METHOD FOR PRODUCING POLYURETHANE SANDWICH MOLDED PARTS

Abstract

Described herein is a process for producing polyurethane sandwich moldings including at least one core layer and at least one reinforcing fiber layer, where (i) at least one reinforcing fiber layer is applied onto a core layer and a moisture-curing polyurethane adhesive is applied to a reinforcing fiber layer, (ii) the part from (i) is placed into a mold and pressed in the mold and the moisture-curing polyurethane adhesive is cured, and (iii) the molding from (ii) is removed from the mold and optionally subjected to further operations, where the moisture-curing polyurethane adhesive is applied before or after application of the reinforcing fiber layer onto the at least one core layer and for the curing the moisture-curing polyurethane adhesive is brought into contact with water or with a solution comprising water. Also described herein are a polyurethane sandwich molding obtainable by such a process and a method of using a polyurethane sandwich molding in vehicles.

Claims

1. A process for producing polyurethane sandwich moldings comprising at least one core layer and at least one reinforcing fiber layer, wherein i. at least one reinforcing fiber layer is applied onto a core layer and a moisture-curing polyurethane adhesive is applied to a reinforcing fiber layer, ii. the part from i. is placed into a mold and pressed in the mold and the moisture-curing polyurethane adhesive is cured, and iii. the molding from ii. is removed from the mold and optionally subjected to further operations, wherein the moisture-curing polyurethane adhesive has a viscosity of 5000 mPas to 50000 mPas, measured at 25 C. according to DIN 53018, wherein the moisture-curing polyurethane adhesive comprises at least 80% by weight, based on the total weight of the moisture-curing polyurethane adhesive, of isocyanate-terminated prepolymer which is obtainable by mixing a stoichiometric excess of aromatic isocyanate with polymeric compounds having at least two isocyanate-reactive groups and optionally compounds having only one isocyanate-reactive group and optionally chain extenders and/or crosslinking agents and the moisture-curing polyurethane adhesive is applied before or after application of the reinforcing fiber layer onto the at least one core layer and for the curing the moisture-curing polyurethane adhesive is brought into contact with water or with a solution comprising water.

2. (canceled)

3. The process according to claim 1, wherein the isocyanate-terminated prepolymer has an NCO content of 5% to 20% by weight.

4. The process according to claim 1, wherein the aromatic isocyanate comprises isocyanates selected from the group consisting of 2,4-MDI, 4,4-MDI, higher polycyclic homologs of MDI or mixtures of two or mores of these components.

5. The process according to claim 1, wherein the polymeric compounds having at least two isocyanate-reactive groups comprise at least one polyetherol obtainable by alkoxylation of a starter molecule having a functionality of 2 to 4 and an average content of ethylene oxide, based on the total weight of alkylene oxide, of 20% to 70% by weight.

6. The process according to claim 1, wherein the polyurethane adhesive is used in an amount of 200 to 2000 g/m2 of reinforcing fiber layer.

7. The process according to claim 1, wherein the moisture-curing polyurethane adhesive is applied to the reinforcing fiber layer on one side or on both sides before application of the reinforcing fiber layer onto the core layer.

8. The process according to claim 7, wherein the moisture-curing polyurethane adhesive is applied to the reinforcing fiber layer by roll application.

9. The process according to claim 7, wherein the reinforcing fiber layer comprising polyurethane adhesive is applied onto the core layer one hour to 3 months after application of the polyurethane adhesive.

10. The process according to claim 1, wherein the moisture-curing polyurethane adhesive is brought into contact with an alkaline, aqueous alkali metal solution for the curing.

11. The process according to claim 10, wherein the concentration of the alkaline, aqueous alkali metal solution is 0.1 to 10 M, based on the alkali metal.

12. The process according to claim 10, wherein the pH of the aqueous, alkaline alkali metal solution is at least 10.

13. The process according to claim 1, wherein the alkaline, aqueous alkali metal solution is applied to the polyurethane adhesive in an amount of 10 to 150 g/m2.

14. The process according to claim 1, wherein the mold in step (ii.) comprises a decorative element.

15. The process according to claim 1, wherein the reinforcing fiber layer is a glass fiber layer or a carbon fiber layer.

16. A polyurethane sandwich molding obtainable by a process according to claim 1.

17. A method of using the polyurethane sandwich molding according to claim 16, the method comprising using the polyurethane sandwich molding in vehicles.

18. The process according to claim 1, wherein the material used for the core layer is paper honeycombs, metal honeycombs or plastic honeycombs.

