Urethane liquid components

This high-pressure impingement mixing delivery of two or more liquid urethane components to a very small mixing chamber that continuously mixes and injects into a closed mold delivers at rates approaching 650 lb/min. The liquid components are heated to maintain low viscosities. 

It will be realized from Chapter 1 that in urethane elastomer formation from liquid components there is the possibility of several reactions occurring simultaneously during a prepolymer or one-shot process, and that the relative proportion of one to the other will affect the overall properties of the final polymer. Thermoplastic and millable urethanes are not, during their processing and fabrication stages, subjected to the type of catalysis discussed in this chapter during their polymer synthesis operations, however, reaction rate-structure considerations will apply. 

The first source of processing variety comes into play when the question of when and how this polymerization reaction takes place. Raw materials may be liquid components or they may be solids in the form of powders, granules, or pellets. The raw materials may be presented for processing in a prepolymerized form (polyethylene or acrylonitrile/butadiene/styrene [ABS]), they may be in a partially reacted form (urethanes = polyols + isocyanates), or they may be in the state of their precursor raw materials (phenolics and alkyds). 

With the exception of fillers, the raw materials used in two-component urethanes are all liquids. The two components have an isocyanate side and a polyol side. The raw materials are combined in various ways in order to produce with liquids that are combined at a 1 1 volume ratio, preferably, thus keeping the dispensing equipment as simple as possible. Fixed ratios of 3 2 or 1 2 are also commonly used. Ratios other than these are possible, but require the use of a... 

Elastomeric materials find use as vial closures, as syringe plungers, and as liquid delivery components. Elastomers, called sometimes simply rubber, are also polymeric materials, and are known by their common names, halobutyl, silicone, urethane, neoprene, polybutadiene, etc. Elastomers themselves... 

The continuous loaf of foam made by the continuous pouring of liquid foaming components on a moving conveyor is called a slabstock foam, and a cut-off segment of the slabstock is called block foam or bun foam. The horizontal-conveyer process has been used widely since the beginning of the urethane foam industry. Recently, however, vertical production processes have been developed. 

Liquid injection molding (LIM) A process of injection-molding thermosetting resins in which the uncured resin components are metered, mixed, and injected at relatively low pressures through nozzles into mold cavities, the curing or polymerization taking place in the mold cavities. The process is most widely used with resins that cure by addition polymerization such as polyesters, epoxies, silicones, alkyds, diallyl phthalate, and (occasionally) urethanes. 

Liquid in-mold coatings are primauily two-component urethane systems. The liquid coating is injected into the mold at high pressure. The coating will cure somewhat faster than the parent plastic. The extent of the spread of the coating is dependent on the pressure of injection of the liquid in-mold coating. Film thickness will be dependent on the... 

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