**6. Application of materials joined using heat**

Hot air welding is mainly used in the healthcare and personal protective product sectors for making seams in nonwoven and coated nonwoven fabrics, also in welding of neoprene wet or dry suits. Hot wedge welding is used for joining heavy fabrics and films in outdoor applications, such as lining of swimming pools, reservoirs, and landfill sites [7]. On the other hand, fusing is mainly used for improving the shape and visual appearance of produced garments [24].

### **6.1. Drape properties of fused panels**

In the same way, it is possible to predict also mechanical and physical properties as well as bond strength of fused panel. The comparison between predicted and measured values of bond strength can be elaborated in the form of a linear coefficient of correlation. In the study [22], a very high correlation, 0.87, between the measured and predicted values has been found. Linear correlation coefficient is shown in **Figure 13**. Unfortunately, in the market there are no

The selection of a welding tape is based on the polymer or natural fiber type, type of textile fabric, tightness of the weave or knit, the weight of the substrate, the mechanical property requirements of the joint, and the environmental conditions of use. The welding parameters, such as the temperature of the hot air, velocity, pressure, and pressure of hot air should be balanced according to selected fabric, welding tape, and machine applied. The suitable selection of a welding tape is important in defining the quality, performance, feel, stretch, and longevity of the joint made. The selection procedure can be the same as for the selection of the fusible interlining [23]. The bond strength is valid for the prior parameter when welding tapes are selected. The influence of welding parameters on bond strength of welded samples is

**Welding tape Temperature (°C) Speed (m/min) Pressure (MPa) Bond strength (N/5 cm)**

280 2.5 0.65 14.13 300 1.5 0.65 16.4 300 2.5 0.65 12.75

WT 280 1.5 0.65 17.55

commercial software programs for selection of the fusible interlinings.

**Figure 13.** Correlation between the measured and predicted values of bond strength.

*5.3.3. Example of selection of welding tapes*

presented in **Table 2**.

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**Table 2.** Bonding strength of welded samples.

The final form of a produced garment depends on the quality of the build‐in material and its construction requirements. The fused panel properties can be estimated subjectively or objectively after the garment is finished. Mainly, they are evaluated on the basis of mechanical properties, bond strength, and drapability. The drapability of the fabric is one of the most significant properties, which characterize the shape of a produced garment and its adaptation to the human body.

The drape parameters depend on construction parameters of a fabric, row materials, and steps of finishing processes of fabric manufacturing, as well as on fusing technology used for production of a garment. The interlining can change the fabric properties, such as stiffness and extension properties, hand, visual appearance of incorporated pattern of a garment regarding to the desired design requirements.

It is a ratio of a projected pleating fold area formed by a piece of fabric after draping under its own weight to the original area of this piece of fabric without draping. The higher the fabric drape coefficient, the lower the fabric drapability [25]. It is the percentage of the ring, between radius *R*1 of the fabric and radius *R*2 of the disc holding the fabric, which is covered by the projected shadow (**Figure 14**), and it can be determined by Cusick [25]:

$$CD = \frac{S\_p - \pi R\_1^2}{\pi R\_2^2 - \pi R\_1^2} \tag{1}$$

**6.2. Seam properties of hot air welded multilayer materials**

a joining seam of a multilayered material for shoes.

**method** 

Sewing + Hot air welding

materials can reach even the strength of 562.5 N/5 cm [27].

**Sewing machine** 

Pfaff KI491‐755/13

**Table 4.** The characteristics and visual appearance of a joining seam of a multilayer material for shoes.

From the point of shoe manufacturer view, all produced seams would reach the desired minimum of bond strength, which is between 10 in 20 N/5 cm. But the traditionally joined

The hot air welding parameters, particularly welding temperature and pressure, had influence on the seam thickness. Thus, the ideal seam thickness of the welded or joint area should be the same as the thickness of the multilayered fabric considering the comfort during the use of the shoes. In comparison, the traditional seams applied by the shoe manufacturer are thicker than the multilayered fabrics. Moreover, the seam stiffness is also higher than the multilayered fabric, therefore the used seam construction is not enough functional during the shoe wearing because the friction problem can appear. To avoid the above‐mentioned problems, the

**Visual appearance of seams**

**Face side Back side**

Applying Heat for Joining Textile Materials http://dx.doi.org/10.5772/64309/ 233

**Position of seamed layers Joining**

LSp Stitch type: zig‐zag

the application of this technology in the shoe manufacturing process.

