Mechanics and Reliability of Flexible Magnetic Media

by Bhushan, Bharat

• ISBN13: 9780387989365
• ISBN10: 0387989366
• Edition: 2nd
• Format: Hardcover
• Copyright: 2000-04-01
• Publisher: Springer Verlag

Summary

The Production of magnetic and optical storage systems for consumer applications (such as video tapes and audio CDs) and for data-processing applications (such as magnetic hard drives and CD-ROMs) is currently an $80-billion industry, growing at about 10% per year, with more than 80% of that in magnetic media. The storage capacity of magnetic devices has increased enormously over the past few years, with storage densities reaching on the order of 100 gigabytes per cubic inch. Increasing these densities for faster access and greater capacity will require materials with unprecedented smoothness, defect density, dimensional stability, and mechanical reliability, as well as devices with greatly improved mechanical stability, reduced dimensions, and higher speeds. This book discusses the issues associated with the reliability of magnetic storage devices, particularly flexible media such as tapes. After a brief introduction to the physics of magnetic recording and data storage, and the basics of manufacturing magnetic media, the book turns to the production, coating, and properties of magnetic media based on polyethylene terephthalate films. This is followed by discussions of the viscoelastic properties of such films, the mechanical stresses encountered by the films in actual use or storage, and the long-term properties of stressed films in storage. This second edition has been revised throughout and includes a new chapter on ultra-thin substrates.