Description

EX. 1

Production of a Polyurethane Adhesive

[0046] 378 g of a mixture of 2,4-MDI, 4,4-MDI and higher polycyclic homologs of MDI having an average isocyanate functionality of 2.7 are initially charged at room temperature and gradually mixed with 420 g of a polyol based on propylene glycol as starter and polyethylene oxide-polypropylene oxide having an ethylene oxide content of approx. 20%, based on the content of ethylene oxide and propylene oxide, and a hydroxyl number of 29.5 mg KOH/g, and 200 g of a polyol based on glycerol as starter and polypropylene oxide-polyethylene oxide having an ethylene oxide content of approx. 70%, based on the content of ethylene oxide and propylene oxide, and a hydroxyl number of 42 mg KOH/g. The mixture is subsequently heated to 60 C. and stirred for 2 hours at 60 C., then cooled down to below 40 C. After cooling down, 0.5 g of diglycol bis(chloroformate) and 0.5 g of 85% orthophosphoric acid were also added to the isocyanate prepolymer.

[0047] The polyurethane prepolymer obtained has a viscosity at 25 C. of 19 150 mPas and an NCO content of 9.9% by weight.

Production of a Sandwich Component

[0048] A preform was produced from a honeycomb paperboard having a thickness of approx. 18 mm, which had been covered on both sides with Unifilo 450 woven fiber fabric from Owens Corning. The polyurethane adhesive obtained was applied to both the upper and lower side of the preform sandwich in an amount of in each case 330 g/m.sup.2 in a roll application process at a roller temperature of 75 C. The surface of the unfinished sandwich component was then sprayed with approx. 100 g/m.sup.2 of a 10% by weight sodium carbonate solution. The unfinished sandwich element was subsequently pressed to a thickness 1 of 11 mm and a thickness 2 of 2 mm in a mold having a mold temperature of 120 C. and demolded after 90 seconds.

EX. 2

[0049] 519 g of a mixture of 2,4-MDI, 4,4-MDI and higher polycyclic homologs of MDI having an average isocyanate functionality of 2.7 are initially charged at room temperature and gradually mixed with 325 g of a propylene glycol-started polyethylene oxide-polypropylene oxide having an ethylene oxide content of approx. 20%, based on the content of ethylene oxide and propylene oxide, and a hydroxyl number of 29.5 mg KOH/g, and 155 g of a glycerol-started polypropylene oxide-polyethylene oxide having an ethylene oxide content of approx. 70%, based on the content of ethylene oxide and propylene oxide, and a hydroxyl number of 42 mg KOH/g. The mixture is subsequently heated to 60 C. and stirred for 2 hours at 60 C., then cooled down to below 40 C. After cooling down, 0.5 g of diglycol bis(chloroformate) and 0.5 g of 85% orthophosphoric acid were also added to the isocyanate prepolymer.

[0050] The polyurethane prepolymer obtained has a viscosity at 25 C. of 8250 mPas and an NCO content of 14.4% by weight.

[0051] A preform was produced from a honeycomb paperboard having a thickness of approx. 18 mm, which had been covered on both sides with Unifilo 450 woven fiber fabric from Owens Corning. The polyurethane adhesive obtained was applied to both the upper and lower side of the preform sandwich in an amount of in each case 330 g/m.sup.2 in a roll application process at a roller temperature of 75 C. The surface of the unfinished sandwich element was then sprayed with approx. 100 g/m.sup.2 of a 10% by weight sodium carbonate solution. The unfinished sandwich element was subsequently pressed to a thickness 1 of 11 mm and a thickness 2 of 2 mm in a mold having a mold temperature of 120 C. and demolded after 60 seconds. A perfect component was obtained. The polyurethane sandwich molding obtained displayed a very good bonding between the reinforcing fiber layer and the honeycomb paperboard, with only a low proportion of the polyurethane adhesive penetrating into the interior of the honeycomb paperboard, signifying a low loss of polyurethane adhesive. The edge formation in the 11 mm/2 mm border area was outstanding, as were the mechanical properties of the polyurethane sandwich molding obtained.

EX. 3

[0052] The experiment was repeated using a woven carbon fiber fabric and a woven natural fiber jute fabric instead of the Unifilo 450 woven glass fiber fabric, under otherwise identical conditions. In this case too, a polyurethane sandwich molding having a very good bonding between the reinforcing fiber layer and the honeycomb paperboard was obtained, with only a low proportion of the polyurethane adhesive penetrating into the interior of the honeycomb paperboard. The edge formation in the 11 mm/2 mm border area and the mechanical properties of the polyurethane sandwich moldings obtained were also outstanding.