Birefringence–An important property of plastic substrates for magneto‐optical storage disks

Siebourg, W.; Schmid, H.; Rateike, F. M.; Anders, Sven; Grigo, U.; Lower, H. A.

doi:10.1002/pen.760301804

Cited by 19 publications

(8 citation statements)

References 3 publications

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“…(5) (8) and data acquired at 12 krpm and = We then compared these results with theoretical values for birefringence using stress equations (Fig.4). These data show a satisfying agreement between experiment and theory, particularly with regard to the predominance of axial birefringence An1.…”

Section: Measurement Theorymentioning

confidence: 97%

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<title>Interferometric analysis of stress-induced birefringence in a rotating glass disk</title>

1998

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Centnpetal forces in a rotating glass disk generate mechanical strains that are visible in polarized light. Dynamic stress birefringence in rotating disks has a practical effect on several classes of optical instruments, including flying-height testers for the data storage industry. We provide a model for stress-induced polarization effects, and describe an interferometric technique for mapping birefringence in a 100-mm diameter disk spinning at 12,000 rpm. The polarization interferometer employs a laser diode and a homodyne phase receiver to detect polarization-dependent phase shifts as small as I mrad at a data rate of 250 kHz.

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Section: Measurement Theorymentioning

confidence: 97%

“…(9) are the same ones that can be calculated by interferometric analysis of the bare glass disk and Eqs. (5)-(8). Consequently, our strategy for improving flying-height measurement accuracy in the presence of birefringence is to measure the c and a values just prior to loading the slider.…”

mentioning

confidence: 99%

<title>Interferometric analysis of stress-induced birefringence in a rotating glass disk</title>

1998

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“…However, PC has some deficient characteristics that deter its use in some areas. Poor moldability is one of the most serious of PC's defects that make it difficult to utilize PC for a substrate of optical‐data disk with higher memory density 13–21. For higher memory density optical data storage systems, pits or grooves, which record or address the memory, should be replicated on the substrate surface with the finer feature and at the narrower track pitches 13–17.…”

Section: Introductionmentioning

confidence: 99%

“…For higher memory density optical data storage systems, pits or grooves, which record or address the memory, should be replicated on the substrate surface with the finer feature and at the narrower track pitches 13–17. In addition, as the size and the spacing of the pits or grooves become smaller, reduction of birefringence becomes increasingly important to maintain the required signal/noise level 13, 17–21. Poor moldability of PC has restricted the process window to extremely high melt temperatures and mold temperatures, even for the standard substrate molding.…”

Section: Introductionmentioning

confidence: 99%

Phase morphology of polystyrene–polyarylate block copolymer/polycarbonate blends and their application to disk substrates

Ohishi¹,

Ikehara²,

Nishi³

2001

J of Applied Polymer Sci

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Polystyrene-polyarylate (PS-PAr) block copolymer was applied as a moldability modifier of polycarbonate (PC). From the 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) extraction results, PS-PAr block copolymer was demonstrated to copolymerize with PC via an in situ reaction between the PAr chain and PC. As a result of the chemical bonding between PS and PC chains, the PS dispersed domain in the PS-PAr block copolymer/PC blend could be reduced, on average, to a size smaller than the visible light wavelength. In particular, by adjusting PAr composition to 30 wt % in the fed PS-PAr block copolymer during the melt-mixing process, the PS domain size was completely reduced to be smaller than the visible light wavelength. As a result the blend substrate could satisfy the transparency required for the optical disk substrate with higher memory density: homogeneity under polarizing light, clarity on the reflective plate, and transparency at 400 nm. The melt viscosity could be lowered to the equal viscosity level of PC at about 30°C higher temperature by blending PC 15 wt % with the PS-PAr block copolymer. The lowered melt viscosity could reduce the retardation in the optical disk substrate, which was equivalent to that of the PC substrate processed at 30°C higher. In addition, the PS-PAr block copolymer/PC blend could attain the exact groove transcription at 20°C lower mold temperature than that of PC as a result of the lowered elastic modulus caused by the PS-rich phase. These features of the PS-PAr block copolymer/PC blend indicated a potential to offer an improved process window for the substrate molding. Because of its excellent transparency and a potential for processing flexibility, the PS-PAr block copolymer/PC blend would be a promising material for optical disk substrates with higher memory density.

