Electrically conductive stretchable and / or flexible INKS, additives for improving electrical conductivity of electrically conductive stretchable and / or flexible INKS, and products comprising same

Abstract

Provided is an additive for a stretchable and / or flexible electrically conductive ink, the additive comprising: small liquid molecules with a high dielectric constant; wherein the additive improves electrical conductivity of the stretchable and / or flexible electrically conductive ink, and wherein the stretchable and / or flexible electrically conductive ink comprises a binder and electrically conductive particles.

Description

ELECTRICALLY CONDUCTIVE STRETCHABLE AND / OR FLEXIBLE INKS, ADDITIVES FOR IMPROVING ELECTRICAL CONDUCTIVITY OF ELECTRICALLY CONDUCTIVE STRETCHABLE AND / OR FLEXIBLE INKS, AND PRODUCTS COMPRISING SAMEFIELD

[0001] The present disclosure generally relates to electrically conductive stretchable and / or flexible inks and additives for improving electrical conductivity of electrically conductive stretchable and / or flexible inks.BACKGROUND

[0002] Stretchable and / or flexible electrically conductive inks are used for printed electronics to manufacture wearables, textile devices and other stretchable and / or flexible devices and sensors in a variety of industries, including, e.g., the health, environmental, communications, lighting, display, and transportation industries. Currently available stretchable conductive inks show lower conductivity (or higher resistivity) compared to their non-stretchable counterparts, due mainly to the inability to add more conductive particles in the ink without compromising stretchability and / or flexibility.SUMMARY

[0003] In an aspect, there is provided an additive that when added to a stretchable and / or flexible electrically conductive ink improves electrical conductivity of the stretchable and / or flexible electrically conductive ink.

[0004] In a further aspect, there is provided a stretchable and / or flexible electrically conductive ink comprising any additive described herein in accordance with any of the aspects described herein.

[0005] In a further aspect, there is provided a stretchable and / or flexible electrically conductive ink comprising an additive, a binder and electrically conductive particles, wherein: the binder comprises neoprene, the electrically conductive particles comprise silver flake, and the additive comprises water, 35% hydrogen peroxide water solution, or formamide; and wherein the additive improves electrical conductivity of the stretchable and / or flexible electrically conductive ink.

[0006] In yet another aspect, there is provided a product comprising a stretchable and / or flexible electrically conductive ink comprising any additive described herein in accordance with any of the aspects described herein.BRIEF DESCRIPTION OF DRAWINGS

[0007] The following description is intended by way of example only, and illustrates only example aspects of electrically conductive stretchable and / or flexible inks and additives for improving electric conductivity and / or stretchability / flexibility of stretchable and / or flexible electrically conductive inks that are consistent with the subject-matter disclosed herein. For a better understanding of the variousaspects described herein and to show more clearly how they may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which:

[0008] FIG. 1 depicts a graph showing sheet resistivity of a stretchable and / or flexible electrically conductive ink comprising a neoprene binder and electrically conductive particles comprising silver flake, with and without deionized water as an additive, according to an example aspect of the present disclosure;

[0009] FIG. 2A depicts a graph showing rate of stretching vs. resistance of samples of electrically conductive S-3 ink on thermoplastic polyurethane (TPU) substrate;

[0010] FIG. 2B is a magnified view of the 0-50% segment of the “Rate of Stretching” axis of FIG. 2A;

[0011] FIG. 2C depicts a graph showing rate of stretching vs. resistance of samples of electrically conductive SH-3 ink on thermoplastic polyurethane (TPU) substrate; and

[0012] FIG. 2D is a magnified view of the 0-50% segment of the “Rate of Stretching” axis of FIG. 2C.DESCRIPTION

