JP2010086656A - Inkjet ink for forming catalyst layer for fuel cell, catalyst layer for fuel cell and its manufacturing method, as well as catalyst layer-electrolyte film laminate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide inkjet ink capable of easily, simply, and stably forming a catalyst layer with uniform thickness, with little crack, and with an appropriate amount of voids. <P>SOLUTION: The inkjet ink forms a catalyst layer for a fuel cell containing catalyst particles, ion conductive polymer electrolyte, a non-anion system surfactant, and a solvent, with the solvent having a boiling point of 120°C or higher. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ink-jet ink for forming a fuel cell catalyst layer, a fuel cell catalyst layer and a method for producing the same, and a catalyst layer-electrolyte membrane laminate.

  A fuel cell is a system in which a catalyst layer is disposed on both sides of an electrolyte membrane, and power is generated by an electrochemical reaction between hydrogen and oxygen. Only water is generated during power generation, and unlike conventional internal combustion engines, it does not generate environmental load gas such as carbon dioxide. Therefore, it is attracting attention as a next-generation clean energy system.

  The polymer electrolyte fuel cell has a structure in which an ion conductive electrolyte membrane is used as an electrolyte membrane, a catalyst layer and an electrode base material are sequentially laminated on both sides, and further sandwiched between separators.

  Of these, the catalyst layer plays a central role in the battery reaction, and therefore high performance is being actively promoted.

  As a method for forming a catalyst layer on an electrolyte membrane, (1) a transfer method / decal method and (2) a direct coating method are known.

  The present invention relates to an inkjet ink for forming a fuel cell catalyst layer used in the latter direct coating method.

  As an ink for forming a catalyst layer for a fuel cell used in the direct coating method, for example, those described in Patent Document 1 are known.

However, when the ink described in Patent Document 1 is applied onto the ion conductive electrolyte membrane using an ink jet, the ink is dried and fixed at the discharge port, so that stable coating cannot be performed, and the catalyst layer There is a disadvantage that the variation in film thickness becomes large.
JP 2003-208903 A

  This invention makes it a subject to provide the ink for inkjets for forming the catalyst layer for fuel cells without the said fault.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, in an ink composition containing catalyst particles, an ion conductive polymer electrolyte, a nonionic surfactant, and a solvent, a desired inkjet ink free from the above-mentioned defects can be obtained by using a specific solvent as the solvent. I found out that The present invention has been completed based on such findings.

The present invention provides an inkjet ink, a fuel cell catalyst layer and a method for producing the same, a catalyst layer-electrolyte laminate, and a fuel cell for forming the fuel cell catalyst layer shown in the following items 1 to 8.
Item 1. Ink-jet ink for forming a catalyst layer for a fuel cell, comprising catalyst particles, an ion conductive polymer electrolyte, a nonionic surfactant and a solvent, wherein the solvent has a boiling point of 120 ° C. or higher. Ink for ink jet.
Item 2. The solvent is at least one selected from the group consisting of diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, dimethyl adipate and diethyl adipate Item 2. The ink according to Item 1.
Item 3. Item 3. The ink according to Item 1 or 2, wherein the ion-conductive polymer electrolyte is contained in a proportion of 100% by weight or less with respect to the catalyst particles.
Item 4. Item 4. A fuel cell catalyst layer produced using the inkjet ink according to any one of Items 1 to 3.
Item 5. Item 5. A catalyst layer-electrolyte membrane laminate in which the catalyst layer according to Item 4 is formed on an ion conductive electrolyte membrane.
Item 6. A fuel cell using the catalyst layer-electrolyte membrane laminate according to Item 5.
Item 7. Item 4. A method for producing a catalyst layer, comprising a step of forming the catalyst layer on an object to be coated by applying the inkjet ink according to any one of Items 1 to 3 to the object to be coated and drying under reduced pressure.
Item 8. Item 8. The method for producing a catalyst layer according to Item 7, wherein drying is performed under a solvent vapor pressure of the same component as the main solvent of the solvent contained in the ink.

Ink for ink jet The ink for ink jet of the present invention contains, for example, catalyst particles, an ion conductive polymer electrolyte, a nonionic surfactant and a solvent.

