AGING-RESISTANT POLYURETHANE SEAL

Abstract

The invention relates to a method for producing seals made of polyurethane, in which (a) aliphatic polyisocyanate, (b) compounds containing at least two isocyanate-reactive groups, (c) catalysts, (d) antioxidants and/or light stabilizers, and, optionally, (e) blowing agents, and (f) auxiliary agents and/or additives are mixed to form a reaction mixture, and the reaction mixture is allowed to complete the reaction to form polyurethane. The seal made of polyurethane has a Shore A hardness of less than 90 and a density of at least 850 g/L. The polymeric compounds having groups reactive toward isocyanate include b1) polyetherols having a functionality of 2 to 4 and a hydroxyl number of 20 to 100 mg KOH/g, b2) hydrophobic polyols having an OH number of less than 180 mg KOH/g and a functionality of greater than 2 to 3, and b3) chain extenders.

Claims

1. A process for the production of polyurethane gaskets, the process comprising: mixing: (a) aliphatic polyisocyanate, (b) compounds having at least two groups reactive toward isocyanates, (c) catalysts, and at least one of antioxidants and light stabilizers to give a reaction mixture, and allowing completion of the reaction mixture to give the polyurethane, wherein the Shore A hardness of the polyurethane gasket is less than 90, the density of the polyurethane gasket is at least 850 g/L, and the polymeric compounds having groups reactive toward isocyanate comprise b1) polyetherols with functionality from 2 to 4 and with hydroxy number from 20 to 100 mg KOH/g, b2) hydrophobic polyols with OH number smaller than 180 mg KOH/g and with functionality from greater than 2 to 3, and b3) chain extenders.

2. The process according to claim 1, wherein the aliphatic polyisocyanate (a) comprises a mixture of monomeric and trimeric isophorone diisocyanate.

3. The process according to claim 1, wherein the hydroxy number of the polyetherol b1) is from 25 to 50 mg KOH/g.

4. The process according to claim 1, wherein the polyetherol b1) has, as alkylene oxide, ethylene oxide units and propylene oxide units, wherein the proportion of ethylene oxide units, based on the total weight of alkylene oxide units in the polyether polyol b1), is smaller than 30% by weight, and the proportion of primary OH groups is greater than 70%, based on the number of OH groups in the polyether polyol b1).

5. The process according to claim 1, wherein the hydrophobic polyol b2) comprises at least one of castor oil, dehydrated castor oil, and alkoxylation products of castor oil or of dehydrated castor oil.

6. The process according to claim 1, wherein the hydrophobic polyol b2) comprises at least one of castor oil, dehydrated castor oil and alkoxylation products of castor oil or dehydrated castor oil.

7. The process according to claim 1, wherein the chain extender b3) has aliphatically bonded OH groups, and its molar mass is less than 160 g/mol.

8. The process according to claim 1, wherein the compounds (b) having at least two groups reactive toward isocyanates further comprise, alongside the compounds b1) to b3), a compound b4) with molar mass smaller than 150 g/mol and with average functionality from 2 to 3 and, as groups having functionality toward isocyanate, functional groups selected from the group consisting of —NH.sub.2, —NH—, and —OH groups, wherein at least one of the functional groups is an—NH.sub.2 group or an—NH— group.

9. The process according to claim 8, wherein the compounds (b) having at least two groups reactive toward isocyanates further comprise, alongside the compounds b1) to b4), a compound b5) with molar mass from 800 to 6000 g/mol and with average functionality from 2 to 4 and, as groups having functionality toward isocyanate, functional groups selected from the group consisting of —NH.sub.2, —NH—, and —OH groups, wherein at least one of the functional group is an NH.sub.2 group.

10. The process according to claim 9, wherein the compounds (b) having at least two groups reactive toward isocyanates further comprise, alongside the compounds b1) to b5), a compound b6) with molar mass smaller than 400 g/mol and with hydroxy functionality from 3 to 6.

11. The process according to claim 1, wherein the catalysts are exclusively amine catalysts.

12. The process according to claim 10, wherein, based on the total weight of components b1) to b6), the proportion of component b1) is from 50 to 90% by weight, the proportion of component b2) is from 5 to 25% by weight, the proportion of component b3) is from 1 to 7% by weight, the proportion of component b4) is from 0 to 5% by weight, the proportion of component b5) is from 0 to 15% by weight, and the proportion of component b6) is from 0 to 5% by weight.

13. The process according to claim 17, wherein the ratio in which components (a) to (f) are mixed is such that the isocyanate index is from 90 to 120.

14. A polyurethane gasket obtainable by a process according to claim 1.

15. (canceled)

16. (canceled)

17. The process according to claim 1, further comprising mixing (e) blowing agents, and (f) auxiliaries and/or additional substances to give the reaction mixture.

Description

[0045] Examples are used below to illustrate the present invention.

Starting Materials:

[0046] Polyol 1: polyetherol based on ethylene oxide and propylene oxide with glycerol as starter, with OH number 35 mg KOH/g, with ethylene oxide content 13% by weight, and with propylene oxide content 85% by weight, based on total weight, and with functionality 2.7.

[0047] Polyol 2: polyol based on dehydrated castor oil with OH number 124 mg KOH/g and with functionality 2.2.

[0048] Polyol 3: castor oil.

[0049] Polyol 4: polyesterol based on adipic acid and monoethylene glycol, and also diethylene glycol, with MEG content 31% by weight and with diethylene glycol content 21% by weight, based on total weight. The OH number of the polyesterol is 56 mg KOH/g and its functionality is 2.0.

