Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-07-18
2004-02-24
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...
C521S137000, C521S170000, C521S173000, C521S174000
Reexamination Certificate
active
06696505
ABSTRACT:
The present invention relates to a process for the preparation of light-stable polyurethane foams of low density by reacting aliphatic polyisocyanates with compounds having at least two hydrogen atoms reactive with isocyanate groups.
Polyurethane foams have long been known and are widely described in the literature. They are usually prepared by reacting isocyanates with compounds having at least two hydrogen atoms reactive with isocyanate groups. The isocyanates generally used are aromatic di- and polyisocyanates, isomers of tolylene diisocyanate (TDI), isomers of diphenylmethane diisocyanate (MDI) and mixtures of diphenylmethane diisocyanate and polymethylene-polyphenylene polyisocyanates (crude MDI) being of the greatest industrial importance.
However, such polyurethane foams based on aromatic isocyanates tend to yellow under the action of light. This tendency to yellow is troublesome for many applications. It is known that polyurethanes which are prepared using aliphatic isocyanates are light-stable and exhibit virtually no yellowing at all. However, the disadvantage of using aliphatic isocyanates for the preparation of polyurethane foam is that the foams thus prepared are generally substantially inferior in many respects, in particular in their mechanical properties, to those based on aromatic isocyanates. Particularly because of the insufficient formation of hard and soft phase segments in the foam, important material properties, such as elongation, tensile strength and flexibility, suffer, and aliphatic polyurethane foams are therefore scarely of any industrial importance to date.
WO 98/52987 describes the preparation of lightfast polyurethane foams using aliphatic isocyanates, hydrogenated polydienediols being used as the compound having at least two hydrogen atoms reactive with isocyanate groups. However, such diols are more expensive in comparison with the alcohols usually used. Moreover, these foams exhibit a deterioration in their mechanical properties and become tacky under the action of light.
U.S. Pat. No. 3,284,415 describes the preparation of polyurethanes, in particular cellular and foamed polyurethanes, by reacting monomeric diisocyanates or polyisocyanates with compounds having at least two hydrogen atoms reactive with isocyanate groups, copolymers of ethylene and from 4 to 35% by weight alkyl acrylates and/or hydroxyalkyl acrylates being used as compounds having at least two hydrogen atoms reactive with isocyanate groups. These ethylene/acrylate copolymers are used as the sole polyol component, and in particular aromatic di- and polyisocyanates such as tolylene diisocyanate, phenylene diisocyanate, diphenylmethane diisocyanate or diphenylmethane diisocyanat oligomer are used as diisocyanates. As a result of using the polyethylene acrylates, the mechanical properties of the polyurethanes, in particular the resilience and the impact strength at low temperatures, and the water resistance of the polyurethanes are improved.
DE-C-22 45 710 describes ethylenically unsaturated vinyl chloride copolymers which are liquid at room temperature and can be used as flameproofing agents in rigid polyurethane foams. However, no influence of the copolymers on the mechanical properties of the foams is mentioned.
It is an object of the present invention to provide light-stable polyurethane foams which have good mechanical properites, in particular elongation and tensile strength, and which can be prepared using starting materials customary in polyurethane chemistry.
We have found that this object is achieved, according to the invention, by using aliphatic polyisocyanates and polyacrylate polyols for the preparation of the polyurethane foams.
The present invention accordingly relates to a process for the preparation of polyurethane foams by reacting
a) polyisocyanates with
b) compounds having at least two hydrogen atoms reactive with isocyanate groups, wherein the polyisocyanates a) are aliphatic polyisocyanates and the compounds having at least two hydrogen atoms reactive with isocyanate groups b) contain at least one acrylate polyol.
The present invention furthermore relates to polyurethane foams which can be prepared by the process described above.
The present invention furthermore relates to polyol blends containing at least one acrylate polyol and at least one further alcohol, preferably an at least difunctional polyether alcohol or a polyester alcohol.
The acrylate polyols used are preferably low molecular weight acrylate polyols, i.e. those whose number average molecular weight is not more than 12 000, preferably not more than 8 000, particularly preferably not more than 6 000, g/mol and not less than 400 g/mol. Below, the terms acrylate polyols and polyacrylate polyols are used synonymously.
The acrylate polyols used according to the invention are prepared by polymerization of hydroxy-functionalized (meth)acrylates, preferably by copolymerization of hydroxy-functionalized (meth)acrylates with (meth)acrylates not having hydroxyl functional groups. Furthermore, they can also be prepared by copolymerization of said acrylate monomers with other aliphatic, ethylenically unsaturated monomers, for example ethene, propene, butene, isobutene, acrylonitrile, acrylamide, acrolein, vinyl esters of carboxylic acids or unsaturated carboxylic acids, such as maleic acid, fumaric acid or crotonic acid or derivatives thereof.
Such copolymerization can be carried out in reactors operated continuously or batchwise, for example kettles, annular gap reactors, Taylor reactors, extruders or tubular reactors.
Reaction conditions which lead to polymers having a low level of impurities are preferably chosen. Thus, in the preparation of the acrylate polyols used according to the invention, polymerization regulators are preferably not used.
In the preparation of the acrylate polyols used according to the invention, polymerization is preferably effected at above 160° C. in the absence of polymerization regulators and with very low initiator concentrations. The chosen procedure for the process is preferably such that acrylate polyols having average molar masses (Mn) of not more than about 12 000 g/mol are present at the end of the reaction.
Homopolymers of hydroxyalkyl (meth)acrylates or copolymers of hydroxyalkyl (meth)acrylates with (meth)acrylic monomers having no OH functional groups are preferred. In particular, halogen-free monomers are used in the preparation of the acrylate polyols used according to the invention.
The acrylate polyols used according to the invention are prepared in particular by polymerization of hydroxy-C
1
- to C
8
-alkyl (meth)acrylates, e.g. hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate.
Particularly suitable acrylic monomers without OH groups, which, if required, may be used as comonomers are aliphatic monomers containing olefinic double bonds and having a wide range of chemical structures, for example alkenes of 2 to 6 carbon atoms, such as ethene, propene, butene or isobutene, acrylonitrile, acrylamide, acrolein, vinyl esters of carboxylic acids or unsaturated carboxylic acids, such as maleic acid, fumaric acid or crotonic acid or derivatives thereof, and particularly preferably alkyl (meth)acrylates having C
1
- to C
10
-alkyl groups, for example n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-butyl (meth)acrylate, propyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, ethylhexyl (meth)acrylate and/or hexanediol di(meth)acrylate. Said monomers can be used individually or in any desired mixture with one another.
The acrylate polyols used according to the invention are preferably prepared by copolymerization of hydroxy-C
1
- to C
8
-alkyl (meth)acrylates with the (meth)acrylic monomers described above and having OH functional groups, any desired combination of different hydroxyalkyl (meth)acrylates with the (meth)acrylates having no functional groups being possible. Preferably, the OH-containing monomers are used in concentrations of from 5 to 95, particularly preferably from 10 to 80, mol %.
The number-average
Binder Horst
Bruchmann Bernd
Hirn Michael
Lutter Heinz-Dieter
BASF - Aktiengesellschaft
Borrego Fernando
Cooney Jr. John M.
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