[0013] The following detailed description is provided with reference to the drawings herein. Example aspects are provided as illustrative examples so as to enable those skilled in the art to practice the subject-matter disclosed herein. It will be appreciated that further variations of the concepts and aspects disclosed herein are contemplated and are within the scope of the present disclosure. The examples of the present disclosure described herein may be used together in different combinations. In the following description, details are set forth in order to provide an understanding of the present disclosure. It will be readily apparent, however, that the present disclosure may be practiced without limitation to any of these details. Also, throughout the present disclosure, the terms “a” and “an” are intended to denote at least one of a particular element. The terms “a” and “an” may also denote more than one of a particular element. Additionally, the term “comprising” and its derivatives, as used herein, are intended to be open-ended terms that specify the presence of the stated features, elements, components, groups, integers, and / or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers, and / or steps (and the foregoing also applies to words having similar meanings, such as the terms “including”, “having” and their derivatives). The phrase “based on” means based at least in part on, the phrase “based upon” means based at least in part upon, the phrase “such as” means such as but not limited to, and the phrase “for example” or “e.g.” is similarly not limited to the specific examples identified. Ranges described herein encompass all values within the stated ranges, including the end values of the stated ranges, fractional values within the stated ranges (where suitable), and any sub-ranges within thestated ranges (e.g., “between 3 and 7” includes the values 3, 4, 5, 6, and 7, any fractional values in the stated range (such as 3.3, 6.24, etc.) and sub-ranges within the stated range, such as “between 3 and 6”, “between 5 and 7”, “between 4 and 6”, and so on). The term “approximately” means a variation of + / -5% in a stated parameter or a value of a stated parameter. Furthermore, in the present disclosure, an aspect showing a singular component should not be considered limiting; rather, the present disclosure is intended to encompass other aspects including a plurality of the same or similar component, and vice versa, unless explicitly stated otherwise herein. The present disclosure also encompasses presently known and future equivalents of the components referred to herein.

[0014] Stretchable and / or flexible electrically conductive inks are generally comprised of a mixture of a stretchable binder (such as neoprene), electrically conductive particles (such as silver, which may, e.g., comprise silver flake), a solvent, and additives. Additives typically used in stretchable and / or flexible electrically conductive inks may include, e.g., a heat stabilizer, anti-oxidant, particle dispersant, or UV-resistant agent. The additives may improve processability and environmental stability of the stretchable and / or flexible electrically conductive ink.

[0015] In an aspect, by adding small liquid molecules with very high polarity (i.e., high dielectric constant) as an additive to a stretchable and / or flexible electrically conductive ink (which, in some aspects, may contain a neoprene binder, and in further aspects, may contain electrically conductive particles comprising silver (such as silver flake)), the electrical conductivity of the stretchable and / or flexible electrically conductive ink may be improved, and in some aspects, a stretchable and / or flexible electrically conductive ink with electrical conductivity matching or at least comparable to that of commercial non-stretchable electrically conductive inks may be obtained (see, e.g., Experiments 2 and 3, below, in which, other than the addition of the tested additives, the tested example inks differed from the reference stretchable electrically conductive ink (S-3) in that the tested example inks did not contain particle dispersant and the coupling agent (organo-siloxane)).

[0016] Three different additives comprising small liquid molecules of high polarity (i.e., high dielectric constant) were tested, as shown in Table 1 . As used herein, “small liquid molecules” refers to additives comprising liquid molecules with a molecular weight of less than 1000 grams per mole (g / mol), and “high dielectric constant” or “high polarity” refers to dielectric constant values higher than 75. Table 1 , below, lists the dielectric constants of the three liquid additives tested:Table 1 : Dielectric Constants of Three Liquid Additives of High Polarity

[0017] Described below are experiments demonstrating the ability of the liquid additives identified in Table 1 to improve electrical conductivity of stretchable and / or flexible inks.

[0018] Experiment 1 : Adding Water to a Formulation comprising Water:Neoprene in a WeightRatio of 8.3%

[0019] FIG. 1 shows test results of a series of neoprene / silver flake-based stretchable and / or flexible electrically conductive inks with and without deionized water as an additive. The test results show that adding water to the formulation (in a weight ratio of deionized watermeoprene of 8.3%) significantly lowered the sheet resistivity of the stretchable and / or flexible electrically conductive inks by >29% within the range of silver / neoprene weight ratio tested. For Experiment 1 , testing samples were screen printed, sheet resistance was measured using the 4-point testing method, and thickness was measured using a micrometer. The stretchable and / or flexible electrically conductive inks were applied to a polyethylene terephthalate (PET) substrate.