The seam properties of hot air welded multilayer materials will be discussed on the basis of

For tracking sport shoes inner part of shoes, i.e., inner sock is usually made from the multilayer, waterproof, and breathable materials. The seams of the inner sock should also provide enough smoothness to avoid the friction between the feet and shoes during the wearing. The multilayer material with the integrated waterproof layer such as SympaTex® or GoreTex® are the most frequently used materials. The traditional joining technique used for joining the multilayer waterproof material for the inner socks of the shoes was carried out in two steps in order to keep the waterproofness [27]. The multilayered fabrics were sewn by zig‐zag stitches with the predefined specifications. For sewing, a needle size 100 N m with the rounded point shape and waterproof sewing thread with fineness of 30 tex/3 S were used. The length and width of stitches were both 5 mm. In the second step, the seam was covered with a waterproof tape using the hot air welding technique. The waterproof tape has to be welded exactly on the middle (±1 mm) of the seam and during welding puckering of the membrane should be avoided. Next, the hot air welding was carried out at the following processing conditions: temperature of hot air was 365–380°C, the speed of welding was 2.5 m/min., the pressure of welding was 0.7 bar, the pressure between welding wheels was 2.5 bar, and the pressure of hot air blowing was 0.6 bar [27]. **Table 4** presents the characteristics and visual appearance of

**Figure 14.** Determination of a drape coefficient.

where:

CD—drape coefficient,

*S*p—projection area of draped specimen, mm2 ,

*R*1 ‐ radius of horizontal disk, mm,

*R*2—radius of nondeformed specimen, mm.

The interpretation of a drape coefficient value is connected with the number, form, amplitude and distribution of folds, and their positions according to weft and warp direction. The high value of drape coefficient means that the fabric is stiff and therefore it could be difficult to reform. Alternatively, low value of drape coefficient means easier reform and at the same time, better adaptation of fabric to the shape of cloth. The shape and number of folds depend on fullness and fabric stiffness. A fabric with higher stiffness has larger and wider folds and less stiff fabrics have narrower folds. **Table 3** shows the drapability of some investigated fused panels [26].


**Table 3.** The drapability of fused panels.

The presented results show that after the fusing process all the fused panels have higher value of drape coefficient in comparison with the shell fabric. The properties of a thermoplastic resin (type of adhesive, amount of adhesive) are the main reason for this effect, because the adhesive blocks up the moving of fabric threads in both warp and weft direction. The fusible interlining with stiffer properties have less nodes and the values of a drape coefficient are higher [26].

### **6.2. Seam properties of hot air welded multilayer materials**

**Figure 14.** Determination of a drape coefficient.

*R*1 ‐ radius of horizontal disk, mm,

*S*p—projection area of draped specimen, mm2

*R*2—radius of nondeformed specimen, mm.

,

The interpretation of a drape coefficient value is connected with the number, form, amplitude and distribution of folds, and their positions according to weft and warp direction. The high value of drape coefficient means that the fabric is stiff and therefore it could be difficult to reform. Alternatively, low value of drape coefficient means easier reform and at the same time, better adaptation of fabric to the shape of cloth. The shape and number of folds depend on fullness and fabric stiffness. A fabric with higher stiffness has larger and wider folds and less stiff fabrics have narrower folds. **Table 3** shows the drapability of some investigated fused

**Sample code F1 F1–FI1 F1–FI2 F2 F2–FI1 F2–FI2** Drape coefficient (%) 0.33 0.65 0.70 0.40 0.58 0.71 Number of folds 8 7 6 8 7 6 Minimum amplitude (mm) 92.9 106.0 120.2 98.2 117.8 122.5 Maximum amplitude (mm) 138.2 142.3 143.7 137.4 143.7 145.9

The presented results show that after the fusing process all the fused panels have higher value of drape coefficient in comparison with the shell fabric. The properties of a thermoplastic resin (type of adhesive, amount of adhesive) are the main reason for this effect, because the adhesive blocks up the moving of fabric threads in both warp and weft direction. The fusible interlining with stiffer properties have less nodes and the values of a drape coefficient are higher [26].

where:

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panels [26].

