JP2011200793A - Method of applying ink and coating film formed by method of applying ink - Google Patents

Abstract

An object of the present invention is to provide a technique capable of continuously, stably and speedily applying low-viscosity ink over a long period of time.
An ink suction process in which ink is sucked into an ink chamber by operation of a piezo element during an operation time (T1), and an ink discharge process in which ink is discharged from the ink chamber by operation of a piezo element during an operation time (T2). An ink application method by an ink jet method by repeating the ink suction step, the ink discharge step, and the standby step as one cycle. Because
The ink is a solid dispersion ink having a viscosity at 25 ° C. of 0.5 to 7 mPa · s,
1/1000 second ≦ (T1 + T2 + T3) ≦ 1/20 second and T3 ≧ 50 × (T1 + T2).

Description

  The present invention relates to an ink application technique.

  Pattern formation by a coating technique using an inkjet apparatus is known. For example, it is conceivable to form a conductive film by an ink jet coating technique. By the way, when the above technique is used, it is considered that the physical property value of the ink must be a desired value in order to perform pattern formation continuously and stably over a long period of time. That is, it is considered that the quality of the coating film formed by the ink jet technique is greatly influenced by the physical properties of the ink. For example, the influence of the viscosity of the ink was considered to be extremely large. Until now, in order to obtain a high-quality coating film by an ink jet technique, a thickener is usually added to the ink. In particular, when the ink is a dispersion-based ink, the addition of a thickener or a dispersing agent plays an important role for the purpose of preventing sedimentation of the dispersed material and enhancing storage stability (preventing phase separation).

  However, the thickener and dispersing agent added to the ink are often unnecessary in view of the original purpose and function of the ink. Furthermore, there is a concern that the original function of the ink is hindered by a thickener or a dispersing agent. When the coating film is, for example, a conductive coating film, it is needless to say that it is preferable from the viewpoint of conductivity that the content of the substance other than the conductive substance in the coating film is small. For this reason, firing is considered to remove substances other than the conductive substance. However, when fired, the conductive metal particles are oxidized by firing and the conductivity is lowered. Further, when the substrate on which the coating film is formed is made of a resin, it is not possible to adopt a method called firing. Therefore, it can be said that if it is not necessary to add a thickener or a dispersant to the ink, that is preferable.

  Now, as a technique for forming a conductive coating film by inkjet technology, for example, acetylacetone indium, organotin compound, cellulose derivative, alkylphenol and / or alkenylphenol, dibasic acid ester and / or benzyl acetate, diethylene glycol derivative, A coating solution for forming a transparent conductive film having a total content of indium acetylacetone and an organic tin compound of 1 to 30% by weight and a cellulose derivative content of 5% by weight or less is applied onto a substrate by ink jet printing and dried. After that, a technique for firing at a temperature of 300 ° C. or higher has been proposed (Japanese Patent Laid-Open No. 2006-28431).

  The conductive oxide fine particles are composed of conductive oxide fine particles, an inorganic binder, and a solvent. The conductive oxide fine particles have an average particle diameter of 10 to 100 nm, and the inorganic binder has an average weight molecular weight (polystyrene conversion) of 3000 to 150,000. And the solvent contains 10 to 90% by weight of γ-butyrolactone and a coating solution for forming a transparent conductive film having a viscosity at 25 ° C. of 2 to 30 mPa · s measured with a B-type viscometer. A technique of heating to 200 to 600 ° C. after being applied on a substrate by inkjet printing has been proposed (Japanese Patent Laid-Open No. 2006-114396).

  As a technique for forming a carbon nanotube coating film by ink jet technology, metal type SWCNT (single wall carbon nanotube) and semiconductor type SWCNT dispersed in DMF (dimethylformamide) are used in an ink jet drawing apparatus (Microjet: Model PicoJet-1000). A drawing technique has been proposed (Japanese Patent Laid-Open No. 2010-10162). Here, it is disclosed that the metal-type SWCNT and the semiconductor-type SWCNT dispersed in DMF have a viscosity of about 1 mPa · s, and that a low-viscosity inkjet head was used in accordance with this. Yes. Further, it is also disclosed that an ink jet head has a piezo element, and ink is dropped by applying a voltage to the piezo element. In addition, in order to perform stable dripping, the speed of the dropped ink is 3 to 8 m / s, and the magnitude and application time of the voltage pulse applied to the piezo element are “90 V” “70 to 75 μs. Is disclosed to be optimal.

