Mechanics and Reliability of Flexible Magnetic Media

1. Introduction.- 1.1. Physics of Magnetic Recording.- 1.1.1. Basic Principle.- 1.1.1.1. Magnetism.- 1.1.1.2. Electromagnetic Induction.- 1.1.1.3. Magnetic Recording.- 1.1.2. Vertical Recording.- 1.1.3. Signal-Processing Methods.- 1.1.4. Design Considerations.- 1.1.4.1. Recording Density.- 1.1.4.2. Reproduced Signal Amplitude.- 1.1.4.3. Signal-to-Noise Ratio.- 1.2. Magnetic Storage Systems.- 1.2.1. History of Magnetic Recording.- 1.2.1.1. Storage Hierarchy.- 1.2.2. Examples of Modern Storage Systems Using Flexible Media.- 1.2.2.1. Tape Drives.- 1.2.2.2. Flexible-Disk Drives.- 1.2.3. Head Materials.- 1.2.3.1. Permalloys.- 1.2.3.2. Mu-Metal and Hy-Mu 800B.- 1.2.3.3. Sendust Alloys.- 1.2.3.4. Alfenol Alloys.- 1.2.3.5. Amorphous Magnetic Alloys.- 1.2.3.6. Ferrites.- 1.2.3.7. Some Examples of Head Constructions.- 1.2.4. Flexible Media Materials.- 1.2.4.1. Base Film.- 1.2.4.2. Magnetic Medium.- 1.2.4.3. Particulate Magnetic Coatings.- 1.2.4.4. Magnetic Thin Films.- 1.2.5. Functional Requirements.- 1.3. Manufacturing Processes of Flexible Magnetic Media.- 1.3.1. Particulate Media.- 1.3.1.1. Tapes.- 1.3.1.2. Flexible Disks.- 1.3.2. Thin-Film Media.- 1.3.2.1. Metal-Evaporated Media.- 1.3.2.2. Sputtered Media.- 1.3.2.3. Electro/Electroless Plated Media.- References.- 2. Physical and Chemical Properties of PET Substrate and Coated Magnetic Media.- 2.1. Manufacturing Process of PET Films.- 2.2. Structure of PET Films.- 2.2.1. One-Way Stretching.- 2.2.2. Two-Way Stretching.- 2.2.3. Heat Setting (or Crystallization).- 2.2.4. Post-Stretching.- 2.2.5. Strain Relaxation (or Annealing).- 2.2.6. Commercial Biaxially-Oriented PET (Mylar A).- 2.2.7. Summary.- 2.3. Physical and Chemical Properties.- 2.3.1. Density.- 2.3.2. Refractive Index, Birefringence, and Infrared Dichroism.- 2.3.3. In-Plane Mechanical Properties.- 2.3.3.1. Effect of Temperature and Strain Rate.- 2.3.3.2. Effect of Annealing.- 2.3.3.3. Effect of Solvents.- 2.3.4. Elastic Modulus in the Thickness Direction.- 2.3.5. Radial Elastic Modulus of the Wound Reels.- 2.3.5.1. Effect of Winding Parameters and Magnetic Coating.- 2.3.5.2. Effect of Storage.- 2.3.5.3. Radial Relaxation Modulus.- 2.3.6. Thermal Expansion Properties.- 2.3.6.1. Heating Rate Effects.- 2.3.6.2. Effect of Annealing.- 2.3.6.3. Mechanisms of Thermal Expansion.- 2.3.7. Hygroscopic Expansion Properties.- 2.3.7.1. Effect of Annealing.- 2.3.8. Long-Term Dimensional Stability (Shrinkage).- 2.3.8.1. Effect of Annealing.- 2.3.9. Hydrolytic Stability.- 2.3.10. Summary.- 2.4. Outlook for Improved PET Substrates.- 2.4.1. Mechanical Properties.- 2.4.2. Coefficient of Thermal Expansion.- 2.4.2.1. Isotropic Polymer Films.- 2.4.2.2. Oriented PET Films.- 2.4.2.3. Laminates.- 2.4.2.4. Incorporation of Fibers and Filaments.- 2.4.3. Coefficient of Hygroscopic Expansion.- 2.4.4. Long-Term Dimensional Stability (Shrinkage).- 2.4.5. Summary.- References.- 3. Viscoelastic Properties of PET Substrate and Coated Magnetic Media.- 3.1. Introduction to Viscoelasticity.- 3.1.1. Elasticity.- 3.1.1.1. Generalized Hooke’s Law.- 3.1.1.2. Material Constants for Orthotropic Material.- 3.1.1.3. Material Constants for Isotropic Material.- 3.1.2. Viscous Liquids.- 3.1.3. Viscoelasticity.- 3.1.3.1. Constitutive Equation.- 3.1.3.2. Description of Time-Dependent Deformation Experiments.- 3.1.3.3. Mechanical Model Analogies of Linear Viscoelastic Behavior.- 3.1.3.4. Time (or Frequency) and Temperature Effects.- 3.2. Dynamic Modulus Data.- 3.2.1. Measurement Techniques.- 3.2.1.1. DMTA.- 3.2.1.2. DMA.- 3.2.2. Experimental Results.- 3.3. Tensile Relaxation and Creep Data.- 3.3.1. Descriptions of Creep and Relaxation Test Apparatuses.- 3.3.1.1. Creep.- 3.3.1.2. Relaxation.- 3.3.2. Constitutive Relations for Analysis of Isothermal Experimental Data.- 3.3.3. Experimental Results.- 3.3.3.1. Linearity of PET Material Response.- 3.3.3.2. Effect of PET Film Thickness.- 3.3.3.3. Effects of Temperature and Humidity in PET Films.- 3.3.3.4. Thermoviscoelastic Behavior of PET Films.