Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1998-09-24
2001-09-04
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...
C521S131000
Reexamination Certificate
active
06284812
ABSTRACT:
The present invention relates to thermally stable rigid foams based on isocyanate and having low brittleness and low thermal conductivity, which foams have been produced without use of blowing agents which damage the ozone layer.
The production of rigid foams based on isocyanate as thermal insulation material has been known for a long time. The most important chemical starting materials for such compounds are polyfunctional isocyanates. Chemical structures formed from the polyisocyanates can be polyurethanes, polyureas, polyisocyanurates and also further isocyanate adducts such as allophanates, biurets, carbodiimides and their isocyanate adducts, oxazolidones, polyimides, polyamides, etc. The type of these structures is controlled by the reaction partners of the isocyanates, the catalysis and the reaction conditions.
These isocyanate adducts are frequently summarized under the term rigid polyurethane (PUR) foams, since the polyurethanes are the most widespread and most important group of materials among the polyisocyanate adducts. Foams having a significant content of isocyanurate structures are frequently referred to as polyurethane-polyisocyanurate (PUR-PIR) foams.
The production of such foams is described, for example, in the Kunststoff-Handbuch, Volume VII “polyurethane”, 3rd Edition, edited by Gunter Oertel, Carl-Hanser-Verlag, Munich, Vienna, 1993.
In recent times, rigid foams having very high long-term thermal stability are being demanded for thermal insulation of pipes conducting very hot media. They should withstand temperatures of 180° C. for more than 10 years. This means that, in a hot storage experiment, the foams have to remain without detectable damage for 4 weeks at 200° C. or for 2 weeks at 220° C. Such high-performance materials are demanded not only for the insulation of heating pipes but also, for example, for space flight. At the same time, the foams still have to have a very low thermal conductivity at these high temperatures. However, the heat resistance of the foams based on isocyanate is usually limited. If, for example, predominantly urethane groups are present in the foam, long-term heat resistance for more than 10 years can be achieved only at 150° C., which in a storage test corresponds to from 4 to 6 weeks at 180° C., even when very strongly crosslinking polyols are used. At 200 or 220° C., the foam is destroyed after only a few hours in the storage test. Under a mechanical load of 0.04 N/mm
2
for 24 hours in accordance with DIN 18164 at a density of 70 kg/m
3
, these foams are stable up to at most 170° C. In the case of PUR-PIR foams, the thermal stability can be improved with rising polyisocyanate content, but the brittleness of the foams increases greatly. After storage for a number of weeks at 200° C. or higher temperatures, the foam is so brittle that it shatters into small pieces even under small mechanical loads.
A further disadvantage of the previously known rigid foams based on isocyanate is the excessively high thermal conductivity at elevated temperatures.
The lowest thermal conductivity values are achieved using chorofluorocarbons (CFCs) as blowing agents. However, even when using these blowing agents which are no longer permitted owing to their high ozone depletion potential (ODP) and global warming potential (GWP), the thermal conductivity of the rigid foams, eg. as described in GB-A-2,041,953, CH-A-527 855 or EP-A-24 524, increases to an undesirable extent at elevated temperatures.
As an alternative to the very environmentally damaging CFCs, it has been proposed that, for example, blowing agents which have only carbon, hydrogen and fluorine in the molecule be used. A further alternative blowing agent is water. However, even the se foams described, for example, in U.S. Pat. No. 5,380,768 are stable for 10 years only up to about 140° C. at the customary densities in the range from 60 to 80 kg/m
3
.
Hydrocarbons, for example pentanes, are likewise suitable as alternative physical blowing agents, but usually also lead to rigid foams having increased thermal conductivities. In addition, the flowability of such foams, as are described, for example, in DE-A-42 22 519, is very restricted.
All previous foam formulations do not meet the requirements for high heat resistance combined with low brittleness and low thermal conductivity even at high temperatures.
It is an object of the present invention to provide rigid foams based on isocyanate which simultaneously have a high thermal stability and low thermal conductivity and low brittleness at high temperature, can be produced using blowing agents which are not environmentally damaging and can be produced using the conventional technology for producing such rigid foams.
We have found that this object is achieved by the joint use of
a) polyether alcohols having a functionality of at least 1.5, preferably from 2.5 to 3.5, and a hydroxyl number of from 10 to 100 mg KOH/g, preferably from 25 to 50 mg KOH/g, in an amount of from 0.2 to 80% by mass, preferably from 1 to 70% by mass and particularly preferably from 20 to 60% by mass, in each case based on the polyols,
b) polyester alcohols in an amount of from 5% by mass to 90% by mass, preferably from 20% by mass to 60% by mass, based on the polyols,
c) water in an amount of at most 2% by mass, preferably from 0.2 to 1.6% by mass and particularly preferably from 0.3 to 1% by mass, based on the polyol component, and
d) physically acting blowing agents composed of the elements carbon and hydrogen and/or of the elements carbon, hydrogen and fluorine in an amount of from 5 to 30% by mass, preferably from 10 to 25% by mass, based on the polyol component.
The present invention accordingly provides rigid foams based on isocyanate and having high thermal stability and low thermal conductivity and low brittleness at high temperatures, able to be produced by reacting
a) polyisocyanates with
b) compounds containing at least two hydrogen atoms which can react with isocyanate groups,
c) water, in the presence of
d) physically acting blowing agents, in the presence or absence of
e) catalysts and auxiliaries and/or additives, wherein the component b) comprises
bi) at least one polyether alcohol having a functionality of at least 1.5, preferably from 2.5 to 3.5, and a hydroxyl number of from 10 to 100 mg KOH/g, preferably from 25 to 50 mg KOH/g, in an amount of from 0.2 to 80% by mass, preferably from 1 to 70% by mass and particularly preferably from 20 to 60% by mass, based on the component b), and
bii) at least one polyester alcohol in an amount of from 5 to 90% by mass, preferably from 20 to 60% by mass, in each case based on b), the component c) is used in an amount of at most 2% by mass, preferably from 0.2 to 1.6% by mass and particularly preferably from 0.3 to 1% by mass, based on the sum of the components b) to e), and the component d) used comprises hydrocarbons and/or fluorine-containing hydrocarbons in an amount of from 5 to 30% by mass, preferably from 10 to 25% by mass, based on the sum of the components b) to e).
As polyether alcohols bi), preference is given to using polyether alcohols which can be prepared according to methods known per se by addition of propylene oxide and/or ethylene oxide onto 2-functional or polyfunctional initiator molecules, as is described, for example, in the Kunststoffhandbuch, loc. cit., pages 57 to 67.
Suitable initiator molecules are, apart from water, all organic molecules containing Zerewitinoff-active hydrogen atoms. Examples which may be mentioned are ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerol, trimethylolpropane (TMP), ethylenediamine, tolylenediamine (TDA), triethanolamine, pentaerythritol, sorbitol, mannitol or sucrose. Preference is given to from 2- to 3-functional polyols.
It is also possible to use mixtures of polyols as component bi). These are obtained, for example, by using initiator mixtures, for example the addition of small amounts of water to the organic initiator molecules. The mixing of polyols is also possible. Adducts of propylene oxide and ethylene oxide onto
Hempel Renate
Rotermund Udo
Schmiade Werner
Seifert Holger
BASF - Aktiengesellschaft
Borrego Fernando A.
Cooney Jr. John M.
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