Fusing Technlogy

By far the most important area of garment construction where an alternative process has significantly taken over from sewing is in the attachment of interlinings. When interlinings are sewn in, it can be difficult on parts such as collars to avoid a wrinkling of the interlining inside the collar and pucker around the edge. On large parts such as jacket fronts, the attachment of interlinings by sewing is expensive and requires skill if a high standard is to be achieved. The alternative process which has been developed is that of fusing, whereby the interlining is bonded to the outer fabric by means of a thermoplastic resin.

The fusible interlining consists of a base cloth, which may be similar to that used for a sew-in interlining, and which carries on its surface a thermoplastic adhesive resin, usually in the form of small dots, which will melt when heated to a specific temperature. If it is laid flat with the resin side onto the garment part and heat and pressure are applied, the resin will flow into the fabric of the garment and it and the interlining will become permanently attached. For the remaining assembly of the garment this laminate, as it is called, will be handled as one piece of material. Not all garment fabrics can be fused, and there will always be some situations where sew-in interlinings continue to be used, but in the vast majority of garment today, fusing is the most common process. The reasons are both economic and technical.

Means of Fusing

The means of fusing are temperature and pressure, applied over a period of time, usually in some kind of specialised fusing press. The rise in temperature at the ‘glue line’, the interface of resin and outer fabric where the resin is active, is caused by the electric heating elements of the press. This changes the state of the resin from a dry solid to a viscous fluid. Only with appropriate pressure will this flow among the fibres of both the outer fabric and the fusible base cloth. On cooling, the resin re-solidifies and forms a bond between the two components of the laminate. The heat has to pass through fabric to activate the resin, and this requires a time measured in seconds, which varies according to the nature of the fabric and the type of resin.

Fusing Action

The equipment must give enough time to allow the temperature and pressure to induce melting of the resin and penetration of the outer fabric in order to produce a satisfactory bond, but not too much or strike-back and strike-through results. It will be appreciated that if a thick fabric and an interlining are put into a heated press in a cool state, it may be several seconds before the resin reaches the required temperature.

These three factors are interrelated. A change in one may necessitate a change in the others, though there is a limit to the extent to which one factor will compensate for another. If the temperature in the press is not high enough, no amount of extra time will enable the resin to soften and flow.

Requirements of Fusing

The process of using interlinings to garments must fulfill certain requirements and avoid certain problems if the garment is to have satisfactory appearance and performance throughout its life.

1.       The laminate produced by fusing should show the aesthetic qualities required by the designer in the finished garment. This relates in particular to the stiffness or draping qualities of the garment. The factors over which the garment manufacturer can exercise choice are the drape of the fusible base cloth and the type and quantity of the fusible resin forming the bond.

2.   The strength of bond of the laminate must be sufficient to withstand handling during subsequent operations in the garment manufacturing process as well as the flexing which takes place in wear. The bond must resist either the temperature and degree of agitation of a washing and drying cycle, with perhaps subsequent ironing, or the solvents, temperature and agitation of a dry-cleaning process, and in some cases both.

3.   Fusing must take place without either ‘strike-through’ or ‘strike-back’ occurring. If strike-through occurs it may show on the right side of the garment as a pattern of dots of resin. If strike-back occurs it can contaminate parts of the equipment used in the fusing process and may also adhere to the garment lining during pressing.

4.    The fusing process must not cause thermal shrinkage in the outer fabric. If this occurs it can cause garments to fit together badly during manufacture and be incorrect in size after manufacture.

5.   A further possible effect of the heat of the fusing process is that of dye sublimation. Fabrics may change colour to a level which is unacceptable and in a way which causes a mismatch between the fused and un-fused parts of the garment.

6.    Since the fusing process involves pressure, there is a risk that pile fabrics may be subject to crushing during fusing. Fused and un-fused parts of the garment, when sewn together, may have a different appearance.

7.  Where shower-proof fabrics are fused, there is a possibility that the presence of a fused interlining in the garment may wick water through the fabric in the fused areas while the un-fused areas remain satisfactorily shower-proofed. Water resistant interlinings have been developed for these situations.

Factors determining the properties of the fused laminate

1.       The base fabric of the interlining – Base fabrics are available in the woven and non-woven constructions described for sew-in interlinings and also as warp knits. The warp knits are either a lock-nit or wet insert construction.

