Preformed tape

Dry adhesives and sealants may be supplied as preformed tapes or ribbons, for instance butyl, acrylic or oleoresinous sealants. They are supplied in rolls and various sections or shapes (Fig. 91) and the surface is protected by a release paper (siliconised paper). 

Solbit is a neoprene, round ribbon which has an electric wire in the centre. It is non-tacky when delivered, but it must be stored at -4°C to prevent any vulcanisation. It is used for bonding and sealing of automotive windshields as shown in Fig. 98 when the electric wire is plugged under 24 V, this heats the rubber which becomes sticky after 30 s the windshield is pressed firmly against the ribbon, and it takes some 4 min to vulcanise the rubber. 

A typical installation includes a carousel with electric plugs and pressure jigs to press the windshield on the metal frame during 4 min. The whole bonding takes 

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Bulyk. Butyl-based materials are sold in the form of preformed tapes, thermoplastic hot melts, and one-part solvent-releasing sealants. Butyl polymers are made by the copolymerization of 97-98 mol % isobutylene with 2-3% isoprene. Another butyl-based polymer, polyisobutylene, is produced by the polymerization of isobutylene. Formulations of butyl-based sealants also include plasticizer, filler, and lackifier resins. Poly butenes are common plasticizers for butyl sealants. Solvents, such as mineral spirits, are used for the one-part solvent-releasing formulations. As the solvent leaves the typical one-part butyl, the sealant hardens and loses its elastomeric ability. This limits the use of solvents to low movement applications where durability is not of high concern. 

Test Method for Adhesion in Peel of Elastomeric Joint Sealants Recommended Practice for Surface Preparation of Concrete for Application of Chemical Resistance Resin Monolithic Surfaces Method of Testing Release Papers Used with Preformed Tape Sealants Test Method for T-Peel Strength of Hot Applied Sealants Test Method for Tensile Adhesive Strength of Preformed Tape Sealants by Disk Method... 

Preforms, tape, or film adhesives, unlike the paste or liquid adhesives, are already in the solid state. They may be thermoplastic or thermosetting but, in both cases, may be purchased as sheets of various thicknesses and cut to size to accommodate specific device or part sizes. In using preforms, the electronics assembler avoids problems associated with the storage, handUng, and dispensing of liquid adhesives. Parts such as leadframes, lids, and substrates may also be purchased with pre-attached preforms, a convenience to the user, who then avoids having to cut and handle individual preforms. Most parts can also be stored for up to one year in ambient conditions without affecting their properties. 

To assure optimum conductance, the adhesive must be applied as thinly and uniformly as possible. To control the thicknesses bond lines, thermally conductive paste adhesives have been formulated with collapsible spacers. The spacers are reported to control bond line thickness to 30 pm. Bond line thicknesses and uniformity may also be achieved by using film or preform tape adhesives and controlling the applied pressure and heat during cure. 

Preform/Tape bonding drip-on-board, hybrid or MCM, single-chip (standard and lead-on-chip) Eliminates fluid dispensing, good thickness control Requires die-cut preforms or manual processing... 

In the last 40 years, many suppliers tried to find methods of clean and easy application of adhesives, glues and sealants. The main idea was to use adhesives in dry form, to avoid the stickiness and dirty application of the old glues. A need for adapted application equipment came from this. The main invention was the pressure sensitive tapes and labels, and then the hot melts supplied as dry solid granulates. There was also the preformed tape sealants, the structural adhesives supplied as film adhesives used in aircraft bonding figure 92, the heat sealable tapes and films, the hot melt sticks and lately the glue sticks for office use. 

Caulks and sealants made from the isobutylene polymer family are available in three forms. As bulk sealant materials, they are usually one-part, plasticized systems, compounded with suitable inert fillers and solvents and designed for application with a standard caulking gun. As preformed tapes or ribbon sealers, they are 100% solids, tacky materials, supplied in roll form on a release paper backing and designed for easy hand application in areas which usually require compressive confinement for an effective seal. Finally, in a newer format as 100% solids, hot melt compositions, they are specif-... 

Sealing Tapes.The 100% solids, preformed tape sealants, because of their form and ease of handling, provide economies in installation often unattainable with other sealants. Tape rolls are available in a variety of widths and thickness and many times contain an embedded string or cured rubber core to prevent stretching or drawdown in use. All tapes have some degree of pressure sensitivity and are sufficiently soft to allow for ease of compression during installation. 

Other insulated glass sealants are designed as hot melt compounds with regular or partially cured butyl as the base. These compounds are either hot pumped into place or are applied in a thermoplastic, preformed tape construction. 

Preformed Tapes. Preformed tapes of butyl, usually vulcanized, are extruded semisolid sections with pressure-sensitive adhesion. Since they are 100% solid, there are no problems of shrinkage or solvent evaporation. Sold in rolls interlined with release paper, they are often used together with liquid sealants or solid spacers, shims, etc. They vary from low cost, highly polybutene-extended tapes for trailers and mobile homes, to partially or fully vulcanized butyl rubbers with little polybutene content for high-rise glazing and automotive windshield sealants. 

Test for low temperature flexibility of preformed tape sealants... 

Test for adhesion after impact of preformed tape sealants Test for weight loss after heat aging of preformed sealing tapes... 

Specification for high solids content, cold liquid-applied elastomeric waterproofing membrane for use.with separate wearing course Methods for testing release papers used with preformed tape sealants... 

Test for tensile adhesive strength of preformed tape sealants by disk method Test for yield strength of preformed tape sealants... 

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