Electrically Conductive PTC Screen Printable Ink with Double Switching Temperatures and Method of Making the Same

Abstract

The invention provides an electrically conductive screen-printable PTC ink with double switching temperatures, which comprising by weight based on total composition, 10-30 wt % conductive particles; 5-15 wt % polymer resin 1; 5-15 wt % polymer resin 2; 40-80 wt % organic solvent; e) 1-5 wt % other additives.

Claims

1. A ink composition having two distinct positive temperature coefficient (PTC) characteristics at two different temperature ranges, comprising: a) 5-15 wt % thermally active polymer resin-1 having a melting point of 30-70° C. and providing the first PTC characteristic in the lower temperature range below 70° C. b) 5-15 wt % thermally active polymer resin-2 having a melting point of 70 -140° C. and providing the second PTC characteristic in the higher temperature range above 70° C.; c) 10-30 wt % carbon black; d) 40-80 wt % organic solvent having a boiling point higher than 100° C. and capable to dissolve both the polymer resin-1 and polymer resin-2; e) 0-5 wt % additives of enhanced dispersing/wetting and rheology properties.

2. The ink composition having two distinct positive temperature coefficient (PTC) characteristics at two different temperature ranges of claim 1, where the thermally active polymer resin-1 is a crystalline polymer.

3. The ink composition having two distinct positive temperature coefficient (PTC) characteristics at two different temperature ranges of claim 1, where the thermally active polymer resin-1 is a semi-crystalline polymer.

4. The ink composition having two distinct positive temperature coefficient (PTC) characteristics at two different temperature ranges of claim 1, where the thermally active polymer resin-2 is a non-crystalline polymer.

5. A film having two distinct positive temperature coefficient (PTC) characteristics at two different temperature ranges made from the ink composition having two distinct positive temperature coefficient (PTC) characteristics at two different temperature ranges of claim 1.

6. A electric device having two distinct positive temperature coefficient (PTC) characteristics at two different temperature ranges made from the ink composition having two distinct positive temperature coefficient (PTC) characteristics at two different temperature ranges of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 presents a typical temperature-resistance curve of the PTC composition in the market.

[0012] FIG. 2 presents the temperature-resistance curves of the PTC ink samples 1-3.

DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention provides an electrically conductive PTC screen-printable ink with double switching temperatures and method of making the same. The electrically conductive PTC ink not only presents an efficient PTC effect at lower temperatures but also shows a PTC effect at higher temperatures. When the present PTC ink is applied in a self-regulating heating element with low regulated temperatures (<70° C.), the safety risks area is completely eliminated.

[0014] The PTC ink with double switching temperatures is a typical screen-printable ink produced by ink/coating technology, which comprises: [0015] (1) 10-30 wt % conductive particles; [0016] (2) 5-15 wt % polymer resin 1; [0017] (3) 5-15 wt % polymer resin 2; [0018] (4) 40-80 wt % organic solvent; [0019] (5) 1-5 wt % other additives

[0020] The conductive particles can be one or mixture of more than one of the metallic powder, metal oxide, carbon black and graphite.

[0021] The polymer resin 1 is some kind of crystalline or semi-crystalline polymer, such as polyurethane, nylon, and polyester.

[0022] The polymer resin 2 is some kind of non-crystalline polymer, such as acrylic resin. The selection of the solvent is based on its proper boiling point and the good solubility of polymer resins used. The polymer resin 1 and resin 2 are completely dissolved in the organic vehicle prior to blending with other components. Any organic, inert liquid may be used as the solvent for the medium (vehicle) so long as the polymer is fully solubilized.

[0023] The preferred solvents are selected from MEK, N-methyl pyrolidone (NMP), toluene, xylene, and the like.

[0024] The other additives include a dispersing/wetting additive and a rheology additive.

[0025] Specifically, this invention discloses an ink composition having two distinct positive temperature coefficient (PTC) characteristics at two different temperature ranges, comprising: [0026] a) 5-15 wt % thermally active polymer resin-1 having a melting point of 30-70° C. and providing the first PTC characteristic in the lower temperature range below 70° C.; preferably being a crystalline polymer or a semi-crystalline polymer.

[0027] b) 5-15 wt % thermally active polymer resin-2 having a melting point of 70 -140° C. and providing the second PTC characteristic in the higher temperature range above 70° C.; preferably being a non-crystalline polymer [0028] c) 10-30 wt % carbon black. [0029] d) 40-80 wt % organic solvent having a boiling point higher than 100° C. and capable to dissolve both the polymer resin-1 and polymer resin-2. [0030] e) 0-5 wt % additives of enhanced dispersing/wetting and rheology properties.