Table of Contents

Preface	vii
Introduction	1	(85)
Physics of Magnetic Recording	1	(19)
Basic Principle	1	(1)
Magnetism	1	(8)
Electromagnetic Induction	9	(1)
Magnetic Recording	9	(2)
Vertical Recording	11	(1)
Signal-Processing Methods	12	(3)
Design Considerations	15	(1)
Recording Density	15	(1)
Reproduced Signal Amplitude	16	(3)
Signal-to-Noise Ratio	19	(1)
Magnetic Storage Systems	20	(48)
History of Magnetic Recording	20	(1)
Storage Hierarchy	21	(1)
Examples of Modern Storage Systems Using Flexible Media	22	(2)
Tape Drives	24	(18)
Flexible-Disk Drives	42	(9)
Head Materials	51	(1)
Permalloys	52	(1)
Mu-Metal and Hy-Mu 800B	52	(1)
Sendust Alloys	52	(2)
Alfenol Alloys	54	(1)
Amorphous Magnetic Alloys	54	(1)
Ferrites	55	(2)
Some Examples of Head Constructions	57	(2)
Flexible Media Materials	59	(1)
Base Film	59	(1)
Magnetic Medium	60	(4)
Particulate Magnetic Coatings	64	(3)
Magnetic Thin Films	67	(1)
Functional Requirements	68	(1)
Manufacturing Processes of Flexible Magnetic Media	68	(18)
Particulate Media	70	(1)
Tapes	70	(5)
Flexible Disks	75	(1)
Thin-Film Media	76	(1)
Metal-Evaporated Media	77	(2)
Sputtered Media	79	(1)
Electro/Electroless Plated Media	79	(1)
References	80	(6)
Physical and Chemical Properties of PET Substrate and Coated Magnetic Media	86	(78)
Manufacturing Process of PET Films	89	(5)
Structure of PET Films	94	(11)
One-Way Stretching	96	(2)
Two-Way Stretching	98	(2)
Heat Setting (or Crystallization)	100	(1)
Post-Stretching	101	(1)
Strain Relaxation (or Annealing)	101	(1)
Commercial Biaxially-Oriented PET (Mylar A)	101	(1)
Summary	102	(3)
Physical and Chemical Properties	105	(46)
Density	106	(1)
Refractive Index, Birefringence, and Infrared Dichroism	106	(6)
In-Plane Mechanical Properties	112	(7)
Effect of Temperature and Strain Rate	119	(1)
Effect of Annealing	120	(1)
Effect of Solvents	121	(1)
Elastic Modulus in the Thickness Direction	122	(2)
Radial Elastic Modulus of the Wound Reels	124	(2)
Effect of Winding Parameters and Magnetic Coating	126	(1)
Effect of Storage	126	(2)
Radial Relaxation Modulus	128	(1)
Thermal Expansion Properties	128	(4)
Heating Rate Effects	132	(3)
Effect of Annealing	135	(1)
Mechanisms of Thermal Expansion	135	(6)
Hygroscopic Expansion Properties	141	(5)
Effect of Annealing	146	(1)
Long-Term Dimensional Stability (Shrinkage)	146	(2)
Effect of Annealing	148	(1)
Hydrolytic Stability	149	(1)
Summary	150	(1)
Outlook for Improved PET Substrates	151	(13)
Mechanical Properties	152	(1)
Coefficient of Thermal Expansion	153	(1)
Isotropic Polymer Films	153	(3)
Oriented PET Films	156	(1)
Laminates	157	(1)
Incorporation of Fibers and Filaments	158	(1)
Coefficient of Hygroscopic Expansion	158	(1)
Long-Term Dimensional Stability (Shrinkage)	159	(1)
Summary	159	(1)
References	160	(4)
Viscoelastic Properties of PET Substrate and Coated Magnetic Media	164	(133)
Introduction to Viscoelasticity	164	(41)
Elasticity	166	(1)
Generalized Hooke's Law	167	(7)
Material Constants for Orthotropic Material	174	(4)
Material Constants for Isotropic Material	178	(4)
Viscous Liquids	182	(1)
Viscoelasticity	182	(1)
Constitutive Equation	183	(3)
Description of Time-Dependent Deformation Experiments	186	(10)
Mechanical Model Analogies of Linear Viscoelastic Behavior	196	(7)
Time (or Frequency) and Temperature Effects	203	(2)
Dynamic Modulus Data	205	(4)
Measurement Techniques	205	(1)
DMTA	205	(1)
DMA	206	(2)
Experimental Results	208	(1)
Tensile Relaxation and Creep Data	209	(69)
Descriptions of Creep and Relaxation Test Apparatuses	213	(1)
Creep	213	(6)
Relaxation	219	(1)
Constitutive Relations for Analysis of Isothermal Experimental Data	220	(5)
Experimental Results	225	(1)
Linearity of PET Material Response	226	(1)
Effect of PET Film Thickness	227	(1)
Effects of Temperature and Humidity in PET Films	227	(20)
Thermoviscoelastic Behavior of PET Films	247	(4)
Viscoelastic Behavior of Coated Tapes and Magnetic Coatings	251	(10)
Effects of Thermal Treatment of PET Films	261	(17)
Compressive Creep Data	278	(19)
Description of Creep Test Apparatus	278	(2)
Experimental Results	280	(1)
PET Films and Cast Films of Magnetic Coatings	280	(1)
Calendered Versus Uncalendered Magnetic Coatings	281	(1)
Recovery Experiments	281	(3)
Summary	284	(1)
References	284	(5)
Appendix 3.A. Analysis of Flexural and Tensile Stress Relaxation of a Multilayered Tape	289	(1)
