Лако-красочные материалы — производство

There are a number of complex reactions that can occur besides the desired reaction of the polyol hydroxyl group with the isocyanate group to form a urethane, as shown in Fig. 4. Isocyanates can continue to react with undesirable consequences under conditions of high heat or strong bases. Basic impurities and excess heat catalyze branching […]

Isocyanates react with active hydrogens as depicted in Fig. 3. This addition reaction occurs with the active hydrogen adding to the nitrogen atom and the electron-rich nucleophile (Lewis base) reacting with the carbonyl group. Generally, the stronger the base, the more readily it reacts with the isocyanate. Table 2 shows typical reaction rates of some […]

The textile market has traditionally been the largest consumer of polyurethane adhesives. There are a number of high-volume applications, including textile lamination, integral carpet manufacture, and rebonded foam. Textile lamination occurs through either a solu­tion coating process or flame bonding. Flame bonding textile lamination is accomplished by melting a polyurethane foam by flame and then […]

Dennis G. Lay and Paul Cranley The Dow Chemical Company, Freeport, Texas, U. S.A. I. INTRODUCTION The development of polyurethane adhesives can be traced back more than 60 years to the pioneering efforts of Otto Bayer and co-workers. Bayer extended the chemistry of poly­urethanes initiated in 1937 [1] into the realm of adhesives about 1940 […]

Polymeric MDI is a versatile compound that has grown from the polyurethane industry, and has become an important wood binder in the forest products industry. As a wood binder, pMDI is highly effective and also quite unusual when compared to traditional thermosetting wood adhesives. The isocyanate functionality provides certain advantages which ensures its position in […]

All isocyanate containing compounds are highly reactive and potentially toxic. Care should be taken to prevent stored isocyanates from reacting with water because the resulting CO2 could produce dangerous pressures in sealed containers. Consequently, isocyanates are often stored under nitrogen gas or anhydrous air. Contact with all isocyanates should be avoided, especially inhalation. Fortunately, pMDI […]

As mentioned previously, neat pMDI does not have gap filling capability for wood bonding because of its low viscosity and propensity for deep penetration. Consequently, neat pMDI is not used for applications such as plywood, laminated veneer lumber, etc. However, gap filling properties may be achieved by modifying pMDI with a wide variety of difunctional […]

The versatility of isocyanate chemistry provides many avenues for synthetic manipulation and product development. Just a few of many examples are mentioned below. 1. Emulsifiable pMDI Polymeric MDI adhesives are rendered water emulsifiable through reaction with hydrophilic chains such as polyethylene oxide, as shown below. Monofunctional hydroxyl terminated polyethylene oxide chains with degree of polymerization […]

A. General Principles While pMDI wood binders are derived from formaldehyde, they are distinguished from other wood binders by a total lack of formaldehyde emission. This performance advantage has not displaced the less expensive UF and melamine-urea-formaldehyde (MUF) adhesives, which are commonly used for particleboard and medium density fiber — board. This is a tribute […]

Organic isocyanates are very reactive with compounds that possess ‘‘active’’ hydrogens, as in the case of carboxylic acids, primary and secondary amides, primary and secondary amines, alcohols, phenols, and water. The relative reactivity of these compounds with isocyanate depends upon the nucleophilicity and steric structure of the attacking com­pound. Primary and secondary amines are typically […]