CONDUCTIVE INK FOR USE IN MANUFACTURING RADIO FREQUENCY IDENTIFICATION (RFID) TAG ANTENNA AND METHOD FOR MANUFACTURING RFID TAG ANTENNA

Abstract

A conductive ink for use in manufacturing RFID tag antennas and a method for manufacturing the RFID tag antennas are revealed. The conductive ink includes sheet-like carbon material containing graphite structure, conductive filler, dispersant, and solvent. The conductive ink is coated on a surface of a fibrous substrate by printing or inkjet printing according to the shape of the antenna so as to form a conductive layer. A part of the conductive layer is infiltrated into pores between fibers of the fibrous substrate and attached to the fibrous substrate. The fibrous substrate together with the conductive layer forms a RFID antenna without non-conductive binder. The conductive ink is binder free so that the electrical conductivity of the antenna is improved while the electrical resistance and the production cost of the antenna are reduced

Claims

1. A conductive ink for use in manufacturing RFID tag antennas comprising: at least one sheet-like carbon material containing graphite structure, at least one conductive filler, at least one dispersant, and at least one solvent.

2. The conductive ink as claimed in claim 1, wherein the sheet-like conductive carbon material is selected from the group consisting of graphene, graphite platelets, natural graphite, pelleted carbon black, and a combination thereof.

3. The conductive ink as claimed in claim 1, wherein the conductive filler is selected from the group consisting of conductive carbon material in shapes other than the sheet, conductive metal particle, conductive oxide, conductive polymer, and a combination thereof.

4. The conductive ink as claimed in claim 3, wherein the conductive carbon material in shapes other than the sheet is selected from the group consisting of graphene, graphite, carbon nanotubes, carbon nanocapsules, conductive carbon black and a combination thereof.

5. The conductive ink as claimed in claim 3, wherein the conductive metal particle is selected from the group consisting of platinum, gold, palladium, ruthenium, silver, copper, nickel, zinc, a combination thereof, and an alloy.

6. The conductive ink as claimed in claim 3, wherein the conductive oxide is selected from the group consisting of palladium (IV) oxide, Ruthenium (IV) oxdie, and a combination thereof.

7. The conductive ink as claimed in claim 3, wherein the conductive polymer is selected from the group consisting of polythiophenes (PTs), polypyrroles (PPys), polyacetylene (PA), polyaniline derivatives, and a combination thereof.

8. A method for manufacturing RFID tag antennas comprising the steps of: (1) preparing a porous fibrous substrate; (2) preparing a conductive ink that includes at least one sheet-like carbon material containing graphite structure, at least one conductive filler, at least one dispersant, and at least one solvent; (3) printing the conductive ink on a surface of the porous fibrous substrate; (4) drying and curing the conductive ink printed on the porous fibrous substrate to form a printed antenna; (5) rolling the cured printed antenna.

9. The method as claimed in claim 8, wherein in the step of rolling the cured printed antenna after the step of drying and curing, a thickness compression ratio of the printed antenna on the surface of the porous fibrous substrate is ranging from 50% to 90% of the original total thickness of the porous fibrous substrate and the printed antenna.

10. The method as claimed in claim 8, wherein the sheet-like conductive carbon material is selected from the group consisting of graphene, graphite platelets, natural graphite, pelleted carbon black, and a combination thereof.

11. The method as claimed in claim 8, wherein the conductive filler is selected from the group consisting of conductive carbon material in shapes other than the sheet, conductive metal particle, conductive oxide, conductive polymer, and a combination thereof.

12. The method as claimed in claim 11, wherein the conductive carbon material in shapes other than the sheet is selected from the group consisting of graphene, graphite, carbon nanotubes, carbon nanocapsules, conductive carbon black and a combination thereof.

13. The method as claimed in claim 11, wherein the conductive metal particle is selected from the group consisting of platinum, gold, palladium, ruthenium, silver, copper, nickel, zinc, a combination thereof, and an alloy.