[0020] Experiment 2: Adding Hydrogen Peroxide (35% water solution) to Formulations comprising Hydrogen Peroxide Water Solution:Neoprene in a Weight Ratio of 8.3%

[0021] Table 2 shows the measured sheet resistivity of neoprene / silver flake-based stretchable and / or flexible electrically conductive inks after adding 35% hydrogen peroxide water solution (i.e., a solution of hydrogen peroxide in water at a ratio of 7 parts hydrogen peroxide to 20 parts water) in a weight ratio of 35% hydrogen peroxide water solutionmeoprene of 8.3%. For comparison, Table 2 also shows the sheet resistivity of two commercial non-stretchable electrically conductive inks, DuPont™ 5025 and Henkel™ PF-050. The results demonstrate that, as compared to ink “S-3” shown in Table 2 (which does not contain hydrogen peroxide), adding hydrogen peroxide water solution (e.g., a 35% hydrogen peroxide water solution) as the additive significantly lowers the sheet resistivity of neoprene / silver-based stretchable and / or flexible electrically conductive inks. The results also show that sheet resistivity comparable to those of the commercial non-stretchable electrically conductive inks can be achieved for stretchable and / or flexible neoprene / silver flake-based electrically conductive inks by adding hydrogen peroxide (e.g., as a 35% hydrogen peroxide water solution) as the additive.Table 2: Measured Sheet Resistivity of Neoprene / Silver Flake Inks containing 35% HydrogenPeroxide Water Solution as an Additive

[0022] For Experiment 2, testing samples were screen printed, sheet resistance was measured using the 4-point testing method, and thickness was measured using a micrometer. Table 2 also shows that the sheet resistivity of the formulated stretchable and / or flexible electrically conductive inks is much lower on thermoplastic polyurethane (TPU) substrate than on polyethylene terephthalate (PET) substrate. This is believed to be due to the thermal expansion coefficient of the TPU substrate better matching that of the formulated stretchable and / or flexible electrically conductive inks than does that of the PET substrate, so that less thermal stress is produced inside the printed conductor during the curing stage.

[0023] Experiment 3: Adding Formamide to Formulations comprising Formamide:Neoprene in a Weight Ratio of 8.3%

[0024] Table 3 shows the measured sheet resistivity of neoprene / silver flake-based stretchable and / or flexible electrically conductive inks after adding formamide in a weight ratio of formamidemeoprene of 8.3%. For comparison, Table 3 also shows the sheet resistivity of two commercial non-stretchable electrically conductive inks, DuPont™ 5025 and Henkel™ PF-050. The results demonstrate that, as compared to ink “S-3” shown in Table 3 (which does not contain formamide), adding formamide as the additive significantly lowers the sheet resistivity ofneoprene / silver-based stretchable and / or flexible electrically conductive inks. The results also show that sheet resistivity comparable to those of the commercial non-stretchable electrically conductive inks can be achieved for stretchable and / or flexible neoprene / silver flake-based electrically conductive inks by adding formamide as the additive.Table 3: Measured Sheet Resistivity of Neoprene / Silver Flake Inks containing Formamide as an Additive

[0025] For Experiment 3, testing samples were screen printed, sheet resistance was measured using the 4-point testing method, and thickness was measured using a micrometer. Table 3 also shows that the sheet resistivity of the formulated stretchable and / or flexible electrically conductive inks is much lower on thermoplastic polyurethane (TPU) substrate than on polyethylene terephthalate (PET) substrate. This is believed to be due to the thermal expansion coefficient of the TPU substrate better matching that of the formulated stretchable and / or flexible electrically conductive inks than does that of the PET substrate, so that less thermal stress is produced inside the printed conductor during the curing stage.

