Positive temperature coefficient heater with distributed heating capability

• US 4,931,627 A
• Filed: 07/13/1989
• Issued: 06/05/1990
• Est. Priority Date: 08/16/1988
• Status: Expired due to Term

• Current Assignee: Illinois Tool Works Inc.
• Original Assignee: Illinois Tool Works Inc.
• Inventors: Watts, Leslie M.
• Primary Examiner(s): Reynolds, Bruce A.
• Assistant Examiner(s): Fuller, Leon K.
• Application Number:
  US07/379,276
• Time in Patent Office: 327 Days
• Field of Search: 219/202, 219/203, 219/219, 219/345, 219/528, 219/543, 219/548, 219/549, 219/553, 15/250.05
• US Class Current: 219/548
• CPC Class Codes: H05B 3/146 Conductive polymers, e.g. polyethylene, thermoplastics
• CPC Class Codes: H05B 3/845 specially adapted for reflecting surfaces, e.g. bathroom - or rearview mirrors

Abstract

A heating device for a mirror includes a substrate having an electrical buss system deposited on one surface thereof including a plurality of interdigitated electrodes and two buss bars. There is provided a plurality of heater-lets formed of an electrically resistive layer of material having a positive temperature coefficient. The plurality of heater-lets have varying sizes and shapes and are deposited over the electrical buss system between the adjacent electrodes of the interdigitated electrodes. Each of the plurality of heater-lets are separated from its neighbor by spaces of varying sizes and shapes so as to form a plurality of individual heating areas of variable intensity. A first adhesive layer is deposited over the resistive layer and adheres to the exposed areas of the substrate. An electrical barrier layer is secured to the first adhesive layer, and a second adhesive layer is disposed on the electrical insulated barrier layer. A removable protective covering is secured to the second adhesive layer. The power distribution over the entire substrate is selectively regulated by varying the density of the heater-lets.

Claims

1. A heating device comprising:

a planar electrically insulated substrate;

an electrical buss system on one surface of said substrate, including a pair of buss bars and two electrode patterns having a plurality of spaced apart parallel interdigitated electrodes, adjacent electrodes of said plurality of interdigitated electrodes connected to different ones of said pair of buss bars, each buss bar extending from one of a pair of terminal connection points along generally opposite portions of a peripheral edge of said substrate;

a plurality of heater-lets formed of an electrically resistive layer of material having a positive temperature coefficient, said plurality of heater-lets having varying sizes and shapes being deposited over said electrical buss system between adjacent electrodes of said interdigitated electrodes. each of said plurality of heater-lets being separated from its neighbor by spaces of varying sizes and shapes so as to form a plurality of individual heating areas of variable intensity; and

at least one adhesive layer being deposited over said electrically resistive layer including the spaces between said heater-lets, said adhesive layer contacting and bonding directly to said substrate in areas of said substrate between said heater-lets,

whereby the power distribution over the entire substrate is selectively regulated by varying the density of the heater-lets.

2. A heating device as claimed in claim 1, further including an electrically insulated barrier layer disposed on said adhesive layer.

3. A heating device as claimed in claim 2, further including a second adhesive layer disposed on said electrically insulated barrier layer.

4. A heating device as claimed in claim 3, further including a removable protective layer disposed on said second adhesive layer.

5. A heating device as claimed in claim 1, wherein predetermined one of said plurality of heater-lets have sizes at predetermined locations on said one surface of said substrate to form heating zones having predetermined power densities at said predetermined locations.

6. A heating device as claimed in claim 5, wherein said plurality of heater-lets at least along a portion of the peripheral edge of said substrate are larger in size than the other of said plurality of said heater-lets in the central portion of said substrate.

7. A heating device comprising;

a planar insulating substrate having a peripheral edge;

an electrical buss system deposited on one surface of said substrate, said buss system including two buss bars extending along generally opposite portions of the peripheral edge of said substrate, a plurality of parallel spaced apart interdigitated electrodes alternately connected to said buss bars defining a plurality of electrode paths;

a plurality of heater-lets formed of an electrically resistive layer of material having a positive temperature coefficient, said plurality of heater-lets having varying sizes and shapes being deposited over said electrical buss system between said adjacent electrodes of said interdigitated electrodes, each of said plurality of heater-lets being separated from its neighbor by spaces of varying sizes and shapes so as to form a plurality of individual heating areas of variable intensity;

first predetermined ones of heater-lets being arranged in a general elliptically-shaped pattern in the center of said substrate to form a first heating zone having a first predetermined power density;

second predetermined ones of said heater-lets being arranged in a general elliptically-shaped pattern and disposed coaxially with said first predetermined ones of said heater-lets to form a second heating zone having a second predetermined power density; and

third predetermined ones of said heater-lets being arranged in a general elliptically-shaped pattern and disposed coaxially with said second predetermined ones of said heater-lets to form a third heating zone having a third predetermined power density and

at least one adhesive layer being deposited over said electrically resistive layer including the spaces between said heater-lets, said adhesive layer contacting and bonding directly to said substrate in areas of said substrate between said heater-lets.

whereby the power distribution over the entire substrate is selectively regulated by varying the density of the heater-lets in said first through third heating zones.

8. A heating device as claimed in claim 7, wherein the sizes of said second predetermined ones of said heater-lets are larger than the sizes of said first predetermined ones of said heater-lets so that the second power density of said second heating zone is higher than the first predetermined power density of said first heating zone.

9. A heating device as claimed in claim 8, wherein the sizes of said third predetermined ones of said heater-lets are larger than the sizes of said second predetermined ones of said heater-lets so that the third power density of said third heating zone is higher than the second predetermined power density of said second heating zone.

10. A heating device as claimed in claim 9, further including an electrically insulated barrier layer disposed on said adhesive layer.

11. A heating device as claimed in claim 10, further including a second adhesive layer disposed on said electrically insulated barrier layer.

12. A heating device as claimed in claim 11, further including a removable protective layer disposed on said second adhesive layer.

13. A planar heating device for attachment to a member to be heated comprising;

an electrically insulated substrate having a predetermined shape conforming to the member to be heated;

an electrical buss system on one surface of said substrate, including a pair of buss bars and two electrode patterns having a plurality of spaced apart parallel interdigitated electrodes, adjacent electrodes of said plurality of interdigitated electrodes connected to different ones of said pair of buss bars, each buss bar extending from one of a pair of terminal connection points along generally opposite portions of a peripheral edge of said substrate;

a plurality of heater-lets formed of an electrically resistive layer of material having a positive temperature coefficient, said plurality of heater-lets having varying sizes and shapes being deposited over said electrical buss system between adjacent electrodes of said interdigitated electrodes, each of said plurality of heater-lets being separated from its neighbor by spaces of varying sizes and shapes so as to form a plurality of individual heating areas of variable intensity; and

at least one adhesive layer being deposited over said electrically resistive layer including the spaces between said heater-lets, said adhesive layer contacting and bonding directly to said substrate in areas of said substrate between said heater-lets,

whereby the power distribution over the entire substrate is selectively regulated by varying the density of the heater-lets.