14. The method as claimed in claim 11, wherein the conductive oxide is selected from the group consisting of palladium (IV) oxide, Ruthenium (IV) oxdie, and a combination thereof.

15. The method as claimed in claim 11, wherein the conductive polymer is selected from the group consisting of polythiophenes (PTs), polypyrroles (PPys), polyacetylene (PA), polyaniline derivatives, and a combination thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The structure and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings, wherein:

[0019] FIG. 1 is a sectional view of a RFID tag antenna of an embodiment according to the present invention;

[0020] FIG. 2 is a schematic drawing showing microstructure of a film formed by sheet-like conductive carbon material and a porous fibrous substrate in the embodiment of FIG. 1 at the position II according to the present invention;

[0021] FIG. 3 is a flow chart showing steps of a method for manufacturing RFID tag antennas of an embodiment according to the present invention;

[0022] FIG. 4 is a schematic drawing showing structure of a RFID tag antenna of an embodiment according to the present invention;

[0023] FIG. 5 is a graph showing return loss of RFID tag antennas at different frequencies of an embodiment according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0024] In the following embodiments and/or implementations, the same or corresponding components in the figures are represented by the same or corresponding reference number.

[0025] A conductive ink for use in manufacturing of RFID tag antennas according to the present invention includes sheet-like conductive carbon material containing graphite structure, at least one conductive filler, at least one dispersant and at least one solvent. The solids content of the conductive ink is ranging from 2% to 85% (percentage by weight, wt %). The sheet-like conductive carbon material is in the powder form and is ranging from 10% to 90% (wt %) of the total solid weight. The sheet-like conductive carbon material includes graphene, graphite platelets, natural graphite, pelleted carbon black, such as KS6. The conductive filler is ranging from 10% to 90% (wt %) of the total solid weight, and is selected from the group consisting of conductive carbon materials in all shapes except the sheet, conductive metal particles, conductive oxides, conductive polymers, and a combination thereof. The conductive carbon materials in shapes other than sheet is selected from the group consisting of graphene, graphite, carbon nanotubes, carbon nanocapsules, conductive carbon black and a combination thereof. The conductive metal particles include platinum, gold, palladium, ruthenium, silver, copper, nickel, zinc, a combination thereof, and an alloy. The conductive oxides include palladium (IV) oxide, ruthenium (IV) oxdie, and a combination thereof. The conductive polymers include polythiophenes (PTs), polypyrroles (PPys), polyacetylene (PA), polyaniline derivatives, or a combination thereof. The dispersant is ranging from 0.0001% to 10% (wt %) of the total solid weight and divided into two groups, ionic dispersants and nonionic dispersants. The ionic dispersants include P-123, Tween 20, Xanthan gum, Carboxymethyl Cellulose (CMC), Triton X-100, Polyvinylpyrrolidone (PVP), Brji 30 and a combination thereof while the nonionic dispersants include Poly(sodium 4-styrenesulfonate) (PSS), 3-[(3-Cholamidopropyl)dimethyl ammonio]-1-propanesufonate (CHAPS), Hexadecyltrimethylammonium bromide (HTAB), Sodium taurodeoxycholate hydrate (SDS), 1-Pyrenebutyric acid (PBA), and a combination thereof.

[0026] The solvent can be pure water or organic solvent. The organic solvent includes N-Methyl-2-pyrrolidone (NMP), IPA (Isopropyl alcohol), ethanol, glycerol, ethylene glycol, butanol, propanol, Propylene glycol monomethyl ether (PGME), and Propylene glycol monomethyl ether acetate (PGMEA).

[0027] Refer to FIG. 1 and FIG. 2, a RFID tag antenna according to the present invention includes a porous fibrous material 10 and a conductive layer 20. The conductive layer 20 is composed of at least one sheet-like conductive carbon material containing graphite structure, at least one conductive filler, and at least one dispersant. The sheet-like conductive carbon material is ranging from 10% to 90% (wt %) of the total solid weight. The conductive filler is ranging from 10% to 90% (wt %) of the total solid weight. As to the dispersant, it is only ranging from 0.0001% to 10% (wt %) of the total solid weight.

