is separately prepared. There is a method of drawing by ejecting and contacting the same recording medium. In addition to this, a composition containing a cross-linking agent is provided in advance to a recording medium by means such as coating or spraying, and the ink composition of the present invention is ejected and brought into contact therewith for drawing. The method of doing is mentioned.

  When the ink composition of the present invention is brought into contact with the composition containing such a crosslinking agent, the concentration of the crosslinking agent is increased, or the ink composition of the present invention is used by using a multifunctional crosslinking agent. It is possible to denature the product into a gel state. In the image forming method of the present invention using a crosslinking agent, it is preferable to use a block polymer having a polyvinyl ether structure. As the preferred monomer for synthesizing the block polymer having a polyvinyl ether structure, the above (Ia) to (Io) can be mentioned. In a preferred embodiment of the present invention in which the composition of the present invention is brought into contact with the composition containing a crosslinking agent, a block polymer having a polyvinyl ether structure is preferably used. a) to (II-e).

For an ink composition containing a block polymer having a polyvinyl ether structure that is preferably used in the present invention, it is preferable to use a compound having a carboxyl group as a functional group as a crosslinking agent. This is because a carboxyl group and a side chain having an oxyethyleneoxy structural unit as shown in the structural example of the polymer are easy to form a complex. Since the compound containing a carboxyl group functions as a crosslinking agent, it preferably has a plurality of carboxyl groups. Therefore, examples of the compound containing a carboxyl group include compounds such as dicarboxylic acid, tricarboxylic acid, and polycarboxylic acid. Specific _{examples, HOOC- (CH 2) p -COOH} , HOOC- (CH 2) p CH (COOH) (CH 2) q -COOH, polyacrylic acid, polymethacrylic acid, polymethyl acrylate acrylic acid copolymer Low molecular and high molecular polyfunctional carboxylic acid compounds such as polymers and polymethyl methacrylate methacrylic acid copolymers can be used. Here, in the above formula, p is an integer of 1 to 40, and q is an integer of 1 to 40.

  It is also preferable to provide a mechanism for stimulating the recording medium in advance. For example, a method of recording on acidic paper using acidic responsive ink among pH responsive inks can be used. In this case, the recording medium has a function of giving a stimulus to the stimulus-responsive ink of the present invention. Such a recording medium is included in the present invention. That is, the present invention relates to a recording medium having a function of giving such a stimulus. In the present invention, the recording medium may be in any known form. For example, plain paper, thermal paper, acid paper, etc. can be mentioned.

  As the ink jet printer using the ink jet ink of the present invention, there are various ink jet recording apparatuses such as a piezo ink jet method using a piezoelectric element and a thermal ink jet method in which ink is foamed by applying thermal energy.

  In the case of inkjet ink, the amount of ink ejected from the ejection port of the ejection head is preferably in the range of 0.1 picoliter to 100 picoliter.

  In particular, in the case of an ink jet recording apparatus, as an aspect thereof, the recording apparatus includes an ink composition having a stimulus responsiveness containing a block polymer, a solvent, and at least one of a pigment and a dye, and a composition for stimulating the composition. And a means for bringing the block polymer into contact with a composition containing an additive for crosslinking (crosslinking agent). In this embodiment, the ink composition is fixed on the recording medium by this contact, and an excellent image is formed. As the substance having a predetermined function, a pigment is preferably used, and specific examples thereof include the pigment group and the dye group described above.

  In the ink composition used in the present invention, a composition containing a component in which at least a part of the polymer structure changes from hydrophobic to hydrophilic at 20 ° C. or lower, preferably 10 ° C. or lower is used. Is preferred.

  In addition, the aqueous dispersion ink of the present invention (the ink composition of the present invention) is also used in an indirect recording apparatus using a recording method in which the ink is printed on an intermediate transfer member and then transferred to a recording medium such as paper. Can do. Also, the present invention can be applied to an apparatus using an intermediate transfer member by a direct recording method.

  In particular, the ink composition of the present invention can be used in an electrophotographic recording type image forming method and an image forming apparatus. For example, the image forming apparatus includes a photosensitive drum for forming a latent image, and includes a means (such as an exposure device) for forming a latent image on the photosensitive drum, an ink applying unit, a transfer mechanism, and a recording medium. Things can be mentioned. In the formation of an image by this apparatus, first, a latent image is formed on a photosensitive drum, the ink composition of the present invention is applied to the latent image or a portion other than the latent image, and the obtained image is transferred to a recording medium by a transfer mechanism. Transfer and fix.

