KR20210097719A - Ink composition for RFID and method for manufacturing RFID conductive pattern using the same - Google Patents

Abstract

Provided are an ink composition for RFID using carbon nanotubes as a conductive material, which can secure the conductivity required for an RFID conductive pattern even if the film thickness is reduced, and a method for manufacturing an RFID conductive pattern using the same. The RFID ink composition of the present invention is an RFID ink composition for forming an RFID conductive pattern, and is characterized in that it is a carbon nanotube dispersion containing carbon nanotubes and a high molecular acid functioning as a dispersant thereof.

Description

Ink composition for RFID and method for manufacturing RFID conductive pattern using the same

The present invention relates to an ink composition for RFID for forming a conductive pattern of a radio frequency identifier (RFID) and a method for manufacturing an RFID conductive pattern using the same.

RFID, which reads and writes data such as RF tags in a non-contact manner using radio waves, connects real-world objects with the digital virtual world so that they can be recognized and manipulated. , distribution, history management, product management, library use, presence management, and sensor network use are expected. For example, the UHF band (ultra-high frequency) has a higher frequency than the HF band (short wave band), so the wavelength is short, and communication is possible even with some obstacles in terms of antenna miniaturization and communication distance among passive tags. Since it is also a frequency that can take a long time, it is attracting attention as a technique for mass distribution.

Conventionally, as a conductive pattern of RFID, a technique for forming an antenna circuit on a substrate for mounting ID information mainly uses metal particles as a conductive material (see Patent Documents 1 and 2, etc.). However, when metal particles are used, processing to improve conductivity, for example, thermal firing or pressure firing, is required in a subsequent step, which leads to an increase in cost. Although RFID antennas using conductive pastes such as silver paste have been studied, they are generally not suitable for mass production because the printing speed is slow due to screen printing. Although RFID antennas using aluminum etching have been studied, since a large amount of acid or alkali etching waste comes out, it leads to an increase in cleaning cost.

Further, in the prior art, the ink coating film must be thickened in order to secure the conductivity required for the conductive pattern of the RFID, which increases the cost of the ink.

When a conductive pattern of RFID is manufactured using a conductive ink, when gravure printing is used, it is possible to obtain a printed pattern at a low cost and at high speed. Gravure printing also leads to cost reduction in that cleaning alcohol is used in a small amount. However, in gravure printing, the coating film thickness is, for example, less than 1 µm to several tens of µm, and it is difficult to ensure the ink film thickness from which the conductivity required for the RFID conductive pattern is obtained.

Carbon nanotubes are conductive carbon materials that are being widely used in various industrial applications. However, when a surface resistivity suitable for the UHF band RFID antenna is formed a film as 50Ω / □ is known as front and rear (10 ~ 100Ω / □), the ink prepared by the general dispersion method for a carbon nanotube, a gravure printing 10 ² ~ It is difficult to secure the conductivity required for the conductive pattern of RFID at about 10 ^{5 Ω/□.}

Japanese Patent Publication No. 2014-527375 Japanese Patent Laid-Open No. 2015-072914

The present invention has been made in consideration of the above circumstances, and an ink composition for RFID using carbon nanotubes as a conductive material, which can secure the conductivity required for an RFID conductive pattern even if the film thickness is reduced, and RFID conductivity using the same It is making it a subject to provide the manufacturing method of a pattern.

In order to solve the above problems, the RFID ink composition of the present invention is an RFID ink composition for forming an RFID conductive pattern, and is a carbon nanotube dispersion containing carbon nanotubes and a high molecular acid functioning as a dispersing agent. is characterized.

The method for manufacturing an RFID conductive pattern of the present invention includes the following steps:

applying the RFID ink composition to a substrate for mounting ID information; and

A step of drying the applied RFID ink composition to form an RFID conductive pattern having a film thickness of 5 μm or less and a surface resistivity of 100 Ω/□ or less.

According to the ink composition for RFID of the present invention and the method for producing an RFID conductive pattern using the same, even if the film thickness is reduced, the conductivity required for the RFID conductive pattern can be secured.

BRIEF DESCRIPTION OF THE DRAWINGS It is a graph which shows the change in the resistance value by ink density and film thickness in the ink produced in Example 1. FIG.
Fig. 2 is a graph showing the change in the resistance value according to the number of times of overlapping in the ink produced in Example 1;

Hereinafter, the present invention will be described in detail. In the following description, "carbon nanotube" is also referred to as "CNT".

