How to make the light diffusion polycarbonate sheet?

In recent years, the global LED industry has developed rapidly, and countries have shown great enthusiasm for the development of LED industry. On May 7, 2012, the 12th five-year Special Plan for the Development of Semiconductor Lighting Science and Technology (draft for soliciting opinions) issued by the Ministry of Science and Technology proposed that by 2015, LED lighting products will account for 30% of general lighting, and 50 pilot demonstration cities of “ten thousand cities” will be built. The market demand and policy support indicate that the market prospect of LED lighting lamps is very broad, and the light diffusion material, as the shell material of LED lighting lamps and lanterns, also ushered in a huge market demand. At present, most of the new photodiffusion materials are produced by the blending of transparent polymer matrix materials and diffuser particles. Inorganic particles are mostly used as light diffusers, including glass beads, SiO2, TiO2, CaCO3, MgSiO3, BaSO4 and sulfide ZnS,BaS. These inorganic particles are usually hard and irregular, and they are easy to wear away the processing equipment during processing, and the particle size of the dispersed phase is difficult to achieve uniformity, which reduces the mechanical properties of the polymer matrix. These particles are sensitive to heat, oxygen and ultraviolet light. If the dispersed particles are too large, it will also lead to uneven surface of the material [1]. Moreover, the addition of inorganic particles will seriously affect the light transmittance. The application of inorganic particles in light diffusion materials is seriously limited. In recent years, organic polymer particles have been widely used as light diffuser, such as polymethyl methacrylate [2], polystyrene [3], silicone resin [5-6], acrylic resin [6], methyl methacrylate-styrene cross-linked copolymer microspheres [7- 8] and so on.

Among the optically diffused materials, the selection, dosage and particle size of light diffusion agent have the most important influence on the optical properties of light diffusive materials. Polycarbonate (PC) with excellent mechanical properties and excellent processability is selected as the matrix material to study the effects of different kinds, dosage and particle size of organic light diffusion agent on the mechanical and optical properties of light diffuser materials. Provide reference for real production and application.

1 Experimental part 1.1 main raw materials.
PC: Bayer Company of Germany.
Light diffuser A: acrylic light diffuser, marketed;

light diffuser B (average particle size 2 μ m), C (average particle size). 3 μ m): silicone light diffuser, from Wanda Chemical Co., limited. ; other auxiliaries: sold in the market.

1.2 main instruments and equipment.
Co-rotating twin-screw extruder: CTE-35 type, Kobelon (Nanjing). Machinery co., Ltd.
Injection molding machine: HTEF90W1, (Ningbo Haitian Plastic Machinery Group. Limited company)
Field emission scanning electron microscope (SEM): QUANTA200. (Type A, American FEI Co., Ltd.)
Light transmittance/haze tester: WGT-S, Shanghai Precision Department.
Xue Instruments Co., Ltd.; Universal Electronic tension testing Machine: SHIMADZU AGS-J.
Shimadzu production Institute of Japan.
Impact testing machine: XJJ-5, Chengde Testing Machine Co., Ltd. Division.

1.3 sample preparation.
Dry the raw materials at 110 °C for 12 hours and divide them according to a certain mass.
Several light diffuser particles and PC are mixed evenly, and then extruded and granulated by a twin-screw extruder. The granules were dried at 110 °C for 12 h and then injected into test samples.

1.4 performance testing.
The tensile strength is tested according to GB/T 1040.2 Mel 2006, the notched impact strength is tested by GB/T 1043.1 Mel 2008, and the light transmittance and haze are tested according to GB/T 2410 Mel 2008.
Thickness is 2 mm.
SEM observation: the light diffuser Apene B and C were evenly sprinkled on the surface.
The surface of the conductive adhesive is sprayed with gold, observed and photographed by SEM. The samples were frozen in liquid nitrogen and brittle broken, gold was sprayed on the fracture surface, observed and photographed by SEM.

2 results and discussion

2.1 compared with inorganic light diffuser

organic light diffuser absorbs less light, so it can be used to prepare light diffusion materials with high light transmittance and high haze. Figure 1 shows the SEM photos of the light diffuser and the PC-based light diffusion agent (0.5% mass fraction of the light diffuser).

