1、IntroductionAudio magnetic recordings of continuing interest andimportance exist on a variety of media types, withearlier records in the analog mode while more recentrecords may be either analog or digital. This recom-mended practice examines the hazards that may limitthe useful life of such recordi
2、ngs and recommendsstorage practices to optimize their future perform-ance.1 ScopeStability and preservation of audio magnetic record-ings require attention to and precautions against allthree of the following hazards: chemical degradation,physical distortion, and magnetic corruption. Analogand digit
3、al recordings are on media with the samesusceptibilities to chemical degradation and physicaldistortion. They do respond somewhat differently tomagnetic corruption effects, and this will be dis-cussed. Recommendations are offered for minimizingeach of these risks.Useful and acceptable reproduction f
4、rom records sopreserved further demands that in the anticipatedreproduction process there be conformance to theessentials of good practice. These essentials are alsoreviewed.1.1 Storage time scalesThis recommended practice specifies the desirablestorage conditions for audio magnetic recordings ofcon
5、tinuing value, as they may remain in library or vaultstorage between periods of intermittent reproductionor duplication. Two categories of storage time aredefined. The categories are in agreement with thosedefined by ANSI/NAPM IT9.11. 121.1.1 Medium-term storage conditions: Storageconditions suitabl
6、e for the preservation ofrecorded information for a minimum of tenyears.1.1.2 Extended-term storage conditions: Storageconditions suitable for the preservation ofrecorded information having permanentvalue.2 Structure of magnetic mediaIn figure 1, the structural components that providemedia integrity
7、 and performance are identified. Whileit is sometimes possible to combine the function of twocomponents within a single physical entity, each ofthe functions is essential and must survive withoutfailure. For the media of interest in audio recording, bothas a final audio release and as audio recorded
8、or presented in conjunction with images, manycompositions of these structural components areencountered. Figure 2 identifies most of those found inarchives, along with those employed in the recordingson current media.RP 190-1996SMPTE RECOMMENDED PRACTICEApproved August 1, 1996Copyright 1996 by theSO
9、CIETY OF MOTION PICTURE AND TELEVISION ENGINEERS595 W. Hartsdale Ave., White Plains, NY 10607(914) 761-1100Care and Preservation ofAudio Magnetic RecordingsPage 1 of 8 pagesREAFFIRMED 2006Tape:PolyvinylAcetateAcetatePolyesterPolyester2.5 1.4 2.0 1.31.5 1.92.2 63 36 51 3338 4856 * * * * * *Audio cass
10、ettes:PolyesterPolyester0.40.6 0.71.2 1015 1830 *Full-coat magnetic film:AcetatePolyesterPolyester5.6 3.63.8 5.65.7 142 9196 142145 *Striped magnetic film:AcetatePolyester5.66.3 5.4 142160 137 *Striped composite prints:AcetatePolyester6.8 5.9 173 150 *Format Mils MicronsNominaltotalthicknessFigure 2
11、 Diversity of analog audio magnetic records(Application and storage procedures need to be tailored to the format)Figure 1 Cross section of magnetic recording media (schematic)Possible thin overcoatMagnetic recording layerPossible integral lubricantInterfacial bonding layerMedia baseInterfacial bondi
12、ng layerStatic/friction control IayerMagnetic mediumOxide, standard baseOxide, medium baseChrome, dioxideOxide, high biasMetallixparticleMetallicfilmRP 190-1996 Page 2 of 8 pages3 Summation of storage recommenda-tions4 Derivation of recommended storageconditionsTemperature and humidity atmospheric c
13、onditions formagnetic media storage are summarized and tabu-lated in clause 3. The values have been derived fromthe extensive practical experience with photographicfilms, as recommended by ANSI/NAPM IT9.11 12for the minimization of various chemical degradationsin monochrome photographic films. Most
14、of the samepolymers and modifiers are the major componentsof magnetic media. Therefore, the environmentalrecommendations for the minimization of chemicaldegradation during the storage of audio magneticrecords have been derived from ANSI/NAPM IT9.11,modified only slightly by applying specific experie
15、ncewith magnetic records. 134.1 Application of the recommendations of clause 34.1.1 Cycling of temperature and/or humidityincreases the severity of the storage conditionsand should be minimized.4.1.2 Control of air-entrained and gaseousimpurities as recommended by ANSI/NAPMIT9.11 for photographic fi
16、lms is equally appli-cable to magnetic media and, therefore, recom-mended.Gaseous impurities: sulfur compounds, acidic vapors,ozone, peroxides, nitrogen oxides, ammonia, etc., areobserved to accelerate chemical degradation.Dust and air-entrained solid particles contribute to dirtand debris, and occa
17、sionally may be reactive.4.1.3 Audio magnetic recordings may exist incassette form, with the media already enclosedby the shell of the cassette. Media in roll formshould be placed in a protective enclosure,selected from one of the following compositions:coated steel, aluminum, polyester plastic, pol