(Ink composition for RFID)

The ink composition for RFID of the present invention contains CNT and a polymeric acid functioning as a dispersant thereof. The ink composition for RFID of this invention makes electrical connection in a CNT network favorable, and is excellent in electrical performance. Therefore, even if the film thickness is reduced, the conductivity required for the RFID antenna can be secured. Therefore, it is possible to apply a high-speed printing method with a small thickness of the ink coating film, such as gravure printing, so that the manufacturing cost can be reduced.

Since the ink composition for RFID of the present invention has good dispersibility during preparation, it is possible to increase the efficiency at the time of ink production and to reduce the production cost.

The ink composition for RFID of the present invention has high abrasion resistance and strong coating film strength. Therefore, damage to the antenna or the like can be suppressed in the post-process after printing the conductive pattern of the antenna or the like.

In addition, CNTs are uniformly dispersed in a small amount of polymeric acid, a homogeneous composite film can be obtained, and a conductive film can be formed without removing the dispersant after film formation, and the post-treatment process is simplified, which is advantageous in the manufacturing process. In addition, since the polymeric acid itself exhibits a doping effect, there is no need to add a separate dopant, and since the polymeric acid is stable and not volatile, a conductive film exhibiting stable conductivity in the long term is obtained. In addition, not only CNTs but also high molecular acids have flexible molecular structures, so a film highly resistant to bending can be obtained.

In the CNT dispersion liquid, which is the ink composition for RFID, of the present invention, the polymer acid surrounds the CNTs except for the region where the CNTs are bonded, and is attached so that the CNTs alone or bundles of CNTs are surrounded.

In one example of the present invention, the CNTs and the polymeric acid in the CNT dispersion are well dispersed without bonding between the CNTs in the portion of the CNTs to which the polymeric acid is attached. On the other hand, in the portion of the CNTs to which the polymeric acid is not attached, the CNTs tend to aggregate due to the van der Waals force, resulting in stronger bonding. Therefore, in the CNT dispersion, it is presumed that the following three local states exist.

A State in which polymeric acid is attached to CNTs and CNTs do not contact each other (stable dispersion state)

The CNTs do not directly contact each other, the intermolecular force in the CNT dispersion is weak, and the CNTs are difficult to bond.

B CNTs in contact with each other (aggregation of CNTs)

It is an unstable dispersed state of CNTs, and the intermolecular forces of CNTs are strong, and CNTs are bonded.

C A high molecular acid is attached to a part of the CNTs, and the CNTs are in contact with each other

In the portion where the CNTs are in contact with each other, the CNTs are in a stable aggregated state, and in the portion where the high molecular acid is attached, the CNTs are in a stable dispersed state. In the portion where the CNTs are in contact with each other, the intermolecular force is strong, and the CNTs are joined.

In the CNT dispersion liquid, a bundle of CNTs is a bundle-shaped structure in which CNTs are aggregated, and the CNTs are oriented locally, but may have a structure in which the CNTs are partially separated. Further, it has at least one of a portion in which CNTs contact each other, a portion in which bundles of CNTs contact each other, and a portion in which CNTs and bundles of CNTs contact each other. Thereby, the CNT constitutes a network as a whole.

On the other hand, in the step where the CNTs take any one state and the CNT dispersion is made into a CNT composite film (the solvent is dried and removed), the CNTs are selectively bonded to each other in the portion where the polymeric acid is not attached by the intermolecular force of the CNTs. .

In the ink composition for RFID of the present invention, the type of CNT is not particularly limited, and a conventionally known one can be used. For example, any of single-layer CNT (SWNT), double-layer CNT (DWNT), multi-layer CNT (MWNT), rope-like CNT, and ribbon-like CNT can be used. It is also possible to use metallic CNTs, semiconducting CNTs, and metallic CNTs or semiconducting CNTs alone.

The length and diameter of the CNTs are not particularly limited, but in order to obtain a highly conductive CNT composite film, the diameter is preferably 0.4 nm or more and 2.0 nm or less and the length is 0.5 µm or more and 20 µm or less. In addition, it is preferable that the single-layered CNTs have excellent crystallinity and have a long length. In addition, the use of high-quality single-layered CNTs synthesized by the direct split pyrolysis synthesis (DIPS) method provides a more homogeneous dispersion, which is preferable for obtaining a highly conductive composite film.

