What is heat setting process?

What is heat setting process?

The purpose of the fixing process is to remove the internal stresses that occur during fiber production to synthetic products, to stabilize the product and to give the material a smooth shape.

Objectives of fixation applied to synthetic products

Ensuring the dimensional stability of the material

To prevent wrinkling and fracture formation in rope finishing processes,

To prevent edge curling of knitted fabrics

To improve the remaining shrinkage values ​​of the product

To prevent possible deformation of sensitive materials.

Fixation process is applied to all textile materials. However, it has special importance in the processing of synthetic polymer fibers such as polyamide, polyester and polyacrylonitrile.

Fixation process on synthetic materials can be applied in filament, yarn and fabric forms. Internal tension is less in materials made of staple synthetic fibers. The internal stresses of the materials made of synthetic fibers are removed by the fixation process. Thus, the wet finishing processes that it will see in the future and the shrinkage of the finished products during use will be prevented. Internal tension is higher in materials made of filament yarns.

Before deciding at what stage and at what temperature the heat setting will be performed, all the finishing processes that the material will see should be known. The choice of heat setting stage also depends on the cleanliness of the material, the dyeing techniques, the available machinery and sometimes the condition of the yarn and fiber. Fixation before washing (heat setting- washing- painting):

While the physical properties and dyeability of the fiber change with heat setting, it becomes difficult to remove the sizing agents and impurities on the fabric. If the heat setting step is carried out before the pretreatment processes, these impurities melt during heat setting and penetrate into the fiber with increased plastic fluidity or become fixed on the fiber surface. Impurities are very difficult to remove after this step. If the fabric coming from the weaving is very clean, heat setting can be done before washing. This fixing step; Warp  knitted  materials are suitable for materials with loop slippage and whose knitting structure may deteriorate prior to heat setting in rope washing. It can also be applied before rope washing of polyester materials that are prone to fracture formation even at low temperatures.

Fixation before dyeing (washing-heat setting-dyeing):

Heat setting is usually done before dyeing but after washing to avoid fixing impurities in the fiber. This is the safest, most convenient way for all  materials . The advantage of heat setting before dyeing is that wrinkles that may occur during the dyeing of the material are avoided. Different heat treated fabrics are dyed in different shades as heat setting affects dye uptake. This coloring in coloring differences resulting from the heat treatment method dashed , is more than painting with the continuous method. The disadvantage of this line is that the fabric must be dried twice, since the thermofixing step is in the middle.

Fixation after dyeing (washing-dyeing-thermofixing):

After dyeing, heat setting removes the wrinkles that occur during dyeing and provides the desired width stability of the material. The disadvantage of heat setting after dyeing is that the dye inside the  fiber is  transferred to the surface by thermal migration and thus the wet fastness of the dyeing is reduced.

Fixing Process

Fixation process for synthetic products is done in the form of yarn and fabric.

Hot air fixation (if thermofixing):

This process is generally the process of fixing the fabric by stretching it under hot weather in the stenter . Processing time varies between 10 seconds and 3 minutes depending on the material.

Fixation with hot water (Hydrophytic):

Fabrics are wrapped on beam; The yarns are fixed in bobbins in pressurized apparatuses by giving hot water.

Fixation with hot steam :

Fabrics are wrapped on beam; The yarns are fixed in bobbins by steaming in pressurized apparatuses.

Dry Heat Setting, Heat Setting

Textile fibers can encounter high temperatures while going through the production stages and while being used. Especially in synthetic fibers, this heat creates a problem, and if heat setting is not performed, it may cause the structure and properties of the textile product to deteriorate. That is why heat setting is applied to synthetic fibers or materials made of these fibers.

All synthetic fibers consist of long chain molecules. After spinning, these chain molecules were spread out randomly. However, it then gravitates to several times their original length, and eventually the longer molecules are oriented and extend parallel to the fiber axis. Depending on the fiber type, these chains in the fiber are connected to each other with different forces. For example, in polyester, chain molecules are bound together by van der Waals forces, whereas in nylon these forces are H-bonds. Important point; These forces keep the chains of molecules together at a very short distance. However, these bonds are strengthened after the parallelization (drawing) process. Therefore, the fibers become stiff and their elongation in drawing decreases. These ties before and after the stretching-pulling process , available on chains. However, it is under force and pressure. If an energy in the form of heat is applied to the fiber, the chains within the fiber start to move and if this energy is enough, the bonds under the force and pressure between the chains are broken. When sufficient heat energy is applied, all of these bonds break and the fiber melts. If this heat energy is stopped when it reaches the minimum energy state, that is, if the fibers are cooled, the bonds between the chains are reconnected in the shortest way. Therefore, when the fiber is exposed to heat up to this fixation temperature, there is no change in its condition (shrinkage, etc.).

