Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D11/00—Inks
  • C09D11/30—Inkjet printing inks
  • C09D11/32—Inkjet printing inks characterised by colouring agents
  • C09D11/322—Pigment inks
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/17—Ink jet characterised by ink handling
  • B41J2/175—Ink supply systems ; Circuit parts therefor
  • B41J2/17503—Ink cartridges
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/21—Ink jet for multi-colour printing
  • B41J2/2107—Ink jet for multi-colour printing characterised by the ink properties
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D11/00—Inks
  • C09D11/30—Inkjet printing inks
  • C09D11/32—Inkjet printing inks characterised by colouring agents

Definitions

• the present invention relates to an ink jet aqueous ink, an ink cartridge including the above-described aqueous ink, and an ink jet recording method.
• the ink jet recording method It is possible to record on various recording medium by the ink jet recording method.
• various inks for example, an ink suitable for recording images with the image quality of a photograph on glossy paper or the like and an ink suitable for recording documents on plain paper or the like, in accordance with the purposes have been proposed.
• the ink jet recording method has been utilized for printing a business document including characters and charts, where plain paper or the like is used as a recording medium.
• the frequency of utilization for such an application has increased significantly.
• a further enhancement in color developability of an image is required.
• the recording speed is important and, therefore, an improvement in ejection characteristics of an ink is required than ever.
• PTL 1 describes an ink containing a self-dispersible pigment, in which a functional group, e.g., a carboxylic acid group, is bonded to a particle surface, and a salt, and it is stated that the color developability of an image is enhanced as the density of the functional group on the particle surface becomes high.
• PTL 2 describes an ink containing a self-dispersible pigment in which a functional group having high reactivity with calcium is bonded to the surface of a pigment particle.
• PTL 2 further describes an ink containing a self-dispersible pigment with a phosphonic acid group and a self-dispersible pigment with another functional group, and an ink containing a self-dispersible pigment with a functional group including both the phosphonic acid group and the carboxylic acid group.
• the color developability can be further enhanced by containing the salt in the ink to a large extent, although the color developability of an image of a recording medium having high permeability is still insufficient. If the salt is contained in the ink to a large extent in order to enhance the color developability, a salting-out effect is exerted pronouncedly, so that the particle diameter of the pigment increases significantly and a problem may occur in ejection of the ink.
• the color developability of a recorded image can be enhanced to some extent by using the self-dispersible pigment, in which the functional group, e.g., a phosphonic acid group is bonded and which has high reactivity with calcium, as a coloring material.
• the ink containing such a self-dispersible pigment exhibited insufficient intermittent ejection stability. Specifically, it was ascertained that the ink was not ejected in some cases where an ink was ejected again after an ejection orifice to eject the ink was left opened for a certain period, such as, several seconds to several ten seconds.
• the ink containing the self-dispersible pigment with the phosphonic acid group and the self-dispersible pigment with another functional group exhibited insufficient intermittent ejection stability.
• the ink containing the self-dispersible pigment with the functional group including both the phosphonic acid group and the carboxylic acid group exhibited relatively high intermittent ejection stability as compared with the ink containing the self-dispersible pigment with the functional group including only the phosphonic acid group.
• the color developability at the level required in recent years was not obtained.
• the present invention provides an aqueous ink exhibiting excellent intermittent ejection stability and being capable of obtaining an image having high color developability and an ink cartridge and an ink jet recording method by using the above-described aqueous ink.
• An aqueous ink for ink jet contains a self-dispersible pigment in which a first functional group including a phosphonic acid group and a second functional group including at least one of a carboxylic acid group and a sulfonic acid group are bonded to a particle surface, wherein a surface charge amount derived from the phosphonic acid group included in the above-described first functional group is 0.3 micromoles/m 2 or more, a total surface charge amount derived from the carboxylic acid group and the sulfonic acid group included in the above-described second functional group is 1.0 micromoles/m 2 or more, and a total surface charge amount derived from anionic groups included in the above-described first functional group and the above-described second functional group is 2.0 micromoles/m 2 or more and 8.0 micromoles/m 2 or less.
• an aqueous ink exhibiting excellent intermittent ejection stability and being capable of obtaining an image having high color developability and an ink cartridge and an ink jet recording method by using the above-described aqueous ink are provided.
• an ink jet aqueous ink may be simply referred to as an ink and a self-dispersible pigment may be simply referred to as a pigment.
• the intermittent ejection stability is different depending on the solubility of the anionic group into water. That is, a salt of carboxylic acid and a salt of sulfonic acid have relatively high solubility in water, whereas a salt of phosphonic acid has relatively low solubility in water. Consequently, when evaporation of water and the like in the ink proceeds, the self-dispersible pigment having the carboxylic acid group or the sulfonic acid group can keep the dispersion state stably. On the other hand, as for the phosphonic acid group, the dispersion state of the self-dispersible pigment becomes unstable easily, so that the viscosity of the ink increases because of aggregation of the pigment and the particle diameter of the pigment increases.
• the self-dispersible pigment with an increased introduced amount of the functional group including the anionic group because of the first functional group and the second functional group was used, so that the image having high color developability was able to be recorded and the ink exhibiting excellent intermittent ejection stability was able to be obtained.
• the mechanism of an improvement in the intermittent ejection stability due to an increase in the introduced amount of the functional group including the anionic group is considered.
• the introduced amount of the functional group including the anionic group increases, the anionic group capable of forming a hydrogen bond with a water molecule increases correspondingly, so that the hydrophilicity of the self-dispersible pigment is improved.
• the concentration of water in the ink in the vicinity of the ejection orifice is reduced locally.
• the self-dispersible pigment moves in the direction of high water concentration, in which a more stable dispersion state thereof is maintained easily because of conformability with water, that is, in the direction with decreasing proximity to the ejection orifice in an ink flow path of a recording head.
• concentration of the pigment in the ink in the vicinity of the ejection orifice is relatively reduced and, thereby, an increase in viscosity of the ink due to evaporation of water and the like is suppressed, so as to improve the intermittent ejection stability of the ink.