In the RFID ink composition of the present invention, the concentration of CNTs in the CNT dispersion is not particularly limited, but considering that the conductivity required for the RFID conductive pattern can be secured even if the film thickness is small, 0.005 wt% or more Preferably, 0.05 weight% or more is more preferable, 0.1 weight% or more is still more preferable, and 0.25 weight% or more is especially preferable. Moreover, 1 weight% or less is preferable, 0.9 weight% or less is more preferable, 0.75 weight% or less is still more preferable, and 0.6 weight% or less is especially preferable.

In the ink composition for RFID of the present invention, as a high molecular acid, a raw material monomer including a monomer having an acidic group, such as a monomer having a carboxylic acid group, a monomer having a sulfonic acid group, or a monomer having a phosphoric acid group, is obtained by (co)polymerizing (co)polymerization. polymers and the like. The monomer which has an acidic group may be used individually by 1 type, and may be used in combination of 2 or more type.

Examples of the monomer having a carboxylic acid group include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethylsuccinic acid. These may be used individually by 1 type, and may be used in combination of 2 or more type. Among these, acrylic acid and methacrylic acid are preferable.

Examples of the monomer having a sulfonic acid group include styrenesulfonic acid such as p-styrenesulfonic acid, vinylsulfonic acid, allylsulfonic acid, 2-acrylamide-2-methylpropanesulfonic acid, and 2-hydroxy-3-allyloxy-1-propanesulfonic acid. , isoprenesulfonic acid, and the like. These may be used individually by 1 type, and may be used in combination of 2 or more type. Among these, p-styrenesulfonic acid is preferable.

The polymeric acid may contain structural units derived from monomers other than the monomer having an acidic group, but preferably, the monomer ratio of the other monomers is 1% or less, and substantially does not contain structural units derived from other monomers. It is preferable not to

As a high molecular acid, high molecular weight carboxylic acid and high molecular weight sulfonic acid are preferable. The high molecular weight carboxylic acid and high molecular weight sulfonic acid are preferably (co)polymers in which the monomer ratio of the monomer having a carboxylic acid group and the monomer having a sulfonic acid group is 97% or more, preferably 100%. Here, the monomer ratio refers to a structural unit derived from a monomer having a carboxylic acid group and a monomer having a sulfonic acid group contained in the (co)polymer when the structural units derived from all monomers constituting the (co)polymer are 100 mol%. indicates the ratio (mol%) of

Among these, polyacrylic acid and polymethacrylic acid are preferable as the high molecular weight carboxylic acid, and poly(p-styrenesulfonic acid) is preferable as the high molecular weight sulfonic acid.

In the ink composition for RFID of the present invention, the weight average molecular weight of the polymer acid is not particularly limited, but the high molecular weight polymer acid disperses CNTs better, shortens the dispersion time, and improves the strength of the coating film wear resistance is improved by In the RFID ink, if the dispersion time is fast, there is a cost advantage in mass production. For the conductive pattern of RFID, for example, the antenna, it is preferable that the coating film strength is high so that damage does not occur in the post-printing process. On the other hand, a polymer acid with a small molecular weight tends to have a larger doping effect, and a one with a smaller molecular weight is preferable for advanced conversion. From the viewpoint of the balance of these properties required for the RFID ink, the weight average molecular weight of the polymer acid (especially polyacrylic acid) is preferably 500 or more, more preferably 1,000 or more, still more preferably 2,000 or more, and 4,000 or more. More preferably, 10,000 or more are particularly preferable, and 20,000 or more are most preferable. Moreover, 500,000 or less are preferable, 250,000 or less are more preferable, 100,000 or less are still more preferable, 50,000 or less are especially preferable, and 30,000 or less are the most preferable.

In addition, as for the said weight average molecular weight, the value of the standard polymer (for example, standard polyacrylic acid) conversion by gel permeation chromatography (GPC method) is referred. Here, the standard polymer refers to a polymer having a narrow molecular weight distribution with a known molecular weight having a structure identical to or close to that of the measurement target.

In the RFID ink composition of the present invention, the concentration of the polymeric acid in the CNT dispersion is not particularly limited, but considering that the conductivity required for the RFID conductive pattern can be secured even if the film thickness is small, 0.005 wt% or more This is preferable, 0.075 weight% or more is more preferable, 0.15 weight% or more is still more preferable, and 0.4 weight% or more is especially preferable. Moreover, 5 weight% or less is preferable, 4.5 weight% or less is more preferable, 3 weight% or less is still more preferable, 1 weight% or less is especially preferable.

