Pressure variations, adhesive

Incomplete matrix curing is due to an incorrect cure cycle and may occur due to inaccurate mixing of compounds or temperature or pressure variations during the manufacturing process. Cure failure can also occur in the adhesive layer and develop into a more significant fault, thus reducing further the structural integrity of a material. 

While a static load test is the commonly accepted procedure, in practice many variations in areas and weights are used, to compensate for the various qualities of adhesive evaluated, so that the test results will fall into a similar time frame, so it becomes difficult to compare different adhesive systems from accumulated data. It has the disadvantage of giving variable results for the same adhesive system, and is essentially a pass/ fail test, as many products remain in place at the end of the test period. Experience has shown that the shear properties of pressure-sensitive adhesives to porous and nonporous substrates can be quite different, and each must be judged on its own merits. 

As with other pressure-sensitive adhesive tests, the temperature is an important variable and tests are typically carried out at room temperature. A variation on this method is the SAFT test (shear-adhesion-failure temperature) in which the test apparatus is placed in an oven where the temperature is set to rise at 4.5°C/min. The temperature at which the tape fails is recorded as the SAFT value. 

Any pressure variations in the adhesive fine delivery system will affect the rate at which the adhesive flows from the applicator nozzle consequently it is important to regulate the pressure and eliminate pressure surges. 

Ishida et al. were some of the first investigators to propose a method for investigating the adhesive properties of tablets [151]. Their method involved placing a tablet onto a membrane under constant pressure for one minute and then measuring the force required to remove it. Most methods published since that time involve essentially the same principle, with variations in the type of membrane used and the... 

Mechanical equilibrium is established when small reductions in free energy due to formation of adhesive contact just balance small increases in mechanical work of deformation of the vesicle (8,11). Tnis variational statement leads to a direct relation between the free energy potential for adhesion and the suction pressure applied to tne adherent vesicle,... 

Fig. 34.15 Variation of thermal volume expansion of dismantlable adhesive containing 50wt.% microcapsules, with pressure as a parameter, measured using the bellows vessel.

In experiments on the adhesion of a powder, HOPE modified by oil-soluble contact Cl containing salts of organic amines or sulfur acids with either carboxyl or hydroxyl groups has been used. The composition of HDPE - - Cl has been applied to a preliminary cleaned and degreased 100—pm-thick aluminum foil at a temperature of T = 155 5°C and a pressure of p = 7—10 MPa. The splices have then been subjected to thermal treatment in an oven at 200° C for one hour, which corresponded to the maximum strength of the adhesive joints. The strength has been estimated by delamination tests under a constant deformation rate. Not less than 20 samples were tested in each point to show 10-30% variation factor at a confidence interval of 0.95. 

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