  Also, a method of manufacturing a thin film transistor including at least a source electrode, a drain electrode, and a semiconductor layer, wherein a dispersion solution preparing step of adjusting SWCNT dispersion solution by dispersing SWCNT in a volatile solvent, and the SWCNT dispersion solution on the substrate A coating step of forming the source electrode, the drain electrode, and the semiconductor layer by an inkjet method, and a drying step of drying the SWCNT dispersion solution applied in the coating step. The amount of SWCNT applied per unit area to form a semiconductor layer is smaller than the amount of SWCNT applied per unit area to form the source electrode and the drain electrode in the applying step. A method of manufacturing a thin film transistor characterized by the above is proposed (Japanese Patent Laid-Open No. 2010-1031). JP) are.

  In addition, Carbon, 2007, Vol. 45, 2712-2716 discloses that a solution containing multi-wall carbon nanotubes (MWCNT) and a polymer compound (dispersant) was printed using a commercially available ink jet printer.

  Also, Carbon, 2009, Vol. 47,752-757 discloses that a solution containing SWCNT and polyethyleneimine (dispersing agent) was printed using a commercially available inkjet printer.

JP 2006-28431 A JP 2006-114396 A JP 2010-10162 A JP 2010-10310 A JP 2000-326511 A

Carbon, 2007, Vol. 45, 2712-2716 Carbon, 2009, Vol. 47,752-757

  The techniques of Patent Documents 1 and 2 have a limitation that they require firing. In other words, it is impossible to cope with the case where baking is not suitable, such as a resin-coated substrate. The inks used in Patent Documents 1 and 2 have a viscosity of 5 to 20 mPa · s. However, as a result of investigations by the present inventors, when the ink has a low viscosity, for example, 7 mPa · s or less, it has been impossible to stably perform inkjet coating continuously for a long time. In addition, the above-mentioned patent documents 1 and 2 have no disclosure regarding this point.

  Also in Patent Document 3, as a result of examination by the present inventors, when the ink has a low viscosity, for example, about 1 mPa · s, it has not been possible to stably and stably perform inkjet coating over a long period of time. In addition, the above-mentioned Patent Document 3 has no disclosure regarding this point.

  Patent Document 4 merely discloses that the SWCNT solution is applied by an ink jet printer. And here is no disclosure of what the viscosity of the SWCNT solution is. And as mentioned above, when the viscosity of the ink was low, it was impossible to stably apply the ink jet continuously over a long period of time. There is nothing.

  Patent Document 5 discloses a technique for stably forming minute ink droplets and discharging / recording them from a nozzle. However, this Patent Document 5 also does not disclose how much the viscosity of the ink is. As described above, when the viscosity of the ink is low, it was impossible to stably perform inkjet coating continuously for a long time. There is nothing.

  In Non-Patent Documents 1 and 2, when the viscosity of the ink is low, the inkjet coating could not be stably performed continuously for a long time, but there is no disclosure regarding this point. .

  Therefore, the problem to be solved by the present invention is to solve the above problems. That is, for example, a thickener is often unnecessary in view of the original function of the applied ink, and the viscosity decreases when the thickener is not contained. In such a case, there is provided a technique capable of continuously and stably performing ink jet coating over a long period of time.

  As a result of intensive studies conducted by the present inventor to solve the above-described problems, when an ink is applied by an ink jet apparatus on which the piezo element is mounted, even when the viscosity of the ink is low, the piezo element It has been found that if sufficient non-operation (standby) time is secured, inkjet coating can be carried out continuously and stably over a long period of time. However, if the non-operation (standby) time of the piezo element is set to be long, it takes too much time for coating, so that an upper limit is required.

  The present invention has been achieved based on the above findings.

That is, the above problem is
Ink suction process in which ink is sucked into the ink chamber by operation of the piezoelectric element during the operation time (T1), ink discharge process in which ink is discharged from the ink chamber by operation of the piezoelectric element in the operation time (T2), and ink suction / discharge An ink application method in an ink jet method by repeating the ink suction step, the ink discharge step, and the standby step as one cycle, and a standby step of a waiting time (T3) where substantially no waiting time is performed,
The ink is a solid dispersion ink having a viscosity at 25 ° C. of 0.5 to 7 mPa · s,
1/1000 second ≦ (T1 + T2 + T3) ≦ 1/20 second,
This is solved by an ink application method characterized by T3 ≧ 50 × (T1 + T2).

