Solvent polyurethane adhesives

Solvent polyurethane adhesives have been of great economical and technical importance because of their easy processing and high performance. They have been used traditionally for the bonding of rubber, leather, textiles, metal, paper, wood, and plastics including highly plasticised polyvinyl chloride. 

Poly(tetramethylene oxide) polyols (PTMEG) are high performance polyethers that are crystalline waxes at molecular weights above 650 and liquids at lower molecular weights. They are only available as diols, but they produce adhesives with good hydrolysis resistance and moisture resistance, which is why these adhesives are even used in medical devices, blood bags, catheters, and heart-assist devices [25]. Certain thermoplastic polyurethane adhesives and solvent-borne adhesives are also based on PTMEG s. 

The market for polyurethane thermoplastic adhesives is small, but growing. TPU s are used to produce some solvent-borne adhesives and also are used in laminating textiles and films for labels and emblems. In addition, they are being considered as an alternative to solvent-borne adhesives in the shoe market. 

Solvent wiping. Rubbers tend to swell by application of solvents and the mechanical interlocking of the adhesive is favored. Although chlorinated hydrocarbon solvents are the most effective, they are toxic and cannot be used toluene and ketones are currently the most common solvents. The treatment with solvents is effective in the removal of processing oils and plasticizers in vulcanized mbbers, but zinc stearate is not completely removed and antiozonant wax gradually migrates to the mbber/polyurethane adhesive interface. Table 27.1 shows the moderate increase in adhesion produced in SBR by MEK wiping. 

Solutions of different carboxylic acids (fiimaric acid [FA], maleic acid, acrylic acid, succinic acid, and malonic acid) in ethanol have been effectively used as primers to increase the adhesion of synthetic vulcanized SBRs. The increase in the adhesion properties of SBR treated with carboxylic acid is attributed to the elimination of zinc stearate moieties and the deposition of acid on the rubber which migrates into the solvent-borne polyurethane adhesive layer once the adhesive joint is formed. The nature of the carboxylic acid determines the rate of diffusion into the adhesive and the extent of rubber-adhesive interfacial interaction. 

Because of the high resistance to chemicals, gluing is not possible with solvents but suitable cyanoacrylate, epoxy and polyurethane adhesives can be used leading to strengths significantly inferior to those of PPS. Preliminary tests are essential. 

Polyurethanes with isocyanate functionality (for polyurethane adhesives) Chlorinated polypropylene in solvent (for polyolefins)... 

The main use of ethene oxide is as ethylene glycol, half of which is used in as anti-freeze and the other half is used in the production of polyesters. Other products are glycol ethers, polyurethanes and polyethylene glycols). We find these in many consumer products such as fibres, foils, bottles, solvents, plasticizers, adhesives, detergents, brake fluids, etc. 

LAWSON, G. et al. (1996) Chemical composition and migration level of packaging adhesives. Summary report Polyurethane adhesives (solvent based). MAFF Project No. IC074. 

Polysulfone A number of adhesives have been found useful for joining polysufone to itself or to other materials. These include 3M Company s EC 880 solvent-base adhesive, EC 2216 room-temperaturecuring epoxy two-part paste, Bloomingdale Division, American Cyana-mid Company BR-92 modified epoxy with DICY curing agent, or curing agent "Z" (both spreadable pastes), vinyl-phenolics, epoxy-nylons, epoxies, polyimide, rubber-based adhesives, styrene polyesters, resorcinol-formaldehyde, polyurethanes, and cyanoacrylates. The EC 880, EC 2216, and the two BR-92 adhesives are recommended by the polysulfone manufacturer. Union Carbide (16) (17). 

Mortrim [Morton], TM for a series of one and two-component solvent-based and water-based polyurethane adhesives. 

Polyurethanes are also used to make paints, available as water-thinnable paints and powder coatings. Items painted with PU paints benefit not only from a lacquer film, but also from an improved chemical resistance. Polyurethane paints are scratch, abrasion, and impact resistant, and they adhere well to a variety of surfaces. Polyurethane adhesives are similarly good choices as they resist heat, water, solvents, grease, and oils. ... 

Polyurethane adhesives were prepared by mixing polyol, diisocyanate (MDI, TDI or HDI), solvent (DMF, benzene or ethylace-tate), and catalyst (T-9) in the following fashion The diisocyanate dissolved in half of the total solvent volume was mixed with two-thirds of the polyol in one-fourth of the solvent in the presence of a trace of the catalyst. The mixture was heated to 50°C until an exothermic reaction starts then, heat was temporarily removed and reapplied for 10 min to maintain a temperature of 80°C. The rest of the polyol, catalyst, and solvent were then added and mixed completely. The resin was ready for application when the consistency of the mixture had reached a suitable level. The adhesive was spread on 11 3/4" x 4 1/2" x 3/4" wood (hard maple or southern pine) strips. The moist adhesive-coated surfaces were exposed to ambient air (vented hood) for 20-30 seconds if DMF was used as solvent, or for 3-5 minutes if either benzene or ethylacetate was used. After pressing (100 psi), the strips were cut into small shear blocks and tested according to ASTM Standard D905-49. Polyurethane coatings were prepared by mixing the polyol (80 parts) in ethylacetate (60 parts) and toluene (40 parts), with a solution of TDI (53 parts) in 80 parts ethylacetate and 30 parts toluene, and T-9 catalyst... 

It is resistant to most hydrocarbons, although polar solvents may extract plasticizer if present. Water swells the PVC polymer imparting an opacity which reverses on drying. PVC can be adhered using polyester, epoxy or polyurethane adhesives. 

As previously noted, the primary use for this elastomer has been as solvent-based adhesives and sealants. Solvent-based products are losing market share to water-based poly-chloroprenes, to other polymer types such as acrylics and polyurethanes, and to hot melt adhesives. However, where the processing facility is able to contain the vapor emissions, a solvent-based adhesive or sealant is preferred because of better wetting of surfaces, faster drying, and higher performance of the cured or dried product. Many rubber bonding... 

Solvent-borne adhesives represent the majority of the volume in the packaging market, with both one- and two-component systems being used. Waterborne polyurethane adhesives are a much smaller segment that has been driven by environmental considerations. Growth has slowed in recent years because of generally inferior performance compared to solvent-based adhesives and because most of the major converters have already made capital investments in solvent recovery systems. 

The furniture industry uses polyurethane adhesives to bond veneers of various composition to boardstock and metal substrates. Both waterborne and solvent-based adhesives are used. 

Adhesives and sealants are manufactured from a variety of polymers. Their selection and their combinations used impact solvent selection. Most solvent systems are designed to optimize the solubility of the primary polymer. Adhesives can be divided into ones which bond by chemical reaction and ones which bond due to physical processes. Chemically reactive adhesives are further divided into three more categories for those that bond through polymerization, polyaddition, or polycondensation. Physically bonding adhesives include pressure sensitive and contact adhesives, melt, or solution adhesives, and plastisols. Polymerization adhesives are composed of cyanoacrylates (no solvents), anaerobic adhesives (do not contain solvents but require primers for plastics and some metals which are solutions of copper naphthenate), UV-curable adhesives (solvent-free compositions of polyurethanes and epoxy), rubber modified adhesives (variety solvents discussed below). 

In view of the above efforts, it is surprising that the majority of recent patents on adhesives are for solvent-based systems.The new inventions include a universal primer, 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), a low VOC adhesive for pipes and fittings, a solvent-containing heat-resistant adhesive based on siloxane polyimide, a water-based polyimide adhesive,and two-component solvent-free polyurethane adhesive system for use in automotive door paneling. ... 

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