Size Add-on Materials:
In addition to a film former polymer various additive are added to a size mix. Additives may be included in the size mix depending on the particular weaving machine requirements or if a particular type finishing is required after the fabric is woven. A huge variety of additives are used. These additives are called size add-on materials. Most common of them are as follows:
There are a number of polymeric materials that can be used in sizing as binder materials. Binders are true film formers but are generally not used alone for sizing; some sizes are useful as both a primary size and as a binder. Binders are typically used to increase weave ability by promoting the adhesion of the primary film forming size to a specific fiber substrate while reducing the cohesion between sized yarns. By judicious selection of a binder, additional sizing advantages can be realized. Most commonly there are three types of binders used;
- Pearl corn starch
- Modified starch
- Starch derivatives
- Polyvinyl alcohol
- Polyester resin binders
- Vinyl acetate resins
Lubricant is almost always added to increase abrasion resistance of the yarn which is especially useful for rapiers and projectile machines. Lubricants with anti-sticking agents (lecithin) also prevent sticking of PVA to dry cans. Emulsifiers are added to the wax to improve desizablity. Paraffin or marine glycerides are added to harden the wax and better lubricate the yarns; however, if not removed properly during desizing some lubricants can cause problems in later operations.
Various other additives include humectants, anti-static and anti-foam agents, removable tints (for warp or style identification), preservatives (if the warp or the fabric is to be stored for long periods of time), penetrating agents (to allow the size to penetrate into tightly constructed styles), weighting agents (to make cloth heavier), anti-mildew.
Softeners such as lubricants, soaps and waxes are used to make the yarn sufficiently extensible, they also prevent cracking of size during weaving. Humectants, such as urea, sugar and glycerin are used to retain moisture in the size product. Moisture makes the size film more flexible and less brittle.
Size Add-on % on Warp Yarn:
Size add-on% on warp yarn depends on many parameters as shown in Figure-1.
Factors Affecting the Quality and Performance of the Sized Yarns:
The increasing production rate of latest looms has made the sizing operation more critical. The optimization of size pick-up can be defined by the substance balance that enters and exits the size box. To keep size pick-up constant, it is essential to maintain the temperature and sizing concentration in the size box as well as keeping the squeezing pressure and sizing speed constant throughout the process. Moisture content in warp thread at the size box exit and pressure of last squeezing rollers are the final process parameters that control the size pick-up. Other parameters like size temperature, sizing speed, thread tension, viscosity of size, levels and circulation of size in the box, sizing agents, conditions of size preparation and yarn properties also have remarkable impact on size pick-up.
Homogeneous sizing ensures very smooth weaving at higher productivity and lower cost. It has been proved that the optimal size pick-up is the one that will allow minimum warp thread breaks on the weaving machine as well as satisfactory efficiency of the weaving machine and fabric quality. It is clearly mentioned in Figure-2 that the optimal size pickup is slightly higher than the minimum, because it is very difficult to maintain the precision and uniformity of size pick-up especially on single cotton yarn. The performance of sizing process depends upon numerous factors which are given below.
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- Maintenance Process of Sizing Machine and Its Importance
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.