1. The core challenge of TPU surface adhesion
The neutral or oily release agent remaining on the surface of TPU products during demoulding is difficult to completely remove even after cleaning, forming a weak interface layer that prevents ink and adhesive from effectively wetting the substrate. In addition, the uneven distribution of polar groups and elastic deformation characteristics of TPU further reduce the mechanical bite force of the coating or adhesive layer.
2. Surface treatment: basic process for improving adhesion
Optimizing the TPU surface by physical or chemical methods is the first key step to solve the adhesion problem:
Special treatment agent spraying
TPU treatment agent penetrates through the molecular layer to form a bridge layer on the surface of the substrate:
Hide the release agent oil stains and eliminate weak interfaces
Provide active groups for chemical bonding with subsequent coatings
Typical process: white oil cleaning → spray treatment agent (3-5μm) → bake at 65℃ for 3-5 minutes → spray primer
Mixed application method
Adding the treatment agent directly to the primer or ink in proportion can simultaneously improve leveling, cover oil stains and enhance interlayer adhesion, simplifying the process flow.
| Method | Operation process | Advantages | Applicable scenarios |
|---|---|---|---|
| Spraying of treatment agent | Cleaning → spraying → baking → painting | Strong oil-covering property, significantly improved adhesion | Vacuum plating of mobile phone cases, high-end spraying |
| Mixed use | Mix the treatment agent and primer → spray directly | Simplified process, improved leveling | Mass production |
| UV surface activation | Ultraviolet light irradiation (need to be used with photosensitizer) | Environmentally friendly, improved surface polarity | UV glue/ink bonding |
3. Material innovation: key adaptation of adhesives and inks
According to the characteristics of TPU, adhesives and inks need to achieve precise matching in molecular structure:
Choice of pressure-sensitive adhesive (PSA)
Rubber-based PSA (SBS/SIS-based): cost-effective, but requires the addition of tackifier resin (such as rosin ester) to compensate for initial tack
Acrylic PSA: excellent weather resistance, suitable for high temperature (120-150℃) or low temperature environment
Silicone-based PSA: the only type of adhesive that can bond low surface energy TPU, with a temperature resistance of 260℃
Curing control of UV adhesive and ink
Oxygen inhibition problem: surface stickiness can be solved by high-power light source or nitrogen protection
Viscosity adaptation: low-viscosity UV adhesive (such as Xinlida plastic UV adhesive) is easier to wet the TPU surface, and it is recommended to use products with a dynamic viscosity of <500 mPa·s
Light-curing thickness: the curing limit of conventional UV adhesive is 0.6-1.3cm, and ultra-thick coatings require a dual-curing formula of light and heat.
4. Innovative solution: Strong and tough UV resin T-7080
In response to the special needs of TPU adhesion, the T-7080 UV resin developed by Shenzhen U-Sunny has achieved a breakthrough through molecular structure innovation:
High toughness design: polyurethane modified acrylate chain segments absorb stress, adapt to TPU elastic deformation, and reach 5B level in Baige test
Increased polar group density: Contains hydroxyl and carboxyl functional groups, forming hydrogen bonds and chemical bonds with TPU substrate
Broad-spectrum compatibility: Can be compatible with inks, pressure-sensitive adhesives and UV adhesive systems, reducing the threshold for formula development.
5. Future Trends: Green and Efficient Cooperative Development
With the tightening of environmental regulations, water-based TPU treatment agents and UV-LED curing technology have become new directions:
UV-LED light sources are mercury-free and low-temperature (<5°C temperature rise), which avoids thermal deformation of TPU and is suitable for precision electronic components
Conclusion
To improve the surface adhesion of TPU, "treatment process + material innovation" is required: from treatment agent spraying, pressure-sensitive adhesive adaptation, to the application of high-performance resins such as T-7080, each step requires precise matching of substrate characteristics. With the advancement of green curing technology and molecular design, TPU will release broader application potential.