In-mold foaming

Stuart, J.B. Skarke, S.C. Ogita, T. et al. Flame retardant polyolefin resin pre-expanded particles and in-mold foamed articles prepared therefrom, PCT US Patent 6,822,023 assigned to Kaneka Corporation, 2001. 

Hydroxy group containing tertiary amines are also used because they become incorporated into the polymer structure, which eliminates odor formation in the foam (3). Delayed-action or heat-activated catalysts are of particular interest in molded foam applications. These catalysts show low activity at room temperature but become active when the exotherm builds up. In addition to the phenol salt of DBU (4), benzoic acid salts of Dabco are also used (5). 

Generally, stronger surfactants are used in making slab foams than are used in molded-foam formulations. 

Uses Cosurfactant for flexible molded and rigid PU reduces surf, imperfections in molded foam applies. 

Creep. The creep characteristic of plastic foams must be considered when they are used in stmctural appHcations. Creep is the change in dimensions of a material when it is maintained under a constant stress. Data on the deformation of polystyrene foam under various static loads have been compiled (158). There are two types of creep in this material short-term and long-term. Short-term creep exists in foams at all stress levels however, a threshold stress level exists below which there is no detectable long-term creep. The minimum load required to cause long-term creep in molded polystyrene foam varies with density ranging from 50 kPa (7.3 psi) for foam density 16 kg/m (1 lb /ft ) to 455 kPa (66 psi) at foam density 160 kg/m (10... 

Another type of polyol often used in the manufacture of flexible polyurethane foams contains a dispersed soHd phase of organic chemical particles (234—236). The continuous phase is one of the polyols described above for either slab or molded foam as required. The dispersed phase reacts in the polyol using an addition reaction with styrene and acrylonitrile monomers in one type or a coupling reaction with an amine such as hydrazine and isocyanate in another. The soHds content ranges from about 21% with either system to nearly 40% in the styrene—acrylonitrile system. The dispersed soHds confer increased load bearing and in the case of flexible molded foams also act as a ceU opener. 

For passenger car seating about 90% is made by the molded foam process. The transportation market has expedenced a decline since 1979 due to decreased automotive production and also because U.S. cars have been downsized, resulting in the use of less polyurethane foam per car. 

Because of low injection pressure, some cost savings are possible in mold and press constmction. Mol ding cycles are somewhat longer than for injection molding. The part must be cooled in the mold long enough to be able to resist swelling from internal gas pressure. In stmctural foam parts there is almost a total absence of sink marks, even in the case of unequal section thickness. Stmctural foam has replaced wood, concrete, sohd plastics, and metals in a variety of appHcations. 

Monofunctional, cyclohexylamine is used as a polyamide polymerization chain terminator to control polymer molecular weight. 3,3,5-Trimethylcyclohexylamines ate usehil fuel additives, corrosion inhibitors, and biocides (50). Dicyclohexylamine has direct uses as a solvent for cephalosporin antibiotic production, as a corrosion inhibitor, and as a fuel oil additive, in addition to serving as an organic intermediate. Cycloahphatic tertiary amines are used as urethane catalysts (72). Dimethylcyclohexylarnine (DMCHA) is marketed by Air Products as POLYCAT 8 for pour-in-place rigid insulating foam. Methyldicyclohexylamine is POLYCAT 12 used for flexible slabstock and molded foam. DM CHA is also sold as a fuel oil additive, which acts as an antioxidant. StericaHy hindered secondary cycloahphatic amines, specifically dicyclohexylamine, effectively catalyze polycarbonate polymerization (73). 

In more recent years, molded flexible foam products are becoming more popular. The bulk of the molded flexible urethane foam is employed in the transportation industry, where it is highly suitable for the manufacture of seat cushions, back cushions, and bucket-seat padding. TDI prepolymers were used in flexible foam mol ding ia conjunction with polyether polyols. The introduction of organotin catalysts and efficient siHcone surfactants faciHtates one-shot foam mol ding, which is the most economical production method. 

Semiflexible molded polyurethane foams are used in other automotive appHcations, such as instmment panels, dashboards, arm rests, head rests, door liners, and vibrational control devices. An important property of semiflexible foam is low resiHency and low elasticity, which results in a slow rate of recovery after deflection. The isocyanate used in the manufacture of semiflexible foams is PMDI, sometimes used in combination with TDI or TDI prepolymers. Both polyester as well as polyether polyols are used in the production of these water-blown foams. Sometimes integral skin molded foams are produced. 

In 1993, a total of over 6 x 10 t of polyurethanes were consumed worldwide (Table 8). The flexible foam market in the United States totaled 932,000 tons in 1994. Flexible slab foam is used predominantly in furniture, carpet underlay, and bedding molded foam is used extensively in transportation. Carpet underlay is manufactured from either virgin or scrap polyurethane foam, which is combined with a binder adhesive. The consumption of flexible polyurethane foam in the various U.S. markets in 1994 is shown in Table 9. 

PVC Plastisols 1940 M-H VG G G G Slush and rotationally molded, foamed, extruded Used in coating machines to cover paper, cloth and metal... 

There are many ways in which foams can be processed and used as slabs, blocks, boards, sheets, molded shapes, sprayed coatings, extruded profiles, foamed in place in existing cavities, in which the liquid material is poured and allowed to foam, and as structural foams (Chapter 6, STRUCTURAL FOAM). Conventional equipment such as extruders, injection, or compression machines is used. However specially designed machines are available to just produce foamed products. 

An outstanding property of EPS is its extremely low density (when compared to other processes), that by alteration of the preforming treatment can be varied according to the end use. Other types of plastics are employed to produce expandable plastic foam (EPF), including PE, PP, PMMA, and ethylene-styrene copolymers. They can use the same equipment, with only slight modifications. These plastics have different properties from those of EPS and open up different markets. They provide improved sound insulation, resistances to additional heat deformation, better recovery of shapes in moldings, and so on. 

Foam accounts for less than half of the polystyrene output. The remaining products have properties very different from foam. PS is an excellent plastic for molded automobile and refrigerator parts. It accepts color so well that it is widely used in molding applications to simulate wood. Probably the wood on your BMW dash is PS. 

Theres a lot of competition between PS and the other five big thermoplastics LDPE, LLDPE, HDPE, PP, and PVC. Polystyrene continues to lose marker share, but it seems to have a permanent place in some applications, particularly molded foams (for carryout food containers), some extrusions, and sheet and film applications. About half the polystyrene ends up in packaging, 17% in electrical/electronics applications, 13% in construction, building products and furniture, and 7% in medical applications. 

The resulting slate of polyols has been demonstrated in conventional flexible slabstock foam [143], viscoelastic foam [144], and high resiliency slabstock and molded foams [145],... 

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