• the mechanism of an improvement in the intermittent ejection stability in particular, in an environment at a high temperature and a low humidity due to introduction of a predetermined amount or more of carboxylic acid group and sulfonic acid group included in the second functional group in addition to the first functional group is considered.
• the phosphonic acid group causes an unstable dispersion state of the self-dispersible pigment easily, the viscosity of the ink is increased by aggregation of the pigment, and the particle diameter of the pigment increases.
• the ink which is described in PTL 2 and which contains the self-dispersible pigment with the functional group including the phosphonic acid group and the self-dispersible pigment with another functional group exhibits insufficient intermittent ejection stability of the ink. This is because even when the self-dispersible pigment with another functional group is present in the ink, the hydrophilicity of the self-dispersible pigment with the functional group including the phosphonic acid group is not enhanced.
• the mechanism of obtainment of an image exhibiting high color developability due to the ink by using the self-dispersible pigment with both the first functional group including the phosphonic acid group and the second functional group including at least one of the carboxylic acid group and the sulfonic acid group is considered.
• high color developability of an image due to introduction of the functional group including the phosphonic acid group is because of aggregation of the pigment on the basis of formation of the cross-linking structure between particles through the phosphonic acid group. Therefore, it is confirmed that degradation in color developability of an image is limitative insofar as the first functional group including the phosphonic acid group is present at an amount more than or equal to the amount required for forming the cross-linking structure.
• the introduced amount of the first functional group including the phosphonic acid group and the second functional group including the carboxylic acid group or the sulfonic acid group is too large, the total introduced amount of anionic groups becomes too large. In this case, too strong electric repulsion occurs between a plurality of pigment particles, formation of the cross-linking structure through the phosphonic acid group is hindered and, as a result, the color developability of an image is degraded.
• the ink which is described in PTL 2 and which contains the self-dispersible pigment with the functional group including both the phosphonic acid group and the carboxylic acid group exhibited intermittent ejection stability at an acceptable level but insufficient color developability of an image.
• a self-dispersible pigment it is estimated that the introduced amount of the anionic group is increased by increasing the introduced amount of the functional group, the hydrophilicity of the self-dispersible pigment is enhanced and, in addition, the intermittent ejection stability of the ink is improved because the carboxylic acid group having high solubility in water is present.
• the total amount of anionic groups included in the first functional group and the second functional group of the self-dispersible pigment is required to become a predetermined value or more and, in addition, the amount of at least one of the carboxylic acid group and the sulfonic acid group included in the second functional group is required to become a predetermined amount or more. Meanwhile, in order to obtain an image exhibiting high color developability, it is necessary that the following two conditions are satisfied.
• the amount of phosphonic acid group included in the first functional group of the self-dispersible pigment is required to become a predetermined amount or more and, in addition, the total amount of anionic groups included in the first functional group and the second functional group of the self-dispersible pigment is required to become a predetermined value or less.
• the surface charge amount derived from the phosphonic acid group included in the first functional group is 0.3 micromoles/m 2 or more
• the total surface charge amount derived from the carboxylic acid group and the sulfonic acid group included in the second functional group is 1.0 micromoles/m 2 or more
• the total surface charge amount derived from anionic groups included in the first functional group and the second functional group is 2.0 micromoles/m 2 or more and 8.0 micromoles/m 2 or less.
• the surface charge amount derived from anionic groups included in the respective functional groups is expressed in the number of moles per unit surface area of a pigment particle. This is because both the formation of the cross-linking structure through the phosphonic acid group and the formation of the hydrogen bond between the anionic group and a water molecule occur on the surface of the pigment particle or in the vicinity thereof and, therefore, the number of moles per unit surface area of a pigment particle becomes dominant to frequency of them.
• the color developability of a recorded image is enhanced by using the self-dispersible pigment, in which a predetermined amount or more of functional group including the phosphonic acid group is bonded, as a coloring material.
• the self-dispersible pigment in which a predetermined amount or more of functional group including the phosphonic acid group is bonded, as a coloring material.
• the relationship between the type of the anionic group included in the functional group which is bonded to the self-dispersible pigment and the long-term ejection stability of the ink containing the free copper ion is explained below.
• the above-described anionic group is the phosphonic acid group
• a cross-linking structure is formed between pigment particles through the phosphonic acid group and a copper ion. Therefore, the phosphonic acid groups to disperse the self-dispersible pigment are reduced and the stability of the dispersion state of the self-dispersible pigment is degraded to some extent as compared with the case of the ink not containing the free copper ion.
• thermo method in which an ink is ejected from a recording head by the action of thermal energy, hydrated water of the phosphonic acid group is eliminated by the thermal energy applied to the ink during ejection, so that the stability of the dispersion state is further degraded. Consequently, part of the self-dispersible pigment lose the dispersibility and is accumulated on the heater of the recording head because of kogation. If long-term ejection is performed, irregular ejection of the ink occurs because of the accumulation.
• anionic group is the carboxylic acid group or the sulfonic acid group
• these anionic groups do not form the cross-linking structure through the copper ion, so that the stability of the dispersion state is not degraded. Therefore, degradation in the long-term ejection stability does not occur regardless of the presence or absence of the free copper ion in the ink.
• the free copper ion in the ink was captured by a so-called chelating agent, but in the case where the content in the ink was specified to be at a level of suppressing degradation in the long-term ejection stability, the color developability was somewhat degraded in some cases as compared with the case where the chelating agent was not used. The reason for this is confirmed to be that formation of the cross-linking structure between pigment particles through the phosphonic acid group and the cation is hindered because the cation is deprived by the chelating agent.
• the former formation of the cross-linking structure is the same mechanism as that of obtainment of high color developability, which is one of the effects of the present invention. Therefore, the long-term ejection stability and the color developability are in the relationship of tradeoff (refer to the above-described action of the chelating agent). Consequently, the present inventors considered that the latter suppression of elimination of hydrated water from the phosphonic acid group by the thermal energy was effective.