[0031] The invented PTC ink is preferably prepared according to the procedure consisting of the following steps. 1) The preparation of 10-30 wt. % polymer solution. For example, 80.0 grams of N-methyl pyrolidone is firstly heated to 80° C. and then 10.0 grams of polyurethane and 10.0 grams of poly(methyl methacrylate) are added slowly into the system. The mixture is heated at 80° C. for 8 hours and yielding a homogenous solution. 2) The preparation of ink base. A dispersing additive 1.0-10.0 wt.% based on the total ink base is firstly added into the above polymer solution under mechanically stirring. Then, the carbon black 30-60 wt. % based on the total ink base is added slowly into the solution under mechanically stirring. This mixture is then subjected to a three-roll mill to assure proper dispersion of the carbon black to form a paste-like ink base. During the three-roll milling, a rheology additive 1.0-10.0 wt. % based on the total ink base may be added to enhance the screen-printing properties of the ink base. 3) The preparation of final PTC ink composition. The final PTC ink can be obtained by mechanically mixing the above polymer solution and ink base at certain ratios range from 0.5/1 to 1/1. The ratios depend on the needs of the application design such as the desired starting resistance.

[0032] The resulting PTC ink is applied to substrates such as polyester films (DuPont Teijin films) by the screen-printing process. After printing the PTC ink on a polyester film, it is cured in an oven at 120° C. for 10 minutes. Subsequently, a conductive paste suitable for use on polyester substrates such as DuPont 5025 silver paste is printed over edges of the PTC ink and cured at 120° C. for 5 minutes. The cured film is tested for resistance change with temperature. The resistance of the cured PTC film is measured as a function of temperature so the PTC characteristics are determined.

EXAMPLES

[0033] The invention will now be described in more detail with reference to the following examples. However, it should be understood that these examples are given for the purpose of illustration only and are not intended to limit the scope of the present invention.

[0034] Compositions for the Examples below are summarized in TABLE 1, where all component concentrations are expressed as percentage by weight based on the total ink composition.

TABLE-US-00001 TABLE 1 Polymer Polymer Carbon Dispersing Rheology Resin 1 Resin 2 black Solvent additive additive Examples (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) Example 1 8.0 8.0 23.0 56.0 2.00 3.00 Example 2 10.0 10.0 21.0 55.0 1.50 2.50 Example 3 12.0 12.0 19.0 54.0 1.00 2.00

Example 1

[0035] The PTC ink and film were made following the typical procedure described above. The polymer resin, carbon black, solvent, dispersing additive, and rheology additive used in this example are respectively polyurethane, carbon black REGAL 350R, NMP, BYK-220S, and BYK-410, and their contents in the PTC compositions are listed in TABLE-1. The yielded resistivity at 25° C. of the PTC film from this example is 3.9 Kohm/sq. FIG. 2 show the temperature-resistance curves of it.

Example 2

[0036] The same conditions were used as Example 1, but more polymer solution was added into the system. The resistivity at 25° C. of the PTC film from this example is 8.0 Kohm/sq. FIG. 2 show the temperature-resistance curves of it.

Example 3

[0037] The same conditions were used as Example 1, but more polymer solution was added into the system. The resistivity at 25° C. of the PTC film from this example is 15.0 Kohm/sq. FIG. 2 show the temperature-resistance curves of it.

[0038] As shown in FIG. 2, the PTC ink of the present invention presents good PTC effect, at 60° C., the PTC ratio RT/R-25 is higher than 10, the value of sample 3 is even higher than 20. As the temperature is raised further, no any NTC effect appear, it still present good PTC effect, at 120° C., the PTC ratio RT/R-25 is higher than 30, the value of sample 3 is even higher than 50. When the present PTC ink is applied in a self-regulating heating element with low regulated temperatures (<70° C.), the safety risks area is completely eliminated.

TABLE-US-00002 REFERENCE CITED U.S. PATENT DOCUMENTS 4,628,187 A December 1986 Sekiguchi et al. 5,198,639 A March 1993 Shafe et al. 5,227,946 A July 1993 Jacobs et al. 5,344,591A September 1994 Smuckler et al. 5,714,096 A February 1998 Dorfman et al. 8,496,854 B July 2013 Franciscus Petrus Maria et al. FOREIGN PATENT DOCUMENTS JP 2008293672 December 2008 Takahito et al. JP 2009151976 July 2009 Keizo et al. JP 2009199794 September 2009 Akihiro et al. EP 0311142 April 1989 Jacobs et al.