  Known or commercially available catalyst particles can be used, and are not particularly limited as long as they cause a fuel cell reaction at the anode or cathode of the fuel cell. Examples of the catalyst particles include platinum, platinum alloys, non-platinum metal compounds, and the like. Examples of the platinum alloy include an alloy of platinum and at least one metal selected from the group consisting of ruthenium, palladium, nickel, molybdenum, iridium, iron and the like. In general, the catalyst particles when used as the cathode catalyst layer are platinum, and the catalyst particles when used as the anode catalyst layer are the alloys described above. Examples of the metal element in the non-platinum metal compound include scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, aluminum, silicon, gallium, germanium, yttrium, zirconium, niobium, molybdenum, and tungsten. Silver, indium, tin, bismuth, lanthanum, samarium, cerium and the like.

  The catalyst particles may be so-called catalyst-supported carbon powder in which catalyst fine particles are supported on carbon powder. The average particle size of the catalyst-supported carbon powder is usually about 10 to 100 nm, preferably about 20 to 80 nm, and most preferably about 40 to 50 nm. The carbon particles constituting the catalyst-supported carbon powder are not particularly limited, and examples thereof include carbon black such as channel black, furnace black, ketjen black, acetylene black, and lamp black, graphite, activated carbon, carbon fiber, and carbon nanotube. . These may be used alone or in combination of two or more.

  The ion conductive electrolyte may be a hydrogen ion conductive one, and a known or commercially available one can be used. Examples thereof include perfluorosulfonic acid-based fluorine ion exchange resins. Moreover, by introducing a fluorine atom having a high electronegativity, it is chemically very stable, the degree of dissociation of the sulfonic acid group is high, and good hydrogen ion conductivity can be realized. Specific examples of such a hydrogen ion conductive electrolyte include, for example, “Nafion” manufactured by DuPont, “Flemion” manufactured by Asahi Glass Co., Ltd., “Aciplex” manufactured by Asahi Kasei Co., Ltd., and Gore manufactured by Gore. "Gore Select" and the like. Examples of the hydrocarbon-based ion conductive electrolyte include sulfonation (polystyrene-block-poly (ethylene-ran-butylene) -block-polystyrene) manufactured by Aldrich.

  Note that “-ran-” is a connection symbol used for naming a random type copolymer (copolymer). For example, “-poly- (A -Ran-B) ". Similarly, “-block-” is a connection symbol indicating a block-type copolymer.

  As the nonionic surfactant, known ones can be widely used. The nonionic surfactant means a dispersant having no ion dissociating group in an aqueous solution. Among such nonionic surfactants, polymer surfactants (polymer dispersants) as exemplified below are preferable.

  Specific examples of the polymer surfactant include polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene alkyl ethers such as polyoxyethylene oleyl ether; polyoxyethylene octylphenyl ether, polyoxyethylene nonylphenyl Polyoxyethylene alkyl phenyl ethers such as ether; polyethylene glycol diesters such as polyethylene glycol dilaurate and polyethylene glycol distearate; sorbitan fatty acid esters; fatty acid-modified polyesters and the like.

  Further, among silicone surfactants and fluorine surfactants, nonionic ones can also be used.

  Examples of such silicone surfactants include those obtained by hydrophilically modifying silicone with polyethylene oxide, polypropylene oxide, and the like.

  Examples of the fluorosurfactant include perfluorobutyl sulfonate, perfluoroalkyl group-containing carboxylate, perfluoroalkyl group-containing trimethylammonium salt, perfluoroalkyl group-containing phosphate ester, perfluoroalkylethylene oxide. Examples of the adducts and perfluoroalkyl group-containing oligomers include nonionic ones.

  By using a nonionic surfactant, it is possible to effectively prevent aggregation with conductive carbon particles. Moreover, since wettability can be improved, the effect as surfactant, such as a dispersibility, can fully be exhibited with a smaller addition amount.

