Hot melt pressure-sensitive adhesives

Butyl Rubber. Butyl rubber is used in conjunction with other thermoplastic hydrocarbon rubbers (for example, polyisobutylene) to make pressure-sensitive hot-melt adhesives. Such formulations include also tackifying resins and oils. Adhesives of low viscosity are produced, and these may be applied by the hot-melt spray technique (see page 106). 

Other hot melts are based on low molecular weight polyethylene, combined with tackifying agents. These tend to be lower in cost and performance than the EVA-based hot melts, and they are used primarily with paper packaging, such as cartons and multi-wall bags. Atactic PP can also be used as the base for hot melt adhesives. Pressure-sensitive hot melt adhesives for tapes and labels often employ thermoplastic elastomers, consisting of block copolymers of styrene and butadiene or isoprene. 

The fundamentals of pressure-sensitive hot-melt adhesives are similar to those of solvent-based systems. Most elastomers and tackifiers are suitable, although ethylene-vinyl acetate copolymers are also used and the conventional rubber types are not. Pressure-sensitive hot melts are dominated by thermoplastic rubbers, which are ideal for use in these applications. Their unique properties arise from their essentially two-phase structure, in which thermoplastic regions of styrene end blocks lock the elastomeric midsections of butadiene or isoprene at room temperature but allow the elastomer to move freely at elevated temperatures or in solvent. This gives the polymer properties that are akin to those of vulcanized rubbers at room temperature, while allowinig it to behave as a thermoplastic when heated or dissolved. This structure is illustrated in Fig. 1. 

Early pressure-sensitive hot-melt adhesives used ethylene-vinyl acetate copolymers as elastomers, but they are seldom used now. Atactic polypropylene is sometimes used on its own or in admixtures. More recently, vinyl ethers and acrylic resins have become available and will probably play an increasingly important role as the technology is developed, especially on polar surfaces. 

Ethylene/VA copolymer SR, insulation Ethylene/VA copolymer SR, lacquers Ethylene/VA copolymer SR, lamp seals Ethylene/VA copolymer SR, moldings/extrudates Ethylene/VA copolymer SR, pressure-sensitive/hot-melt adhesives Ethylene/VA copolymer SR, sealants Ethylene/VA copolymer SR, waterproof sheeting Ethylene/VA copolymer stabilization, latex Sodium laureth-4 phosphate stabilization, soil Acrylamide stabilizer... 

Figure H.3 shows a typical metallized hot stamping foil. The carrier film supports the decorative coatings until they are pressed on the plastics part. A lacquer coating is passed over the releasing layer to provide protection for the metal foil. If paints are used, the lacquer and paint pigment are combined into one layer. The bottom layer functions as a heat- and pressure-sensitive hot-melt adhesive. Heat and pressure must have time to penetrate the various film coating and layers to bring the adhesive to a liquid state. Before the carrier film is stripped away, a short cooling time is required to ensure that the adhesive is solidified.

It typically ranges from fractions of seconds to minutes to infinity (in pressure-sensitive hot-melt adhesives). 

Pressure-sensitive hot-melt adhesives are surface-tacky and can be used by the application of pressure alone. These adhesives have infinite open times and are used at room temperature. Typically, pressure-sensitive hot-melt adhesives are supplied in form of blocks or cubes in silicone coated packaging units or preferably in polyethylene bags, which after melting form part of the adhesive. 

The adhesives industry is the third most important market for rosin. Rosin, modified rosins, and rosin derivatives are used in several types of adhesives, including the pressure-sensitive, hot-melt, and elastomer-based latices, and solvent rubber cements. 

Uses Tackifier, plasticizer, extender, binder in PVC sealers, automotive adhesives/sealers, rubber, plastics, pressure sensitives, hot melts, asphalt coatings, sound deadeners, sealant tapes, caulks impact modifier for plastics... 

Uses Tackifier. plasticizer for adhesive systems (pressure-sensitive, hot-melt) plasticizer/coupling agent for lacquers, high-solids coalings food pkg. adhesives... 

