Ultraviolet-curable Nanozirconia/polyurethane Acrylate Encapsulation Materials For LEDs With Enhanced Moisture-Resistance And Optical Performance

With the development of lighting equipment,LEDs are enjoying a big market increase due to their energy-saving,green,and wide color temperature characteristics.They have been widely used in all walks of life,including industries which require high precision such as medical lighting and exploration lighting.Different from general lighting,LEDs application in special environments such as oceans and rainforests,as well as in wearable medical devices that directly contact the human body suffer the exposure to extreme temperatures,high humidity,and susceptible to friction and impact.Water and impurity ions in the air could enter the surface of the LED chip which may cause the PN junction of the chip and form an electrostatic over-voltage beyond the withstand value.This could lead to the discharge between the electrodes,resulting a phenomenon of partial melting,which may cause a leak and short circuit in LED,hindering the LED application in exploration,shipping,wearable equipment etc.For LED devices in the field,the encapsulation layer needs to have higher chemical stability and mechanical strength.At the same time,the moisture resistance is another major indicator that needs to be met for encapsulation layer.In view of the above requirements,this paper designs a LED device packaging composite material with high humidity resistance,high wear resistance,and high refractive index at the same time.First of all,in terms of substrate,this experiment uses aliphatic polyurethane acrylate(PUA),a liquid resin system,which is conducive to industrial operation.When ultraviolet light is irradiated on the resin system,the system is triggered by the light excited by the ultraviolet light.The bond breaks of the agent generate free radicals can initiate a series of polymerization reactions of monomers and oligomers in the system,and finally form a super-high molecular weight polymer.Compared with traditional packaging materials such as silicone and epoxy resin,PUA has better hardness and aging resistance.To obtain a light-initiated curing,moistureproof,anti-corrosion,high-hardness and high-fold LED encapsulation layer is strongly needed.However,it is difficult for a single-component resin material to meet multiple requirements at the same time.Compared with singlecomponent traditional materials,such as resins and other polymers,the organicinorganic nanocomposite made of two or more materials has not only the superior properties of inorganic nanomaterials such as mechanical strength,but also the superior properties of organic polymers such as flexibility.Zirconium dioxide(ZrO2)nanoparticles have excellent properties such as stable properties,high refractive index,no photocatalysis,anti-corrosion and moisture-proof properties.They are suitable for use as fillers and PUA compound.However,the problem of easy agglomeration and poor dispersion of inorganic particles are among the obstacles for compounding.In this paper the method of preparing nanoparticles is adopted firstly,and then surface grafting is designed according to the environment of the filler to be used with the encapsulating resin.The influence of some important process parameters in the surface modification of ZrO2 nanoparticles is discussed as well.Methacrylic acid(MA)and y-methacryloxypropyl trimethoxysilane(KH570 silane coupling agent)double modification method based on two modifiers is chosen,and a high solid content organic phase transparent ZrO2@MA-KH570 nano-dispersion is prepared based on this method.Based on the above experimental results,double modification method is employed to prepare cubic phase ZrO2@MA-KH570 nanoparticles with an average particle size at about 3.7 nm,which can be dispersed in tetrahydrofuran solvents with a maximum solid content of 35 wt%.Preparation of ZrO2@MA-KH570/PUA nanocomposite film and series of performance studies have been carried out.The average light transmittance of ZrO2@MA-KH570/PUA nanocomposite film is greater than 97%,and the refraction rate of ZrO2@MA-KH570/PUA50%composite increases by 10%compared with pure PUA substrate.After long-term high temperature baking or ultraviolet ray aging,the light transmittance is still above 90%;the hardness is increased to above 9H,while the adhesion is basically 100/100.When the material is soaked in water,the lowest water absorption rate can reach 0.011%.At the same time,LED devices are prepared with ZrO2@MA-KH570/PUA composite encapsulation layer and performance research is conducted.It is concluded that the light transmittance of LEDs with ZrO2@MA-KH570/PUA encapsulation layer can reach 30.115 lm in high humidity environment.The highest luminous flux retention rate can reach 97.037%.The LED device nanocomposite packaging materials prepared in this experiment have broad application prospects in high humidity and special environments.