It can be seen from Fig. 1A, Fig. 1C and Fig. 1e that light diffusion agent An and C are regular spherical particles, but the particle size distribution of light diffusion agent An is wide, the range of particle size distribution is 1 ~ 4 μ m, and the average particle size is 2 μ m; the particle size of light diffusion agent B is not uniform, the range of particle size distribution is 1 ~ 3 μ m, and the average particle size is 2 μ m; the particle size of light diffusion agent C is uniform, the particle size distribution is concentrated, and the average particle size is 3 μ m.

It can be seen from figs. 1B, FIG. 1D and FIG. 1f that the light diffusion agent can be uniformly dispersed in the PC matrix and keep its original shape. However, there are voids in the interface between the light diffusion agent and the matrix in fig. 1D and fig. 1F, and there are also a large number of voids in the sample, indicating that the compatibility of silicone light diffusion agent and matrix resin is poor. In addition, because the sample is prepared at 280 ~ 300 °C, and the light diffusion agent keeps its original shape in the sample, it shows that the three kinds of light diffusion agent have good heat resistance.

2.2 Mechanical properties.
Figure 2 shows the effect of the amount of light diffuser on the mechanical properties of PC-based light diffusion materials.
As can be seen from figure 2, with the increase of the mass fraction of light diffuser, the tensile strength of the material shows a fluctuating downward trend, but the range of change is very small; the notched impact strength of the material shows a downward trend, and its change range is also very small. Generally speaking, the tensile strength of pure PC is 63 MPa. After adding the light diffusion agent, the tensile strength fluctuates between 60.5 and 62.5 MPa, which shows that the light diffusion agent has no obvious effect on the tensile strength of the material.

This is because the number of defects in the material is less than that of the material itself, so there is no significant increase in the number of defects in the material as a whole after the addition of light diffusion agent. the most obvious effect on the tensile strength of the material is the defect that leads to stress concentration. After the addition of light diffusion agent, the notched impact strength of the material fluctuates between 12 and 14 kJ/m2. With the increase of the mass fraction of light diffusion agent A, the notched impact strength of the material basically does not change, while the notched impact strength of the material with the addition of light diffusion agent Bmind C decreases with the increase of its mass fraction. This may be because the compatibility of acrylic light diffusion agent with PC is better than that of silicone light diffuser with PC, and PC is a notch sensitive material, so the material is prone to brittle fracture after adding silicone light diffusion agent, which leads to the decrease of notched impact strength. However, due to the addition of less light diffusion agent, the decrease is small.

2.3 Evaluation of optical properties

The two main indicators of optical diffusion materials are light transmittance and.
Haze [9]. Light transmittance refers to the ratio of the luminous flux through the sample to the luminous flux irradiated on the sample, which is an important performance index to characterize the transparency of transparent polymer materials. The higher the light transmittance of polymer material, the better its transparency; haze, also known as turbidity, is the ratio of the scattered light flux to transmission light flux that deviates from the direction of incident light through the sample, which is used to measure the degree of ambiguity or turbidity of a transparent or translucent material, which is caused by discontinuity or irregularity on the interior or surface of the material. The haze is usually used to characterize the light scattering intensity of light scattering materials.

The main results are as follows: (1) the effect of the amount of light diffuser on the light transmittance and haze of the sample. The cause of light scattering phenomenon [10] is the result of the destruction of the uniformity of the medium, that is, there are great differences in optical properties (such as refractive index) among the adjacent medium elements of the wavelength order of magnitude, under the action of incident light, they are used as secondary wave sources to treat secondary waves with different radiation amplitudes, and their phases are also different from each other. As a result of the coherent superposition of secondary waves, except that some light waves still propagate in the direction specified by geometrical optics, they can not be offset in other directions, resulting in scattering. Therefore, scattering is bound to occur when the incident light is irradiated at the interface of two substances with different refractive index.

It can be seen from figure 3 that when the mass fraction of light diffuser An is 0.2%, the light transmittance of the sample is 88.6% and the haze is 59.3%. With the increase of the mass fraction of light diffuser A, the light transmittance of the sample decreases gradually and the haze increases. When the mass fraction of light diffusion agent An is 0.6%, the light transmittance of the sample is 78.4%, the haze is 79.3%, the haze is relatively low, and the haze (≥ 90%) is far away from the required haze (≥ 90%). It is necessary to continue to increase the mass fraction of light diffuser A to meet the requirements.

As can be seen from figure 4, when the mass fraction of light diffuser B is 0.2%, the light transmittance of the sample is 86.5%, and the haze is 73.8%; when the mass fraction of light diffuser B increases to 0.3%, the light transmittance of the sample decreases to 73.5%, and the haze increases to 92.5%; if the mass fraction of light diffuser B continues to increase, the light transmittance of the sample decreases rapidly, while the haze increases slowly.