[0026] By adding any of the additives described herein to a stretchable and / or flexible electrically conductive ink, it is expected that electrical conductivity of the stretchable and / or flexible electrically conductive ink may improve (as compared to a stretchable and / or flexible electrically conductive ink without the additive), and further, as a result of the addition of the additive, the amount of theelectrically conductive particles in the ink formulation may be reduced while maintaining (or surpassing) a certain degree or value of electrical conductivity, which may present cost savings. For example, in a stretchable and / or flexible electrically conductive ink comprising neoprene as the binder and silver (e.g., silver flake) as the electrically conductive particles, the addition of an additive comprising water (e.g., deionized water), hydrogen peroxide water solution (e.g., a 35% hydrogen peroxide water solution) or formamide may improve electrical conductivity of the ink which may accordingly allow for a reduction in the amount of the electrically conductive particles (e.g., silver, such as silver flake) required in the ink formulation in order to effect a certain degree of electrical conductivity. In some aspects, such additives may allow for the amount of the electrically conductive particles (e.g., silver, such as silver flake) to be reduced while also improving the electrical conductivity of the ink, as compared to the ink when not containing such additive.

[0027] Accordingly, in accordance with some aspects, there is provided herein an additive that when added to a stretchable and / or flexible electrically conductive ink improves electrical conductivity of the stretchable and / or flexible electrically conductive ink. Additives identified as yielding such improvements in electrical conductivity, in some aspects, comprise small liquid molecules having a high dielectric constant, such as additives with a molecular weight less than 1000 g / mol, and a dielectric constant higher than 75. In some aspects, additives resulting in such improvement in the electrical conductivity of stretchable and / or flexible electrically conductive inks include water (such as deionized water), hydrogen peroxide water solution (such as 35% hydrogen peroxide water solution), and formamide, although it will be appreciated that other additives having a sufficiently small molecular size and sufficiently high dielectric constant or polarity may be suitable to effect an improvement in electrical conductivity as compared to stretchable and / or flexible electrically conductive inks not containing such additive.

[0028] As described above, stretchable and / or flexible electrically conductive inks may contain a binder (such as neoprene), an additive, a solvent, and electrically conductive particles (such as silver particles, including, e.g., silver flake). In some aspects, the addition of the example additives described herein into the stretchable and / or flexible electrically conductive inks in an additive:binder weight ratio of between 0.02 to 0.2 (such as an additive:binder weight ratio of 0.083, as shown in Experiments 2 and 3 described above) may yield improvements in the electrical conductivity of stretchable and / or flexible electrically conductive inks.

[0029] In accordance with some aspects, the addition of the example additives described herein, such as in the additive:binder weight ratios described herein, may further yield improvements in the stretchability and / or flexibility of the stretchable and / or flexible electrically conductive inks. FIGs. 2A and 2B show the rate of stretching and / or flexibility vs. resistance of samples of electrically conductive S-3 ink, which did not contain any of the additives described herein (see Tables 2 and 3, above), on thermoplastic polyurethane (TPU) substrate. Each S-3 sample in FIGs. 2A and 2B had an initialsample length of 10 cm, and two S-3 conductor samples were tested, one 5 mm wide and one 10 mm wide. Comparatively, FIGs. 2C and 2D show the rate of stretching and / or flexibility of samples of electrically conductive SH-3 ink, which contained 35% hydrogen peroxide water solution as an additive (see Table 2, above), on thermoplastic polyurethane (TPU) substrate. Each SH-3 sample in FIGs. 2C and 2D had an initial sample length of 10 cm, and three SH-3 conductor samples were tested, one 2.5 mm wide, one 5 mm wide, and one 10 mm wide. It can be seen by comparison of FIGs. 2C and 2D to FIGs. 2A and 2B that by simply adding 35% hydrogen peroxide water solution as an additive, both electrical conductivity and stretchability / flexibility were significantly improved. The improvement in the stretchability / flexibility of the stretchable and / or flexible electrically conductive inks is expected to be due to the reduction in the amount of electrically conductive silver flake particles in the formulation, as made possible by the addition of the 35% hydrogen peroxide water solution additive (as described above).

