Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1999-02-18
2001-05-08
Cooney, John (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S174000, C521S175000
Reexamination Certificate
active
06228899
ABSTRACT:
The present invention relates to a process for producing flexible foams based on polyisocyanate polyaddition products by reacting polyisocyanates with compounds which are reactive toward isocyanates in the presence of catalysts, blowing agents and, if desired, flame retardants, auxiliaries and/or additives and to the flexible foams which can be produced using this process.
The production of flexible polyurethane foams by reacting polyisocyanates, for example aromatic diisocyanates, with compounds which are reactive toward isocyanates, for example polyether polyalcohols and/or polyester polyalcohols, hereinafter also referred to generally as polyols, and, if desired, chain extenders and/or crosslinkers in the presence of catalysts, blowing agents and, if desired, flame retardants, auxiliaries and/or additives is generally known. An overview of polyols, their preparation, properties and applications in polyurethane chemistry is given in, for example, “Kunststoff-Handbuch”, Volume 7, Polyurethane, 3rd edition, 1993, edited by G. Oertel, Carl Hanser Verlag, Munich.
Furthermore, it is known that flexible foams having an increased hardness can be produced by using, in addition to customary polyols having an average functionality of from 2 to 3, polyols having a higher functionality which can be prepared, for example, by addition of alkylene oxides onto initiator substances having a functionality of at least 4. This molecular addition of the alkylene oxides can be carried out as described in U.S. Pat. Nos. 4,111,865, 4,288,562 or DD-A 248129, in a mixture comprising customary 3-functional initiator substances and at least 4-functional initiator substances, where the initiator substances can be mixed before the alkoxylation or else can be reacted separately with the alkylene oxides and only subsequently mixed as prepolymers and alkoxylated with further alkylene oxides.
Significant disadvantages of these processes are that the alkoxylation, in particular of sugars as substances having a functionality of at least 4, proceeds in an unsatisfactory manner, the reaction mixtures have inhomogeneities and the polyols prepared have an unfavorable molecular weight distribution for the production of highly elastic flexible polyurethane foams.
It is an object of the present invention to develop a process for producing flexible foams based on polyisocyanate polyaddition products by reacting compounds which are reactive toward isocyanates with isocyanates, which flexible foams should have a relatively high hardness, a low compressive set and a high tensile strength.
We have found that this object is achieved by using polyether polyalcohols (c) which are obtainable by addition of alkylene oxides onto substances containing active hydrogens as substances which are reactive toward isocyanates, where, in a first stage, at least one substance (a) containing 2 or 3 active hydrogens is reacted with at least one alkylene oxide in the presence or absence of catalysts, subsequently at least one substance (b) which contains at least four active hydrogens and, if desired, further catalyst is added to the reaction mixture from the first stage and this mixture is then reacted in a second stage with at least one alkylene oxide.
Suitable initiator substances (a) are generally customary compounds which have 2 or 3 active hydrogens. As compounds (a), it is possible to use, for example, aliphatic, araliphatic and/or aromatic amines and/or imines which may bear a hydroxyl group in addition to the amino group or imino group, and preferably ethylene glycol, 1,2- and/or 1,3-propanediol, 1,2-, 1,3- and/or 1,4-butanediol, di- tri- and/or tetra-ethylene, -propylene and/or -butylene glycol, trimethylolpropane and/or glycerol. Furthermore, it is possible to use addition products having a molecular weight of from 100 to 1000 of alkylene oxides onto 2-and/or 3-functional alcohols as compound (a).
The reaction in the first stage by addition of customary alkylene oxides, for example tetrahydrofuran, styrene oxide, 1,3-propylene oxide, 1,2- and/or 1,3 butylene oxide and/or ethylene oxide, preferably ethylene oxide, onto the components (a) and (b) present in the mixture can be carried out by generally known methods. For example, the mixture comprising the initiator substance (a) can be treated at, for example, from 70 to 160° C., preferably from 80 to 150° C., with the alkylene oxide in a customary reactor (stirred tank reactors, tube reactors, etc.) which can be equipped with customary facilities for cooling the reaction mixture. The addition of the alkylene oxides is preferably carried out such that the reaction temperature is within a range from 10 to 160° C., preferably from 80 to 150° C. The reaction times usually depend on the temperatures in the reaction mixture and are thus dependent, inter alia, on the batch size, the reactor type and the cooling facilities. The reaction can be carried out at pressures of from 0.1 MPa and 1 MPa, preferably from 0.1 MPa and 0.7 MPa.
Preferably, a customary amount, for example from 0.02 to 1% by weight, preferably from 0.04 to 0.08% by weight, based on the component (a), of a strong base is added to the initiator substance (a) before and/or during the reaction with the alkylene oxides. As strong base, preference is given to using alkali metal hydroxides, particularly preferably NaOH and/or KOH in dissolved or preferably solid form. For example, the component (a) can, prior to the reaction with the alkylene oxides, be distilled at customary temperatures and under reduced pressure in the presence of the strong bases mentioned, so that the component (a) is present at least partly as alkoxide at the end of the distillation. The component (a) is preferably used as alkoxide in the molecular addition of the alkylene oxides in the first stage.
The reaction product of the first stage usually has a hydroxyl number of from 100 to 1000, preferably from 200 to 900, particularly preferably from 250 to 900, and a functionality of >2.
Subsequent to the first stage, the initiator substance (b) which contains at least 4 active hydrogens is added to the reaction mixture from the first stage which does not necessarily have to have been worked up by customary methods and is preferably intensively mixed with the reaction mixture.
As initiator substance (b), it is possible to use alcohols having a functionality of ≧4, for example sugar alcohols and/or saccharides, preferably pentaerythritol, sorbitol, and/or sucrose. Preference is also given to using addition products having a molecular weight of from 100 to 1000 of alkylene oxides and at least 4-functional alcohols.
It is also possible to add a part, in particular up to 80% by weight, of the initiator substance (b) during the reaction in the first stage. The partial addition of the substance (b) can be carried out all at once at the beginning and/or in portions during the reaction with alkylene oxide in the first stage over a period of 0.5-1.5 h after commencement of the metered addition of the alkylene oxide.
In the process of the present invention, the molar ratio of the initiator substances (a):(b) in the mixture, ie. the molar ratio of (a) used in the first stage and (b) used in the second stage, is usually from 5:1 to 0.2:1, particularly preferably from 2:1 to 0.5:1.
If desired, a strong base as has already been described for the first stage can be added to the reaction product from the first stage before, during or after the addition of the initiator substance (b). Like the initiator substance (a) in the first stage, the initiator substance (b) in the second stage can also be used as alkoxide.
After the addition of the initiator substance (b) to the reaction product from the first stage, the reaction in the second stage by addition of customary alkylene oxides, for example propylene oxide, butylene oxide and/or ethylene oxide, preferably ethylene oxide, onto the components (a) and (b) present in the mixture can be carried out by generally known methods. For example, the reaction mixture can be treated at, for example, from 70 to 160° C., preferably fr
Güttes Bernd
Kuhn Simone
Schuster Marita
Wetterling Monika
BASF - Aktiengesellschaft
Borrego Fernando A.
Cooney John
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