US20050151700A1 - Method and system for forming electrically conductive pathways - Google Patents

Abstract

A system and two methods for forming electrically conductive pathways. These pathways can be connected with a microchip in order to form a radio frequency identification tag. A first method uses a thermal transfer ribbon, coated with a conductive material that is engaged with a receiver substrate. A thermal print head will heat a composition on the thermal transfer ribbon in order to transfer it to the receiver substrate. This transfer composition forms the electrically conductive pathway or antenna. In an alternative method, a receiver substrate is heated in order to react conductive material thereon. This receiver substrate is also heated by a thermal print head to form an electrically conductive pathway.

Description

• This application is a Divisional of co-pending application Ser. No. 09/839,126, filed on Apr. 23, 2001, and for which priority is claimed under 35 U.S.C. § 120; the entire contents of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The present invention relates to a system and method for forming electrically conductive pathways. In particular, the system and method is for making variably printed radio frequency antennas for radio frequency tags.
• 2. Description of the Background Art
• Various printing arrangements for forming antennas are known. However, variable demand printing for forming electrically conductive pathways or antennas is not known.
SUMMARY OF THE INVENTION
• Accordingly, it is an object of the present invention to provide a method and system to produce variable on-demand printing of conductive pathways. Such pathways can be used to form antennas for radio frequency tags. Two different methods can be utilized for forming such conductive pathways.
• In one of these methods, the following steps are carried out: providing a thermal transfer ribbon, moving the thermal transfer ribbon past a heat source, engaging the thermal transfer ribbon with a receiver substrate as the thermal transfer ribbon moves past the heat source, selectively heating portions of the thermal transfer ribbon with the heat source, and transferring a composition from the thermal transfer ribbon to the receiver substrate, the selective heating enabling a desired pattern of the composition to be transferred to the receiver substrate, the composition including an electrically conductive material.
• In another method for forming electrically conductive pathways, the following steps are carried out: providing a substrate coated with reactive material, moving the substrate past a heat source, selectively heating portions of the substrate with the heat source, and developing the reactive material on the substrate during exposure to heat from the heat source to develop a desired pattern on the substrate, the reactive material becoming an electrically conductive material.
• Yet another object of the invention is to enable a radio frequency tag to be produced by using a receiver substrate which has an electrically conductive pathway formed thereon and by using a microchip. This microchip can be affixed on or embedded in the receiver substrate before or after the electrically conductive pathway is formed.
• Further, it is an object of the present invention to also provide a system for producing radio frequency tags comprising a conveyor for moving a substrate, a thermal print head, the conveyor moving the substrate past the thermal print head, the thermal print head being selectively actuatable to heat a desired pattern on the substrate, means on the substrate for reacting with the heat source to form electrically conductive pathways, the means including a heat sensitive composition on the substrate.
• Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
• The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:
• FIG. 1 is a schematic side view of a first system for forming electrically conductive pathways of the present invention;
• FIG. 2 is a schematic side view of a second system for forming electrically conductive pathways of the present invention; and
• FIG. 3 is a perspective view of a radio frequency tag produced by either method of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
• Referring in detail to the drawings and with particular reference toFIG. 1, a first system10 for forming electrically conductive pathways is shown. This system10 includes aconveyor12 for infeeding athermal transfer ribbon14 and a receivedsubstrate16. Thisconveyor12 is only schematically shown inFIG. 1 as a pair of feed rolls. It should be appreciated that any type of conveyor system could be utilized. For example, a belt conveyor, chain conveyor, series of rollers, or any other known conveyor system could be used. Moreover, while only a pair ofrollers12 are shown, it should be contemplated that a continuous conveyor can be used over the length of the system10 or any suitable number of conveyor units can be incorporated into the conveyor system.
• Thethermal transfer ribbon14 andreceiver substrate16 are fed past a heat source orthermal print head18. Thethermal print head18 will selectively heat portions of thethermal transfer ribbon14 to ultimately form a desired pattern on thereceiver16, as will be discussed below. While such athermal print head18 is known, its use in a method for forming electrically conductive pathways is new. In addition, abacking roller20 is provided to support thethermal transfer ribbon14 andreceiver substrate16. While abacking roller20 is shown, it should be noted that other support surfaces could be used. For example, a flat supporting table or other structure could be opposed to theprint head18.