Figures of draped samples

**Table 3.** The drapability of fused panels.

CD—drape coefficient,

The seam properties of hot air welded multilayer materials will be discussed on the basis of the application of this technology in the shoe manufacturing process.

For tracking sport shoes inner part of shoes, i.e., inner sock is usually made from the multilayer, waterproof, and breathable materials. The seams of the inner sock should also provide enough smoothness to avoid the friction between the feet and shoes during the wearing. The multilayer material with the integrated waterproof layer such as SympaTex® or GoreTex® are the most frequently used materials. The traditional joining technique used for joining the multilayer waterproof material for the inner socks of the shoes was carried out in two steps in order to keep the waterproofness [27]. The multilayered fabrics were sewn by zig‐zag stitches with the predefined specifications. For sewing, a needle size 100 N m with the rounded point shape and waterproof sewing thread with fineness of 30 tex/3 S were used. The length and width of stitches were both 5 mm. In the second step, the seam was covered with a waterproof tape using the hot air welding technique. The waterproof tape has to be welded exactly on the middle (±1 mm) of the seam and during welding puckering of the membrane should be avoided. Next, the hot air welding was carried out at the following processing conditions: temperature of hot air was 365–380°C, the speed of welding was 2.5 m/min., the pressure of welding was 0.7 bar, the pressure between welding wheels was 2.5 bar, and the pressure of hot air blowing was 0.6 bar [27]. **Table 4** presents the characteristics and visual appearance of a joining seam of a multilayered material for shoes.


**Table 4.** The characteristics and visual appearance of a joining seam of a multilayer material for shoes.

From the point of shoe manufacturer view, all produced seams would reach the desired minimum of bond strength, which is between 10 in 20 N/5 cm. But the traditionally joined materials can reach even the strength of 562.5 N/5 cm [27].

The hot air welding parameters, particularly welding temperature and pressure, had influence on the seam thickness. Thus, the ideal seam thickness of the welded or joint area should be the same as the thickness of the multilayered fabric considering the comfort during the use of the shoes. In comparison, the traditional seams applied by the shoe manufacturer are thicker than the multilayered fabrics. Moreover, the seam stiffness is also higher than the multilayered fabric, therefore the used seam construction is not enough functional during the shoe wearing because the friction problem can appear. To avoid the above‐mentioned problems, the ultrasonic welding as the alternative technological process were proposed by Jevšnik et al. [27– 29]. The first results have shown that that the stiffness of the traditional seams applied by the shoe manufacturer was higher than those of ultrasonic welded seams. However, the results have shown that ultrasonic welding damaged the water proof membrane and low thickness and high stiffness in seam areas of multilayered fabrics also appeared, which can be stated as disadvantages of ultrasonic welding for manufacturing the joints [27].

dictable influence on the linear electrical resistance and signal transmission noise [23], therefore very precise tests under standard environmental condition should be carried out to avoid the problems with the electrical components later. In the second step, the bond strength between the welding tape and base fabric should necessary be evaluated. It is recommended that the bond strength is higher than 10 N/5 cm when the tape and fabric can be smoothly divided [23]. In the literature, it has been reported that bonding problem can appear when Teflon and silicon finishes are used [3]. It is also mentioned that since some dyestuffs react differently to heat, therefore they may affect bond strength of the welded fabrics, above all when darker colors are used [3]. If all above‐mentioned parameters reach satisfactory results, in the thread step we should evaluated the mechanical properties and visual appearance of welded transmission lines. Kurson Bahadir et al. [23] were studied the influence welding parameters on properties of e‐textile transmission lines manufactured with seven different conductive yarns (four stainless steel and three silver‐coated PA) under following hot air

> **Velocity (***v***/m min‐1)**

**Pressure (***p***/bar)**

Applying Heat for Joining Textile Materials http://dx.doi.org/10.5772/64309/ 235

welding condition, **Table 5**.

