JP7190694B2 - Manufacturing method of conductive pattern for RFID - Google Patents

Description

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

RFID, which uses radio waves to read and write data such as RF tags without contact, has various ripple effects on society in that it becomes possible to recognize and operate objects in the real world by connecting them with the virtual world of digital. It is expected to be used for distribution, history management, article management, use in libraries, presence management, sensor networks, and the like. For example, the UHF band (ultrahigh frequency) has a higher frequency than the HF band (short wave band) and has a shorter wavelength. Among tags, it is also a frequency that allows a long communication distance, so it is attracting attention as a technology for mass diffusion.

Conventionally, a technique for forming an antenna circuit on a substrate for mounting ID information as a conductive pattern of RFID mainly uses metal particles as a conductive material (see Patent Documents 1 and 2, etc.). However, when metal particles are used, processing to improve the conductivity in a post-process, such as heat firing or pressure firing, is required, leading to an increase in cost. An RFID antenna using a conductive paste such as silver paste has been studied, but it is generally based on screen printing and the printing speed is slow, making it unsuitable for mass production. RFID antennas using aluminum etching are also being considered, but they generate a large amount of acidic or alkaline etching waste, leading to an increase in cleaning costs.

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 ink cost.

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

Carbon nanotubes are electrically conductive carbon materials that are gaining popularity in various industrial applications. However, although the surface resistivity suitable for UHF band RFID antennas is said to be around 50 Ω/□ (10 to 100 Ω/□), the ink produced by the general method of dispersing carbon nanotubes cannot be coated by gravure printing. is formed, it is difficult to secure the conductivity required for the conductive pattern of the RFID at about 10 ² to 10 ⁵ Ω/□.

Japanese translation of PCT publication No. 2014-527375 JP 2015-072914 A

The present invention has been made in view of the circumstances as described above, and is for RFID using carbon nanotubes as a conductive material, which can ensure the conductivity necessary for the conductive pattern of RFID even if the film thickness is reduced. An object of the present invention is to provide an ink composition and a method for producing an RFID conductive pattern using the ink composition.

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, comprising carbon nanotubes and a polymer functioning as a dispersant thereof It is characterized by being a carbon nanotube dispersion containing an acid.

The manufacturing method of the RFID conductive pattern of the present invention includes the following steps:
A step of applying the RFID ink composition to a substrate for mounting ID information; and drying the applied RFID ink composition, and the RFID conductivity having a film thickness of 5 μm or less and a surface resistivity of 100 Ω / □ or less. forming a sex pattern.

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

4 is a graph showing changes in resistance value depending on ink concentration and film thickness in the ink produced in Example 1. FIG. 4 is a graph showing the change in resistance value of the ink prepared in Example 1, depending on the number of repeated coatings.

The present invention will be described in detail below. In the following description, "carbon nanotube" is also referred to as "CNT".
(Ink composition for RFID)
The RFID ink composition of the present invention contains CNTs and a polymer acid that functions as a dispersant thereof. The RFID ink composition of the present invention provides good electrical connection in a CNT network and is excellent in electrical performance. Therefore, even if the film thickness is reduced, the electrical conductivity necessary for the RFID antenna can be ensured. Therefore, it is possible to apply a high-speed printing method such as gravure printing in which the thickness of the ink coating film is small, and to reduce the manufacturing cost.

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

The RFID ink composition of the present invention has high abrasion resistance and strong coating film strength. Therefore, it is possible to suppress damage to the antenna or the like in a post-process after printing the conductive pattern such as the antenna.

Furthermore, the CNTs can be uniformly dispersed with a small amount of polymer acid, making it possible to obtain a homogeneous composite film.In addition, a conductive film can be obtained without removing the dispersant after film formation, and the post-treatment process is simple. , which is advantageous in terms of the manufacturing process. Further, since the polymeric acid itself exhibits a doping effect, there is no need to add a separate dopant, and the polymeric acid is stable and non-volatile, so a conductive film that exhibits long-term stable conductivity can be obtained. Furthermore, since not only CNT but also polymeric acids have flexible molecular structures, a film that is extremely resistant to bending can be obtained.

