Light stable one-shot urethane-urea elastomers

Details Light stable one-shot urethane-urea elastomers Light stable one-shot urethane-urea elastomers

2001-10-12

2003-05-13

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...

C528S064000, C528S085000

Reexamination Certificate

active

06562932

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to optically clear, light stable polyurethane-urea elastomers having an onset softening point of at least 130° C., and to a process for their production. This process comprises reacting A) a liquid polyisocyanate or a polyisocyanate prepolymer having an NCO group content of about 5 to about 50% by weight, an average functionality of 2 to 3, and a viscosity of less than 5,000 mPa.s at 25° C.; and B) an isocyanate-reactive component comprising 1) an aromatic amine group containing compound, and 2) a hydroxyl group containing cmpound; in the presence of C) an organometallic catalyst; with the components being processed at ambient temperature and casted into a mold at an isocyanate index of 95 to 120.
Various light stable cast elastomers and processes for the production of these elastomers are known and described in the art. See, for example, U.S. Pat. Nos. 3,755,262, 3,866,242, 4,153,777, 4,404,353 and 4,808,690, and German Offenlegungsschrift 2,109,901.
Transparent high-impact polyurethane products are disclosed by U.S. Pat. No. 3,755,262. These products may be elastomeric or non-elastomeric in nature. Suitable liquid polyurethane reaction mixtures for preparing these optical polyurethanes are made by the one-shot or prepolymer method. Preferred mixtures comprise a non-aromatic polyisocyanate and a reactive hydrogen containing polyol having an average of more than two hydroxyl groups per molecule and molecular weights of up to about 800. Suitable isocyanates include (cyclo)aliphatic isocyanates such as rMDI. Amine group containing compounds are not disclosed by this reference.
U.S. Pat. No. 3,866,242 discloses protective shields consisting of a polyurethane, shaped in the contour of a clipboard, windshield, face shield, etc. These polyurethanes are described as being transparent and having excellent optical clarity. Suitable polyurethanes are prepared by reacting a polyester glycol or a polyether glycol with methylenebis(cyclohexylisocyanate) to form a prepolymer, and reacting this prepolymer with methylenebis(2-chloroaniline). Suitable curing agents are broadly described as having only primary amine groups, and preferably having a methylene bridge between two aromatic rings. Mixtures of curing agents wherein both amine groups and hydroxyl groups are present are not disclosed by this patent.
U.S. Pat. No. 4,153,777 describes polyurethanes having improved physical properties. This reference specifically discloses non-porous polyurethanes which exhibit good optical clarity and resistance to weathering, ultra-violet and thermal exposure. These polyurethanes comprise an isocyanate-terminated prepolymer which is formed by first reacting the isocyanate with water, and then with a polyol to form the prepolymer. This prepolymer is then chain extended or crosslinked with a polyol to form the cured polyurethane. Suitable isocyanates include (cyclo)aliphatic isocyanates such as, for example, 4,4′-dicyclohexylmethane diisocyanate (rMDI). Suitable chain extenders and crosslinkers to be reacted with the prepolymers include compounds such as, for example, 1,4-butanediol and trimethylolpropane. Amine group containing compounds are not disclosed by this reference.
Urethane elastomers for printing belts and a process for preparing these are disclosed in U.S. Pat. No. 4,404,353. These elastomers comprise a prepolymer which is reacted with a diamine curing agent (i.e. trimethylene glycol di-p-aminobenzoate, POLACURE 740M). The prepolymers disclosed are formed by reacting an aromatic isocyanate, i.e. toluene diisocyanate (TDI), with a polyether having difunctional primary hydroxyl groups (e.g. PTMEG). Then, the prepolymer is reacted with the diamine curing agent for form the urethane elastomers. Hydroxyl group containing compounds are not described by U.S. Pat. No. 4,404,353 as being suitable for a portion of the curing agent to be reacted with the isocyanate prepolymer. The elastomers formed by this process are not light stable and require rather high temperatures (e.g >170° F.) to be cast.
High heat distortion temperature transparent polyurethanes which are highly crosslinked are described by U.S. Pat. No. 4,808,690. These comprise a prepolymer prepared from a polyisocyanate and at least one multifunctional hydroxy containing intermediate, with a polyol curing component. Suitable multifunctional hydroxyl containing intermediates include polyhydric alcohols, polyester polyols and blends thereof. Suitable polyisocyanates include (cyclo)aliphatic polyisocyanates as well as aromatic and alkyl aromatic polyisocyanates. The polyol curing component can be a polyester or a polyhydric alcohol, and typically has a low equivalent weight. Amine group containing curing components are not described by U.S. Pat. No. 4,808,690.
German Offenlegungsschrift 2,109,901 discloses a hydrolysis resistant polyurethane. This polyurethane is prepared from an aromatic isocyanate prepolymer reacted with polyols and chain extenders which include polyamines and aminoalcohols, and an alicyclic or aliphatic diisocyanate. An example of polyurethanes described by this patent is a prepolymer based on toluene diisocyanate (TDI) and polycaprolactone, which is reacted with 3,3′-dichloro4,4′-diaminodiphenylmethane (MOCA) and 4,4′-dicyclohexylmethane diisocyanate (rMDI). However, aliphatic isocyanate prepolymers are not disclosed.
RIM elastomers based on prepolymers of (cyclo)aliphatic isocyanates are described in U.S. Pat. Nos. 5,668,239, 5,710,230 and 5,739,253. U.S. Pat. No. 5,668,239 requires an isocyanate-reactive component wherein the OH:NH equivalent ratio of from 1:1 to 15:1, but expressly discloses that aromatic amines are preferably not included as part of the isocyanate-reactive component. The isocyanate prepolymers of U.S. Pat. No. 5,710,230 are reacted with an isocyanate-reactive component comprising a relatively high molecular weight component and a chain extender. Amine group containing compounds are described, but aromatic amines are disclosed as being less preferred. U.S. Pat. No. 5,739,253 requires an isocyanate-reactive blend comprising a high molecular weight polyether polyol and a low molecular weight chain extender wherein the equivalent ratio of hydroxyl groups to amine groups is from 1:2 to 20:1. This patent also discloses that aromatic amine group containing compounds are less preferred. Because these products are processed by an injection reaction molding (RIM), the reaction mixture is injected in a closed mold.
Other light stable elastomers are disclosed in, for example, U.S. Pat. Nos. 5,510,445, 5,646,230, 5,714,562 and 6,174,984. These elastomers may be polyurethanes as in U.S. Pat. Nos. 5,714,562 and 6,174,984; polyurethane/ureas in as U.S. Pat. No. 5,646,230 or polyureas as in U.S. Pat. No. 5,510,445.
Isocyanate-terminated prepolymers and a process of preparing polyurethane/urea elastomer from these prepolymers are described by U.S. Pat. No. 5,646,230. These prepolymers have an NCO content of 3 to 10% and comprise the reaction product of a) an aromatic diisocyanate, b) a polyether polyol having an OH number of 25 to 125 and from 1.8 to 2.5 OH groups, and c) an aliphatic diisocyanate. The polyurethane/urea elastomers are prepared by reacting the isocyanate-terminated prepolymers with a sterically hindered aromatic amine group containing compound such as, for example, DETDA or ETHACURE 300. Hydroxyl group containing compounds are not described as possibly chain extenders for the isocyanate-terminated prepolymers. The reaction products do not exhibit light stability.
The light stable elastomers of U.S. Pat. No. 5,714,562 are described as having good dynamic properties. These elastomers comprise the reaction product of a) an isocyanate prepolymer having an NCO group cotnent of about 3 to 15%, b) a chain extender containing two hydroxyl groups and having a MW of 62 to 400, and c) a catalyst selected from a specific group of catalysts. Suitable isocyanate prepolymers comprise the reaction product of 1) 4,4′-dicyclohexylmet

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