Bonded films film curing

Fig. 23a. Hydration and dehydration reactions of the silica surface and the IR absorption frequencies of the surface species. Chemisorption of water produces surface silanols, which serve as adsorption sites for water, b Reaction of octadecyltrichlorosilane (OTS). Hydrolysis of the chloride group by trace amounts of water in solution to silanol is followed by condensation with surface silanols, resulting in covalent bond formation between the monolayer and the substrate. OTS molecules can also cross-link to form polymeric species during film curing [201]...

Films. Both structural and nonstructural adhesives are commonly available in film form. Adhesives applied in the form of dry films offer a clean, hazard-free operation with minimum waste and excellent control of film thickness. However, the method is generally limited to parts with flat surfaces or simple curves. Optimum bond strength requires curing under heat and pressure, which may involve considerable equipment and floor space, particularly for large parts. Film material cost is high in comparison to liquids, but waste or material loss is the lowest of any application method. 

The initial properties of bonded films as applied vary considerably depending on the type of binder, the ratio of binder to molybdenum disulphide and other components, the nature of the drying or curing process, and the way in which the film was applied, in particular there is a wide variation in hardness from very soft (silicones and alkyds) to very hard (metals and ceramics), and this has important implications for the way in which a film is used and even the purpose for which it is used. 

As a result Bertrand and Vukasovitch of Climax Molybdenum carried out an intensive study of different cleaning techniques applied to various forms of molybdenum disulphide film. The types of film used were a burnished film from a sub-micron sized powder, a burnished film from a soap-containing molybdenum disulphide powder, an air-cured inorganic-bonded coating, and a film formed from a dispersion in oil. The films were formed on steel pins which were then pressed through an undersized bush. This ensured highly-loaded contact on the film, and consolidation of the film. The burnished powder and the resin-bonded films could be... 

Sample films were cured at 100 °C for 12 h under vacuum. Bonding direction indicates the approximate angle between dipole of chromophore and two bonding sites. A alues in parenthesis indicate retained percentage of initial NLO activity at the corresponding temperature. 

Analysis of Cure. Infrared spectroscopy was utilized to examine film cure and the effect of stabilizers upon the cure of the epoxy acrylate. Pre-cured material has absorptions at 1635, 1410 and 810 cm-1 which clearly diminish after the resin is UV-irradiated (Figure 6). The 1635 cm-1 absorption can be assigned to the carbon-carbon stretch of an olefinic bond in conjugation with a carbonyl group the 1410 cm-1 can be assigned to the CH2 in-plane deformation of a vinylic group. The 810 cm-1 can also be assigned to some aspect of vinylic... 

The brittleness of films from cured UF resins may be attributed to the strong hydrogen bonding of the urea (-NH-CO-NH) interunit linkages and the stiff methylene (-CHj-) units. Any structure that will increase the flexibility of UF polymer chain will therefore reduce the brittleness of the cured UF resin. The phenyl rings wfll enhance stiffiiess, while long sequences of (CHj) will enhance flexibility. Consequently, the brittleness of cured UF films wfll be reduced in the order b < c < d < a. 

The assembly of composite structural elements into a complete integrated structure will often involve bonding processes. These may be co-bonds or secondary bonds. In co-bonds, a cured composite is assembled with a film adhesive to an uncured laminate layup. The assembly is cured in an oven or autoclave. Secondary bonds are bonds between two cured laminates. The adhesive may be film or paste, and the cure may be in an oven or at room temperature. Composite repair following a damage event usually involves a co-bond by scarfing out the damage area, laying... 

For film adhesives, ultrasonic welding (112) at a frequency of approximately 15,000 kHz can be used instead of weld-bonding. The subsequent curing can also be completed in a regular oven. This technique has been applied to small... 

Nitrile-phenolic and nylon-epoxy adhesives are also available as solvent solutions as well as in film form. The nitrile-phenolic film is cured at 150-260°C for 15-30 minutes with bonding pressures from 0.12 to 1.8 MPa. The liquid alloy is dried at 80°C and cured for 15-30 minutes at 90°C and contact at 0.7 MPa of pressure. The nylon-epoxy paste is cured for 3 days at 20°C to 1 day at 150°C under bonding pressure from 0.11 to 0.32 MPa. Cure temperatures for some formulations can be increased to 200°C with corresponding reduction in cure time (4 hours). No volatiles are released during cure, so large areas can be bonded without venting. " ... 

ABF dry film TBR-25A-3 thermoset ink HBI-200BC thermal cure ink MACuVia-L liquid dielectric Envision liquid dielectric Electronic bonding film Polynorborene liquid dielectric... 

Polyurethane adhesives bond well to many substrates, including hard-to-bond plastics. Since they are very flexible, pol5nirethane adhesives are often used to bond films, foils, and elastomers. Moisture curing one-part nrethanes are also available. These adhesives utilize the humidity in the air to activate their curing mechanism. 

Plastisols are used in automotive assembly for lower performance applications, e.g. the bonding of panel reinforcements. An advantage here is that they are capable of bonding oily surfaces some absorb the oil film during cure, reducing the required surface preparation. Also, the adhesive may be formulated such that it cures during the paint-stoving process. 

The necessity to resist 250 C soldering temperature limits the adhesives that can be used to bond cop r foil to laminated printed wiring boards. The copper foil can be bonded during the lamination operation if the base resin has sufficient adhesive strength. If the foil is applied to the cured board it is first coated with a B-staged epoxy or thermoplastic and then heat bonded. A film of B-staged epoxy or polyvinyl butyral can be used in place of the precoat. 

Addition reaction Pis are also based on aromatic diamines and dianhydrides, but in addition have Nadic imide end groups. These systems also contain solvents to make the adhesive film pliable. Curing of these adhesives initially proceeds via a condensation reaction at low pressure. However, unlike the conventional condensation reaction Pis, after completion of the condensation reaction and removal of solvent, these adhesives are still thermoplastic. At this point the temperature and pressure are increased to density the bond line and the... 

Film adhesives Film adhesives are supplied as foils and can be cut to the shape and size of the area to be bonded. The matrices, therefore, are solid at room temperature but, critically, will liquefy but do not cross-link on moderate heating. Thus, on heating from ambient to cure temperature they will first melt, then flow and displace the air in the bond and, in so doing, wet the substrates to be bonded and finally cure to an infusible solid. This can be readily seen by examining the dynamic viscosity traces for three typical film adhesives Redux 312, Redux 319 and Redux 322 (Fig. 44). 

The rotor tips are usually clad in electroformed nickel sheet this is chemically pretreated (usually a nitric acid etch [35]), primed and then bonded with a film adhesive curing at 120-130°C. In some cases, due to the increased service temperature requirements caused by underlying heater mats, an adhesive is used, which has enhanced temperature performance. 

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