In the ink composition for RFID of the present invention, the weight ratio of CNT and polymeric acid is preferably 1:0.8 or more, considering that even if the film thickness is small, the conductivity required for the RFID conductive pattern can be secured. : 1 or more is more preferable. Moreover, 1:5 or less is preferable, 1:4 or less is preferable, and 1:3 or less is more preferable. If the weight ratio of the polymeric acid and CNT is within this range, in the CNT composite film obtained by applying the ink composition for RFID of the present invention, electrical contact between CNT and CNT, electrical contact between bundle and bundle, and electrical contact between CNT and CNT bundle It is difficult to be disturbed by a high molecular acid. In this range, the high molecular acid adsorbs to cover the periphery of CNTs or CNT bundles and disperses CNTs well, but the high molecular acid cannot cover the entire surface of CNTs or CNT bundles, resulting in exposed CNTs or CNT bundles. do. Therefore, in order not to interfere with the electrical contact between CNTs or CNT bundles, the CNT composite film exhibits good conductivity.

In the ink composition for RFID of the present invention, the solvent for dispersing the polymer acid and CNTs is not particularly limited, but water and organic solvents can be used. As the organic solvent, for example, an alcohol-based organic solvent (eg, methanol, ethanol, 2-propanol, glycerin, ethylene glycol, etc.), a ketone-based organic solvent (eg, acetone, methyl ethyl ketone, methyl isobutyl ketone) etc.), ether-based organic solvents (eg, diethyl ether, THF, etc.), ester-based organic solvents (methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, isobutyl acetate, etc.), hydrocarbon-based organic solvents solvents (toluene, methylcyclohexane, etc.); and the like. These may be used individually by 1 type, and may be used in combination of 2 or more type. Among them, water, an alcohol-based organic solvent, or a mixed solvent thereof is preferable in consideration of dispersibility, response to environmental problems, and printability and drying properties of the ink composition, for example, water, methanol, ethanol , 2-propanol, glycerin, ethylene glycol, a mixture of water and ethanol, and a mixture of ethanol and 2-propanol.

In the ink composition for RFID of the present invention, other components other than the above-described CNT, high molecular acid, and solvent may be blended within a range that does not impair the effects of the present invention.

The ink composition for RFID of the present invention can be produced, for example, as follows.

(1) pre-doping process

CNT powder is added to a solution in which a dopant such as an oxidizing agent is dissolved, and vigorously stirred with water for several 10 minutes to 1 day with a magnetic stirrer. Thereafter, the dispersion is filtered, and the CNT powder remaining on the filter paper is washed to obtain a doped CNT powder. In addition, the pre-doping process is a process arbitrarily performed when preparing the ink composition for RFID of the present invention.

By pre-doping the CNTs with an acid or an oxidizing agent before dispersing them in a solvent, the conductivity of the CNTs can also be improved. In the pre-doping process, a dopant selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid, iodine, bromine, chlorosulfonic acid (acetic acid), hydroiodic acid, hydrobromic acid, and mixtures thereof can be used.

As a solvent for dissolving the dopant, a solvent for dispersing the above-described polymeric acid and CNTs can be used. In addition, these solvents can be used also in washing|cleaning of the CNT powder remaining on filter paper.

(2) pre-dispersion process

CNT powder is added to the solution in which the polymer acid, which is a dispersing agent, is dissolved, and vigorously cultivated for several 10 minutes to 1 day with a magnetic stirrer. As a solvent for dispersing the CNTs, the solvent described above may be used. The pre-dispersion step is a step that is mainly essential when producing the ink composition for RFID of the present invention.

(3) this dispersion process

Using the pre-dispersed liquid, the CNTs are further finely dispersed by an ultrasonic homogenizer, ultrasonic bus, jet mill high-pressure dispersion, or the like to obtain a CNT dispersion liquid in which CNTs do not easily aggregate and settle. This dispersion process is mainly essential in manufacturing the ink composition for RFID of this invention.

