WO1993009646A1

WO1993009646A1 - Connection system for conductive ink flexible heaters

Info

Publication number: WO1993009646A1
Application number: PCT/US1992/009089
Authority: WO
Inventors: Ronald F. Steingrubey; Peyton W. Wofford
Original assignee: Ristance Corporation
Priority date: 1991-10-30
Filing date: 1992-10-27
Publication date: 1993-05-13

Abstract

A connection assembly (14) for a conductive ink flexible heater (10) is provided. The connection assembly (14) comprises a semiconductor pattern (18) printed on an electrically-nonconductive substrate (16). Conductive trace stripes (24) overlay the semiconductor pattern (18) and are in good electrical contact therewith. The conductive trace stripes (24) and semiconductor pattern (18) are sealed between the substrate (16) and a layer of electrically-insulating material (20). A connector mating piece (28) is affixed to the substrate (16) on the side facing away from the semiconductor pattern (18). A portion of the conductive trace stripes (24) is not covered by the sealing sheet (20) so as to provide electrical contact when the connection assembly (14) is inserted into a socket or connector housing (34).

Description

CONNECTION SYSTEM FOR CONDUCTIVE INK FLEXIBLE HEATERS

Field of the Invention

The present invention relates to conductive ink flexible heaters. More particularly, the present invention relates to an assembly for connecting such a heater to a source of electricity.

Background of the Invention

Electrical resistance heaters employing conductive ink technology are known in the art. Typically, such heaters comprise a nonconductive substrate on which is printed a semiconductor pattern and a nonconductive sealing sheet positioned on top of and bonded to the substrate to hermetically seal the se iconduct or between the substrate and sealing sheet. The sealing sheet and the substrate are bonded together at those areas of the substrate not covered by the semiconductor. The semiconductor typically is a colloidal graphite ink.

Various means have been proposed for connecting conductive ink heaters to a source of electricity. One commercially available means involves the use of bifurcated leaf connectors, such as those available from AMP Inc. of Harrisburg, Pennsylvania. Bifurcated leaf connectors comprise crimped, snap-in contact leads which are inserted into a connector housing which, in turn, is connected to a source of electricity. At the heater end, the leads may include a crimp-on connector having pins which pierce the sealing sheet and engage the conductive electrodes. At the contact end, the leaf-type contacts are designed to provide good electrical contact when inserted into the connector housing. The bifurcated design achieves contact redundancy. Typically, an extraction tool is necessary to remove the contacts from the connector housing. A disadvantage of crimp-type connectors is that they do not. perform well under high humidity conditions. Another commercially available means of connecting conductive ink heaters to a power source is a conventional pin and socket connection assembly. The pin and socket design is similar to the leaf-type design except that a pin connection is used instead of a leaf-type connection. Typically, the pins are held within a pin housing which is inserted into a socket or receptacle housing connected to a source of electricity.

While these and other proposed connection means may be suitable for their intended purposes, there still remains a need for a simple, easy-to-manufacture and easy-to-use connection assembly for electrical resistance heaters employing conductive ink technology. There is also a need for a flexible heater that can be installed quickly and easily. Finally, there is a need for a flexible heater and connection system with improved reliability.

OBJECTS OF THE INVENTION It is, therefore, an object of the invention to provide a conductive ink heater and connection system which attains the aforestated desirable characteristics. It is a further object of the invention to provide a conductive ink heater and connection system which is easy and inexpensive to manufacture. It is a still further object of the invention to provide a conductive ink heater and connection system that is reliable and easy to use.

Yet another object of the invention is to provide a conductive ink heater and connection system that can be installed quickly and easily.

SUMMARY OF THE INVENTION

The foregoing and other objects are achieved by a connection assembly for a conductive ink flexible heater comprising a substrate composed of electrically insulating material and having a first side, a second side, a heater end and a connection end; a semiconductor pattern arranged on at least a portion of the heater end of the first side of the substrate; a layer of conductive material adjacent to and in electrical contact with the semiconductor pattern and extending to the connection end of the first side of the substrate; a continuous layer of electrically insulating material; and a connector mating piece having at least a portion of one surface fixedly-secured adjacent to the second side of the substrate at the connection end, the other surfaces being exposed. The layer of electrically insulating material overlays all but a portion of the layer of conductive material at the connection end.