Flexural Relaxation at Constant Curvature	289	(4)
Tensile Relaxation at Constant Elongation	293	(1)
Appendix 3.B. Analysis of Thermal Curling of a Multilayered Magnetic Tape in the Elastic Regime	293	(4)
Physical Properties of Advanced Ultra-Thin Polymeric Substrates and Coated Magnetic Media	297	(63)
Standard and Advanced Substrates	300	(3)
Tensile Properties	303	(2)
Viscoelastic (Nonpermanent Deformation) Properties	305	(26)
Time-Dependent Creep Behavior	305	(1)
Description of Creep Test Apparatus and Experimental Procedure	306	(2)
Data Reduction Method	308	(1)
Experimental Results	308	(10)
Frequency-Dependent Dynamic Mechanical Behavior	318	(13)
Shrinkage, Thermal Expansion, and Hygroscopic Expansion (Permanent Deformation)	331	(4)
Shrinkage	331	(3)
Thermal and Hygroscopic Expansion	334	(1)
Comparison of Deformation Characteristics of Various Substrates	335	(3)
Tribological Properties	338	(7)
Surface Roughness	338	(4)
Friction	342	(3)
Summary	345	(1)
Mechanical Design Considerations	345	(15)
Tape-to-Head Conformity and Dynamic Tape-Head Interactions	345	(6)
Transverse Curvature Due to Anisotropy	351	(5)
Critical Tension for Tape Flyability	356	(1)
Summary	357	(1)
References	358	(2)
Stress Analysis of Flexible Media	360	(59)
Wound Magnetic Tape Reels	360	(37)
Initial Stress Field	361	(2)
Analytical Techniques	363	(7)
Measurement of Radial Stresses in a Wound Tape Reel	370	(1)
Role of Reel Geometry and Winding Parameters	370	(5)
Environmental Stresses	375	(4)
Summary	379	(1)
Stress Relaxation	380	(1)
Constitutive Relationships	380	(2)
Relaxation Matrix from Experimental Measurements	382	(1)
Axisymmetric Finite-Element Model	383	(5)
Numerical Results	388	(5)
Summary	393	(4)
Flexible Disks	397	(22)
Elasticity Solution	397	(1)
Orthotropic Solid Disk	398	(2)
Annular Disk: Fixed Inner Boundary	400	(5)
Approximate Scheme for Annular Disk: a/b << 1	405	(2)
Estimates Based on Incomplete Knowledge of Elastic Compliances	407	(3)
Viscoelasticity Solution	410	(1)
Solution	411	(2)
Estimates for Large Times	413	(2)
Summary	415	(1)
References	416	(3)
Long-Term Reliability of Magnetic Tapes	419	(86)
Interlayer Slip (ILS)	421	(5)
Various Forms of Tape Distortions	421	(2)
Cinching	423	(1)
Spoking	423	(1)
Windowing	423	(1)
Telescoping	423	(1)
Model for Reel Slippage	424	(1)
Methods to Contain ILS	424	(1)
Estimate of Periods Between Rewinds	425	(1)
Environment for Archival Storage	425	(1)
Instantaneous Speed Variations (ISV)	426	(6)
Loose Wraps	427	(2)
Tape Vibrations	429	(3)
Uneven Tape-Stack Profile (Hardband)	432	(23)
Sources and Methods of Preventing Distortions	433	(1)
Substrate and Coating-Thickness Variations	434	(1)
Entrapped Air Pockets, Tension Ridges, and Scratches	435	(13)
How Does an Uneven Tape Stack Affect Data Reliability?	448	(7)
Summary	455	(1)
Mechanical Print-Through	455	(6)
Staggered Wraps	461	(23)
Sources of Tape Stagger	462	(3)
Effect of Winding Parameters and Storage Conditions	465	(1)
Analysis of Elastic Droop of a Staggered Wrap	465	(3)
Experimental Study	468	(7)
How Does Staggered Tape Cause Errors?	475	(4)
Methods of Preventing Tape Stagger	479	(3)
Summary	482	(2)
Design of Tape Reels	484	(21)
Hub	484	(5)
Flanges	489	(1)
Reel Materials	490	(1)
References	490	(2)
Appendix 6.A. Tension-to-Flatten Analysis for a Tape Reel with a Circumferential Bump	492	(2)
Tape Substrate	494	(1)
Composite Tape	495	(1)
Appendix 6.B. Tension-Gradient Measurement Technique	496	(2)
Appendix 6.C. Instantaneous Failure Rate Model to Assess Failures Due to Viscoelastic Deformation-Related Defects	498	(3)
Effect of ``Burn-In''	501	(4)
Long-Term Reliability of Flexible Disks	505	(14)
Analysis of Disk Deformation	506	(2)
Thermal Expansion	506	(1)
Hygroscopic Expansion	506	(1)
Shrinkage	507	(1)
Centrifugal Stresses and Displacements	507	(1)
Summary	508	(1)
Measurements of Disk Deformation	508	(11)
Description of Disk Deformation Measurement Apparatuses	509	(1)
Stroboscopic-Disk Deformation Measurement Apparatus	509	(1)
Scanning-Laser-Disk Deformation Measurement Apparatus	510	(2)
Experimental Results	512	(1)
Thermal and Hygroscopic Deformations	513	(2)
Shrinkage	515	(1)
Creep	516	(1)
Summary	517	(1)
References	517	(2)
Appendix A. Requirements and Supporting Test Methods for Magnetic Tapes and Tape Reels	519	(25)
Appendix B. Analysis of Life Data	544	(73)
Author Index	617	(8)
Subject Index	625