Urethane adhesives heat resistance

Uses Urethane-acrylic for lithographic/offset/screen inks, wood/paper coatings, electronics, photopolymers, elastomers, adhesives Features Offers flexibility, water resist., chem. resist., adhesion, heat resist., abrasion resist., impact str. 

Chem. Descrip. Aliphatic polyester-based urethane diacrylate oligomer Uses Urethane-acrylic for coatings, flexible pkg., screen inks Features Difunctional low vise. exc. conformal props. good weatherability, chem. resist., flexibility, adhesion, heat resist., abrasion resist., impact str., water resist. low shrinkage Properties APHA 55 clear liq. dens. 9.213 Ib/gal vise. 660 cps (60 C) ref. index 1.4882 tens. str. 945 psi 1% mod. 3557 psi elong. 53% CN996 [Sartomer]... 

Poly(ethyl methacrylate) (PEMA) yields truly compatible blends with poly(vinyl acetate) up to 20% PEMA concentration (133). Synergistic improvement in material properties was observed. Poly(ethylene oxide) forms compatible homogeneous blends with poly(vinyl acetate) (134). The T of the blends and the crystaUizabiUty of the PEO depend on the composition. The miscibility window of poly(vinyl acetate) and its copolymers with alkyl acrylates can be broadened through the incorporation of acryUc acid as a third component (135). A description of compatible and incompatible blends of poly(vinyl acetate) and other copolymers has been compiled (136). Blends of poly(vinyl acetate) copolymers with urethanes can provide improved heat resistance to the product providing reduced creep rates in adhesives used for vinyl laminating (137). 

Polyester polyols are used widely in urethane adhesives because of their excellent adhesive and cohesive properties. Compared to polyether-based polyols, polyester-based polyol adhesives have higher tensile strengths and improved heat resistance. These benefits come at the sacrifice of hydrolytic resistance, low-temperature performance, and chemical resistance. One of the more important application areas for these products is in the solvent-borne thermoplastic adhesives used in shoe sole binding. These products are typically made from adipic acid and various glycols (see Fig. 15). 

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. 

Table VI. Heat Resistance of Urethane Structural Adhesive Bonds ...

Also, as the thickness of the adhesive bondline increases, read through problems become worse. The heat resistance of urethane-bonded SMC composites has also been a problem. This is believed to be due to the out-gassing of volatiles from the plastic which decreases the bond integrity. This is evidenced in Table VI, which compares the heat resistance of metal-metal bonds and SMC composites prepared with urethane adhesives. It can also be seen that the composition of the SMC has a significant affect on the heat resistance. The urethane-modified SMC was also reported to give off less volatiles than the unmodified SMC. Recent work has indicated that certain primers may be able to protect the adhesive from the substrate. 

NeoPac E-850 is a formaldehyde-free, water-based aliphatic polyester urethane-acrylic dispersion. This system was developed specifically for use in wood furniture adhesives due to its bond strength and excellent water and heat resistance. As a water-based polymer, it can be highly loaded with mineral fillers to reduce the overall water content in the formulated adhesive without loss of adhesion properties. This is a necessary requirement for most wood laminating production methods in controlling viscosity, wood penetration and faster drying. 

Urethanes Urethane adhesion promoters are used widely to bond PVC to polyester, nylon, and other fabrics, including sized glass fiber. In multicoat operations, the additive is used only in the first coat. With, polyester fabric, the isocyanate component in urethane formation can be used alone. Solvent or plasticizer solutions of oligomerized toluene diisocyanate (TDl) are available under the trade names Vulcabond (Akzo Nobel), Vanchem HM-50 (Vanderbilt), Thanecure T9 (TSE Industries), and Desmodur (Bayer). For improved resistance of the bond to heat and moisture, products based on bisphenyl diisocyanate (MDl) are also used. These include Vanchem HM-4346 and Rubinate 9480 (Huntsman). These are typically used at 3-7 phr levels in plastisols for coating polyester fabric. The second or subsequent coats should contain titanium dioxide and UV light stabilizer for outdoor service. With translucent products, an aliphatic isocyanate such as Desmodur N-lOO or TMl META (Cytec) should be used. 

Block copolymers can contain crystalline or amorphous hard blocks. Examples of crystalline block copolymers are polyurethanes (e.g. B.F. Goodrich s Estane line), polyether esters (e.g. Dupont s Hytrel polymers), polyether amides (e.g. Atofina s Pebax grades). Polyurethanes have enjoyed limited utility due to their relatively low thermal stability use temperatures must be kept below 275°F, due to the reversibility of the urethane linkage. Recently, polyurethanes with stability at 350°F for nearly 100 h have been claimed [2]. Polyether esters and polyether amides have been explored for PSA applications where their heat and plasticizer resistance is a benefit [3]. However, the high price of these materials and their multiblock architecture have limited their use. All of these crystalline block copolymers consist of multiblocks with relatively short, amorphous, polyether or polyester mid-blocks. Consequently they can not be diluted as extensively with tackifiers and diluents as styrenic triblock copolymers. Thereby it is more difficult to obtain strong, yet soft adhesives — the primary goals of adding rubber to hot melts. 

Adhesives recommended for polyphenylene sulfide include epoxies, and urethanes. Joint strengths in excess of 1000 psi have been reported for abraded and solvent-cleaned surfaces. Somewhat better adhesion has been reported for machined surfaces. The high heat and chemical resistance of polyphenylene sulfide plastics makes them inappropriate for either solvent cementing or heat welding. 

This compound is not employed in urethanes. It is a cross-linking agent for adhesives and is used to increase bonding to rubber and plastic substrates and resistance to heat and solvents. 

Thermoset plastics are cross-linked by chemical reaction so that their molecules cannot slip by one anotber. They are rigid when cool and cannot be softened by the action of heat. If excessive heat is applied, thermoset plastics will degrade. Consequently, they are not weldable. Because of their chemical resistance, they cannot be solvent cemented. Thermoset plastics are usually joined by either adhesive bonding or mechanical fastening. Typical thermosetting plastics are epoxy, urethane, phenolic, and melamine formaldehyde. 

NeoRez R-1400 is an aliphatic polyester urethane polymer dispersion developed for heat-activated adhesive formulation. NeoRez R-1400 offers the combined properties of low temperature activation, good early green strength, and high temperature resistance when crosslinked with poly-dispersible isocyanate. 

---