GB2533782A

GB2533782A - Method of manufacturing conductive ink composition, antenna structure, and antenna for RFID tag

Info

Publication number: GB2533782A
Application number: GB1423287.0A
Authority: GB
Inventors: Ping Lai Chung
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-12-29
Filing date: 2014-12-29
Publication date: 2016-07-06
Also published as: GB201423287D0

Abstract

A conductive ink for an RFID tag comprises a solvent as well as 90-99.9999 wt.% conductive carbon and 0.0001-10 wt.% dispersant based on the solid content of the ink. When used in an RFID tag, the ink accounts for 2-85 wt.% of the tags solid content. The conductive carbon may be carbon flake/sheet, graphene, natural graphite, ball-shaped graphite, or carbon black flakes, each having a thickness of 1-10000 nm and a grain size of 0.1-100 microns. The dispersant may be ionic, e.g. xanthan gum, carboxymethylcellulose, polyvinylpyrrolidone or non-ionic, e.g. poly(sodium-4-styrenesulphonate), 3-[(3-chloramidopropyl)dimethyl ammonio]-1-propanesulphonate, hexadecyltrimethylammonium bromide, sodium taurodeoxycholate hydrate, or 1-pyrenebutyric acid. An antenna structure for an RFID tag also contains a conductive layer 20 on a fibre substrate 10, the layer comprising 90-99.9999 wt.% conductive carbon and 0.0001-10 wt.% dispersant based on the solid content of the antenna. The conductive layer is printed on the substrate such that part of the layer percolates into substrate pores.

Description

METHOD OF MANUFACTURING CONDUCTIVE INK COMPOSITION, ANTENNA STRUCTURE, AND ANTENNA FOR RFID TAG

FIELD OF THE TNVENTION

The present invention relates to a Radio Frequency Identification (RFID), and more particularly to a method of manufacturing a conductive ink composition, an antenna structure, and antenna for a RFID tag which enhances conductivity and reduces resistance and production cost of the RFID tag.

BACKGROUND OF THE INVENTION

A conventional radio frequency identification system contains a reader and a RFID tag, wherein the REID tag has antenna and IC chip. Reader transmits electromagnetic waves to RFID labels. Antenna in RFID transfers electromagnetic waves into current to initiate the IC chips. Data stored in IC chips send back to reader through electromagnetic waves generated by antenna. The low frequency (LH) of the radio frequency identification system is 125 or 134.2KHz, the high frequency (HF) is 13.56MHz, the ultra-high frequency (UHF) ranges from 868 to 956MHz, and the microwave is 2.45G Hz. In general, the higher the frequency is, the longer the received distance is, and the faster the transmitting speed is.

There are mainly two kinds of processes to produce antenna for wireless application. One is copper/aluminum foil etching. Such process involves complicated procedures, high-pollution chemicals like etchant, and corrosion-resistance 5 substrates required. It is a high-cost process with high-pollution waste, and needs expensive equipment for photo-lithography process. Another is ink printing process including screen printing, inkjet printing, gravure printing, etc. Ink printing has the advantage of simple process, fast production, and low cost. However, its 10 popularity is confined by inadequate performance of the conductive inks. Lack of both high conductivity and stability is the main issue for conductive inks on the market.

By far, metal powders and metal coated powders are the primary conductive materials in conductive inks for application of 15 antenna. Common-used metals are copper and silver. Copper is easily oxidated, while silver has high price.

Adhesion of metal powders is another issue. Metal powders cannot form a film onto substrate. Therefore, adhesion of metal powders relies on the addition of binders. Since binder is insulator, it affects the conductivity of ink as well. For conductive metal inks, it is hard to balance both adhesion and conductivity.

US Publication No. 2012/0277360A1 disclosed that conductive compositions consisted of graphene sheets and at least one polymeric binder to have good adhesion. Metals, alloys, and conductive metal oxides are optionally contained. The surface resistivity lies between 0.001 to 500 ohm/sq.

US Publication No. 2004/0175515 disclosed that 5 conductive particulate and/or flake materials can be printed to have sufficient conductivity for antenna by flexographic or gravure printing. Polymers or resins are also used at about 15 -25 wt% as binder. Conductive materials are metal oxide material, metal particles, and graphite. The sheet resistance is relatively at 200 10 ohm/sq In addition, US Patent No. 7017822 taught that a conductive loaded resin-based material to form RFID antenna. The conductive materials include carbon, graphite, and metal powders like nickel, copper, and silver. Adhesion to substrates is reinforced by an epoxy adhesive, or direct molding onto resin-based materials. The sheet resistance is between 5 to 25 olun/sq TW Patent No. 1434456 disclosed that an inkjet printing method to produce RFID antenna. Metal ions such as nickel, gold, and copper are dissolved in the ink, and are reduced back to metals by electroless-plating after drying. Such process is very complicated, and the substrate is confined to be non-woven slag fiber paper.