• the bonding energy to hydrated water is different depending on the type of the anionic group. Therefore, it is considered that the dispersion state of the self-dispersible pigment is able to be suppressed from becoming unstable on the basis of the thermal energy by specifying the introduced amount of the functional group including the anionic group exhibiting strong bonding energy to hydrated water to be a predetermined amount or more.
• the present inventors performed studies on the type of the anionic group and the introduced amount of the functional group including the anionic group.
• the color developability of a recorded image is enhanced by using the self-dispersible pigment, in which a predetermined amount or more of functional group including the phosphonic acid group is bonded, as a coloring material.
• the self-dispersible pigment in which a predetermined amount or more of functional group including the phosphonic acid group is bonded, as a coloring material.
• the present inventors performed studies in order to suppress deformation and swelling of the synthetic rubber in the case where the ink in the above-described first embodiment further contained the free copper ion and was applied to an ink jet recording apparatus including a member formed from a material containing synthetic rubber. As a result, it was found that in addition to the conditions required of the self-dispersible pigment in the above-described first embodiment, satisfaction of the surface charge amount derived from the phosphonic acid group included in the first functional group of 2.0 micromoles/m 2 or more was necessary. Such an ink according to the third embodiment is allowed to suppress deformation or swelling of the synthetic rubber included in the ink jet recording apparatus even when the free copper ion is contained.
• the self-dispersible pigment is used as a coloring material of the ink according to aspects of the present invention.
• usable pigment species include inorganic pigments, e.g., carbon black, calcium carbonate and titanium oxide; and organic pigments, e.g., azo, phthalocyanine and quinacridone.
• inorganic pigments e.g., carbon black, calcium carbonate and titanium oxide
• organic pigments e.g., azo, phthalocyanine and quinacridone.
• dye and the like may be used in combination in addition to the pigment.
• the content (percent by mass) of the self-dispersible pigment in the ink is preferably 0.1 percent by mass or more and 15.0 percent by mass or less, and further preferably 1.0 percent by mass or more and 10.0 percent by mass or less with reference to the total mass of the ink.
• the first functional group including the phosphonic acid group and the second functional group including at least one of the carboxylic acid group and the sulfonic acid group are chemically bonded to the surface of the pigment particle.
• the first functional group including the phosphonic acid group does not include the carboxylic acid group and the sulfonic acid group. This is because the effect of enhancing the color developability of an image by the ink is hindered, where the ink contains the self-dispersible pigment with the functional group including the anionic group, which is only the phosphonic acid group, as described above.
• a phosphonic acid group in the ink, may be in the state of being partly dissociated or in the state of being wholly dissociated. That is, the phosphonic acid group may take any form of -PO 3 H 2 (acid type), -PO 3 H - M 1 + (monobasic salt) and -PO 3 2- (M 1 + ) 2 (dibasic salt).
• M 1 represents independently at least one type selected from the group consisting of a hydrogen atom, an alkali metal, ammonium and organic ammonium. Examples of alkali metals represented by M 1 include lithium, sodium and potassium.
• Examples of organic ammonium represented by M 1 include alkylamines having the carbon number of 1 or more and 3 or less, e.g., methylamine and ethylamine; and alkanolamines having the carbon number of 1 or more and 4 or less, e.g., monoethanolamine, diethanolamine and triethanolamine.
• two phosphonic acid groups can be included in the first functional group including the phosphonic acid group.
• the color developability of an image is more enhanced. If three or more phosphonic acid groups are included in the first functional group, the storage stability of the ink is not obtained sufficiently in some cases.
• the other atomic group can have at least one of an alkylene group and an arylene group and a group exhibiting a hydrogen bonding property (amide groups, sulfonyl groups, amino groups, carbonyl groups, ester groups and ether groups).
• amide groups, sulfonyl groups, amino groups, carbonyl groups, ester groups and ether groups can be included in the first functional group.
• the structure of -CQ(PO 3 [M 1 ] 2 ) 2 can be included in the first functional group bonded to the surface of the pigment particle.
• Q represents any one of a hydrogen atom, R, OR, SR and NR 2
• R represents independently any one of a hydrogen atom, an alkyl group, an acyl group, an aralkyl group and an aryl group.
• R represents a group including a carbon atom
• the number of carbon atoms included in the group is preferably 1 to 18.
• M 1 represents independently at least one type selected from the group consisting of a hydrogen atom, an alkali metal, ammonium and organic ammonium.
• the first functional group including the structure of -CH(PO 3 [M 1 ] 2 ) 2 , where Q described above represents a hydrogen atom, can be bonded to the surface of the pigment particle.
• these anionic groups can be present at a terminal of the functional group, that is, other atomic group (-R-) can be present between the surface of the pigment particle and these acid groups.
• other atomic groups include the same groups as the above-described groups.
• a carboxylic acid group (-COOM 1 ) or a sulfonic acid group (-SO 3 M 1 ) may be either in the state of being partly dissociated or in the state of being wholly dissociated.
• M 1 include the same as those described above.
• the introduced amount of each functional group is specified to be as described below. It is necessary to adjust the introduced amount of the first functional group in such a way that the surface charge amount derived from the phosphonic acid group included in the first functional group becomes 0.3 micromoles/m 2 or more.
• the surface charge amount derived from the phosphonic acid group included in the first functional group is further preferably 0.5 micromoles/m 2 or more. If the surface charge amount derived from the phosphonic acid group included in the first functional group is less than 0.3 micromoles/m 2 , the color developability of an image is not obtained.
• the upper limit of the surface charge amount derived from the phosphonic acid group included in the first functional group is preferably 3.0 micromoles/m 2 or less. Meanwhile, it is necessary to adjust the introduced amount of the second functional group in such a way that the total surface charge amount derived from the carboxylic acid group and the sulfonic acid group included in the second functional group becomes 1.0 micromoles/m 2 or more. If the total surface charge amount derived from the carboxylic acid group and the sulfonic acid group included in the second functional group is less than 1.0 micromoles/m 2 , the intermittent ejection stability is not obtained.