[0030] In accordance with some aspects, there is also provided herein a stretchable and / or flexible electrically conductive ink comprising any additives described herein, in accordance with any of the aspects described herein. There is also provided herein a product comprising any such stretchable and / or flexible electrically conductive ink, comprising any product, including components, devices, and the like, for which any such stretchable and / or flexible electrically conductive ink would be suitable, including, e.g., medical patches, textiles (such as functional textiles), wearables, sensors, wearable sensors, energy harvesters, smart surfaces, antennas, lighting, displays, electrodes, electrical connections, and / or any other suitable components or devices requiring stretchable and / or flexible electrically conductive inks. Generally, it is expected that the aspects described herein could be used for any suitable flexible and / or stretchable component or device fabrication.

[0031] The terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting of the disclosure. It will be appreciated that the above-disclosed and other features, compositions, ingredients, combinations, functions, and steps, or alternatives thereof, may be combined into other compositions, combinations, systems, applications or methods. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements to any of the aspects described herein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure. Any method steps described herein may be performed in any suitable sequence, order or arrangement, despite that particular example sequences, orders or arrangements have been shown and / or described herein.

Claims

CLAIMS1 . An additive for a stretchable and / or flexible electrically conductive ink, the additive comprising: small liquid molecules with a high dielectric constant; wherein the additive improves electrical conductivity of the stretchable and / or flexible electrically conductive ink.

2. The additive of claim 1 wherein the additive has a molecular weight of less than 1000 g / mol.

3. The additive of claim 1 or claim 2 wherein the additive has a dielectric constant higher than 75.

4. The additive of any one of claims 1 to 3 wherein the additive comprises water.

5. The additive of any one of claims 1 to 3 wherein the additive comprises hydrogen peroxide water solution.

6. The additive of claim 5 wherein the additive comprises a 35% hydrogen peroxide water solution.

7. The additive of any one of claims 1 to 3 wherein the additive comprises formamide.

8. The additive of any one of claims 1 to 7 wherein the stretchable and / or flexible electrically conductive ink comprises a binder and electrically conductive particles, and wherein the additive is said added to the stretchable and / or flexible electrically conductive ink in an additive:binder weight ratio of between 0.02 to 0.2.

9. The additive of claim 8 wherein the additive:binder weight ratio is 0.083.

10. The additive of claim 8 or claim 9 wherein the binder comprises neoprene and the electrically conductive particles comprise silver particles.11 . The additive of claim 10 wherein the silver particles comprise silver flake.

12. A stretchable and / or flexible electrically conductive ink comprising the additive of any one of claims 1 to 11.

13. A product comprising the stretchable and / or flexible electrically conductive ink of claim 12.

14. The product of claim 13 wherein the product comprises a medical patch, textile, wearable, sensor, wearable sensor, energy harvester, smart surface, antenna, lighting, display, electrode, electrical connection, component, and / or device.

15. A stretchable and / or flexible electrically conductive ink comprising an additive, a binder and electrically conductive particles, wherein: the binder comprises neoprene,the electrically conductive particles comprise silver flake, and the additive comprises water, 35% hydrogen peroxide water solution, or formamide; and wherein the additive improves electrical conductivity of the stretchable and / or flexible electrically conductive ink.

16. The stretchable and / or flexible electrically conductive ink of claim 15 comprising a weight ratio of the additive to the binder of between 0.02 to 0.2.

17. The stretchable and / or flexible electrically conductive ink of claim 16 wherein the weight ratio of the additive to the binder 0.083.

18. A product comprising the stretchable and / or flexible electrically conductive ink of any one of claims 15 to 17.

19. The product of claim 18 wherein the product comprises a medical patch, textile, wearable, sensor, wearable sensor, energy harvester, smart surface, antenna, lighting, display, electrode, electrical connection, component, and / or device.

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