18、y-ethylene or polypropylene plastic, or acid-freepaperboard, meeting ANSI IT9.2. 204.1.4 It is preferable for magnetic media to bestored with the rolls in vertical orientation. If themedia is not on a substantial reel, or within acassette, the rolls should be supported by theirhubs to eliminate asym
19、metric pressures on therolls.4.2 Moisture content and temperature of the mediaAll of the studies on chemical stability confirm that itis the precise moisture content and temperature of theactual media that controls, not the moisture contentand temperature of the surrounding environment.4.2.1 It must
20、 be recognized that a compact rollof tape or film can achieve temperature equilib-rium with its environment rather quickly, but canachieve moisture equilibrium only by moleculardiffusion of moisture into or out of the face of theroll, all the way to the midplane of the tape orfilm, which can be agon
21、izingly slow. 194.2.2 Media storage should be in a protectiveenclosure or in a cassette. Such enclosedrecordings will require even more time toachieve a different equilibrium relative humidity.4.2.3 Actual media moisture content: Duringthe generation and prior history of the audiomagnetic recordings
22、, there may have beensignificant exposure to higher humidities andsome equilibrium expedited by multiple trans-porting, as in a reproducer. Recognizing the veryslow rates of moisture equilibration in mediarolls not in active use, 4.2.1 predicts that anymagnetic media which may enter a storage vaulto
23、f lower humidity than the equivalent relativeMedium-term Extended-term Equilibriumtemperature C 23 max 20 maxEquilibrium relativehumidity % 20-45 20-30Alternate 1: TempAlternate 1: R.H.Alternate 2: TempAlternate 2: R.H.15 max20-4010 max20-50Physical status:WindingEnclosureOrientationCo-planarProtect
24、iveVerticalCo-planarProtectiveVerticalExternal magneticfield:dc: 0eac: 0e50 max10 max50 max10 maxRP 190-1996 Page 3 of 8 pageshumidity of the media itself may take manymonths or even longer to equilibrate to vaultconditions. Consequently, the effort at achievinglow vault humidities may be less effec
25、tive inpreserving such media. 194.2.4 Actual media temperature: Magnetic mediawhich may enter a storage vault maintained atreduced temperature, however, will be veryquickly cooled to environmental temperatures19, thus effectively retarding hydrolytic decom-position.4.2.5 Optimum extended-term storag
26、e: Inasmuchas the rate effects of temperature and of equilib-rium relative humidity (i.e., actual moisturecontent of the media itself) upon chemical deg-radation are cooperative, it is still desirablewhen maximum useful life of the recordings isimportant to attempt reconditioning of the mediabefore
27、storage, and to store at the lower rangeof recommended relative humidities.5 Removal of media from low-temperature storage5.1 To minimize the formation of moisturecondensation on the media or its enclosures,material removed from the low temperatures ofextended-term storage should be “equilibrated” f
28、orat least 24 hours at medium-term conditions. Themaximum temperature and humidity gradient duringtransition should not exceed 10C/hr or 10%RH/hr. This gradient refers to the maximumtemperature and humidity change to which themedia (not the reel, cassette, or container) is sub-jected. The media shou
29、ld remain in its containerduring acclimatization to help control relativehumidity and temperature gradient extremes.The same preconditioning period should be appliedto media received for storage, that is presumed tohave been exposed to low temperatures during trans-portation, etc.5.2 Physical effect
30、s of low-temperature storageRolls that have been stored at low temperatures willbe found somewhat looser than when first introducedfrom the dimensional changes noted in 8.4. Additionalcare in handling may be required.6 Chemical stabilityStability of the organic carrier-matrix bearing themagnetic par
31、ticles must hold the composite in itsas-recorded structure to maintain the reproducibilityof the record.ANSI/NAPM IT9.11 provides guidance for storageconditions that minimize the chemical degradation ofphotographic films. Although specific audio magneticrecords may incorporate additional chemical co
32、m-pounds not normally found in processed photographicfilms, it is perhaps fortunate that the chemical stabili-ties of the major components are controlled by thesame environmental factors.6.1 Polymeric hydrolysisA major chemical degradation mechanism for eachof the organic compounds present, both in
33、photo-graphic films and in magnetic recording media, ishydrolysis paced by the moisture content andtemperature of the medium, and possibly also cata-lyzed by some industrial pollutants. This moisturecontent tends over time toward an equilibrium withoperational and storage atmospheres.11, 2, 7, 16,17
