Powder adhesives, application

Spray-dried powders find application in adhesives to build solids, increase viscosity, improve tack, and decrease drying time (145). A primary use is in joint compounds with other applications in mastics and grouts, and patching compounds (146). 

Unfilled poly(amide imide) powder for adhesive applications High-strength grades perform more like metals at elevated temperature cmd are recommended for repetitively-used precision mechanical and load-bearing parts... 

Apart from their use as tie layers in coextension, the modified polymers can find other adhesive applications such as improving adhesion of extrusion coatings, thermal lamination interplies, and as dispersions or powder coatings. As coatings, the modified polymers applied to metal surfaces can act as an adhesive layer to bond plastic components. A particularly useful version is to prepare a coextended film of a non-modified base polymer such as polyethylene or polypropylene, forming the bnlk of the structure, and apply a thin layer of the modified polymer to one or both external surfaces. This steucture may now be used to thermally bond to a metal substrate. 

There are also a number of applications in the garment industry that require the use of heat-activated powdered adhesives. They can be applied to aU sorts of textile products, although nonwovens are the most popular substrate. Powder adhesives are especially important when the manufacturer wants to provide a strong but discontinuous bond such as in the case of breathable fabrics. 

One disadvantage of powdered adhesives is that it is difficult to control their application to substrates. The effect of the electrostatic field employed in spraying is to pull particles of powder to all exposed metal objects. In most cases, however, the adhesive bond area will be only a limited portion of the total part. These types of powders are used extensively, however, as protective coatings. In these cases, the total surface of the part is usually coated, although masking can be used to prevent coating of critical surfaces. 

As mentioned above, both thermoplastic and thermosetting type acrylic resins are commercially available for coatings, elastomers, sealants and adhesive applications. These resins are supplied in many different delivery forms such as powders or pellets, solutions in organic solvents and aqueous dispersions. These resin types are briefly described below. 

Their multiple use-forms (e.g., in in situ-XQ-acting, neat, liquid systems solutions aqueous dispersions films webs powders) and other valuable attributes (e.g., adhesion to a variety of substrates vibration-damping bonds " gasoline, oil, and solvent resistance etc.) continue to make polyurethane- and isocyanate-based adhesives the materials of choice in many adhesive applications. 

Thermoplastic polyurethanes continue to hold the imposing inroads they have made in adhesive applications. And ecological considerations direct growing attention to nonpolluting urethane adhesive forms, e.g., powders. Aims, aqueous dispersions, and 100% solids reactive systems. 

Of the available polyurethane types, the virtually crosslinked thermoplastic polyurethane elastomers would seem to be best and ideally suited for supply and use in powdered form. Their uses include adhesive applications which exploit the advantages of the powder form. 

Figure 15 Application of Redux liquid and powder adhesive to an airframe component.

The manufacture of sintered parts such as gears and bushings and that of composite materials are, in a sense, also applications of particle adhesion. After all, a sintered part is simply a part manufactured from a powder that has been subjected to conditions that would encourage the particles to strongly cohere. Similarly, a composite material is one where particles of one or more materials are combined in some fashion so as to adhere within a matrix, thereby imparting certain properties to the composite that none of the materials possess in their own right. 

Weld joints may be coated in the field with FBE powder, utilising a portable blast cleaning/induction heating and powder application system. Alternatively joints may be provided with self-adhesive laminate tapes or heat-shrink crosslinked polyethylene sleeves. 

Rheology is the study of flow and deformation of materials under the influence of external forces. It involves the viscosity characteristics of powders, liquids, and semisolids. Rheological studies are also important in the industrial manufacture and applications of plastic materials, lubricating materials, coatings, inks, adhesives, and food products. Flow properties of pharmaceutical disperse systems can be of particular importance, especially for topical products. Such systems often exhibit rather complex rheological properties, and pharmaceutical scientists have conducted fundamental investigations in this area [58-64],... 

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