[0050] Fatty acid ester: aliphatic fatty acid ester based on glycerol with functionality 0.0.

[0051] Polyetheramine: linear polypropylene glycol having terminal amino functions, with amine number 56.7 mg KOH/g and with functionality 2.0.

[0052] Crosslinking agent: polyetherol based on ethylene oxide with 1,1,1-trimethylolpropane as starter, with OH number 935 mg KOH/g, with ethylene oxide content 23% by weight, based on total weight, and with functionality 3.0.

[0053] MEG: monoethylene glycol

[0054] DEA: diethanolamine

[0055] Catalyst 1: amine catalyst based on an annellated amidine structure.

[0056] Catalyst 2: mixture of 35% by weight of phenol, 55% by weight of catalyst 1, and 10% by weight of diethylene glycol.

[0057] Catalyst 3: dimethyltin dineodecanoate

[0058] Stabilizer 1: ethylenebis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate] (Irganox® 245)

[0059] Stabilizer 2: 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (Tinuvin® 328)

[0060] Black paste: dispersion of 50% by weight of carbon black in polyol 1.

[0061] Isocyanate: Mixture of monomeric isophorone diisocyanate and trimeric isocyanurates based on isophorone diisocyanate with 29.1% NCO content in the mixture.

[0062] TNPP: trisnonylphenyl phosphite

[0063] Stabilizer 3: bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate

[0064] A mixture 1 was produced via mixing of the components listed in table 1.

TABLE-US-00001 TABLE 1 Composition of mixture 1 in percent by weight Comp. Inv. Inv. Comp. Inv. Comp. ex. 1 ex. 1 ex. 2 ex. 2 ex. 3 ex. 3 Polyol 1 74.84 64.84 64.84 64.84 66.59 68.04 Polyol 2 0.00 10.00 0.00 0.00 10.00 0.00 Polyol 3 0.00 0.00 10.00 0.00 0.00 0.00 Polyol 4 0.00 0.00 0.00 10.00 0.00 0.00 Fatty acid ester 0.00 0.00 0.00 0.00 0.00 9.09 Polyetheramine 6.00 6.00 6.00 6.00 6.00 5.46 Crosslinking 2.50 2.50 2.50 2.50 1.25 2.27 agent MEG 5.70 5.70 5.70 5.70 5.20 5.18 DEA 3.30 3.30 3.30 3.30 3.30 3.00 Catalyst 1 0.48 0.48 0.48 0.48 0.48 0.44 Catalyst 2 0.48 0.48 0.48 0.48 0.48 0.44 Stabilizer 1 0.95 0.95 0.95 0.95 0.95 0.86 Stabilizer 2 0.95 0.95 0.95 0.95 0.95 0.86 Black paste 4.80 4.80 4.80 4.80 4.80 4.36

[0065] A mixture 2 is produced via mixing of the components listed in table 2.

TABLE-US-00002 TABLE 2 Composition of mixture 2 in percent by weight Comp. Inv. Inv. Comp. Inv. Comp. ex. 1 ex. 1 ex. 2 ex. 2 ex. 3 ex. 3 Isocyanate 88.20 88.20 88.20 88.20 88.20 88.20 Catalyst 3 1.50 1.50 1.50 1.50 1.50 1.50 TNPP 8.60 8.60 8.60 8.60 8.60 8.60 Stabilizer 3 1.70 1.70 1.70 1.70 1.70 1.70

Manual Experiments:

[0066] Mixture 1 was mixed with mixture 2, the isocyanate index being 100, and the material was charged to a closed mold to give moldings.

Machine Experiments:

[0067] In a standard high-pressure RIM process, a compact test sample with maximum surface smoothness, thickness 4 mm, and width 4 cm is produced via mixing of mixtures 1 and 2 with an isocyanate index of 100. This process is described by way of example in “Kunststoffhandbuch, 7, Polyurethane” [Plastics handbook, 7, Polyurethanes], Carl Hanser-Verlag, 3rd edition 1993, chapter 4.2.

[0068] On this test sample, a test sample made of EPDM with thickness 2 mm is secured centrally by mechanical clamping, care being taken here to achieve full contact between EPDM and polyurethane without any gaps. The width of the EPDM strip is 1 cm, and there is therefore a residual uncovered polyurethane surface measuring 1.5 cm on both the left-hand and the right-hand side.

[0069] The EPDM (ethylene-propylene-diene)-monomer elastomer used is a compact, deep-black-colored, plasticized sealing material used in the automobile industry, with from 30 to 40% by weight content of naphtha-based plasticizers. The test sample is subjected to artificial aging for 2500 h in accordance with ASTM G155, cycle 7; the side of the test sample oriented toward the source of light/weathering here is that with the mechanically secure EPDM strip. Any cracking that may occur, caused by plasticizer migration and UV-weathering, is observed on the polyurethane surface alongside the EPDM on the left-hand and right-hand sides.

[0070] Sheets from the standard high-pressure RIM process from the machine experiments were likewise used prior to weathering for determination of Shore hardness values in accordance with DIN 53505.

Results:

[0071]

TABLE-US-00003 Comp. Inv. Inv. Comp. Inv. Comp. Property ex. 1 ex. 1 ex. 2 ex. 2 ex. 3 ex. 3 Shore A 85 88 88 86 77 76 hardness in Accordance with DIN 53505 Cracking yes no n.d. yes no yes