• the upper limit of the total surface charge amount derived from the carboxylic acid group and the sulfonic acid group included in the second functional group is preferably 7.7 micromoles/m 2 or less.
• the total surface charge amount derived from anionic groups included in the first functional group and the second functional group is further preferably 2.5 micromoles/m 2 or more and 6.0 micromoles/m 2 or less, and particularly preferably 2.5 micromoles/m 2 or more and 5.0 micromoles/m 2 or less.
• the total surface charge amount derived from anionic groups included in the first functional group and the second functional group is less than 2.0 micromoles/m 2 , the intermittent ejection stability is not obtained, and if more than 8.0 micromoles/m 2 , the color developability of an image is not obtained.
• the second functional group in addition to the indispensable conditions of the self-dispersible pigment in the first embodiment, can have the sulfonic acid group, and the surface charge amount derived from the sulfonic acid group included in the second functional group can be adjusted to 1.0 micromoles/m 2 or more. If the surface charge amount derived from the sulfonic acid group included in the second functional group is less than 1.0 micromoles/m 2 or more, in some cases, the long-term ejection stability is not obtained sufficiently when the ink containing a free copper ion is applied to the thermal method.
• the upper limit of the surface charge amount derived from the sulfonic acid group included in the second functional group is preferably 7.7 micromoles/m 2 or less.
• the surface charge amount derived from the phosphonic acid group included in the first functional group can be adjusted to 2.0 micromoles/m 2 or more. If the surface charge amount derived from the phosphonic acid group included in the first functional group is less than 2.0 micromoles/m 2 , when the ink containing the free copper ion is brought into contact with the synthetic rubber contained in the ink jet recording apparatus, deformation and swelling of the synthetic rubber are not suppressed sufficiently in some cases.
• the upper limit of the surface charge amount derived from the phosphonic acid group included in the first functional group is preferably 3.0 micromoles/m 2 or less.
• first embodiment, second embodiment and third embodiment may be combined. That is, in the case where an ink containing the free copper ion is applied to an ink jet recording apparatus in which synthetic rubber is contained in a member to be brought into contact with the ink and which is provided with a thermal method recording head, the combination of the above-described conditions can be satisfied.
• the surface charge amount derived from the phosphonic acid group included in the first functional group is preferably 2.0 micromoles/m 2 or more
• the surface charge amount derived from the sulfonic acid group included in the second functional group is preferably 1.0 micromoles/m 2 or more
• the total surface charge amount derived from anionic groups included in the first functional group and the second functional group is preferably 2.0 micromoles/m 2 or more and 8.0 micromoles/m 2 or less.
• the measurement of the surface charge amount derived from anionic groups included in the first functional group and the second functional group which is bonded to the self-dispersible pigment is performed by a colloidal titration method.
• This method has merits, that is, in the case where the amount of anionic groups per unit surface area of pigment is determined, this method is simple as compared with the conventional method in which the amount of anionic groups is determined on the basis of quantification of counter ions, the accuracy is high, and the amount of anionic groups is measured directly.
• the surface charge amount of the pigment in a pigment dispersion was measured by using an automatic potentiometric titrator (trade name "AT-510"; produced by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a stream potential titration unit (PCD-500) on the basis of colloidal titration utilizing a potential difference.
• PCD-500 stream potential titration unit
• methyl glycol chitosan was used as a titrant.
• the surface charge amount derived from the first functional group including the phosphonic acid group is calculated from the quantitative value of phosphorus atom on the basis of an ICP emission spectrochemical analyzer and NMR. More specifically, the amount of phosphorus atom is determined by using the ICP emission spectrochemical analyzer. In the whole phosphorus atoms included in the self-dispersible pigment, the proportion of phosphorus atoms derived from the first functional group including the phosphonic acid group is specified by analyzing the structure thereof on the basis of NMR and the like.
• the number of dissociation of the phosphonic acid group in the ink is determined by using potentiometric titration and the like.
• the number of dissociation of the phosphonic acid group is 1 in the pH range of 8 to 10 which is a pH range of an ink used usually.
• the specific surface area of the self-dispersible pigment used in aspects of the present invention is preferably 50 m 2 /g or more and 250 m 2 /g or less. If the specific surface area is less than 50 m 2 /g, the particle diameter of the pigment in the state of being dispersed in an ink tends to become large, and the storage stability of the ink may be degraded to some extent.
• the specific surface area in the present invention is a value measured by a nitrogen adsorption method (BET method) on the basis of the Brunaur-Emmett-Teller method.
• the second embodiment and the third embodiment according to the present invention are predicated that a free copper ion is present in the ink.
• This free copper ion refers to a copper ion which does not constitute a coordinate structure with other substances and which is present in the state of being dissolved in an aqueous medium constituting the ink. Therefore, for example, a copper ion contained as a center atom of a phthalocyanine structure, that is, a copper ion constituting a coordinate structure, is not included in the free copper ion according to the aspects of the present invention.
• the copper ion constituting the coordinate structure does not cause the technical issues to be solved in the second and third embodiments.
• control may be performed in such a way that the free copper ion is added to an ink intentionally to increase the electrolyte concentration in the ink and, thereby, the pigment is aggregated in a recording medium after water and the like are evaporated.
• the free copper ion may be unintentionally mixed as impurities of various materials, e.g., a coloring material and a water-soluble organic solvent, constituting the ink.
• the free copper ion may be eluted from members and the like constituting an ink cartridge and the free copper ion may be mixed into an ink.
• the free copper ion may be mixed as impurities thereof.
• the content of the free copper ion in common deionized water or ion-exchanged water is less than or equal to the detection limit.
• the total amount of phosphonic acid groups included in the first functional group is preferably 10.0 times the content of the free copper ion in the ink on a molar ratio basis. If the total amount of phosphonic acid groups included in the first functional group is less than 10.0 times the content of the free copper ion in the ink on a molar ratio basis, deformation or swelling of the synthetic rubber may not be suppressed sufficiently. This is considered to be related to the capability of the phosphonic acid group to form a chelate structure with the free copper ion and it is considered that if the amount of phosphonic acid group is small, the free copper ion is not captured effectively by the phosphonic acid group.