  An outline of the ink jet recording apparatus will be described below with reference to FIG. However, FIG. 1 is merely an example of the configuration and does not limit the present invention.

  FIG. 1 is a block diagram showing the configuration of the ink jet recording apparatus.

  FIG. 1 shows a case where recording is performed on a recording medium by moving the head. In FIG. 1, an X direction drive motor 56 and a Y direction drive motor 58 for driving the head 70 in the XY directions include an X motor drive circuit 52 and a Y motor drive circuit 54 for the CPU 50 that controls the overall operation of the manufacturing apparatus. Connected through. In accordance with an instruction from the CPU, the X direction drive motor 56 and the Y direction drive motor 58 are driven through the X motor drive circuit 52 and the Y motor drive circuit 54, and the position of the head 70 with respect to the recording medium is determined.

  As shown in FIG. 1, a head drive circuit 60 is connected to the head 70 in addition to the head 70 in addition to the X direction drive motor 56 and the Y direction drive motor 58, and the CPU 50 controls the head drive circuit 60. The head 70 is driven, that is, ink jet ink is discharged. Further, an X encoder 62 and a Y encoder 64 for detecting the head position are connected to the CPU 50, and position information of the head 70 is input. A control program is also input into the program memory 66. The CPU 50 moves the head 70 based on this control program and the positional information of the X encoder 62 and the Y encoder 64, disposes the head at a desired position on the recording medium, and ejects ink for inkjet. In this way, desired drawing can be performed on the recording medium. Further, in the case of an image recording apparatus capable of loading a plurality of ink jet inks, desired drawing can be performed on a recording medium by performing the above-described operation for each ink jet ink a predetermined number of times.

  In addition, after ejecting the ink jet ink, the head 70 is moved to a position where removing means (not shown) for removing excess ink adhering to the head is arranged, if necessary. It can also be cleaned by wiping or the like. As a specific method of cleaning, a conventional method can be used as it is.

  When drawing is completed, the drawn recording medium is replaced with a new recording medium by a recording medium conveyance mechanism (not shown).

  Note that the present invention can be modified or modified without departing from the gist of the present invention. For example, in the above description, the example in which the head 70 is moved in the XY axis direction has been shown. However, the head 70 is moved only in the X axis direction (or Y axis direction), and the recording medium is moved in the Y axis direction (or X axis). The image may be drawn while moving in the axial direction) and interlocking with each other.

  The present invention includes means for generating thermal energy (for example, an electrothermal converter, a laser beam, etc.) as an energy source used for ejecting inkjet ink, and ejects inkjet ink by the thermal energy. The head has an excellent effect. According to this method, high definition of drawing can be achieved. By using the ink-jet ink of the present invention, further excellent drawing can be performed.

  The typical configuration and principle of the apparatus provided with the means for generating thermal energy are disclosed in, for example, US Pat. Nos. 4,723,129 (Patent Document 10) and 4740796 (Patent Document 11). Those which are carried out using the basic principles that are described are preferred. This method can be applied to both the so-called on-demand type and the continuous type. In particular, in the case of the on-demand type, the liquid is retained and electrothermal conversion is arranged corresponding to the flow path. By applying to the body at least one drive signal corresponding to the ejection information and providing a rapid temperature rise exceeding the nucleate boiling, heat energy is generated in the electrothermal transducer, and film boiling occurs on the heat acting surface of the head. As a result, bubbles in the liquid corresponding to the drive signal on a one-to-one basis can be formed, which is effective. By the growth and contraction of the bubbles, the liquid is discharged through the discharge opening to form at least one droplet. It is more preferable that the drive signal has a pulse shape, since the bubble growth and contraction is performed immediately and appropriately, and thus it is possible to achieve liquid discharge with particularly excellent responsiveness. As this pulse-shaped drive signal, those described in US Pat. No. 4,463,359 (Patent Document 12) and US Pat. No. 4,345,262 (Patent Document 13) are suitable. In addition, if the conditions described in U.S. Pat. No. 4,313,124 (Patent Document 14) of the invention relating to the temperature rise rate of the heat acting surface are adopted, further excellent discharge can be performed.

