POLYURETHANE FOAMS WITH REDUCED AROMATIC AMINE CONTENT

Abstract

Described herein is a process for producing polyurethane foams having a density of 30 g/dm.sup.3 to 70 g/dm.sup.3, in which (a) aromatic polyisocyanate is mixed with (b) polymeric compounds having isocyanate-reactive groups, (c) optionally chain extender and/or crosslinking agent, (d) catalyst, (e) blowing agent including water, (f) 0.1% to 5% by weight of lactam, and (g) optionally additives, at an isocyanate index of 50 to 95 to form a reaction mixture, and the reaction mixture is converted to the polyurethane foam, wherein the catalyst includes metal catalyst and amine catalyst, and the amine catalyst has tertiary nitrogen atoms and the content of tertiary nitrogen atoms in the amine catalyst is from 0.0001 to 0.003 mol/100 g of foam. Also described herein is a polyurethane foam and a method of using such a flexible polyurethane foam for the production of cushions, seat cushions, or mattresses.

Claims

1. A process for producing polyurethane foams having a density of 30 g/dm.sup.3 to 70 g/dm.sup.3, the process comprising mixing a) aromatic polyisocyanate, b) polymeric compounds having isocyanate-reactive groups, c) optionally chain extender and/or crosslinking agent, d) catalyst, e) blowing agent comprising water, f) 0.1% to 5% by weight of lactam, based on the total weight of components (a) to (f), and g) optionally additives, at an isocyanate index of 50 to 95 to form a reaction mixture, and converting the reaction mixture to a flexible polyurethane foam, wherein the catalyst comprises metal catalyst and amine catalyst, and the amine catalyst has tertiary nitrogen atoms and is used in such an amount that a content of tertiary nitrogen atoms in the amine catalyst, based on the weight of starting components (a) to (f), is from 0.0001 to 0.003 mol/100 g of foam.

2. The process according to claim 1, wherein the amine catalyst has a reactivity of at least 5%, based on 1,4-diazabicyclo[2.2.2]octane.

3. The process according to claim 1, wherein the catalysts are used in amounts such that the polyurethane reaction mixture has a rise time of 30 to 150 seconds.

4. The process according to claim 1, wherein a content of water, based on components (b) to (f), is 1% to 5% by weight.

5. The process according to claim 1, wherein no further blowing agents other than water are present.

6. The process according to claim 1, wherein the lactam (f) is ε-caprolactam.

7. The process according to claim 1, wherein the amine catalyst has at least one isocyanate-reactive group.

8. The process according to claim 1, wherein the amine catalyst has two tertiary nitrogen atoms.

9. The process according to claim 1, wherein the tertiary nitrogen atoms of the amine catalyst have at least one methylene radical H.sub.3C— or ethylene radical H.sub.3C—H.sub.2C—.

10. The process according to claim 1, wherein the amine catalyst is selected from the group consisting of bisdimethylaminopropylurea, bis(N,N-dimethylaminoethoxyethyl)carbamate, dimethylaminopropylurea, N,N,N-trimethyl-N-hydroxyethylbis(aminopropyl ether), N,N,N-trimethyl-N-hydroxyethylbis(aminoethyl ether), diethylethanolamine, bis(N,N-dimethyl-3-aminopropyl)amine, dimethylaminopropylamine, 3-dimethylaminopropyl-N,N-dimethylpropane-1,3-diamine, dimethyl-2-(2-aminoethoxyethanol) and (1,3-bis(dimethylamino)propan-2-ol), N,N-bis(3-dimethylaminopropyl)-N-isopropanolamine, bis(dimethylaminopropyl)-2-hydroxyethylamine, N,N,N-trimethyl-N-(3 aminopropyl)bis(aminoethyl ether), 3-dimethylaminoisopropyldiisopropanolamine, N-[2-[2-(dimethylamino)ethoxy]ethyl]-N-methyl-1,3-propanediamine, and mixtures thereof.

