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Method of molding rigid polyurethane foams
Updated: 2013-10-22 14:40 Source: PUWORLD share:

Various terms used in the text of the present invention have the following meaning:

o    Gel or gelation time: The gel time extends from the start of mixing to the moment from which a stick introduced into the foam draws fibers when withdrawn.

Rise time: The rise time extends from the start of mixing to the moment when foam rise is completed.

Tack free time: The tack free time extends from the start of mixing to the moment when foam surface does not stick to the operator finger.

Demolding time: The time between the end of foam injection and the mold opening

Polyol Formulation: The polyol composition including additives, such as catalysts, surfactants, excluding the blowing agent.

Premix: The polyol formulation including water.

System or Foam Formulation: The combination of premix and isocyanate component.

Free Rise Density (FRD): The density measured from a 100x100x100 mm block, obtained from the center of a free rising foam (at ambient air-pressure) produced from a total system formulation weight of 300 grams or more. FRD is reported in kg/m3.

Min. Fill Density (MFD) The density determined from the minimum weight needed to fill the in-mold cavity completely and the volume of this in-mold cavity. MFD is reported in kg/m3.

Min. Fill Weight (MFW): The minimum weight needed to fill the in- mold cavity completely. MFW is reported in kg.

Moulded Density (MD): The density determined from the injected weight in the in-mold cavity and the volume of this in-mold cavity. MD is reported in kg/m3. The measured moulded density is determined from the average of minimum 5 samples of 100x100x"thickness" in mm (including skin) by weighing the samples and dividing the weight by the measured volume of the samples.

Overpack: The overpack is defined as [injected weight* 100/MFW]. Overpack is reported in percent.

Packing factor: The packing factor is defined as [moulded density/FRD]. The packing factor is reported as a unit-less number.

Pressure: Pressures can either be air pressure in the mold or foam mass pressure on mold walls. All pressures are reported in absolute pressure, with the unit mbar (or hPa). The reference pressure is 1000 mbar = 1000 hPa = approx 1 atmosphere at sea level = 0 bar gauge.

Injection of an appliance foam formulation in a mold maintained at a low internal pressure allows foam formation without auxiliary physical blowing agent and with a low level of water. A low level of carbon dioxide as blowing agent in the foam, as produced from the reaction of water and isocyanate, reduces the Lambda increase over time. Additionally the water reduction in foam formulations allows for a reduction in the amount of isocyanate consumption.

In the present invention, more viscous systems either due to the type of polyols or due to the fast reactivity (increased catalysis) of the foaming mass can be processed. The present invention has an absence of physical blowing agent which reduces volatile organic compound emissions upon disposal of an appliance containing such a foam.

The method of the first aspect of the present invention is suitable for use with any polyurethane formulation having the required chemical blowing agent only. However, certain formulations are particularly suited for use in the claimed method, such as those of the third aspect of the present invention.

 

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