As with most of the other sections of this chapter, the basic reference to the applications of rosin and its derivatives as components of adhesive formulations up to the mid-1980s, is the corresponding chapter by Kennedy et al. [73] of the classical Naval Store book. The major emphasis in that chapter was placed on the tackifying properties of rosin-based resins in pressure-sensitive, hot melt and sealant adhesives. Therefore, before proceeding to a critical bibliographic survey, it seems appropriate to define the concept of tack and its repercussion in the broad area of adhesion, as opposed to other contexts, like printing inks, paints and coatings. 

Heteroatom functionalized terpene resins are also utilized in hot melt adhesive and ink appHcations. Diels-Alder reaction of terpenic dienes or trienes with acrylates, methacrylates, or other a, P-unsaturated esters of polyhydric alcohols has been shown to yield resins with superior pressure sensitive adhesive properties relative to petroleum and unmodified polyterpene resins (107). Limonene—phenol resins, produced by the BF etherate-catalyzed condensation of 1.4—2.0 moles of limonene with 1.0 mole of phenol have been shown to impart improved tack, elongation, and tensile strength to ethylene—vinyl acetate and ethylene—methyl acrylate-based hot melt adhesive systems (108). Terpene polyol ethers have been shown to be particularly effective tackifiers in pressure sensitive adhesive appHcations (109). 

Styrenic block copolymers (SBCs) are also widely used in HMA and PSA appHcations. Most hot melt appHed pressure sensitive adhesives are based on triblock copolymers consisting of SIS or SBS combinations (S = styrene, I = isoprene B = butadiene). Pressure sensitive adhesives typically employ low styrene, high molecular weight SIS polymers while hot melt adhesives usually use higher styrene, lower molecular weight SBCs. Resins compatible with the mid-block of an SBC improves tack properties those compatible with the end blocks control melt viscosity and temperature performance. 

Uses ndReactions. Some of the principal uses for P-pinene are for manufacturing terpene resins and for thermal isomerization (pyrolysis) to myrcene. The resins are made by Lewis acid (usuaUy AlCl ) polymerization of P-pinene, either as a homopolymer or as a copolymer with other terpenes such as limonene. P-Pinene polymerizes much easier than a-pinene and the resins are usehil in pressure-sensitive adhesives, hot-melt adhesives and coatings, and elastomeric sealants. One of the first syntheses of a new fragrance chemical from turpentine sources used formaldehyde with P-pinene in a Prins reaction to produce the alcohol, Nopol (26) (59). 

Although pressure-sensitive and hot-melt adhesives can be manufactured, they are not common because lower-cost formulations using other elastomers can be prepared. 

Polystyrene-PDMS block copolymers4l2), and poly(n-butyl methacrylate-acrylic acid)-PDMS graft copolymers 308) have been used as pressure sensitive adhesives. Hot melt adhesives based on polycarbonate-PDMS segmented copolymers 413) showed very good adhesion to substrates with low surface energies without the need for surface preparation, such as etching. 

Elastomeric block polymers of styrene and butadiene or iso-prene and their products of hydrogenation are finding increasing use in a variety of fields.44. Linear and radial block polymers are used extensively in injection molded rubber goods, footwear, pressure sensitive and hot melt adhesives and in mechanical rubber goods such as hose, tubing, cove base, toys, drug sundries, rubber bands, stoppers, erasers, etc. 

Styrene Copolymers. The so-called thermoplastic rubbers based on styrene-butadiene-styrene and styrene-isoprene-styrene block copolymers can be used for hot-melt adhesives, particularly when extended with tackifying resins and oils. They can be made into pressure-sensitive adhesives, as melts with low viscosity—being applied from fine spinnerets which are oscillated to make a... 

Hot-melt adhesives are applied in molten form and a bond forms between the substrates on cooling. These adhesives are used mainly for high-speed operations such as container formation and for some pressure-sensitive labels. The archetypal hot-melt adhesive is sealing wax, but nowadays they are mainly synthetic products such as high molecular weight ethylene-vinyl acetate co-polymers. 

Use In pressure-sensitive wet lay-up and hot-melt adhesives, dip coating, spraying, and spreading applications. 

Use Pressure-sensitive and hot-melt adhesives, bonding of paper to polyethylene, laminating adhesive, tackifier and plasticizer for coatings, heat sensitizer for rubber latex, pigment binder in textile finishing and printing inks, protective colloid in emulsions. 

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