11. The process according to claim 1, wherein the metal catalyst is a tin(IV) catalyst.

12. The process according to claim 1, wherein the aromatic polyisocyanate comprises isomers and homologs of diphenylmethane diisocyanate.

13. The process according to claim 1, wherein, for the preparation of the reaction mixture, an isocyanate component (A), comprising aromatic polyisocyanate (a), and a polyol component (B), comprising a mixture comprising polymeric compounds having isocyanate-reactive groups (b), catalyst (d), and blowing agent comprising water (e), are mixed.

14. The process according to claim 1, wherein the reaction mixture is converted to the flexible polyurethane foam in a mold.

15. A polyurethane foam obtainable by the process according to claim 1.

16. A method of using the polyurethane foam according to claim 15, the method comprising using the polyurethane foam for the production of cushions, seat cushions, or mattresses.

Description

[0035] The invention shall be elucidated hereinbelow with reference to examples:

[0036] The following feedstocks were used to produce the polyurethane foams of the examples: [0037] Polyol 1: A glycerol-started polyoxypropylene-polyoxyethylene having a polyoxyethylene content of 13% by weight based on the alkylene oxide content, a hydroxyl number of 28 mg KOH/g and predominantly primary hydroxyl groups. [0038] Polyol 2: Polymer polyol based on styrene and acrylonitrile in a ratio of 2:1, solids content 44% by weight and a hydroxyl number of 20 mg KOH/g. [0039] Polyol 3: Glycerol-started polyoxypropylene-polyoxyethylene having a polyoxyethylene content, based on the alkylene oxide content, of 74% by weight and a hydroxyl number of 42 mg KOH/g. [0040] Polyol 4: Propylene glycol-started propoxylate having an OH number of 55. [0041] Polyol 5: Glycerol-started polyoxypropylene-polyoxyethylene having a polyoxyethylene content of 14% by weight based on the alkylene oxide content and a hydroxyl number of 30 mg KOH/g. [0042] Polyol 5: Polyoxypropylene-polyoxyethylene started with a mixture of glycerol and diethylene glycol (74 to 26 parts by weight) and having a polyoxyethylene content, based on the alkylene oxide content, of 10% by weight and a hydroxyl number of 48 mg KOH/g. [0043] Polyol 6: Glycerol-started polyoxypropylene having a hydroxyl number of 42 mg KOH/g. [0044] Catalyst 1: 33% by weight solution of triethylenediamine in dipropylene glycol. [0045] Catalyst 2: Incorporable, tertiary amine catalyst from Evonik, obtainable under the trade name Dabco®NE 300 (N-[2-[2-(dimethylamino)ethoxy]ethyl]-N-methyl-1,3-propanediamine). [0046] Catalyst 3: N,N-Dimethyl-N′,N′-di(2-hydroxypropyI)-1,3-propanediamine, available from Huntsman under the trade name Jeffcat®DPA. [0047] Catalyst 4: 3-(Dimethylamino)propylamine-started polyoxypropylene having a polyoxypropylene content of 77% by weight and a hydroxyl number of 250 mg KOH/g. [0048] Catalyst 5: 3-(Dimethylamino)propylamine. [0049] Catalyst 6: 1,4-Diazabicyclo[2.2.2]octane (25%) in butane-1,4-diol (75%). [0050] Catalyst 7: Dabco® 2025 amine catalyst from EVONIK (formerly Air Products). [0051] Catalyst 8: Diethanolamine. [0052] Catalyst 9: Hydroxymethyltriethylenediamine (66.7% by weight) in dipropylene glycol. [0053] Catalyst 10: N-[2-[2-(Dimethylamino)ethoxy]ethyl]-N-methyl-1,3-propanediamine (available from Evonik under the trade name Dabco NE 300). [0054] Catalyst 11: N-(3-Dimethylaminopropyl)-N,N-diisopropanolamine (available from Huntsman under the trade name Jeffcat®DPA). [0055] Catalyst 12: 10% by weight solution of dimethyltin dineodecanoate in polyol 1, available under the trade name Fomrez®UL 28; PU catalyst from Momentive. [0056] Catalyst 13: Zinc complex available from King Industries under the trade name K-Kat XK-614. [0057] Isocyanate 1: Mixture of MDI and higher polycyclic homologs of MDI having a viscosity at 25° C. of 210 mPas and an NCO content of 31.5% by weight. [0058] Isocyanate 2: Mixture of 49 parts by weight of 4,4′-MDI, 48.6 parts by weight of 2,4′-MDI and 2.4 parts by weight of 2,2′-MDI; the NCO content is 33.5% by weight. [0059] Isocyanate 3: Monomeric 4,4′-MDI having an NCO content of 33.5% by weight. Stabilizer: Low-emission silicone stabilizer. [0060] Scavenger: Dodecylsuccinic anhydride.

