Nominated Difficult-to-Bond Polymeric Substrates—
• Ethylene vinylacetate/polypropylene (EVA/PP) blend,
• Polyoxymethylene (Acetal).
• DC 983 (Dow Corning): two-component, neutral alkoxy system,
• RP-4 (Rhone Poulenc): acetoxy-curing system,
• GE 100 (General Electric): acetoxy-curing system.
• N-(2-aminoethyl)-3-aminopropyltrimethoxy silane (2-AE-3-APTMS): Z – 6020 (Dow Corning),
• 3-Glycidoxy-propyltrimethoxy silane: Z-6040 (Dow Corning).
• Polyethylene imines (PEI) from BASF: MW = 800; 2000; 25,000; 750,000.
Graft Chemical Preparation and Application—Two following types of graft chemicals, as listed in the sections above on “Organo-Functional Silanes" and “Polyfunctional Amines," were used for surface modification of nominated polymers targeting enhancement of adhesion:
1. Organo-functional silanes, and
Silanes were first hydrolyzed with distilled water at a 1:3 silane/water mole ratio for 24 h and were then diluted with isopropanol to obtain solutions of graft chemical in the range of 0.05 to 1 %. Non-silane graft chemicals (polyethylene imines [PEI’s]; see the section below on “Adhesion Improvement by Surface – Grafted Connector Molecules Interpenetrating into Silicone Adhesives" for more details) were diluted in deionized water to an appropriate concentration.
Aqueous solutions of graft chemicals were sprayed onto the sample surface using commodity industrial spray equipment. Throughout this work, this task is performed on a conveyor line (Fig. 8(c)), or using a robotized spray system at the speed controlled within the range of 2 to 10 m/min. The sample-to-nozzle distance is kept constant at 150 mm and the atomizing air pressure maintained at 1.5 bar.
The deposition rate of spray-applied graft chemical is adjusted to maintain a constant level of the “normalized deposition rate" [ml/m] expressed as the ratio of the fluid flow rate through the nozzle (ml/min) divided by conveyor speed in m/min]. After spraying, the samples surface is dried using either the conveyer-controlled exposure to infrared lamps or by allowing an ambient air flash-off (approximately 2 min) under the standard laboratory conditions (20°C/ 50 % RH).
The standardized parameters of an on-line application of graft chemicals are as follows:
i Spray pressure: 1.5 bar,
ii Chemical deposition rate (at 1.5 bar): ~3.5 ml/min per 1 m/min of conveyor speed,
iii Conveyor speed: calculated as per (ii),
iv Spray nozzle distance: 150 mm,
v Specimens location on conveyor belt: 120 mm out from conveyor edge,
vi No. of spray passes: 1,
vii Surface drying: RT air. If fast flash-off needed: one-pass-IR lamps.