Another CN Patent No. 101921505B taught that a conductive ink for RFID antenna. The conductive materials are composed of both nano-wires and nano-particles of silver, and 2 toiO% epoxy resin is used as binders, thus increasing production cost.

CN103436099 disclosed that a composite conductive ink includes both silver and graphene. However, silver and resin account for 20-40%, and 5-30% of the composition, respectively. That is, most composition still remained as silver and resin.

The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.

SUMMARY OF THE INVENTION

The primary objective of the present invention is to provide a method of manufacturing a conductive ink composition, an antenna structure, and antenna for a RFID tag which enhances conductivity and reduces resistance and production cost of the RFID tag.

To obtain above objective, a conductive ink composition for a RFID tag provided by the present invention contains: conductive ink composition for a RFID tag comprises: a conductive carbon flake/sheet made of carbon powders, a dispersant, and a solvent.

The conductive carbon flake/sheet accounts for 90 to 99.9999 wt% of a total solid content in a conductive ink composition, the dispersant is added at 0.0001 to 10 wt% of the total solid content in the conductive ink composition, and the conductive ink composition accounts for 2 to 85 wt% of a total solid content in a RFID tag.

An antenna structure for a RFID tag provided by the present invention contains: a fiber substrate and a conductive layer, wherein the conductive layer includes a conductive carbon flake/sheet and a dispersant, wherein the conductive carbon flake/sheet accounts for 90 to 99.9999 wt% of a total solid content in an antenna structure, and the dispersant is added at 0.0001 to 10 wt% of the total solid content in the antenna structure, wherein the conductive layer is formed on the fiber substrate in a printing manner based on a profile of an antenna so that a part of the conductive layer percolates into plural pores of the fiber substrate.

Furthermore, a method of manufacturing an antenna structure for a RFID tag provided by the present invention comprising steps of: A. preparing a fiber substrate; B. providing a conductive ink composition which includes a conductive carbon flake/sheet, a dispersant, and a solvent, wherein the conductive carbon flake/sheet accounts for 90 to 99.9999 wt% of a total solid content in the conductive ink composition, and the dispersant is added at 0.0001 to 10 wt% of the total solid content of the conductive ink composition, and wherein the conductive ink composition accounts for 2 to 85 wt% of a total solid content in an antenna structure; C. forming conductive ink composition on the fiber 5 substrate in a printing manner based on a profile of an antenna; D. evaporating the solvent of the conductive ink composition in a thermal drying manner, such that the conductive layer forms on the fiber substrate, and a part of the conductive layer percolates into plural pores of the fiber substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG 1 is a cross sectional view showing the assembly of an antenna structure for a RFID tag according to a preferred embodiment of the present invention.

FIG 2 is a plan view showing a co-filming area at an interface between a carbon flake and a fiber substrate according to the preferred embodiment of the present invention.

FIG 3 is a flow chart of a method of manufacturing an antenna structure for a RFID tag according to the preferred 20 embodiment of the present invention.

FIG 4 is a plan view showing the assembly of an antenna structure for a RFID tag according to the preferred embodiment of the present invention.

FIG. 5 is return loss behaviour of different antenna patterns being printed with the binder-free conductive carbon inks according to the preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED 5 EMBODIMENTS A conductive ink composition for a RFID tag according to a preferred embodiment of the present invention comprises: a conductive carbon flake/sheet made of carbon powders, a dispersant, and a solvent.

The conductive ink composition accounts for 2 to 85 wt% of a total solid content in the RFID tag; the conductive carbon flake/sheet consists of at least one of graphene, natural graphite, flake-shaped carbon black (Ex: KS6) and ball-shaped graphite, a thickness of the conductive carbon flake/sheet ranges from 1 to 10000nm(nanometer), and a grain size of the conductive carbon flake/sheet is from 0.1 to 100frm (micrometer), the conductive carbon flake/sheet accounts for 90 to 99.9999 wt% of the total solid content in the conductive ink composition.

