How to make the light diffusing polycarbonate used in LED illumination ?

Light diffusion material refers to the material that can convert point and line light sources into line and surface light sources. it is generally prepared by dispersing light diffusion particles with different refractive coefficients from the substrate in a transparent substrate. it is also called light scattering material or astigmatism material. The application of light diffusion materials in light-emitting diode (LED) lighting is a new application field opened up in recent years. LED lighting is stronger and softer than liquid crystal backlight, and the light diffusion materials used for LED lighting should minimize light loss while diffusing light, and have good toughness. Therefore, organic light diffusion particles and polycarbonate (PC) are often used to prepare LED lighting light diffusion materials with high light transmittance and high light diffusion properties. The principle of light diffusion material for LED lighting is shown in figure 1.

In recent years, more and more LED lighting optoelectronic enterprises and users have realized the importance of light diffusion materials as LED lighting uniform lampshade materials; in this experiment, acrylic and silicone light diffusion particles were used to prepare light diffusion PC for LED lighting. The effects of these two kinds of light diffusion particles on the properties of PC materials were studied, and the dispersibility, optical properties and thermal stability of the two kinds of light diffusion materials were compared.

Experimental part

1.1 Raw materials and equipment.

PC,1250Y; acrylic light diffusion particles and organosilicon light diffusion particles, sold in the market. TE35 co-directional twin-screw extruder, produced by Nanjing Keya Co., Ltd.; PT80 injection molding machine, produced by Lijin Technology Co., Ltd.; SU70 scanning electron microscope, produced by Hitachi, Japan; WGT-S light transmittance/haze tester, produced by Guangzhou Standard International Packaging Equipment Co., Ltd. CMT6104 universal testing machine and ZBC1400-B plastic pendulum impact testing machine are all produced by Meter Industrial Systems (China Co., Ltd.); XNR-400AM melt flow rate meter, produced by Chengde Dahua testing Machine Co., Ltd.; Q50 thermogravimetric analyzer, Q200 differential scanning calorimeter, all produced by American TA instrument Company.

1.2 sample preparation

The PC was dried at 110C for 12h, and then the light scattering particles were fully mixed with PC according to a certain mass fraction. The samples were tested by injection molding after granulation by a twin-screw extruder.

1.3 performance testing.

Dispersion of light diffusion particles: the sample was brittle and broken in liquid nitrogen, and the surface was sprayed with gold and observed by scanning electron microscope (SEM). The optical diffusivity was tested according to GB/T 2410 Mel 2008, the notched impact strength of simply supported beams was tested by GB/T 1043.1 Mel 2008, the tensile properties was tested by GB/T 1040 Mel 2006, and the melt flow rate (MFR) was tested according to GB/T 3682 Mel 2000, 260 °C and 2.16 kg. Thermogravimetric (TG) analysis: the sample was weighed for about 10 mg, nitrogen atmosphere and heating rate of 20 °C/min. Differential scanning calorimetry (DSC) analysis: about 10 mg samples were heated to 150 °C with 20 °C/min, kept at a constant temperature of 3 min, then rapidly cooled to-20 °C, and then heated to 150 °C with 20 °C/min. The glass transition temperature (Tg) of the second heating process was selected.

In order to obtain light diffusion agent materials with excellent properties, the good dispersion of light diffusion agent particles in polymers is very important. It can be seen from figure 3 that there are a large number of light diffusion particle microspheres and corresponding holes in the light diffusion PC relative to the pure PC cross-section. The pore size of acrylic light diffusion materials is larger than that of organosilicon light diffusion materials, and the two kinds of light diffusion particles can be well dispersed in PC.

2.2 Light transmittance and haze of light diffusion materials.

It can be seen from Table 1 and Table 2 that whether acrylic light diffusion PC or silicone light diffusion PC, with the increase of the amount of light diffusion particles, the haze of light diffusion materials increases and the light transmittance decreases. Compared with 1.00 phr light diffusion particle 2 mm thick light diffusion plate and 2.00 phr light diffusion particle 1 mm thick light diffusion plate, it can be seen that the effect of plate thickness on light transmittance and haze is greater than the amount of light diffusion particles.