• Downstream from thethermal print head18 is adevice22 for applying amicrochip30 onto the treatedreceiver substrate16. While thesubstrate16 is shown inFIG. 1 as terminating before thedevice22, it is contemplated that thesheet16 could instead be continually fed through thedevice22. Alternatively, after treatment, thereceiver16 can be cut and then the cut sections fed to thedevice22. Thisdevice22 can be any known device which will apply amicrochip30 onto the treated receivedsubstrate16 in order to form a radio frequency tag24, as shown inFIG. 3. Alternatively, thisdevice22 could be omitted and thereceiver substrate16 can have microchips already incorporated thereon. Themicrochips30 can be applied to the surface or embedded in thereceiver substrate16.
• Thethermal transfer ribbon14 has a reactive coating or a conductive transferable material thereon. When this reactive coating or material is heated by thethermal print head18, an electrically conductive pathway can be printed on thereceiver substrate16.Thermal transfer ribbon14 either has a conductive material or a material that becomes conductive upon the application of heat. The heat fromprint head18 will serve to transfer the material toreceiver substrate16 and in some instances will also serve to activate the material to make it conductive. In those circumstances, the transferred composition will be an electrical conductor precursor.
• The use of thisprint head18 allows printing of a conductive pathway in any shape, length, or size onto thereceiver substrate16. Thus, great flexibility is had with the use of thethermal print head18. The electricallyconductive pathway26 is schematically shown inFIG. 1. When the device for applying amicrochip22 handles thereceiver substrate16 with the electricallyconductive pathway26, a microchip can be placed thereon in order to form a radio frequency tag. While a generally U-shaped pathway is shown, it is important to note that the length, width, shape and size of the pathway can easily be varied by usingprint head18. Theconveyor12 will enable on-the-fly printing ofpathways26. Of course, batch processing is also possible. In such an arrangement, a continuous transfer ribbon and receiver substrate can be incrementally fed past theprint head18 or discrete portions of aribbon14 andsubstrate16 could be used. For example, a feeder conveyor could move rectangular overlaying sheets of transfer ribbon and substrate through the system10 past theprint head18.
• Thethermal transfer ribbon14 is brought into engagement with thereceiver substrate16. This engagement, along with the heating of thethermal transfer ribbon14 by thethermal print head18, will cause transfer of a conductive composition from theribbon14 to thereceiver substrate16. Thus, a complicated arrangement using magnets, as taught in U.S. Pat. No. 5,061,093 to Yamaguchi et al. for example, is not needed.
• Thethermal transfer ribbon14 is coated with the conductive composition. The transfer ribbon is made up of a transfer substrate which can be made from a polymeric film or paper. Suitable transfer substrate materials include, but are not limited to, paper, polyester, polyethylene naphthalate, polyamide, polyolefin, cellulose and polycarbonate. One preferred transfer substrate is polyester film, manufactured by Dupont™ under the Mylar™ brand name. Generally, Mylar™ is a polyester flexible film. Important properties of the transfer substrate include high tensile strength, thin thickness and low heat resistance.
• The transfer substrate of the thermal transfer ribbon is coated with a conductive composition that is designed to be transferred to the receivedsubstrate16 using thethermal print head18. This coating is comprised of a conductive material, wax, binders, surfactants, dispersants and other additives. The primary component of the transfer layer is the electrically conductive material. The conductive material may be comprised of metallic inks, metallic substances, metallic dispersions, metallic salts, carbon based inks, or other conductive substances, etc. A preferred metallic substance is manufactured by Parelec™ under the Paramod™ brand name. The higher the conductivity of the conductive material, the better.
• The transfer coating for thethermal transfer ribbon14 also contains a wax as another main component. The wax is designed to melt or soften under the heat supplied by thethermal print head18. This will aid in the transfer of the coating layer to thereceiver substrate16. Examples of suitable waxes are carnuaba wax, paraffin wax, low molecular weight polyethylene wax, etc.
• Binders are also included in thethermal transfer ribbon14. These binders in the coating layer aid in cohesion of the coating and provide tack properties for adhesion to thereceiver substrate16. Examples of suitable binders are styrene copolymers, polyethylene resin, polystyrene, vinyl chloride polymers, vinyl acetate polymers, etc. Surfactants, dispersant and other additives are incorporated as needed for proper processing, coating and to aid in the transfer properties.
