Viscoelastic polyurethane foams
Flexible polyurethane foams having high airflows and excellent viscoelastic properties are made using a polyol mixture that includes a certain liquid polyester, certain ethylene oxide polyols and certain propylene oxide polyols, and a polymeric MDI. When used in applications such as bedding, the high airflows contribute to an improved sense of comfort by the user.
1. A flexible polyurethane foam comprising a reaction product of a reaction mixture that comprises
a) a polyol mixture that comprises
i) 45 to 80 weight-%, based on the weight of the polyol mixture, of an ethylene oxide copolymer containing 45 to 70% by weight polymerized ethylene oxide based on the total weight of the ethylene oxide copolymer, or mixture of two or more thereof, the ethylene oxide copolymer or mixture thereof having a number average hydroxyl functionality of 2 to 4 and an average hydroxyl equivalent weight of 175 to 600;
ii) 10 to 30 weight-%, based on the weight of the polyol mixture, of a propylene oxide polymer containing at least 70% by weight polymerized propylene oxide based on the total weight of the propylene oxide polymer, a hydroxyl functionality of 2 to 4 and a hydroxyl equivalent weight of greater than 500 to 2000, or mixture of two or more thereof, and
iii) 5 to 29 weight-%, based on the weight of the polyol mixture, of a liquid polyester polyol having a hydroxyl functionality of 2 to 4 and a hydroxyl equivalent weight of 175 to 900 with the proviso that the hydroxyl equivalent weight is 175 to 600 when the polyester polyol is a polycaprolactone, or a mixture of two or more thereof;
b) water in an amount of 1 to 4 parts by weight per 100 parts by weight of the polyol mixture;
c) an aromatic polyisocyanate that comprises polymeric diphenylmethane isocyanate (MDI), in an amount sufficient to provide an isocyanate index of 50 to 120;
d) at least one urethane catalyst and
e) at least one foam-stabilizing surfactant.
2. The flexible polyurethane foam of claim 1 wherein the polyester polyol is selected from polyester polyols corresponding to a condensation product of one or more of ethanediol, 1,2-propanediol, 1,3-propanediol, glycerol, trimethylolpropane, 1,6-hexanediol, 1,2,6-hexanetriol, butenediol, sucrose, glucose, sorbitol, pentaerythritol, mannitol, triethanolamine, N-methyldiethanolamine with one or more of maleic acid, fumaric acid, 1,6-hexanedioic acid, dodecanedioic acid, azelaic acid, sebacic acid, adipic acid, 1,18-octadecanedioic acid, phthalic acid, terephthalic acid and succinic acid.
3. The flexible polyurethane foam of claim 2 wherein the polyester polyol is selected from the group consisting of diethylene glycol-phthalic acid polyols, diethylene glycol-adipic acid polyols and diethylene glycol/trimethylolpropane-adipic acid polyols.
4. The flexible polyurethane foam of claim 1 wherein the polyester polyol the a polycaprolactone.
5. The flexible polyurethane foam of claim 1 wherein the polyester polyol has a hydroxyl equivalent weight of up to 400.
6. The flexible polyurethane foam of claim 1 wherein the polyol mixture further comprises iv) 5 to 20 weight percent, based on the weight of the polyol mixture, of one or more propylene oxide homopolymers or copolymers containing at least 70% by weight polymerized propylene oxide based on the weight of the copolymer, the propylene oxide homopolymer or copolymer having a hydroxyl equivalent weight of 175 to 600 and a hydroxyl functionality of 2 to 8.
7. A method of making a flexible polyurethane foam, comprising
A. forming a reaction mixture by mixing at least the following components:
a) a polyol mixture that comprises
i) 45 to 80 weight-%, based on the weight of the polyol mixture, of an ethylene oxide copolymer containing 45 to 70% by weight polymerized ethylene oxide based on the total weight of the ethylene oxide copolymer, or mixture of two or more thereof, the ethylene oxide copolymer or mixture thereof having a number average hydroxyl functionality of 2 to 4 and an average hydroxyl equivalent weight of 175 to 600;
ii) 10 to 30 weight-%, based on the weight of the polyol mixture, of a propylene oxide polymer containing at least 70% by weight polymerized propylene oxide based on the total weight of the propylene oxide polymer, a hydroxyl functionality of 2 to 4 and an average hydroxyl equivalent weight of greater than 500 to 2000, or mixture of two or more thereof, and
iii) 5 to 29 weight-%, based on the weight of the polyol mixture, of a liquid polyester polyol having a hydroxyl functionality of 2 to 4 and a hydroxyl equivalent weight of 175 to 900 with the proviso that the hydroxyl equivalent weight is 175 to 600 when the polyester polyol is a polycaprolactone, or a mixture of two or more thereof;
b) water in an amount of 1 to 4 parts by weight per 100 parts by weight of the polyol mixture;
c) an aromatic polyisocyanate that comprises polymeric diphenylmethane isocyanate (MDI), in an amount sufficient to provide an isocyanate index of 50 to 120;
d) at least one urethane catalyst and
e) at least one foam-stabilizing surfactant,
and
B. subjecting the reaction mixture formed in step A. to conditions at which the reaction mixture reacts to form the flexible polyurethane foam.
8. A flexible polyurethane foam made in accordance with claim 7 .
9. The flexible polyurethane foam of claim 8 which has an airflow of at least 2.6 L/s as measured according to ASTM D3574.
10. The flexible polyurethane foam of claim 9 which has a density of 40 to 80 kg/m 3 as measured according to ASTM D3574.
11. The flexible polyurethane foam of claim 10 which has resiliency of 10% or less as measured according to ASTM D3574.
12. The flexible polyurethane foam of claim 11 which has recovery time of at least one second.
13. A cushion comprising a flexible polyurethane foam of claim 1 .
14. The cushion of claim 13 , which is a pillow, mattress topper, mattress, comforter, furniture seat or back, automotive seat or back; quilt or article of insulated clothing.