Interlinings made of woven fabric can be used on all types of garments where strength, stability and good draping qualities are required. On the other hand knitted interlinings are used on women’s tight clothing e.g. blouses and dresses made of silk, georgettes and knit fabrics.

2.       The type of fusible resin – The choice of resin is restricted by limits imposed by the outer fabric, the fusing equipment to used, the end use requirements, and the precise behaviour of the resins in response to heat.

a)     Polyethylene – Resins are washable and dry-cleanable and require high bonding pressures on the fusing press, used as interlining for shirt collars.

b)  Polypropylene – This is especially suitable for fusing applications where rapid, high-temperature drying is part of the garment laundering process.

c)  Polyamides – These can have a wide range of fusing properties, according to the proportions of the basic ingredients of different nylons employed as well as the amount of plasticiser added. Polyamides are very widely used in dry-cleanable garments.

d)   Polyesters – These resins are used in garments which are dry-cleanable and washable, because polyesters are less water-absorbent than polyamides and therefore resist washing better.

e)      Poly Vinyl Chloride (PVC) – Is both dry-cleanable and washable. It is commonly used in large area applications on coats fronts.

f)       Plasticised Polyvinyl Acetate (PVA) – This resin is normally in the form of a continuous coating for fusing to leather and fur at low pressures and temperatures.

3.       Methods of applying resins to base cloth

a)  Scatter coating – Specifically designed scattering heads are used to provide an even scatter under automatic control. The resin is then softened in an oven, pressed onto the base cloth and cooled. This is the cheapest method of making a fusible but the product is not as uniform nor as flexible as printed coatings.

b) Dry dot printed coatings – The powdered resin fills engraved holes on a roller. The base cloth passes over a heated roller and then against the engraved roller. The powdered resin adheres to the cloth in the form of dots. Oven heating follows the printing operation to ensure permanent adhesion. Patterns of dots can vary from 3 to 12 dots per cm according to the garment manufacturer’s requirements. Generally, lighter weight garment fabrics require interlining with smaller dots in higher concentration while heavier weight fabrics require larger dots in lower concentration to allow good penetration into the fabric surface and give a satisfactory bond.

c) Paste coating – Fine resin powders are blended with water and other agents to form a smooth paste and are printed onto the base cloth. Heat removes the water and the dots coalesce into solid resin. This type of coating gives precisely shaped dots and is used to produce the finer dots used in shirt collar fusible.

Fusing Machines

1.       Specialised Fusing Presses:-

a)      Flat Bed Fusing Press – This consists of two horizontal metal plates between which the fabric and interlining laminate are sandwiched. The top plate is unpadded but the bottom plate has a resilient cover, typically silicon rubber, though it may be a felt pad. This can be cleaned to prevent staining and build up of resins. Heat is provided by electric elements usually on the top plate only. But sometimes in the bottom also, uniform temperature is provided over the whole surface. Pressure is applied by closing the plates together mechanically, hydraulically and pneumatically. Pressure system must be strong and provide accurate closing over a large area and be free from distortion through heat, or mechanical falls. The resilient bottom cover should be changed regularly to avoid pressure problems. Vertical action closures give more accurate pressure than the scissor action.

Fusing time is controlled by autotimer whose cycle can be varied to suit different requirements. It is generally 8 to 12 seconds. The operator places the garment part faced down on the lower plate, places the interlining resin side down on top of it, in the correct position and closes the press. This is slow and time consuming. These presses do not cover a very large area, often not more than one meter by half a meter. Where small parts are being used output may be increased by laying them on a sheet of card which is then placed in the press.

Advantage of this press is that it is used in small clothing industries, simplest version and low cost. They also tend to reduce fabric shrinkage since the fabric is held under pressure throughout the fusing cycle. The disadvantage is that there is a tendency to crush fabrics.

b)      Continuous fusing system – In this system the garment with the interlining placed on it is passed through a heat source (chamber) and pressure is applied to it.

Heat is provided in one of the following three ways:

                                     i.            With direct heating, the conveyor belt carries the components to be fused into direct contact with a heated surface, either drum or curved plates.

                                   ii.            With indirect heating, components to be fused are carried through a heated chamber.

                                  iii.            With low temperature, gradual heating the components are carried through a preheating zone. Heating is either direct or indirect. With this approach the temperature reached at the glue-line is only just above that required to make the resin a viscous fluid and in some cases fusing takes place satisfactorily.