• The transfer coating layer can be applied to the transfer ribbon substrate using a Meyer rod, airknife, roll coater, blade or any suitable coating method. The coat weight applied is in the range 1.5 g/m²to 30 g/m².
• The coated transfer ribbon can then be used with thethermal print head18 and a thermal printer to create any size, shape, length, etc. of an antenna to be incorporated with a microchip for a construction of a radio frequency identification tag24. The conductive material is transferred onto thereceiver sheet16. This receiver sheet is a substantially non-conductive substrate such as paper, plastic film and the like. Alternatively, the sheet can be a conductive substrate that has been coated with an electrical insulating layer.
• Turning now toFIG. 2, a second method and system10′ for forming electrically conductive pathways will be described. These pathways can also be used for antennas in radio frequency tags24, similarly to that described inFIG. 1. Many of the components and alternative arrangements in this second system10′ are the same as that in the first system, and their description will not be repeated.
• In the second system10′, athermal transfer ribbon14 is not used. Rather, asecond receiver substrate16′ is utilized. This substrate used can be selected from paper, polymeric films, cellulose materials and other thin, flat substrates. This substrate is coated with a composition that is designed to react when exposed to heat generated from thethermal print head18. This coating is comprised of a reducible metallic material, binders, fillers, surfactants, dispersants, and other additives.
• The primary component of the transfer layer is the reducible metallic material. This reducible material may be comprised of sorbitol copper formate, copper sulfate, cuprite, tenorite, silver nitrate, and the like. The higher the conductivity of the reduced reducible material, the better.
• Binders are included in the coating layer to aid in cohesion of the coating while not inhibiting the conductivity of the reduced material. Examples of suitable binders are styrene butadiene copolymers, polyvinyl alcohols, starch, vinyl chloride polymers, vinyl acetate polymers, methyl cellulose, etc. Surfactants, dispersants and other additives are incorporated as needed for proper processing, coating, and to aid in the transfer properties. The coating layer can be applied to the substrate using a Meyer rod, airknife, roll coater, blade or any other suitable coating method. The coat weight applied is in the range of 1.5 g/m²to 30 g/m².
• The antenna may be formed by either method to create the antenna portion of a radio frequency tag. The antenna or electrically conductive pathway may be printed either before or after the microchip is affixed to the substrate. Thus, while thedevice22 is shown downstream from theprint head18 inFIGS. 1 and 2, thisdevice22 could instead be upstream so that the microchip is first applied to thereceiver substrate16 or16′. Alternatively, thedevice22 can be omitted andsubstrates16 or16′ using already incorporated microchips could instead be used. Optionally, aninterposer28 may be used to decrease the precision needed when forming an electrically conductive pathway relative to the microchip connection.
• With the present system, variable, on-demand printed electrically conductive pathways can be formed. The invention utilizes two methods for printing the conductive pathways, thermal transfer and direct thermal. The printed conductive pathways are suitable for use as an antenna for a radio frequency identification tag24. With the first described thermal transfer method, aribbon14 coated with a conductive material is used that is transferred to anothersubstrate16 upon application of heat by thethermal print head18. In the direct thermal method, areceiver substrate16′ is used that has a conductive material which, when exposed to heat from athermal print head18, will form the conductive pathways.
• To summarize the steps of the first method of forming electrically conductive pathways, athermal transfer ribbon14 is provided. Thisthermal transfer ribbon14 is moved past a heat source orthermal print head18 byconveyor12. Thethermal transfer ribbon14 is engaged with a receiver substrate as it moves past the heat source orthermal print head18. Thisthermal print head18 will selectively heat portions of thethermal transfer ribbon14, in order to transfer a composition to thereceiver substrate16. This transferred composition forms an electricallyconductive pathway26. The selective heating by thethermal print head18 enables a desired pattern of composition to be transferred to thereceiver substrate16.
• In the second method, asubstrate16′ is provided with a reactive material. Thissubstrate16′ is moved byconveyor12 past a heat source orthermal print head18. The heat source orthermal print head18 can selectively heat portions of the substrate. This will develop the reactive material on thesubstrate16′ to develop a desired pattern on the substrate. This desired pattern will form the electricallyconductive pathway26.
• With either method, a system10 or10′ can be used. The conductive composition onribbon14 or the reducible material on the second receiver substrate will act as means on the substrate for reacting to heat from the heat source orprint head18. The conductive composition or reducible material is a heat sensitive composition onsubstrate14 or16′.
• The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims (16)