In the CNT dispersion, which is the RFID ink composition of the present invention, the polymer acid surrounds the CNTs, except for the regions where the CNTs are joined together, and adheres to surround the single CNT or the CNT bundle. .

In one example of the present invention, the CNTs and the polymer acid in the CNT dispersion liquid are in a well-dispersed state without bonding between the CNTs in the portion of the CNTs to which the polymer acid is attached. On the other hand, in the portion of the CNTs to which the polymer acid is not attached, the CNTs tend to agglomerate due to the van der Waals force, resulting in a stronger bond. Therefore, it is inferred that the following three local states exist in the CNT dispersion.
A State where polymer acid adheres to CNTs and CNTs do not contact each other (stable dispersion state)
The CNTs do not contact each other directly, the intermolecular force in the CNT dispersion is weak, and the CNTs are difficult to bond.
B State in which CNTs are in contact with each other (CNT aggregation state)
The CNTs are in an unstable dispersed state, the intermolecular force of the CNTs is strong, and the CNTs are bonded.
C State where polymer acid adheres to a part of CNT and CNTs are in contact with each other In the part where CNTs are in contact with each other, the CNTs are in a stable aggregation state, and in the part where the polymer acid is attached, the CNTs are in a stable dispersed state. . At the portion where the CNTs are in contact with each other, the intermolecular force is strong and the CNTs are bonded.

In the CNT dispersion, the CNT bundle is a bundle-like structure in which CNTs are aggregated, and the CNTs are locally oriented, but may have a structure in which the CNTs are partially separated. It also has one or more of a portion where CNTs are in contact with each other, a portion where CNT bundles are in contact with each other, and a portion where CNTs and CNT bundles are in contact. Thereby, the CNT constitutes a network as a whole.

On the other hand, at the stage where the CNTs are in one of the states and the CNT dispersion liquid is turned into a CNT composite film (the solvent is dried and removed), the intermolecular force of the CNTs causes the CNTs to selectively dissolve the polymer acid. Join the parts that are not attached.

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

Although the length and diameter of the CNT are not particularly limited, the diameter is preferably 0.4 nm or more and 2.0 nm or less and the length is preferably 0.5 μm or more and 20 μm or less in order to obtain a highly conductive CNT composite film. Moreover, single-walled CNTs having excellent crystallinity and having a long length are preferable. Furthermore, the use of high-quality single-walled CNTs synthesized by the direct injection pyrolysis synthesis (DIPS) method is preferable for obtaining a highly conductive composite film because a more homogeneous dispersion can be obtained.

In the RFID ink composition of the present invention, the concentration of CNTs in the CNT dispersion is not particularly limited. 0.005% by weight or more is preferable, 0.05% by weight or more is more preferable, 0.1% by weight or more is still more preferable, and 0.25% by weight or more is particularly preferable. Also, it is preferably 1% by weight or less, more preferably 0.9% by weight or less, still more preferably 0.75% by weight or less, and particularly preferably 0.6% by weight or less.

In the RFID ink composition of the present invention, as the polymeric acid, a raw material monomer containing a monomer having an acidic group such as a monomer having a carboxylic acid group, a monomer having a sulfonic acid group, and a monomer having a phosphoric acid group (covalent ) (co)polymers obtained by polymerization. Monomers having an acidic group may be used singly or in combination of two or more.

Examples of monomers having a carboxylic acid group include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, 2-methacryloyloxymethylsuccinic 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, acrylic acid and methacrylic acid are preferred.

Examples of monomers having a sulfonic acid group include styrenesulfonic acid such as p-styrenesulfonic acid, vinylsulfonic acid, allylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 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 preferred.

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

As polymeric acids, polymeric carboxylic acids and polymeric sulfonic acids are preferred. Here, the polymer carboxylic acid and polymer sulfonic acid are preferably (co)polymers having a monomer ratio of 97% or more, preferably 100%, of a monomer having a carboxylic acid group and a monomer having a sulfonic acid group. Here, the monomer ratio refers to a monomer having a carboxylic acid group contained in the (co)polymer, a sulfonic acid group, and a refers to the ratio (mol%) of structural units derived from monomers having

Among these, polyacrylic acid and polymethacrylic acid are preferred as the polymeric carboxylic acid, and poly(p-styrenesulfonic acid) is preferred as the polymeric sulfonic acid.