  As the solvent, as long as the boiling point is 120 ° C. or higher, known solvents can be widely used. Examples of such solvents include ethylene glycol monoalkyl ether acetates such as ethylene glycol monomethyl ether acetate; diethylene glycol monoalkyl ethers such as diethylene glycol monomethyl ether and diethylene glycol monoethyl ether; and diethylene glycol such as diethylene glycol mono-n-butyl ether acetate. Monoalkyl ether acetates; propylene glycol monoalkyl ether acetates such as propylene glycol monomethyl ether acetate and propylene glycol monoethyl ether acetate; other ethers such as diethylene glycol dimethyl ether; ketones such as cyclohexanone, 2-heptanone and 3-heptanone ; 2-hydroxypropi Lactic acid alkyl esters such as ethyl acetate; 3-methyl-3-methoxybutylpropionate, ethyl 3-methoxypropionate, methyl 3-ethoxypropionate, n-butyl acetate, n-amyl formate, isoamyl acetate, Other esters such as n-butyl propionate, ethyl butyrate, isopropyl butyrate, n-butyl butyrate, ethyl pyruvate; and high-boiling solvents such as γ-butyrolactone can be used.

  The proportions of the catalyst particles, ion conductive electrolyte, nonionic surfactant and solvent contained in the ink jet ink of the present invention are not limited and can be appropriately selected within a wide range.

  For example, the ion conductive electrolyte is 0.5 to 5 parts by weight (preferably 1 to 4 parts by weight) with respect to 5 parts by weight of catalyst particles (in the case of catalyst-supported carbon powder, 5 parts by weight of the catalyst-supported carbon powder). The nonionic surfactant may be contained in an amount of about 0.01 to 36 parts by weight (preferably 1.1 to 6.3 parts by weight).

  A solvent is mix | blended in the ratio of 10 to 350 weight% (preferably 18 to 200 weight%) with respect to the whole quantity of the inkjet ink containing the said solvent. When the blending amount of the solvent is within the above range, the ejection performance from the ink jet head is further improved, and the amount of ink that can be deposited without protruding from the site (catalyst layer forming site) where the ink is to be adhered is further increased. There is an advantage that it becomes more sufficient and can give a film thickness of a predetermined amount or more to the catalyst layer after drying.

  The ink-jet ink of the present invention is produced by mixing the catalyst particles, ion conductive electrolyte, nonionic surfactant and solvent. The mixing order of the catalyst particles, the ion conductive electrolyte, the nonionic surfactant and the solvent is not particularly limited. For example, the ink for inkjet can be prepared by mixing the catalyst particles, the ion conductive electrolyte, the nonionic surfactant and the solvent sequentially or simultaneously and dispersing the catalyst particles.

  In addition, other known additives (for example, carbon fiber etc.) and the like can be appropriately blended with the ink-jet ink of the present invention as long as the effects of the present invention are not impaired.

Method for Producing Catalyst Layer The catalyst layer of the present invention is produced , for example, by applying the ink jet ink of the present invention to an object to be coated and drying under reduced pressure to form a catalyst layer on the object to be coated.

  In applying the ink jet ink of the present invention to an object to be coated, the ink of the present invention may be sprayed onto the object to be coated so as to have a desired layer thickness by an ink jet method. The conditions for ink spraying are not particularly limited.

  Examples of the object to be coated include an ion conductive electrolyte membrane, a conductive porous substrate, and a transfer substrate.

  The ink applied to the object to be coated is dried under reduced pressure. In the present invention, drying is preferably performed under the same solvent vapor pressure as the main solvent of the solvent contained in the ink. Thereby, it becomes a moderate drying speed and can arrange | position a catalyst particle so that a catalyst layer may comprise a moderate space | gap during drying. As a result, it is possible to produce a catalyst layer exhibiting excellent battery performance in which generation of cracks and blockage of voids in the catalyst layer are suppressed. Moreover, this process does not require a special apparatus and a complicated process, because the inside of the drying apparatus may be filled with a specific gas and adjusted to a specific pressure.

  In the present invention, the main solvent is a solvent that is contained in the largest amount among all the solvents contained in the ink jet ink, preferably 25% by weight or more, more preferably 50% by weight or more in the total solvent. Solvent.

  A catalyst layer is formed on an object to be coated (for example, on an ion conductive electrolyte film) by applying such ink for ink jet and drying.

