Optical properties of high‐density polyethylene in injection press molding for IR system lenses

Abstract

An experimental investigation of injection press molding (IPM) was conducted to assess high infrared radiation (IR) transmittance with an opaque state (low‐visibility ray (VR) transmittance) necessary for IR system lenses as a target high‐density polyethylene (HDPE) IR transmission material. The changed conditions were the cavity open distance and delay time considering the polymer melt flowability. Other molding conditions were held constant. Mold surface roughnesses of two kinds were used. Data for IR and VR transmittance were evaluated using measurements or observation results obtained for surface roughness, thickness, differential scanning calorimetry (DSC), crystallinity, and the internal structure. Results show that the surface roughness and thickness of molded parts did not influence IR or VR transmittance. For thin skin layers with low orientation of molecular chains, the IR transmittance was higher for longer delay times. For low molecular chain orientation in the shear–core layer, the VR transmittance was also low. The molecular chain orientation differed depending on IPM conditions. Setting a longer delay time produced a uniform distribution of the molded part thickness. Furthermore, thickness became a constant value when a mold with high surface roughness was used. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

Influence mechanism of injection process parameters on iridescent pattern defects on optical molded parts

“…The results showed that the increase of holding pressure was favorable to improving the uniformity of the refractive index distribution. Kaneda et al [23][24][25] investigated the effects of mold temperature and holding pressure on the transmittance of polyethylene lenses and concluded that the mold temperature and holding pressure affected the transmittance mainly by changing the degree of orientation and the crystallinity of part. Furthermore, the transmittance decreased as the orientation decreased and the crystallinity increased.…”

Mold replication in injection molding of high density polyethylene

“…In analogy with several references, HDPE has been selected for the experimentation as it is an easy-to-mold polymer with linear viscoelastic behavior. [2][3][4]8,9] The aim is to understand if relaxation effects may have a role in the definition of the polymer surface morphology. For this aim, many steel inserts have been prepared with different surface textures.…”

“…Recently, in the case of high density polyethylene (HDPE), it has been observed that when the mold Ra became high, the Ra of molded parts became high, too. [ 2 ] Ra of HDPE is important as it could affect infrared transmittance. [ 3 ] In the case of metallic fillers, reflectance values decrease proportionally with the Ra .…”

“…[ 2 ] Ra of HDPE is important as it could affect infrared transmittance. [ 3 ] In the case of metallic fillers, reflectance values decrease proportionally with the Ra . [ 4 ] By fixing the mold surface and changing process parameters, roughness of the molded surface changes as well.…”

Effect of recycling and injection parameters on gloss properties of smooth colored polypropylene parts: Contribution of surface and skin layer

“…It has been found that the haze of polyethylene (PE) blown films is primarily caused by the scattering of light due to surface irregularities . Surface scattering is one of the major reasons for the loss of optical transparency . Nonetheless, optical transparency is also lowered because the scattering takes place when light passes through boundaries between the domains of different refractive indices, for example, between amorphous and crystalline domains in polymers.…”