It can be seen from figure 4 that with the addition of a small amount of organic silicon light diffusion particles (such as 0.5 phr), the haze of the PC plate can reach the effect of 2 phr acrylic light diffusion plate, but the light transmittance is lower. The reason is that organosilicon light diffusion particles have smaller particle size and refractive index, so they have a better effect of increasing haze. It can also be seen from figure 4 that although the amount of acrylic light diffusion particles is significantly larger than that of organosilicon particles at the same haze, acrylic light diffusion materials have higher light transmittance than organosilicon light diffusion materials. The reason is that acrylic acid particles absorb less light than organosilicon particles.

2.3Mechanical properties and MFR.

It can be seen from tables 3 and 4 that the tensile strength, tensile fracture strain and MFR of PC do not change much with the amount of light diffuser particles. However, acrylic light diffusion particles can reduce the impact strength of PC, but the addition of a small amount of acrylic light diffusion particles to PC causes a significant decrease in impact strength, while organosilicon light diffusion particles have little effect on the impact strength of PC. The reason is that the particle size of acrylic acid light diffusion particles is larger (3 ~ 5 μ m). Large particles are easy to cause defects, resulting in a significant decrease in impact strength. However, the particle size of organosilicon particles is only about 2 μ m, which has little effect on the impact strength.

2.4 Thermal stability

The initial thermal decomposition temperature of particles is about 290 °C. the initial thermal decomposition temperature of PC is about 430 °C. It can be seen that the thermal stability of the two kinds of light diffusion particles is worse than that of PC, and organosilicon light diffusion materials have better thermal stability than acrylic light diffusion materials.
PC has high viscosity and high processing temperature, so light diffusion particles are required to have certain thermal stability. It can be seen from figure 5 that the initial thermal decomposition temperature of acrylic light diffusion particles is about 230 °C silicone light diffusion.

Because the initial thermal decomposition temperature of organosilicon photodiffusion materials is about 290 °C and the dosage is less than 1.00 phr, it has good thermal stability for molding processing below 300 °C.

The weight loss of acrylic light diffusion materials does not occur until 354 °C, which has little effect on the processing at 300 °C. However, the 200 °354 °C curve (the dotted frame in figure 5) is enlarged as shown in figure 5b, and it can be seen that the light diffusion material with light diffusion particles has experienced slight thermal weight loss at 230 °C. The comparison of curve 2 and curve 3 shows that with the increase of the amount of light diffusion particles (from 1.00 phr to 4.00 phr), the thermal weight loss of light diffusion PC is more obvious. Therefore, the propenic acid photodiffusion particles will affect the thermal stability of PC, and its addition should not be too large, otherwise the thermal decomposition of the photodiffusion particles in the processing process will affect the properties of the light diffusion materials.

It can be seen from figure 6 that the Tg of acrylic light diffusion particles is 137.7 °C, and the Tg of Tg,PC is 150.2 °C when silicone light diffusion particles are lower than 200 °C. The addition of light diffusion particles to PC makes its Tg decrease. The reason is that the spherical light diffusion particles uniformly dispersed in PC contribute to the movement of PC molecular segments, so Tg is reduced.

3 conclusion.

A) preparation of acrylic and silicone light diffusion particles.
The light diffusion PC materials for LED lighting are obtained, and the two kinds of light diffusion agent particles are micron spherical and can be well dispersed in PC.

B) the particle size of acrylic light diffusion particles is larger than that of organosilicon light diffusion particles, and the corresponding light diffusion materials have more light transmittance when they reach the same haze (2.00 ~ 5.00 phr).

C) silicone light diffusion materials can achieve high haze by adding a small amount of light diffusion particles (less than 1.00 phr), and can maintain the high impact strength and good processing thermal stability of PC.