Urethane adhesives heat cure

More recent efforts have focused on developments that create true hybrids. For example, blocked isocyanate prepolymers have been mixed with epoxy resins and cured with amines [68-70]. These blocked prepolymers will react initially with the amines to form amine-terminated prepolymers that cross-link the epoxy resin. Several blocked isocyanates are commercially available. The DESMOCAP (Bayer) llA and 12A products are isocyanates (believed to be blocked with nonylphenol) used as flexibilizing agents for epoxy resins. ANCAREZ (trademark. Pacific Anchor, Inc.) 2150 is a blocked isocyanate epoxy blend used as an adhesion promoter for vinyl plastisols. A one-package, heat-cured hybrid adhesive was reported consisting of isophorone diisocyanate, epoxy resin, and a dispersed solid curative based on the salt of ethylenediamine and bisphenol A [71]. Urethane amines are offered commercially that can be used with epoxy resins to develop hybrid adhesive systems [72]. 

One component of a two-part urethane adhesive typically contains an NCO-terminated prepolymer and possibly fillers. The second component consists of polyfunctional, NCO-reactive materials, such as polyols and/or polyamines, and may also contain fillers and catalysts. The work life and rate of cure can be adjusted by the selection of catalysts, the catalyst level, and the starting materials used to prepare the resins. Table III lists the cure times for three adhesives which have identical bond strengths when cured, but different work lives. Two-part urethane systems usually cure at room temperature, but the cure can be accelerated by the use of heat. Although... 

When using two-part urethane structural adhesives, priming of the substrates is often required in order to obtain optimum bond durability, particularly when bonding metals. Primers are generally developed for use with a particular combination of adhesive and adherends. There are various types of primers for polyurethane adhesives, including one-part heat cure epoxies, two-part heat and room temperature cure epoxies, and one-part urethanes. 

Table V. Physical Properties of a One-Part Heat Cure Urethane Structural Adhesive "...

Dual-cure resins for wood composites. These resins (heat and EB irradiation systems) are based on urethane-acrylate thermoplastic adhesive demonstrate efficacy to bond wood. Eow amounfs of EB radiation were needed to produce a wood bond that survived shipping and that improved the composite modulus. The system demonstrated promise and a new direction for wood adhesives. 

Uses Urethane-acrylic for radiation and peroxide curing uses incl. anaerobic adhesives, optical/paper/plastic/PVC floor/wood coatings, and inks Features Chem, water, and heat resist. nonyellowing Properties APHA25 clear liq. dens. 9.262 Ib/gal vise. 590 cps... 

Uses Urethane-acrylic for coatings, screen inks, overprint varnishes Features Difunctional nonyellowing (cured film) good solv. resist., pigment dispersibility, adhesion, chem. resist., flexibility, heat resist., weath-erability low shrinkage... 

Uses Urethane-acrylic, solv. resist, aid, abrasion resist, aid in coatings, screen inks, overprint varnishes, wood coatings, plastic film, laminating adhesives, floor tile, and metal coating finishes Features Resilient, nonyel. supplied as base resin or as resin/monomer blends which offer resilience, water-wh. clarity, and exc. heat and light stability to UV/EB-cured prods. 

Uses Conditioner alkyd resin comonomer mfg. of varnishes, synthetic drying oils, urethane foams and coatings, silicone lube oils, lactone plasticizers, textile finishes, surfactants, epoxidation products crosslinking agentfor PU reactive diluent for radiation-cured inks, lacquers heat costabilizer for PVC in food-pkg. adhesives in food-contact coatings... 

There are three main polymers presently used for structural adhesive bonding and they are phenolics, epoxies and urethanes. We can also include in our classification, the initial physical state of the uncured adhesive since it governs the type of application and curing conditions. Structural adhesives are manufactured in the form of films or pastes. The films are one-part adhesives, i.e., they contain a latent catalyst which requires heat for activation. Structural adhesive films are made in a number of different thicknesses and can either be supported (containing a scrim) or unsupported. In general, film adhesives require the application of pressure during cure in order to obtain ultimate properties. Paste adhesives are either one- or two-part materials. That is, pastes can either contain a latent heat activatable catalyst, or they can be a system which is separated into two parts, one of which contains the cur a t i ve/ca talys t. Two-part pastes cure at room temperature. In this section the chemistry of one-... 

The linear film of polyethylene terephthalate (Mylar ) surface can be pretreated by alkaline etching or plasma for maximum adhesion, but a special treatment often is unnecessary. A strong bond can be achieved by immersing the surface in a warm solution of sodium hydroxide or in an alkahne cleaning solution for 2 to 10 min. Commonly used adhesives for both PBT and PET substrates are isocyanate cured polyesters, epoxies, and urethanes. Polyethylene terephthalate cannot be solvent cemented or heat welded. 

The most common textile adhesives are available as solutions in water or solvent, as dispersions in water, or as solids that melt under the appUcation of heat. However, 100% reactive liquid adhesives such as epoxies and moisture-cured urethanes are also used. 

Acrylate-terminated urethane resins have been formulated with peroxides and have been cited as being useful as molding and adhesive compositions. " These systems are said to be insensitive to moisture. Curing is brought about by heating to 140°C. 

Some of the curing adhesives require heat, whereas others react at room temperature with the help of catalysts, and in some instances with activation by light. Again, it is an advantage to make a bond without the aid of an oven. Among the adhesives which can be processed in the cold, with proper formulation, are resorcinol formaldehyde, unsaturated polyesters, methyl methacrylate, cyanoacrylate esters, epoxies, and urethanes. The polymerization reaction is usually exothermic, so that the glue line may become somewhat warmer than the ambient... 

Ex. 1. Tuftane film is ideally suited for bonding emblems, numerals, and letters to many fabrics by heat and pressure alone. It also flame-bonds well to both polyester- and polyether-urethane foams at commercial bonding speeds. Since it contains no volatiles it does not require cure times as do solvent- or water-based adhesive systems. All Tuftane films can be adhered thermally by hot bar, thermal impulse, ultrasonic, or dielectric methods over a wide range of temperatures. Adhesive lamination to many substrates is possible by the heated drum, curing oven, or multiple can methods. Fabric bonds made with Tuftane are strong and withstand laundering and dry cleaning. 

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