BOND­ING AND WELD­ING: A SEAM­ING AL­TER­NA­TIVE?

Stitch World - - NEWS -

With sewfree or stitch­less fab­ric join­ing tech­nique gain­ing mo­men­tum in tech­ni­cal ap­parel as well as fash­ion ap­parel seg­ment, the weld­ing and bond­ing tech­nol­ogy is com­ing un­der re­view again and again. Although the tech­nol­ogy was pri­mar­ily ini­ti­ated for func­tional ap­pli­ca­tions like wa­ter­proof­ing and air­proof­ing, it is now grad­u­ally mov­ing to­wards com­fort and aes­thetic ap­pli­ca­tions. And sur­pris­ingly for a change, this tech­nol­ogy is mov­ing from con­tin­u­ous pro­cess­ing (faster) to­wards batch pro­cess­ing (slower). Dr. Pra­bir Jana, NIFT Delhi, Pa­trick Weiss­ger­ber, Pres­i­dent & CEO, DAP (Duerkopp Adler PFAFF) Amer­ica and An­shu­man Dash, Mar­ket­ing Di­rec­tor, H&H Asia per­form a re­al­ity check on this...

Sewing, bond­ing and weld­ing share the com­mon aim of join­ing ma­te­rial plies to­gether. Sewing is con­tin­u­ous join­ing of two or more plies of ma­te­rial by pen­e­trat­ing the ma­te­rial with a nee­dle and us­ing a third ma­te­rial (thread) to join plies to­gether. The sewn seam re­tains the elas­tic­ity of the base ma­te­rial.

Weld­ing is clocked or con­tin­u­ous join­ing of two plies of ma­te­rial by liq­ue­fy­ing the ma­te­rial and press­ing it to­gether, ma­te­rial is not pen­e­trated and no third ma­te­rial (thread or glue) is re­quired, whereas bond­ing is clocked or con­tin­u­ous join­ing of two plies of ma­te­rial by ap­ply­ing a third ma­te­rial (glue) in be­tween the plies. While the welded seam has lim­ited elas­tic­ity in com­par­i­son to sewing, the bonded seam has sim­i­lar elas­tic­ity like sewing.

Both bond­ing and weld­ing can be achieved by con­tin­u­ous pro­cesses on espe­cially de­signed ma­chines. While sewing and weld­ing are sin­gle stage pro­cesses, bond­ing is a three-stage process.

In weld­ing, two plies of ma­te­ri­als are fed through a set of rollers in the pres­ence of heat and pres­sure. The heat can be ap­plied through hot wedge, hot air or by ul­tra­sonic weld­ing.

“I strongly feel that the flat­ness of bonded seam will be the key driver for growth of in­no­va­tive ap­pli­ca­tions in com­ing years.” – Dr. Pra­bir Jana, NIFT Delhi

Hot wedge and hot air weld­ing tech­nol­ogy, although giv­ing high seam strength, are only suit­able for ma­te­rial thick­ness from 0.2 mm to 2.0 mm and there­fore have very lim­ited ap­pli­ca­tion in fash­ion and per­for­mance ap­parel seg­ment. These are cur­rently used in most of the tech­ni­cal tex­tiles ap­pli­ca­tions. Ul­tra­sonic weld­ing, how­ever giv­ing av­er­age seam strength, is suit­able for 0.05 mm to 0.4 mm ma­te­rial thick­ness, and hence is fit for ap­parel use.

How­ever, a com­par­a­tively com­mon ap­pli­ca­tion of hot air weld­ing is seam seal­ing, which is a twostage process. In seam seal­ing, an ex­ist­ing sewn seam is lay­ered with ad­he­sive tape to seal the nee­dle per­fo­ra­tions. Hot air is used to melt the ad­he­sive in the tape and paste it over the seam line.

A quick com­par­i­son of hot wedge, hot air and ul­tra­sonic weld­ing is given be­low in Ta­ble 1:

Types of ul­tra­sonic weld­ing ma­chines

The up­per feed­ing wheel of the ul­tra­sonic weld­ing ma­chine is called anvil wheel and the lower feed­ing wheel is called sonotrode or horn. The com­mer­cially avail­able ul­tra­sonic weld­ing ma­chines are of four types. The most pop­u­lar is the ver­ti­cally ro­tat­ing sonotrode and anvil wheel, which works on 35kHz tech­nol­ogy (only PFAFF ma­chines work with 35kHz, oth­er­wise you can also get those with 20kHz), in­audi­ble to the hu­man ear. The se­cond type is the stand­ing sonotrode and ver­ti­cally ro­tat­ing anvil wheel. The third type is the hor­i­zon­tally ro­tat­ing sonotrode and ver­ti­cally ro­tat­ing anvil wheel. Both se­cond and third type work on 20kHz tech­nol­ogy, au­di­ble to the hu­man ear, and hav­ing po­ten­tially nox­ious ef­fect! The fourth type is the ver­ti­cally up-down presser foot type anvil and stand­ing sonotrode. While the ver­ti­cally ro­tat­ing, sonotrode and anvil wheel type is of­fered by al­most all lead­ing brands, the presser foot type anvil is spe­cific to ap­parel use and cur­rently of­fered by lim­ited brands.