**Temperature (***T***/°C)**

**Table 5.** Welding parameters for manufacturing e‐textile transmission lines.

account the applied materials need to be carefully controlled.

(**Table 5**) are presented in **Table 6**.

Weld set 1 350 2.5 6.5 Weld set 2 450 2.5 6.5 Weld set 3 350 1.5 6.5

*6.3.1. Influence of the welding parameters on conductivity of e‐textile transmission lines*

The researchers tested the influence of hot air welding parameters on textile transmission lines from different aspects, as will be presented in the next sections. The presented studies have confirmed that hot air welding techniques can be suitable for constructing reliable and durable transmission lines. The investigation tests have shown that beside the suitable selected welding tape, conductive yarns, and base fabrics also the suitable welding parameters taking into

The linear resistances of the welded conductive yarns according to the defined welding sets

**Table 6** illustrates the changes in the linear resistances of conductive yarns when subjected to welding processes. Mainly, if the temperature increases, the linear resistances of the conductive yarns decrease for both stainless steel and silver‐coated polyamide yarns in comparison with the original linear resistance of stainless steel and silver coated yarns. The decrease of con‐ ductivity is smaller for stainless steel yarns then for silver‐coated polyamide yarns. As the temperature increases the conductivities of the welded conductive yarns, those having conductivity values of less than 70 Ω/m, remain almost at the same values. However, the linear resistance of the yarn silver‐coated polyamide (yarn no. 6) dramatically increases from 420

#### **6.3. E‐textile transmission lines made using the hot air welding**

Transmission lines built on electrical circuit to interconnect electrical elements, such as sensors, actuators, transistors, power sources for gathering sensitive information, monitor vital functions, and for sending information through the textile structure for further processing [1, 2, 23], can be obtained by different conductive yarns. Conductive yarns are either pure metal yarns or composites of metals and nonconductive textile materials, single or multiple strands, and mono‐ or multifilament. Nowadays, different integration methods for manufacturing the textile transmission lines by conductive yarns, such as woven, knitted, sewn, couched, e‐ broidery, printed, and welded can be used. Use of the hot air welding presents new, very promising technology for manufacturing the e‐textile transmission lines [23, 30].

As mentioned above, the transmission lines can connect the electronic components integrated into textile materials. E‐textile transmission line manufacture by hot air welding technologies are composed of a base fabric and endless welding tape with integrated conductive yarn. The conductive yarn is positioned on the base fabric and therefore hidden between the fabric and welding tape, **Figure 15**.

**Figure 15.** Schematic diagram and real photo of a hot air welded transmission line.

The base fabric can be any fabric based on natural or synthetic raw material composition. According to the kind of base fabric and function of textile products, welding tape and hot air welding parameters were selected. For total protection of the conductive yarn, it is recom‐ mended that the welding tape is waterproof and resistance against the friction and other mechanical loads. From the functional point of view, for example, if the smart garment will have protection or sports function, it is also recommended that breathability and windproof properties are considered.