In this dispersion process, the ultrasonic homogenizer disperses CNTs strongly, but there is a risk of damaging the CNTs or the polymeric acid if it takes too much time. In addition, when the high molecular acid solution is heated when preparing the CNT dispersion, it is presumed that the high molecular acid partially self-aggregates in the CNT dispersion, the area where the high molecular acid comes into contact with the CNTs decreases, and the doping effect becomes small. In general, in dispersion treatment of CNTs by an ultrasonic homogenizer, high heat is generated locally by vibrating solvent molecules or polymeric acid molecules, so that the polymeric acid violently aggregates. Then, while the doping effect becomes small, the contact of CNTs is also prevented.

For this reason, it is effective to minimize the processing time in the ultrasonic homogenizer or to irradiate the ultrasonic wave while cooling the pre-dispersed liquid. For example, by performing pre-dispersion for about 12 hours, a uniform dispersion can be obtained even if the time of ultrasonic homogenizer irradiation in the main dispersion is shortened, and damage to CNTs and polymeric acids caused by ultrasonic homogenizer irradiation is reduced. can be suppressed to a minimum. In addition, when a uniform dispersion liquid can be obtained in this way, the next ultracentrifugation treatment can be omitted, which is very advantageous in the manufacturing process. In addition, in order to shorten the processing time in the ultrasonic homogenizer, it is also effective to perform the processing in the ultrasonic bus prior to the processing in the ultrasonic homogenizer.

(4) centrifugation process

The CNT dispersion liquid subjected to this dispersion is centrifuged with an ultracentrifugation apparatus, and the obtained supernatant is used as a dispersion liquid for film forming. The centrifugal separation process is a process arbitrarily performed in preparing the ink composition for RFID of the present invention.

In centrifugation, the rotation speed of the rotor is preferably 2,000 rpm or more and 60,000 rpm or less, more preferably 45,000 rpm, and the centrifugation time is about 2 hours. In addition, when a CNT dispersion is prepared using high-quality SWNTs, since a homogeneous CNT dispersion can be prepared, it is also possible to omit ultracentrifugation.

(Manufacturing method of conductive pattern of RFID)

When manufacturing an RFID conductive pattern using the RFID ink composition of the present invention described above, the RFID ink composition of the present invention is applied to a substrate for mounting ID information, and the applied RFID ink composition is dried. .

The application method is not particularly limited, but, for example, gravure printing, screen printing, casting method, dip coating method, spin coating method, bar coating method, blade coating method, die coating method, spray coating method, inkjet method, etc. can be heard

Among these, gravure printing is preferable from an industrial viewpoint. When gravure printing is used, it is possible to obtain a printing pattern at low cost and at high speed. Gravure printing also leads to cost reduction in that cleaning alcohol is used in a small amount. Although the thickness of the coating film is generally reduced in gravure printing, according to the ink composition for RFID of the present invention, even if the film thickness is reduced, the conductivity required for the conductive pattern of the RFID can be secured.

In gravure printing, for example, when printing the ink composition for RFID of the present invention, it is diluted as necessary so as to have an appropriate viscosity according to printing conditions at the atmospheric temperature at the time of printing, and the ink composition is printed on the substrate. Gravure printing is performed by transferring the ink supplied to the gravure plate to a material to be printed. For example, in the gravure printing apparatus, ink is introduced from an ink inlet formed at the bottom of the ink plate. And, the surplus ink is discharged from the ink outlet so that the ink liquid level at a constant height is always maintained. The gravure plate is installed so that its lower part is immersed under the ink liquid level, and the surface of the rotating gravure plate is immersed in the ink, so that the ink is supplied to the surface of the gravure plate. Then, of the ink supplied to the surface of the gravure plate, an excess amount is scraped off by a doctor, and an appropriate amount of ink is transferred to the printing material supplied between the top of the gravure plate and the pressure plate for printing.

The coating film printed by the above method is dried by heating if necessary, and an RFID conductive pattern is obtained as a CNT composite film.

The conductive pattern of RFID may be arbitrarily provided in the next step.

(5) cleaning process

When it is desired to obtain a conductive CNT composite film, the dispersant may interfere with the conductivity of the CNTs. In this case, the dispersant is removed from the CNT composite film by a method such as washing. A washing|cleaning process is an arbitrary process in this invention.

In general, when a non-conductive dispersant is used, in order to form electrical contact between CNTs or CNT bundles and to exhibit conductivity to the CNT composite film, it is necessary to remove the non-conductive dispersant of the CNT composite film after film formation. For this, for example, a method such as immersion in a solvent and removal can be considered. However, in the present invention, although the polymer acid used for dispersion is non-conductive, it can be dispersed in a small amount. Therefore, when the weight of the polymer acid relative to the CNT is up to several times, the high conductivity of the CNT is exhibited without removing it. .