[0061] Proceeding from the starting materials given in table 1, test panels with dimensions of 18.5×19.5×3.8 cm were produced in a closed mold. This involved preparing a polyol component according to the compositions given in the tables, mixing said polyol component with the specified isocyanate component at the specified isocyanate index in a high-pressure mixing head at 35° C., and placing this mixture into the mold heated to 60° C. The amounts of the feedstocks are based on the parts by weight in percent, the content of tertiary nitrogen per 100 g of foam is given in mol/100 g of foam and the MDA concentration is given in ppm. Only compounds having a relative reactivity, based on triethylenediamine, of at least 5% were included for the calculation of the content of tertiary nitrogen. The molding was removed from the mold after 5 minutes; the density was approx. 50 g/dm.sup.3.

TABLE-US-00001 TABLE 1 Comparison Comparison Comparison Comparison Comparison 1 2 3 4 5 Polyol component Polyol 1 64.85 64.22 64.22 63.60 63.35 Polyol 2 15.00 15.00 15.00 15.00 15.00 Polyol 3 14.00 14.00 14.00 14.00 14.00 Catalyst 1 0.10 0.10 0.10 0.10 0.10 Catalyst 2 0.10 0.10 0.10 0.10 0.10 Catalyst 3 1.00 1.00 1.00 1.00 1.00 Catalyst 4 1.00 1.00 1.00 1.00 1.00 Catalyst 12 — — — — — ε-caprolactam 0.00 0.31 0.63 1.25 1.50 Stabilizer 0.50 0.50 0.50 0.50 0.50 Water 3.45 3.45 3.45 3.45 3.45 Isocyanate component Isocyanate 1 37.5 37.5 37.5 37.5 37.5 Isocyanate 2 42.1 42.1 42.1 42.1 42.1 Isocyanate 3 20.4 20.4 20.4 20.4 20.4 Index 75.0 75.0 75.0 75.0 75.0 2,4’-MDA 87 77 70 57 32 4,4’-MDA 6 5 4 3 <1 Tertiary nitrogen 0.021 0.021 0.021 0.021 0.021 content/100 g of foam Comparison Example Comparison Example Comparison Example 6 1 7 2 8 3 Polyol component Polyol 1 62.35 65.85 Polyol 2 15.00 15.00 32 32 Polyol 3 14.00 14.00 78 76.5 4.8 4.8 Polyol 4 — — 16 16 Polyol 5 2 2 58.05 58.10 Catalyst 1 0.10 — 0.4 Catalyst 2 0.10 0.10 0.2 0.2 Catalyst 3 1.00 — Catalyst 4 1.00 Catalysts 0.1 0.25 Catalyst 6 0.45 Catalyst 7 0.25 Catalyst 8 0.2 0.2 Catalyst 12 — 0.10 0.3 0.3 Dodecylsuccinic 2.50 — anhydride ε-caprolactam 1.50 1.50 0.5 Stabilizer 0.50 0.50 0.02 0.02 0.4 0.4 Water 3.45 3.45 3.5 3.5 3.55 3.55 Isocyanate component Isocyanate 1 37.5 37.5 20 20 40 40 Isocyanate 2 42.1 42.1 80 80 50 50 Isocyanate 3 20.4 20.4 10 10 Index 75.0 75.0 75 75 2,4-MDA 3 <1 2,4’-MDA 49 <1 18 <1 24 <1 4,4’-MDA 2 <1 <1 <1 3 <1 Tertiary nitrogen 0.021 0.00066 0.0043 0.00066 0.003 + 0.0013 content/100 g of x(Dabco foam 2025)