Providing the suitable quality of hot air welded transmission lines, the optimization process of selection of the suitable welding tape and conductive yarn, as well as welding parameters should be very careful planned. The optimization process can be divided into three steps. In the first step, the linear electrical resistance and signal transmission noise of the conductive yarn after welding parameters should be tested. The hot air welding parameters have unpre‐ dictable influence on the linear electrical resistance and signal transmission noise [23], therefore very precise tests under standard environmental condition should be carried out to avoid the problems with the electrical components later. In the second step, the bond strength between the welding tape and base fabric should necessary be evaluated. It is recommended that the bond strength is higher than 10 N/5 cm when the tape and fabric can be smoothly divided [23]. In the literature, it has been reported that bonding problem can appear when Teflon and silicon finishes are used [3]. It is also mentioned that since some dyestuffs react differently to heat, therefore they may affect bond strength of the welded fabrics, above all when darker colors are used [3]. If all above‐mentioned parameters reach satisfactory results, in the thread step we should evaluated the mechanical properties and visual appearance of welded transmission lines. Kurson Bahadir et al. [23] were studied the influence welding parameters on properties of e‐textile transmission lines manufactured with seven different conductive yarns (four stainless steel and three silver‐coated PA) under following hot air welding condition, **Table 5**.


**Table 5.** Welding parameters for manufacturing e‐textile transmission lines.

ultrasonic welding as the alternative technological process were proposed by Jevšnik et al. [27– 29]. The first results have shown that that the stiffness of the traditional seams applied by the shoe manufacturer was higher than those of ultrasonic welded seams. However, the results have shown that ultrasonic welding damaged the water proof membrane and low thickness and high stiffness in seam areas of multilayered fabrics also appeared, which can be stated as

Transmission lines built on electrical circuit to interconnect electrical elements, such as sensors, actuators, transistors, power sources for gathering sensitive information, monitor vital functions, and for sending information through the textile structure for further processing [1, 2, 23], can be obtained by different conductive yarns. Conductive yarns are either pure metal yarns or composites of metals and nonconductive textile materials, single or multiple strands, and mono‐ or multifilament. Nowadays, different integration methods for manufacturing the textile transmission lines by conductive yarns, such as woven, knitted, sewn, couched, e‐ broidery, printed, and welded can be used. Use of the hot air welding presents new, very

As mentioned above, the transmission lines can connect the electronic components integrated into textile materials. E‐textile transmission line manufacture by hot air welding technologies are composed of a base fabric and endless welding tape with integrated conductive yarn. The conductive yarn is positioned on the base fabric and therefore hidden between the fabric and

The base fabric can be any fabric based on natural or synthetic raw material composition. According to the kind of base fabric and function of textile products, welding tape and hot air welding parameters were selected. For total protection of the conductive yarn, it is recom‐ mended that the welding tape is waterproof and resistance against the friction and other mechanical loads. From the functional point of view, for example, if the smart garment will have protection or sports function, it is also recommended that breathability and windproof

Providing the suitable quality of hot air welded transmission lines, the optimization process of selection of the suitable welding tape and conductive yarn, as well as welding parameters should be very careful planned. The optimization process can be divided into three steps. In the first step, the linear electrical resistance and signal transmission noise of the conductive yarn after welding parameters should be tested. The hot air welding parameters have unpre‐

promising technology for manufacturing the e‐textile transmission lines [23, 30].

disadvantages of ultrasonic welding for manufacturing the joints [27].

**6.3. E‐textile transmission lines made using the hot air welding**

**Figure 15.** Schematic diagram and real photo of a hot air welded transmission line.

welding tape, **Figure 15**.

234 Joining Technologies

properties are considered.

The researchers tested the influence of hot air welding parameters on textile transmission lines from different aspects, as will be presented in the next sections. The presented studies have confirmed that hot air welding techniques can be suitable for constructing reliable and durable transmission lines. The investigation tests have shown that beside the suitable selected welding tape, conductive yarns, and base fabrics also the suitable welding parameters taking into account the applied materials need to be carefully controlled.

#### *6.3.1. Influence of the welding parameters on conductivity of e‐textile transmission lines*

The linear resistances of the welded conductive yarns according to the defined welding sets (**Table 5**) are presented in **Table 6**.

