Factors Affecting Scratch Resistance of Water-Based Self-Matte Resin Applied on PET Film

When water-based self-matte polyurethane resin is applied on PET film, the core factors affecting its scratch resistance undergo significant changes. Unlike the leather applications discussed previously, PET film is a rigid, low-surface-energy, smooth substrate, and often involves high-speed printing and optical performance requirements. Therefore, scratch resistance no longer relies solely on the lubricity of the coating itself, but places greater emphasis on the coating's cohesive strength, adhesion to the PET substrate, and how to achieve surface densification while maintaining the matte effect. Below is a detailed analysis of the specific influencing factors for PET film applications, ranked by importance:

1. Crosslink Density and Cohesive Strength of the Resin

This is the primary factor determining the scratch resistance of PET film.

• Crosslinking is Key: PET film surfaces are smooth and non-polar. If the coating's cohesive strength is insufficient, scratching can easily cause the coating to fail from within or at the interface. It is clearly stated that for PET film, excessively low crosslink density results in a soft film with poor scratch resistance, while excessively high crosslink density makes the film brittle and prone to cracking. Therefore, moderate crosslink density is crucial.

• Application of Crosslinkers: Almost all self-matte resin product specifications targeting PET emphasize the need to add aziridine, carbodiimide, or polyisocyanate-type crosslinkers during use. For example, adding 1%–2% aziridine crosslinker can significantly improve the coating's adhesion to PET and chemical resistance (e.g., alcohol wipe resistance), thereby indirectly greatly enhancing scratch resistance.

• Self-Crosslinking Resins: Choosing self-crosslinking water-based polyurethane (e.g., containing NCO end groups that self-crosslink upon heating) is a superior option, as it can improve coating strength without the addition of external crosslinkers.

2. Soft Segment Structure and Toughness of the Resin

PET film may experience slight stretching or bending during processing and use, so the coating needs to possess adequate flexibility to match the substrate and avoid reduced scratch resistance due to stress cracking.

• Flexibility Requirements: It is recommended to select resins with high elongation at break (e.g., ≥100%). If the coating is too hard (excessively high tensile strength, low elongation at break), fine cracks or brittle fracture are likely to occur when external forces are applied.

• Soft Segment Selection: Resins using polycarbonate diol (PCDL) or polybutylene adipate (PBA) as soft segments not only provide good flexibility but also balance hydrolysis resistance and weatherability. A patent explicitly states that using a blend of polycarbonate diol and polytetrahydrofuran ether diol can effectively improve the scratch and abrasion resistance of self-matte coatings.

3. Balance Between Surface Lubricity and Matting Mechanism

• Silicone Modification is Effective: On PET film, introducing silicone chain segments is also an effective means to improve scratch resistance. Silicone-modified water-based polyurethane can significantly reduce the coefficient of friction on the coating surface, allowing scratching objects to slide easily. Patent technology shows that using silicone-modified water-based polyurethane combined with UV resin and nano-silica can produce high-strength, washable protective films. Additionally, UV-curable silicone-modified resins have also been proven to possess 内部技能lent abrasion resistance and ethanol wipe resistance.

• Self-Matte vs. Added Matting Powder: On PET film, self-matte resins should be prioritized over added matting powders. Research shows that while added matting powders such as silica can achieve matting, filler particles tend to aggregate on the coating surface, resulting in uncontrollable surface roughness and a consequent decline in scratch and abrasion resistance. Self-matte resins achieve matting through large particle size and phase separation, and if film densification can be properly controlled, a better balance between matte effect and scratch resistance can be achieved.

4. Adhesion: Preventing Delamination During Scratching

On PET film, if adhesion is insufficient, the coating will directly delaminate from the interface when scratched, manifesting as poor scratch resistance. Therefore, adhesion is the foundation of scratch resistance.

• Functional Group Design: Water-based polyurethanes containing hydroxyl (-OH), carboxyl (-COOH), or epoxy groups should be prioritized. These functional groups can form hydrogen bonds or weak chemical bonds with the ester groups on the PET surface, thereby improving adhesion.

• Specialized Adhesion Promoters: Research has shown that oxazolidine-functionalized crosslinkers (such as EPOCROS™ K-2035E from Nippon Shokubai) exhibit 内部技能lent adhesion to polyester-based substrates (such as PET) while simultaneously improving coating film performance. This means that adding such additives to the formulation can effectively enhance interfacial bonding strength.

Summary: Core Paths to Improve Scratch Resistance on PET Film

(This article is for reference only. For technical questions, please consult our online engineers.)