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“…These stringent requirements can be fulfilled by specially designed polycarbonates. 2 However, PC shows a large positive birefringence, 5 which might cause optical distortion, owing to the presence of aromatic groups in the main chain. This positive birefringence can be eliminated substantially by blending with a polymer which has negative birefringence and can form a single phase with the constituent polymer.…”

mentioning

confidence: 99%

Solvent-Induced Crystallization and Interaction Parameter of the Blends of Bisphenol A Polycarbonate and Poly(phenyl methacrylate)

Park

Hong

1997

Polym J

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ABSTRACT:Blends of bisphenol A polycarbonate (PC) and poly(phenyl methacrylate) (PPMA) were crystallized by tetrahydrofuran (THF) solvent to investigate the phenomena of solvent-induced crystallization. The optimum conditions for solvent induced crystallization in PC have been determined. Interaction parameter has been calculated based on the melting point depression method to estimate the extent of miscibility. A negative interaction parameter (z 12 = -0.21) obtained from the melting point depression method suggests that there is some attractive interaction between the blend components.KEY WORDS Blend / Solvent Induced Crystallization / Interaction Parameter / Polycarbonate (PC) has been widely used both as a blend partner and by itself because it has outstanding engineering properties. Furthermore, due to its remarkable transparency, PC has been recognized as a suitable plastic for optical storage disc. 1 -4 The criteria of such optical materials 4 require low birefringence, low hygroscopicity, high transmission, dimensional stability, processability, and good mechanical properties. These stringent requirements can be fulfilled by specially designed polycarbonates. 2 However, PC shows a large positive birefringence, 5 which might cause optical distortion, owing to the presence of aromatic groups in the main chain. This positive birefringence can be eliminated substantially by blending with a polymer which has negative birefringence and can form a single phase with the constituent polymer. Poly(phenyl methacrylate) (PPMA) may be chosen as the blend partner of PC to form a miscible birefringence-free blend. For this reason, the birefringence-free composition of the PC/PPMA blend may be determined. The copolymers of PPMA and their blends often been reported to be used as optical lenses 6 -16 and optical disk recording materials 1 7 because of the high refractive index (1.5706) and high transparency of PPMA. But PPMA is very brittle and has low dimensional and thermal stability. 18 On the other hand, PC shows tough and ductile properties, good processability, thermal stability, and good electrical properties, but its poor scratch resistance and thermal stresscracking with its large birefringence are disadvantages. lt can be expected, therefore, that the drawbacks of each pure component can be overcome by blending the two components. By controlling the compositions of the blends, the improvement of physical properties may be achieved.We have demonstrated that the blends of the PC/ PPMA are completely miscible 19 and the birefringence and tensile properties of the blends were excellent. It is therefore of paramount importance to identify the origin of miscibility and to estimate the extent of miscibility by determining z12 interaction parameter. It has been known that solvent-induced crystallization can occur in PC. In this paper, the phenomena of solvent-induced 970 crystallization and the melting behavior of PC in the blends have been investigated. Subsequently, z12 interaction parameter was calculated based on ...

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Birefringence–An important property of plastic substrates for magneto‐optical storage disks

Cited by 19 publications

References 3 publications

<title>Interferometric analysis of stress-induced birefringence in a rotating glass disk</title>

<title>Interferometric analysis of stress-induced birefringence in a rotating glass disk</title>

Phase morphology of polystyrene–polyarylate block copolymer/polycarbonate blends and their application to disk substrates

Solvent-Induced Crystallization and Interaction Parameter of the Blends of Bisphenol A Polycarbonate and Poly(phenyl methacrylate)

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