  As the configuration of the head, in addition to the combination configuration (straight liquid channel or right-angle liquid channel) of the discharge port, the liquid channel, and the electrothermal transducer as disclosed in each of the above-mentioned specifications, A configuration using US Pat. No. 4,558,333 (Patent Document 15) and US Pat. No. 4,459,600 (Patent Document 16) disclosing a configuration arranged in a bending region is also included in the present invention. . In addition, for a plurality of electrothermal transducers, Japanese Unexamined Patent Publication No. 59-123670 (Patent Document 17) that discloses a configuration in which a common slit is used as a discharge portion of an electrothermal transducer or a pressure wave of thermal energy is disclosed. The effect of the present invention is also effective as a configuration based on Japanese Patent Application Laid-Open No. 59-138461 (Patent Document 18) that discloses a configuration in which an opening to be absorbed corresponds to a discharge portion. In other words, regardless of the form of the head, according to the present invention, it is possible to reliably and efficiently discharge ink jet ink.

  Further, the present invention can be effectively applied to a full-line type head having a length corresponding to the maximum width of a recording medium in the image forming apparatus of the present invention. As such a head, either a configuration satisfying the length by a combination of a plurality of heads or a configuration as a single head integrally formed may be used.

  In addition, a serial type head that is fixed to the main body of the apparatus or mounted on the main body of the apparatus can be electrically connected to the main body of the apparatus and ink can be supplied from the main body. The present invention is also effective when a chip-type head is used.

  Furthermore, the apparatus of the present invention may further include a droplet removing unit. When such means is provided, a further excellent discharge effect can be realized.

  In addition, it is preferable to add preliminary auxiliary means or the like as the configuration of the apparatus of the present invention because the effects of the present invention can be further stabilized. Specifically, a capping unit for the head, a pressurizing or sucking unit, an electrothermal converter or a heating element different from this, or a preheating unit for heating using a combination thereof, A preliminary ejection means for performing ejection other than the ejection of ink can be used.

  The most effective for the present invention is to execute the above-described film boiling method.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples. In the following examples, a pigment dispersion ink will be described as an example of a method for synthesizing a block polymer containing a polyvinyl ether structure of the present invention and an ink composition. In the examples of these polymer synthesis and pigment dispersion inks, only some specific examples are described, but the present invention is not limited thereto.

<Polymer synthesis>
Preparation of monomer: 2-methoxyethyl vinyl ether (hereinafter abbreviated as MOVE) and 2-ethoxyethyl vinyl ether (hereinafter abbreviated as EOVE) were obtained by combining 2-chloroethyl vinyl ether, sodium methoxide and sodium ethoxide, respectively, with tetrabutylammonium. It was synthesized by refluxing using an iodide catalyst (HJ Schneider, US Pat. No. 30,628,921 (1962) (Patent Document 19)). 2-vinyloxyethyl methacrylate (hereinafter abbreviated as VEM) was synthesized by the Williamson reaction.

1) Synthesis of AB diblock polymer composed of MOVE and EOOVE. (External stimulus: temperature)
Preparation of monomer: Prepared in the same manner as in Example 1.
Synthesis of AB diblock polymer: The inside of a glass container equipped with a three-way cock was replaced with nitrogen, and then heated at 250 ° C. in a nitrogen gas atmosphere to remove adsorbed water. After returning the system to room temperature, 12 mmol of MOVE, 16 mmol of ethyl acetate, 0.1 mmol of 1-isobutoxyethyl acetate and 11 ml of toluene were added, and when the temperature in the system reached 0 ° C., ethylaluminum sesquichloride was reduced to 0. Polymerization was started by adding 2 mmol, and the A component of the AB block polymer was synthesized. The molecular weight was monitored in a time-sharing manner using molecular sieving column chromatography (GPC), and after the polymerization of the A component was completed, synthesis was carried out by adding 12 mmol of EOVE as the B component. The polymerization reaction was stopped by adding a 0.3 wt% ammonia / methanol solution to the system. Diluted by adding dichloromethane to the mixed solution after the reaction, washed 3 times with 0.6N hydrochloric acid solution, then 3 times with distilled water, concentrated and dried with an evaporator, and vacuum dried to obtain the desired product A MOVE-EOVE diblock polymer was obtained. The compound was identified using NMR and GPC, and satisfactory spectra were obtained in both cases (Mn = 2.5 × 10 ⁴ , Mn / Mw = 1.3).

