Curing inhibitors

Table 6 Effect of Cure Inhibitor Concentration on the Charpy Notched Impact Strength (ak) at O C...

Gel lacquer formulations used for dip coating. The early catapult propellants were inhibited by dipping in a lacquer consisting of toluene 80p, acetone 20p and a total solids content of 15-18%. The grains were dipped twice and had a cured inhibitor thickness of 20 to 30 mils. As the size of experimental slotted tube catapults increased, coatings of 100 mils were required. This necessitated an increase of the solid content to 25-27%. As this soln was too viscous some methylol was incorporated in solvent formulation. In order to improve the room temp gelling characteristics an aliphatic hydrocarbon was added... 

Performance applications focus on properties imparted by a particular compound. Whereas CHEC-II(1996) <1996CHEC-II(5)245> did not specifically cover performance applications, they were addressed under an additives section with subsections on antistatics, curing, inhibitors (for corrosion), stabilizers (against light), and others. 

This decay rate is nearly equivalent to that exhibited by one g of radium in equilibrium with its disintegration products. A miUicurie (mCi) is 0.001 curie, curie point See magnetized curie point, curing See autoclave nitrogen atmosphere cure extruder wire and cable process, dry cure inhibitor prepreg volatile content reinforced plastic resin transfer molding test, Barcol hardness test, scorch Mooney thermoset plastic vulcanization welding, induction. 

Standard curing systems are based on two catalyst groups. Several different terms are used in the industry to cover these curing agents catalyst (not technically accurate, but widely used) and hardener or initiator. There are activators (also called promoters or accelerators) that are used to speed up and enhance the cure. Inhibitors (also known as retarders) perform the opposite function and are used to extend the curing time. 

Triforine cure accelerator Dipentaerythrityl acrylate cure activator, oxidation butyl rubber Benzothiazyl disulfide cure inhibitor, RTV systems Dimethicone, vinyidimethyl-terminated cure moderator, RTV systems Dimethicone, vinyidimethyl-terminated cure promoter, polyesters Benzene phosphinic acid cure promoter amine-cured epoxies Furfuryl alcohol curing agent... 

A typical low temperature cure inhibitor is dimethyl fumarate which reacts with Karstedt s catalyst to form a platinum-fumarate complex as shown in equation 12 (20). 

Ammonia reacts with phthalic anhydride to produce phthalimide to be used as a feedstock for CTP cure inhibitor. 

Polyester Curing Inhibitors Di-tert.butyl p-cresol 40% Solution in xylene... 

Polyester Curing Inhibitors tert.Butyl catechol 10% Solution in styrene... 

Amongst catalyst modifications that achieve purely rate effects, two reports are noteworthy. One is the hydrosilation rate enhancement in the presence of j -cyclodextrins, for Karstedt s catalyst Pt2(s ym-tetramethyldivinyldisiloxane)3] and Lamoreaux s catalyst. Lamoreaux s catalyst (prepared from H2PtCl6 and 1-octanol), showed the most dramatic rate accelerations. The second instance of rate moderation is reported by Endo and collaborators. They report the use of isocyanides in just 2 1 molar ratio with Pt, to dramatically suppress hydrosilation of vinylsilane (with EtsSiH) or vinyl-terminated siloxane with methylhydrogensiloxane copolymer until 60-70 °C. Above this temperature, rapid hydrosilation occurs. This is in contrast with traditional cure inhibitors where a large excess of inhibitor (relative to Pt), typically alkynols or maleates, is needed to prevent premature cure. 

In the case of metals, sensitivity is not quite so marked, although some adhesives in the anaerobic class are sensitive to the presence of certain metal ions, in particular copper which can act as a cure inhibitor. In contrast, the presence of other metal ions on the surface is essential for the curing process to occur at all and anaerobic adhesives will not work to bond together nonmetallic substrates. A simple selection guide is provided in O Table 16.1. 

Copper naphthenate added to the resin at levels between 100—200 ppm effectively extends gel and cure characteristics, resulting in a reduction in exothermic heat (Eig. 7). Copper additives are used widely in commercial laminating resins to modify process exothermic effects. a-Methylstyrene [98-83-9] substituted for styrene at levels of 5—8% has also been used effectively in resins cured at above ambient temperatures. The inhibitor 2,5-di-/-butyIhydroquinone exerts significant exotherm suppression at levels of 200—400 ppm and is useful in high temperature mol ding processes. 

Reiaforced plastics may also iaclude fillers (qv), which are iaexpeasive materials such as calcium carboaate used to displace resia and reduce cost curing agents (catalysts), promoters, inhibitors, and accelerators, which affect thermosetting resia cure colorants release agents (qv) to faciUtate removal from the mold and other additives which can impart a wide variety of properties to the finished part, such as fire resistance, electrical conductivity, static dissipation, and ultraviolet resistance. 

Inhibitors are often iacluded ia formulations to iacrease the pot life and cute temperature so that coatings or mol dings can be convenientiy prepared. An ideal sUicone addition cure may combine iastant cure at elevated temperature with infinite pot life at ambient conditions. Unfortunately, real systems always deviate from this ideal situation. A proposed mechanism for inhibitor (I) function is an equUibtium involving the inhibitor, catalyst ligands (L), the sUicone—hydride groups, and the sUicone vinyl groups (177). 

Hydrosdylation can also be initiated by a free-radical mechanism (227—229). A photochemical route uses photosensitizers such as peresters to generate radicals in the system. Unfortunately, the reaction is quite sluggish. In several apphcations, radiation is used in combination with platinum and an inhibitor to cure via hydro sdylation (230—232). The inhibitor is either destroyed or deactivated by uv radiation. 

New efficient vulcanization systems have been introduced in the market based on quaternary ammonium salts initially developed in Italy (29—33) and later adopted in Japan (34) to vulcanize epoxy/carboxyl cure sites. They have been found effective in chlorine containing ACM dual cure site with carboxyl monomer (43). This accelerator system together with a retarder (or scorch inhibitor) based on stearic acid (43) and/or guanidine (29—33) can eliminate post-curing. More recently (47,48), in the United States a proprietary vulcanization package based on zinc diethyldithiocarbamate [14324-55-1]... 

The best oxidation inhibitors are not usually the best antio2onants (qv). A disubstituted i ra-phenylenediamine such as AJ-isopropyl-AT-phenyl- -phenylenediamine is often selected for that purpose. -Phenylenediamine derivatives iaterfere with cure chemistry and scorchiness, and can stain objects ia contact with the vulcani2ate (114). On balance, /V-(1,3-dimethy1buty1)-/V-phenyl- -phenylenediamine and phenyl /to1y1- -pheny1enediamines have the best combination of properties. They are less scorchy and provide excellent o2one and heat resistance. Additional protection is gained ia blends with a small amount of EPDM mbber (126). 

---