**Table 6** illustrates the changes in the linear resistances of conductive yarns when subjected to welding processes. Mainly, if the temperature increases, the linear resistances of the conductive yarns decrease for both stainless steel and silver‐coated polyamide yarns in comparison with the original linear resistance of stainless steel and silver coated yarns. The decrease of con‐ ductivity is smaller for stainless steel yarns then for silver‐coated polyamide yarns. As the temperature increases the conductivities of the welded conductive yarns, those having conductivity values of less than 70 Ω/m, remain almost at the same values. However, the linear resistance of the yarn silver‐coated polyamide (yarn no. 6) dramatically increases from 420 Ω/m (see **Table 1**) to 524 Ω/m when the temperature increased. In case of increasing the temperature when using the silver‐coated polyamide yarn (yarn no. 7), the transmission line could not be formed because the welding parameters damaged the yarn and the conductivity was interrupted. The reason for this is melting of the coated polyamide fibers at the interface, which led to failure of the transmission line [23].

processes those transmission lines made of silver‐coated polyamide conductive yarns showed better signal transference capabilities compared with those transmission lines made of stainless

Applying Heat for Joining Textile Materials http://dx.doi.org/10.5772/64309/ 237

The visual appearance of welded e‐textile transmission lines plays an important role when the transmission line should be integrated on the face side of the product. From the functionality point of view, it is recommended that the transmission lines are integrated between the layers of garment in order to be protected against the mechanical damages. The investigations have shown that the visual appearance in terms of visibility of conductive yarns trough out of welding tape, and puckering of the welding tape around the conductive yarns after welding are the most frequently appearing phenomena. Those parameters are important for the final

The visibility of conductive yarns after hot air welding depend on used thickness and twisting of conductive yarns, as well as on thickness of the welding tape. **Figure 15** shows the visibility of conductive yarns when three‐layer welding tape and two different conductive yarns are used, i.e., stainless steel and silver‐coated PA. Due to three‐layer construction of the welding tape, it thoroughly overlaps the structure of the used conductive yarns in terms of visibility after the welding processes irrespective of the selected welding parameters. Thus, stainless steel conductive yarn (yarn no. 1, **Table 4**) despite of diameter 315 μm is slightly visible, while the silver‐coated PA conductive yarns (**Table 4**) are after welding processes completely

*6.3.3. Influence of the welding parameters on visual appearance of e‐textile transmission lines*

steel conductive yarns.

quality of the manufactured product [22, 30].

invisible because they are thinner and with less twists.

**Figure 17.** Estimation of a visual appearance of welded samples.


\* Indicates that no seam was formed; therefore, no result was obtained.

**Table 6.** Linear resistances of welded conductive yarns (Ώ/m).

*6.3.2. Influence of the welding parameters on signal transference capabilities of e‐textile transmission lines*

It was found out that the signal amplitudes of the welded conductive yarns were slightly higher than their reference values after hot welding process, **Figure 16**. It can be clearly seen that the samples within the weld set 3 (*T* = 350 °C; *v* = 1.5 m/min; *p* = 6.5 bar), obtained higher SNR values [23].

**Figure 16.** Comparison of SNR values of welded samples (weld set 1: *T* = 350°C, *v* = 2.5 m/min, *p* = 6.5 bar; weld set 2: *T* = 450°C, *v* = 2.5 m/min, *p* = 6.5 bar; weld set 3: *T* = 350°C, *v* = 1.5 m/min, *p* = 6.5 bar).

Moreover, it is also evident that after the welding processes the SNR values of the silver‐coated polyamide yarns (yarn no. 5, yarn no. 6, and yarn no. 7) were higher than in stainless steel yarns (yarn no. 1, yarn no. 2, yarn no.3, and yarn no. 4). In other words, after the welding processes those transmission lines made of silver‐coated polyamide conductive yarns showed better signal transference capabilities compared with those transmission lines made of stainless steel conductive yarns.

