Cure rate, adhesive

Strength, durability and general versatility. Unlike the surface-activated adhesives, cure rate is generally quite independent of surface chemistry. 

The utihty of these adhesives arises from the electron-withdrawing character of the groups adjacent to the polymerizable double bond, which accounts for both the extremely high reactivity or cure rate and thek polar nature, which enables the polymers to adhere tenaciously to many diverse substrates. 

Fig. 10. Generalized formulation design outline for radiation-curable coatings and adhesive systems. The cross-linker is a multifimctional unsaturated cross-linking agent or oligomer, rj = viscosity CR = cure rate S = shrinl ge H = hardness F = flexibility A = adhesion 7 = surface energy ...

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. 

Even the earliest reports discuss the use of components such as polymer syrups bearing carboxylic acid functionality as a minor component to improve adhesion [21]. Later, methacrylic acid was specifically added to adhesive compositions to increase the rate of cure [22]. Maleic acid (or dibasic acids capable of cyclic tautomerism) have also been reported to increase both cure rate and bond strength [23]. Maleic acid has also been reported to improve adhesion to polymeric substrates such as Nylon and epoxies [24]. Adducts of 2-hydroxyethyl methacrylate and various anhydrides (such as phthalic) have also been reported as acid-bearing monomers [25]. Organic acids have a specific role in the cure of some blocked organoboranes, as will be discussed later. 

The air in the autoclave is slowly heated to the cure temperature of the adhesive. Heating rate is monitored and controlled to within a given range. Increasing the temperature too slowly can cause partial cure of the adhesive at lower temperature... 

Conditions have been defined for applying polyimide coatings onto the silicon wafer as passivation and/or dielectric. Processing variables studied included the critical areas of adhesion, cure cycle and thermostability. Aminosilane was shown to be effective adhesion promoter. The rate of imidization was followed by F.T.I.R. employing time lapse technique. 

On the other hand, the alkoxide system presented several problems in formulation. The system first chosen as a model consisted of a trimethoxymethyl silane crosslinker, 8000 centistoke HEB siloxane, and a catalyst. A number of catalysts were used and each exhibited different cure rates and electrical properties. DuPont tetraalkoxytitante-Tyzor appears to he one of the better catalysts used in this type of curing system. Fillers are usually incorporated into the silicone formulation to improve mechanical properties, promote adhesion, and to serve as light screening and pigment agents. Cab-o-sil, a form of fumed silica, carbon-black, titanium dioxide and calcium carbonate are then used as RTV fillers. 

Cure Rate of the Phenolated SEL Resins. 13C NMR spectra of the phenolated SEL formaldehyde-treated resins revealed the formation of methylol groups. A similar cure reaction to resole type phenolic resins is expected to occur with the phenolated lignin-based resins. Since cure rate normally determines production capacity of a board mill, it is important that new types of adhesives have at least the same cure rate as the conventional phenolic adhesives. Cure analysis of resins has usually been examined by... 

Evaluation of Adhesive Bond Strength. Since the cured product of LP-A was brittle, probably due to the low level of formaldehyde charged, LP-B and LP-C were selected as adhesive resins. In order to increase their cure rate, the pH s of LP-B and LP-C resins were adjusted to around 11.2 and 12.0, respectively, prior to adhesive formulation. For the purpose of comparison, the bond strength of the methylolated SEL resin adhesive was examined as well. 

After deposition, the films are cured by heating at a controlled rate in a convection oven, hot plate, or tube furnace to evaporate solvents and reaction products (primarily H20) and to convert the polyamic acid to the polyimide. The final properties and adhesion of polyimide films depend on the curing rate and final curing temperature, which can range from 300 to 450 °C. 

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