| Soft-coating is revived in modern systems to contribute to relieving the environment, and to reduce the use of resources in the manufacture of technical textilesby Kurt van Wersch |
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Coating is a widespread application in the finishing of technical and functional textiles. But not "everything" always has to be coated. Many finishing processes with products in aqueous liquors can be applied more easily and better using other methods. Examples can be found in the soft-coating process.
Soft-coating is a "revival" of an existing technique. It is an application of selective quantities of liquor and can be performed:
On one side with one formulation
On two sides with one formulation
On two sides with two different formulations
Principle of the soft-coating range |
The "minimum liquor application" is understood as the quantity that permits energy-efficient drying with maximum fabric effects.
Two liquor vats with two coating rolls controlled independently of one another by two Pleva AF 120 microwave measuring units form the heart of the range.
It allows dry-in-wet and wet-in-wet processes to be carried out exactly to order. Adjustable guide rolls help to influence wetting, application time and penetration depth. Soft-coating enables drying costs to be cut, production speeds to be increased, processes to be changed, functionalities to be created and two-sided effects to be achieved.
For which processes are soft-coating applicable?
The application of the soft-coating range can be explained with four examples from practice.
Example 1: Hydrophobing of a glass fibre fabric before coating
At constant production speed, 65% less heat energy and 85% less electrical energy |
The purpose of hydrophobing is to reduce the penetration depth of the coating compound.
Originally the glass fibre fabric was padded with 50% liquor absorption and then dried.
The padding process has been replaced by soft-coating with single-sided application of 15% liquor (fluorocarbon).
Case I is the padding process with 50% liquor absorption
Case II is the soft-coating process with 15% liquor absorption, but drying conditions as for Case I.The result is an increase in production speed from 32 m/min to 107 m/min.
Case III involves reduced temperatures, reduced fan speeds and increased chamber climate, i.e. reduction in the exhaust air.
Case III shows that with the same production speed and desired fabric effect (hydrophobing of one fabric side), a saving of 65% in heat energy and a saving of 85% in electrical energy can be achieved for this drying process. The condensing of the products occurred during the coating step.
Example 2: Fluorocarbon finishing (hydrophobing) with UV protection
With reduced range setting higher production speed of 97 m/min and thereby 49% less heat energy and 82% less electrical energ |
Originally the PES fabric was padded with 70% liquor absorption.
This process has been replaced by soft-coating with 25% liquor absorption.
Here we can see that by reducing the liquor absorption from 70% to 25% (Case II), an increase in the production speed to approximately 224 m/min. would be theoretically possible. It is better, however, to accept only a slight increase in production speed accompanied by 49% less heat energy and 82% less electrical energy, as shown in Case III.
For single-sided liquor application, Monforts offers a further alternative. On many of the Monforts Montex stenters, an application head can be integrated into the stenter infeed section, as illustrated on the bottom right. It is possible to apply a liquor using the soft-coating method, to coat, or both can also be carried out at the same time.
Example 3: Two-sided application with one liquor
An application head can be integrated into the stenter infeed section on stenters |
The capillaries of cotton are saturated with about 40% liquor absorption. After a liquor application on the padder, the squeeze effects are approximately 70%, that means 30% liquor is still contained in the yarn and between the stitches and has to be "unnecessarily" dried out.
The soft-coating process allows the liquor quantities to be applied selectively to both sides, e.g. 2 x 20%, i.e. with 40% liquor absorption (with stronger formulation) 30% less has to be dried compared with the 70% liquor absorption. Less initial moisture means less heat energy and less electrical energy with the same production speed, as already shown in the examples 1 and 2.
Example 4: Two-sided application with two different liquors
The aims of the soft-coating process are not only to achieve savings in electrical and heat energy, but also to obtain two-sided effects and new finishing possibilities in a single pass.
Coating each side of the fabric differently meant until now two passes of the fabric, 2x drying and 2x treating. while avoiding unnecessary liquor quantities and achieving maximum fabric effects
A small selection of the potential applications of applying a liquor to two sides (left); and A small selection of the potential applications of applying two different liquors simultaneously to a textile fabric web |
With soft-coating it is possible to apply two different liquors at the same time and to dry the fabric with minimum energy utilisation. There are practically no limits to the user's needs and requirements.
Source: A.Monforts
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