Therefore, heat setting is done as follows:

The fiber is heated to the desired temperature.

The fiber is kept constant so that no shrinkage occurs.

Serial cooling should be done.

After the heat setting process, there is no deterioration in the structure of synthetic fibers up to the temperature they are thermoset, and they can be worked up to these temperatures.

Features Provided by Fixing

The fixed fabric is also provided with anti-wrinkle properties. The tendency of the fibers to wrinkle is reduced .

Heat fixation ensures that polyester products remain stable in width and length during dyeing. Finishing operations can also be performed on the fixed product in the form of a rope. Heat setting affects the paint uptake of the product. By increasing the fixing temperature, dyeability first decreases, then increases again around 200 ° C. After heat setting, the handle of the fiber becomes hard and its elasticity decreases. The properties to be gained to synthetic products depend on the type of fixation. The most common fixation method is fixation with dry hot air. Pilling is reduced in the heat-setting product. In the advance heat setting process, the attitude of the product becomes harder as the temperature is increased. Textured yarns should be fixed at low temperatures.

Factors Affecting Fixation Results

Heat Setting Temperature: The effect of temperature on the product is that it releases the internal tensions in the fibers under control. With the effect of heat, the crystallites in the fiber melt and form again. The heat setting temperature should be determined according to the heat setting temperature the product has seen before.

Heating Rate: It is determined according to the type of the product and its weight / meter. Fast heating is performed in perforated drum dryers and stenter, and slow heating is performed in hot-flue.

Residence Time at Heat Setting Temperature: It  is the sum of the time taken for the fabric to warm up and the waiting time at the heat setting temperature. Two important factors in determining the elapsed time again until the heat set temperature ,  the machine type and the fabric is made of thermosetting meters / net weight.

Tension: As the tension increases during the heat setting process, the breaking strength of the fibers increases and the glass transition points increase. The heat setting tension is determined by determining the amount of tension that the product has seen during the thermofixing process.

Cooling Speed: The cooling process should be done slowly. Thanks to this, small crystallites are formed in the fibers. These combine to form large crystallites, reducing internal stresses. Thus, since the mobility of the product will be restricted, the product does not shrink or deform in subsequent finishing processes.

Performing the Heat Setting Process

Heat setting is a process with hot dry air in order to reduce the shrinkage tendency of the fabrics consisting of synthetic fibers and their blends and to eliminate the internal tensions in the fibers. In the fixation process, sufficient heat energy must be given to dissolve and reorient intermolecular bonds. Heat setting is based on changing the internal stress conditions in synthetic products. During the thermofixing process, the crystalline regions combine to form larger crystallites. Amorphous regions decrease in amount. Thus, as macromolecules have a tighter structure, their mobility decreases and dye intake becomes difficult. However, after a certain temperature, dye uptake increases again.

Heat setting for synthetic products;

It can be done in both stages: before painting, after painting, before and after painting. Since oligomers may form in polyester products during heat setting, if heat setting is performed before pre-washing, oligomers will be removed during washing. The fixation process consists of two stages as heating and cooling. The important point here is that both the temperature effect and the cooling effect must be done very quickly in a shock manner. Cooling process must be done under 50 C. The thermofix temperature should always be higher than the next hot treatment temperature (eg 30-40 C).

Heat Setting Machines:

Stenter : Heat setting of synthetic products is usually done with dry hot air in the stenter. In this way, it is possible to adjust the width and length of the woven and knitted products. The thermofixing process is applied to the fabrics in the stenter. In stenter, hot air flow is given to the fabric vertically from the bottom and top. The heat transfer coefficient (W / m² K) in stenter is 175-325. The heating time of the fabric is 5-20 seconds.

Hot-flue Heat Setting Machines: Synthetic products are fixed open (open width fabric) in hot-flue machines. It is one of the most suitable machines for the heat setting of hot-flue polyester. In hot-flue machines, the hot air flow is sent parallel to the fabric surface. The heat transfer coefficient in these machines is 35-58. It has the lowest heat conduction coefficient among other heat setting machines. The heating time of the fabric is 30-60 seconds.

