Skin Flexible Urethane Foams

Integral-skin foam is referred to as self-skinning foam or self-skiimed foam. The foams have high-density skin layers and low-density cores. The overall densities vary in the range of about 200 to 1,100 kg/m (12 to 70 px f). 

Integral-skin urethane foams are classified into two types, flexible and rigid. The former foams will be described here, and the latter will be described in the rigid-foam section. 

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Preparation of Integral-Skin Flexible Foams. The major polyisocyanates for use in making integral-skin flexible urethane foams are liquid MDl and TDl prepolymers. In order to make light-stable integral-skin foams, aliphatic diisocyanates, e.g., HDl (hexamethylene diisocyanate) and IPDl (isophorone diisocyanate) in modified forms are used. 

Properties of Integral-Skin Flexible Urethane Foams. The foam densities of integral-skin foams of commercial products are in the range of about 300 to 950 kg/m and their Shore A hardnesses are in the range of about 90. Shore D hardnesses are about 40 to 90. Figure 13 shows an example of density distribution of integral-skin foams. 

Use is made of integral skin foams. They are flexible urethane foams with a high density skin. They are used in applications such as steering wheels, arm rests, and protective covers that must combine a tough surface and a soft feel. 

Molded flexible urethane foams have been used for producing intricate foam products, such as automotive seats and furniture cushions. Molded foams are composed of high-density foam skin and low-density foam core. An example of density distribution of a 10-cm thick molded mattress foam is shown in Figure 9. 

Uses Surfactant surf. tens, depressant wetting agent emulsifier foam builder humectant softener used for producing flexible slab stock urethane foam plasticizer for hair resins imparts spreadability. It. nongreasy feel, and detackification to hair sprays, shampoos, skin care lotions, perfumes, shaving soaps lubricant, antistat on polyamide/polyester/spandex fibers Properties Gardner 2 hazy, vise, liq. sol. in water, alcohol, hydroalcoholic systems, propylene glycol, IPM sp.gr, 1,07 vise. 465 cs HLB 13.6 f.p. 50 F b.p. > 200 C flash pt. (COC) 149 C pour pt, 52 F ref. index 1.454 100% cone. 

The alkoxylation process is easy to apply to PU foams having a low concentration of urethane and urea groups such as flexible and semiflexible foams, integral skin foams, PU elastomers and so on. Urea groups react in a similar way with urethane groups, with the formation of oxazolidones and amines by an intramolecular alcoholysis of urea groups (reaction 20.15). 

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The water-isocyanate reaction forming carbon dioxide is commonly used to form open-cell flexible foams. Trichlorofluoromethane (TCFM) is a physical blowing agent relying on heat from the urethane reaction exotherm to boil this is used to form rigid closed-cell foams and most self-skinned moulded products. There is considerable concern over the effect of fluorocarbons on the Earth s ozone layer, and suitable replacements are actively being sought. 

This newer process allows the foam expansion to be controlled so that a cellular core and a non-cellular outer skin are obtained in one moulding process. The raw materials used are similar to those used in conventional semi-flexible foam but water is ommitted. The foam reaction is provided solely by the exothermic heat causing an auxiliary blowing agent (eg Refrigerant 11 or methylene chloride) to vaporise. The heat of reaction will be removed at the mould surfaces, retarding foam formation and producing a coherent urethane skin. 

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