Chemical Finishing

Softeners & Hand Builders

Finishing is defined as any chemical process other than preparation or the application of color that imparts useful or desired properties to a textile or apparel product. Although it can be performed on fibers or yarns, finishing usually occurs after the fabric or garment has been prepared and dyed, and is often the last step.

Finishing processes can affect many qualities of a fabric or garment, including appearance, performance, or serviceability, and hand, through the use of softeners or hand builders.

Softeners are classified by their ionic charge: anionic, cationic, and non-ionic (neutral).

Anionic Softeners

Anionic softeners have a negative charge as does wet cotton. Anionic softeners can impart pliability without making the fabric too silky or slick. Because of their charge, they must be padded onto fabric. Not extremely durable, these softeners are normally applied for a one-time effect, often before mechanical finishes such as napping, shearing or compaction are introduced.

Advantages

Anionic softeners are desirable because they provide the right amount of lubrication between a fabric and a mechanical device. Another advantage is that fabric that is finished with anionics doesn’t easily yellow because these softeners show good stability to heat and are compatible with optical brighteners. They also have good rewetting properties so are preferred for fabrics such as towels that must absorb water.

Disadvantages

Their disadvantage is that, when compared to other softeners, more product must be used. Anionics are hard to exhaust and may be incompatible with baths containing products such as stabilized cationic emulsions, electrolytes, or resins.

Cationic Softeners

Cationic softeners have a positive charge while wet cotton has a negative charge. Due to their opposing natures, cotton has a high affinity for cationic softeners.

Advantages

This type of softener produces a fluffy and silky and, on most fabrics, and it doesn’t take much to get this effect on cotton because of the ionic charge of these chemicals. Cationics easily exhaust and are compatible with most resin finishes. Cationics are good for fabric sewability and are quite durable with good tear and abrasion resistance.

Disadvantages

Cationics are not often used at high levels on white because they tend to yellow at higher processing temperatures. They may also affect shade or lightfastness. Also, in some applications, cationics may cause unwanted water repellency. It is important to note that Anionic and Cationic chemistries are incompatible. Strong cationic softeners can complex or bind with anionic dyestuffs, creating a problem with crocking. Also, the shade may not be reproducible.

Nonionic Softeners

Nonionic softeners have a neutral charge. This includes ethylene oxide derivatives, silicones, and polyethylene. Nonionics have no ionic affinity for cotton and must be applied by a pad application. These softeners show excellent resistance to discoloration and heat, give a dry pliable hand, and can be applied by various methods. The polyethylene type of nonionic softeners creates a soft hand and has excellent non-yellowing properties. The silicone gives a slick, lubricated, and silky hand and blooms the shade, making it look richer and more vibrant. They also increase the performance of durable press. Both polyethylene and silicone softeners improve tear and abrasion resistance, providing sewing lubricity, and are somewhat durable.

Hand Builders

Another class of chemistry for finishing is referred to as hand builders. These finishes are applied when garments require fabrics of strength, firmness, and resistance to abrasions. Hand builders make fabrics less pliable, and control curling when fabrics are difficult to sew.

Functional Chemistry

Various chemistries and application methods can be used to improve the serviceability of fabrics.

Fluorochemicals

Fluorochemicals are particularly useful for providing water and soil resistance. Water repellency works because the chemistry increases the surface tension causing water to bead. Fluorochemicals are the most water-repellent of all finishes but are also the most expensive.

The same repellency also prevents soils or stains from entering the fabric and forming a bond, and this type of finish is durable to laundering. Clothes that are easily soiled must be finished to repel and release dirt and grime. Fluorochemicals can be adjusted to provide less surface tension so that the finish releases dirt and removes soil during washing. Contemporary lifestyle dictates that we look neat while we work hard and play hard so fabrics can be treated to resist wrinkling, retain a smooth appearance, and keep creases and pleats in place even after laundering. Currently, the most popular chemistry used to resist wrinkling is resin-based.

Methods of Resin Application

Many factors related to chemical reactions influence wrinkle resistant properties. The reactant concentration, the catalyst type, and the catalyst resin ratio are of utmost importance. There are three main methods of resin application: pre-cure, fabric post-cure, and garment post-cure.

Pre-Cure Process

The pre-cure process occurs after the fabric has been dyed. First the resin, a catalyst, and softener are padded onto the fabric, then the fabric is dried and cured at an elevated temperature. After this, the fabric is cut and sewn. The process is quick, inexpensive, and reproducible. Following the pre-cure process, the garment is assembled and sent to the customer. Almost all shirts and most slacks are made from pre-cured fabric. Because the fabric now has a memory for the flat, smooth state in which it was cured, creases in slacks will not be as durable as those produced by the post-cure process.

Post-Cure Process

In the post-cure process, the order of events is different. It begins the same way by padding on the resin and drying the fabric at a low temperature. Next, the garment is cut and sewn. The desired creases or pleats are firmly pressed into the garment. As the final step, the treated garment passes through an oven to cure at higher temperatures, so creases are more permanent.

