Water-clear aliphatic polyurethane pultrusion formulations and processes

1. A pultrusion process for preparing a fiber reinforced polyurethane composite comprising:

(a) continuously pulling a roving or tow of continuous fiber reinforcing material successively through an impregnation chamber and a die;

(b) continuously feeding a polyurethane-forming system to the impregnation chamber;

(c) contacting the fiber reinforcing material with the polyurethane-forming system in the impregnation chamber such that substantially complete wetting of the material by the formulation occurs;

(d) directing the fiber reinforcing material through a die heated to reaction temperature to form a solid composite; and

(e) drawing the composite from the die,

wherein the polyurethane-forming system comprises:

(1) a clear, aliphatic polyisocyanate having a viscosity at 25° C. of no more than 1000 centipoise, and

(2) an isocyanate-reactive component comprising:

(i) a colorless amine-initiated polyol having a molecular weight of from about 150 to about 400 and an OH functionality greater than or equal to 3,

(ii) a colorless pentaerythritol-initiated polyol having a molecular weight less than 410 and a functionality greater than 3, and

(iii) a polyol having a molecular weight of 60 to less than 200 and an isocyanate-reactive group functionality of 2 to 4,

(3) a catalyst,

wherein the fiber reinforced polyurethane composite is clear, and

wherein one impregnation chamber is used in the process.

2. The pultrusion process of claim 1 in which the fiber reinforcing material is selected from the group consisting of single strands, braided strands, woven mat structures, non-woven mat structures and combinations thereof.

3. The pultrusion process of claim 1 in which the fiber reinforcing material comprises one or more of glass fibers, glass mats, carbon fibers, polyester fibers, natural fibers, aramid fibers, basalt fibers and nylon fibers.

4. The pultrusion process of claim 1 in which the fiber reinforcing material comprises glass fibers.

5. The pultrusion process of claim 1 in which the clear, aliphatic polyisocyanate having a viscosity at 25° C. of no more than 1000 centipoise is based on 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane and/or dicyclohexylmethane-4,4′-diisocyanate.

6. A clear fiber reinforced polyurethane composite made by the process of claim 1 .

7. The pultrusion process of claim 1 , wherein the amine-initiated polyol having a molecular weight of from about 150 to about 400 has an OH functionality of at least 4.

8. The pultrusion process of claim 7 , wherein the amine-initiated polyol is present in an amount of at least 20% by weight, based on the total weight of the isocyanate-reactive component.

9. The pultrusion process of claim 7 , wherein the polyols of the isocyanate-reactive component consist essentially of colorless polyols having a molecular weight less than 410 and a functionality of at least 3.

10. The pultrusion process of claim 1 , wherein the clear, aliphatic polyisocyanate having a viscosity at 25° C. of no more than 1000 centipoise is based on HMDI.

11. The pultrusion process of claim 1 , wherein the clear, aliphatic polyisocyanate having a viscosity at 25° C. of no more than 1000 centipoise is based on IPDI.

12. The pultrusion process of claim 8 , wherein the amine-initiated polyol having a molecular weight of from about 150 to about 400 and an OH functionality of at least 4 is present in an amount of at least 25% by weight, based on the total weight of isocyanate-reactive component.

13. The pultrusion process of claim 1 , wherein conditions in the impregnation chamber are such that substantially no polymerization takes place.

14. The pultrusion process of claim 1 , wherein the amine-initiated polyol has a molecular weight of from about 150 to about 300 and an OH functionality of 4 to 5.

15. The pultrusion process of claim 1 , wherein the catalyst consists of:

(1) one tin catalyst; and

(2) a tertiary amine catalyst.

16. The pultrusion process of claim 15 , wherein the tertiary amine catalyst comprises:

(a) 1,8-diazabicycloundec-7-ene, and

(b) N-benzyl dimethylamine.

17. The pultrusion process of claim 1 , wherein:

(i) the colorless amine-initiated polyol comprises a tetra-functional amine-based polyether polyol having a molecular weight of 290;

(ii) the colorless pentaerythritol-initiated polyol has a functionality of 4, and

(iii) the polyol having a molecular weight of 60 to less than 200 and an isocyanate-reactive group functionality of 2 to 4 comprises a polypropylene oxide-based triol having a molecular weight of 160.