2) Synthesis of AB diblock polymer consisting of MOVE and VEM. (External stimulus: light, heat)
Synthesis of AB diblock polymer: The inside of a glass container equipped with a three-way cock was replaced with nitrogen, and then heated at 250 ° C. in a nitrogen gas atmosphere to remove adsorbed water. After returning the system to room temperature, 12 mmol of MOVE, 16 mmol of ethyl acetate, 0.1 mmol of 1-isobutoxyethyl acetate and 11 ml of toluene were added, and when the temperature in the system reached 0 ° C., ethylaluminum sesquichloride was reduced to 0. Polymerization was started by adding 2 mmol, and the A component of the AB block polymer was synthesized. The molecular weight was monitored in a time-sharing manner using molecular sieve column chromatography (GPC), and after the polymerization of the A component was completed, the polymerization was carried out by adding 12 mmol of VEM as the B component. The polymerization reaction was stopped by adding a 0.3 wt% ammonia / methanol solution to the system. Diluted by adding dichloromethane to the mixed solution after the reaction, washed 3 times with 0.6N hydrochloric acid solution, then 3 times with distilled water, concentrated and dried with an evaporator, and vacuum dried to obtain the desired product A MOVE-VEM diblock polymer was obtained. The compound was identified using NMR and GPC, and satisfactory spectra were obtained in both cases (Mn = 2.6 × 10 ⁴ , Mn / Mw = 1.3).
In the same manner, other block polymers were synthesized.

<Preparation of pigment dispersion ink>
Example 1
[Method for Preparing Inkjet Ink of the Present Invention]
In this example, only the method for preparing the black ink was described. The inks of other colors can be prepared by the same operation procedure as described below (the pigment composition is changed to the pigment of each color).

A pigment, a polymer containing a polyvinyl ether structure, and diethylene glycol were added to ion-exchanged water and dispersed using an ultrasonic homogenizer. The dispersion was processed with a centrifuge (20,000 rpm × 20 minutes), and coarse particles were removed to obtain a pigment dispersion.
Appropriate amounts of an aqueous solvent, ion-exchanged water, and additives were added to the pigment dispersion, followed by pressure filtration through a 1 μm filter to prepare an inkjet ink. (Total 100 parts)
Various stimulus-responsive inks were prepared using the pigment dispersions obtained as described above.
(A) Ink-jet ink responding to stimulation by density change According to the above-described ink-jet ink preparation method, it was prepared using the following composition.

(B) Ink for inkjet responding to stimulation due to pH change According to the method for preparing the inkjet ink described above, it was prepared using the same composition as the inkjet ink responding to stimulation due to the concentration change in (a) above.
(C) Ink-jet ink responding to temperature stimulus According to the ink-jet ink preparation method described above, the ink-jet ink was prepared using the same composition as the ink-jet ink responding to the stimulus due to the concentration change in (a).

Comparative Example 1
[Method for preparing ink-jet ink using self-dispersing pigment]
According to the same operation method as in Example 1 (a polymer containing a polyvinyl ether structure was not used), an inkjet ink was prepared using the following composition.

<Bulk characteristics of ink>
The bulk characteristics of the inks (a), (b) and (c) will be described below.
15 parts by weight of a block polymer MOVE-b-EOOVE was added to 100 parts by weight of the ink (a) after being cooled to 10 ° C. and dissolved. When this was heated to 45 ° C., it thickened rapidly and gelled. This is probably because the EOVE block was hydrophilic at a low temperature, and the EOVE block was hydrophobized and gelled by raising the temperature of the block polymer dissolved in the solvent to 45 ° C. This also means that at 45 ° C., the block polymer MOVE-b-EOOVE exhibits a good dispersion state at a low concentration, while causing gelation when the concentration is increased.

  When an aqueous solution of 5 wt% polyacrylic acid at pH 2 was added to the ink of (b) and adjusted to pH 3, a black precipitate was formed also in this case, and a part of the gel was also generated. This is thought to be because the carboxylic acid of polyacrylic acid and the block polymer formed a complex.

  In the ink (c), carbon black was well dispersed at room temperature to form a black ink, but when heated to 85 ° C., a black precipitate was formed. This is thought to be because dispersibility deteriorated because the block of MOVE was modified to be hydrophobic.

