Open-cell rigid polyurethane foams

Details Open-cell rigid polyurethane foams Open-cell rigid polyurethane foams

2001-10-18

2002-09-03

Cooney, Jr., John M. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

C521S118000, C521S128000, C521S129000, C521S130000

Reexamination Certificate

active

06444720

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to open-cell rigid foams containing urethane and/or isocyanurate groups and/or urea groups which are prepared using a polyol component containing long-chain polyether polyols having a low double bond content.
Polyurethane rigid foams are generally prepared from polyols having on average at least three hydroxyl groups per molecule, at least difunctional isocyanates, catalysts, stabilisers, blowing agents and optionally conventional additives.
The polyol component used is generally polyether polyols or polyester polyols or mixtures thereof, on average at least three hydroxyl groups per molecule being present in the polyol mixture used and the hydroxyl value of the polyol mixture used being from 100 to 900.
Examples of blowing agents used include volatile organic compounds having boiling points below 60° C., or water. Water reacts with the isocyanate component with the formation of carbon dioxide and amine which in turn continues to react with the isocyanate component to polyurea.
The resulting rigid foams are mostly predominantly closed-cell foams with a density from 5 to 950 kg m
−3
. In order to obtain open-cell rigid foams, polyols with a high content of oxyethylene groups and/or special silicone stabilisers and/or additives such as calcium stearate, solids or oleochemical derivatives are used.
Open-cell rigid foams are used, e.g., as a hydrophilic substrate for flower cultivation. Further applications for rigid foams with a high open cell content are insulating applications (the components are optionally evacuated for this purpose), applications as an energy-absorbing material, e.g. in bumpers, or motor vehicle interior applications, and for motor vehicle headlinings.
More recent developments in the field of rigid foams relate to the controlled preparation of largely open-cell, particularly fine-cell polyurethane- or polyisocyanurate-modified polyurethane rigid foams. These may be used as insulating materials, e.g., in vacuum panels.
FR-A 1457824 describes the preparation of open-cell rigid foams using a polyether polyol mixture containing a large proportion of a long-chain polyether polyol having an hydroxyl value from 50 to 200.
EP-A 622 388 describes the preparation of open-cell rigid foams using a long-chain polyether polyol having an hydroxyl value from 25 to 60, a maximum of 5% of oxyethylene groups and a maximum of 5% of primary terminal hydroxyl groups, in combination with water as the sole blowing agent, and a polyether polyol with an hydroxyl value from 150 to 800 which has a maximum of 5% of primary terminal hydroxyl groups and has a polyfunctional amine as the starter molecule.
SUMMARY OF THE INVENTION
It has now been found that rigid foams containing urethane and/or isocyanurate groups and/or urea groups and having a high open cell content may be prepared easily and in a controlled manner by using, in the polyol mixture employed, poly(oxyalkylene)polyols with an hydroxyl value from 3 to 90 which have a carbon-carbon double bond content of less than 15 mmole.kg1
−1
.
DETAILED DESCRIPTION OF THE INVENTION
The invention provides predominantly open-cell rigid foams containing urethane and/or isocyanurate groups and/or urea groups which may be obtained by reacting
a) di- or polyisocyanates with
b) a polyol component with on average at least two groups which are reactive towards isocyanates,
c) water and/or one or more physical blowing agents,
d) optionally catalysts,
e) optionally further auxiliaries and additives, characterised in that the component b) contains at least one poly(oxyalkylene)polyolwhich has an hydroxyl value from 3 to 90, preferably 3 to 60 and contains not more than 15 mmole.kg
−1
, preferably not more than 12 mmole.kg
−1
of carbon-carbon double bonds.
