Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1999-04-30
2001-12-18
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...
C521S051000, C521S137000, C521S160000, C521S170000, C521S172000, C521S174000
Reexamination Certificate
active
06331577
ABSTRACT:
Elastic polyurethane moldings having a compact surface and a cellular core, known as flexible integral polyurethane foams, have been known for a long time and have various applications. Typical fields of use are elastic parts in the automobile sector, for example armrests, foam cladding of steering wheels and spoilers, or shoe soles.
Particularly in the case of shoe soles, very good mechanical properties, high elasticity and low abrasion are demanded.
The production of polyurethane shoe soles is usually carried out by the following process:
In a mixing machine, the constituents of the polyurethane system, viz. the polyol component, usually designated as the A component, and the isocyanate component, usually designated as the B component, are mixed and the mixture is poured into a metal mold. In the mold, the foaming process occurs to form an integral density distribution.
The A component, also described as the polyol component, usually consists of
one or more high molecular weight polyols, customarily polyether and/or polyester polyols,
one or more low molecular weight H-functional chain extenders,
the blowing agent, catalysts, foam stabilizers and other foam auxiliaries.
The isocyanate component used is usually 4,4′-diisocyanatodiphenylmethane, also described as “pure MDI”. Since pure MDI is solid at room temperature and therefore difficult to process, it is usually “liquefied” by modification. Thus, the pure MDI can be modified by partial formation of carbodiimide or uretonimine structures. However, in the production of shoe soles, this modification can only be used to a subordinate extent, since it increases the functionality of the B component which leads to poorer mechanical properties of the foams. The use of higher-functional MDI homologues, known as raw MDI, also leads to a drastic increase in the crosslinking density and thus to a fall in the mechanical property values, so that this modification plays practically no role in the production of shoe soles.
The customary way of liquefying the MDI is the preparation of prepolymers by reacting pure MDI with polyols. Typical polyols for this purpose are dipropylene glycol, tripropylene glycol, or else higher molecular weight polyols as are used in the A component.
To prepare the prepolymers, the pure MDI is reacted with an amount of polyol, in particular diol, such that the prepolymer has an NCO content of from 18 to 23% by weight.
A series of possible ways of preparing prepolymers is known from the prior art. Thus, EP-A-013 487 describes uretonimine-modified MDI prepolymers. The prepolymers have NCO contents of about 18% by weight. EP-A-235 888 describes microcellular elastomers based on polyester polyols containing alkanolamines. The isocyanate component used comprises prepolymers of MDI and amine-containing polyester alcohols having an NCO content of about 18% by weight. In EP-A-451 559, urethane- and carbodiimide-modified MDI is reacted with polyether polyols to form cellular polyurethane integral foams. EP-A-582 385 describes an NCO-terminated prepolymer of MDI and polyether polyols having an NCO content of from 17 to 21% by weight, which can be converted into microcellular elastomers. DE-A-1 618 380 describes NCO-terminated prepolymers which are liquid at room temperature, have molecular weights up to 700 and are prepared from MDI and branched aliphatic dihydroxy compounds. The NCO content of these prepolymers is from 15 to 25% by weight. WO 91/17197 describes the production of microcellular polyurethane elastomers which are used, for example, for shoe soles. The isocyanate component used here comprises prepolymers of MDI and polytetramethylene glycol having NCO contents of from 14 to 28% by weight. However, the storage stability of such prepolymers based on polytetramethylene glycol is unsatisfactory. WO 92/22595 describes prepolymers of MDI and a polyol mixture comprising a branched diol or triol and at least one 2- to 4-functional polyoxyalkylene polyol. The NCO contents of the prepolymers are in the range from 15 to 19% by weight.
A substantial disadvantage of the processes of the prior art is that when water is used as blowing agent it is not possible to produce shoe soles having a density of less than 400 g/l, since the parts then shrink. Furthermore, the elasticity of such foams is unsatisfactory: the rebound resilience of such plates is only from 20 to 25%, which is insufficient for use in shoe sole systems.
It is an object of the present invention to find a process for producing flexible integral polyurethane foams which uses water as blowing agent and gives parts which have a high elasticity and do not shrink even at densities of the moldings of below 400 g/l.
We have found that this object is achieved when the isocyanate component used in the production of flexible integral foams is a prepolymer of pure MDI and at least one polyoxypropylene polyol and/or polyoxypropylene-polyoxyethylene polyol having an NCO content of <15% by weight, preferably <13% by weight, and the mixing ratio of polyol to isocyanate component in the foaming process is <1.
The invention accordingly provides a process for producing high elasticity polyurethane moldings having a compact surface and a cellular core by reacting
a) modified organic polyisocyanates with
b) at least one compound containing at least two reactive hydrogen atoms and having a molecular weight of from 1000 to 8000
c) chain extenders in the presence of
d) blowing agents,
e) catalysts and, if desired,
f) customary auxiliaries and/or additives
in a closed mold with compaction, wherein the modified organic polyisocyanate (a) which is used is a reaction product of 4,4′-diisocyanatodiphenylmethane with at least one polyoxypropylene polyol and/or polyoxypropylene-polyoxyethylene polyol having an NCO content of <15% by weight, in particular <13% by weight, and the weight ratio of a) to (b+c+d+e+f) is greater than 1, the chain extenders c) used are diols having a molecular weight of <400 and the blowing agent d) used is water.
For the purposes of the present invention, “high elasticity” means that the rebound resilience in accordance with DIN 53512 is at least 35%.
The polyoxypropylene polyols and polyoxypropylene-polyoxyethylene polyols used for preparing the modified organic polyisocyanates are preferably 2- to 3-functional. They are usually prepared by the generally known base-catalyzed molecular addition of propylene oxide, alone or in admixture with ethylene oxide, to H-functional, in particular OH-functional, initiator substances. Examples of initiator substances used are water, ethylene glycol or propylene glycol, or else glycerol or trimethylolpropane.
When ethylene oxide/propylene oxide mixtures are employed, the ethylene oxide is preferably used in an amount of 10-50% by weight, based on the total amount of alkylene oxide. The alkylene oxides can here be incorporated blockwise or as a random mixture. Particular preference is given to the incorporation of an ethylene oxide end block (“EO cap”), in order to increase the content of more reactive primary OH end groups.
The polyether polyols used for preparing the modified organic polyisocyanates have a functionality of from 2 to 3 and molecular weights of from 1000 to 8000, preferably from 2000 to 6000.
Preference is given to using diols based on polyoxypropylene having about 20% by weight of polyoxyethylene units at the chain end, so that >80% of the OH groups are primary OH groups. The molecular weight of these diols is preferably from 2000 to 4500.
The prepolymers used according to the present invention are prepared in a manner known per se, by reacting the pure MDI at about 80° C. with the polyols to give the prepolymer. To prevent secondary reactions caused by atmospheric oxygen, the reaction vessel should be flushed with an inert gas, preferably nitrogen. The polyol/polyisocyanate ratio is selected such that the NCO content of the prepolymer is <15% by weight, preferably <13% by weight.
The pure MDI used can contain small amounts, up to about 5% by weigh
Pittrich Klaus
Volkert Otto
BASF - Aktiengesellschaft
Borrego Fernando A.
Cooney Jr. John M.
LandOfFree
Process for producing elastic polyurethane moldings with... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for producing elastic polyurethane moldings with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for producing elastic polyurethane moldings with... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2587187