Perforated Drum Heat Setting Machines: In perforated drum heat setting machines, the heat setting process is carried out by sucking hot air through the product. In perforated drum fixing machines, hot air is sucked through the textile product, so the effective fabric surface increases and the thickness of the air boundary layer gets smaller. In these machines, the heat conduction coefficient is the highest (290-470). The warm-up time of the fabric is 2-8 seconds.

Contact (cylinder, drum) Heat Setting Machines: Contact (contact) fixation is the heat setting performed by direct contact of synthetic products on the surface of hot metal cylinders. Fixing effect gives good results. However, the product  becomes a little thinner , hardened and shiny. Heat conduction in contact heat setting machines is by contact. The heat transfer coefficient is quite high (230-290) as the fabric touches the hot cylinder surface and contacts it directly. The heating time of the fabric in these machines is 3-12 seconds.

Thread Heat Setting Machines (autoclave): It is  applied to polyester sewing threads. The purpose of this is to prevent shrinkage of sewing threads in future finishing processes. The fixation of sewing threads is done in autoclaves in the wrapped state.

Fixing Process of Knitted Fabrics

Thermosetting process can be applied to knitted products both before dyeing (pre-fixing) and after dyeing. The stage at which the fixation is applied depends on the structure of the knitted product. The purpose of fixing in knitted products: to give the material dimensional stability , To reduce edge folds, to reduce the risk of creasing in subsequent bleaching and dyeing processes, to prevent possible fabric deformation. Circular knitted fabrics are generally fixed at open width. Saturated steam or hot air is used in the fixation process. Fixing of open width knitted fabrics is done in stenter. The fabric is fixed in a transverse stretch in the stenter. Fixing of knitted fabrics can also be done in perforated drum drying machines. In these machines, the fabric can be conveyed onto the drums with the help of tension chains. Knitted fabrics can also be fixed in the form of a hose. For this process, the fabrics are first wrapped on top of each other. It is then fixed in the wrapped state by treating with steam in the autoclave or with hot water in HT-Levent dyeing machines.

Fixing Process of Synthetic Blended Fabrics

In synthetic blended fabrics, fixation is applied only when the amount of synthetic fiber is higher. In the fixing process , the  structure and properties of other fibers that make up the mixture should also be taken into consideration. The fixing conditions of synthetic blended fabrics , including  fiber blend, fixing temperature and applied hot air time,

PES / Wool : 180-200 degrees, 10-20 seconds,

PES / Cellulose: 190-210 degrees, 10-20 seconds,

PES / PA 6: 192-195 degrees ,  20 seconds,

PES / PA  6,6: 210 degrees, 20 seconds,

PES / PAC: 190-200 degrees, 60 seconds,

PES / Triacetate: 200 degrees, 30 seconds.

Important Points To Be Considered In The Fixing Process

The stage at which a synthetic product will be fixed in the pretreatment depends on the structure of the fabric. For example, if the product is fixed without removing the size, it becomes very difficult to remove the size residues from the fabric. The preparation and finishing agents evaporate due to the fixing effect, causing contamination of the fixing machines. The fixing process should be done in an open width to the fabrics. Heat setting time and temperature depend on the type of material (yarn, carding band , fabric, etc.). The heat setting in all parts of the stenter machine should be performed at the same extent. The fixing time varies according to the type of the machine to be fixed (stenter, hot-flue, etc.). The polyester products to be dyed with light-colored disperse dyestuffs should be heat set at 190-200 C before dyeing. If saturated steam is used in the fixation of knitwear, the fixing temperature decreases and the product’s attitude improves. However, the fixation time extends to 5-10 minutes. Heat setting process should be applied equally to all sides of the product. Otherwise, it will cause unevenness in painting processes. The fixation process should be applied after the width of knitted and woven synthetic fabrics is calculated considering the shrinkage that may occur during the heat setting process. In fixing processes after pre-washing, first the fabric should be dried properly and then fixing process should be done. During the thermofixing process, the product at the exit of the machine should be wrapped in a uniform tension, there should be no air gap. Fixation process should be done in a way that does not affect the dyeability of the product. Care should be taken to ensure that the drying speed and temperature are equal during the simultaneous drying and thermofixing of wet products.

Heat setting: These are the procedures applied to adjust and improve the attitude and appearance in synthetic products with properties such as size stability and shape stability. All processes in fibers, yarns, fabrics, and even shaped textile products, at temperatures above the glass transition temperature of the fibers are heat setting process. Since the chemical energy of water is also used in processes such as washing, dyeing and steaming, the fixation effect applied in such processes is also called thermohydrofixing. The results obtained with the heat setting process depend largely on the product properties and the way the process is performed