[0028] Refer to FIG. 3, a method for manufacturing RFID tag antennas according to the present invention includes a plurality of steps.

1. preparing a porous fibrous substrate 10. The materials for the porous fibrous substrate 10 include general paper, hemp paper and polyethylene terephthalate (PET).
2. preparing a conductive ink composite without polymer binders. The conductive ink includes sheet-like conductive carbon material containing graphite structure, at least one conductive filler, at least one dispersant, and at least one solvent. The sheet-like conductive carbon material is ranging from 10% to 90% (wt %) of the total solid weight. The conductive filler is ranging from 10% to 90% (wt %) of the total solid weight. The dispersant is ranging from 0.0001% to 10% (wt %) of the total solid weight. The solids content of the conductive ink is ranging from 2% to 85% (wt %).
3. coating the conductive ink on a surface of the porous fibrous substrate 10 according to a shape of the antenna. The conductive ink is coated by printing (including screen printing, relief printing, and gravure printing) or inkjet printing.
4. evaporating the solvent of the conductive ink by thermal drying to form a conductive layer 20 on the surface of the porous fibrous substrate 10 while a part of the conductive layer 20 is infiltrated into pores between fibers of the porous fibrous substrate 10 and attached to the porous fibrous substrate 10.
5. rolling the conductive layer 20 on the surface of the porous fibrous substrate 10 after the step of drying and curing. The thickness compression ratio is ranging from 50% to 90% of the original total thickness of the porous fibrous substrate 10 and the conductive layer 20 (the printed antennas).

[0029] As to the conductive paste that contains polymer resin (binder), a conductive layer with good adherence is obtained after curing due to conductive filler held tightly by the shrunk and cured resin. Refer to the following table 2, the present binder-free graphene/metal composite conductive paste is compared with commercial conductive silver paste with epoxy resin. In the conductive layer produced by the commercial conductive silver paste with epoxy resin, the conductive filler originally held tightly by the polymer binder becomes loose while being squeezed and pressed during the rolling process. The binder/adhesive material is also squeezed and dispersed in the conductive filler to break original conductive paths. Thus the electrical resistance between two ends of the printed antenna is increased from 2.1 ohm () to 2.5 ohm (). The resistance is increased 19% after the rolling process. Moreover, the polymer resin may be attached to the roller when too much rolling force is applied. A part of the printed antenna may be released from the substrate and attached to the roller. Thus the conductive paste with polymer binder will not be treated by the rolling process after being printed and cured. As to the present conductive ink, it is prepared in the form of a conductive paste, especially a conductive paste without polymer binder. The molecules of the conductive filler are in contact with each other more closely by the rolling process. Without the non-conductive polymer binder therein, the resistance between the ends of the printed antenna is dramatically reduced (from 1.8 ohm to 0.9 ohm). The resistance is decreased up to 50% after the rolling. The adherence of the whole conductive layer is stabilized by the sheet-like carbon material after the rolling process. In addition, the adhesion of polymer resin to the roller caused by too much force applied will not occur.

TABLE-US-00002 TABLE 2 resistance of commercial conductive silver paste with epoxy resin/ conductive paste without polymer binder before and after rolling resistance between ends of the antenna (Ohm) item before rolling after rolling rate of change conductive silver 2.1 2.5 +19% paste with epoxy resin conductive paste 1.8 0.9 50% without polymer binder

[0030] According to the shape of the antenna, the conductive ink mentioned above is coated on the surface of porous fibrous material 10 by printing or inkjet printing. A part of the conductive ink is infiltrated into fibers of the porous fibrous substrate 10. Owing to good film-forming ability of the sheet-like conductive carbon material 21 contained in the conductive ink, the sheet-like conductive carbon material 21 forms the film together with the porous fibrous substrate 10 without addition of the adhesives, as shown in FIG. 2. The sheet-like conductive carbon material 21 and the porous fibrous substrate 10 form a RFID tag antenna containing no metal and no adhesive. Without the non-conductive binder in the conductive ink, the antenna has higher electric conductivity, lowered electrical resistance and reduced production cost.