  Further, the ink application method is preferably solved by an ink application method characterized by T3 ≧ 100 × (T1 + T2). In addition, the above ink application method is more preferably solved by an ink application method characterized by T3 ≧ 200 × (T1 + T2). Further, the ink application method is more preferably solved by an ink application method characterized by T3 ≧ 235 × (T1 + T2).

The above issues are
Ink suction process in which ink is sucked into the ink chamber by operation of the piezoelectric element during the operation time (T1), ink discharge process in which ink is discharged from the ink chamber by operation of the piezoelectric element in the operation time (T2), and ink suction / discharge An ink application method in an ink jet method by repeating the ink suction step, the ink discharge step, and the standby step as one cycle, and a standby step of a waiting time (T3) where substantially no waiting time is performed,
The ink is a solid dispersion ink having a viscosity at 25 ° C. of 0.5 to 7 mPa · s,
1/1000 second ≦ (T1 + T2 + T3) ≦ 1/20 second,
T3 ≧ 50 × (T1 + T2),
And T3 is solved by the ink application method characterized in that it is a length of time that allows continuous ink application over 10 minutes.

  In addition, the above-described ink application method is preferably solved by an ink application method characterized in that 1/400 seconds ≦ (T1 + T2 + T3) ≦ 1/80 seconds.

  And it is the said ink application method, Comprising: An ink is solved by the ink application method characterized by being a conductive paint, for example. In the case of a conductive paint, various kinds of conductive materials can be mentioned. The ink is preferably a carbon nanotube-containing solution. More preferred are carbon nanotube and fulleran-containing solutions. At least 50% or more of the carbon nanotubes are single wall carbon nanotubes (SWCNT).

  In addition, the above-described ink application method is solved by the ink application method characterized in that the amount of one ink droplet ejected in the ink ejection process is preferably 20 to 100 pL.

  In the ink application method, the substrate to which the ink is applied is preferably solved by an ink application method characterized by being made of resin.

  In addition, the above-described ink application method is preferably solved by an ink application method that does not include a high-temperature heat treatment step of 150 ° C. or higher.

  The above-mentioned problem is solved by a coating film characterized by being formed by the ink application method.

  The above-mentioned problem is solved by a coating film having a surface resistance value of 500 Ω / □ or less, which is formed by the ink application method.

  According to the present invention, when an ink having a low viscosity is used as in the case where an unnecessary thickener is not included in terms of the original function of the ink, the ink is continuously used for a long time (for example, 10 minutes or more). Thus, inkjet coating can be performed stably and smoothly. Therefore, it is not necessary to use an extra component for the purpose of achieving the original function of the ink. This means that extra work is not necessary when it is desired to remove excess components due to the original function of the ink. And the cost is not so much.

  The first aspect of the present invention is an ink application method. This ink application method includes an ink suction process in which ink is sucked into the ink chamber by operation of the piezo element during the operation time (T1), and an ink discharge process in which ink is discharged from the ink chamber by operation of the piezo element during the operation time (T2). And a standby process of a waiting time (T3) during which ink suction / discharge is not substantially performed, and ink in an ink jet system by repeating the ink suction process, the ink discharge process, and the standby process as one cycle. Application method.

<Ink>
The ink used in this ink application method is a solid dispersion ink. This solid dispersion ink has a viscosity at 25 ° C. of 0.5 to 7 mPa · s. Preferably, it is 2 mPa · s or more. More preferably, it is 2.5 mPa · s or more. Preferably, it is 6.5 mPa · s or less. That is, since it is such a low-viscosity ink, a so-called thickener is substantially not used. Even if used, there are few. That is, the ratio of the original component of ink is high.

  When the ink is a conductive paint, the components are mostly a conductive substance and a solvent. The conductive material is preferably a carbon nanotube. At least 50% or more of the carbon nanotubes are single wall carbon nanotubes (SWCNT). The carbon nanotubes are preferably those in which carbon nanotubes are intertwined from the viewpoint of conductivity. That is, if the carbon nanotubes are intertwined, the conductivity is improved.