(6) Post doping process

The CNT composite film obtained by the above method is doped by applying to the vapor of an oxidizing agent or immersing in a solution containing an oxidizing agent. A post doping process is an arbitrary process in this invention.

In general, since the conductivity of a film made of only CNTs is not sufficient, a method of doping using an oxidizing agent such as nitric acid or the like is well employed. In this case, in general, a process of immersing the film in a solution of an oxidizing agent or fading in the vapor of the oxidizing agent is required. In addition, when a volatile oxidizing agent such as nitric acid is used, the obtained film has unstable conductivity. However, in the present invention, since the polymeric acid itself as a dispersant functions as a dopant, there is no need to go through the doping step again after film formation, and since the polymeric acid is non-volatile, the conductivity of the obtained CNT composite film is very stable. do.

In the present invention, the high molecular acid as a dispersing agent is only added in a very small amount of 1:1 to 5:1 with respect to CNT, and since the high molecular acid itself serves as a dopant, the above (5) washing step and ( 6) It is possible to omit the post-doping process, which is advantageous in terms of the manufacturing process. Further, in the production of the RFID ink composition of the present invention, the (4) centrifugal separation step can be omitted by optimizing the (2) pre-dispersing step or (3) the main dispersing step, which is advantageous in terms of the manufacturing process. Moreover, the electroconductivity of the obtained film|membrane is stable for a long period of time.

As described above, in the present invention, a high-conductivity film can be obtained without removing the polymer acid as a dispersing agent after film formation, but part or all of the polymer acid may be removed after film formation if necessary. The method of removing the polymeric acid is not particularly limited, and examples thereof include thermal firing (heat treatment), pulse light firing (heat treatment), washing with a solvent, and washing with an alkaline developer (alkali treatment).

In the present invention, RFID transmits and receives information from an RF tag equipped with ID (identification) information by wireless communication at a short distance (several cm to several m depending on frequency band) using an electromagnetic field or radio wave, etc., and overall technology includes In addition to the wireless communication technology between the tag and the reader, it includes the overall operating system that attaches tags to various objects or people, and grasps their positions and operations in real time. RFID is a semi-active combination of a passive tag (passive tag) and an active tag (active tag), in addition to an IC tag used with ID information mounted on a one-chip IC (integrated circuit), especially a passive type IC tag. A tag (actuation type active tag) or the like may be used. A contactless IC card using the same technology as RFID is also included in RFID in the present invention.

It does not specifically limit as a base material for ID information mounting to which the ink composition for RFID is apply|coated of this invention, A flexible base material may be sufficient, and a rigid base material may be sufficient. For example, cellulosic substrates such as paper and thick paper, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethylene (PE), polypropylene (PP), polyimide (PI), polyether sulfone (PES) ), resin-made substrates, such as polycarbonate (PC), glass-made substrates, etc. are mentioned.

In the conductive pattern of RFID obtained by the manufacturing method of the present invention, the CNT composite film forming the conductive pattern contains a polymeric acid and CNTs. The polymeric acid is attached to surround a single CNT or bundle of CNTs by van der Waals force. A bundle of CNTs is a bundle-shaped structure in which CNTs are aggregated, and although CNTs are oriented locally, they may have a structure in which CNTs are partially separated. Further, it has at least one of a portion where CNTs are bonded, a portion where bundles of CNTs are bonded, and a portion where CNTs and bundles of CNTs are bonded. Thereby, the CNT constitutes a network as a whole. In this network of CNTs, electrical contact between CNTs and CNTs, electrical contact between bundles and bundles, and electrical contacts between CNTs and bundles of CNTs, is provided at the contacts, and conductivity is imparted to the network as a whole.

The CNT composite membrane includes a network of polymeric acids and CNTs, and the CNTs are in contact with each other as the polymeric acids are arranged around the CNTs. Therefore, in the CNT composite film, the electrical contact between CNTs and CNTs, the bundles and the bundles, and the CNTs and the bundles of CNTs are not disturbed by the polymeric acid. Therefore, the CNT composite film|membrane makes good electrical bonding in a CNT network, and is excellent in electrical performance.