• the upper limit of the above-described molar ratio is preferably 10,000 times or less.
• the ink according to aspects of the present invention can contain an aqueous medium which is water or a mixed solvent of water and a water-soluble organic solvent.
• a water-soluble organic solvent As for the water, deionized water or ion-exchanged water can be used.
• the ink according to aspects of the present invention is an aqueous ink containing at least water as an aqueous medium.
• the content (percent by mass) of water in the ink is preferably 40.0 percent by mass or more and 95.0 percent by mass or less with reference to the total mass of the ink.
• any solvent usable for an ink jet ink e.g., alcohols, glycols, glycol ethers and nitrogen-containing compounds, may be used, and at least one type of them may be contained in the ink.
• the water-soluble organic solvent can have a vapor pressure lower than that of water at 25 degrees Celsius.
• the content (percent by mass) of the water-soluble organic solvent in the ink is preferably 3.0 percent by mass or more and 50.0 percent by mass or less, and further preferably 20.0 percent by mass or more and 25.0 percent by mass or less with reference to the total mass of the ink.
• the value of this content includes the content of the compound.
• the present inventors pursued the mechanism of enhancement in the above-described intermittent ejection stability of the ink and performed studies. Specifically, studies were performed to intentionally control the conformability of the above-described self-dispersible pigment to water on the basis of the type of the water-soluble organic solvent contained in the ink together with the self-dispersible pigment and maintain the dispersion state more stably with ease. As a result, the intermittent ejection stability of the ink was further improved by containing at least one of the compound represented by Formula (1) described below and the compound represented by Formula (2) described below as the water-soluble organic solvent into the ink.
• the content (percent by mass) of at least one of the compound represented by Formula (1) described below and the compound represented by Formula (2) described below is preferably 0.5 percent by mass or more and 10.0 percent by mass or less with reference to the total mass of the ink. In the case where the compound represented by Formula (1) and the compound represented by Formula (2) are used in combination, this range of the content is a total content thereof.
• R-(O-CH 2 CH 2 ) n -OH Formula (1) where n represents an integer of 3 or more and 30 or less, R represents a hydrogen atom or C m H 2m+1 and m represents an integer of 1 or more and 4 or less) OH-C k H 2k -OH Formula (2) (where k represents an integer of 4 or more and 6 or less)
• Examples of compounds in which R in Formula (1) is a hydrogen atom include triethylene glycol, tetraethylene glycol and polyethylene glycol having a number average molecular weight of 200 to 1,000.
• Examples of compounds in which R in Formula (1) is C m H 2m+1 include ethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monopropyl ether and triethylene glycol monobutyl ether.
• Examples of compounds represented by Formula (2) include 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol.
• the compounds represented by Formula (1) and Formula (2) are water-soluble organic solvents which exhibit relatively high hydrophobicity, which is capable of forming a hydrogen bond with water, and which has a vapor pressure lower than that of water at 25 degrees Celsius, so as to function to reduce the water activity. If such a water-soluble organic solvent is present in the ink, the water activity is reduced and, thereby, formation of a hydrogen bond between the anionic group of the self-dispersible pigment and the water molecule is hindered. As a result, the conformability of the self-dispersible pigment to the water is reduced.
• the ink according to aspects of the present invention can contain a salt constituted by combining a cation and an anion. Consequently, an image exhibiting further high color developability is obtained.
• the cation is at least one type selected from the group consisting of an alkali metal ion, an ammonium ion and an organic ammonium ion.
• salts constituted by combining the cation and the anion examples include (M 2 )Cl, (M 2 )Br, (M 2 )I, (M 2 )ClO, (M 2 )ClO 2 , (M 2 )ClO 3 , (M 2 )ClO 4 , (M 2 )NO 2 , (M 2 )NO 3 , (M 2 ) 2 SO 4 , (M 2 ) 2 CO 3 , (M 2 )HCO 3 , HCOO(M 2 ), (COO(M 2 )) 2 , COOH(COO(M 2 )), CH 3 COO(M 2 ), C 2 H 4 (COO(M 2 )) 2 , C 6 H 5 COO(M 2 ), C 6 H 4 (COO(M 2 )) 2 , (M 2 ) 3 PO 4 , (M 2 ) 2 HPO 4 and (M 2 )H 2 PO 4 .
• the above-described M 2 represents at least one type selected from the group consisting of an alkali metal ion, an ammonium ion and an organic ammonium ion.
• alkali metal ions include a lithium ion, a sodium ion and a potassium ion.
• organic ammonium include alkylamines having the carbon number of 1 or more and 3 or less, e.g., methylamine and ethylamine; and alkanolamines having the carbon number of 1 or more and 4 or less, e.g., monoethanolamine, diethanolamine and triethanolamine.
• M 2 can be a potassium ion from the viewpoint of the color developability of an image and the storage stability of the ink.
• the anion constituting the salt can be, in particular, at least one type selected from the group consisting of C 2 H 4 (COO - ) 2 , C 6 H 4 (COO - ) 2 and SO 4 2- .
• the salts constituted containing these anions can be employed because the dispersion stability of the pigment is especially excellent even when water and the like in the ink are evaporated.
• the enhancement in the color developability due to the salt occurs because the electrolyte concentration in the ink increases, an electric double layer is compressed more easily and, thereby, aggregation of the pigment is facilitated. Therefore, from the viewpoint of enhancement in the color developability, it can be said that the electrolyte concentration in the ink, that is, the number of moles of the salt, is more dominant than the type of ion constituting the salt.
• the present inventors studied the influence of addition of the salt to the ink on the intermittent ejection stability of the ink and the color developability of an image. Specifically, examination was performed by using two types of the inks, that is, the ink according to an aspect of the present invention containing a predetermined self-dispersible pigment and a conventional ink containing a self-dispersible pigment having the phosphonic acid group. As a result, the intermittent ejection stability of the ink according to an aspect of the present invention was not degraded, whereas that of the conventional ink was degraded significantly.
