Patent Application
20160183328
1. Field of the Disclosure
The present invention relates to the design, construction and manufacture of a novel high temperature heater utilizing a resistive film and a high temperature polymer thick film conductor paste.
2. Description of the Related Art
Silver (Ag)-based thick film pastes for application to polymeric substrates are well-known in the state of the art. Such pastes are typically dispersions of Ag flakes and/or spherical Ag powders in organic vehicles comprising polymeric resins dissolved in various solvents. These pastes are typically 40 to 85 weight percent Ag, with the paste viscosities being typically 5 to 250 Pas at shear rates of 0.4/sec at room temperature. The solvents used in such pastes are those best suited to screen printing in that they are non-toxic, do not have an offensive smell, dry in appropriate times and temperatures, have adequate working time on printing screens, and dissolve the given polymeric resins completely to make a solution which has proper viscosity for screen printing when mixed with the powders in various ratios with those powders dispersed into the solution. A primary issue, however, with such technology is that the polymeric resins contained in common Ag thick film pastes are not capable of sustained high temperature operation. The polymers included in such pastes are, for example, phenoxy, polyolefins, polyurethanes, and acrylics and the like, with glass transition temperatures and thermal degradation limits which preclude effective use at continuously high temperatures. Such polymers would decompose and render the thick film prints useless at those elevated and continuous temperatures. As such, using these types of compositions are not possible as electrical bus bars for polymeric heating films such as like Kapton® 200RS100 without eventual degradation and possible safety and long term performance consequences.
Polymers based on polyimide chemistries offer the possibility of continuous high temperature operation if they can be used in an equivalent polymer thick film paste. A particular issue with current commercially available polyimide resins is that they are typically supplied as only dissolved in solvents such as DMAC and/or NMP, or as dried polymer powders which are only soluble in such solvents. Solvents such as DMAC and NMP and the like are not amenable to use as solvents in screen printing pastes due to their smell, toxicity, poorly-matched drying rates and reactivity with equipment and printing screens. And such commercially available solutions of polyimides in DMAC and/or NMP are typically dilute with respect to the polyimide content resulting in organic solutions that are too low in viscosity and too low in resin content for use as the basis for a thick film paste. As such, commercially available polyimide solutions and polyimide powders are not amenable to use as the basis for formulating and manufacturing a thick film paste.
Needed in the art is a replacement for the standard polymeric composition of routine and well-known electrically Ag conductive thick film pastes which make printed and dried paste survivable at continuously elevated temperatures and is an enabling technology for using, e.g. the like Kapton® 200RS100, film as an electrically resistive high temperature heater in temperature ranges attractive for devices which require temperatures of approximately 200° C.
The present invention is directed to a polymeric composition of electrically Ag conductive thick film pastes with a polyimide type of polymer which makes the printed and dried paste survivable at continuously elevated temperatures and is an enabling technology for using, e.g. the like Kapton® 200RS100, film as an electrically resistive high temperature heater in temperature ranges attractive for devices which require temperatures of a maximum of approximately 100 to 210° C.
In a first embodiment, the present invention is directed to a method to prepare a high temperature heater construct including an electrically conductive polyimide film to which bus bars made of electrically conductive polymer thick film paste containing a dispersion of Ag particles in a thick film paste are applied. The technology is enabling in using the conductive polyimide film in that the Ag polyimide-based paste allows the printing and construction of an electrical contact with the polyimide film such that the polyimide film can then be used as an electrode. For example, like Kapton® 200RS100 film is an electrically resistive high temperature heater in temperature ranges attractive for devices which require temperatures of approximately 25° C. to 210° C. However adequate thick film paste compositions enabling its use as an electrode do not exist.
In another embodiment, the invention is directed to a process for the preparation of a high temperature heater wherein the electrode is made of the thick film paste deposition on the electrically resistive polyimide film is folded or curved to be placed into a device for heating a substance such as food or water.