Preferably the layer of conductive material comprises trace stripes wherein all but a portion of the trace stripes at the connection end is sealed between the substrate and the sealing sheet.

In the preferred embodiment, the connector mating piece is substantially rectangular and formed of plastic. Preferably, the connector mating piece has a thickness such as to form a rigid piece for insertion into a connector. The connector mating piece may have beveled edges at one end to facilitate easy insertion of the connection assembly into a socket or connector housing.

Preferably, the semiconductor pattern comprises a conductive ink. The conductive ink may be a blend of graphite and metal particles in a polymer paste. Typically, the semiconductor pattern is printed on the substrate using a silkscreening process.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the invention reference is made to the drawings where:

FIG. 1 is a top elevational view of a conductive ink flexible heater according to the present invention. FIG. 2 is a cross-sectional view on a magnified scale of the conductive ink heater of FIG. 1, taken along the line 2-2 of FIG. 1.

FIG. 3 is a front (end on) view of a connection assembly according to the present invention.

FIG. 4 is a side view of the connection assembly of FIG. 3.

FIG. 5 is a perspective view of the connection assembly of FIG. 3, shown with a connector housing.

Detailed Description of the Invention

Referring first to FIG. 1, a conductive ink flexible heater 10 embodying the present invention is shown. The heater comprises a heating portion 12 and a connection portion 14. As best shown in FIG. 2, the heating portion 12 comprises a nonconductive substrate 16, a semiconductor or conductive ink pattern 18 printed thereon, and a nonconductive sealing sheet or overcoat 20. Optionally, a layer of adhesive 21 is adjacent the substrate 16 on the side opposite the sealing sheet or overcoat 20 for securing the flexible heater 10 to the object to be heated. As shown in FIG. 2, the adhesive may be covered by a peel-off backing 22.

The connection portion 14 comprises a plastic substrate 16, a semiconductor pattern 18 printed thereon, conductive trace stripes 24 overlaying the semiconductor pattern 18, -and a sealing sheet or overcoat 20. At one end of the connection portion 14 is a connection assembly 26, which includes a connector mating piece 28 adhered to the plastic substrate 16 on the side opposite the semiconductor pattern 18. A portion 30 of the trace stripes 24 at the connection end is exposed so as to allow contact with a source of electricity.

The semiconductor pattern 18 may comprise any of a variety of suitable conductive inks, including graphite inks, silver-based inks, copper-based inks, nickel-based inks, or a blend thereof. Where a graphite/metal ink blend is used, the amount of metal may be varied in order to achieve different sheet resistances. In addition, varying the length, width, and thickness of the semiconductor line creates different resistances in the product.

Conductive inks suitable for use in the present invention are commercially available. One such suitable ink comprises a blend of electrically-conductive silver ink in a carbon or graphite-based electrically-conductive ink. Properties for these two inks are given in the following table:

Typical Cured Properties of Selected Conductive Inks

Silver Ink Graphite I

Consistency Smooth Paste Smooth Pas

Filler Silver (85%) Carbon

Sheet Resistivity (ohms/sq/mil) 0.019 50

Sheet resistivity is the resistance of a conductor or resistor in sheet form, and is measured in ohms per square per mil. The length of the sheet (L) divided by the width of the sheet (W) is the number of squares. Both conductive inks feature excellent adhesion to Kapton, Mylar, glass and a variety of other surfaces.

The percent of silver ink in the silver-graphite blend may be varied to achieve the desired sheet resistivity

(SR) . For example, it has been found that a blend of 10% silver ink and 90% graphite ink results in a resistivity of 20 ohms/square/mil, while a blend of 90% silver ink and 10% graphite ink results in a resistivity of 0.05 ohms/square/mil

The following formula may be used to calculate the resistance of a conductive ink film:

R - (SR) (L) (W) (T) where: SR is the sheet resistivity, in ohms per square per mil, w is the width of the semiconductor line, in inches,

T is the thickness of the semiconductor line, in mil (1 mil = 0.001 in.), L is the length of the semiconductor line, in inches, and R is the resistance of the conductive ink film, in ohms per square. Thus, where W equals 0.138 inches, T equals 0.8 mil, L equals 14.2 inches, and SR equals 3 ohms/square/mil, the resistance of the conductive ink film (R) is 385 ohms/square.

