Urethanes, applications

Organotin catalysts are used in a wide variety of urethane applications, aiding formation of the urethane bond in applications such as ... 

The three secondary hydroxyl groups in the 12-posihon are somewhat slow to react with diisocyanates and generally require heat for the completion of reaction. This can be of advantage or disadvantage depending upon the specific application. Modifications of CO and particularly of ricinoleic acid through esterification results in products that are of considerable interest as polyols for various urethane applications [88, 89]. 

Albemarle Corporation. "Ethacure 300 Curative a Convenient Liquid for All Urethane Applications." Trade literature (1999) 1-6. 

BASF Wyandotte Corp. Urethane Applications Research Bulletin, "Pluracol Polyol 637. A Graft Polyol for Slab Stock Foam," Jan 8, 1974. 

Nonfoam urethane applications utilize urethane polyether polyols. The largest is for microcellular products including reaction injection molded (RIM) materials. A variety of polymeric materials are made with ure-... 

When comparing ultra-low monol PPG polyols with PTMEG it is essential to keep in mind the fundamental differences between these two high-performance polyether polyols in order to obtain the maximum benefit in urethane applications. Table 9.13 summarises these differences in terms of their chemical structure, hydroxyl type (reactivity), MWD and crystallisability. 

Gexol, High-performance wire and cable insulation compounds. Union Carbide Corp. Givsorb UV-l, UV absorbers (formamidine) for urethane applications, Givaudan-Route Corp. 

Catalysts for urethane applications are sold by Air Products (Dabco), Abbott (Polycat), Kao Corp. (Kaolizer), Tosoh Corp. (Toyocat), and Union Carbide (Niax). Organic mercury compounds were used in cast elastomers and in RIM systems to extend cream time, ie, the time between mixing of all ingredients and the onset of creamy appearance, but are no longer used today because of toxicity concerns. 

The poly(alkylene oxide)s for urethane applications are generally characterized by composition, molecular weight, and functionality (also see Chapter 4, Section V, and Chapter 5, Section I.A. Molecular weight and functionality are related by hydroxyl number. Hydroxyl number is determined by titration of the fully reacted phthalic anhydride adduct of the monol, diol, or polyol in question and is expressed in terms of milli-... 

Urethane rubbers have found steadily increasing use for oil seals, shoe soles and heels, fork-lift truck tyres, diaphragms, chute linings and a variety of mechanical applications. Fabric coatings resistant to dry cleaning are a recent development. In many of these applications high elasticity is not an important prerequisite so that the polyurethane rubbers must be compared not only with other rubbers but also with a variety of thermoplastics. 

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. 

The vast majority of reactive hot melts are moisture-curing urethane adhesives. Radiation (UV/EB) curable adhesives have been explored in the laboratory since the mid-1970s, but are only recently beginning to gain significant market penetration, particularly for PSA applications. The formulation and properties of these two classes of adhesives are discussed below. 

Catalysts such as dibutyl tin dilaurate or tertiary amines are added to promote the urethane reaction and/or subsequent moisture cure. Dimorpholine diethyl ether is particularly effective at promoting moisture cure without promoting allophanate side reactions at the application temperature (which leads to instability in the hot melt pot) [29]. 

To improve on penetration and heat resistance (properties normally in opposition when formulating hot melts), reactive hot melt systems are being developed. Moisture curing urethanes have already gained wide acceptance in a number of wood and automotive applications. UV cure is slowly gaining acceptance in PSA, labeling, and other markets. 

Each of these product types will be discussed, including the method of application, the type of substrates that are bonded by each approach, and one or more typical adhesive formulations. In order to understand the adhesive cure mechanism, a brief review of the common urethane reactions is needed. 