• the self-dispersible pigment contained in the ink according to an aspect of the present invention the carboxylic acid group or the sulfonic acid group included in the second functional group are present in the state of ionic dissociation easily and, therefore, the dispersion state of the pigment is suppressed from becoming unstable in the vicinity of the ejection orifice, as described above.
• the term "resin is water-soluble” refers to that when this resin is neutralized by alkali equivalent to the acid value, no particle having a measurable particle diameter is formed.
• the resin satisfying such a condition is referred to as a water-soluble resin in the present specification.
• the term "(meth)acryl” in the present specification refers to acryl and methacryl.
• the resin has low water solubility and, therefore, is present not in the dissolved state, but in the state of having a particle diameter (dispersed state, that is, the state of emulsion or dispersion) in the ink.
• a particle diameter dispersion or dispersion
• the polyvalent cation concentration in the ink of the recording medium increases, a large aggregate is not formed because the resin is originally in the phase-separated state and is not newly precipitated, and in some cases, an effect of further enhancing the color developability of an image is not obtained sufficiently.
• the suitable ranges of the acid values of the acrylic resin and the urethane resin are different because the hydrophilicity/hydrophobicity of the main structures of the respective resins are different and, thereby, the ranges of acid values suitable for efficient aggregation on the recording medium are different.
• the degree of enhancement in the color developability was limitative.
• the reason for this is confirmed to be that the water-soluble resin is adsorbed by the surface of pigment particles because the surface charge amount of the pigment is low and the water-soluble resin in the dissolved state is prevented from becoming insoluble rapidly.
• the dispersion state of the self-dispersible pigment is stabilized by adsorption of the water-soluble resin. This may contributes to the fact that enhancement in the color developability was not observed.
• the color developability was not enhanced to a large extent.
• the reason for this is estimated to be that the aggregability of the pigment is originally low, and the timings of formation of aggregate on the recording medium of the water-soluble resin and the self-dispersible pigment are different.
• the weight average molecular weight of the water-soluble resin is preferably 5,000 or more and 200,000 or less as a weight average molecular weight in terms of polystyrene obtained by gel permeation chromatography (GPC). If the weight average molecular weight is less than 5,000, even when salts, e.g., calcium, contained in the recording medium are dissolved into the ink applied to the recording medium, large aggregates are not formed easily, and in some cases, an effect of enhancing the color developability of an image is not obtained sufficiently. On the other hand, if the weight average molecular weight is more than 200,000, the viscosity of the ink becomes too high, and in some cases, a sufficiently high level of ejection stability of the ink is not obtained.
• GPC gel permeation chromatography
• the content (percent by mass) of the water-soluble resin in the ink is preferably 0.5 percent by mass or more and 5.0 percent by mass or less with reference to the total mass of the ink. If the content of the water-soluble resin is less than 0.5 percent by mass, an effect of enhancing the color developability of an image recorded on a recording medium, e.g., plain paper, which is the original purpose, may not be obtained sufficiently. On the other hand, if the content of the water-soluble resin is more than 5.0 percent by mass, the viscosity of the ink becomes too high, and in some cases, a sufficiently high level of ejection stability of the ink is not obtained.
• a monomer which becomes a hydrophilic unit by polymerization and which has a hydrophilic group examples include acid monomers having a carboxy group, e.g., (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, acid monomers having a phosphonic acid group, e.g., (meth)acrylic acid-2-phosphonic acid ethyl and anionic monomers, e.g., anhydrides and salts of these acid monomers; monomers having a hydroxy group, e.g., 2-hydroxyethyl (meth)acrylate and 3-hydroxypropyl (meth)acrylate; and monomers having an ethylene oxide group, e.g., methoxy(mono,di,tri,poly)ethylene glycol (meth)acrylate.
• acid monomers having a carboxy group e.g., (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid
• Examples of cations constituting salts of the above-described anionic monomers include ions of lithium, sodium, potassium, ammonium and organic ammonium.
• the resin can be a resin which becomes water-soluble by being neutralized by neutralizing agents, e.g., hydroxides of alkali metals (lithium, sodium, potassium and the like) and ammonia water.
• a monomer which becomes a hydrophobic unit by polymerization and which has a hydrophobic group examples include monomers having an aromatic ring, e.g., styrene, alpha-methyl styrene and benzyl (meth)acrylate; and monomers having an aliphatic group, e.g., ethyl (meth)acrylate, methyl (meth)acrylate, (n-,iso-)propyl (meth)acrylate, (n-,iso-,t-)butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate.
• monomers having an aromatic ring e.g., styrene, alpha-methyl styrene and benzyl (meth)acrylate
• monomers having an aliphatic group e.g., ethyl (meth)acrylate, methyl (meth)acrylate, (n-,iso-)propy
• a copolymer having at least a hydrophilic unit derived from a monomer having a carboxy group and a hydrophobic unit derived from a monomer having an aromatic ring or a monomer having an aliphatic group can be used as the water-soluble acrylic resin.
• the urethane resin can be obtained by a reaction between polyisocyanate and polyol or a chain extender may be further reacted.
• polyisocyanates include aliphatic, alicyclic, aromatic and araliphatic polyisocyanates.
• polyols include polyester polyol, polyether polyol and polycarbonate polyol, and these polyols may further have an acid group.
• both a polyether polyol and a diol having an acid radical can be used as the polyol, and the acid value of the urethane resin is adjusted by the proportion of the diol having an acid radical.
• the chain extender is a compound which reacts with isocyanate groups remaining without forming an urethane bond among polyisocyanate units of an urethane prepolymer obtained by a reaction between the polyisocyanate and the polyol.
• the ink according to an aspect of the present invention may contain organic compounds which are solid at ambient temperature, for example, trimethylolethane, trimethylolpropane and nitrogen-containing compounds, e.g., urea and ethyleneurea, besides the above-described components, as necessary.