The dispersant is added at 0.0001 to 10 wt% of the total 20 solid content in the conductive ink composition, wherein the dispersant is ionic dispersant or non-ionic dispersant. The ionic dispersant is any one of P-123, Tween 20, Xanthan gum, Carboxymethyl Cellulose (CMC), Triton X-100, Polyvinylpyrrolidone (PVP), and Brji 30. The non-ionic dispersant is Poly (sodium 4-styrenesulfonate) (PS S), 3-[(3-Cholamidopropyl)dimethyl ammonio]-I-propanesufonate (CHAPS), Hexadecyltrimethylammonium bromide (HTAB), Sodium taurodeoxycholate hydrate (SDS), and 1-Pyrenebutyric acid (PBA).

The solvent is aqueous or organic and includes Methyl-2-pyrrolidone (NMP), IPA (Isopropyl alcohol), ethanol, glycerol, ethylene glycol, butanol, propanol, propylene glycol monomethyl ether (PGME), propylene glycol monomethyl ether acetate ( PG M EA).

With reference to FIGS. 1 and 2, an antenna structure for a RFID tag according to a preferred embodiment of the present invention comprises: a fiber substrate 10 and a conductive layer 20, wherein the conductive layer 20 includes a conductive carbon flake/sheet and a dispersant, wherein the conductive carbon flake/sheet accounts for 90 to 99.9999 wt% of a total solid content in the antenna structure, and the dispersant is added at 0.0001 to 10 wt% of the total solid content in the antenna structure.

Referring to FIG 3, a method of manufacturing an antenna structure for a REID tag according to a preferred 20 embodiment of the present invention comprises steps of: A. preparing a fiber substrate 10, wherein the fiber substrate 10 includes any one of cotton, flax, and Polyethylene Tereplithal ate (PET); B. providing a conductive ink composition which 25 includes a conductive carbon flake/sheet, a dispersant, and a solvent, wherein the conductive carbon flake/sheet accounts for 90 to 99.9999 wt% of a total solid content in the conductive ink composition, and the dispersant is added at 0.0001 to 10 wt% of the total solid content of the conductive ink composition, and wherein the conductive ink composition accounts for 2 to 85 wt% of a total solid content in an antenna structure; C. forming conductive ink composition on the fiber substrate 10 in a printing manner based on a profile of an antenna, wherein the printing manner is any one of screen printing, flexographic printing, gravure printing, and inkjet printing; and D. evaporating the solvent of the conductive ink composition in a thermal drying manner, such that the conductive layer 20 forms on the fiber substrate 10, and a part of the conductive layer 20 percolates into plural pores of the fiber substrate 10.

Thereby, the conductive ink composition is formed on the fiber substrate in a printing manner based on the profile of an antenna so that a part of the conductive layer 20 percolates into plural pores of the fiber substrate 10. Because the conductive ink composition contains the conductive carbon flake/sheet 21 with film formation, the conductive carbon flake/sheet 21 is co-filmed with the fiber substrate 10 tightly (as shown in FIG. 2), such that the antenna structure for the RFID tag does not contain metal and insulating binder additive. Furthermore, the conductive ink composition does not have metal and insulating binder additive, thus enhancing conductivity, reducing resistance and production cost.

Preferably, when the conductive ink composition is formed on the fiber substrate 10 in the screen printing manner, screen grids of a printing screen are from 100 to 400 meshes, and a printing precision of a screen printing is up to 100m. When the conductive ink composition is formed on the fiber substrate 10 in the inkjet printing manner, screen grids of a printing screen are from 100 to 400 meshes, a printing precision of inkjet printing is up to mechanical positioning, and the best one can reach 0.1 urn level today. As shown in FIG. 4, the conductive ink composition is printed on the antenna structure for the RFID tag, wherein there is no difference in the appearance, compared with aluminum-etched antenna. The printing precision in a chip-bonding area of the conductive layer 20 and IC chip is 10 gm without any short circuit (as illustrated in a partial amplified portion of FIG 4). In another embodiment, direct printing on papers remarkably simplifies the production process that once involved metal etching or antenna transmission. Also, easy destruction of the antenna by simply ripping it is one of the unique characteristics, resulting from versatile substrates and low-cost process.

The fiber substrate is made of flexible material, such as a paper or a flax, wherein a basis weight of the paper or the flax ranges from 10 to 500 g/m, a density of the paper or the flax is between 0.5 -2.5 g/cm, and an average pore size of the paper or the flax is within 0 02 -500 [im.