[0031] The mesh count is ranging from 100 to 400 with the printing accuracy of 100 m when the conductive ink is coated on the surface of the porous fibrous substrate 10 by screen printing. Once the conductive ink is coated on the surface of the porous fibrous substrate 10 by inkjet printing, the optimal printing accuracy can even reach the level of 0.1 um depending on positioning accuracy of the inkjet printing device. Refer to FIG. 4, a schematic drawing showing structure of a RFID tag antenna created by printing of the present conductive ink. The appearance of the conductive layer 20 produced by printing of the present conductive ink looks the same as that of the conductive layer produced by etching of the aluminum foil. The accuracy of the contacts between the conductive layer 20 and the IC chip can reach the level of 10 um without a short circuit (as shown in the partial enlarged view of FIG. 4). In a further embodiment of the present invention, the conductive ink can be directly printed on paper for preparation of RFID tags that is easily removed. Compared with the complicated process of the conventional metal etching and patterning, the method of the present invention simplifies the process significantly.

[0032] In a further embodiment, materials for the porous fibrous substrate 10 can be materials with higher fiber density and more capillary holes. For example, the material can be paper with metric weight of 30-200 g/m2, a density of 0.5-2.5, and an average pore size of 0.02-500 m.

[0033] After the printing of the conductive layer 20, a drying step is carried out to evaporate solvent in the conductive ink. The drying is performed by heat drying and the heating temperature is up to 50-300 C. The higher the heating temperature, the shorter the drying time. In an embodiment of the present invention, the method further includes a rolling step. After the drying, the conductive layer 20 attached on the surface of the porous fibrous substrate 10 is treated by the rolling step to be compressed into 50-90% of the original thickness. Thus the conductive layer 20 has higher compactness and higher conductivity. The reduction of the resistance can be achieved by coating of the thicker conductive layer 20 or improvement of the compactness of the conductivity layer 20. Therefore the sheet-like conductive carbon material with higher thickness and larger particle size can be selected and used. The sheet-like conductive carbon material applied to the RFID tag has a resistance of 0.1-50 ohm/sq (resistivity of 110.sup.6-2.510.sup.4 ohm-metre (.Math.m)).

[0034] Refer to FIG. 5, a graph showing return loss of RFID tag antennas at different frequencies is revealed. The present conductive ink without polymer binder for use in preparing RFID tag antennas is printed on the surface of the porous fibrous substrate 10 to form different antenna patterns and then the return loss of the respective antenna is shown in FIG. 5. It is learned that different antennas have better performance at specific frequency bands. Thus the antennas are able to be applied to RFID tags that operate in specific frequency bands. The antennas prepared by the present conductive ink printed on the surface of the porous fibrous substrate 10 have better return loss in Ultra High Frequency (UHF) band and Microwave frequency band.

[0035] The RFID tag antenna of the present invention is electrically connected to the IC chip and is tested by RFID readers. The antenna pattern of the antenna tested is common for ultra-high frequency (UHF) band. One is a simple linear antenna and the other is a more complicated antenna with a plurality of curves. The sheet resistance and reading test results of the two antennas are shown in the following table 3. The test results have proved that the RFID tag antennas manufactured by the present binder-free conductive ink being printed on the surface of the porous fibrous substrate 10 can be applied to HF tags that operate at 13.56 MHz, UHF tags that operate at 868-956 MHz and Microwave tags that operate at 2.45 G Hz.

Table 3 shows results of reading test of RFID tag antenna connected to the IC chip

TABLE-US-00003 sheet antenna antenna resistance reading test result pattern frequency (ohm/sq) obtained by RFID reader sample 1 linear UHF 8.38 readable sample 2 curved UHF 5.34 readable

[0036] Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, and representative devices shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalent.