Adhesives curing

For individual bonds, screw clamps and weights are suitable for pressure application, however, these technical aids are only reasonable for small numbers of items. For series bonds it is necessary to manufacture special fixing devices according to the geometry of the adherends. 

The fixing of adherends is also possible in a simple way with adhesive tapes that, in case of hot curing, have to be heat resistant. 

To be able to determine the required contact pressure for an intended adhesive layer thickness in pretests, the insertion of wires with diameters corresponding to those of the adhesive layer thicknesses in the area of the overlap ends has proven its worth. 

When discussing this topic, it is advisable to differentiate between two terms drying and curing. 

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The compression of the O-ring may work against the needs of an adhesive cure on final assembly with an end unit. 

Cyanoacrylate adhesives cure by anionic polymerization. This reaction is catalyzed by weak bases (such as water), so the adhesives are generally stabilized by the inclusion of a weak acid in the formulation. While adhesion of cyanoacrylates to bare metals and many polymers is excellent, bonding to polyolefins requires a surface modifying primer. Solutions of chlorinated polyolefin oligomers, fran-sition metal complexes, and organic bases such as tertiary amines can greatly enhance cyanoacrylate adhesion to these surfaces [72]. The solvent is a critical component of these primers, as solvent swelling of the surface facilitates inter-... 

Plasticizers and oils, curatives and accelerators may also be added. In solvent-borne adhesives, curing agents are generally packed separately. 

Each of these product types will be discussed, including the method of application, the type of substrates that are bonded by each approach, and one or more typical adhesive formulations. In order to understand the adhesive cure mechanism, a brief review of the common urethane reactions is needed. 

Monomeric MDI Pure 4,4 -MDI 2.0 Solid (MP = 37 C) Flexible prepolymers Liquid 1-K adhesive Thermoplastic adhesives Curing hot melts Solvent-borne adhesives... 

Catalysts serve a dual purpose in one-component moisture-curing urethanes. The first purpose is to accelerate the prepolymer synthesis. The second purpose is to catalyze the curing reaction of the adhesive with moisture. The most common catalysts used to promote both prepolymer formation (NCO/OH) and later the adhesive curing reaction (NCO/H2O) are dibutyltin dilaurate and DMDEE ((tertiary amine. A stabilizer such as 2,5-pentanedione is sometimes added when tin is used, but this specific stabilizer has fallen from favor in recent years, due to toxicity concerns. DMDEE is commonly used in many one-component moisture-curing urethanes. DMDEE is one of the few tertiary amines with a low alkalinity and a low vapor pressure. The latter... 

Acrylic adhesives cure by a free radical chain growth mechanism. In contrast, epoxy and urethane adhesives cure by a step growth mechanism. This has a major impact on the cure kinetics, as well as the composition of the adhesive during cure ([9], pp. 6-9). Cyanoacrylate adhesives (such as Super Glue ) also cure by chain growth, but the mechanism is ionic with initiation by surface moisture. 

Adhesive Curing dose (kGy) Man. specs. Lap shear strength (MPa) ... 

Inspection. After the final adhesive cure cycle, the bonded assembly is removed from the tool and inspected. The first and most cursory inspection is a simple visual check. Major problems such as crushed core and significantly mis-located details can be seen with the unaided eye. A lack of continuous adhesive squeeze-out ( flash or spew ) around the periphery of details can be indicative of insufficient adhesive and subsequent voids. 

They are more difficult to overcoat then most types, and this can lead to problems of intercoat adhesion. Cured films require abrading before subsequent coats will adhere ... 

In this paper, we shall discuss the processing steps used in a typical PI coated wafer. The chemistry that is relevant to processing and film properties will also be discussed with special emphasis on adhesion, cure cycle, and thermostability. 

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. 

Specimen preparation Film thickness 0.3 mil (7.7 im) the substrate was corona treated to 42 dynes/cm adhesive cured through the laminate film using a 300 wpi (120 W/cm) mercury lamp. 

The photoinitiator (single or in a combination) is vital to the manner in which an adhesive cures. The desired property of the PSA is a balance of good tack and good adhesion. If the state of cure is too high, the tack will be too low, and if the state of cure is too low, the adhesive will stick to the substrate, but will be difficult or impossible to remove. 

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... 

Fig. 3.10 Porcine aorta sections bonded with adhesive cured with polymerization (red arrow shows adhesive bond (see Fig. 3.13).

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