The first urethane reaction in Fig. 1 is used in two major ways in adhesives. In one case, a two-component adhesive usually employs a polyol and polyisocyanate with catalyst. This can react at room temperature to form the polyurethane. The second use of this reaction is to make an isocyanate-terminated prepolymer. Reacting a stoichiometric excess of isocyanate with polyol can produce an isocyanate-terminated prepolymer. A prepolymer is often made with an NCO/OH ratio of 2.0, as shown below, but the isocyanate ratio can range from 1.4 to over 8.0, depending upon the application ... 

Several large applications for one-component moisture-cure urethane adhesives are available. Polymeric MDI is an exceptional binder for wood products, such as oriented strand board and particleboard. One-component urethane windshield adhesives are used almost exclusively in both the OEM and automotive aftermarket. One-part urethane adhesives are used to assemble the sidewalls for recreational vehicles (RV s), manufactured housing, and mobile homes. In construction applications, one-part urethanes are used to bond metal doors, hardwood flooring, panels, and partitions. 

Windshield sealants comprise some of the most significant applications of one-component urethane adhesives. Several years ago, the requirements for these sealants were increased. In an accidental rollover, in certain automobiles, the windshield becomes a structural part of the car. Therefore, the windshield adhesive, which holds the windshield in place, must have structural strength. An example of a one-component windshield sealant is shown below [48] ... 

Moisture-curing hot melts are a small but fast growing segment of the urethane adhesive market. They are used mostly in construction and furniture assembly applications. Recent applications include RV sidewall assembly and other OEM automotive applications. Smaller applications include bookbinding and footwear. A typical adhesive is shown below ... 

Solvent-home urethanes are still widely used to bond leather and athletic shoes. The OEM automotive market uses some solvent-home urethanes together with chlorosulfonated polyethylene as a primer. Some urethane solvent-home packaging adhesives are used for cap liners and for paper and foil lamination. Some textile laminating applications are still based on solvent-home urethanes. 

Applications for blocked urethane adhesives are small. However, they may be used as flocking adhesives or as crosslinkers for solvent-borne adhesives. Blocked urethane adhesives are also used as splicing adhesives for belts. Blocked isocyanates based on TDI, IPDI, and derivatives of hexamethylene diisocyanate are most commonly commercially available. 

Two-component urethane adhesives are used to bond sheet molding compound (SMC) panels for automotive OEM and aftermarket applications. Two-part urethanes are used as laminating adhesives in the RV industry. 

One application for a two-part urethane adhesive is a windshield adhesive/sealant... 

Two-component waterborne urethanes are the preferred choice to replace solvent-borne urethane adhesives, especially in the packaging and shoe industries. At this time, the packaging area is the largest application of two-part waterborne urethanes. Good strides have been made by the two-part waterborne urethanes in the shoe industry, especially in the athletic shoe market. Waterborne urethanes are also replacing the solvent-borne products in the OEM door panels. 

Certain fillers are commonly added to protect the urethane backbone from oxidative degradation. Carbon black and titanium dioxide are commonly used in conjunction with antioxidants to protect polyether polyurethanes in exterior adhesive applications that may be exposed to oxygen and light (Fig. 12). 

The paint is sensitive to moisture during storage and application but then becomes exceptionally water-resistant. Its best use is for exterior exposure in an aggressive environment but where the maximum gloss and color retention is required. It is preferable to apply the urethane as a finishing coat over epoxy undercoating and priming. 

Solventless urethanes These are similar to solventless epoxies but can be applied in even thicker films without adhesion problems. They are considered to have better water and abrasion resistance than the epoxy but cost more and application is even more critical. Their main use would be for large areas requiring abrasion resistance. 

Moisture-curable urethane systems (one-pack) can be considered as two-component systems which use atmospheric moisture as the second component. One-pack urethane coatings can be produced that are similar in physical properties to the two-pack systems for almost all applications. These highly complex systems can have a great deal of flexibility. Claimed advantages are a one-pack system, rapid cure, even at low temperatures, excellent chemical and abrasion resistance and good flexibility. Although these systems have been available for some time in other countries of Europe, they are only recently beginning to be of interest in the UK. 

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