The presentation of foam
It can be stated that because of the variety of properties polyurethanes are generally considered to be the most versatile among plastics. They are foam materials that can be manufactured in a wide range of density and softness, and which can be hard, soft, elastic or rigid, depending on the initial raw material. Their structure consists of a system of dodecahedron shaped cells that behave like micro-springs.
Polyurethanes can be found in almost all fields of life. In vehicle seats, as thermal and sound insulation in buildings, in coolers, paints and other protective coatings, shoes, textiles, adhesives, in the upholstery of chairs, and in mattress cores. As polyurethane foams are usually combined with other materials, such as textiles, metals, wood and other plastics, they are rare to find in finished products.
They can be grouped from several aspects. According to the chemical composition two big groups are distinguished:
- polyether-polyol based foams (ether-foams)
- polyester-polyol based foams (ester-foams)
According to hardness polyurethane foams are very diverse from the super soft to rigid foam types; there are three main categories used till today:
- rigid, hard (thermal insulation)
- semi-hard
- soft (furniture industry)
According to reactivity polyurethane foams can be thermosetting at room temperature and thermo reactive.
From the point of manufacturing technology the foams can be produced by continuous or intermittent technology; based on the character of the technology the foams can be foam slabs, shaped foams, cast and spray foams.
The properties are determined by the following factors:
- chemical compounds
- thickness of cell walls
- solid substance /air ratio
- concentration of cell membranes (air permeability)
If we want to sort our products according to the above grouping aspects we can say that Eurofoam Hungary Kft. produces polyether based soft polyurethane foam expanding at cold temperature in the form of slabs using continuous technology, and the slabstocks are further converted as required.
Two raw materials play a key role in manufacturing polyurethane foam: polyol and isocyanate. Both raw materials are crude oil derivatives. The petrochemical industry sells 95% of the crude oil as fuel, and only the 5% residue can be further refined in one or more steps into plastic industrial raw materials.
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Polyols are multifunctional alcohols obtained from propylene oxide. Two types are used for polyurethane foam manufacturing: polyether and polyester polyols. Their structure determines the rigidity (stiffness) or softness of the polyurethane foam.
Typically two types of isocyanates are used: TDI (toluene-diisocyanate) and MDI (methylene-diphenyl-diisocyanate). These chemical compounds easily react with compounds containing active hydrogen such as alcohols.
Other catalysts or stabilisers are used to initiate and regulate the reaction, whereas to achieve certain special properties such as flame retardancy, colour, antistatic effect, and antibacterial protection several other auxiliary substances should be added to the recipe. During the manufacturing process basic and auxiliary substances are fed into the mixing head in the proportion specified by the manufacturing recipe - that determines the components of the foam and thus its properties – where they get mixed and form a homogeneous reaction mixture. This mixture is poured onto a properly designed and continuously advancing conveyor where the chemical reaction i.e. the foaming starts between the substances, involving heat and carbon dioxide generation. Depending on the recipe foaming takes about 60 seconds and the foam reaches a strength level when it is manageable in a further 60 seconds. The ready foam slab rises to a height of approx. one meter. The ready foam slabstocks that are 50 meter long should be cured for a further 12 – 24 hours until the final reactions of polymer forming and cross-linking take place and the final properties of the foam take shape.
Depending on their properties the cured, cross linked and cooled down slabstocks can be used in comfort and/or technical areas and can be confectioned in several ways.