In the RFID ink composition of the present invention, the weight average molecular weight of the polymeric acid is not particularly limited, but a polymeric acid having a large molecular weight can disperse CNTs well, shorten the dispersion time, and improve the strength of the coating film. improves wear resistance. In RFID inks, a fast dispersion time is cost effective in mass production. It is desirable that the RFID conductive pattern, such as an antenna, have a high coating film strength so as not to cause damage in post-processing after printing. On the other hand, a polymeric acid with a small molecular weight tends to have a greater doping effect, and a smaller molecular weight is desirable for high conductivity. From the viewpoint of the balance of these properties required in 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, and even more preferably 2,000 or more. , 4,000 or more is particularly preferred, 10,000 or more is particularly preferred, and 20,000 or more is most preferred. It is preferably 500,000 or less, more preferably 250,000 or less, even more preferably 100,000 or less, even more preferably 50,000 or less, and most preferably 30,000 or less.

As for the weight average molecular weight, a value converted to a standard polymer (for example, standard polyacrylic acid) by gel permeation chromatography (GPC method) is referred to. Here, the standard polymer refers to a polymer with a narrow molecular weight distribution with a known molecular weight and a structure that is the same as or similar to that of the object to be measured.

In the RFID ink composition of the present invention, the concentration of the polymer acid in the CNT dispersion is not particularly limited, but considering the fact that the conductivity required for the conductive pattern of RFID can be secured even if the film thickness is reduced. Then, 0.005% by weight or more is preferable, 0.075% by weight or more is more preferable, 0.15% by weight or more is still more preferable, and 0.4% by weight or more is particularly preferable. Also, it is preferably 5% by weight or less, more preferably 4.5% by weight or less, even more preferably 3% by weight or less, and particularly preferably 1% by weight or less.

In the RFID ink composition of the present invention, the weight ratio of CNT to polymeric acid is 1:0, considering that the conductivity required for the conductive pattern of RFID can be ensured even if the film thickness is reduced. 0.8 or more is preferred, and 1:1 or more is more preferred. Also, the ratio is preferably 1:5 or less, preferably 1:4 or less, and more preferably 1:3 or less. When the weight ratio between the polymer acid and the CNT is within this range, the CNT composite film obtained by applying the RFID ink composition of the present invention has electrical contact between the CNTs and between the bundles. Electrical contact and electrical contact between CNTs and CNT bundles is less likely to be disturbed by polymeric acids. In this range, the polymeric acid is adsorbed so as to cover the CNTs or CNT bundles, and the CNTs are well dispersed. A portion where the CNT bundle is exposed is generated. Therefore, the CNT composite film exhibits good electrical conductivity because it does not interfere with electrical contact between CNTs or between CNT bundles.

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

The RFID ink composition of the present invention may contain other components in addition to the CNTs, polymer acid, and solvent described above, as long as the effects of the present invention are not impaired.

The RFID ink composition of the present invention can be produced, for example, as follows.
(1) Pre-doping step CNT powder is added to a solution in which a dopant such as an oxidizing agent is dissolved, and the mixture is vigorously stirred with a magnetic stirrer or the like for several ten minutes to one day. After that, the dispersion is filtered, and the CNT powder remaining on the filter paper is washed to obtain doped CNT powder. The pre-doping step is a step that is optionally carried out when producing the RFID ink composition of the present invention.

The conductivity of the CNTs can also be improved by pre-doping the CNTs with an acid, an oxidizing agent, or the like before dispersing them in a solvent. The pre-doping step can use a dopant selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid, iodine, bromine, chlorosulfonic acid (superacid), hydroiodic acid, hydrobromic acid and mixtures thereof. can.

