Preventing Ostwald Ripening in Rigid PU Foams

Title: PRODUCTION OF FINE CELL FOAMS USING A CELL AGING INHIBITOR

Number/Link: WO2017093058  (German)

Applicant/Assignee: Evonik

Publication Date: 8 June 2017

“Gist”: Perfluorinated hydrocabons reduce Ostwald ripnening in PU foam formulations

Why it is interesting: Polymeric foams form by nucleation and growth of gass bubbles in the reacting mixture followed by (or simultaneous with) ageing of the bubbles through coalesence and Ostwald ripening, i.e. the growth of larger bubbles at the expense of smaller bubbles. Ostwald ripening ultimately results in fewer and larger cells, which has a negative effect on the thermal insulation properties of rigid foams. According to this invention the ripening effect can be prevented or reduced by incorporating in the foam formulation an “Ostwald hydrophobe”, i.e. a highly hydrophobic liquid which is largely immiscible with the reacting mixture. Examples of such liquids are perfluorinated hydrocabons with a boiling point of less than 150°C, e.g. perfluoropentane, perfluorocyclohexane and perfluoroisohexene (used in the examples).

Perfluorocyclohexane

 

Classic PU patent of the Month: PORON ® Foams (1979)

Title: Polyurethane foam product and process of manufacture thereof from thermosetting frothed mixture

 Number/Link: US4216177

Applicant/Assignee: Rogers

Publication date: 5-08-1980

Gist”: Frothed flexible foam

Why it is interesting: PORON is a popular brand of microcellular elastomeric/flexible polyurethane foams produced by Rogers Corporation. The original process, as documented in this patent, is quite simple:  a flexible foam formulation (in the examples) based on TDI, caprolacton diol, polymer polyol, some chain extender, amine catalyst and surfactant is frothed instead of blown with water or a physical blowing agent. The reacting froth is poured on release paper and heated to cure. Release paper can also be applied on top resulting in an integral skin on both sides of the layer. Frothing instead of blowing results in an improved compression set, different hardness-density relationship and a better control over cell structure. A unique material.

PORON foams

PORON foams

Flexible Foams with Enlarged Cell Size

Title: PUR FOAM WITH ENLARGED CELL STRUCTURE

 Number/Link: WO2014/170198 (German)

Applicant/Assignee: Evonik

Publication date: 23-10-2014

Gist”: The cell size of PU flexible foam is enlarged by using microcrystalline wax.

Why it is interesting: Enlarging the cell size of flexible foams can improve comfort properties by enhancing ‘breathabibility’, that is by enhancing airflow and moisture- and heat transport.  According to this invention the cell size of flex foams can be increased without affecting foam density or hardness by using a specific type of wax.  The wax (preferably) is a microcrystalline wax (as opposed to a paraffinic wax) with a congealing temperature of between 60 and 75°C.  The wax is used as a dispersion in a solvent (e.g. a sorbitan ester)  in an amount of about 0.05 to 2.0 php.

Cell structure of a flexible polyurethane foam.

Cell structure of a flexible polyurethane foam.