  More specifically, for example, in a drying apparatus such as a desiccator, (1) an ion conductive electrolyte membrane coated with ink jet ink, and (2) a liquid having the same component as the main solvent contained in the ink jet ink The opening container filled with (for example, a petri dish or the like) is allowed to stand, and then dried by reducing the pressure in the drying apparatus to a predetermined pressure. What is necessary is just to deaerate the inside of an apparatus continuously or intermittently at the time of pressure reduction as needed.

  Furthermore, if necessary, a very small amount of solvent remaining in the catalyst layer may be reliably removed by further reducing the pressure after the drying step.

  The pressure during drying is usually 1 to 5000 Pa, preferably 3 to 800 Pa. In particular, in the present invention, it is preferable to carry out near the saturated vapor pressure of the main solvent. For example, when the main solvent is diethylene glycol monobutyl ether, it is preferably performed at 20 ° C. in the range of about 3 Pa (± 2 Pa). Similarly, when the main solvent is diethylene glycol monobutyl ether acetate, 5 Pa (± 2 Pa at 20 ° C.). When the main solvent is dipropylene glycol monomethyl ether acetate, it is preferably carried out at 20 ° C. in the range of about 500 Pa (± 50 Pa).

  The drying time is determined according to the pressure during drying, the type of solvent and the like, but is usually about 1 to 120 minutes, preferably about 5 to 60 minutes, more preferably about 15 to 30 minutes.

  The temperature during drying is not limited, but is preferably about 15 to 100 ° C, more preferably about 20 to 80 ° C.

  The catalyst layer obtained by the production method of the present invention has a porosity in the voids having a pore diameter of 10 nm to 200 nm, preferably 6 to 30%, more preferably 12 to 30%, relative to the catalyst layer, or It is 7.5 to 20%, More preferably, it is 15 to 20%. The porosity in the pores with a pore size of 5 μm to 50 μm is preferably 2 to 18%, more preferably 2 to 9% or 4 to 17% with respect to the catalyst layer, depending on the case. .5% is most preferred.

  The porosity in the present invention is measured by a mercury porosimeter (manufactured by Shimadzu Corporation, product name “AUTOPORE 9500”).

  The thickness of the catalyst layer is not limited, and is usually about 5 μm to 120 μm, preferably about 10 μm to 50 μm, more preferably about 15 μm to 30 μm.

  The content of catalyst particles in the catalyst layer (in the case of catalyst-supported carbon powder, the content of the catalyst-supported carbon powder) is usually about 10 to 90% by weight, preferably about 40 to 80% by weight, based on the total amount of the catalyst layer. It is.

  The catalyst layer of the present invention can be used in, for example, a solid polymer fuel cell and a direct fuel fuel cell.

Catalyst layer-electrolyte membrane laminate The catalyst layer-electrolyte membrane laminate of the present invention is obtained by forming a catalyst layer obtained by the production method of the present invention on one or both surfaces of an electrolyte membrane.

  The electrolyte membrane (catalyst layer-electrolyte membrane laminate) on which the catalyst layer of the present invention is laminated is produced, for example, by applying ink jet ink to one surface of the electrolyte membrane and then drying under reduced pressure. By repeating this operation once or twice, a catalyst layer-electrolyte membrane laminate in which the catalyst layer is laminated on both surfaces of the electrolyte membrane is produced.

  In addition, the catalyst layer with the catalyst layer formed on the conductive porous substrate is formed on the other surface of the catalyst layer-electrolyte membrane laminate in which the catalyst layer is formed on the one surface of the electrolyte membrane by the above manufacturing method. An electrode may be arranged.

  Here, the electrolyte membrane is a known one. The thickness of the electrolyte membrane is usually about 20 to 250 μm, preferably about 20 to 80 μm. Specific examples of electrolyte membranes include “Nafion” membrane manufactured by DuPont, “Flemion” membrane manufactured by Asahi Glass Co., Ltd., “Aciplex” membrane manufactured by Asahi Kasei Co., Ltd., and “Gore Select” manufactured by Gore. Examples include membranes.