As the solvent for dissolving the dopant, the solvent for dispersing the polymer acid and the CNT described above can be used. These solvents can also be used for washing the CNT powder remaining on the filter paper.
(2) Pre-dispersion step CNT powder is added to a solution in which a polymer acid as a dispersant is dissolved, and the mixture is vigorously stirred with a magnetic stirrer or the like for several 10 minutes to a day. The solvent described above can be used as the solvent for dispersing the CNTs. The pre-dispersion step is mainly an essential step in producing the RFID ink composition of the present invention.
(3) Main dispersing step Using the pre-dispersed liquid, the CNTs are further finely dispersed by an ultrasonic homogenizer, an ultrasonic bath, a jet mill, or the like to obtain a CNT dispersion in which the CNTs do not easily aggregate or sediment. . This dispersing step is mainly an essential step in producing the RFID ink composition of the present invention.

In this dispersing step, the ultrasonic homogenizer strongly disperses the CNTs, but if too much time is spent, the CNTs and polymer acid may be damaged. In addition, when the polymer acid solution is heated when preparing the CNT dispersion, the polymer acid partially self-aggregates in the CNT dispersion, and the contact area of the polymer acid with the CNTs decreases, resulting in doping. It is presumed that the effect will be small. Generally, in the dispersion treatment of CNTs by an ultrasonic homogenizer, vibrating solvent molecules and polymeric acid molecules generates localized high heat, causing violent aggregation of the polymeric acid. As a result, the doping effect is reduced and contact between CNTs is also prevented.

Therefore, it is effective to minimize the treatment time with an ultrasonic homogenizer or apply ultrasonic waves while cooling the pre-dispersed liquid. For example, by performing pre-dispersion for about 12 hours, it is possible to obtain a uniform dispersion even if the ultrasonic homogenizer irradiation time in the main dispersion is shortened, and damage to CNTs and polymeric acids due to ultrasonic homogenizer irradiation is minimized. can be reduced to Moreover, when a uniform dispersion can be obtained in this way, the subsequent ultracentrifugation treatment can be omitted, which is very advantageous in terms of the manufacturing process. In order to shorten the treatment time with the ultrasonic homogenizer, it is also effective to perform the treatment with an ultrasonic bath prior to the treatment with the ultrasonic homogenizer.
(4) Centrifugal Separation Step The CNT dispersion obtained by this dispersion is centrifuged by an ultracentrifuge, and the obtained supernatant is used as the dispersion to be used for membrane formation. The centrifugation step is an optional step in producing the RFID ink composition 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. Note that when a CNT dispersion is prepared using high-quality SWNTs, a homogeneous CNT dispersion can be prepared, so the ultracentrifugation process can be omitted.
(Method for manufacturing RFID conductive pattern)
When producing 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 coated RFID Dry the ink composition for

The coating method is not particularly limited, and examples thereof include gravure printing, screen printing, casting, dip coating, spin coating, bar coating, blade coating, die coating, spray coating, and inkjet. .

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

In gravure printing, for example, when printing the RFID ink composition of the present invention, the ink composition is diluted as necessary so as to have an appropriate viscosity according to the printing conditions at the ambient temperature during printing, and printed on the substrate. . Gravure printing is performed by transferring ink supplied to a gravure cylinder to a material to be printed. For example, in a gravure printing apparatus, ink is introduced from an ink inlet provided at the bottom of an ink pan. Excess ink is discharged from the ink discharge port so that the ink level is always maintained at a constant height. The gravure cylinder is provided so that its lower part is immersed below the liquid surface of the ink, and the surface of the rotating gravure cylinder is immersed in the ink, whereby ink is supplied to the surface of the gravure cylinder. Then, of the ink supplied to the surface of the gravure cylinder, excess ink is scraped off by a doctor, and an appropriate amount of ink is applied to the material to be printed between the gravure cylinder and the impression cylinder. It is transferred and printed.

The coating film printed by the method described above is heated and dried as necessary to obtain an RFID conductive pattern as a CNT composite film.

The RFID conductive pattern may optionally be subjected to subsequent steps.
(5) Washing 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 step is an optional step in the present invention.