• various additives e.g., a surfactant, a pH regulator, an antifoaming agent, a rust inhibitor, an antiseptic, a fungicide, an antioxidant, a reduction inhibitor and a vaporization promoter, may be further contained in the ink, as necessary.
• the ink according to aspects of the present invention has an ink viscosity of 1.0 mPas or more and 5.0 mPas or less, and further preferably 1.5 mPas or more and 4.0 mPas or less at 25 degrees Celsius.
• the pH of the ink is preferably 5 or more and 9 or less at 25 degrees Celsius.
• the ink cartridge according to aspects of the present invention includes an ink and an ink storage portion to store the ink.
• the ink stored in the ink storage portion is the above-described ink according to aspects of the present invention.
• a structure in which the ink storage portion is formed from a negative pressure generation member-holding chamber to store a negative pressure generating member to hold the ink while being impregnated with the ink through the use of a negative pressure and an ink storage chamber to store the ink in the state of not being impregnated into the negative pressure generating member is mentioned.
• An ink jet recording method is a method in which an image is recorded on a recording medium by ejecting the above-described ink according to an aspect of the present invention from a recording head of an ink jet method.
• a method in which mechanical energy is applied to the ink and a method in which thermal energy is applied to the ink are mentioned.
• any method described above can be adopted.
• the known steps may be employed as the steps of the ink jet recording method except that the ink according to aspects of the present invention is used.
• the ink jet recording method by utilizing thermal energy can be adopted and the surface charge amount derived from the sulfonic acid group included in the second functional group is specified to be preferably 1 micromole/m 2 or more.
• the ink jet recording apparatus including the member formed from the material containing the synthetic rubber can be used and the surface charge amount derived from the phosphonic acid group included in the first functional group is specified to be preferably 2.0 micromoles/m 2 or more.
• the member which is included in the ink jet recording apparatus which is formed from the material containing the synthetic rubber, and which is to be brought into contact with the ink, the following members are mentioned.
• Examples include a member constituting the ink cartridge, a member constituting the ink path of the recording head, a member constituting the connection portion of the ink cartridge and the recording head, and a wiper to wipe the surface provided with the ejection orifice of the recording head (ejection orifice surface).
• a wiper to wipe the surface provided with the ejection orifice of the recording head (ejection orifice surface).
• general-purpose rubber may be used. Examples include acrylic rubber, nitrile rubber, isoprene rubber, urethane rubber, ethylene propylene rubber, chlorosulfonated polyethylene rubber, epichlorohydrin rubber, chloroprene rubber, silicone rubber, styrene-butadiene rubber, butadiene rubber, fluororubber, butyl rubber and chlorinated butyl rubber.
• urethane rubber, ethylene propylene rubber, butyl rubber and chlorinated butyl rubber can be employed from the viewpoints of ease of molding and stability of the member, and in particular, urethane rubber is employed as the material constituting the wiper.
• the self-dispersible pigment in the pigment dispersion was measured. Specifically, measurement was performed on the basis of potentiometric titration by using an automatic potentiometric titrator (trade name "AT-510", produced by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a stream potential titration unit (PCD-500), where methyl glycol chitosan was used as a titrant.
• an automatic potentiometric titrator trade name "AT-510", produced by Kyoto Electronics Manufacturing Co., Ltd.
• PCD-500 stream potential titration unit
• Phosphorus of the thus obtained measurement samples of Liquid A and Liquid B was quantified by using an ICP emission spectrochemical analyzer (trade name "SPS5100", produced by SII Nano Technology Inc.).
• the amount of phosphonic acid group was determined from a difference in the resulting amounts of phosphorus of Liquid A and Liquid B.
• the measurement result of the surface charge amount of self-dispersible pigment 31 including only a functional group including the phosphonic acid group was contrasted with the phosphonic acid group, and it was ascertained that the surface charge amount of 1 corresponds to phosphonic acid group 1. Then, the amount of the phosphonic acid group was taken as the surface charge amount derived from the functional group including the phosphonic acid group.
• Liquid A was prepared by diluting the pigment dispersion with pure water in such a way that the content of the pigment, which was a measuring object, became about 0.03%. Meanwhile, the pigment dispersion was subjected to ultracentrifugation under the condition of 5 degrees Celsius, 80,000 rpm, and 15 hours, a supernatant liquid, from which the self-dispersible pigment had been removed, was taken, and this was diluted by a factor of about 80 with pure water, so as to prepare Liquid B.
• Sulfur of the thus obtained measurement samples of Liquid A and Liquid B was quantified by using an ICP emission spectrochemical analyzer (trade name "SPS5100", produced by SII Nano Technology Inc.).
• the amount of sulfonic acid group was determined from a difference in the resulting amounts of sulfur of Liquid A and Liquid B.
• the measurement results of the amounts of surface charge of self-dispersible pigments 36 and 38 including only a functional group including the sulfonic acid group were contrasted with the sulfonic acid group, and it was ascertained that the surface charge amount of 1 corresponds to sulfonic acid group 1. Then, the amount of the sulfonic acid group was taken as the surface charge amount derived from the sulfonic acid group.
• the surface charge amount derived from the carboxylic acid group included in the second functional group of the self-dispersible pigment was not able to be measured with the ICP emission spectrochemical analyzer and was calculated as described below.
• the acid value of the resulting resin was determined by the following method.
• the resin was precipitated by adding hydrochloric acid to a resin aqueous solution.
• the resin was vacuum-dried at 40 degrees Celsius for a night.
• the resulting resin was dissolved into tetrahydrofuran, and the acid value was measured with the automatic potentiometric titrator (trade name "AT-510", produced by Kyoto Electronics Manufacturing Co., Ltd.) by using a potassium hydroxide methanol titrant.
• the weight average molecular weight of the resulting resin was measured as a weight average molecular weight in terms of polystyrene by using gel permeation chromatography (GPC).