Solid polymer fuel cell A known or commercially available electrode base material (for example, carbon paper, carbon cloth, etc.) and a separator are sequentially laminated on both surfaces of the catalyst layer-electrolyte membrane laminate of the present invention to thereby obtain a solid polymer fuel cell of the present invention. A molecular fuel cell is obtained.

  If the ink-jet ink of the present invention is used, the catalyst layer can be formed easily, simply and stably by the ink-jet method. In addition, since the formed catalyst layer has a uniform thickness, few cracks are generated, and has appropriate voids, the catalyst layer obtained in the present invention can be favorably incorporated into the fuel cell. Battery performance can be demonstrated.

  In addition, the method for producing a catalyst layer of the present invention only needs to be dried under an atmosphere filled with a specific gas and under a specific pressure, and therefore does not require special equipment and complicated processes.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. In addition, this invention is not limited to a following example.

Example 1
5 parts by weight of catalyst-supporting carbon particles (Tanaka Kikinzoku, TEC10E50E), 25 parts by weight of ion conductive polymer electrolyte (DuPont, Nafion DE520CS), 1 part by weight of a nonionic surfactant (Kao, Rheodor TW-120V) and 69 parts by weight of a solvent (dipropylene glycol monomethyl acetate, boiling point: 146 ° C.) was mixed and dispersed using a disperser to prepare an ink jet ink of the present invention.

Example 2
When the inkjet ink of the present invention prepared in Example 1 was filled in an inkjet head and dropped toward the ion conductive polymer electrolyte membrane (NafionNRE212CS) as a coating object with a drop diameter of 30 μm, The ink could be easily applied on the ion conductive polymer electrolyte membrane.

Next, the coated material was put in a sealed container, and the vacuum pump was operated to reduce the pressure in the container to about 1 Pa. As a result, the ink was dried without problems, and a catalyst layer (platinum supported amount: 0.5 mg / cm ² ) was obtained.

Example 3
The ink jet ink of the present invention prepared in Example 1 was filled in an ink jet head and dropped from the head with a drop diameter of 30 μm toward an ion conductive polymer electrolyte membrane (NafionNRE212CS) as an object to be coated.

Next, the coated product was put in a sealed container, kept constant at 500 Pa in a solvent vapor pressure atmosphere of dipropylene glycol monomethyl acetate, and then the pressure was reduced to about 1 Pa with a vacuum pump. As a result, the ink was dried without problems, and a catalyst layer (platinum supported amount: 0.5 mg / cm ² ) was obtained.

Comparative Example 1
5 parts by weight of catalyst-supported carbon particles (Tanaka Kikinzoku, TEC10E50E), ion conductive polymer electrolyte (DuPont, Nafion DE2020CS) 6.25 parts by weight, nonionic surfactant (Kao, Rheodor TW-120V) 1 weight And 1.25 parts by weight of a solvent (isopropanol) were mixed and dispersed using a disperser to prepare an inkjet ink for comparison.

Comparative Example 2
When the inkjet ink of the present invention prepared in Comparative Example 1 was filled in an inkjet head and dropped toward the ion conductive polymer electrolyte membrane (Nafion NRE212CS) as a coating object with a drop diameter of 30 μm, The ink was dried at the head portion of the ink jet, and stable coating could not be performed.

Example 4 (Production of catalyst layer transfer film)
When the ink jet ink of the present invention prepared in Example 1 was filled in an ink jet head and dropped onto the transfer substrate (Toyobo: PET E5100 (12 μm)) with a drop diameter of 30 μm, the ink was transferred. It could be easily applied on the substrate.

Next, the coated material was put in a sealed container, and the vacuum pump was operated to reduce the pressure in the container to about 1 Pa. As a result, the ink dried without any problem, and a catalyst layer (platinum supported amount: 0.5 mg / cm ² ) could be formed on the transfer substrate.

Example 5 (Manufacture of catalyst layer-electrolyte membrane laminate)
When the inkjet ink of the present invention prepared in Example 1 was filled in an inkjet head and dropped toward the ion conductive polymer electrolyte membrane (NafionNRE212CS) as a coating object with a drop diameter of 30 μm, The ink could be easily applied on the ion conductive polymer electrolyte membrane.

