Solvent Bonding
Solvent bonding is one of several alternatives for joining thermoformed parts and probably the least expensive joining method for permanent bonds. Solvent bonding joins one plastic to itself or another type of plastic that dissolves in the same solvent. Typically, this process involves treating the bonding area with the minimum amount of solvent needed to soften the surface, and then clamping the parts together until they bond.
Solvents: Suitable bonding solvents vary with resin. You can bond parts made of Makrolon polycarbonate and /or Bayblend resins using methylene chloride or ethylene dichloride. Methylene chloride’s fast evaporation rate helps to prevent solvent vapor entrapment for simple assemblies. For complex assemblies that require more curing time, use ethylene dichloride because it has a slower evaporation rate allowing for longer assembly times. Mixing methylene chloride and ethylene dichloride in a 60/40 solution, a commonly used mixture, will give you a longer time to assemble parts than pure methylene chloride because of the reduced evaporation rate.
When using solvent bonding techniques with Bayblend resins, some embrittlement may occur. Parts can lose some of their excellent impact strength at the weld joint.
A five to ten percent solution of polycarbonate in methylene chloride helps to produce a smooth, filled joint when mating parts made of Makrolon resin. Bayblend PC/ABS resin does not fit perfectly. Do not use this mixture to compensate for severely mismatched joints. Increasing the concentration can result in bubbles at the joint.
Curing Solvent - Bonded Parts : For parts that are ultimately intended for room temperature service for 24 to 48 hours, formed from Makrolon resin, and bonded with methylene chloride, cure them in a well-ventilated area at room temperature. Never cure these parts in an air-tight enclosure where solvent vapors might be trapped. These vapors could attack parts and embrittle them.
When working with polycarbonate resins and blends, curing parts for elevated service use and maximum bond strength is much more complicated. You may have to use a complicated treatment schedule of gradually increasing temperatures for these applications (see table 1). For example, if an assembly is going to operate in an ambient temperature of 200°F (93°C), the bonded parts should be cured at 73°F (23°C) for eight hours, then at 100°F (38°C) for 12 hours, 150°F (65°C) for 12 hours, and finally 200°F (93°C) for 12 hours. Smaller bond areas can cure in shorter times, while large areas usually require longer times or smaller temperature intervals.
Uncured parts suddenly exposed to elevated-temperature service can suffer complete joint failure. Generally, the highest cure temperature should be equal to, or slightly higher than, the highest expected service temperature.