The conductive pattern obtained by the method for producing an RFID conductive pattern of the present invention has a film thickness after drying, preferably 5 μm or less, more preferably 2 μm or less, in consideration of the application of gravure printing and cost aspects, etc. More preferably, it is 1 micrometer or less. Further, in consideration of the conductivity required for RFID, it is preferably 0.05 µm or more, and more preferably 0.1 µm or more.

In addition, the surface resistivity of the conductive pattern obtained by the method for manufacturing an RFID conductive pattern of the present invention is preferably 100 Ω/□ or less in consideration of the suitable point for UHF versus RFID antennas and the like. Moreover, Preferably it is 10 ohms/square or more.

In the method for producing an RFID conductive pattern of the present invention, the step of forming the RFID conductive pattern and the step of drying the applied RFID ink composition may be repeated. For example, by performing these steps at least twice, respectively, an RFID conductive pattern having a film thickness of 5 µm or less and a surface resistivity of 100 Ω/square or less may be formed. In this way, by repeating application and drying, and applying overlapping coating, it becomes possible to achieve further advancement, and it is possible to easily adjust the resistance value suitable for the conductive pattern of the RFID.

(Example)

Hereinafter, the present invention will be described in more detail by way of Examples, but the present invention is not limited to these Examples.

In the following comparative examples and Examples, the resistance value was measured with the following structure.

Surface resistance measuring device type: Loresta-GP MCP-T600

Resistance meter (Mitsubishi Chemical Analytech Co., Ltd.)

Coating mechanism bar coater (Daichi Rika Co., Ltd.)

The wet film thickness referred to the bar coater coat film thickness, and the dry film thickness was calculated by calculation from the solid content in the dispersion.

(Comparative Example 1)

Ink was produced with the following formulation.

240 g of solvent (water:2-propanol=5:1)

5~10g of dispersant (BYK DISPERBYK-190 block copolymer)

MWCNT (Nanoseal NC7000) 3.2g

The above materials were mixed and pre-dispersed with a stirrer for 15 minutes. Then, it disperse|distributed for 90 minutes with the ultrasonic disperser. The finished ink was applied to a PET film with a wet film thickness of 22 to 28 μm to check the surface resistivity.

An evaluation result is shown in Table 1.

From Table 1, by reducing the dispersant and increasing the proportion of CNTs, it can be highly converted. However, if the amount of the dispersing agent is lower than the required amount, the dispersion becomes impossible, so there is a limit to the advanced conversion.

(Comparative Example 2)

In Comparative Example 1, the CNTs were highly converted from multi-walled CNTs (MWCNTs) to single-walled CNTs (SWCNTs).

Ink was produced with the following formulation.

240 g of solvent (water:2-propanol=5:1)

Dispersant (BYK DISPERBYK-190) 6~10g

SWCNT (Oxyal TUBALL CNT 93%) 0.8g

The above materials were mixed and pre-dispersed with a stirrer for 15 minutes. Then, it disperse|distributed for 90 minutes with the ultrasonic disperser. The finished ink was applied to a PET film with a wet film thickness of 22 to 28 µm to check the surface resistivity.

Table 2 shows the evaluation results.

From Table 2, it was confirmed that by using SWCNTs, conductivity equivalent to that of MWCNTs could be secured with a small amount of CNTs. However, similarly to MWCNT, if the amount of the dispersant is lower than the required amount, dispersion becomes impossible, so there is a limit to the advanced conversion.

From Comparative Examples 1 and 2, in the CNT ink produced by dispersing with a general CNT dispersion method (using a commercially available dispersant), when applied to a film thickness of gravure printing, about 10 ² to 10 ⁵ Ω/□ is required for the RFID antenna. Conductivity cannot be ensured.

(Example 1)

Ink was produced with the following formulation.

150 g of solvent (2-propanol: ethanol = 9: 1)

PAA (Fujifilm Wako Junyaku molecular weight 5000) 0.3-0.9 g

SWCNT (Oxyal TUBALL CNT 93%) 0.2~0.6g

The above materials were mixed and pre-dispersed with a stirrer for 15 minutes. Then, it disperse|distributed for 90 minutes with the ultrasonic disperser. The finished ink was applied to a PET film with a wet film thickness of 22 to 28 µm to check the surface resistance value.

Table 3 shows the evaluation results. The change of the surface resistivity according to the ink density and the film thickness is shown in FIG.