  The manufacturing method of the SWCNT is not limited. For example, it can be produced using a production method such as an arc discharge method, a chemical vapor phase method, or a laser evaporation method. However, SWCNT obtained by the arc discharge method is preferable from the viewpoint of crystallinity. This is easily available.

  The SWCNT is preferably SWCNT subjected to acid treatment. The acid treatment is to bring an acidic liquid into contact with SWCNT. For example, it is the process which immerses SWCNT in an acidic liquid. Or it is the process which sprays acidic liquid on SWCNT. There are no particular restrictions on the acidic liquid used. An inorganic acid or an organic acid can be used as appropriate. Specific examples include nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and mixtures thereof. Nitric acid or a mixed solution of nitric acid and sulfuric acid is preferable. And as for the conditions of an acid treatment, it is preferable that temperature is 80 to 100 degreeC, and it is preferable that time is 1 to 7 days. When SWCNT and carbon fine particles are physically bonded via amorphous carbon by such acid treatment, they are separated by decomposition of amorphous carbon. In addition, the fine particles of the metal catalyst used at the time of SWCNT preparation are decomposed. As a result, the conductivity is improved. That is, when the acid treatment is compared with the case where the acid treatment is not performed, the former has improved conductivity.

  The SWCNT is preferably filtered. That is, the impurities are removed by filtration, the purity is improved, and the decrease in conductivity and the decrease in light transmittance can be prevented. There is no particular limitation on the filtration method. For example, suction filtration, pressure filtration, cross flow filtration, or the like can be used. However, cross-flow filtration using a hollow fiber membrane is preferable from the viewpoint of scale-up.

  The SWCNT-containing solution used in this ink coating method preferably also contains fullerene (including fullerene analogues). This is because the durability is improved as compared with the conductive film containing no fullerene. Any fullerene may be used. For example, C60, C70, C76, C78, C82, C84, C90, C96 etc. are mentioned. Of course, a mixture of these fullerenes may be used. C60 is particularly preferable from the viewpoint of dispersion performance. Furthermore, C60 is easy to obtain. Further, not only C60 but also a mixture of C60 and another kind of fullerene (for example, C70) may be used. Further, metal atoms may be appropriately included in the fullerene. The analogs include those having a known functional group such as hydroxyl group, epoxy group, ester group, amide group, sulfonyl group, ether group, phenyl-C61-propyl acid alkyl ester, phenyl-C61-butyric acid alkyl ester. And hydrogenated fullerene. Among these, those having an OH group (hydroxyl group) are particularly preferable. This is because the dispersibility when applying SWCNT as a dispersion is high. In addition, when there is little quantity of a hydroxyl group, the dispersibility improvement degree of SWCNT will fall. On the other hand, if too much, synthesis is difficult. Accordingly, the amount of hydroxyl groups is preferably 5 to 30 per molecule of fullerene. In particular, 8 to 15 is preferable. If the amount of fullerene added is too large, the conductivity is lowered. On the other hand, if the amount is too small, the effect is difficult to occur. Therefore, the amount of fullerene is preferably 10 to 1000 parts by mass with respect to 100 parts by mass of SWCNT. Particularly, it is preferably 20 to 500 parts by mass with respect to 100 parts by mass of SWCNT.

  The ink used in this ink coating method contains a solvent in addition to the SWCNT and fullerene. There are no particular restrictions on the solvent. However, a solvent having a boiling point of 200 ° C. or lower (preferably lower limit is 25 ° C., further 30 ° C.) is preferable. The low boiling point solvent is preferable because it is easy to dry after coating. Specifically, water, alcohol compounds such as methanol, ethanol, normal propanol, and isopropanol (particularly alcohols having 7 or less carbon atoms, especially aliphatic alcohols), or a mixture thereof are preferable. This is because the hydroxyl group-containing fullerene is highly soluble, and a higher concentration SWCNT dispersion can be obtained. And in the case of water, since the solvent (volatile component) process after application | coating is unnecessary, it is especially preferable. In addition, for example, ketone compounds such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ester compounds such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, methoxyethyl acetate, diethyl ether, ethylene glycol dimethyl ether, Ethyl cellosolve, butyl cellosolve, phenyl cellosolve, ether compounds such as dioxane, aromatic compounds such as toluene and xylene, aliphatic compounds such as pentane and hexane, halogenated hydrocarbons such as methylene chloride, chlorobenzene and chloroform, and mixtures thereof Can also be used. When the dispersibility of SWCNT is inferior, it is preferable to perform ultrasonic irradiation because the dispersibility increases.