Thermal drying is a main drying method of the conductive layer 20, and a heating temperature is within 30 to 300 C. The higher the temperature is, the faster the drying is. After thermal drying, the conductive layer 20 on the fiber substrate 10 is further compressed to raise a density and a conductivity of the conductive layer 20, wherein a compression ratio of the conductive layer 20 is 0.5 to 99% of an original thickness of the conductive layer 20. Without any insulating binder additives, conductive carbon ink in this patent can reach very low resistance. In this regard, resistance is relative to coating thickness, size and shape of carbon powders, and density of the coating film. In general, resistance can be decreased by increasing the coating thickness, raising the density of coating film, and choosing carbon powders with larger diameter and thickness. Without any insulating binder additives, the conductive layer of the present invention can reach very low resistance. In this regard, resistance is relative to coating thickness, size and shape of the carbon powders. In general, the resistance is decreased by increasing the coating thickness and choosing carbon powders with larger diameter and thickness. For the application of the conductive carbon flake/sheet for the RFID tag, the resistance of the conductive carbon flake/sheet is from 0.1-50 ohmisq (corresponding resistivity -6 -4 1 X 10 to 2.5 x10 ohm-m) is preferred.

As illustrated in FIG. 5, different antenna patterns are printed with the conductive ink composition, wherein a return loss behavior is measured as shown in FIG. 5. It is clearly illustrated that signals at different frequency range correspond to specific antenna patterns. In this exhibition, significant signals can be found in both UHF and microwave frequency for wireless antenna application.

IC chips are bonded onto antennas structure for the RFID tag. As illustrated in FIG 6, a readability test is carried out by a wireless signal reader. Two types of antenna structures are printed.

One is a straight-line pattern, and the other is a meandered-line pattern. Sheet resistance of the antenna structure is shown in following table 1. It is exhibited that both types of antenna structure are readable. Accordingly, the antenna structure is applicable in RFID tag at HF (such as 13.56MHz), UHF (such as 868 to 956 MHz), and Microwave such as 2.45G Hz).

