| 1. |
Adhesive
strength - the interaction that develops between the resin
and the glass causing a subsequent bond to the glass. |
| A. |
Adhesion
- resin properties that causes a bond to the glass. |
| A-1. |
Absorption
- the property of the interface between the resin and the glass. |
| A-2. |
Interface
- the molecular linking of the resin to the glass. |
| A-3. |
Interaction
- the atoms of the resin interact with the atoms of the glass causing
the molecules to link together. |
| A-4. |
Wetting
- the filling of the surface crevices and irregularities; a must
for good absorption and adhesive strength. |
| 2. |
Cohesive
strength - the internal strength of the adhesive mass or
it's resistance to creep under stress; the ability of the resin
to resist splitting. To increase cohesive strength it is necessary
to increase the molecular weight and the consequent chain entanglement
contributions or to provide cross linking. |
| A. |
Viscosity
(thickness of resin) - the property of resins that causes them to
resist flowing. It is caused by internal friction from the resin's
molecules moving against each other. One way to increase a liquid's
viscosity is to dissolve polymers (long-chain molecules) in it.
These molecules become entangled and resist flowing. Putting solid
particles in suspension in a resin also increases viscosity as will
adding strengthening fillers. Temperature determines how strongly
molecules interact; hot resins have lower viscosity than cold. To
increase an adhesive's cohesive strength will also increase it's
viscosity. |
| B. |
Molecular
weight - the number and size of the resin's molecules. As the molecular
weight is increased, the cohesive strength rises as well as the
viscosity. Low molecular weight (viscosity) resins have lower cohesive
strength. |
| C. |
Creep -
describes the slow deformation of a polymer (windshield repair resin)
under constant stress. |
| D. |
Structural
adhesives - able to carry sizable loads without yielding, will support
stress as well as the weight of the surfaces bonded. Structural
adhesives are higher in viscosity -- over 100 cps. |
