Fast curing

Table 10 compares the values of different experimental uv-curable cross-linked polymers with those of BPA-PC for the most important properties of substrate materials (220). In spite of this remarkable progress in the development of fast curing cross-linked polymers, BPA-PC and, to a small extent, glass are still the materials of choice for substrates for optical data storage. 

Low pressure presses are usually operated at about 180°C as compared to high pressure presses at about 135°C, but the extra low pressure press heat is not adequate to compensate for the short dwell time. Special fast curing resins must be used in conjunction with the low pressure presses. 

Some fabrication processes, such as continuous panel processes, are mn at elevated temperatures to improve productivity. Dual-catalyst systems are commonly used to initiate a controlled rapid gel and then a fast cure to complete the cross-linking reaction. Cumene hydroperoxide initiated at 50°C with benzyl trimethyl ammonium hydroxide and copper naphthenate in combination with tert-huty octoate are preferred for panel products. Other heat-initiated catalysts, such as lauroyl peroxide and tert-huty perbenzoate, are optional systems. Eor higher temperature mol ding processes such as pultmsion or matched metal die mol ding at temperatures of 150°C, dual-catalyst systems are usually employed based on /-butyl perbenzoate and 2,5-dimethyl-2,5-di-2-ethyIhexanoylperoxy-hexane (Table 6). 

Polyurethane adhesives are known for excellent adhesion, flexibihty, toughness, high cohesive strength, and fast cure rates. Polyurethane adhesives rely on the curing of multifunctional isocyanate-terrninated prepolymers with moisture or on the reaction with the substrate, eg, wood and ceUulosic fibers. Two-component adhesives consist of an isocyanate prepolymer, which is cured with low equivalent weight diols, polyols, diamines, or polyamines. Such systems can be used neat or as solution. The two components are kept separately before apphcation. Two-component polyurethane systems are also used as hot-melt adhesives. 

Fig. 1. Gel time as a function of temperature for A, residual heat curing B, fast curing C, medium-fast curing and D, slow curing powders.

Selection of the proper viscosity and cure rheology are very important due to the occurrence of high shear and fast cures. 

Silicon—Ca.rbon Thermoset. The Sycar resins of Hercules are sihcon—carbon thermosets cured through the hydrosilation of sihcon hydride and sihcon vinyl groups with a trace amount of platinum catalyst. The material is a fast-cure system (<15 min at 180°C) and shows low moisture absorption that outperforms conventional thermosets such as polyimides and epoxies. Furthermore, the Sycar material provides excellent mechanical and physical properties used in printed wiring board (PWB) laminates and encapsulants such as flow coatable or glob-top coating of chip-on-board type apphcations. 

The polyester alkyd resins are lower in cost than the DAP resins but are weaker mechanically, have a lower resistance to cracking round inserts and do not maintain their electrical properties so well under severe humid conditions. Fast-curing grades are available which will cure in as little as 20 seconds. 

It is thus seen that as a class the primarily aliphatic amines provide fast-curing hardeners for use at room temperatures. With certain exceptions they are skin sensitisers. The chemical resistance of the hardened resins varies according to the hardener used but in the case of the unmodified amines is quite good. The hardened resins have quite low heat distortion temperatures and except with diethylenetriamine seldom exceed 100°C. The number of variations in the properties obtainable may be increased by using blends of hardeners. 

DET-glycidyl adduct 25 10 min room temp. yes 75 fast cure adhesives laminating... 

As a very general rule it may be said that the amines are fast curing and give good chemical resistance but most are skin sensitive. The organic anhydrides are less toxic and in some cases give cured resins with very high heat distortion temperatures. They do not cross-link the resins at room temperature. 

Radiation cure system. Other addition reaction cure systems that have emerged in recent years are the ultra-violet (UV) and electron beam (EB) radiation cure systems. The development of these systems has been prompted by the ever-increasing need for fast cure rates and low cure temperatures. The U V cure system... 

Theoretically, this system offers the advantages of the thermal cure systems that include fast cure and low temperature processing. However, these systems are sensitive to atmospheric humidity and the possible toxicity of the catalyst may represent an issue. 

The ability to tailor acrylic adhesives to fast cure times allows their use on fast, highly mechanized production lines such as those for audio speakers [150]. 

Ethyl cyanoacrylate is the monomer which is most widely used in both consumer and industrial applications, because of its combination of fast cure speed and ease of manufacture. 

Cyanoacrylates. Fast curing cyanoacrylates are used for holding shims in place during assembly of components and other applications where fast cure is useful. 

In general, exceptionally thick films, very fast curing ... 

A Review of Fast-Cure Systems for VAMAC Elastomers, Technical Bulletin E.I. DuPont de Nemours and Company, Inc., Document reference VAM020507, 2002. 

Functionally, accelerators are classified as primary or secondary. Primary accelerators provide considerable scorch delay, medium fast cure, and good modulus development. Secondary accelerators, on the other hand, are usually scorchy and provide very fast cure. There are a wide variety of accelerators available to the compounder including accelerator blends this number well over 100. In order to rationalize the extensive range of materials it is useful to classify them in terms of their generic chemical structure listed below and shown in Figure 14.4. 

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