Post-cure advantages

Its composition makes it particularly suitable for permanent-press finishing with zinc nitrate as catalyst for white and coloured goods. Compared with FIXAPRET CPN, it has the advantage that it does not change the shade of coloured goods or impair the whiteness of finished fabrics, not even under the severe curing conditions of the post-cure method when applied in combination with zinc nitrate. 

The most important crosslinking agent for pressureless hot air vulcanization of silicone rubber is DClBP(Bis-2,4-dichloro-benzoyl-peroxide) (Fig. 14). It generates decomposition products, which are removed in a post-curing process with air blowing. This product provides the advantage of a fast cure rate and bubble-free cured transparent rubber. 

Advantages of stereolithography are the excellent dimensional accuracy, excellent surface hnish, variable vat size and ability to use a range of materials. The disadvantages are the need for handling of liquid photopolymers and the requirement of post-processing (removal of supports) and post-curing in some cases. 

The advantages of polymerized parts are very good surface quality and fine details. As a disadvantage the supports must be designed prior to and removed after the build, and most processes need post curing. 

Recently, inorganic catalysts have been suggested for use as cyanoacrylate initiators, particularly for use in wood bonding. One patent teaches the use of strong bases such as sodium hydroxide in a calcerous binder which provides a chalk-like primer coating for wood. Another patent teaches the use of weakly basic and weakly acidic ionic compounds as wood primers. These last mentioned primers, such as potassium bromide in aqueous ethanol, have the advantage that while they promote rapid polymerization on wood, they do not cause post-cure hydrolysis of the polycyanoacrylate, a problem noted with the strong bases. 

More typical, though, is hot-melt processing of these adhesives. The rubber is blended with tackifier and/or plasticizer in a bulk mixer or extruder at elevated temperature (eg, 150-200°C), coated as a molten liquid, and cooled. The lack of need for post-curing is a significant advantage over natural rubber PSAs. The high purity and consistency of the input rubber is also an advantage when compared to natural rubber. 

HyTemp NPC-25 is the cure system of choice as it contributes a very fast rate of cure excellent shelf stability, and fair scorch safety. Processing conditions must be carefully controlled to maintain a maximum temperamre of 85°C in the compound to prevent scorch. The very fast cure rate limits the use of the NPC cure system for injection or transfer molding. The NPC cure system does work well for injection or transfer molding operations provided that care is taken to process the compound under 85°C and control runner temperatures. Very good compression set with out post-cure offers a major advantage and if even lower compression set is required, a post-cure will give values of less than 15%, 70 h at 150°C. 

Transmission Oil Cooler Hose compounds are shown in Table 5.24 in which two non-post-cure systems are given. Both the NPC-25 and Zeonet system provides low compression set without post-cure. The temperature of the NPC-25 compound during processing must NOT exceed 85°C, as measured in the stock. During vulcanization, a moisture barrier such as Mylar film should be wrapped on under the nylon tape. The Zeonet cure mechanism also does not require a post-cure and it has the added advantage that it may be used in open steam without a moisture barrier. 

Another remarkable fact about ionic polymerization in general, in contrast to other polymerization techniques, is that in the absence of adventitious terminators, ionic polymerization will go on after irradiation has ceased, and will often continue until most of the monomer has been exhausted. Although such post-irradiative polymerization may be an advantage in UV curing, it is undesirable in imaging applications where it limits resolution and degrades feature sharpness. ... 

BT laminates have a Tg of 180°C and a high degradation temperature. For most high-temperature applications, they are a direct substitute for polyimide. They have the added advantage that the moisture sensitivity and processibility of BT are much closer to those of conventional epoxy than those of polyimide. Other than a high-temperature post lamination bake required for a full cure, the BT process is the same as an epoxy process. The major drawback of the BT laminate is cost. Although BT is much less expensive than polyimide, it is still up to 1.5 times the cost of epoxies. The result is that BT is a popular replacement for polyimide, but its use is limited to specialty applications. The trend for most high-temperature commercial applications is either a multifunctional epoxy or an epoxy-PPO blend. 

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