[0062] Further polyurethane foams were produced in accordance with table 2 in an analogous process and the mechanical properties were also ascertained in addition to the MDA content. These are also given in table 2. In comparative experiment 10 and example 8, an isocyanate prepolymer was respectively used which had been obtained from the components specified.

TABLE-US-00002 TABLE 2 Polyol Comparison Example Example Example Example Comparison Example component 9 4 5 6 7 10 8 Polyol 1 64.85 63.85 66.25 65.15 65.05 76.6 76.6 Polyol 2 15.00 15.00 15.00 15.00 15.00 15 15 Polyol 3 14.00 14.00 14.00 14.00 14.00 2 2 Catalyst 1 0.10 — — — — 0.1 Catalyst 2 0.10 0.10 0.10 0.10 0.20 Catalyst 3 1.00 — — — — Catalyst 4 1.00 1.0 Catalyst 9 0.2 Catalyst 10 0.1 0.2 Catalyst 11 1 Catalyst 12 — 0.10 0.20 0.30 0.30 Catalyst 13 0.3 ε-caprolactam — 3.00 1.50 1.50 1.50 1.5 Stabilizer 0.50 0.50 0.50 0.50 0.50 0.7 0.7 Water 3.45 3.45 3.45 3.45 3.45 3.5 3.5 Isocyanate 14.00 14.00 14.00 14.00 14.00 component Isocyanate 1 37.5 37.5 37.5 37.5 37.5 36 36 Isocyanate 2 42.1 42.1 42.1 42.1 42.1 32 32 Isocyanate 3 20.4 20.4 20.4 20.4 20.4 20 20 Polyol 3 2 2 Polyol 6 10 10 Index 70.0 70.0 70.0 70.0 70.0 70 70 Cream time 14 22 22 21 16 12 12 [s] Gel time [s] 53 104 104 93 70 51 49 Rise time [s] 76 145 145 135 100 72 70 2,2′-MDA 6 1 2,4’-MDA 96 <1 <1 <1 <1 78 2 4,4’-MDA 7 <1 <1 <1 <1 5 <1 Tertiary 0.021 0.00066 0.00066 0.00066 0.0013 0.0072 0.0013 nitrogen content/100 g of foam

TABLE-US-00003 TABLE 3 lists the mechanical properties that were ascertained for the foams of comparative example 8 and examples 2 to 5. Comparison Example Example Example Example Comparison Example 7 4 5 6 7 8 10 Compression hardness 40% [kPa] 4.1 6.4 6.4 5.0 4.9 3.9 3.6 Compression hardness 65% [kPa] 9.2 14.3 14.3 11.0 10.7 8.8 8.1 Hysteresis at 70% compression [%] 24.0 27.7 27.7 23.0 23.4 n.d. n.d. Density [kg/m.sup.3] 55.3 56.4 56.4 50.6 51.0 55.2 55.2 Compression set at 50% compression [%] 9.5 5.8 5.8 6.2 6.5 9.5 11.7 Compression set at 75% compression [%] 62.8 7.1 7.1 7.3 7.8 n.d. n.d. Compression set at 90% compression [%] 83.2 57.5 57.5 64.9 76.3 n.d. n.d. Tensile strength [kPa] 90 107 107 117 122 92 80 Elongation at break [%] 99 106 106 107 109 95 97 Air permeability [dm.sup.3/s] 0.349 0.901 0.901 0.477 0.410 Closed index open-cell celled Rebound resilience [%] 54 52 52 58 58 54 48 Tear propagation resistance [N/mm] 0.37 0.52 0.52 0.42 0.41 0.40 0.35 Compression set after autoclave aging (50% 55.0 10.1 10.1 12.3 11.3 44.1 27.4 compression/5 h/120° C., 3 cycles) [%] Formaldehyde emission [μg/m.sup.3] 726 n.d. n.d. n.d. 341 n.d. n.d. Acetaldehyde emission [μg/m.sup.3] 140 n.d. n.d. n.d. 60 n.d. n.d. FOG* [ppm] 259 n.d. n.d. n.d. 109 n.d. n.d. *measured according to the instructions for determining the emission values. n.d. = not determined

