Handbook of Solvents - George Wypych - ChemTech - Ventech!

14.1 Adhesives and sealants 851
tured with solvents for shoes, food packaging, and textile and plastic film lamination.
Current technologies use TPU in the form of a hot melt, as a reactive PUR and as a thermoplastic
laminating film. 3 Reactive hot-melts were first introduced in the early 1980s and
since than have grown very rapidly. After application the adhesive is cured by moisture. 14
These adhesives are already in use by the automotive industry (bonding carpet to door panels,
tray assembly, lenses to headlamp housing, and lamination of foam to fabric) and in furniture
and building products (moldings, picture frames, decorative foil, edgebanding), in
bookbinding, and in the footwear industry. Polyurethane water dispersions are expected to
grow 8-10%/year from the current 5,000-6,000 tones/year market in Europe. 14 Applications
are similar to those of hot melts.
UV-curable pressure-sensitive adhesives are the most recent application of the advancing
radiation curing technology. 16 Low viscosity formulations allow the use of standard
application techniques with several advantages such as improved production rate, energy
efficiency, improved properties of the final products, and new potential applications for
pressure-sensitive additives in thicker films with mechanical performance. It is expected
that radiation cured materials will expand at a rate of 10%/year. 17 Adhesives constitute 16%
by value and 13% by volume of radiation cured products (two major applications for radiation
cured materials are coatings and inks). Henkel introduced a series of water-based laminating
adhesives. 18 Hot melt systems, high-solids solvent systems with a 3 times higher
solids content, and water based adhesives have been introduced to textile lamination to replace
traditional low-solids solvent-based adhesives. 19
Odor elimination is the additional benefit which has helped to drive the replacement of
solvent-based systems. 20 In packaging materials, most odors are related to the solvents used
in inks, coatings and adhesives. Also, coalescing solvents from water-based systems caused
odors. Elimination of solvent is a priority but solvent replacement may also change the response
to the odor because solvents such as toluene and xylene smell like lubricating oils or
turpentine whereas isopropanol smells more like a disinfectant. Odors stem not only from
solvents but also from products of the thermal and UV degradation of other components and
solvents. 20
In view of the above efforts, it is surprising that the majority of recent patents on adhesives
are for solvent-based systems. 21-26 The new inventions include a universal primer, 21 an
adhesive composition in which solvents have been selected based on Snyder’s polarity
(only solvents which belong to group III are useful in adhesive for automotive applications
to avoid a deleterious effect on paint), 22 a low VOC adhesive for pipes and fittings, 23 a solvent-containing
heat-resistant adhesive based on siloxane polyimide, 24 a water-based
polyimide adhesive, 25 and two-component solvent-free polyurethane adhesive system for
use in automotive door paneling. 26
REFERENCES
1 R Vabrik, G Lepenye, I Tury, I Rusznak, A Vig, International Polym. Sci. Technol., 25, No.3, T/1-9
(1998).
2 D Raftery, M R Smyth, R G Leonard, International J. Adhesion Adhesives, 17, No.4, 349-52 (1997).
3 J B Samms, L Johnson, J. Adhesive Sealant Coun., Spring 1998. Conference proceedings, Adhesive &
Sealant Council, Orlando, Fl., 22nd-25th March 1998, p. 87.
4 A Stevenson, D Del Vechio, N Heiburg, Simpson R, Eur. Rubber J., 181, 1, 2829, (1999).
5 K Menzefricke, Adhesive Technol., 15, No.1, 6-7 (1998).
6 L White, Eur. Rubber J., 179, No.4, 24-5 (1997).
7 J Baker, Eur. Chem. News, 69, No.1830, 20-2 (1998).