In general, when a non-conductive dispersing agent is used, electrical contact is provided between CNTs or between CNT bundles, and in order for the CNT composite film to exhibit conductivity, the CNT composite film must be dispersed in a non-conductive manner after film formation. agent must be removed. For this purpose, for example, a method of removing by immersion in a solvent can be considered. However, in the present invention, even though the polymer acid used for dispersion is non-conductive, dispersion is possible with a small amount. The high conductivity of CNT is exhibited as it is.
(6) Post-doping process The CNT composite film obtained by the above method is doped by exposing it to vapor of an oxidant or soaking it in a solution containing an oxidant. A post-doping step is an optional step in the present invention.

In general, a film made of only CNTs does not have sufficient conductivity, so a method of doping with an oxidizing agent such as nitric acid is often employed. In this case, a step of immersing the film in a solution of an oxidizing agent or exposing it to the vapor of the oxidizing agent is generally required. Also, when a volatile oxidizing agent such as nitric acid is used, the conductivity of the resulting film is unstable. However, in the present invention, since the polymer acid itself serving as the dispersant functions as a doping agent, there is no need to go through a doping step again after film formation. The electrical conductivity of the CNT composite film is extremely stable.

In the present invention, the polymer acid as the dispersing agent can be added in a very small amount of about 1:1 to 5:1 with respect to the CNT. The above (5) cleaning step and (6) post-doping step can be omitted, which is advantageous in terms of the manufacturing process. Further, in the production of the RFID ink composition of the present invention, optimization of the above (2) pre-dispersion step and (3) main dispersion step makes it possible to omit the (4) centrifugal separation step. Advantageous. Furthermore, the electrical conductivity of the obtained membrane is stable for a long period of time.

As described above, in the present invention, a highly conductive film can be obtained without removing the polymeric acid as a dispersant after film formation. Part or all can also be removed. The method for removing the polymeric acid is not particularly limited, but examples thereof include thermal baking (heat treatment), pulsed light baking (heat treatment), washing with a solvent, and washing with an alkaline developer (alkaline treatment).

In the present invention, RFID is an RF tag equipped with ID (identification) information that exchanges information by wireless communication at short distances (several cm to several meters depending on the frequency band) using electromagnetic fields, radio waves, etc., and technology Including general. In addition to wireless communication technology between tags and readers, it also includes all operational systems that attach tags to various objects and people and grasp their positions and movements in real time. RFID is an IC tag that uses a one-chip IC (integrated circuit) with ID information, especially a passive type IC tag, and a combination of both passive tags and active tags. A semi-active tag (activation type active tag) or the like may also be used. A contactless IC card using technology similar to RFID is also included in RFID in the present invention.

The base material for mounting ID information on which the RFID ink composition of the present invention is applied is not particularly limited, and may be a flexible base material or a rigid base material. For example, cellulosic substrates such as paper, cardboard, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethylene (PE), polypropylene (PP), polyimide (PI), polyethersulfone (PES), polycarbonate (PC) resin substrates, glass substrates, and the like.

In the conductive pattern of RFID obtained by the manufacturing method of the present invention, the CNT composite film forming the conductive pattern contains polymeric acid and CNT. The polymeric acid adheres to a single CNT or a bundle of CNTs by van der Waals forces so as to surround them. A CNT bundle is a bundle-like structure in which CNTs are aggregated, and the CNTs are locally oriented, but may have a structure in which the CNTs are partially separated. It also has one or more of a portion where CNTs are bonded together, a portion where CNT bundles are bonded together, and a portion where CNTs and CNT bundles are bonded. Thereby, the CNT constitutes a network as a whole. In this network of CNTs, the contacts provide CNT-to-CNT electrical contact, bundle-to-bundle electrical contact, and CNT-to-bundle electrical contact to provide electrical conductivity to the entire network. .

The CNT composite film includes a network of polymer acid and CNTs, and contact between CNTs is ensured while the polymer acid is arranged around the CNTs. Therefore, in the CNT composite film, CNT-to-CNT electrical contact, bundle-to-bundle electrical contact, and CNT-to-bundle electrical contact are not hindered by the polymeric acid. Therefore, the CNT composite film has good electrical bonding in the CNT network and excellent electrical performance.