  In the present invention, the conductive coating film composed of SWCNTs is a tangled SWCNT. As a result, the SWCNTs are in contact with each other, in particular, in contact with each other at a plurality of locations, and the conductivity is good. Whether the SWCNTs are intertwined can be confirmed by observing the surface of the conductive layer with a scanning electron microscope.

<Application method>
A major feature of the present ink application method is that the waiting time (T3) during which ink suction / discharge, which is a piezo element non-operation (non-operation), is substantially not performed is much longer than in the past. Conventionally, the waiting time is a time when application is not performed, and thus is a useless time and is as short as possible. However, as a result of studies by the present inventors, in the case of low viscosity ink, this waiting time is not a wasteful time, and the length of the waiting time has a great influence on continuous and stable application over a long time. It turned out to be a factor. In other words, it has been found that the waiting time has a positive meaning. When the condition [T3 ≧ 50 × (T1 + T2)] was satisfied, continuous and stable coating was performed for a long time. Preferably, the condition [T3 ≧ 100 × (T1 + T2)] was satisfied. More preferably, the condition [T3 ≧ 200 × (T1 + T2)] is satisfied. More preferably, the condition [T3 ≧ 235 × (T1 + T2)] was satisfied. That is, the longer T3, the longer the continuous coating was performed stably.

  The piezo element operating time (T1) in the ink suction process and the piezo element operating time (T2) in the ink ejection process are substantially determined by the amount of ink ejected from the ink jet nozzles, although they depend on the ability of the ink jet apparatus. It's time. By the way, if the above condition [T3 ≧ 50 × (T1 + T2)] [T3 ≧ 100 × (T1 + T2)] [T3 ≧ 200 × (T1 + T2)] [T3 ≧ 235 × (T1 + T2)] is only satisfied, time ( It is only necessary to make T3) longer. However, if T3 is long, it takes a long time for coating. As a result, the coating is not performed smoothly (speedy). As a result of further studies from such a viewpoint, it was found that the condition [1/1000 seconds ≦ (T1 + T2 + T3) ≦ 1/20 seconds] should be satisfied. Further preferable conditions were [1/400 seconds ≦ (T1 + T2 + T3) ≦ 1/80 seconds]. A more preferable condition was [1/300 seconds ≦ (T1 + T2 + T3) ≦ 1/100 seconds].

  In the present ink application method, the amount of one drop of ink ejected in the ink ejection process is preferably 20 to 100 pL. This is because if the amount is too small, the number of repeated coatings must be increased. On the other hand, when the amount is too large, the vibration of the ink in the ink chamber continues for a long time after ink ejection, and stable ejection is difficult to be performed.

  Various substrates can be used as the substrate on which the ink used in the present ink application method is applied. Resin, glass, metal and so on. However, since an unnecessary thickener or the like is not used in terms of the original function of the ink, it is not necessary to remove these originally unnecessary components. For example, it is not necessary to remove by heat treatment. This means that the present ink application method is advantageous when the resin is not suitable for high-temperature heating (for example, heating at 150 ° C. or higher). For example, polyester resin, cellulose resin, vinyl alcohol resin, vinyl chloride resin, cycloolefin resin, olefin resin such as polyethylene, acrylic resin such as PMMA, polycarbonate resin, ABS resin, aramid When a thermoplastic resin such as resin or PS resin is used, the present ink application method is suitable. A photocurable resin, a thermosetting resin, or the like can also be used. These substrates may be subjected to easy coating treatment, easy adhesion treatment, hard coat treatment, and the like on the surface. The resin may contain an inorganic substance such as an inorganic filler, a plasticizer, and the like. This ink application method is particularly suitable when the substrate is in the form of a sheet (thickness is, for example, about 50 μm to 10 mm) or film (thickness is, for example, about 1 μm to 500 μm). The width and length of the substrate are arbitrary.

<Coating film>
The second aspect of the present invention is a coating film formed by the above ink coating method. In particular, the coating film has a surface resistance value of 500Ω / □ or less. The total light transmittance of this coating film was 80% or more. It was a so-called transparent conductive film.

  Hereinafter, the present invention will be described with specific examples. However, the present invention is not limited by the following examples.

