Introduction

One of the most crucial things to consider when assessing the longevity of an iron-on patch is its ability to hold. All the factors such as type of fabric, heat settings, pressure etc. affect the bonding of the adhesive, but the bonding strength, flexibility and durability of the final bond will depend on the adhesive itself. 

Two of the most popular professional models are TPU (Thermoplastic Polyurethane) and PES (Polyester-based adhesive) models, which are used in various performance conditions and are more popular in the market.

The properties of TPU and PES are very different with respect to flexibility, wash resistance, thermal properties and durability. TPU is characterized by its softness, elasticity and garment performance, while PES is recognized for its rigidity and high-temperature performance. The decision of which to use hinges on the purpose for the garment, the frequency of washing and the lifespan of the patch.

1. What Is TPU Adhesive Backing?

a) What TPU is and how it behaves under heat?

The flexible heat-activated adhesive TPU (Thermoplastic Polyurethane) is a widely used adhesive in high quality garment applications. Under heat, TPU becomes soft and very elastic, flows into fibres of fabrics and then solidifies to form a flexible bond. This elasticity is particularly well suited to wear items such as garments that move, stretch or flex while in use.

b) What are the Mechanical properties?

Technically, TPU is soft touch, extremely flexible and can retain its softness and elasticity even after repeated use. It starts to work at relatively low temperatures, compared to many industrial adhesives, so that there is a lesser chance of damaging the fabric during application. It can be melt through fibers without any lumpiness after solidification due to its controlled melt flow.

c) Best uses:

TPU finds many applications in the manufacture of performance-wear, sportswear, fashion-wear and stretchable fabrics where comfort and flexibility are key.

2. What Is PES Adhesive Backing? 

a) What PES is and how its structure differs from TPU

PES (Polyester based adhesive) is a stronger and harder thermoplastic adhesive, which is used to provide durability and structural stability. PES will retain its shape after bonding, which means it's well suited for long-lasting strength and harsh weather applications, compared to TPU.

b) Its Mechanical properties

Most commonly, PES must be activated at higher temperatures, but after bonding, it has a good heat resistance and dimensional stability. This implies that the adhesive will not be subject to softening or weakening when it is washed and is not subjected to high temperatures.

c) Common uses and applications:

Due to its retention attributes, PES has numerous applications such as uniforms, industrial workwear, military clothing and hard-duty textiles where toughness is of greater significance than flexibility.

3. Bonding Performance Comparison

• TPU typically bonds more rapidly to fabric when it comes to initial adhesion strength, since it can melt at lower temperatures, and flow more rapidly into the fibers of the fabric.
• PES will need more heating and time to come to full activation but will form a more rigid bond when set.
• TPU has better, smoother and more flexible penetration, and it works well with soft or stretch fabrics.
• PES will penetrate more aggressively in stable fabrics while performance in elastic fabrics may be less than desired.
• Generally, the uniformity of the bond is better on flexible articles with TPU, and better on structured articles with PES.
• As time goes on, PES will usually offer greater edge stability, particularly when subjected to heavy washing or mechanical stress.

4. Wash Durability Comparison 

• TPU is very strong during normal washing cycles, but can gradually weaken during excessive cycles of hot washings or industrial washings. 
• It is very flexible and does not cause cracking, however harsh detergents over a period of time will decrease the strength of the adhesion
• PES is extremely durable to wash and has excellent resistance to hot water, detergents and chemicals.
• Does not deteriorate easily over time and is perfect for uniforms and clothes used regularly.
• Edge delamination is slightly more likely to occur with TPU because it is softer, but with PES, it is more likely to retain the edges due to the rigid bonding characteristics.

5. Flexibility and Wear Performance

The most important advantage of TPU is its flex fatigue resistance, as it is still flexible after bonding. This enables it to glide with the garments without cracking or splitting, perfect for stretch attire and active wear.

• PES can be a bit stiffer on soft clothes.
• TPU offers of soft feel on the surface of the garment while PES is not that soft in order to make the garment durable.
• TPU has better crack resistance when bent repeatedly, and PES exhibits stability, but can exhibit stress when bent a great deal.

6. Fabric Compatibility

• Both TPU and PES do a good job on cotton, TPU is more flexible, and PES is more durable in holding the cotton to the garment.
• For polyester, temperature control is critical while TPU activation is less, which makes it safer for use with heat sensitive polyester fabrics.
• When it comes to denim, PES has a slight edge because of its strength, and for TPU, it's still good, but it's more concerned with flexibility.
• The fabrics are clearly in favor of the TPU, as PES is a potential for cracking when stretched.
• both types of adhesives have a number of limitations on nylon and coated fabrics, although the TPU is more versatile in borderline conditions.

7. Heat Press Settings Comparison

• The activation temperature of TPU is low, which is easier to apply as well as safer for fragile fabrics.
• It also needs medium pressure and brief dwell time when compared to PES.
• Higher activation temperatures and dwell times are necessary for PES to be completely bonded with fibers.
• This makes it more appropriate for an organized industrial setting as opposed to a quick do-it-yourself application.

Once pressed, TPU changes to a flexible form and PES cools to a more rigid form.

8. Problems that arise in both

1. Edge lifting is more likely to occur in TPU as it has a softer structure compared to the other plastics. But, due to its elasticity is not much prone to crack.
2. Adhesive cracking can occur on PES when the fabric is flexed over and over, or when applied to fabrics that are being stretched, and the movement is greater than the rigidity of the fabric. Typical causes of delamination in PES are the wrong temperature control or the wrong fabrics used.
3. Both the adhesives can be damaged by high temperatures, and PES has a higher temperature tolerance than TPU.

9. Cost vs Performance

The advantage of the superior flexibility and polymer structure of TPU makes it more expensive in general. It provides good value in applications such as performance apparel and fashion where comfort and mobility are key.
PES is more cost effective for large scale production and industrial applications. The uniform or workwear applications where flexibility is not as critical as durability and lower material cost are best suited for its application.
The selection should be made based on application requirements and not price alone because each adhesive is designed to perform a different function.

10. Which Adhesive for Which Use Case?

• In terms of fashion, TPU is ideal for garments that require flexibility, comfort, and stretch, such as in streetwear and sportswear.
• It is also suitable for today's fashion clothes designs which demand soft and flexible bonding.
• For uniforms, industrial workwear, or outdoor clothing, where strength, heat resistance, and longevity are the key considerations, PES may prove to be more suitable.

Conclusion

TPU and PES are both high performance adhesive systems; however, they are designed to solve different problems when the patch is applied. TPU is engineered for flexibility, comfort and dynamic movement, whereas PES is engineered for strength, stability and long lasting use. This choice will vary depending on the garment type, the washer's wash environment and the end use environment. The correct glue is matched to the application to ensure the best possible performance, patched life and bonding consistency.