Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2002-03-12
2004-08-03
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...
C252S182270, C568S619000, C568S620000, C568S624000
Reexamination Certificate
active
06770684
ABSTRACT:
DESCRIPTION
The present invention relates to a process for the production of flexible polyurethane foams, particularly highly resilient flexible foams and flexible foams having a high load-bearing capacity, using a specific polyether alcohol.
The synthesis of polyurethane—also referred to below as PU for short—flexible foams by reaction of polymolecular polyhydroxyl compounds and, optionally, chain-extenders with organic polyurethanes is known and is described in numerous patent specifications and other publications.
An example thereof is Kunststoffhandbuch, Vol. VII, “Polyurethane”, Carl Hanser Verlag, Munich, 1st Edition, 1966, edited by Dr. R. Vieweg and Dr. A. Hoechtlen, and 2nd Edition, 1983, and 3rd Edition 1993, edited by Dr. G. Oertel.
In order to produce the flexible PU foams, polyester polyols and/or polyoxyalkylene polyols based on 1,2-propylene oxide, ethylene oxide or mixtures thereof and also mixtures of such polyoxyalkylene polyols and graft polyoxyalkylene polyols are usually employed as polymolecular polyhydroxyl compounds, and alkanediols, oxyalkylene glycols or low-molecular compounds containing hydroxyl and/or amino groups and having a functionality of from 2 to 4, such as glycerol, trimethylol propane, or alkanolamines are used as chain-extenders. The organic polyurethanes used are mostly commercial toluylene-diisocyanates (TDI), diphenylmethane diisocyanate isomers (MDI), mixtures of diphenylmethane diisocyanates and polyphenylpolymethylene polyisocyanates (crude MDI), and mixtures of crude MDI and TDI.
According to DE-C 1,520,737 (U.S. Pat. No. 3,336,242) flexible polyurethane foams having an open cellular structure can be produced by a single-stage process by causing polyurethanes to react with polyoxypropylene-polyoxyethylene triols having molecular weights of from 3000 to 8000 and containing, as end block, from 3 to 5 wt % of bound ethylene oxide and, as initiator, bound glycerol.
Very soft flexible polyurethane foams are obtained, according to GB-A 1,079,105, from a polyether alcohol or a mixture of polyether alcohols having a hydroxyl value of from 70 to 170 and containing trifunctional polyoxyalkylene polyol, such as propoxylated glycerol and up to 40 wt % of a polyoxyalkylene glycol, eg, propoxylated ethylene glycol, and an organic polyurethane, preferably TDI, in the presence of water and a fluorochlorinated hydrocarbon, preferably trichlorofluoromethane, as expanding agent. Flexible PU foams are also described in GB-A 1,064,576. According to this patent specification, organic diisocyanates, preferably TDI, are caused to react with a mixture of from 50 to 90 wt % of a polyoxyalkylene triol having a hydroxyl value of from 30 to 170 and from 10 to 50 wt % of a polyoxyalkylene diol having a hydroxyl value of from 40 to 110, which mixture has a content of primary hydroxyl groups of from 10 to 65%, in the presence of water.
According to GB-A 1,480,972, flexible polyurethane foams having improved resilience properties are produced in the absence of silicone foam stabilizers by causing organic polyurethanes to react with a mixture of polyetherols comprising at least one polyether polyol having a functionality of from 2 to 4, an equivalent weight of between 1000 and 3000, and, optionally, an ethylene oxide content of up to 30 wt %, and from 0.5 to 20 wt %, based on polyether polyol, of at least one polyoxypropylene-polyoxyethylene alcohol having a functionality of from 1 to 4, an equivalent weight of from 500 to 5000, and an ethylene oxide content of from 30 to 95 wt %, in the presence of catalysts and expanding agents.
DE-A 2,425,657 discloses a process for the production of flexible cellular polyurethanes, in which, in addition to an expanding agent and a polyoxyalkylene polyol, a diphenylmethane-diisocyanate composition is used as a component essential to the invention, which composition has an average isocyanate functionality of less than 2.4 and contains not more than 60 wt % of 4,4′-MDI and at least 15 wt % of 2,4′-MDI. The preferred polyoxyalkylene polyols used are polyoxypropylene-polyoxyethylene polyols with random or block binding of the oxyalkylene groups, for the production of which initiators comprising, in particular, mixtures of one diol and one triol, eg, diethylene glycol/glycerol mixtures, are used. The products described possess good mechanical properties, particularly high compressive strength and a good sag factor. The sag factor is the compressive strength at 65% indentation divided by the compressive strength at 25% indentation. The higher the sag factor, the more resilient the foam. Higher resilience imparts a more comfortable feeling.
An essential factor regarding the preparation of flexible polyurethane foams and the properties of the resulting foamed plastics is the reactivity of the polyether alcohols used, which must be selected with great care.
If the reactivity of a polyether alcohol used for the production of flexible polyurethane foams is too high, the polyether alcohols are too active. As a result of this overactivation, molded foams may, for example, become deformed immediately after leaving the mold. An adequate content of open cells is necessary in the foam matrix in order to prevent subsequent shrinking of the shaped article. This phenomenon is directly governed by the reactivity of the polyether polyols. If the cells open too late and/or not enough due to the high reactivity of the polyalcohol, the shaped article (on release from the mold) or the block (during the production of block foams) does not stay dimensionally stable because CO
2
located in the cell can diffuse out of the cell, which therefore shrinks, whilst the atmospheric air cannot diffuse into the cell to the same extent. If the number of open cells is too high, the foam collapses.
Unduly low activity, on the other hand, reduces the release time, which in turn lowers the speed of production of shaped foams, so that the foamed plastics can no longer be produced within a specified minimum cycle period. In the production of block foams there occurs, in this case, the sink-back phenomenon, ie the formation of a concavity in the block, or so-called cold flow, which means the formation of a trapeziform block cross-section, which increases the cutting involved during further processing of the foamed plastics and consequently leads to product losses.
It is known that raising the reactivity of a block polyoxypropylene/polyoxyethylene/polyol will increase the reaction rate in the production of polyurethanes. The reactivity is usually determined by the amount of ethylene oxide added to the chain end during synthesis of the polyether polyol. When the amount of ethylene oxide added to the chain end is raised, the proportion of more reactive primary hydroxyl groups usually rises and thus the reactivity of the polyether alcohols increases.
This experience should lead one to expect that a linearly increasing content of ethylene oxide in the block polyoxypropylene/polyoxyethylene/polyols would make it possible to set the reactivity to a desirably high value. It has been found, however, that this is not the case.
Particularly in the case of high-load-bearing flexible foams, also known as HLB foams, and highly resilient foams, also known as HR foams, optimal reactivity of the polyalcohols is necessary in order to obtain good-quality products not suffering from the above drawbacks.
It is the object of the present invention to provide flexible polyurethane foams, for the production of which a polyether alcohol of optimal reactivity is used as polyalcohol component and the above drawbacks of the prior art are avoided.
We have now found that, surprisingly, polyether alcohols containing from 15 to 17 wt % of terminally bound ethylene oxide units, based on the total amount of the alkylene oxide, and having a hydroxyl value ranging from 20 to 60 mg KOH/g exhibit optimal reactivity, particularly in the case of HLB foams and HR foams, when used for manufacturing both block and molded flexible foams.
Accordingly, the invention relates to a process for the production o
Bruchmann Bernd
Lutter Heinz-Dieter
Müller Jens
Wagner Klaus
BASF - Aktiengesellschaft
Borrego Fernando A.
Cooney Jr. John M.
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