In one embodiment, the substrate comprises 5 mil Mylar polyester film. One commercially available substrate, manufactured by ICI Films and sold under the name Melinex

St 505, has been found to be suitable. Alternative substrates include polycarbonate film, paper and fabric.

Printing of the semiconductor pattern 18 on the substrate 16 can be accomplished by using a silkscreening process, although other methods of arranging the semiconductor pattern 18 on the substrate 16 may be used.

The conductive ink blend may be thinned and retarder added prior to application. A stainless steel screen may be used for the silkscreening process. During the preparation of one embodiment, drying of the semiconductor pattern was accomplished in a forced air oven at a temperature of

250^*F. It will be noted, however, that a range of temperatures may be necessary to properly cure the printed substrate. Equipment employing known technology can be used to print the semiconductor pattern 18 on the substrate 16.

The thickness of the sealing sheet or overcoat 20 preferably varies from about 2 to about 5 mil. In one embodiment, the sealing sheet 20 comprises an acrylic film. The sealing sheet 20 is secured to the substrate by self-stick adhesive so that there are no air pockets between the overlay 20 and the substrate 16.

A connection assembly 26 according to the present invention is illustrated in FIGS. 3, 4 and 5. In the illustrated embodiment, conductive trace stripes 24 overlay and are in electrical contact with a pair of substantially parallel semiconductor stripes 18. The trace stripes 24 and semiconductor stripes 18 are interposed between an electrically nonconductive substrate 16 and a sealing sheet or overcoat 20. A connector mating piece 28 is affixed to the substrate 16 on the side facing away from the semiconductor stripes 18.

As best shown in FIGS. 1, 4 and 5, the end portions 30 of the conductive trace stripes 24 are not covered by the sealing sheet or overcoat 20. Instead, the end portions 30 of the conductive trace stripes 24 are exposed to facilitate electrical contact with a power source.

In one embodiment, the length of the conductive trace stripes not covered by the sealing sheet is about 5/8 inch. However, the length of the conductive trace stripes left exposed may be varied, and need only be long enough to allow a good electrical connection between the conductive ink heater and the source of electricity. In the preferred embodiment, the width of each conductive trace stripe 24 is about the same as the width of the semiconductor stripe 18 where the two stripes are in electrical contact.

In one embodiment, the connector mating piece 28 is about 0.5 in. wide, about 1 in. long and about 0.06 in. thick. However., these dimensions too may be varied to accommodate various heater configurations and still be within the scope of the present invention.

The connector mating piece 28 has beveled edges 32 on its front end surface to facilitate insertion of the connection assembly 26 into a corresponding socket or connector housing 34. The connector mating piece 28 is formed of a non-conductive material such as plastic, and is secured to the substrate 16 by adhesive.

During operation of the conductive ink flexible heater, the connection assembly 26 is inserted into a connector housing 34 such as that shown in Figure 5. Commercially-available connector housings suitable for accommodating the connection assembly of the present invention include those manufactured by AMP Inc. as part of their Bifurcated Leaf Connector Series. Many further modifications will readily occur to those skilled in the art to which the invention relates. Those specific embodiments described herein should be taken as illustrative of the invention only and not as limiting its scope in accordance with the accompanying claims. For example, it is anticipated that the sealing sheet or overcoat 20, rather than comprising an acrylic adhesive film, could comprise a silkscreened ultraviolet dielectric overcoat or other insulating coating.

Claims

What is claimed is:

1. A connection assembly for an electrical resistance heater comprising: a substrate composed of electrically-insulating material and having a first side and a second side, a heater end and a connection end; a semiconductor pattern arranged on at least a portion of said heater end of said first side of said substrate; a layer of conductive material adjacent to and in electrical contact with said semiconductor pattern and extending to said connection end of said first side of said substrate; a continuous layer of electrically-insulating material overlaying all but an exposed portion of said layer of conductive material at said connection end; and a connector mating piece having at least a portion of one surface fixedly-secured adjacent to said second side of said substrate at said connection end, the other surfaces thereof being exposed, to provide support for said exposed portion and means for direct disconnectible connection to a source of electricity.