It is known that the surface resistivity suitable for the antenna of UHF vs. RFID is around 50Ω/□ (10~100Ω/□). From Table 3, when PAA is used as a dispersant, high conductivity is obtained with a general coating film thickness (less than 1 μm to several tens of μm) in gravure printing, and an RFID antenna can be manufactured at low cost and high speed by gravure printing or the like.

(Example 2)

When four types of polyacrylic acids (MW=5000, 25000, 250000, 1000000) were respectively used, the dispersion|distribution time in the case of using, a viscosity, and coating-film strength were verified.

Ink was produced with the following formulation.

SWCNT OCSiAl TUBALL 93%: 0.20g

PAA (polyacrylic acid) Fujifilm Wako Junyaku Co., Ltd.: 0.30 g

IPA (2-propanol): 135 g

Ethanol: 15 g

The dispersion time, the viscosity, and the coating film strength were evaluated under the following conditions.

Dispersion time: Apply a portion of the dispersion to the tabletop at any dispersion time to visually check the dispersion and resistance value

Viscosity: Measured in cups (Rigosha) and converted to CPS

Coating film strength: Abrasion resistance evaluation by abrasion fastness tester Load 200g

Table 4 shows the evaluation results.

From Table 4, when evaluating electroconductivity, the direction using PAA with a small molecular weight is more advantageous for advanced conversion. However, when evaluated as a printing ink from the viewpoint of printing an RFID antenna, the use of PAA having a large molecular weight has advantages in shortening the dispersion time of SWCNTs and improving the coating film strength. These points WHEREIN: PAA molecular weights 5,000 and 25,000 were the most favorable. As for the dispersion time, a molecular weight of 25,000 is the fastest to be dispersed, and there is an advantage in ink production cost.

(Example 3)

Using the ink (solvent 150 g, PAA 0.3 g, SWCNT 0.2 g) prepared in Example 1 with a concentration magnification of 1, the PET film was applied over 1 to 4 times with a wet film thickness of 22 µm to confirm the surface resistivity. Table 5 shows the evaluation results. The change in surface resistivity according to the number of overlaps is shown in FIG. 2 .

From Table 5, it is possible to further upgrade the coating by overlapping with a printing machine, and adjustment to a surface resistivity suitable for an RFID antenna is easy.

Claims (8)

An ink composition for RFID for forming a conductive pattern of RFID, comprising:
An ink composition for RFID, which is a carbon nanotube dispersion liquid comprising carbon nanotubes and a high molecular acid functioning as a dispersing agent. The method of claim 1,
The concentration of the carbon nanotubes is 0.005 wt% or more and 1 wt% or less, the concentration of the polymeric acid is 0.005 wt% or more and 5 wt% or less, and the weight ratio of the carbon nanotubes to the polymeric acid is 1:0.8 or more and 1:5 The following ink composition for RFID. 3. The method according to claim 1 or 2,
The concentration of the carbon nanotubes is 0.05 wt% or more and 0.9 wt% or less, the concentration of the polymeric acid is 0.075 wt% or more and 4.5 wt% or less, and the weight ratio of the carbon nanotubes to the polymeric acid is 1:1 or more and 1:4 The following ink composition for RFID. 4. The method according to any one of claims 1 to 3,
The high molecular acid is at least one selected from polyacrylic acid, polymethacrylic acid and poly(p-styrenesulfonic acid). 5. The method according to any one of claims 1 to 4,
The high molecular acid is polyacrylic acid, and the weight average molecular weight of the ink composition for RFID is 500 or more and 250,000 or less. A method of manufacturing an RFID conductive pattern comprising the following steps:
The process of apply|coating the ink composition for RFID in any one of Claims 1-5 to the base material for ID information mounting; and
A step of drying the applied RFID ink composition to form an RFID conductive pattern having a film thickness of 5 μm or less and a surface resistivity of 100 Ω/□ or less. 7. The method of claim 6,
A method for producing an RFID conductive pattern, wherein the applied RFID ink composition is dried to form an RFID conductive pattern having a film thickness of 1 μm or less and a surface resistivity of 100 Ω/□ or less. 7. The method of claim 6,
The step of forming the RFID conductive pattern and the step of drying the applied RFID ink composition are repeated at least twice, respectively, to form an RFID conductive pattern having a film thickness of 5 μm or less and a surface resistivity of 100 Ω/□ or less A method for manufacturing an RFID conductive pattern.

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