In a first embodiment, the invention is directed to a method to prepare a high temperature heater including preparing an electrically high temperature conductive paste; printing and drying the paste on an electrically resistive polyimide film and attaching a power source to the electrically conductive high temperature paste electrodes. The electrically high temperature conductive paste includes a polyimide polymer represented by formula I:
wherein X is C(CH3)2, O, S(O)2 or C(CF3)2, O-Ph-C(CH3)2-Ph-O, O-Ph-O— or a mixture of two, or more of C(CH3)2, O, S(O)2, and C(CF3)2, O-Ph-C(CH3)2-Ph-O, O-Ph-O—;
wherein Y is diamine component or mixture of diamine components selected from the group consisting of:
m-phenylenediamine (MPD), 3,4′-diaminodiphenyl ether (3,4′-ODA), 4,4′-diamino-2,2′-bis(trifluoromethyl)biphenyl (TFMB), 3,3′-diaminodiphenyl sulfone (3,3′-DDS), 4,4′-(Hexafluoroisopropylidene)bis(2-aminophenol) (6F-AP) bis-(4-(4-aminophenoxy)phenyl)sulfone (BAPS) and 9,9-bis(4-aminophenyl)fluorene (FDA); 2,3,5,6-tetramethyl-1,4-phenylenediamine (DAM), 2,2-bis[4-(4-aminophenoxyphenyl)]propane (BAPP), 2,2-bis[4-(4-aminophenoxyphenyl)] hexafluoropropane (HFBAPP), 1,3-bis(3-aminophenoxy) benzene (APB-133), 2,2-bis(3-aminophenyl)hexafluoropropane, 2,2-bis(4 aminophenyl)hexafluoropropane (Bis-A-AF), 4,4′-bis(4-amino-2-trifluoromethylphenoxy) biphenyl, 4,4′-[1,3-phenylenebis(1-methyl-ethylidene)]bisaniline (Bisaniline-M) with the proviso that:
i. if X is O, then Y is not m-phenylenediamine (MPD), bis-(4-(4-aminophenoxy)phenyl)sulfone (BAPS) and 3,4′-diaminodiphenyl ether (3,4′-ODA); BAPP, APB-133, Bisaniline-M;
ii. if X is S(O)2, then Y is not 3,3′-diaminodiphenyl sulfone (3,3′-DDS);
iii. if X is C(CF3)2, then Y is not m-phenylenediamine (MPD), bis-(4-(4-aminophenoxy)phenyl)sulfone (BAPS), 9,9-bis(4-aminophenyl)fluorene (FDA), and 3,3′-diaminodiphenyl sulfone (3,3′-DDS);
iv. if X is O-Ph-C(CH3)2-Ph-O or O-Ph-O—, then Y is not m-phenylene diamine (MPD), FDA, 3,4′-ODA, DAM, BAPP, APB-133, bisaniline-M.
This paste is advantageous in that it contains solvents which are not based on the typical DMAC or NMP solvents normally used with polyimides, but based on solvents which are more amenable to screen printing, having less toxicity and better handling, viscosity and drying processing windows for routine screen printing. Because this conductive paste is based on polyimide chemistry, it is also thermally stable after printing and drying and enables an electrical connection to the polymeric resistive film such that a high temperature electrode and subsequent heater can be made.
More particularly, the present embodiment relates to the formulation and application of a Ag or other conductive metal powder in an organic solution of a solvent soluble polyimide to form a thick film paste, those solvents being amenable to screen printing, including such solvents as Dowanol DPM, Dowanol PMA, di-basic esters, lactamides, acetates, diethyl adipate, texanol, glycol ethers, carbitols, and the like. Such solvents can dissolve the solvent-soluble polyimide resin and render a solution to which Ag and other electrically conductive metal powders can be dispersed, rendering a screen-printable thick film paste composition. Solution of the polyimide resin in the selected solvents is possible through the selection of the monomers used to make the polyimide. Metals other than Ag, such as Ni, Cu, Pt, Pd and the like, and powders of various morphologies and combinations of those morphologies are possible for use in the present invention.
Referring to
Referring to
To enable electrical connection to the film, the thick film paste having a dispersion of silver particles in a polyimide resin vehicle is used provide electrical connection through the formation of spaced bus bars via screen printing. This paste comprising the bus bars can be connected to power sources using electrical clamps or clips commonly known in the industry.
Preferably the paste includes an inorganic filler of Ag in the amount of 40 to 80% by weight and has a thickness of 5 to 40 microns dried, thereby have an electrical resistivity of about 4 to 70 mohms/sq/mil. Such a high temperature heater could be, for example, wrapped around a thermally conducting (non-electrical conducting) container for supply of heat to a device for heating food or water (refer to
In another embodiment, the invention is directed to a device for maintaining the temperature of materials. The device would include a base portion having a chamber section with a high temperature heater contacting the chamber section. In addition, the device would include a power source for the high temperature heater and a lid for the chamber section. The electrically conductive high temperature paste comprises a polyimide resin as represented by formula I:
wherein X is C(CH3)2, O, S(O)2 or C(CF3)2, O-Ph-C(CH3)2-Ph-O, O-Ph-O— or a mixture of two, or more of C(CH3)2, O, S(O)2, and C(CF3)2, O-Ph-C(CH3)2-Ph-O, O-Ph-O—; wherein Y is diamine component or mixture of diamine components selected from the group consisting of:
m-phenylenediamine (MPD), 3,4′-diaminodiphenyl ether (3,4′-ODA), 4,4′-diamino-2,2′-bis(trifluoromethyl)biphenyl (TFMB), 3,3′-diaminodiphenyl sulfone (3,3′-DDS), 4,4′-(Hexafluoroisopropylidene)bis(2-aminophenol) (6F-AP) bis-(4-(4-aminophenoxy)phenyl)sulfone (BAPS) and 9,9-bis(4-aminophenyl)fluorene (FDA); 2,3,5,6-tetramethyl-1,4-phenylenediamine (DAM), 2,2-bis[4-(4-aminophenoxyphenyl)]propane (BAPP), 2,2-bis[4-(4-aminophenoxyphenyl)] hexafluoropropane (HFBAPP), 1,3-bis(3-aminophenoxy) benzene (APB-133), 2,2-bis(3-aminophenyl)hexafluoropropane, 2,2-bis(4-aminophenyl)hexafluoropropane (Bis-A-AF), 4,4′-bis(4-amino-2-trifluoromethylphenoxy) biphenyl, 4,4′-[1,3-phenylenebis(1-methyl-ethylidene)] bisaniline (Bisaniline-M)
with the proviso that:
i. if X is O, then Y is not m-phenylenediamine (MPD), bis-(4-(4-aminophenoxy)phenyl)sulfone (BAPS) and 3,4′-diaminodiphenyl ether (3,4′-ODA); BAPP, APB-133, Bisaniline-M
ii. if X is S(O)2, then Y is not 3,3′-diaminodiphenyl sulfone (3,3′-DDS);
iii. if X is C(CF3)2, then Y is not m-phenylenediamine (MPD), bis-(4-(4-aminophenoxy)phenyl)sulfone (BAPS), 9,9-bis(4-aminophenyl)fluorene (FDA), and 3,3′-diaminodiphenyl sulfone (3,3′-DDS);
iv. if X is O-Ph-C(CH3)2-Ph-O or O-Ph-O—, then Y is not m-phenylene diamine (MPD), FDA, 3,4′-ODA, DAM, BAPP, APB-133, bisaniline-M.
This polyimide resin is dissolved in screen-printing solvents as described above, and then electrically conductive powders dispersed within the solution to from a thick film paste which is then printed on the film, dried, and formed into the electrode.
In an embodiment, the heater or heating device may be used in applications such as: rigid, semi rigid, flexible, semi flexible, single sided, multilayer additive or semi-additive printed heating applications including but not limited to: mobile devices, power electronics, automotive, avionics, aviation, green power, deicing et. Al., high reliability, high speed, high frequency, telecom, medical, wearable, energy storage and wind power, transportation; train, boat, clothing, industrial processes, and cooking applications.
The concepts described herein will be further described in the following examples, which do not limit the scope of the invention described in the claims.
A polyimide resin was prepared in the dry and powdered state by reacting monomers TFMB, 6FAP and 6FDA in a ratio of 33/10/57 through the well-known process of first making polyamic acid in DMAC solvent, controlling the molecular weight of said polyamic acid with end-capping additives, then chemically imidizing and precipitating the polyimide polymer using methanol neat additions to the DMAC solution. The precipitate was washed several times with methanol neat, filtered and then dried at approximately 200 C to form a dry and handleable powder and to eliminate DMAC residuals to below 0.1% basis weight. The resulting powder was dry, fluffy and stored at room temperature.
The polymer of Example 1 was dissolved in a solvent which was favorable for use in screen printing. Such solvents comprise of, but are not limited to: dibasic esters, Dowanol solvents, acetates, carbitols, ethers, glycol ethers, triethyl phosphate, diethyl adipate, and the like. In all cases a ratio of approximately 5 to 50% resin and 95 to 50% solvent was used, with various combinations of chemically different solvents used. The polyimide resin easily dissolved in these solvents, and viscosities of about 5 to 250 Pas at a shear rates of 0.4/sec were measured at room temperature. Such solutions were temperature and time stable, with the polyimide resin dissolved completely in the solvents to from a clear and translucent solution.
The polyimide solution of Example 2 was used as the basis for the manufacture of a polymer thick film paste. The polyimide solution was mixed with Ag particulates of sizes typically of below 20 microns in largest dimension, those particulates being spherical or flaked in nature, or mixtures thereof. Typical ratios of polymeric solution and powders were 60/40 powder/polymer solution, but this varied from 80/20 to 50/50. Flaked Ag is the preferred powder morphology since it gives the highest electrical conductivity, but spherical Ag and mixtures of flake and spherical are possible. Furthermore, use of other electrically conductive metal powders are possible including, but not limited to, Cu, Pt, Pd, Ni, Au and Ag-coated Cu.
Film heater samples made from the polymer thick film paste of Example 3 were prepared by both screen printing and lab paint masking plus oven drying techniques onto Kapton® 200RS100 as shown in
The Kapton® 200RS100 resistive film and conductor paste composition structure proved to be capable of thermal cycling from room temperature to temperatures around 200 C, and stable when heated in air for more than 700 hours at temperature using an applied voltage of approximately 220 VAC. Such composites structures could be used for high temperature heaters in a variety of electrical devices.
A polymer thick film paste of Example 3 was screen printed as two electrodes (positive and negative bus bars) with dimensions of 0.5 cm width×4.5 cm length with a trace spacing of 3.0 cm between electrodes as shown in
| Number | Date | Country | |
|---|---|---|---|
| 62093021 | Dec 2014 | US |
