Polyols laminating adhesives

The polyester type polyols used in polyurethane laminating adhesives are produced by the direct esterification of polyfunctional carboxylic acids and glycols. Polyester polyols provide the soft segment in polyurethane products giving the adhesive flexibility. Ester groups of the polyol also contribute to adhesion. Polyester polyols provide limited wetting and adhesion of olefinic surfaces with amide slip additives (in contrast to polyether polyols). Typical examples include adipic acid, caprolactone, maleic acid and isophthalic based polyester polyols. 

Rucoflex . [Ruco Polymer] Polyester polyols for polyurethanes, sol n. laminating adhesives, sol n. coatings, prepolymers, dierm(q>lastic elastomers, and one-shot castables. 

Chem. Descrip. Sat., aliphatic, linear, hydroxyl-terminated polyester polyol Uses Polyester for sol n. coatings, thermoplastic elastomers, laminating adhesives, and castable prepolymers Features PUs exhibit solv. resistance, high strength elastomers, and resiliency melts at mod. temps. 

Phenol-formaldehyde resin Phenolic resin Polyvinyl methyl ether laminating adhesive mfg., solution Polyester polyol laminating resin Isopropyl glycidyl ether laminating resin, (chemical plant components/handling equip.)... 

The cohesive polyester-polyol crystals of commercially available PU adhesives melt at about 50 °C - the lamination adhesive is thermally activated and becomes soft and capable of heat-sealing (Fig. 8-26). During coohng, the polyester-polyol segments re-crystaUize, resulting in a rapid increase in the internal strength of the adhesive film. 

Because the reaction between isocyanates and polyols continues for many days after lamination (i.e. the adhesive continues to cure), it is crucial to test laminates for residual isocyanates and for PAA release in a realistic manner. This must not be sooner or later than food packaging would conunence. One must also use realistic pre-test storage conditions for the film (especially with respect to temperature and humidity). Indeed, many laminators routinely determine the extent of the cure of the adhesive over time. Only when a predefined level of cure has been reached can a laminated film be considered to be ready for packaging food. 

Lawson et al. (2000) examined the migration of constituents from solvent-free adhesives used to bond 12 pm PET film to 45 pm LDPE. The technique of MALDl-MS, a soft ionisation technique capable of looking at sample mixtures over a mass range of 150-500,000 Da without prior separation, was employed. The adhesives studied were based on a solution of mixed isomers of MDl in polymeric MDI with either polyether or polyester-based polyols. Pouch testing of cured laminates with distilled water was undertaken (two hours at 70 °C) with the LDPE surface in contact with the water. 

Migration of unreacted polyol components through the polyethylene for the polyether-based laminate was observed. Although an excess of isocyanate was present, diffusion of polyol components into the polyethylene prior to reaction with isocyanate was postulated to explain the migration. Cyclic oligomers from the polyol starting materials were identified as the main migrants from the polyester-based adhesive. 

Rapra Technology Ltd has undertaken a detailed investigation into the migration of species from different types of adhesives used with laminated multi-layer materials (Barber et al, 2003). Migration of aromatic amines, BADGE, bisphenol A and polyols were examined. A description of the samples used and a brief summary of some of the results obtained from this analytical work are given below. 

Polyurethanes are produced by the chemical action of di-isocyanate and polyol. The properties can be varied by the type of isocyanate used and the proportion of the two monomers. There are four main groups of classification for the thermoplastic groups of polyurethane, i.e. rigid foam, flexible foam, non-cellular and cellular polymers. Two main isocyanates used are toluene di-isocyanate (TDI) and diphenylmethane diisocyanate (MDI). Polyurethanes have limited application in the pharmaceutical or medical industries. Polyurethane is used as an adhesive for laminations (thermosetting material). Like thermosetting polyurethane, thermoplastic polyurethanes can be found as esters and ethers. 

Much research is being performed in the field of drop-in biopolymers toward biobased PU, based on renewable polyester polyols. Merquinsa markets a biobased thermoplastic PU under the brand names Pearlthane and Pearlbond ECO these have a biobased content ranging from 20 to 90%. Arkana produces biobased thermoplastic copolyamide hotmelt Platamid (based on castor oil) having a biobased content up to 100%. UNl-REZ are thermoplastic polyamide, pine-based, adhesive resins from Arizona Chemicals. The previously desalbed biobased thermoplastics can be applied to textile coating and lamination. 

Propylene oxide, made by reacting propylene with chlorine to form propylene chloro-hydrin which is then dehydrochlorinated with caustic soda or lime (Eqs. 3-5), is used in the production of polyether polyols used for producing urethane foam. It also finds use in propylene glycol for making unsaturated polyester resins and in the pharmaceutical and food industries. Epichlorohydrin (EPI), formed by chlorination of propylene to allyl chloride and then dehydrochlorination (Eqs. 6 and 7), is used to make epoxy resins for producing laminates, fiber-reinforced composites, protective coatings, and adhesives. 

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