[Example]
* An ink suction process in which ink is sucked into the ink chamber by operation of the piezo element during the operation time (T1), an ink discharge process in which ink is discharged from the ink chamber by operation of the piezo element in the operation time (T2), A commercially available inkjet apparatus that includes a standby process of waiting time (T3) during which ejection is not performed and that employs repetition of the ink suction process, the ink discharge process, and the standby process as one cycle. . The amount of ink ejected at one time from the nozzles of this ink jet apparatus (the amount of one ink drop) was 42 pL.
* The ink used is a mixed solvent of water and isopropanol, contains 200 to 2000 ppm of carbon nanotubes (SWCNT amount of 90% or more), and contains 100 to 5000 ppm of fullerene.

Since the conductive ink was applied under the above conditions, the results are shown in Table 1 below.
Table-1
Viscosity (mPa · s) 2.71 4.46 5.70 6.50
T1 (μsec) 9.0 9.4 9.0 9.0
T2 (μsec) 18.0 18.8 18.0 18.0
T1 + T2 (μsec) 27.0 28.2 27.0 27.0
T3 / (T1 + T2)
= 400 ○ ○ ○ ○
= 250 ○ ○ ○ ○
= 200 ○ ○ ○
= 100 × × ○ ○
= 80 × × × ○
= 60 × × × ○
= 40 × × × ×
= 20 × × × ×
= 10 × × × ×
* In the table, ◯ indicates a case where continuous coating over 10 minutes or more was possible.
A cross indicates a case where the coating cannot be performed at a stage before 10 minutes.

According to Table 1, it can be seen that when the standby time T3 is set as in the present invention, continuous coating over a long period of time was stably performed.

Claims (15)

Ink suction process in which ink is sucked into the ink chamber by operation of the piezoelectric element during the operation time (T1), ink discharge process in which ink is discharged from the ink chamber by operation of the piezoelectric element in the operation time (T2), and ink suction / discharge An ink application method in an ink jet method by repeating the ink suction step, the ink discharge step, and the standby step as one cycle, and a standby step of a waiting time (T3) where substantially no waiting time is performed,
The ink is a solid dispersion ink having a viscosity at 25 ° C. of 0.5 to 7 mPa · s,
1/1000 second ≦ (T1 + T2 + T3) ≦ 1/20 second,
An ink application method, wherein T3 ≧ 50 × (T1 + T2). 2. The ink application method according to claim 1, wherein T3 ≧ 100 × (T1 + T2). 2. The ink application method according to claim 1, wherein T3 ≧ 200 × (T1 + T2). 2. The ink application method according to claim 1, wherein T3 ≧ 235 × (T1 + T2). Ink suction process in which ink is sucked into the ink chamber by operation of the piezoelectric element during the operation time (T1), ink discharge process in which ink is discharged from the ink chamber by operation of the piezoelectric element in the operation time (T2), and ink suction / discharge An ink application method in an ink jet method by repeating the ink suction step, the ink discharge step, and the standby step as one cycle, and a standby step of a waiting time (T3) where substantially no waiting time is performed,
The ink is a solid dispersion ink having a viscosity at 25 ° C. of 0.5 to 7 mPa · s,
1/1000 second ≦ (T1 + T2 + T3) ≦ 1/20 second,
T3 ≧ 50 × (T1 + T2),
And T3 is the time of the length in which continuous ink application over 10 minutes is possible, The ink application method characterized by the above-mentioned. The ink coating method according to claim 1, wherein 1/400 seconds ≦ (T1 + T2 + T3) ≦ 1/80 seconds. The ink application method according to claim 1, wherein the ink is a conductive paint. The ink application method according to claim 1, wherein the ink is a carbon nanotube-containing solution. 8. The ink application method according to claim 1, wherein the ink is a carbon nanotube and fulleran-containing solution. 10. The ink coating method according to claim 8, wherein at least 50% of the carbon nanotubes are single wall carbon nanotubes. The ink application method according to any one of claims 1 to 10, wherein the liquid amount of one drop of ink discharged in the ink discharge step is 20 to 100 pL. The ink application method according to claim 1, wherein the substrate to which the ink is applied is made of resin. The ink coating method according to any one of claims 1 to 12, wherein the ink coating method does not include a high-temperature heat treatment step of 150 ° C or higher.   A coating film formed by the ink application method according to claim 1. The coating film according to claim 14, wherein the surface resistance value is 500Ω / □ or less.