Resin Application

Garment Dip

Instead of applying finishes to fabrics, resins can be applied to a completed garment. One method is garment dip. Garments that are first cut and sewn are immersed in a chemical bath, after this the garment is tumble dried at a low temperature which also pre-shrinks the fabric. Next, the garment is pressed. Finally, the garment goes to an oven for curing which is when the resin chemically reacts. A benefit of this process is better inventory control because garments are finished only when orders arrive. The garments produced by applying resins and garment dipping shrink less and have a better fit, there is a softer hand than that produced by the conventional post-cure method.

Metered Edition

A second method associated with garment resin applications is metered edition. With this approach, cut and sewn garments are sprayed while tumbling in a garment machine. There is much less waste in chemicals because a metered or measured amount of water and chemistry, just what is needed, is sprayed on the garment. You’ve seen many ways that garments or fabrics can be treated with chemicals to improve wash and wear, and wrinkle resistance.

Enzymes

There is yet another way to soften and improve the appearance of fabric that is becoming more important. Found in all living organisms, enzymes are specialized proteins that serve to attack natural catalysts for biochemical reactions. Safe and easy to use, enzymes attack and degrade specific substrates under mild conditions. Enzymes replace hash solvents and other organic compounds used to finish fabrics. Enzymes are specifically engineered to create certain attributes. Improved effects include softness and better color washdown. The stone-washed look applied to denim is usually produced by combining enzyme treatment with the action of pumice stones. Also, enzymes impact the removal of surface fiber or fuzz that appears and makes fabric look worn after many washings. Fabrics treated with enzymes and subjected to mechanical agitation are less likely to display these undesirable surface characteristics.

Application Systems

There are different ways to apply chemistry to fabric. Regardless of the mechanical means used, it’s important that the chemistry be applied in a uniform manner. The chemistry which is used with water or with a solvent is either solubilized, dispersed, or emulsified. In the most conventional method, the chemical is diluted in water which is padded onto the fabric. Next, the fabric must dry allowing the water to evaporate. Depending on which finishing chemicals are used, it may be necessary to apply a higher temperature for cross-linking or curing.

Vertical padders are the most common. As the fabric moves through a series of rollers located in a trough, it is immersed in a bath containing the chemistry. By the time it comes out of the trough, the fabric has been thoroughly wet out. Then it is guided up through two round squeeze rolls. Called a mangle, these squeeze together precisely with consistent pressure so that chemistry is uniformly applied to the fabric at the lowest practical wet pickup.

A variation on this is the use of horizontal padders to apply chemistry. When the fabric leaves the trough, it moves vertically up between horizontally positioned rolls. As in vertical padding the chemistry, the construction of the fabric, and the hardness and pressure of the roll determine how much water and chemistry is picked up by the fabric.

An alternative to padding chemicals onto fabric is to spray. With this method, a liquid bath is pumped through spray nozzles onto both surfaces of fabric as it moves along. You can choose to apply chemistry to only one side or both sides of the fabric. The object of the spray system is to achieve less wet pickup than what is achievable with padding. With lower wet pick up, the same amount of chemistry can be present, but less water is used, less energy is used to evaporate water, and energy consumption is reduced.

Another system, called kiss roll also applies chemistry gently without pressure. With this method, the fabric rides just above a container where a roll turns in a bath, picks up the chemistry in the trough, and carries it to the top to kiss the surface of the fabric. This is normally a one-sided application but two units can be oriented so chemistry is applied to both sides of the fabric. In fact, each side can receive different chemistry.

The engraved roll system is like the kiss roll technique. In this case, an engraved roll with lines or cavities etched on its surface is placed partially in a chemical bath. As the engraved roll picks up the chemistry and turns out of the bath, a blade (called a doctor knife) works like a squeegee to wipe the excess off leaving chemistry only in the etchings. The fabric moves between the engraved roll and a squeeze roll, and some pressure is applied. The application of chemistry must be very precise because the fabric never goes into a bath. With this technique, you can get very low wet pickups of water and chemistry

Another system for applying low levels of chemistry or to only one side of fabric is called the knife over roll. This takes advantage of thickened chemistry or foam placed in a crevice under a doctor knife. As the fabric moves under it, chemistry is spread along the fabric which then moves through two final squeeze rolls. Coatings are often applied with this type of system. Why use foam? Foam is a collection of many small bubbles; the chemistry is around the outside while the inside is air. When foam is used instead of a bath, very little water is needed and there is less wet pick up.

Another way to apply foam is on a horizontal roll padder. In this configuration, stable foam rests in the crotch of the rollers. As the fabric is pulled straight down through the foam and then the two squeeze rolls, the pressure collapses the foam. Stale foam needs this pressure to burst the bubbles that hold the chemistry

Alternatively, unstable foam with bubbles that pop upon contact with fabric, can be used with systems designed without a mechanism for applying pressure. This illustration shows you how unstable foam is pumped into distribution chambers that release foam through slots both below and above fabric traveling horizontally. The surface contact with the foam is sufficient to collapse the bubbles that contain the chemistry.