UV high refractive index anti yellowing adhesive/resin

UV high refractive index yellowing resistant adhesive/resin: UV curable optical grade material that meets the requirements of high refractive index (n_d ≈ 1.55-1.68), long-term yellowing resistance (QUV 1000h Δ b ≤ 1-2, no color difference in the double 85 test), high transmittance (>95% visible light), low shrinkage (<1-3%), and stable adhesion/coating performance. Its core is used for optical lenses AR/VR、 Scenarios such as optical communication have strict requirements for light efficiency and reliability.

 

Mainstream material system in the market

Core causes of yellowing

 

 

1. Molecular structure: Aromatic rings (benzene rings) undergo photo oxidation to form quinone chromophores, which are the main cause of yellowing;

 

2. Impurity residue: Incomplete reaction of photoinitiators/amine additives leads to oxidation and decomposition, producing colored substances;

 

3. Environmental aging: High temperature and high humidity (double 85), long-term UV irradiation triggers thermal/photo oxidative degradation, generating carbonyl (C=O) conjugated structures.

 

 Reference for the design of anti yellowing formula

 

 1. Main resin: Prioritize aliphatic polyurethane/sulfur modified/benzene ring free epoxy, and prohibit aromatic epoxy acrylate (high risk of yellowing);

 

2. Photoinitiator: Use cracked (hydroxy ketone, acylphosphine oxide) to avoid benzophenones (residual and prone to yellowing), combined with amine free co initiators;

 

3. Compound of anti yellowing additives (dosage 0.1-3%):

 

UV absorbers: Benzotriazole (UV-327), triazine (Tinuvin 400), broad-spectrum absorption of 280-390nm UV;

 

Hindered amine light stabilizer (HALS): high molecular weight type (HALS-944), UV-3853, quenches free radicals, reduces Δ b by 50%;

 

❸ Antioxidant: Compound of hindered phenol (IrgaNOx 1010, 0.3-0.5%) and hypophosphite (168, 0.1-0.3%) synergistically inhibits thermal oxidative aging;

 

4. Process optimization:

 

❶ Fully cured: Double bond conversion rate ≥ 90%, avoiding unreacted residues;

 

❷ Control adhesive thickness: Thin adhesive layer (<0.5mm) reduces light aggregation aging, while thick adhesive layer solidifies in layers;

 

❸ Clean production: Control impurities in the adhesive layer and avoid catalytic oxidation of metal ions.

 

 

Application scenario selection matching

 

1. Principle of refractive index matching

 

 ① Glass substrate (n=1.51-1.52): Choose n=1.55-1.60 (such as T-6601, T-6605) to reduce interface reflection and improve transmittance efficiency;

 

② High refractive index crystal/sapphire (n=1.65+): Choose n=1.63-1.68 (such as T-6603, K-6088, nano hybrid) to reduce light loss;

 

③ Flexible display/film: Choose n=1.60-1.625 (such as T-6604), balance refraction and flexibility, and prevent film curling.

 

 

2. Selection of yellowing resistance grade

 

① Indoor/conventional electronics (mobile phones, security lenses): QUV 500h Δ b ≤ 2, dual 85 500h without significant color difference, choose T-6605, T-6158D;

 

② Outdoor/car mounted (car mounted lens, LED packaging): QUV 1000h Δ b ≤ 1, dual 85 1000h pass, choose T-6603, VS-701, nano hybrid version;

 

③ Medical/high-end optics: Δ E<1 (85 ℃/500h aging), choose low yellowing customized version (amine free system+high-purity resin).

 

 

3. Process adaptation and selection

 

 ① Precision glue dispensing (lens assembly): Choose a viscosity of 5000-9000 mPa · s (such as T-6605, T-6158D), low shrinkage, anti displacement, and low overflow glue;

 

② Spray coating/roll coating (optical film): Choose viscosity of 7500-20000 mPa · s (such as T-6601), good leveling, no sagging;

 

③ 3D printing/nanoimprint: Choose low viscosity (<5000 mPa · s), fast curing version (such as T-6600), high molding accuracy.

 

 

Reliability Verification Standards (Third Party Testing)

 

1. Optical performance: transmittance>95% (400-700nm), haze<0.3%, refractive index uniformity ≤± 0.002;

 

2. Yellowing resistance: QUV/xenon lamp aging for 1000 hours, Δ b ≤ 1-2, Δ E<1; Double 85 (85 ℃/85% RH) 1000h, chromaticity change<1 level;

 

3. Mechanics and Environment: Shear strength ≥ 15MPa (glass to glass), no cracking due to thermal shock (-40 ℃~85 ℃/1000 times), Tg higher than the operating temperature of the equipment;

 

4. Environmental compliance: Passed RoHS, REACH, ISO 10110-12 optical standards.

 

 

Future Development Trends and Directions

 

① High refractive index upgrade: n=1.65-1.70+(sulfur modification+nanohybridization), suitable for AR/VR high refractive index waveguide requirements;

 

② Long term yellow resistance: no amine+UV absorber+HALS compound, outdoor life increased from 3 years to 8 years;

 

③ Process adaptation: low viscosity (<3000 mPa · s)+low shrinkage (<1%), meeting the requirements of precision micro nano structure dispensing/embossing;

 

④ Environmental upgrade: solvent-free, low VOC system, in compliance with electronic material environmental regulations.

 

 

 

List of typical application scenarios

 

1、 UV glue for brightening film

 

Application Introduction:

 

With the increasing demand for high brightness and high color gamut in LCD display screens, TV manufacturers use optical film products with core optical technology to increase screen brightness and color saturation. The optical film used here is called brightening film.

 

The micro prism structure with a thickness of about 25 μ m in the brightening film adjusts the angle of light through refraction and reflection, reducing light scattering and improving the luminous efficiency of the light source. The main preparation process of prism lenses is to coat UV cured optical resin on PET film substrate, and then irradiate UV light for rapid curing and molding after being pressed by a roller with micro prism structure.

 

Adhesive reference indicators

 

2. OCA adhesive for touch screen

Application direction:

 

Touch screens are currently the largest single application of UV optical adhesives. The UV optical adhesive in touch screens has three functions: bonding, increasing transparency, and improving impact resistance. It needs to meet strict performance requirements, including color, weather resistance and environmental stability, electrical performance, optical performance, etc. The adhesive materials involved in touch screen bonding mainly include glass, ITO conductive layer, PET, PMMA, PC, etc. When sapphire is used for touch screens, higher refractive index UV glue will be required to improve transparency.  

 

Application features:

 

It has excellent optical transparency, clarity, good adhesion performance, and small curing shrinkage rate, and is widely used in optical components such as 3C electronic product display screens. It plays an important role in bonding and packaging, reducing interface reflection, improving screen brightness and contrast.

 

3.  UV glue for fixing optical components:

 

Application direction:

 

In the optical system of a microscope, certain optical components may need to be fixed in specific positions with UV glue to ensure their accurate alignment during microscope operation.

 

Optical lenses can be widely used in various fields such as security, automotive, digital cameras, lasers, optical instruments, etc. In order not to damage the quality of optical components, UV glue used for bonding optical lenses must have extremely high purity and low shrinkage rate to prevent stress on glass lenses.

 

Application features:

 

Excellent optical performance, good transparency, and a light transmittance of over 99% after adhesive curing; 2. Low curing stress and low linear shrinkage rate; 3. Has good solvent resistance and weather resistance; 4. Strong adhesion, resistance to yellowing and aging; 5. Stable mechanical and chemical properties, resistant to vibration, impact, etc.