• Title, Summary, Keyword: Birefringence

Search Result 357, Processing Time 0.029 seconds

Improvement of Birefringence Characteristics of Injection-Molded Plastic Parts by Rapid Heating (급속 가열에 의한 사출성형품의 복굴절특성 개선)

  • Park, Keun;Kim, Byung-H.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
    • /
    • /
    • pp.195-198
    • /
    • 2007
  • The present work focuses on the prediction of birefringence in injection-molded plastic part and its improvement by rapid mold heating. To calculate birefringence, flow-induced residual stress is computed through a fully three-dimensional injection molding analysis. Then the stress-optical law is applied from which the order of birefringence can be evaluated and visualized. The birefringence patterns are predicted for a rectangular plate with a variation of mold temperatures, which shows that the amount of molecular orientation and birefringence level decreases with an increase of mold temperature. The effect of mold temperature on the order of birefringence is also studied for a thin-walled rectangular strip, and compared with experimental measurements. Both predicted and experimental patterns of birefringence are in agreements on the observation that the birefringence level diminishes significantly when the mold temperature is raised to above the glass transition temperature.

  • PDF

A Study on Improvement of Birefringence Characteristics of Injection-Molded Plastic Parts by Rapid Mold Heating (급속 금형가열에 의한 사출성형품의 복굴절특성 개선에 관한 연구)

  • Park, Keun;Kim, Byung H.
    • Transactions of Materials Processing
    • /
    • v.16 no.4
    • /
    • pp.229-233
    • /
    • 2007
  • The present work focuses on the prediction of birefringence in injection-molded part and its improvement by rapid mold heating. To calculate birefringence, flow-induced residual stress is computed through a fully three-dimensional injection molding analysis. Then the stress-optical law is applied from which the order of birefringence can be evaluated and visualized. The birefringence patterns are predicted for a rectangular plate with a variation of mold temperature, which shows that the amount of molecular orientation and birefringence level decreases with an increase of mold temperature. The effect of mold temperature on the order of birefringence is also studied for a thin-walled rectangular strip, and the relevant results are compared with experimental measurements. Both predicted and experimental patterns of birefringence are in agreements on the observation that the birefringence level diminishes significantly when the mold temperature is raised over the glass transition temperature.

Control of Wavelength Dispersion of Birefringence by Miscible Polymer Blends

  • Ougizawa, Toshiaki;Kuboyamaima, Keiichi
    • Proceedings of the Polymer Society of Korea Conference
    • /
    • /
    • pp.365-365
    • /
    • 2006
  • The wavelength dispersion of birefringence (or retardation) is very important property for optical use of polymer films. Birefringence free film and retardation film have been widely used for applications such as liquid crystal display (LCD). In this study, miscible polymer blends which consist of polymers of positive and negative birefringence were found. By operating composition and orientation of molecules in the transparent blend films, the behavior of wavelength dispersion of birefringence (retardation) was controlled. The applicability to wideband birefringence free film and quarter wave (retardation) film was discussed.

  • PDF

An Experimental Study on the Reduction of a Birefringence Distribution in LGP by Injection-Press Molding (형체압축성형을 이용한 도광판의 복굴절 저감효과에 관한 실험적 연구)

  • Min I. K.;Kim J. S.;Ko Y. B.;Park H. P.;Yoon K. H.;Hwang C. J.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
    • /
    • /
    • pp.17-22
    • /
    • 2005
  • The residual birefringence in molded plastic parts can be divided into two kinds of residual birefringence, i.e., the flow induced residual birefringence produced in flowing stages and the thermally induced residual birefringence produced in cooling stage. In this paper, the effect of new injection-press molding process with normal injection mold, i.e. I) injection-compression mode, ii) injection-press mode, on the distribution of birefringence was studied. It was found that the values of the birefringence was reduced at i) low clamping force and ii) longer mold opening length by injection-press molding.

  • PDF

An Theoretical Investigation on the Minimization of Birefringence Distribution in Optical Disk Substrate (광디스크 기판 성형시 발생하는 복굴절의 최소화를 위한 이론적 연구)

  • 김종성;강신일
    • Transactions of Materials Processing
    • /
    • v.9 no.2
    • /
    • pp.103-111
    • /
    • 2000
  • It is necessary to improve mechanical and optical properties in the optical disk substrates as the information storage density using short wavelength laser are being developed. The birefringence distribution is regarded as one of the most important optical properties for optical disk. In the present study, the birefringence distrubution is calculated using the Leonov model for viscoelastic constitutive equations and Cross/WLF model for viscosity approximation. The effects of processing conditions upon the development of birefringence discosity approximation. The effects of processing conditions upon the development of birefringence distribution in the optical disk were examined theoretically. It was found that the values of the birefringence distributions were very sensitive to the mold wall temperature history which minimizes the birefringence distribution. The analytical results showed the possibility of improving mechanical and optical properties in the optical disk substrates by active control of the mold wall temperature history.