<Printing test>
Example 2
Using the ink-jet ink prepared in Example 1 and Comparative Example 1, the fixing strength was evaluated. The ink-jet inks of Example 1 and Comparative Example 1 were filled in a print head of EPSON Stylus COLOR 900 (manufactured by EPSON) and recorded on plain paper using the ink-jet printer.
The evaluation was made by checking whether another blank plain paper was pressed to the printing section with a load of 4.9 × 10 ⁴ N / m ² one minute after recording, and whether ink adhered to the blank plain paper.

(A) Evaluation of Inkjet Ink Responding to Stimulation Due to Density Change In recording using the present inkjet ink, the landing portion of the ejected ink in the inkjet printer was recorded by heating to about 40 ° C. with a heater.

Evaluation of fixing strength Ink adhesion to white plain paper was not observed.
It is considered that the aqueous solvent was evaporated or absorbed by the recording medium, and the MOVE-b-EOOVE concentration exceeded the critical phase transition concentration, causing phase transition.

(B) Evaluation of inkjet ink responding to stimulation by pH change In recording using the inkjet ink, first, a 5% by weight aqueous solution of polyacrylic acid having a pH of 4 is sprayed on plain paper as a recording medium. A recording medium that can be stimulated was created. This was subjected to ink jet recording in the same manner as described above.

Evaluation of fixing strength Ink adhesion to white plain paper was not observed. It is thought that MOVE-b-EOVE and polyacrylic acid have complexed.

(C) Evaluation of inkjet ink responding to temperature stimulus In recording using the inkjet ink, the landing portion of the ejected ink in the inkjet printer was heated to about 80 ° C. for recording.

Evaluation of fixing strength Ink adhesion to white plain paper was not observed.
It is considered that MOVE-b-EOVE has undergone phase transition by heating to 80 ° C.

Comparative Example 2
Evaluation of Inkjet Ink Using Self-Dispersing Pigment Recording was performed using the inkjet ink prepared in Comparative Example 1 above.

  Compared with the results of the ink-jet ink of the present invention of Example 1, it took time to dry.

Evaluation of fixing strength Ink adhesion was observed on plain white paper.

Example 3
The carbon black used in Example 1 was dissolved in water-soluble dye C.I. I. Ink was prepared with the same composition in place of Food Black 2 and evaluated in response to the pH stimulation. The same results were obtained.

Example 4
Cyan dye C.I. I. A cyan ink having a pH of 3 or higher was prepared using the following composition using Basic Blue 75.

  Using this ink as a cyan ink and using the black ink of Example 1 (a), a vertical stripe pattern of cyan and black was printed on plain paper with BJC-600J manufactured by Canon Inc. Further, the same output was performed with the ink attached to the BJC-600J. When these were visually evaluated for sensory evaluation, the former using the ink of the present invention had less color bleeding.

Example 5
Using the MOVE-b-VEM block polymer synthesized in 2) above, inkjet inks were similarly prepared using the compositions shown in Table 1. This was used to perform a printing test in response to pH stimulation in Example 2. That is, spraying a 5 wt% aqueous solution of polyacrylic acid having a pH of 4 onto plain paper, which is a recording medium, to create a recording medium that can be stimulated, and performing inkjet recording on the recording medium as described above, As in the previous examples, good fixability could be realized.

  Although the example in the case of drawing by contacting the composition of this invention and the composition which gives irritation | stimulation by the following examples is demonstrated in detail, this invention is not limited to these Examples.

Example 6
Ion-exchange 5 parts by weight of pigment (Cabot Mogul L), 4 parts by weight of AB block polymer of MOVE-b-VEM (Mn = 2.6 × 10 ⁴ , Mn / Mw = 1.3), and 4 parts by weight of diethylene glycol. In addition to 87 parts by weight of water, the mixture was dispersed using an ultrasonic homogenizer. The dispersion was processed with a centrifuge (20,000 rpm × 20 minutes), and coarse particles were removed to obtain a pigment dispersion.

  The pigment dispersion was pressure filtered through a 1 μm filter to prepare an inkjet ink.

A composition for providing irritation was prepared as follows.
(I) A composition for stimulating was prepared by mixing 6 parts by weight of adipic acid, 5 parts by weight of diethylene glycol, and 89 parts by weight of ion-exchanged water.
(Ii) 3 parts by weight of polymethacrylic acid, 5 parts by weight of diethylene glycol, and 92 parts by weight of ion-exchanged water were mixed to prepare a composition that gives stimulation.