1. A method of forming electrically conductive pathways, comprising the steps of:

providing a substrate coated with reactive material;

moving the substrate past a heat source;

selectively heating portions of the substrate with the heat source; and

developing the reactive material on the substrate during exposure to heat from the heat source to develop a desired pattern on the substrate, the reactive material forming an electrically conductive material.

2. The method of forming electrically conductive pathways as recited inclaim 1, further comprising the steps of:

using a cellulosic material, a polymeric film or paper as the substrate;

coating the substrate with the conductive material and with at least one of binders, surfactants and dispersants, the conductive material being a reducible material.

3. The method of forming electrically conductive pathways as recited inclaim 2, further comprising the step of using at least one of sorbitol copper formate, copper sulfate, cuprite, tenorite and silver nitrate as reactive material which forms the electrically conductive material.

4. The method of forming electrically conductive pathways as recited inclaim 2, further comprising the step of using at least one of styrene butadiene copolymers, polyvinyl alcohols, starch, vinyl chloride polymers, vinyl acetate polymers and methyl cellulose as the binders of the substrate.

5. The method of forming electrically conductive pathways as recited inclaim 1, further comprising the step of using a thermal print head as the heat source.

6. The method of forming electrically conductive pathways as recited inclaim 1, further comprising the step of combining the substrate with a microchip to form an antenna.

7. The method of forming electrically conductive pathways as recited inclaim 6, wherein the antenna is used as a radio frequency identification tag and further comprising the step of affixing the microchip to the receiver substrate either before or after the step of transferring the composition.

8. A radio frequency tag produced according to the method ofclaim 7.

9. A system for producing radio frequency tags comprising:

a conveyor for moving a substrate;

a thermal print head, the conveyor moving the substrate past the thermal print head, the thermal print head being selectively actuatable to heat a desired pattern on the substrate;

means on the substrate for reacting with the heat source to form electrically conductive pathways, the means including a heat sensitive composition on the substrate.

10. The system for producing radio frequency tags as recited inclaim 9, wherein the substrate is a thermal transfer ribbon and wherein the conveyor further conveys a receiver substrate past the heat source, the receiver substrate and the thermal transfer ribbon being engaged at the thermal print head and the heat sensitive composition being initially provided on the thermal transfer ribbon being heated in the desired pattern by the thermal print head and thereafter being transferred to the receiver substrate, the heat sensitive composition which is not heated by the thermal print head remaining on the thermal transfer ribbon, the heat sensitive composition transferred to the receiver substrate forming electrically conductive pathways on the receiver substrate.

11. The system for producing radio frequency tags as recited inclaim 10, further comprising a device for applying a microchip onto the receiver substrate with the electrically conductive pathways to form a radio frequency tag.

12. The system for producing radio frequency tags as recited inclaim 9, wherein the heat sensitive composition on the substrate includes at least one of metallic inks, metallic substances, metallic salts, metallic dispersions and carbon based inks.

13. The system for producing radio frequency tags as recited inclaim 9, wherein the heat sensitive composition on the substrate is at least one of sorbitol copper formate, copper sulfate, cuprite, tenorite and silver nitrate and wherein the thermal print head only reacts with the heat sensitive composition in the desired pattern to form the electrically conductive pathways with the reacted heat sensitive composition while unreacted heat sensitive composition remains on the substrate.

14. The system for producing radio frequency tags as recited inclaim 13, further comprising a device for applying a microchip onto the receiver substrate with the electrically conductive pathways to form a radio frequency tag.

15. A radio frequency tag produced by the steps of:

providing a thermal transfer ribbon;

moving the thermal transfer ribbon past a heat source;

engaging the thermal transfer ribbon with a receiver substrate as the thermal transfer ribbon moves past the heat source;

selectively heating portions of the thermal transfer ribbon with the heat source; and

transferring a composition from the thermal transfer ribbon to the receiver substrate, the selective heating enabling a desired pattern of the composition to be transferred to the receiver substrate, the composition including an electrically conductive material.

16. A method of forming electrically conductive pathways for radio frequency tags, comprising the steps of:

providing a thermal transfer ribbon including a precursor which is nonconductive;

moving the thermal transfer ribbon past a heat source;

engaging the thermal transfer ribbon with a flexible receiver substrate as the thermal transfer ribbon moves past the heat source;

using paper or pliable film as the receiver substrate;

selectively heating portions of the thermal transfer ribbon with the heat source to activate said nonconductive precursor to form an electrically conductive material; and

transferring a composition from the thermal transfer ribbon to the receiver substrate, the selective heating

enabling a desired pattern of the composition to be transferred to the paper or film receiver substrate, the composition transferred from the thermal transfer ribbon being an electrically conductive material.

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