It can be seen from figure 5 that when the mass fraction of light diffuser C is 0.2%, the light transmittance of the sample is 83.2% and the haze is 90.8%. If the mass fraction of light diffuser C continues to increase, the light transmittance of the sample decreases significantly and the haze increases. When the mass fraction of light diffuser C is 0.3%, the light transmittance of the sample decreases to 80.8%, and the haze increases to 94.9%. After that, when the mass fraction of light diffuser C continues to increase, the haze of the sample decreases.

To sum up, when the mass fraction of the light diffusion agent is the same, the light transmittance of the sample with light diffusion agent A (acrylic acid) is higher than that of the sample with light diffusion agent BMagine C (organosilicon), and the haze of the former is obviously lower. This is because silicone light diffuser absorbs more light than acrylic light diffuser.

(2) the effect of the amount of light diffuser on the effective light diffusion coefficient of the sample.
In general, the effective light diffusivity of the material is expressed by light transmittance × haze. The higher the value, the smaller the light loss when the specular diffusion intensity is obtained. The ideal light transmittance and fog value can be obtained by changing the amount of light diffuser, which can be transformed into effective light diffusion coefficient [2].

It can be seen from figure 6 that the effective light diffusion coefficient of the sample increases at first and then decreases with the increase of the mass fraction of light diffuser. In the sample added with light diffusion agent A, when the mass fraction is 0.2%, the effective light diffusion coefficient is 52.5%; when the mass fraction is 0.5%, the effective light scattering coefficient reaches the maximum value, which is 63.0%; when the mass fraction of light diffusion agent A continues to increase, the effective light scattering coefficient of the sample decreases. When the mass fraction of the light diffuser BMague C is 0.3%, the effective light scattering coefficient reaches the maximum, which is 68.0% and 76.7% respectively and continues to increase the mass fraction of the light diffusive. the effective light scattering coefficient of the sample decreases rapidly. The results show that the silicone light diffuser can achieve a higher effective light diffusion coefficient at a small dosage, and the effect of its dosage on the effective light diffusion coefficient is very obvious.

(3) the effect of the particle size of light diffusion agent on the haze of the sample. 

The effect of the particle size of the light diffusion agent on the haze of the sample is shown in figure 7.

As can be seen in figure 7, the haze of the material using optical diffuser B is generally lower than that of using optical diffuser C, but the difference between the two is relatively small. This is because the particle size of the light diffuser used in this experiment is larger than the wavelength of visible light, and its scattering effect belongs to Mie scattering. According to the Mie scattering theory, the spherical particles are uniformly dispersed in the matrix resin, and the scattering intensity of the system is a function of the refractive index, particle size, scattering angle and the wavelength of incident light in the surrounding medium [10]. The scattering angle and the wavelength of incident light in the medium around the particles are not considered, and only the effects of refractive index and particle size on the optical properties of the samples are considered. in a certain range, the larger the particle size is, the greater the difference of refractive index is, and the higher the scattering intensity of the material is. According to.

According to the calculation formula in GB/T 2410 Mel 200 “determination of light transmittance and haze of 8 transparent plastics”, materials with high scattering intensity have high haze. The particle size of light diffusion agent C is larger than that of light diffusion agent B, so the haze of the sample with light diffusion agent C is higher than that of light diffusion agent B. because the difference of particle size is small, the haze difference is small.

3 conclusion.

The main results are as follows: (1) the compatibility of organosilicon light diffusion agent and PC matrix is poor, while the compatibility of acrylic light diffusion agent and PC matrix is better. The addition of organosilicon light diffuser has no effect on the tensile strength of PC, but has a certain effect on the notched impact strength.

(2) the amount of light diffuser has a great influence on the light transmittance and haze of the material. For acrylic light diffuser, in order to make the material reach a certain haze, it is necessary to increase its dosage, but it has higher light transmittance; adding a small amount of silicone light diffuser can make the material achieve higher haze, at the same time, the light transmittance does not decrease obviously. When the mass fraction of silicone light diffuser C is 0.3%, the effective light diffusion coefficient of the material can reach 76.7%, the light transmittance is 80.8%, and the haze is 94.9%, which has good practical application value.

(3) the particle size of the light diffusion agent has an effect on the haze of the material in a certain range, and the haze of the material with the large particle size of the light diffusion agent is higher.