<Printing test>
Example 7
Fixing strength was evaluated using the inkjet ink prepared in Example 6 and the stimulating compositions (i) and (ii).

The ink was filled into a Canon BJF800 print head and recorded on plain paper. Each of the inkjet ink and the compositions (i) and (ii) was recorded and evaluated at the same location in a range of 1 cm ² .

The evaluation was made by checking whether another blank plain paper was pressed to the printing section with a load of 4.9 × 10 ⁴ N / m ² one minute after recording, and whether ink adhered to the blank plain paper.

Evaluation of fixing strength Ink adhesion to white plain paper was not observed.

<Bulk characteristics of the stimulus-responsive ink and the cross-linking agent composition>
When 1 ml of the ink of Example 6 and 1 ml each of the compositions (i) and (ii) were mixed, remarkable thickening was observed in both. In particular, when the ink of Example 7 and the composition (ii) were mixed, a gel was formed.

<Evaluation of dispersion stability>
Example 8
The dispersion stability of the prepared ink composition was evaluated. For the evaluation, an ink having the composition described in Table 1 was used and left in a constant temperature layer at 20 ° C. and 10 ° C., and the dispersion state after 40 days was visually observed. As a result, no precipitate was observed in the ink composition described in the present invention, and good dispersion stability was exhibited particularly on the low temperature side.

It is a block diagram which shows the structure of an inkjet recording device.

Explanation of symbols

20 Inkjet recording device 50 CPU
52 X motor drive circuit 54 Y motor drive circuit 56 X direction drive motor 58 Y direction drive motor 60 Head drive circuit 62 X encoder 64 Y encoder 66 Program memory 70 Head

Claims (11)

  An ink composition comprising a block polymer having a hydrophilic part and a hydrophobic part, an aqueous solvent, and at least one of a pigment and a dye, wherein the block polymer is dispersed in a micelle form in the solvent. The block polymer has a stimulus-responsive block that causes a phase transition of the block polymer by a block segment that exhibits hydrophilicity when dispersed responds to a stimulus and the block segment changes from hydrophilic to hydrophobic. An ink composition characterized by comprising:   The ink composition according to claim 1, wherein the block polymer has a function of dispersing the pigment.   The ink composition according to claim 2, wherein the block polymer has a polyvinyl ether structure in the hydrophilic portion and the hydrophobic portion.   The ink composition according to claim 3, wherein the block polymer has an oxyalkylene structure in at least a part of side chains. The ink composition according to claim 3, wherein the polyvinyl ether structure has a repeating unit structure represented by the following formula (1).
^{_{- (CH 2 -CH (OR 1}} )) - (1)
[Wherein R ¹ is a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms, or — (CH (R ² ) —CH (R ³ ) —O) ₁ —R ⁴ or — (CH ₂ ) _m -(O) _n -R ^{4 is} selected. l and m are each independently selected from an integer of 1 to 12, and n is 0 or 1. R ² and R ³ are each independently H or CH ₃ . R ⁴ is H, a linear, branched or cyclic alkyl group having 1 to 6 carbon atoms, Ph, Pyr, Ph-Ph, Ph-Pyr, —CHO, —CH ₂ CHO, —CO—CH═CH ₂ , When —CO—C (CH ₃ ) ═CH ₂ , CH ₂ COOR ⁵ and R ⁴ is other than hydrogen, the hydrogen on the carbon atom is a linear or branched alkyl group having 1 to 4 carbon atoms or F , Cl, Br, and carbon in the aromatic ring can be substituted with nitrogen, respectively. R ⁵ is H or an alkyl group having 1 to 5 carbon atoms. ]   2. The ink composition according to claim 1, wherein the stimulus response block changes from hydrophobic to hydrophilic at a certain temperature or lower.   The ink composition according to claim 1, further comprising a surfactant.   An image forming method comprising forming an image by applying the ink composition according to claim 1 onto a recording medium.   The image forming method according to claim 8, wherein the recording medium includes a substance that gives a stimulus to the block polymer.   The image forming method according to claim 8, wherein the ink composition is ejected and applied onto a recording medium by the action of thermal energy.   9. The image forming method according to claim 8, wherein the substance that gives a stimulus to the ink composition is a substance containing a crosslinking agent that crosslinks the block polymer contained in the ink composition.

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