### *6.3.3. Influence of the welding parameters on visual appearance of e‐textile transmission lines*

Ω/m (see **Table 1**) to 524 Ω/m when the temperature increased. In case of increasing the temperature when using the silver‐coated polyamide yarn (yarn no. 7), the transmission line could not be formed because the welding parameters damaged the yarn and the conductivity was interrupted. The reason for this is melting of the coated polyamide fibers at the interface,

*6.3.2. Influence of the welding parameters on signal transference capabilities of e‐textile transmission*

It was found out that the signal amplitudes of the welded conductive yarns were slightly higher than their reference values after hot welding process, **Figure 16**. It can be clearly seen that the samples within the weld set 3 (*T* = 350 °C; *v* = 1.5 m/min; *p* = 6.5 bar), obtained higher SNR

**Figure 16.** Comparison of SNR values of welded samples (weld set 1: *T* = 350°C, *v* = 2.5 m/min, *p* = 6.5 bar; weld set 2: *T*

Moreover, it is also evident that after the welding processes the SNR values of the silver‐coated polyamide yarns (yarn no. 5, yarn no. 6, and yarn no. 7) were higher than in stainless steel yarns (yarn no. 1, yarn no. 2, yarn no.3, and yarn no. 4). In other words, after the welding

= 450°C, *v* = 2.5 m/min, *p* = 6.5 bar; weld set 3: *T* = 350°C, *v* = 1.5 m/min, *p* = 6.5 bar).

**Yarn no. Reference Weld set 1 Weld set 2 Weld set 3** <12 12.33 12.00 12.33 <25 25.00 25.00 25.67 <35 30.67 33.33 34.00 <70 69.00 69.67 70.67 <50 50.33 52.00 52.40 <420 507.33 524.33 592.00 <2000 3003.33 \* 3046.67

which led to failure of the transmission line [23].

Indicates that no seam was formed; therefore, no result was obtained.

**Table 6.** Linear resistances of welded conductive yarns (Ώ/m).

\*

236 Joining Technologies

*lines*

values [23].

The visual appearance of welded e‐textile transmission lines plays an important role when the transmission line should be integrated on the face side of the product. From the functionality point of view, it is recommended that the transmission lines are integrated between the layers of garment in order to be protected against the mechanical damages. The investigations have shown that the visual appearance in terms of visibility of conductive yarns trough out of welding tape, and puckering of the welding tape around the conductive yarns after welding are the most frequently appearing phenomena. Those parameters are important for the final quality of the manufactured product [22, 30].

The visibility of conductive yarns after hot air welding depend on used thickness and twisting of conductive yarns, as well as on thickness of the welding tape. **Figure 15** shows the visibility of conductive yarns when three‐layer welding tape and two different conductive yarns are used, i.e., stainless steel and silver‐coated PA. Due to three‐layer construction of the welding tape, it thoroughly overlaps the structure of the used conductive yarns in terms of visibility after the welding processes irrespective of the selected welding parameters. Thus, stainless steel conductive yarn (yarn no. 1, **Table 4**) despite of diameter 315 μm is slightly visible, while the silver‐coated PA conductive yarns (**Table 4**) are after welding processes completely invisible because they are thinner and with less twists.

**Figure 17.** Estimation of a visual appearance of welded samples.

The puckering phenomena were observed after all welding processes with stainless steel conductive yarns where thinner welding tapes are used, **Figure 17** [30]. The stainless steel yarn is stiffer with higher twisting ratio and weight in comparison of PA‐coated silver yarns. To sum up, the visual appearance of the welded transmission lines mainly depends on the selected conductive yarn properties and textile materials for layers rather than the selected welding parameters.

**Author details**

Zoran Stjepanovič<sup>5</sup>

Athens, Greece

**References**

6.50022‐6.

vina

Simona Jevšnik1\*, Savvas Vasiliadis2

1 Inlas d.o.o., Slovenske Konjice, Slovenia

\*Address all correspondence to: simonajevsnik@gmail.com

3 Faculty of Textile Technologies and Design, İstanbul, Turkey

204 p., DOI: 10.1533/9780857095626.

, Senem Kurson Bahadir3

2 Piraeus University of Applied Sciences (TEI Piraeus), Department of Textile Engineering,

4 University of Banja Luka, Faculty of Technology, Republic of Srpska, Bosnia and Herzego‐

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and

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