The maintenance of the required temperature is less of a problem inside a fully enclosed continuous operating press than that with flat bed press. On drum presses, tension of the conveyor belt presser the component continuously against the heated drum during the fusing process. Fusing time depends on the speed of the conveyor belt which can be adjusted to give various DWELL times in the heated zone.

Companies engaged in high volume garment production generally use continuous fusing systems.

c)       High Frequency Fusing – In the other fusing presses described so far heat is provided by electric heating elements. This limits the number of thicknesses of fabric which can be fused at once since time taken for the heat to transfer through the fabric to the resin. If multiple layers of fabrics and interlinings could be stacked up and fused simultaneously, productivity can be increased. Heat is generated by means of high frequency energy, in the same way as in a microwave cooker. The platens of the press are plates generating high frequency field and the heating affect is uniformly distributed in length, width and full height between the platens. This effect is known as di-electric.

The heating effect is different between natural and man-made materials and the fuseable adhesive material generally heats up faster than either the interlining base fabric or garment fabric.

Multiple plies of garment and interlining can be stacked up to 70mm high and since the heating effect is not dependent on its distance from a heat source, the adhesive at each joint should be raised to the same temperature. Less pressure is needed than with conventional fusing presses. The time required to generate the heat depends on the capacity of the high frequency unit and the weight of the load to be fused.

The difficulty which arises with this method of fusing is that the press must be set to allow for the particular natural or man-made materials being used, the weight and thickness of those materials, and their moisture content. If incorrect estimates are made, it is possible for the press to over-fuse and bond the whole stack together or under-fuse and produce a poor bond on each garment part.

2.       Hand Iron – Only those interlinings which can be fused at relatively low temperatures, low pressures and in relatively short times are at all suitable for fusing by hand iron.

There are a number of difficulties – the operator cannot know the temperature at the glue-line and cannot apply pressure uniformly. The operator estimates the time subjectively. Only small parts can be fused with any degree of success, and then only by pressing the iron for a fixed time onto the fusible, covering the area step-by-step and using steam to help the heat transfer. It is particularly in this situation that garment parts may appear to be satisfactorily fused initially but deficiencies will show up as de-lamination during wearing or cleaning of the garment.

3.       Steam Press – In this case fusing takes place on presses of the type used for intermediate and final pressing of made-up garments. Temperature at the glue-line is achieved by steam from the head of the press. The temperature reached depends on the steam pressure at the press head, the efficiency of the press. Pressure is provided mechanically or pneumatically by closing the press head on the buck. Vacuum in the lower part of the press, or buck, assists rapid cooling. Best results are obtained if the pressing cycle is controlled automatically. The resins which fuse most successfully on a steam press are polyvinyl acetate and the lower melting range of polyamides.

Fusing Fault	Reason
Flattening effect	Pressure too high
Shining	Pressure/ temperature too high
Colour changing	Temperature too high
Shrinkage	Temperature/ moisture content high
Deformation	Pressure high, wrong handling
Hand handle	Temperature too high, resin dots too big
Resin soiling	Wrong settings
Move of interlining	Electrostatic/ wrong handling

Methods of Fusing

 

Sandwich Fusing

Reverse fusing

Double Fusing

1.    Reverse fusing – In this method the outer fabric lies on top of the fusible. It is sometimes used in fusing shirt and blouse collars. On flat bed presses with elements only in the top platen, it is necessary to adjust temperature settings. Since the interlining is normally slightly smaller than the garment part, accurate positioning may be difficult.

2.       Sandwich fusing – This is effectively carried out only on a horizontal continuous press where heat is applied both from above and below. Two pairs of components, forming two laminates, are fused together, with the two outer fabrics on the outside of the sandwich (of four layers) and the two interlinings on the inside. With correct temperatures settings, the glue line temperature may be achieved in both laminates but the potential for strike-back occurring and causing all the layers to adhere together is considerable. A small amount of fusing time will be saved but preparation will take longer and the quality of the results may be unsatisfactory.

3.  Double fusing – this is the fusing of two sorts of interlinings to the outer fabric in one operation. It is most commonly used in shirt collars and men’s jacket fronts. This construction of jacket front has a body interlining fused right across and a chest piece fused on top of it.