Hot melt adhesives application

Some grades of polyurethane and polyester copolymers are used as hot-melt adhesives. Applications include shoe manufacture and as an adhesive interlayer in coextmsion. 

Table 4. Polyolefin Polymer Suppliers for Hot Melt Adhesive Applications.

A substantial part of the market for the ethylene-vinyl acetate copolymer is for hot melt adhesives. In injection moulding the material has largely been used in place of plasticised PVC or vulcanised rubber. Amongst applications are turntable mats, base pads for small items of office equipment and power tools, buttons, car door protector strips and for other parts where a soft product of good appearance is required. Cellular cross-linked EVA is used in shoe parts. 

Whilst approximately twice the raw material cost of TPO- and S-B-S-type polymers, thermoplastic polyurethane elastomers find applications where abrasion resistance and toughness are particular requirements. Uses include gears, timing and drive belts, footwear (including ski boots) and tyre chains. Polyether-based materials have also achieved a number of significant medical applications. There is also some minor use as hot melt adhesives, particularly for the footwear industry. 

For many bonding applications a variety of adhesives can perform adequately. Hot melt adhesives are normally chosen where process speed is critical. Since hot melts have no carrier vehicle (solvent or water), and thicken rapidly as they cool, they are limited in their ability to (1) penetrate low porosity substrates or wet out very rough surfaces (2) cut through or imbibe surface contaminants and (3) wet out high thermal conductivity substrates (e.g. metals). Nonetheless, hot melts are increasingly the adhesive of choice in automated production environments because of their fast set speed. 

Case and carton sealing is a high volume application for hot melt adhesives. Typical formulas use 20-30% wax, 25-40% polymer, and 35-55% tackifier resin. The basic requirements for packaging adhesives will be described followed by formulating guidelines for specific market areas. The focus of this discussion will be on EVA and EnBA-based systems, which are the most common. 

Applications Applications of SEC-FTIR include quantitative analysis of copolymers [701] product deformulation of hot melt adhesives characterisation of polymer compositional heterogeneity analysis of complex mixtures of urethane oligomers and eventually also the identification and quantitative analysis of polymer additives... 

Nylons 6/6 and 6 comprise more than 90% of the polyamide market. The two have similar properties but nylon 6 has a lower Tm (223°C). Small amounts of nylons 6/9, 6/10, 6/12, 11, 12, 12/12, and 4/6 are produced as specialty materials. Those with more methylene groups than nylons 6/6 and 6 have better moisture resistance, dimensional stability, and electrical properties, but the degree of crystallinity, Tm, and mechanical properties are lower. Specialty nylons made from dimerized fatty acids find applications as hot-melt adhesives, crosslinking agents for epoxy resins, and thermographic inks. 

Hot melt adhesive compositions are used among others to bond edgebands. During edgebanding, the hot melt adhesive is maintained in the molten state in the glue pot of the edgebanding apparatus for extended periods of time. Fillers are added to hot melt adhesive compositions in order to decrease the costs of the adhesive composition and to improve the break action, such that it provides a clean break from the roller during the application procedure (25). 

Desirable fixative properties superior to PVP homopolymer can be specified by judicious selection of the amount of vinyl acetate. Hair sprays are limited in the molecular weight of the resin because if they are too hLgh the resulting viscosity of the formulation will result in a poor (coarse) spray pattern. Increasing the VP/VA ratio causes properties to increase in the direction shown by the arrows. Other applications for VP/VA copolymers are uses as water-soluble or remoistenable hot melt adhesives, pharmaceutical tablet coatings, binders, and controlled-release substrates. 

Essentially, hot-melt adhesives are blends of polymers that are melted and kept at an elevated temperature until applied to a cooler substrate the second substrate is brought into contact immediately with the molten film and afterwards the adhesive cools rapidly, a bond being formed almost instantaneously. The temperature of the molten adhesive generally is in the region 160 to 200 °C, so that its viscosity is low enough for application—and this means that the substrates to be bonded must be capable of withstanding the effect of adhesive at this temperature (this can cause difficulties with some thermoplastics, especially expanded materials). 

For successful use of such adhesives, not only must the formulation be suitable but the system for application also must be efficient. The molten adhesive must be maintained in a fluid condition and at the correct temperature for application over-heating could cause degradation, and if it is too cold the viscosity of an adhesive might be too high. The hot fluid is pumped to the substrate through a suitable nozzle but if the distance between the reservoir and the nozzle is appreciable there may be cooling and a need for heated hoses. Sometimes, molten adhesive is transferred to a coater of the heated-roller type, where again the control of temperature is important. There is a wide variety of equipment for application and every manufacturer of hot-melt adhesives will advise on systems that are suitable for use with them. 

Other applications for VP/VA copolymers are uses as water-soluble or remoistenable hot melt adhesives (140), pharmaceutical tablet coatings, binders, and controlled-release substrates. 

SBS copolymers are used in a wide variety of applications because of their clarity, toughness, and ease of processing. A major application is hot melt adhesives where they are compounded with hydrocarbon resins and oil.72 The SIS polymers are very popular in... 

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