34、6.2 Magnetic particle chemical stabilityThe inorganic magnetic materials in the media mayinclude oxides of extended thermodynamic stability,or metallic elements potentially subject to oxidation which is frequently facilitated by increased moisturecontent and/or increased temperature. 11, 14,15,181Th
35、e actual moisture content of the media, either photographic or magnetic, increases with increasing partial pressure ofwater in the atmosphere (the absolute humidity), and decreases with increasing temperature of the medium. For mostmaterials of interest over temperature ranges near “room temperature
36、,” this relationship by pure chance correlatesapproximately with relative humidity of the atmosphere. Thus, ANSI/NAPM IT9.11 and related guides recommendequilibrium relative humidity ranges.RP 190-1996 Page 4 of 8 pages7 Construction of environmentally con-trolled storage vaultsThe design, construct
37、ion, and maintenance of storagevaults required to be maintained at a lower relativehumidity than their environment is expensive andtechnically challenging. Maintenance of storagevaults at a lower temperature than their environment,however, is much easier and less expensive.This balance was reviewed
38、during the reaffirmation ofANSI/NAPM IT9.11, resulting in the identification,reproduced in clause 3, of three operating conditionsfor extended-term storage, experimentally shown tobe equally effective in controlling the rate of hydrolyticdecompositions. 128 Physical distortionReproduction of magneti
39、c recordings (as well as theoriginal recording process itself) requires consistent,intimate contact of the magnetic head with the mediasurface. Physical distortions interfere with achievingthis requirement, and thus degrade the reproduction.8.1 Plastic flowThe deformation thresholds for plastic mate
40、rials suchas magnetic recording media are greatly dependentupon time. The yield point stress, beyond whichnonelastic and irrecoverable deformation occurs, willbe nearly as high as the break stress for suddenlyapplied shock loads, and may be nearly zerofor stresses maintained over a period of years.
41、Therelative importance of potentially deforming stresses,therefore, depends upon both the magnitude of eachstress and the time over which it continues to act.8.2 Quality of roll windingSince the prior use of the recording may have resultedin an irregularly-wound roll, perhaps with protrudingconvolut
42、ions, or with tension changes from pro-grammed interruptions in the transport of the medium,a full-length rewind is desirable to provide a uniformroll before storage.8.3 Tail-out storageMagnetic records are preferentially wound tail-out forstorage, and should be rewound to head-out orienta-tion imme
43、diately before use.8.3.1 Rewinding in itself is somewhat beneficialin relieving physical stresses, and in counteringsome of the magnetic corruption.8.4 Dimensional changesThe plastic materials in magnetic recording mediashow a measurable dimensional increase with theabsorption of moisture, as well a
44、s with the increase intemperature. For most of the formats, the thicknessdirection has the highest coefficient and shows thegreatest change. Temperature changes equilibraterelatively rapidly and, thus, result in relatively uniformchanges in inter-layer pressure. The slow equilibriumof moisture, howe
45、ver, produces sustained dimen-sional differentials, as by the subjecting of a tightly-wound roll to a relative humidity gradient such that theexposed edges of the medium condition rapidly whilethe midplane may require weeks or months thusinducing plastic flow and its resultant physical distor-tion.8
46、.5 ShrinkageMagnetic media may suffer some shrinkage over timefrom loss of volatile components and/or release ofmanufacturing-induced strains. This is normally ofinsignificant magnitude, if it is not accompanied byother physical distortions.8.5.1 For the magnetic films, perforated for com-patibility
47、 with motion-picture systems, shrinkagewill change the perforation pitch. Unless accom-modation is made in the reproducing transport,the level of flutter may be increased.9 Magnetic corruptionMagnetic recording is a reversible process, and themagnetic pattern representing information in a recordrema
48、ins capable of alteration by subsequent expo-sure to an appropriate magnetic field. Thus, record-ings stored for later reproduction must be kept in areasfree of excessive extraneous magnetic fields.9.1 Magnetic particle populationsAn indication of the nature of possible changes isgiven by the statis
49、tical properties of the individualparticle population or of the metallic film domain popu-lation. The characteristic curve of magnetic inductionvs applied field (the hysteresis curve) is composed ofsloping and curving lines, indicating a distribution ofRP 190-1996 Page 5 of 8 pagesparticles over a range of coercivities within the popu-lation. (A population of identical particles, each ofidentical coercivity, would give a rectangular hysteresiscurve.) Thus, some particles can have their ma