Organic di- or polyisocyanates are used as component a) in the process according to the invention. Suitable di- or polyisocyanates include aliphatic, cycloaliphatic, araliphatic, aromatic and heterocyclic polyisocyanates of the kind described in Justus Liebigs Annalen der Chemie 562 (1949) 75, for example, those corresponding to the formula
Q(NCO)
n
wherein
n means an integer from 2 to 4, preferably 2, and
Q means an aliphatic hydrocarbon radical having 2 to 18, preferably 6 to 10 carbon atoms, a cycloaliphatic hydrocarbon radical having 4 to 15, preferably 5 to 10 carbon atoms, an aromatic hydrocarbon radical having 6 to 15, preferably 6 to 13 carbon atoms, or an araliphatic hydrocarbon radical having 8 to 15, preferably 8 to 13 carbon atoms.
Polyisocyanates of the kind described in DE-OS 28 32 253 are preferred. As a rule, the polyisocyanates which are easy to obtain industrially are particularly preferred, e.g., 2,4- and 2,6-toluene diisocyanate and any mixtures of said isomers (“TDI”), polyphenylpolymethylene polyisocyanates of the kind prepared by aniline-formaldehyde condensation followed by phosgenation (“crude MDI”) and polyisocyanates containing carbodiimide groups, urethane groups, allophanate groups, isocyanurate groups, urea groups or biuret groups (“modified polyisocyanates”), particularly those modified polyisocyanates derived from 2,4- and/or 2,6-toluene diisocyanate or from 4,4′- and/or 2,4′-diphenylmethane diisocyanate. It is also possible to use prepolymers of the aforementioned isocyanates and organic compounds having at least one hydroxyl group. Examples therefor of suitable hydroxyl compounds include polyols or polyesters having one to four hydroxyl groups and (number-average) molecular weights from 60 to 1,400. The polyisocyanates available industrially under the name “polymeric diphenylmethane diisocyanate” with a functionality greater than 2.0 and prepolymers prepared therefrom are very particularly preferred.
According to the invention, the polyol component b) contains at least one poly(oxyalkylene)polyol which has an hydroxyl value from 3 to 90, preferably 3 to 60 and not more than 15 mmole.kg
−1
, preferably not more than 12 mmole.kg
−1
of carbon-carbon double bonds. It is also, however, possible to use mixtures of said polyols. The poly(oxyalkylene) polyols preferably have an average functionality from 2 to 8, particularly preferably from 2 to 6. The proportion of said polyols in component b) is preferably from 0.1 to 50 wt. %, particularly preferably 1 to 30 wt. %.
The poly(oxyalkylene)polyols used according to the invention may be prepared, e.g., by polyaddition of alkylene oxides to polyfunctional starter compounds in the presence of caesium, rubidium, strontium or barium hydroxide or alternative basic catalysts, or by rearrangement of allylic C—C double bonds to propenylic C—C double bonds in a polyol having a C—C double bond content of >15 mmole.kg
−1
prepared in the conventional way by catalysis by means of alkali hydroxides or alkoxides followed by hydrolysis with acid. The poly(oxyalkylene)polyols used according to the invention are preferably prepared using a highly active double metal cyanide catalyst from a starter compound having an average of 2 to 8, preferably 2 to 6 active hydrogen atoms and one or more alkylene oxides, as described, for example, in EP-A 761 708.
Preferred starter compounds are molecules having two to eight hydroxyl groups per molecule such as water, triethanolaamine, ethane 1,2-diol, propane 1,2-diol, propane 1,3-diol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, butane 1,2-diol, butane 1,3-diol, butane 1,4-diol, hexane 1,2-diol, hexane 1,3-diol, hexane 1,4-diol, hexane 1,5-diol, hexane 1,6-diol, glycerol, trimethylolpropane, pentaerythritol, sorbitol and sucrose. Further preferred starter compounds include ammonia or compounds having at least one primary or secondary amino group, such as, for example, aliphatic amines such as 1,2-diaminoethane, oligomers of 1,2-diaminoethane (for example, diethylenetriamine, triethylenetetramine or pentaethylenehexamine), ethanolamine or diethanolamine, 1,3-diaminopropane, 1,3-diaminobutane, 1,4-diaminobutane, 1,2-diaminohexane, 1,3-diaminohexane, 1,4-diaminohexan

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