The conductive pattern obtained by the method for producing a conductive pattern of RFID of the present invention has a film thickness after drying of preferably 5 μm or less, more preferably 2 μm or less, considering the application of gravure printing, cost, etc. It is preferably 1 μm or less. Considering the conductivity required for RFID, the thickness is preferably 0.05 μm or more, more preferably 0.1 μm or more.

Further, the surface resistivity of the conductive pattern obtained by the RFID conductive pattern manufacturing method of the present invention is preferably 100Ω/□ or less, considering that it is suitable for use as an antenna for UHF band RFID. Moreover, it is preferably 10Ω/□ 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, these steps may be performed at least twice to form an RFID conductive pattern having a film thickness of 5 μm or less and a surface resistivity of 100Ω/□ or less. By repeating coating and drying in this way and coating in layers, it becomes possible to further increase the conductivity, and it is possible to easily adjust the resistance value suitable for the conductive pattern of the RFID.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples.

In the following comparative examples and examples, resistance values were measured with the following configuration.
Surface resistance measuring device Model: Loresta-GP MCP-T600
Resistance meter (Mitsubishi Chemical Analytech Co., Ltd.)
Coating equipment Bar coater (Daiichi Rika Co., Ltd.)
The wet film thickness was calculated with reference to the bar coater coat film thickness, and the dry film thickness was calculated from the amount of solid content in the dispersion.
(Comparative example 1)
An ink was prepared with the following formulation.
Solvent (water: 2-propanol = 5: 1) 240 g
Dispersant (BYK DISPERBYK-190 block copolymer) 5-10g
MWCNT (Nanosil NC7000) 3.2g
The above ingredients were mixed and pre-dispersed with a stirrer for 15 minutes. Next, it was dispersed for 90 minutes with an ultrasonic disperser. The completed ink was applied to a PET film with a wet film thickness of 22 to 28 μm, and the surface resistivity was confirmed.

Table 1 shows the evaluation results.

From Table 1, it is possible to increase the conductivity by reducing the dispersant and increasing the proportion of CNT. However, if the amount of the dispersant is less than the required amount, the dispersant cannot be dispersed, so there is a limit to how high the conductivity can be achieved.
(Comparative example 2)
In Comparative Example 1, the CNTs were changed from multi-wall CNTs (MWCNTs) to single-wall CNTs (SWCNTs) to increase conductivity.

An ink was prepared with the following formulation.
Solvent (water: 2-propanol = 5: 1) 240 g
Dispersant (BYK DISPERBYK-190) 6-10g
SWCNT (Oxyal TUBALL CNT 93%) 0.8g
The above ingredients were mixed and pre-dispersed with a stirrer for 15 minutes. Next, it was dispersed for 90 minutes with an ultrasonic disperser. The completed ink was applied to a PET film with a wet film thickness of 22 to 28 μm, and the surface resistivity was confirmed.

Table 2 shows the evaluation results.

From Table 2, it has been confirmed that by using SWCNTs, it is possible to ensure conductivity comparable to that of MWCNTs with a small amount of CNTs. However, as with MWCNT, if the amount of dispersant is less than the required amount, dispersing becomes impossible, so there is a limit to how high the conductivity can be achieved.

From Comparative Examples 1 and 2, with the CNT ink prepared by dispersing by a general CNT dispersing method (using a commercially available dispersant), when applied with a film thickness of gravure printing, RFID is obtained at about 10 ² to 10 ⁵ Ω/□. The conductivity required for the antenna cannot be secured.
(Example 1)
An ink was prepared with the following formulation.
Solvent (2-propanol:ethanol=9:1) 150g
PAA (Fuji Film Wako Pure Chemical, molecular weight 5000) 0.3 to 0.9 g
SWCNT (Oxial TUBALL CNT 93%) 0.2-0.6g
The above ingredients were mixed and pre-dispersed with a stirrer for 15 minutes. Next, it was dispersed for 90 minutes with an ultrasonic disperser. The completed ink was applied to a PET film with a wet film thickness of 22 to 28 μm, and the surface resistance value was confirmed.

