Contact bonding

Latex Adhesive Applications. Polychloroprene latex adhesives have a long history of use in foil laminating adhesives, facing adhesives, and constmction mastics. Increasingly stringent restrictions on the emission of photoreactive solvents has heightened interest in latex compounds for broader apphcations, particularly contact bond adhesives. Table 10 makes a general comparison of solvent and latex contact bond adhesives (158). 

Table 10. Comparison of Latex and Solvent Contact Bond Adhesives ...

Bond strength can vary from a temporary bond (non-curing compound) to a substrate tearing bond (using phenolic-modified curing products). Solvent-borne CR adhesives can be formulated to have very short open times for fast production operations or to retain contact bond characteristics for up to 24 h. Heat and solvent reactivation can be used to re-impart tack to dried surfaces. 

Haisma, J. Spierings G. A. C. M. 2002. Contact bonding, including direct-bonding in a historical and recent context of materials science and technology, physics and chemistry—Historical review in a broader scope and comparative outlook. Mater. Sci. Eng. R-Reports 37 1-60. 

There are many other processing methods which can reduce the viewing angle dependence of the optical properties of LCDs, e.g. pixel-divided cells and multidomain cells. However, these are beyond the scope of this monograph and will not be discussed further. Optical retardation sheets are often preferred by LCD manufacturers and systems integrators of FPDs, because commercially available compensation films can simply be laminated to the LCD using contact bonding. 

An emulsion polymer-isocyanate adhesive, a crosslinked polyvinyl acetate adhesive, a resorcinol-formaldehyde adhesive, a phenol-resorcinol-formalde-hyde adhesive, and an acid-catalyzed phenolic-formaldehyde adhesive developed bonds of high shear strength and wood failure at all levels of acetylation in the dry condition. A neoprene contact bond adhesive and a moisture-curing polyurethane hot-melt adhesive performed as well on acetylated wood as untreated wood in tests of dry strength. Only a cold-setting resorcinol-formal-... 

Double-sided bonding This refers to the actual contact bonding that has to be applied whenever solvent-impermeable or dense materials (metals, glass, plastics) are to be bonded or when the bonded joint is required to show very high initial strength. Absorptive materials may require a second adhesive application. 

A typical example of contact bonding is the patching up of a rubber tube with a rubber solution . After evaporation of the solvent, the rubber polymers in the rubber solution combine with themselves under pressure and with the parts of the rubber surface areas swollen by solvents. 

Due to the development of the adhesive layer described above, high contact pressure is more important for the strength of a contact bonding than long contact time. 

Contact-Bond Adhesives. Another group of glues, referred to collectively as contact cements or contact-bond adhesives, bear some similarities to the pressure-sensitive adhesives in that they do not rapidly achieve full hardening. Until a few years ago, contact-bond formulations were mainly organic solvent solutions of elastomers, compounded with tackilying resins and antioxidants. However, with recent concerns over energy, environmental, and fire safety questions, interest has turned to water-based systems. 

Contact-bond adhesives are applied to both of the surfaces to be bonded, allowed to dry until approximately nontacky to the touch, and then pressed together to form a bond. The elastomers in these adhesives have the property known as autohesion. This means that when the dried adhesive-coated surfaces are brought together under some pressure, the films join by a process of molecular difiusion and form a completed bond. 

The solvent-based candidates include various solvent-soluble natural and synthetic polymers (e.g., shellac, coniferous resins, cellulose nitrate, acrylics, contact-bond glues). 

The percentage of contact bonds broken in the quartz vein after six hours of heat exchange is... 

A second case study, in which the fracture is assumed to be located exclusively in a hydrothermalized facies, revealed better resistance to thermal loading than the previous case. In fact, the percentage of contact bonds broken is closed to 0,25% of the total contacts in the model. 

Pressure sensitives are contact-bond adhesives. Usually rubber based, they provide a low-strength, permanently tacky bond. They have a number of consumer applications (e.g., cellophane tape), but they are also used in industrial applications where a permanent bond is not desirable or where a strong bond may not be necessary. The adhesive itself is applied rapidly by spray. Assembly is merely a matter of pressing the parts together. 

Variety of bonding methods The numerous forms and types of rubber-based adhesives and sealants also provide for numerous mechanisms for developing bonds to surfaces. Contact bond, pressure sensitive, wet bond, heat reactivation, and solvent reactivation are all feasible modes of product assembly with these products. 

Thermoplastic or thermosetting While many contact bond applications require no curing process because an extra strength requirement is not present, in certain formulations polychloroprene will provide ambient cure for improved properties, and can be cured by several different mechanisms for high performance properties. Ambient cure systems are typically one component, while high performance formulations are often two-part systems, or one-component systems cured in elevated temperature conditions. 

High initial tack Even without tackifying resin, the inherent tack of certain grades provides for excellent contact bond and pressure sensitive adhesives. 

Good processing characteristics Adhesives can be supplied as contact bonding types—either in water- or solvent-based systems—hot-melt, pressure sensitive, or as reactive systems—either 100% solids content or solvent based. 

Good processing characteristics Adhesives are often used as a contact bond type— either in water- or solvent-based systems—as a hot melt, or as a pressure sensitive, in curing systems, or as heat or solvent reactivatible systems. Block copolymers provide superior pressure sensitive adhesives, but can also be compounded for contact bond adhesive or sealant applications. 

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