Process for preparing a polyurethane material

Details Process for preparing a polyurethane material Process for preparing a polyurethane material

2003-01-30

2004-10-19

Gorr, Rachel (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From reactant having at least one -n=c=x group as well as...

C521S176000

Reexamination Certificate

active

06806342

ABSTRACT:

FIELD OF THE INVENTION
The present invention is related to a process for preparing a polyurethane material. More specifically, the present invention is related to a process for preparing a polyurethane material using a polyoxyethylene polyoxypropylene polyol having a high oxyethylene content and a polyisocyanate having a high 4,4′-diphenylmethane diisocyanate (4,4′-MDI) content.
BACKGROUND OF THE INVENTION
The preparation of polyurethane materials having a high hardblock content from polyols having a high oxyethylene content, polyisocyanates comprising at least 85% by weight of 4,4′-MDI or a variant thereof and water has been disclosed in the prior art (i.e. WO 98/00450). The materials made are elastomers and hence show a glass transition temperature of less than 25° C. Further, it has been disclosed in the prior art (i.e. EP 608626) to produce shape memory polyurethane foams by reacting a polyisocyanate comprising a high amount of 4,4′-MDI and a polyol with a high oxyethylene content with water. The foams have a glass transition temperature above 25° C., and the amounts of chain extender and cross-linker used are relatively low, leading to products with a limited hard-block content giving products which are not as stiff as sometimes desirable.
SUMMARY OF THE INVENTION
Surprisingly, it has now been found that if a polyol is used which has a high oxyethylene content and a high level of primary hydroxyl groups together with an amount of a chain extender or cross-linker sufficient to provide a high hard block ratio, a polyurethane material is obtained which has a glass transition temperature of at least 25° C. and shows a high stiffness at a given density. The material obtained shows less surface defects (improved mixing, less bubbles) and a relatively high “ductility” (i.e. not brittle). The combination of ingredients used for making these materials show a good wetting of fibrous materials and in particular of glass fibres which makes the process particularly suitable for reaction injection moulding (RIM), especially for reinforced RIM (RRIM) and structural RIM (SRIM).
DETAILED DESCRIPTION
Therefore, the present invention is concerned with a process for preparing a polyurethane material having no glass transition temperature below 25° C., which process comprises reacting a polyisocyanate and an isocyanate-reactive composition, optionally in the presence of water in an amount of less than 5% by weight on the below isocyanate-reactive composition, wherein the reaction is conducted at an isocyanate index of 80 to 140, the polyisocyanate consists of a) 80-100% by weight of diphenylmethane diisocyanate comprising at least 40%, preferably at least 60% and most preferably at least 85% by weight of 4,4′-diphenylmethane diisocyanate and/or a variant of said diphenylmethane diisocyanate which variant is liquid at 25° C. and has an NCO value of at least 20% by weight (polyisocyanate a), and b) 20-0% by weight of another polyisocyanate (polyisocyanate b), and wherein the isocyanate-reactive composition consists of a) 80-100% by weight of a polyether polyol having an average nominal functionality of 3-8, an average equivalent weight of 200-2000, an average molecular weight of 600-8000, an oxyethylene (EO) content of 50-100% and preferably of 75-100% by weight and a primary hydroxyl content of 70-100% calculated on the number of primary and secondary hydroxyl groups in the polyol, b) an isocyanate-reactive chain extender and/or cross linker in an amount such that the hard block ratio is 0.60 or more and preferably at least 0.65 and c) 20-0% by weight of one or more other isocyanate-reactive compounds excluding water, the amount of polyol a) and isocyanate-reactive compound c) being calculated on the total amount of this polyol a) and compound c).
The materials prepared according to the present invention have no glass transition temperature, Tg, below 25° C. and preferably not below 60° C. The Tg is defined as the temperature at which the tan 6 curve reaches its maximum value as measured by Dynamic Mechanical Thermal Analysis (DMTA) at 1 Hz and a heating rate of 3° C./min).
In the context of the present invention, the following terms have the following meaning:
1) isocyanate index or NCO index or index: the ratio of NCO-groups over isocyanate-reactive hydrogen atoms present in a formulation, given as a percentage
[
NCO
]
×
100
[active hydrogen]
⁢
(
%
)
.
In other words the NCO-index expresses the percentage of isocyanate actually used in a formulation with respect to the amount of isocyanate theoretically required for reacting with the amount of isocyanate-reactive hydrogen used in a formulation.
It should be observed that the isocyanate index as used herein is considered from the point of view of the actual polymerisation process preparing the elastomer involving the isocyanate ingredient and the isocyanate-reactive ingredients. Any isocyanate groups consumed in a preliminary step to produce modified polyisocyanates (including such isocyanate-derivatives referred to in the art as prepolymers) or any active hydrogens consumed in a preliminary step (e.g. reacted with isocyanate to produce modified polyols or polyamines) are not taken into account in the calculation of the isocyanate index. Only the free isocyanate groups and the free isocyanate-reactive hydrogens (including those of the water) present at the actual polymerisation stage are taken into account.
2) The expression “isocyanate-reactive hydrogen atoms” as used herein for the purpose of calculating the isocyanate index refers to the total of active hydrogen atoms in hydroxyl and amine groups present in the reactive compositions; this means that for the purpose of calculating the isocyanate index at the actual polymerisation process one hydroxyl group is considered to comprise one reactive hydrogen, one primary amine group is considered to comprise one reactive hydrogen and one water molecule is considered to comprise two active hydrogens.
3) Reaction system: a combination of components wherein the polyisocyanates are kept in one or more containers separate from the isocyanate-reactive components.
4) The expression “polyurethane material” as used herein refers to cellular or non-cellular products as obtained by reacting polyisocyanates with isocyanate-reactive hydrogen containing compounds, optionally using foaming agents, and in particular includes cellular products obtained with water as reactive foaming agent (involving a reaction of water with isocyanate groups yielding urea linkages and carbon dioxide and producing polyurea-urethane foams) and with polyols, aminoalcohols and/or polyamines as isocyanate-reactive compounds.
5) The term “average nominal hydroxyl functionality” is used herein to indicate the number average functionality (number of hydroxyl groups per molecule) of the polyol or polyol composition on the assumption that this is the number average functionality (number of active hydrogen atoms per molecule) of the initiator(s) used in their preparation although in practice it will often be somewhat less because of some terminal unsaturation.
6) The word “average” refers to number average unless indicated otherwise.
7) The term “hard block ratio” refers to the amount (in pbw) of polyisocyanate+isocyanate-reactive materials having a molecular weight of 500 or less (wherein polyols having a molecular weight of more than 500 incorporated in the polyisocyanates are not taken into account) divided by the amount (in pbw) of all polyisocyanate+all isocyanate-reactive materials used.
8) The glass transition temperature is measured according to Dynamic Mechanical Thermal Analysis (DMTA) according to ISO/DIS 6721-5 at 3° C./min.
Preferably, the polyisocyanate a) is selected from 1) a diphenylmethane diisocyanate comprising at least 40%, preferably at least 60% and most preferably at least 85% by weight of 4,4′-diphenylmethane diisocyanate and the following preferred variants of such diphenylmethane diisocyanate: 2) a carbodiimide and/or uretonimine modified variant of polyiso

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