Table 3 shows the evaluation results. FIG. 1 shows changes in surface resistivity depending on ink concentration and film thickness.

It is said that the surface resistivity suitable for a UHF band RFID antenna is around 50 Ω/□ (10 to 100 Ω/□). From Table 3, when PAA is used as a dispersant, high conductivity is obtained with a general coating thickness (less than 1 μm to several tens of μm) in gravure printing, and RFID antennas can be manufactured at low cost and at high speed by gravure printing. can.
(Example 2)
Dispersion time, viscosity and coating film strength were verified when four types of polyacrylic acid (MW=5000, 25000, 250000 and 1000000) were used.

An ink was prepared with the following formulation.
SWCNT OCSiAl TUBALL 93%: 0.20g
PAA (polyacrylic acid) Fuji Film Wako Pure Chemical Co., Ltd.: 0.30 g
IPA (2-propanol): 135g
Ethanol: 15g
The dispersion time, viscosity and coating film strength were evaluated under the following conditions.
Dispersion time: Part of the dispersion liquid is applied to a desk for an arbitrary dispersion time, and the dispersion state and resistance value are visually confirmed. : Abrasion resistance evaluation using an abrasion fastness tester Load 200 g Kanakin No. 3 abrasive tip Speed 30 reciprocations per minute Table 4 shows the evaluation results.

From Table 4, when evaluating conductivity, it is advantageous to use PAA with a small molecular weight for higher conductivity. However, from the viewpoint of printing an RFID antenna, when evaluated as a printing ink, the use of PAA with a large molecular weight is advantageous in shortening the SWCNT dispersion time and improving the coating strength. In these respects, PAA molecular weights of 5,000 and 25,000 were the best. The dispersing time is the shortest when the molecular weight is 25,000, which is advantageous in terms of ink preparation cost.
(Example 3)
The ink (150 g of solvent, 0.3 g of PAA, 0.2 g of SWCNTs) prepared in Example 1 and having a concentration magnification of 1 was applied to a PET film at a wet film thickness of 22 μm 1 to 4 times to confirm the surface resistivity. Table 5 shows the evaluation results. FIG. 2 shows changes in surface resistivity depending on the number of times of stacking.

As can be seen from Table 5, repeated coatings using a printing machine can further increase the conductivity and facilitate adjustment to a surface resistivity suitable for RFID antennas.

Claims (6)

A method of manufacturing a conductive pattern for RFID, comprising the steps of:
An ink composition that is a carbon nanotube dispersion containing a conductive material and a polymer acid that functions as a dispersant thereof,
The conductive material consists only of carbon nanotubes,
The carbon nanotube is a single-walled carbon nanotube,
The polymeric acid is polyacrylic acid and has a weight average molecular weight of 2,000 or more and 50,000 or less,
The concentration of the carbon nanotubes is 0.005% by weight or more and 1% by weight or less, the concentration of the polymeric acid is 0.005% by weight or more and 5% by weight or less, and the weight ratio of the carbon nanotubes to the polymeric acid is 1. : 0.8 or more and 1:5 or less ink compositionto a base material for mounting ID information; and
The applied RFID ink composition is dried to have a film thickness of 5 μm or less and a surface resistivity of 100 Ω / □ or less, consisting only of the membraneforming a conductive pattern for the RFID; 2. The method for producing a conductive pattern for RFID according to claim 1, wherein the polyacrylic acid has a weight average molecular weight of 20,000 or more and 50,000 or less. 2. The method of manufacturing a conductive pattern for RFID according to claim 1, wherein said application is performed by a high-speed printing method. 2. The method of manufacturing a conductive pattern for RFID according to claim 1, wherein said coating is performed by gravure printing. 2. The method for producing an RFID conductive pattern according to claim 1 , 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. The step of forming the conductive pattern of the RFID and the step of drying the applied RFID ink composition are repeated at least twice each, and the conductive RFID having a film thickness of 5 μm or less and a surface resistivity of 100 Ω / □ or less 2. The method of manufacturing a conductive pattern for RFID according to claim 1 , wherein the conductive pattern is formed.

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