2. The connection assembly of claim 1 wherein said substrate is selected from the group consisting of polyester films and polycarbonate films.

3. The connection assembly of claim 1 wherein said semiconductor pattern comprises a conductive ink.

4. The connection assembly of claim 3 wherein said conductive ink comprises a blend of graphite and metal particles.

5. The connection assembly of claim 4 wherein said metal is selected from the group consisting of silver, copper and nickel.

6. The connection assembly of claim 3 wherein said semiconductor pattern is arranged on said substrate using a silkscreening process.

7. The connection assembly of claim 3 wherein said layer of electrically-insulating material is an acrylic film.

8. The connection assembly of claim 7 wherein said acrylic film has a thickness of between about 2 and about 5 mil.

9. The connection assembly of claim 3 wherein said layer q electrically-insulating material is an ultraviolet dielectric overcoat.

10. The connection assembly of claim 3 wherein said connector mating piece comprises a substantially- rectangular piece of plastic.

11. The connection assembly of claim 10 wherein said connector mating piece comprises a front portion and a rear portion, said front portion having beveled edges.

12. The connection assembly of claim 10 wherein said connector mating piece has a width substantially the same as the width of said substrate.

13. An electrical resistance heater comprising a heating portion and a connection portion, said connection portion comprising: a substrate composed of electrically-insulating material; a^*semiconductor pattern arranged on at least a portion of said substrate; conductive trace stripes disposed on and in electrical contact with said semiconductor pattern; a continuous layer of an electrically-insulating material overlaying all but an exposed portion of said conductive trace stripes on the side opposite said semiconductor pattern; and a connector mating piece having at least a portion of one surface fixedly-secured adjacent to said substrate on the side opposite said semiconductor pattern and conductive trace stripes, the other surfaces of the connector mating piece being exposed, whereby support and orientation for said exposed portion of said conductive trace stripes for direct disconnectible connection to a source of electricity are provided.

14. An electrical resistance heater comprising a heating portion and a connection portion, the connection portion having a heater end adjacent the heating portion and an opposed connection end, said heating and connection portions comprising: an integrally-formed substrate for both said heating and connection portions, said substrate being composed of electrically-insulating material; an integrally-formed semiconductor pattern arranged on at least limited areas of both said heating portion and at least the heater end of said connection portion of said substrate; conductive trace stripes on said connection portion disposed in electrical contact with the portion of said integrally-formed se iconductive pattern on said connection portion, said conductive trace stripes extending adjacent the connection end of said connection portion; an integrally-formed layer of an electrically- insulating material overlaying and sealed to all of said heating and connection portions except for an exposed portion of said conductive trace stripes adjacent said connection end of said connection portion on the side opposite said substrate; and a connector mating piece having at least a portion of one surface fixedly-secured adjacent said connection end of said connection portion and said substrate on the side opposite said conductive trace stripes, the other surfaces of the connector mating piece being exposed, whereby to provide support and orientation for said exposed portion of said conductive trace stripes for direct disconnectible contact with a source of electricity.

15. The electrical resistance heater of claim 14 wherein said integrally-formed substrate is selected from the group consisting of polyester films and polycarbonate films.

16. The electrical resistance heater of claim 14 wherein said integrally-formed semiconductor pattern comprises a conductive ink.

17. The electrical resistance heater of claim 14 wherein said layer of electrically-insulating material is an acrylic film.

18. The electrical resistance heater of claim 14 wherein said integrally-formed semiconductor pattern is arranged on said integrally-formed substrate using a silkscreening process.

19. The electrical resistance heater of claim 14 wherein said connector mating piece is ixedly-secured to said integrally-formed substrate by adhesive.

20. The electrical resistance heater of claim 14 wherein said connector mating piece comprises a front portion and a rear portion, said front portion having exposed beveled edges to facilitate insertion into a corresponding connector socket.