Table 1

Antennas pattern Frequency range Sheet Test result for resistance (ohm/sq) RFID reader sample 1 straight-line pattern UHF 8.38 Readable sample meandered-line UHF 5.34 Readable 2 pattern While the preferred embodiments of the invention have been set forth for the purpose of disclosure, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS: 1. A conductive ink composition for a RFID tag comprises: a conductive carbon flake/sheet made of carbon powders, a dispersant, and a solvent; wherein the conductive carbon flake/sheet accounts for 90 to 99.9999 wt% of a total solid content in a conductive ink composition, the dispersant is added at 0.0001 to 10 wt% of the total solid content in the conductive ink composition, and the conductive ink composition accounts for 2 to 85 wt% of a total solid content in a RFID tag.
2. The conductive ink composition for the RFID tag as claimed in claim 1, wherein the conductive carbon flake/sheet consists of at least one of graphene, natural graphite, flake-shaped carbon black and ball-shaped graphite, a thickness of the conductive carbon flake/sheet ranges from 1 to 10000nm, and a grain size of the conductive carbon flake/sheet is from 0.1 to 100gm.
3. The conductive ink composition for the RFID tag as claimed in claim 1, wherein the dispersant is ionic dispersant or non-ionic dispersant; the ionic dispersant is any one of P-123, Tween 20, Xanthan gum, Carboxymethyl Cellulose (CMC), Triton X-100, Polyvinylpyrrolidone (PVP), and Brji 30; and the non-ionic dispersant is Poly (sodium 4-styrenesulfonate) (PSS), 3-[(3-Ch ol am i dopropyl)di m ethyl am m on i o]-1-propane sufonate (CHAPS), Hexadecyltrimethylammonium bromide (HTAB), Sodium taurodeoxycholate hydrate (SDS), and 1-Pyrenebutyric acid (PBA).
4. An antenna structure for a RFID tag comprising: a fiber substrate and a conductive layer, wherein the conductive layer 5 includes a conductive carbon flake/sheet and a dispersant, wherein the conductive carbon flake/sheet accounts for 90 to 99.9999 wt% of a total solid content in an antenna structure, and the dispersant is added at 0.0001 to 10 wt% of the total solid content in the antenna structure, wherein the conductive layer is formed on the fiber 10 substrate in a printing manner based on a profile of an antenna so that a part of the conductive layer percolates into plural pores of the fiber substrate.
5. The antenna structure for the RFID tag as claimed in claim 4, wherein the fiber substrate includes any one of cotton, flax, 15 and Polyethylene Terephthalate (PET).
6. The antenna structure for the RFID tag as claimed in claim 5, wherein a basis weight of the paper or the flax ranges from to 500 g/m, a density of the paper or the flax is between 0.5 -2.5 g/cm, and an average pore size of the paper or the flaxis 20 within 0.02 -500 jim.
7. The antenna structure for the RFID tag as claimed in claim 4, wherein the conductive carbon flake/sheet consists of at least one of graphene, natural graphite, flake-shaped carbon black and ball-shaped graphite, a thickness of the conductive carbon flake/sheet ranges from 1 to 10000nm, and a grain size of the conductive carbon flake/sheet is from 0.1 to 100nm.
8. The antenna structure for the RFID tag as claimed in 5 claim 4, wherein the dispersant is ionic dispersant or non-ionic dispersant; the ionic dispersant is any one of P-123, Tween 20, Xanthan gum, Carboxymethyl Cellulose (CMC), Triton X-100, Polyvinylpyrrolidone (PVP), and Brji 30; and the non-ionic dispersant is Poly (sodium 4-styrenesulfonate) (PSS), 10 3-[(3-Cholamidopropyl)dimethyl ammonio]-1-propanesufonate (CHAPS), Hexadecyltrimethylammonium bromide (HTAB), Sodium taurodeoxycholate hydrate (SDS), and 1-Pyrenebutyric acid (PBA).
9. A method of manufacturing an antenna structure for a 15 RFID tag as claimed in claim 4 comprising steps of A. preparing a fiber substrate; B. providing a conductive ink composition which includes a conductive carbon flake/sheet, a dispersant, and a solvent, wherein the conductive carbon flake/sheet accounts for 90 to 99.9999 wt% of a total solid content in the conductive ink composition, and the dispersant is added at 0.0001 to 10 wt% of the total solid content of the conductive ink composition, and wherein the conductive ink composition accounts for 2 to 85 wt% of a total solid content in an antenna structure; C. forming conductive ink composition on the fiber substrate in a printing manner based on a profile of an antenna; D. evaporating the solvent of the conductive ink 5 composition in a thermal drying manner, such that the conductive layer forms on the fiber substrate, and a part of the conductive layer percolates into plural pores of the fiber substrate.
10. The method of manufacturing the antenna structure for the RFD tag as claimed in claim 9, wherein the fiber substrate 10 includes any one of cotton, flax, and Polyethylene Terephthalate (PET).
11. The method of manufacturing the antenna structure for the RFID tag as claimed in claim 9, wherein the conductive carbon flake/sheet consists of at least one of graphene, natural graphite, flake-shaped carbon black and ball-shaped graphite, a thickness of the conductive carbon flake/sheet ranges from 1 to 10000nm, and a grain size of the conductive carbon flake/sheet is from 0.1 to 100um
12. The method of manufacturing the antenna structure for the RFID tag as claimed in claim 9, wherein the dispersant is ionic dispersant or non-ionic dispersant; the ionic dispersant is any one of P-123, Tween 20, Xanthan gum, Carboxymethyl Cellulose (CMC), Triton X-100, Polyvinylpyrrolidone (PVP), and Brji 30; and the non-ionic dispersant is Poly (sodium 4-styrenesulfonate) (PSS), 3-[(3-Cholamidopropyl)dimethyl ammonio1-1 -propane sufonate (CHAPS), Hexadecyltri methyl ammonium bromide (HTAB), Sodium taurodeoxycholate hydrate (SDS), and 1-Pyrenebutyric acid 5 (PBA)
13. The method of manufacturing the antenna structure for the RFID tag as claimed in claim 9, wherein the printing manner is any one of screen printing, flexographic printing, gravure printing, and inkjet printing.
14. The method of manufacturing the antenna structure for the RFID tag as claimed in claim 9, wherein a heating temperature of the thermal drying manner is within 30 to 300 C.
15. The method of manufacturing the antenna structure for the RFID tag as claimed in claim 9, wherein after evaporating the solvent of the conductive ink composition in the thermal drying manner, the conductive layer on the fiber substrate is further compressed, and a compression ratio of the conductive layer is 0.5 to 99% of an original thickness of the conductive layer.
16. A conductive ink composition for a RFID tag 20 substantially as hereinbefore described with reference to and as shown in the accompanying drawings.
17. An antenna structure for a RFID tag substantially as hereinbefore described with reference to and as shown in the accompanying drawings.
18. A method of manufacturing an antenna structure for a RF1D tag substantially as hereinbefore described with reference to and as shown in the accompanying drawings.