The main dif­fer­ence among the four types is the ma­te­rial feed­ing ver­ti­cally ro­tat­ing sonotrode and anvil wheel which move the ma­te­rial in the same di­rec­tion, thus guar­an­tee­ing a smooth ma­te­rial move­ment. The ma­te­rial move­ment is not syn­chro­nized (in the same di­rec­tion) in all the three types ex­cept in the se­cond type, where the sonotrode does not trans­port the ma­te­rial at all. The cu­ri­ous rea­son be­hind the ver­ti­cally stand­ing and hor­i­zon­tally ro­tat­ing sonotrode seems to be the cheaper cost of the ma­chine.

Con­di­tions for weld­ing

While dif­fer­ent types of ma­te­rial can be sewn or bonded to­gether, weld­ing re­quires two min­i­mum con­di­tions to be met. Firstly, only ther­mo­plas­tic ma­te­ri­als can be welded, and se­condly, both the plies should also be hav­ing sim­i­lar fibre com­po­si­tion to be welded to­gether. For ex­am­ple, ther­mo­plas­tics such as PVC (Polyvinyl chlo­ride), PU (Polyurethane), PA (Polyamide/ Ny­lon), PES (Polyester), PE (Poly­eth­yl­ene) and PP (Polypropy­lene) can be welded but cot­ton and silk can’t be welded. Fur­ther­more, only ply of PVC can be welded with an­other ply of PVC; PES can­not be welded with PVC and PU can­not be welded with PES. Ul­tra­sonic weld­ing can do regular weld­ing, cut and seal or dual sys­tem of cut and seal with si­mul­ta­ne­ous weld­ing (unique to PFAFF ma­chines).

Log­i­cally, a non-wo­ven would be eas­ier to weld as it of­fers more sur­face to be joined to­gether. If we take it to the ex­treme and im­age two plies of a wo­ven ma­te­rial like a fish net, we can only join the fi­bres (strains) that lie on top of each other. All other ar­eas will not be joined. This does not mean that it can­not be welded but the seam strength will be of course lower.

Bond­ing – A pre­ferred choice

Bond­ing com­par­a­tively of­fers wider ap­pli­ca­tions like any type of fibre com­po­si­tions which can be bonded to­gether; for ex­am­ple, cot­ton fab­ric can be bonded with polyester. Only dis­ad­van­tage with bond­ing is that it is a slow process. In the first stage, the dou­ble-sided ad­he­sive tape will be laid on one fab­ric layer along the seam line. In the se­cond stage, the pa­per back­ing is re­moved man­u­ally fol­lowed by po­si­tion­ing of the se­cond layer of fab­ric on the ad­he­sive tape. The third stage is the heat press­ing of the seam for fi­nal bond­ing.

Ma­chines used for bond­ing

Although nu­mer­ous brands of­fer con­tin­u­ous ad­he­sive tape lay­ing ma­chines (for first stage), in re­al­ity the process is of­ten done man­u­ally in most of the com­pa­nies. There are sev­eral rea­sons be­hind this; firstly, the tape lay­ing ma­chines are good for lay­ing ad­he­sive tape con­tin­u­ously for long length. But, if the seam line is not a straight line but curved or if the seam line has in­ter­mit­tent sewn ap­pli­ca­tions, then man­ual tape lay­ing by small hand iron is a bet­ter op­tion.

“Bonded seams have a pre­de­ter­mined life ex­pectancy. We have a cus­tomer who is do­ing func­tional un­der­wear for ath­letes. They only guar­an­tee 20 wash cy­cles on some gar­ments. A sewn or welded seam usu­ally does not have such re­stric­tions. I do not ex­pect a bonded seam to fall apart dur­ing wear, but over time the glue will be dis­solved, espe­cially when talk­ing about chem­i­cal wash­ing cy­cles as seen in dry clean­ers. Sewn and welded seams are re­sis­tant to wash­ing. In a sewn seam, the thread stays in place. A welded seam con­sists of the ma­te­rial it­self only. If the welded seam would open that would mean the ma­te­rial it­self would dis­solve dur­ing wash­ing. It is not made to last for­ever. Huge dis­ad­van­tage in my opin­ion.” – Pa­trick Weiss­ger­ber

There are also tape lay­ing ma­chines with cloth edge trim­mer (just sim­i­lar to fab­ric edge trim­ming in over­lock sewing). The me­chan­i­cal trim­mer is a bet­ter op­tion than ul­tra­sonic trim­mer. Although ul­tra­sonic trim­mer seals the edge (thereby pro­duc­ing neater edge), in re­al­ity trim­ming ap­pli­ca­tions of­ten re­quire cross­over seams to be trimmed and in such cases, ul­tra­sonic trim­ming fails (due to vari­able thick­ness). Me­chan­i­cal trim­mer can trim vari­able thick­ness along seam as well as has the ad­di­tional ad­van­tage of work­ing on any fab­ric type whereas ul­tra­sonic trim­mer can work for ther­mo­plas­tic fab­ric type only.