- 3.3.3.5. Viscoelastic Behavior of Coated Tapes and Magnetic Coatings.- 3.3.3.6. Effects of Thermal Treatment of PET Films.- 3.4. Compressive Creep Data.- 3.4.1. Description of Creep Test Apparatus.- 3.4.2. Experimental Results.- 3.4.2.1. PET Films and Cast Films of Magnetic Coatings.- 3.4.2.2. Calendered Versus Uncalendered Magnetic Coatings.- 3.4.2.3. Recovery Experiments.- 3.4.2.4. Summary.- References.- Appendix 3.A Analysis of Flexural and Tensile Stress Relaxation of a Multilayered Tape.- 3.A.1. Flexural Relaxation at Constant Curvature.- 3.A.2. Tensile Relaxation at Constant Elongation.- Appendix 3.B Analysis of Thermal Curling of a Multilayered Magnetic Tape in the Elastic Regime.- 4. Physical Properties of Advanced Ultra-Thin Polymeric Substrates and Coated Magnetic Media.- 4.1. Standard and Advanced Substrates.- 4.2. Tensile Properties.- 4.3. Viscoelastic (Nonpermanent Deformation) Properties.- 4.3.1. Time-Dependent Creep Behavior.- 4.3.1.1. Description of Creep Test Apparatus and Experimental Procedure.- 4.3.1.2. Data Reduction Method.- 4.3.1.3. Experimental Results.- 4.3.2. Frequency-Dependent Dynamic Mechanical Behavior.- 4.4. Shrinkage, Thermal Expansion, and Hygroscopic Expansion (Permanent Deformation).- 4.4.1. Shrinkage.- 4.4.2. Thermal and Hygroscopic Expansion.- 4.5. Comparison of Deformation Characteristics of Various Substrates.- 4.6. Tribological Properties.- 4.6.1. Surface Roughness.- 4.6.2. Friction.- 4.6.3. Summary.- 4.7. Mechanical Design Considerations.- 4.7.1. Tape-to-Head Conformity and Dynamic Tape—Head Interactions.- 4.7.2. Transverse Curvature Due to Anisotropy.- 4.7.3. Critical Tension for Tape Flyability.- 4.7.4. Summary.- References.- 5. Stress Analysis of Flexible Media.- 5.1. Wound Magnetic Tape Reels.- 5.1.1. Initial Stress Field.- 5.1.1.1. Analytical Techniques.- 5.1.1.2. Measurement of Radial Stresses in a Wound Tape Reel.- 5.1.1.3. Role of Reel Geometry and Winding Parameters.- 5.1.1.4. Environmental Stresses.- 5.1.1.5. Summary.- 5.1.2. Stress Relaxation.- 5.1.2.1. Constitutive Relationships.- 5.1.2.2. Relaxation Matrix from Experimental Measurements.- 5.1.2.3. Axisymmetric Finite-Element Model.- 5.1.2.4. Numerical Results.- 5.1.2.5 Summary.- 5.2. Flexible Disks.- 5.2.1. Elasticity Solution.- 5.2.1.1. Orthotropic Solid Disk.- 5.2.1.2. Annular Disk: Fixed Inner Boundary.- 5.2.1.3. Approximate Scheme for Annular Disk: a/b Coating-Thickness Variations.- 6.3.1.2. Entrapped Air Pockets, Tension Ridges, and Scratches.- 6.3.2. How Does an Uneven Tape Stack Affect Data Reliability?.- 6.3.3. Summary.- 6.4. Mechanical Print-Through.- 6.5. Staggered Wraps.- 6.5.1. Sources of Tape Stagger.- 6.5.2. Effect of Winding Parameters and Storage Conditions.- 6.5.2.1. Analysis of Elastic Droop of a Staggered Wrap.- 6.5.2.2. Experimental Study.- 6.5.3. How Does Staggered Tape Cause Errors?.- 6.5.4. Methods of Preventing Tape Stagger.- 6.5.5. Summary.- 6.6. Design of Tape Reels.- 6.6.1. Hub.- 6.6.2. Flanges.- 6.6.3. Reel Materials.- References.- Appendix 6.A. Tension-to-Flatten Analysis for a Tape Reel with a Circumferential Bump.- 6.A.1. Tape Substrate.- 6.A.2. Composite Tape.- Appendix 6.B. Tension-Gradient Measurement Technique.- Appendix 6.C. Instantaneous Failure Rate Model to Assess Failures Due to Viscoelastic Deformation-Related Defects.- 6.C.1. Effect of “Burn-In”.- 7. Long-Term Reliability of Flexible Disks.- 7.1. Analysis of Disk Deformation.- 7.1.1. Thermal Expansion.- 7.1.2. Hygroscopic Expansion.- 7.1.3. Shrinkage.- 7.1.4. Centrifugal Stresses and Displacements.- 7.1.5. Summary.- 7.2. Measurements of Disk Deformation.- 7.2.1. Description of Disk Deformation Measurement Apparatuses.- 7.2.1.1. Stroboscopic-Disk Deformation Measurement Apparatus.- 7.2.1.2. Scanning-Laser-Disk Deformation Measurement Apparatus.- 7.2.2. Experimental Results.- 7.2.2.1. Thermal and Hygroscopic Deformations.- 7.2.2.2. Shrinkage.- 7.2.2.3. Creep.- 7.2.2.4. Summary.- References.- Appendix A. Requirements and Supporting Test Methods for Magnetic Tapes and Tape Reels.- Appendix B. Analysis of Life Data.- Author Index.