VAPOR PHASE CONSOLIDATION OF BOOKS WITH THE PARYLENE POLYMERS
Bruce J. Humphrey
2 SOME GENERAL CHARACTERISTICS OF THE POLYMER PHASE OF PARYLENE
- THE DIMER OF PARYLENE (DI-PARA-XYLYLENE) is a white powder. When converted to the polymer (POLY-PARA-XYLYLENE) the material exhibits very little absorption in the visible range and is therefore colorless and transparent.
- The polymer form is extremely resistant to chemical attack and is insoluble in most known chemicals. Parylene can be removed in heated orthodichlorobenzene or chloronapthalene (temp of 180°C). A very limited number of substrates can withstand this process.
- Parylene exhibits a poly-crystalline structure which is extremely resistant to moisture in any form (Contact Angle = 87°). This means that a drop of moisture on a parylene film will produce an 87° angle at the junction of the drop and the parylene surface. The closer this number is to 90° the more hydrophobic the material.
- The material remains stable at continuous temperatures as high as 130in air or 220in the absence of oxygen.
- Polymerization of the film is accomplished at ambient room temperature in a medium vacuum and is solvent-free.
- As a result, there is no thermal, mechanical or chemical stress placed upon substrates which are compatable with the degree of vacuum used.
- The diradical phase of parylene is an extremely active molecule, which results in superior penetration power and a high degree of conformability to the surface being coated. The diradicals are the molecules that are formed after the raw material is split (see deposition process). They reunite on the surface to be coated, thus forming the finished polymer.
- Parylene exhibits impressive mechanical strength and flexibility in a thin film coating. The following are some stress test figures for a 25 micron thick free film of parylene polymer.
- Tensile Strength = 6.90 × 107 n/m2
- Yield Strength = 5.52 × 107 n/m2
- Elongation to Break, % = 200
- Yield Elongation, % = 2.9