[0063] Table 3 shows that use of the catalysts according to the invention brings about in some cases considerable improvements in the measured mechanical properties. Improvements are seen, with comparable density of the foams, in the compression sets, measured at 50, 75 and 90% deformation, the open-cell content (measured as air permeability) and in particular and surprisingly the compression set after autoclave aging (50% compression/5 h/120° C., 3 cycles). These values were determined as follows:

TABLE-US-00004 Mechanical testing Method Compression hardness at 25%, 40% and 65% DIN EN ISO 3386 compression Hysteresis at 70% compression DIN EN ISO 3386 Density DIN EN ISO 845 Compression set (22 h/70° C./50% compression) DIN EN ISO 1856 Compression set after autoclave aging In accordance with DIN ISO 1856, after 5 h of storage in an autoclave at 120 degrees Celsius and 50% compression (3 cycles). Tensile strength DIN EN ISO 1798 Elongation at break DIN EN ISO 1798 Tear propagation resistance (Graves with notch) DIN EN ISO 34-1,B (b) Rebound resilience DIN EN ISO 8307

[0064] Emission Values:

[0065] The foam specimens from comparative example 8 and example 9 were analyzed using the chamber method followed by HPLC. Formaldehyde was determined by a procedure analogous to ASTM D-5116-06. The chamber size was 4.7 liters. The polyurethane specimens used were foams having a size of 110 mm×100 mm×25 mm from the core of the foam. The temperature in the measuring chamber during the measurement was 65° C., the relative humidity 50%. The air change rate was 3.0 liters per hour. The exhaust air stream comprising volatile aldehydes from the polyurethane was passed through a cartridge comprising silica coated with 2,4-dinitrophenylhydrazine over 120 minutes. The DNPH cartridge was then eluted with a mixture of acetonitrile and water. The concentration of formaldehyde in the eluate was determined by HPLC. In this setup the limit of detection for formaldehyde emissions is ≤11 μg/m.sup.3.

[0066] In the context of the present invention, the content of aromatic amines was determined as follows:

[0067] The concentration of aromatic amines was determined on moldings made from molded flexible polyurethane foam in accordance with the ISOPA I.I.I. test method: detection method for MDA (ISOPA I.I.I. ref. 11399, “Robust method for the determination of the diaminodiphenylmethane content of flexible polyurethane foams”). To this end, the specimens were sawn after production and immediately packed in aluminum foil and a plastic bag. The duration between demolding and packaging was 30 min.

[0068] The surface of the molded foam was cut off in the form of panels having a thickness of 0.5 cm. Specimens measuring 3 cm×3 cm each were cut out from these panels and stacked together to form a cube of 3×3×3 cm and measured. The flexible foam cube was placed in a beaker with 10 ml of 1% acetic acid (given in % by mass). The cube was squeezed out twenty times using a ram (approx. 4 cm diameter) and the solution was transferred into a 50 ml flask. The compaction process was then repeated twice with 10 ml of 1% acetic acid each time, this acetic acid also being transferred into the flask after the compaction process. After combining the extracts obtained, the mixture was made up to 50 ml with 1% acetic acid. This solution was filtered through a 0.45 μm filter for preparation for the HPLC analysis. A double determination was carried out in all cases. The MDA contents are given in ppm.