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...
Reexamination Certificate
1998-05-13
2001-06-05
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...
C528S056000, C528S058000, C528S060000, C528S076000, C528S077000, C524S710000, C524S718000, C524S720000, C524S739000, C524S741000, C521S108000, C521S117000, C521S128000, C521S127000, C521S126000, C521S124000, C521S161000, C521S159000
Reexamination Certificate
active
06242555
ABSTRACT:
The present invention relates to micro-cellular or non-cellular, light-stable, elastomeric, flexible or semi-flexible polyurethane mouldings having a density of at least 900 kg/m
3
and a flexural modulus according to ASTM D790 of between 5 and 300 MPa, and in particular between 10 and 120 MPa, from a reaction mixture by the reaction injection moulding process (RIM) and to a process for the production thereof.
For the production of light-stable polyurethanes, it is known to use aliphatic or alicyclic isocyanates instead of aromatic isocyanates. In comparison with aromatic isocyanates, aliphatic or alicyclic isocyanates have however a much lower reactivity which causes problems with respect to obtaining a sufficiently short demoulding time. From a commercial point of view, the demoulding times should preferably be shorter than 60 seconds.
Reducing the demoulding time by using particular catalytic systems have already been considered for example in U.S. Pat. No. 4,150,206 and U.S. Pat. No. 4,292,411, more particularly for integral skin applications. The catalytic systems proposed in these U.S. patents consisted essentially in the combination of a low-molecular weight amine-initiator with an organolead or respectively an organobismuth catalyst. The proposed catalytic systems were described with reference to a broad range of different integral skin foams or elastomers, and numerous examples were given wherein the demoulding time ranged from 1 to 6 minutes.
The present invention is, however, directed to very particular light-stable polyurethane elastomers which are also especially suited for so-called window-encapsulation applications wherein a gasket is moulded around the periphery of a window, in particular a car window, which gasket serves to mount the window in the car frame. This gasket or other moulded structures on the window, must meet very severe requirements as to light and heat stability, mechanical strength, softness and adhesion to the window and the frame. Moreover, it is clear that the moulding process should enable a sufficiently short demoulding time, preferably less than 60 seconds, to be economically feasible.
In the process according to the invention, use is made of an IPDI based isocyanate component since it is more user friendly than for example HDI, from which the monomer fraction has first of all to be stripped off as described in EP-A-0 690 085, in view of its high volatility and its strong eye-irritating effects. An important drawback of IPDI is however its reactivity, which is even lower than the reactivity of HDI. In this respect, EP-A-0 690 085 and U.S. Pat. No. 5,502,147 teach to use HDI instead of IPDI as isocyanate since the use of IPDI in the cited prior U.S. Pat. No. 4,772,639 requires generally demoulding times of about 3 to 10 minutes, and in the specific examples even 5 to 10 minutes, notwithstanding the fact that an organometal catalyst was used in combination with an amine-initiator and with particular trimerization products on the basis of HDI and optionally IPDI.
According to the invention, a new process and a new polyurethane elastomer have been found which enable to produce, within an economically acceptable cycle-time, light-stable elastomeric polyurethane mouldings on the basis of an IPDI based isocyanate component, which mouldings are in particular suited for window encapsulation applications.
The process according to the invention is characterized to this end more particularly by the composition of the different components of the polyurethane reaction mixture and by the conditions wherein the reaction injection moulding process is carried out, as defined in annexed claim
1
.
In general the process according to the present invention is directed to the production of light-stable elastomeric polyurethane mouldings by the reaction injection moulding (RIM) process, which mouldings are suited for window-encapsulation applications but which may also be used for other applications, for example for interior trim parts of cars or other vehicles such as door panels, coverlids, etc. or even furniture parts. The obtained polyurethane mouldings are non-cellular or micro-cellular and have a density of at least 900 kg/m
3
. They are flexible or semi-flexible and have more particularly a flexural modulus according to ASTM D790 of between 5 and 300 MPa, typically between 10 and 120 MPa and most typically between 10 and 70 MPa.
In the process according to the invention, a reaction mixture is injected under a high pressure in a closed mould wherein an insert has usually been positioned in advance, for example the periphery of a window. This reaction mixture comprises an IPDI based isocyanate component A, isocyanate-reactive components B and at least one catalyst, at least one pigment and at least one antioxidant and UV absorber.
The isocyanate component A comprises an IPDI trimer/monomer mixture which has an NCO content of from 24.5 to 34, preferably from 26 to 32% by weight, and hence an average calculated functionality of from 2.2 to 2.7 and a calculated trimer content of from 20 to 70% by weight. These calculated values are based on the presumption that pure monomeric IPDI has a theoretic NCO content of 37.8% and a functionality of 2 whilst pure trimeric IPDI has a theoretical NCO content of 18.9% and a theoretical functionality of 3, thus possible oligomers which may be present in the IPDI trimer are not taken into account in the above calculated values. It has been found that, in combination with the particular selection of the other components described hereinafter, a sufficiently short demoulding time and a good light and heat stability can be obtained for values above the given lower limits whilst these values should remain below the given upper limits, since otherwise the mechanical strength would be lower (i.e. a more brittle polyurethane material), the material would be more rigid and the viscosity of the isocyanate component would be too high in view of an optimal processability and mixing of the components. The most preferred IPDI trimer is the isocyanurate derivative IPDI.
In addition to the IPDI monomers and trimers, the isocyanate component may optionally further comprise up to 10% by weight of IPDI prepolymers with isocyanate-reactive compounds containing 2 to 4 isocyanate-reactive hydrogen containing groups, preferably hydroxyl groups. The addition of such prepolymers may enhance the glass adhesion properties.
As to the isocyanate component, it should be noted that this component may comprise, in addition to the IPDI monomer/trimer mixture, small amounts of further isocyanate monomers or polymers, in particular HDI trimers, preferably in an amount lower than 5% by weight, based on the weight of the isocyanate component.
The isocyanate-reactive components B comprise a polyetherpolyol component (b1), a chain extender component (b2) with only OH groups, in particular glycols, and an amine-initiator (b3) which forms a co-catalytic system with the main catalyst(s) (C) and which comprises cross-linkers and/or chain extenders.
The polyetherpolyol component b1 comprises only polyetherpolyols with terminal OH groups. It should be noted that use can be made of single polyols or of polyol mixtures. They have an average equivalent weight of from 800 to 4000, preferably from 1000 to 2000 and a nominal average functionality of between 2 and 4. The primary OH content is generally comprised between 0 and 95% and more particularly between 0 and 90% , except when use is made, in a first embodiment of the invention, of a polytetramethylene glycol (PTMG) as polyetherpolyol. Indeed, such PTMG's have a primary OH content of 100% and a nominal functionality of 2.
In a preferred embodiment of the process according to the invention, use is however made as polyetherpolyol component b1 of an addition product of propylene oxide (PO) and optionally ethylene oxide (EO) on a low molecular weight initiator of the polyalcohol type, the amount of ethylene oxide, if present, being lower than 30% of the total amount of ethylene oxide and propylene oxide.
The nominal
Coppens Pierre
Du Prez Eddie
Gorr Rachel
Recticel
Sughrue Mion Zinn Macpeak & Seas, PLLC
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