POLYURETHANE FOAM - GENERAL INTRODUCTION

Polyol is a macro molecules of poly hydric alcohols with molecular weights ranging from 200 - 20000 with functionalities ranging between 2 and 8. The polyol when reacted with isocyanate, which contains a NCO functional group, reacts with the OH functionality of the polyol in the presence of suitable catalysts to form urethane/urea linkages. The catalysts accelerate the reaction to the required level. The blowing agents blows the cells increasing its volumes to form the light weight polyurethane foam. The surfactants promote and stabilizes the polyurethane cells and helps to retain the shape into which it has been blown to. Blowing agents are produced in situ as well as externally added into the reaction mixture. Non-foaming applications normally do not contain blowing agents.

*Absent in non-foam applications

**Maybe present or absent in non-foam applications

Depending on the type of polyol and isocyanate used the generated foam exhibits different properties. By careful selection of the polyol and isocyanate, foam with varying properties can be generated. It could be soft and flexible with totally open cells, which are used in the furniture industry to very hard dense wood like closed cell rigid foam. The non-foam applications are generally in the coatings, adhesives, sealants and elastomers (CASE). The various categories are :-

  • Flexible slab stock
  • Flexible cold cure moulded
  • Rigid foam
  • Footwear or micro-cellular
  • Coatings, adhesives, sealants and elastomeric applications

FFLEXIBLE SLAB STOCK

Flexible slab stock reacts with TDI (TDI 80/20) to generate flexible slab stock foam. Polyol of molecular weight 3000, 3500 and 4000 are used in its production. Usually these polyols are of functionality 3 and produced out of naturally occurring glycerin or tri methylol propane.

Above materials are propoxylated to form tri functional linear chain polyol. The most commonly used polyol is of 3000 molecular weight with a hydroxyl number of 56.

Higher molecular weights leads to dense soft and high resilient foam.

The slab stock foam are produced in INDIA by the following three methods:-

  • Hand mix / Box foam - Tiny units
  • Box foaming - Automated units
  • Continuous conventional and max foam units
The foam is utilized for the following applications :-
  • Furniture
  • Carpet underlay
  • Bedding
  • Accoustic insulation
  • Garment
  • Scores of other applications
FLEXIBLE COLD CURE MOULDING

Medium functional ethylene oxide capped reactive polyol are used in the production of the moulded foam. In the slab stock industry, the foam is produced in big large blocks and cut into different sizes. Whereas in the moulded industry, the product is directly moulded into required shapes. The wastage is minimum and the technology is ideally suited for automated mass production. The notable industries are automotive car seating and two wheeler seatings.

Here the polyol is pre blended and supplied in "ready to use" form along with the recommended isocyanate and the operator only adjust the machine to the required ratios and shot weights, wherein foams of predictable properties are directly moulded to required shape.

Dialogue with the raw materials manufacturer are required to select the appropriate product to suit the machinery available with the operator with regard to various parameters like cream time, gel time and demould time and the properties of foam that are required by the ultimate customer.

The foam can be produced with different types of isocyanate and the principle technologies available are :-

  • Polyol with variants MDI – from medium density to high density foam
  • Polyol with TDI / MDI blend for medium density high resilience foam for four and two wheelers application
  • Polyol with TDI for ultra light to medium density foam
RIGID FOAM

Rigid foam can be produced in densities between 20 - 800 Kg/Cu.m. In the lower ranges, it is used as a insulating material and in the higher ranges as structural and as wood imitation.

Here again the material is supplied in the "ready to use" form with the required isocyanate, which is usually polymeric MDI. The principle industry were it is used are :-

  • Refrigerators – The primary insulating medium and the foam also provides the structural stability to the refrigerator
  • Thermoware – Manufacturers of casserole and water bottles
  • Industrial insulations
  • Insulation of cold rooms and ammonia tanks
  • Furnitures
ELASTOMERIC APPLICATIONS

Here again the material is supplied in the "ready to use" form with the required isocyanate, which is usually polymeric MDI. The principle industry were it is used are :-


  • Coatings
  • Adhesives
  • Sealants
  • Other elastomeric applications like rollers, shock absorbers, wiper rings etc.
The notable user industries are Paints, Varnishes, Water Proofing Compounds, Fire Retardants, PU adhesives and speciality adhesives used in the automotive industry.







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