  • PDF

A Study on the Rotation-Induced Birefringence in Plastic Disk Substrate (회전에 의해 플라스틱 기판에 추가로 발생하는 복굴절의 측정에 관한 연구)

  • 김종선;윤경환
    • Transactions of Materials Processing
    • /
    • v.12 no.8
    • /
    • pp.730-737
    • /
    • 2003
  • Extensive studies have been conducted for reducing the residual stresses and birefringence in injection-molded optical disk substrate Flow-induced and thermally-induced stresses and birefringence have been found as two main sources during injection molding process. However, high speed rotation also induces extra stresses and birefringence in real operation of disk drives. In the present paper rotation-induced in-plane birefringence has been measured and presented for CD and DVD substrates at different radial position. About 10 - 15 nm of extra retardation in one pass has been measured up to 4,800 rpm. The distribution of extra rotation-induced birefringence will be valuable data for designing an optimal optical disk substrate. Finally, experimental results were compared with the extra stresses calculated from simple formulation.

Numerical Analysis of Residual Stresses and Birefringence in Injection/Compression Molded Center-gated Disks (II) - Effects of Processing Conditions - (사출/압축 성형 Center-gated 터스크에서의 잔류 응력과 복굴절의 수치 해석 (II) - 공정조건의 영향 -)

  • Lee, Young-Bok;Kwon, Tai-Hun;Yoon, Kyung-Hwan
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.26 no.11
    • /
    • pp.2355-2363
    • /
    • 2002
  • The accompanying paper, Part 1, has presented the physical modeling and basic numerical analysis results of both the flow-induced and thermally-induced residual stress and birefringence in injection molded center gated disks. The present paper, Part II, has attempted to investigate the effects of various processing conditions of injection/compression molding process on the residual stress and birefringence. The birefringence is significantly affected by injection melt temperature, packing pressure and packing time. Birefringence in the shell layer increases as melt temperature gets lower. The inner peak of birefringence increases with packing time and packing pressure. On the other hand, packing pressure, packing time and mold wall temperature affect the thermally-induced residual stress rather significantly in the shell layer, but insignificantly in the core region. Injection/compression molding has been found to reduce the birefringence in comparison with the conventional injection molding process. In particular, mold closing velocity and initial opening thickness in the compression stage of injection/compression molding process have significant effect on the flow-induced birefringence, but not on tile thermal residual stress and the thermally induced birefringence.

A Study on the Prediction of Thermally-Induced Residual Stress and Birefringence in Quenched Polystyrene Plate Including Free Volume Theory (자유 체적이론을 고려한 급냉 폴리스티렌판에 발생하는 잔류응력과 복굴절 형성에 관한 연구)

  • Kim, Jong-Sun;Yoon, Kyung-Hwan
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.27 no.1
    • /
    • pp.77-87
    • /
    • 2003
  • The residual stress and birefringence in injection-molded plastic parts can be divided into the flow-induced residual stress and birefringence produced in flowing stage, the thermally-induced residual stress and birefringence produced in cooling stage. However, the physics involved in the generation of the thermally-induced residual stress and birefringence still remains to be understood. Because polymer experiences viscoelastic history near the glass-transition temperature it is hard to model the entire process. Volume relaxation phenomenon was included to predict the final thermally-induced residual stress and birefringence in quenched plastic parts more accurately. The present study focused on comparing the predicted values far thermally-induced residual stress and birefringence with and without volume relaxation behavior (or free volume theory) under free and constrained quenching conditions. As a result, tile residual stress remained as a tensile stress at the center and as a compressible stress near the surface for the free quenching cases. In contract the residual stress remained as a compressible stress at the center and as a tensile stress near the surface fur the constrained quenching cases. The residual birefringence remained as minus values at the center and as plus values near the surface for the free quenching cases. Interestingly the residual birefringence showed minus values in entire zone for the constrained quenching cases. In the prediction of birefringence only the case including free volume theory showed the correct result for the distribution of birefringence in thickness direction.

A Study on the Rotation-induced Birefringence in Plastic Disk Substrate (회전에 의한 플라스틱 기판에 야기되는 복굴절의 측정에 관한 연구)

  • 김종선;윤경환
    • Proceedings of the Korean Society for Technology of Plasticity Conference
    • /
    • /
    • pp.470-473
    • /
    • 2003
  • Extensive studies have been conducted for reducing the residual stresses and birefringence in injection-molded optical disk substrate. Flow-induced and thermally-induced stresses and birefringence have been found as two main sources during injection molding process. However, high speed rotation also induces extra stresses and birefringence in real operation of disk drives. In the present paper rotation-induced in-plane birefringence has been measured and presented for CD and DVD substrates at different radial position. About 10 - 15 nm of extra retardation has been measured up to 4,800 rpm.

  • PDF

An experimental study on the birefringence and extinction angle distribution in the injection/compression molded optical disk (사출/압축 성형된 광디스크 내의 복굴절 및 광축의 분포에 관한 연구)

  • Kim J. S.;Yoon K. H.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
    • /
    • /
    • pp.445-448
    • /
    • 2005
  • Recently, injection molding process became more popular than ever to produce large quantities of high precision products or optical products. Injection molding products can cause sensorial problems because of high birefringence or deformation from the residual stresses in the optical media. In the present study, we have focussed on the effect of holding and compression pressures on the optical anisotropy remaining in the MOD by examining the gapwise distribution of birefringence and extinction angle The effect of holding pressure was found to form the inner two birefringence peaks. But the effect of compression pressure on the birefringence distribution was found to make the uniform distribution near the center in the gap-wise direction. Finally, the value of the birefringence near the wall decreased as the mold temperature increased.

  • PDF