THREAD

Technical Field of the Invention

The invention relates to a production method of conductive and stretchable thread.

The invention more particularly relates to a production method of conductive and stretchable thread which is obtained by applying Ag nanowire (AgNW) on pre- stretched multifilament fibers or elastic threads.

Background of the Invention

Conductive threads present creative means used for adapting various electronic connections on the garment. Such threads are capable of carrying current for power and signals. They have a structure that is more easily adaptable than the method used in traditional printed circuits. The conductive threads are produced independent of the textile products and integrated in the textile products as an additional part.

The metal wires used instead of conductive thread, on the other hand, have an adverse impact on the cloth form and handle. The garments produced with such fabrics do not meet the comfort standards expected by the users.

Another material used instead of conductive thread is stretchable polymer films. Stretchable conductive materials can be obtained using these films. However, such films prevent the body from breathing as they are adhered to the fabric surface or skin. Various developments have been made in the art in order to overcome these problems.

The U.S. Patent Application Numbered US2003209003 in the state of the art discloses an electrically conductive thread comprising metal fibers. The thread consists of stainless steel fibers. The conductive thread comprises an elongated element which has an outer surface being provided out of metal or metal alloy having a lower specific electrical resistance as the stainless steel fibers.

Another prior art document U.S. Patent Application No. US2009145533 discloses an electrically conductive elastic thread and the production method thereof. The electrically conductive electric composite thread comprises an elastic member that is surrounded by at least one conductive covering filament(s). The elastic member has a predetermined relaxed unit length (L) and a predetermined drafted length of NxL. (N is a number preferably in the range from 1.0 to 8.0).

The Chinese Patent Application Numbered CN103820909 in the state of the art discloses a conductive thread, made by wrapping a thread with a metal nanowire and carbon nanomaterial, and a production method thereof. First, the thread is soaked in a metal nanowire solution, evaporated and dried, followed by obtaining the metal nanowire wrapped conductive thread. As a second alternative, the metal nanowire wrapped thread is soaked in carbon nanomaterial solution, evaporated and dried, and these steps are repeated several times. The production method is very simple, easy for industrialized production and applicable to production of textile electronics.

Another prior art document U.S. Patent Application No. US2007059524 discloses an electrically conductive and elastically stretchable hybrid thread, the production method of such thread and how it will be produced as a textile product. The elastically stretchable core filament is surrounded by an electrically conductive fiber sheath. This results in improved technical properties of a hybrid thread of this kind in conjunction with a simplified manufacturing method. However, the threads disclosed in the documents mentioned above have problems including limited elongation, losing conductive properties subsequent to elongation, etc. Moreover, some of the basic problems as to the systems in which the threads in the state of the art or similar threads are used include: the final product not being woven in the fabric, but being provided in the fabric as an additional part; the electronic devices not being washable; the fabric being non- resistant against elongation and flexion.

In the art, PDMS, a flexible polymer film, is combined with many conductive materials such as Ag nanowire, liquid metal, and thus used in wearable electronic applications. This film allows for producing flexible conductors. Nevertheless, it is used by being adhered to the body since it cannot be transformed into fabric form. This, in turn, prevents the contact of the skin with air, thereby causing various problems. ^{1 2}

There exists an example in the art where conductive materials such as Ag nanowire are applied on fibers like cotton, elastane by means of dripping or soaking methods. ^{3 4 5} Yet, such techniques do not permit producing flexible conductive materials. The tension applied on the thread causes the conductive materials to be no longer in contact, and thus prevents electrical conduction and increases the resistance. There exist examples in which, in order to prevent the above, Ag nanowire and carbon nanotube are trapped in SBS, an extensible polymer. Although extensible conductive materials were produced in these studies, SBS cannot be transformed into fabric form since it is non-resistant against washing due to the low glass transition pointthereof. ^{6 7}

Graphene, a two-dimensional conductive material which has attracted great attention in recent years, is combined with PVA, thereby producing extensible conductive materials. However, PVA is not washable as it is water-soluble. ⁸

As a result, there is a need for producing a thread which is 100% extensible, does not lose its conductivity subsequent to elongation, can be easily transformed into fabric form, and is resistant against washing. Objects and Summary of the Invention

The object of the present invention is to provide a production method of conductive and extensible thread.

Another object of the present invention is to provide a production method of conductive and extensible thread which is obtained by applying Ag nanowire (AgNW) on pre-tensioned fibers.

Another object of the present invention is to provide a production method of thread allowing for manufacturing the devices which are fully adapted to the fabric, flexible, extensible, easily washable and breathable.

And another object of the present invention is to provide a production method of thread which comprises the process step of dissolving spandex in dimethylacetamide and diluting it with toluene, and then coating the fibers with the thus obtained spandex-toluene solution, thereby making them non-conductive.

The production method of conductive and extensible thread according to the invention comprises the process steps of: coating the pre-tensioned fibers with Ag nanowire solution and making them conductive, dissolving spandex in dimethylacetamide and then diluting it with toluene, thereby obtaining a spandex-toluene solution, coating the fibers having been made conductive with spandex-toluene solution and thus making the outer surfaces thereof non-conductive, and ensuring that the conductive fiber is highly resistant against washing by coating it with spandex. Detailed Description of the Invention

A production method of conductive and extensible thread, wherein it comprises the following process steps: stretching the fiber in free form by elongating it at least 30% from its free length,

coating the stretched fiber with conductive Ag nanowire solution (AgNWs) by drop casting or dipping method, and thus providing the fiber with conducting property, dissolving spandex in dimethylacetamide and then diluting it with toluene, thereby obtaining a spandex-toluene solution, coating the fibers having been made conductive with spandex-toluene solution and thus making the outer surfaces thereof non-conductive, and drying the spandex-toluene solution, followed by releasing the obtained fiber.

