EFFECTS OF MOISTURE ON TAPES
Exposure to water is the primary environmental factor that causes damage to magnetic tape.
Moisture, often absorbed into the tape from humid air, breaks down the long-chain polyester molecules that are the major structural ingredient of the recording and back-coat layers. The reaction, called binder hydrolysis, produces a residue of low-molecular weight oligomers and carbolic acid. This residue has adhesive properties that interfere with tape usage. The hydrolysis reaction can also weaken the tape structure.
The amount of moisture a tape is exposed to determines the speed and degree of hydrolytic decay. Long-term exposure to high relative humidity conditions will tend to increase the amount of “adhesive” oligomer residue. Extended exposure to low RH can stabilize or even reduce the amount of residue.
Humidity has three additional effects on magnetic tape. It can impact the physical dimension of tape, it can allow for damaging fungal growth and it can compromise a tape’s elasticity.
Tape expands and contracts with moisture content. Even though tape can be thousands of feet long and only a very small fraction of an inch thick, the primary vector of expansion is thickness. As tape absorbs moisture, the tape gets thicker and tightens the pack. This can cause stretching. As tape releases moisture in low RH environments, it gets thinner and loosens the pack. This can result in tape slippage, folding and cinching.
If relative humidity is high enough for an extended time, fungus can grow on and damage tape. For this reason, tape should never be stored in an environment that exceeds 50% RH.
Should tape actually be submerged, even for short periods of time, the elasticity and structural integrity can be compromised. Extreme care must be taken handling wet tapes as physical stress put on tape when the elasticity is compromised can cause permanent deformation.
Moisture, often absorbed into the tape from humid air, breaks down the long-chain polyester molecules that are the major structural ingredient of the recording and back-coat layers. The reaction, called binder hydrolysis, produces a residue of low-molecular weight oligomers and carbolic acid. This residue has adhesive properties that interfere with tape usage. The hydrolysis reaction can also weaken the tape structure.
The amount of moisture a tape is exposed to determines the speed and degree of hydrolytic decay. Long-term exposure to high relative humidity conditions will tend to increase the amount of “adhesive” oligomer residue. Extended exposure to low RH can stabilize or even reduce the amount of residue.
Humidity has three additional effects on magnetic tape. It can impact the physical dimension of tape, it can allow for damaging fungal growth and it can compromise a tape’s elasticity.
Tape expands and contracts with moisture content. Even though tape can be thousands of feet long and only a very small fraction of an inch thick, the primary vector of expansion is thickness. As tape absorbs moisture, the tape gets thicker and tightens the pack. This can cause stretching. As tape releases moisture in low RH environments, it gets thinner and loosens the pack. This can result in tape slippage, folding and cinching.
If relative humidity is high enough for an extended time, fungus can grow on and damage tape. For this reason, tape should never be stored in an environment that exceeds 50% RH.
Should tape actually be submerged, even for short periods of time, the elasticity and structural integrity can be compromised. Extreme care must be taken handling wet tapes as physical stress put on tape when the elasticity is compromised can cause permanent deformation.