Next, the coated material was put in a sealed container, and the vacuum pump was operated to reduce the pressure in the container to about 1 Pa. As a result, the ink is dried without problems, a catalyst layer in ionic conductive polymer electrolyte film (platinum content: 0.5mg / cm ²⁾ it was possible to form a.

  Thereafter, when the ink is dropped from the head with a drop diameter of 30 μm toward the back surface on which the catalyst layer of the ion conductive polymer electrolyte membrane is formed, the ink can be easily applied on the back surface of the ion conductive polymer electrolyte membrane. did it.

Next, the coated material was put in a sealed container, and the vacuum pump was operated to reduce the pressure in the container to about 1 Pa. As a result, the ink dries without problems, and a catalyst layer (platinum supported amount: 0.5 mg / cm ² ) can be formed on the back surface of the ion conductive polymer electrolyte membrane. (Catalyst layer / ion conductive polymer electrolyte membrane / catalyst layer) was obtained.

Example 6 (Production of membrane-electrode assembly)
The inkjet ink of the present invention prepared in Example 1 was filled in an inkjet head, and dropped from the head with a drop diameter of 30 μm toward the conductive porous substrate (SGL34BC, SGL Carbon Co., Ltd.) that was the object to be coated. However, the ink could be easily applied on the conductive porous substrate.

Next, the coated material was put in a sealed container, and the vacuum pump was operated to reduce the pressure in the container to about 1 Pa. As a result, the ink dried without any problem, and a catalyst layer (platinum supported amount: 0.5 mg / cm ² ) could be formed on the conductive porous substrate.

  Thereafter, the ion conductive polymer electrolyte membrane (NafionNRE212CS) is sandwiched between the catalyst layer surfaces by the conductive porous substrate after the formation of the catalyst layer, and hot pressing is performed to form a membrane-electrode assembly (conductive porous substrate / catalyst). Layer / ion conductive polymer electrolyte membrane / catalyst layer / conductive porous substrate).

Example 7 (Battery evaluation)
Using the catalyst layer-electrolyte membrane laminate produced in Example 2 or 3, a catalyst layer-electrolyte membrane laminate was produced according to the method of Example 5. Moreover, the catalyst layer was formed on both surfaces of the ion conductive polymer electrolyte membrane (Nafion NRE212CS) using the transfer method from the catalyst layer transfer film of Example 4 to produce a catalyst layer-electrolyte membrane laminate. A gas diffusion layer (SGL34BC, SGL Carbon) was joined to both surfaces of these catalyst layer-electrolyte membrane assemblies, and the cells were assembled into a JARI standard cell. Further, Example 6 was assembled into a JARI standard cell. Humidified hydrogen was supplied to the fuel electrode side at 80 ° C., and humidified air was supplied to the air electrode side. Humidified hydrogen and humidified air were supplied so that the fuel electrode had a fuel utilization of 70% and the air electrode had a fuel utilization of 40% with respect to the applied current. As a result, all the cells showed a good electromotive force of 0.9 to 1.1V.

Claims (8)

An ink jet ink for forming a catalyst layer for a fuel cell, comprising catalyst particles, an ion conductive polymer electrolyte, a nonionic surfactant and a solvent,
The solvent has a boiling point of 120 ° C. or higher.
Ink for ink jet.   The solvent is at least one selected from the group consisting of diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, dimethyl adipate and diethyl adipate The ink according to claim 1.   The ink according to claim 1 or 2, comprising an ion conductive polymer electrolyte in a proportion of 100% by weight or less based on the catalyst particles.   The catalyst layer for fuel cells manufactured using the ink for inkjets in any one of Claims 1-3.   A catalyst layer-electrolyte membrane laminate, wherein the catalyst layer according to claim 4 is formed on an ion conductive electrolyte membrane.   A fuel cell using the catalyst layer-electrolyte membrane laminate according to claim 5.   The manufacturing method of a catalyst layer provided with the process of forming the catalyst layer on a to-be-coated material by apply | coating the inkjet ink in any one of Claims 1-3 to a to-be-coated material, and drying under reduced pressure.   The method for producing a catalyst layer according to claim 7, wherein drying is performed under a solvent vapor pressure of the same component as the main solvent of the solvent contained in the ink.