The invention is a production method of conductive and stretchable thread, wherein acetone, water, or isopropyl alcohol is used as solvent in the Ag nanowire solution, which provides the fiber with conducting property.

The invention is a production method of conductive and extensible thread, wherein the prepared spandex-toluene solution comprises 51 to 95% toluene by volume.

In the developed method, the spandex fiber in free form is stretched, and then coated with conductive nanowire solution by means of drop casting method. Subsequent to oven drying for 30 minutes in 50 °C, the spandex fiber in stretched form is coated with spandex-toluene solution by drop casting method again. After the spandex-toluene solution is dried, the resulting fiber is released. As a consequence, a conductive fiber whose outer surface is coated with an insulating material and with a uniform distribution is achieved. If the fiber is directly coated with spandex-dimethylacetamide in order to make it non-conductive, dimethylacetamide dissolves and breaks the fiber. Therefore, in the invention after dissolving spandex in dimethylacetamide it is diluted it with toluene, and thus a spandex-toluene solution is obtained and the fiber is coated therewith. Here, the surface can be fully insulated by adjusting the toluene amount, or if desired, coating is performed such that the AgNWs will be prevented from delamination and the surface can remain conductive.

The interaction of polymers with the solvents is classified into: good solvent, theta solvent, and bad solvent. For instance, dimethylacetamide (DMAc) is a good solvent for spandex. In other words, it dissolves spandex. Water, on contrary, is a bad solvent. That is, the moment the water contacts with spandex solution, spandex starts to aggregate since it is hydrophobic. Toluene, on the other hand, is theta solvent. Toluene neither dissolves nor aggregates spandex solution. Therefore, in the invention first spandex is dissolved in dimethylacetamide, and then toluene is well diluted. In the mixture dilute, spandex remains dissolved in the solution. When the solution is coated on the fiber, however, it does not break the fiber, unlike in the DMAc-spandex solution, due to the fact that most of the solvent is toluene (51-95% by volume).

According to the results of the studies, when the fiber in free form is elongated 200% (two-fold) and coated with conductive Ag nanowire solution (AgNWs), a stretched and conductive fiber is achieved. It is observed, as a result of coating such fibers with spandex-toluene solution, thoroughly drying, and then releasing, that AgNWs are buckled on the fiber, hold onto the fiber, and no delamination occurs.

With this wavy structure formed by the AgNWs buckled on the fiber, the wavy structure does not break but becomes smooth when the fiber is released again. No breakage between AgNWs is observed. Hence, the AgNWs which are in fact rigid are provided with extensibility. When the fibers are extended, the wavy AgNW structure becomes smooth and is elongated. When the fiber is released AgNW’s, return back to their wavy structures. This process can be repeated.

Further, coating with spandex-toluene solution in stretched form makes it easier for the AgNWs molecules to adhere to the fiber and at same time prevents the molecules from splitting off the fiber. Thus, a conductive fiber resistant against tensioning-releasing is obtained.

The surface of the fiber can be made fully or partly insulating by adjusting the spandex concentration in spandex-toluene solution.

The newly developed method aim to serve for today's technologies which are commonly used. With the present invention, all of the technological devices can be produced such that the touch screens, transistors, electronic circuit components, and optoelectronics will be extensible, flexible and easily washable. Hence, such devices can also be integrated with textile products. As a result, it will be possible to access to any technological device by means of the clothes that we are wearing. Moreover, with the devices integrated in the garments, it will be possible to monitor heart rate, blood sugar and similar medical issues; thus, the risk of a sudden health problem will be minimized. With our invention having such and numerous applications, it will be easier to adapt the technology to our daily lives.

It has been experimentally proved that the thread obtained with the developed method is 100% resistant against elongation and does not lose its conductivity. A circuit was prepared with a conductive thread originally of 5 cm and the LED was lightened. When the fiber is elongated to 10 cm, it was seen that the LED continued illuminating. This proves that the conductivity is not lost and the circuit continued operating.

Following the preparation of conductive thread it has been observed upon the cycle test in which the thread is stretched 100 % 250 times and returned back to its original state that the conductivity of the fiber did not change significantly. REFERENCES

¹ M Amjadi. et al. Adv.FunctMater. 26, 1678. (2016) ² A Hirsch. et al. Adv.Mater. 28, 4507, (2016) ³ JP Wang et al. Mat.Sci.Eng.A 528, 2863, (2011)

⁴ HW Cui. et al. Nano Res, 8, 1604, (2015)

⁵ Y Wei. et al. J. Mater.Chem.C. 4, 935, (2016)

⁶ S Lee. et al. Adv.Funct. Mater. 25, 3114. (2015)

⁷ ZF Liu. et al. Science 349, 400, (2015)

8 Y Meng. et al. Adv.Mater. 25, 2326, (2013)