Con­tin­u­ous ma­chines are also avail­able for at­tach­ing the se­cond layer of fab­ric (se­cond stage) and heat press (third stage), how­ever for both the stages, it is seen that man­ual batch process is pre­ferred. The se­cond stage is the most cru­cial stage as the qual­ity of seam will de­pend on this process. As a pre­cau­tion, mostly the se­cond layer of fab­ric is spot welded to avoid any shift­ing or dis­tor­tion. The heat press or fi­nal stage is 100 per cent batch process and nowa­days, there are ma­chines that of­fer hot press fol­lowed by cold press. Pos­i­tive cool­ing en­sures gar­ments can be pro­cessed for next op­er­a­tion im­me­di­ately with­out any fear of dis­tor­tion/ per­ma­nent wrin­kle/fold. In case of hot press, the glue melts and spreads as per ac­tual shape of the seam and cold press im­me­di­ately freezes it oth­er­wise the fab­ric takes the orig­i­nal po­si­tion while get­ting dry and we see wavi­ness along seam. Ad­di­tion­ally, cold press claims an in­crease in the bond­ing strength by 30 per cent due to the quench­ing prin­ci­ple.

Ul­tra­sonic weld­ing or bond­ing?

The flat­ness of seam is the key ad­van­tage of weld­ing or bond­ing over sewing. As there is no nee­dle pen­e­tra­tion, no con­tin­u­ous move­ment of two plies, no chances of ei­ther puck­er­ing due to struc­tural jam­ming or puck­er­ing due to ply slip­page. How­ever, there are many dis­ad­van­tages of ul­tra­sonic weld­ing for ap­parel use such as poor seam strength, re­verse vis­ual look of seam ap­pear­ance. The stiff­ness of seam is de­bat­able among ex­perts and needs more in-depth study. The ap­pear­ance of the welded seam is de­ter­mined by the choice of anvil wheel. Some ex­perts feel it is pos­si­ble to cre­ate a very elas­tic welded seam for lin­gerie (which is com­fort­able to wear) by us­ing spe­cially de­signed anvil. Ma­chine man­u­fac­tur­ers re­quire work­ing more with prod­uct de­vel­op­ers to im­prove on seam strength and vis­ual look, which is tech­ni­cally pos­si­ble.

Bond­ing of­fers wider ap­pli­ca­tions like any type of fibre com­po­si­tions can be bonded to­gether; for ex­am­ple, cot­ton fab­ric can be bonded with polyester.

Bonded seams, on the con­trary, have equal seam strength, com­par­a­tively softer seam han­dle and ab­so­lutely neat and flat ap­pear­ance. The sin­gle-most ad­van­tage of bonded seam is flat seam. It is com­mon prac­tice in men’s for­mal shirt con­struc­tion to ap­ply dou­ble-sided fused tape sand­wiched be­tween seam to cre­ate a flat­ter seam ap­pear­ance, and bonded seam will give you that nat­u­rally! Ta­ble 2 shows the com­par­a­tive ad­van­tages and dis­ad­van­tages of sewing, bond­ing and ul­tra­sonic weld­ing. While sewing still en­joys over­whelm­ing ac­cept­abil­ity and pro­duc­tiv­ity ad­van­tages, bond­ing is gain­ing niche due to ap­pear­ance and com­fort, and weld­ing is yet to prove its ver­sa­til­ity in ap­parel ap­pli­ca­tions.

Con­clu­sion

There are nu­mer­ous ad­van­tages evolv­ing out of the bond­ing process although the process is cur­rently dead slow to make any pro­duc­tive ad­van­tage. Till the tech­nol­ogy of ap­ply­ing ad­he­sive tape changes dras­ti­cally, pro­duc­tiv­ity will re­main an is­sue. While Brother briefly showed a pro­to­type of liq­uid glue dis­pens­ing in con­tin­u­ous bond­ing process three years ago, in­dus­try watch­ers say a newer method of dis­pens­ing ad­he­sive is the key to the com­mer­cially pop­u­lar­iz­ing bond­ing process. In­ter­est­ingly, while most of the sewing op­er­a­tions are faster than sim­i­larly con­structed bond­ing op­er­a­tions, there may be light at the end of the tun­nel. The bond­ing of­fers clever ma­nip­u­la­tion and engi­neer­ing of cer­tain seams to clock equal or faster time than sewing! One such po­ten­tial op­er­a­tion is polo T-shirt placket mak­ing.

Ver­ti­cally up-down presser foot type anvil and stand­ing sonotrode

Hor­i­zon­tally ro­tat­ing sonotrode and ver­ti­cally ro­tat­ing anvil wheel

Ver­ti­cally ro­tat­ing sonotrode and anvil wheel

Stand­ing sonotrode and ver­ti­cally ro­tat­ing anvil wheel

Hem­line of a gar­ment with partly bond­ing and partly elas­ti­cated sewing

A flat zip­per

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