• Each monomer (unit: part) shown in Table 2 was used and was copolymerized by a common method, so as to synthesize water-soluble Acrylic resins A1 to A7.
• a potassium hydroxide aqueous solution was used, whole anionic groups in the resin were neutralized, and ion-exchanged water was further added, so as to prepare an aqueous solution of each acrylic resin, where the content of resin (solid content) was 20.0%.
• the composition and the characteristics of the acrylic resin are shown in Table 2.
• the resulting resin solution was heated and decompressed to remove methyl ethyl ketone by distillation, and ion-exchanged water was further added, so as to obtain an aqueous solution of Urethane resins U1 to U7, where the content of resin (solid content) was 20.0%.
• the composition and the characteristics of the urethane resin are shown in Table 3.
• IPDI represents isophorone diisocyanate
• HDI represents hexamethylene diisocyanate
• PPG 2000 represents polypropylene glycol having a number average molecular weight of 2,000
• PHCD 2000 represents polyhexamethylenecarbonate diol having a number average molecular weight of 2,000
• DMPA dimethylolpropionic acid.
• the inks corresponding to the second and third embodiments copper (II) chloride was added in such a way that the content (ppm) of the free copper ion present in the ink became the value indicated in the lower part of Tables 4 to 6, and the total was adjusted to 100.0% with ion-exchanged water. Therefore, the contents of the ion-exchanged water in the inks corresponding to the second and third embodiments are shown as values containing copper (II) chloride.
• the coloring materials were not C.I. Pigment Blue 15:3 or C.I.
• Pigment Blue 15:4 in the case where copper (II) chloride was not added, the contents of the free copper ion were less than the detection limit (in Table, expressed as "ND").
• the coloring materials were C.I. Pigment Blue 15:3 or C.I. Pigment Blue 15:4, in the case where copper (II) chloride was not added, the contents of the free copper ion were 23 ppm.
• a modified ink jet recording apparatus (trade name "PIXUS iP3100", produced by CANON KABUSHIKI KAISHA) equipped with a recording head which ejects a liquid by the action of thermal energy was used for recording images.
• Each of the inks obtained as described above was filled into an ink cartridge, and the ink cartridge was set at the position of the black ink.
• the recording condition was specified to be 1-pass one-way recording in which an image with a width corresponding to an arrangement width of ejection orifice of a recording head was recorded by only scanning started from the home position of the recording head.
• 1/600 inch by 1/600 inch was defined as 1 pixel, and in the case of a solid image with a recording duty of 100%, the amount of application of ink to a recording medium was specified to be 25 ng per pixel.
• PB Paper GF-500 produced by CANON KABUSHIKI KAISHA
• BUSINESS MULTIPURPOSE 4200 PAPER produced by Xerox Corporation
• Bright White Inkjet Paper produced by Hewlett-Packard
• the optical density of the solid image was measured by using a spectrophotometer (trade name "Spectrolino", produced by Gretag Macbeth) under the condition of light source: D50 and visual field: 2 degrees, and the color developability was evaluated on the basis of the average value of three types of recording medium.
• the evaluation criteria of the color developability were as described below.
• AA average value was 1.5 or more
• A average value was 1.4 or more and less than 1.5
• B average value was 1.2 or more and less than 1.4
• C average value was less than 1.2.
• AA average value was 1.2 or more
• A average value was 1.1 or more and less than 1.2
• B average value was 1.0 or more and less than 1.1
• C average value was less than 1.0.
• An ink cartridge was set into the same ink jet recording apparatus as that used in the above-described evaluation of the color developability of an image under an environment at a temperature of 30 degrees Celsius and a relative humidity of 15%.
• a cap covering the ejection orifice of the recording head was taken off, and after 30 seconds was elapsed in that state, characters of 5 points and 8 points were recorded.
• the characters at the initial stage of writing were visually examined, so as to evaluate the intermittent ejection stability.
• the evaluation criteria of the intermittent ejection stability were as described below.
• Each of the inks obtained as described above was put into a polytetrafluoroethylene container and was sealed. This was put into an oven at a temperature of 60 degrees Celsius, and was stood for 2 months. After the ink was returned to ambient temperature, the viscosity of the ink and the particle diameter of the pigment were measured.
• the viscosity of the ink was measured by using an E type viscometer (trade name "RE-80L”, produced by TOKI) at a temperature of 25 degrees Celsius and at 50 rpm.
• the particle diameter of the pigment was measured with a concentrated system particle analyzer (trade name "FPAR-1000", produced by OTSUKA ELECTRONICS CO., LTD.).
• A the rates of increase in the viscosity of ink and the particle diameter of the pigment after storage were less than 3% as compared with those before storage
• B the rates of increase in the viscosity of ink and the particle diameter of the pigment after storage were 3% or more and less than 5% as compared with those before storage
• C the rates of increase in the viscosity of ink and the particle diameter of the pigment after storage were 5% or more as compared with those before storage
• An ink cartridge was set into the same ink jet recording apparatus as that used in the above-described evaluation of the color developability of an image. Then, 3,000 sheets of solid image with a recording duty of 50% were recorded all over A4-size PB Paper GF-500 (produced by CANON KABUSHIKI KAISHA). Thereafter, characters of 5 points and 8 points were recorded. The characters were visually examined, so as to evaluate the long-term ejection stability.
• the evaluation criteria of the long-term ejection stability were as described below.
• An urethane rubber wiper in the state of being immersed in each ink was placed in a constant temperature bath at a temperature of 60 degrees Celsius for 1 month. Thereafter, the wiper was washed with ion-exchanged water, and was attached to a predetermined place of the same ink jet recording apparatus as that used in the above-described evaluation of the color developability of an image.
• This recording apparatus was used, and 5 sheets of solid image with a recording duty of 50% were recorded all over A4-size PB Paper GF-500 (produced by CANON KABUSHIKI KAISHA). After a cleaning operation was performed, characters of 5 points and 8 points were recorded. The characters and the ejection orifice surface of the recording head were visually examined, so as to evaluate the wettability.

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