In the fields of high-end electronic packaging, optical device assembly and precision medical device manufacturing, the shrinkage stress faced by traditional pressure-sensitive adhesives has long plagued engineers with pain points such as warping and debonding. The emergence of low-shrinkage UV PSA (pressure-sensitive adhesive) oligomers is rewriting the rules of precision bonding at the molecular level. This type of material can be cured in seconds under ultraviolet light, while controlling the volume shrinkage rate to less than 5% (the shrinkage rate of traditional UV resins is usually 8-15%), providing unprecedented stability for micron-level precision assembly.
1. Core technology principle: the chemical code of low shrinkage
Molecular structure design is the core of low shrinkage characteristics. Unlike conventional UV resins, low shrinkage UV PSA oligomers achieve dimensional stability through three key technologies:
Synergy between cyclic monomers and flexible segments: Introducing alicyclic structures (such as isophorone diisocyanate IPDI) and long-chain alkyl monomers (isooctyl acrylate) into the polyurethane acrylate skeleton can both inhibit shrinkage and maintain initial viscosity. Shenzhen U-Sunny's T-7333 resin uses a trifunctional aliphatic polyurethane acrylate structure to achieve a balance between high crosslinking density and low shrinkage (measured shrinkage <6%).
"Anchored" photoinitiator system: Using a polymerizable photoinitiator (such as HIH mixture), the initiator group is chemically bonded to the polymer main chain to reduce the shrinkage stress caused by small molecule migration. Studies have shown that this technology can reduce the residual amount by 67%, and the peel strength can be controlled from 6.96N/25mm to 0.49N/25mm.
Inorganic-organic hybrid strategy: Add nano-silica (such as Evonik TEGO® Rad 2330) or recycled carbon black to disperse shrinkage stress through physical crosslinking points and improve thermal stability (temperature resistance > 200°C).
Optimization of the photoinitiator system is also critical:
The cleavage initiator (TPO/LAP) is combined with a cationic monomer (such as cyclohexene oxide) to achieve free radical-cationic hybrid curing, and the shrinkage rate is 30% lower than that of the pure acrylic system.
The application of visible light initiators (such as bisacylphosphine oxide) increases the curing depth to the millimeter level, avoiding gradient shrinkage caused by too fast curing of the surface layer.
2. Key application areas: revolution in precision and reliability
1. Pressure-sensitive tapes and functional labels
In the field of high-temperature resistant labels, the formula based on T-7333 resin shows unique advantages:
177℃ dry heat shrinkage <1.8% (conventional PET substrate shrinkage >3%), ensuring that the battery label does not wrinkle during thermal cycles;
When used with silicone release agent, the peeling force can be controlled in the range of 2-20N/dm, and there is no residual glue after removal
2. Precision bonding of electronic devices
Wafer cutting temporary fixing glue needs to take into account high initial adhesion and low residue:
Polyacrylate containing HIH photosensitive groups makes the peel strength drop from 6.96N to 0.49N/25mm after UV curing, and the residue is reduced by 66%;
When T-7333 resin is used for camera module bonding, the shear strength retention rate after aging at 85℃/85%RH is >90%, which is better than 70% of epoxy glue.
3. Functional coatings and inks
The field of glass electroplating requires zero warping of the coating:
Due to its extremely low shrinkage, T-7333 still maintains an adhesion rating of 5B (ASTM D3359) after vacuum aluminum plating, and its water boiling resistance time is >2 hours;
Adding 0.5% phosphate adhesion promoter (such as AM-330) can achieve 0-level peeling on the stainless steel surface in the 100-grid test.
4. 3D printing and additive manufacturing
The dimensional distortion problem of DLP printing is solved by low shrinkage resin:
Adding a composite resin with 20% recycled carbon black reduces the secondary curing shrinkage to 0.8%, while increasing the tensile strength by 40%;
Polyurethane acrylate is combined with tetrahydrofuran acrylate to take into account both leveling and interlayer bonding strength.
4. Future trends: from "low shrinkage" to "zero stress"
The rise of bio-based oligomers: Cardanol-modified polyurethane acrylate has achieved a biocarbon content of >30%, and the shrinkage rate is maintained below 7%;
Smart response bonding: Photothermal dual-curing PSA achieves shadow area curing through latent amine initiators, and the shrinkage stress distribution is more uniform;
New path for nano-enhancement: MXene (titanium carbide) nanosheets are oriented in UV resin to form a mechanical interlocking network, which further reduces the shrinkage rate to 3.5%.