Solvent-Borne Adhesives

Adhesion of paints and adhesives to TPOs is especially problematical due to the aliphatic nature of the substrate material. In Europe, plasma and corona treatment is employed to render these surfaces wettable and obtain strong adhesion by adhesives and paints in automotive manufacture. In the United States, however, primers based on solvent-borne chlorinated polyolefin oligomers (CPOs) have become the treatment of choice for these substrate materials. The VOC emissions from these primers are considerable (as in all solvent-borne adhesives), but the less... 

In recent years, the use of solvent-borne adhesives has been seriously restricted. Solvents are, in general, volatile, flammable and toxic. Further, solvent may react with other airborne contaminants contributing to smog formation and workplace exposure. These arguments have limited the use of solvent-bome adhesives by different national and European regulations. Although solvent recovery systems and afterburners can be effectively attached to ventilation equipment, many factories are switching to the use of water-borne rubber adhesives, hot melts or 100% solids reactive systems, often at the expense of product performance or labour efficiency. 

Several types of polychloroprene elastomers have been commercialized. The most important polymers used in solvent-borne adhesives are the following. 

Neoprene AH (1975). It is a methylacrylate-modified elastomer which is non-crystallizing and is chemically peptizable in aliphatic solvents. However, it is generally prepared as a dispersion in hexane, and has balanced properties between conventional solvent-borne adhesives and aqueous systems. 

Compatibility. Clear definition of compatibility is rather difficult. Compatibility has been defined as the ability of two or more materials to exist in close and permanent association for an indefinite period without phase separation and without adverse effect of one on the other [28]. On the other hand, compatibility is easily recognized in solvent-borne adhesives as a homogeneous blend of materials without phase separation. Normally, compatibility is understood as a clear transparent mixture of a resin with a given polymer. But, compatibility is a more complex thermodynamic phenomenon which can be evaluated from specific... 

Very good water and moisture resistance. Solvent-borne adhesives have an advantage over latex, which contains surfactants. 

Hydrocarbon resins, rosin, rosin ester, coumarone indene resins, and terpene resins can be directly added to solvent-borne adhesives. For latex adhesives, resin emulsification must be produced before addition. 

Plasticizers and oils, curatives and accelerators may also be added. In solvent-borne adhesives, curing agents are generally packed separately. 

Solvent-borne adhesives. Although the NR polymer is inherently tacky, tack-ifying resins are generally added to improve bonding to polar surfaces. Because the solids content in these adhesives is lower than 35 wt%, they are not suitable for gap filling. The quick-grab (cements) adhesives are particular because they contain about 65 wt% rubber, and set within a few seconds under finger pressure. 

Monomeric MDI Pure 4,4 -MDI 2.0 Solid (MP = 37 C) Flexible prepolymers Liquid 1-K adhesive Thermoplastic adhesives Curing hot melts Solvent-borne adhesives... 

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. 

An example of a solvent-borne adhesive is shown below ... 

In certain instances, for additional performance, polyisocyanates may be added to the solvent-borne adhesive or may be incorporated [55]. 

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. 

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. 

The global adhesives market was about 32 billion in 2010 [Ij. This included about 14.3 billion in water-borne adhesives, 6.9 billion in solvent-borne adhesives, and 5.3 billion in 100% solids adhesives. The 2012 market for adhesives and sealants combined was estimated at 42.5 billion for 2012 [2], with North American accounting for 11.8 billion. Western Europe 8.7 billion. Southeast Asia and Australia 13.8 billion, Russia and Eastern Europe 4.5 billion, and the rest of the world 3.7 billion. In 2010, sealants accounted for about 21% of the overall adhesives and sealants category [Ij. If this percentage remained steady, this would put the global adhesives market at about 34 billion for 2012. The amount of adhesives used globally in 2010 was estimated at 9 million metric tons [3]. 

Use of organic solvent borne adhesives has declined considerably in recent years, while use of hot melt and water borne adhesives has increased. Why ... 

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. 

Traditional pressure-sensitive adhesives were solutions of rubber and resin in solvent, and these dominated the market until well after World War II. From that time, as an increasing array of elastomers became available, as the price of solvents soared, and as environmental opposition to the use of solvents increased, water-based and hot-melt types made substantial inroads into the solvent-based market. This trend is likely to continue, although solvent-borne adhesives will probably always retain niches in areas where drying speed or ability to key into specific surfaces will outweigh environmental, handling, or price considerations. 

Solvent-borne adhesives are of two different types reactive and non-reactive. The reactive solvent-borne adhesives are usually high molecular weight oligomers with isocyanate functionality. When applied, these adhesives can react further, increasing physical properties. The non-reactive solvent-borne adhesives will not react further after application. 

To counter energy-saving problems, low-temperature curing by radiation has gained acceptance. For a long-term solution of pollution problems, hot-melt adhesives and the waterborne systems are being increasingly used as a substitute for the solvent-borne adhesives. In the future, the waterborne systems could dominate the entire adhesive industry. 

Adhesives made from the various forms of NR exhibit similar characteristics, although some properties are altered by adding curatives. They exhibit high flexibility, high resilience and fatigue resistance combined with low to moderate cost. The non-polar nature of the base NR (Fig. 1) means that there is very good water and moisture resistance and electrical insulation. In these respects, solvent-borne adhesives have an advantage... 

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