CA2088414C

CA2088414C - Process for preparing open cell, resilient, flexible polyurethane foams

Info

Publication number: CA2088414C
Application number: CA002088414A
Authority: CA
Inventors: Sven Meyer-Ahrens; Gundolf Jacobs; Hans Hettel
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1992-02-03
Filing date: 1993-01-29
Publication date: 2004-07-06
Anticipated expiration: 2013-01-29
Also published as: DE59307585D1; NO930181L; DK0554721T3; EP0554721B1; DE4202992A1; ATE159740T1; JPH05271379A; NO930181D0; NO302891B1; EP0554721A1; ES2108142T3; CA2088414A1

Abstract

Resilient polyurethane flexible foams of open cell structure are prepared by reacting a) polyisocyanates with b) a mixture containing 1. from 0.5 to 20 wt-% of a polyether comprising at least two hydroxyl groups having an oxyethylene group content greater than 50 wt-% and having an average molecular weight of from 400 to 10,000 and 2. from 99.5 to 80 wt-% of a compound produced by the addition of alkylene oxide to glycerol, optionally in mixture with ethylene glycol of an average molecular weight of from 400 to 10,000, and comprising a maximum of 20 wt-% oxyethylene groups, in the presence of c) water and optionally organic blowing agents, and d) catalysts, e) optionally, compounds having at least two hydrogen atoms capable of reacting with isocyanates, having molecular weights of from 32 to 399 and f) optionally, surface-active or flame-retardant additives and additional auxiliary substances, whereby the reaction is conducted in an index range of from 95 to 110.

Description

2~~84~4 Mo-3847 LeA 28 830-US
PROCESS FOR PREPARING OPEN CELL, RESILIENT, F~XIBLE POLYURETHANE FOAMS
BACKGROUND OF THE INVENTION
Flexible polyurethane foams are familiar in a wide range of upholstering material applications in the furniture and motor vehicle industries. Physical blowing agents, such as, e.g., monofluorotrichloromethane (R11) have been used to adjust the relationship between apparent density and compression stress value in the manner required for each field of to application. Such blowing agents do not increase the polyurea content of the polymer as does water. Many physical blowing agents which are currently known have considerable dis-advantages, such as potential to destroy ozone, greenhouse .
effect, combustibility or toxicity.
is An object of the present invention was therefore to adjust the compression stress value of flexible polyurethane foams (hot foams) in the desired way without using the physical blowing agents which have been used to date.
It is known that the compression stress value of a Zo flexible polyurethane foam can be reduced by reducing the isocyanate index. For example, if a compression stress value of 2.0 kPa is to be obtained with an apparent density of 23 kg/m3 (a specification which is widely used), it is necessary to reduce the isocyanate index from 107 to 92. As 25 can be seen from Examples A and C herein, however, reducing the index leads to an unacceptable loss in mechanical properties.
Another known method of reducing compression stress value consists of proportionally co-using polyethers having a high oxyethylene unit content (DE-OS 1 248 286). However, polyethylene glycols 3o frequently have high melting points which makes them difficult LeA 28 830-US

to process. In addition, their co-use in the quantities required to reduce hardness gives rise to problems in the foaming process (specifically, a tendency to form closed cells in the case of linear polyethers and unstable foam in the case of higher-function polyethers).
DESCRIPTION OF THE INVENTION
It has now surprisingly been found that it is possible to prepare open ceH
polyurethane foams of reduced hardness and good resilience if small quantities of oxyethylene-group-rich polyethers having oxyethylene group contents of more than 50% and functionalities at least two are co-used and an isocyanate index range of between 95 and 110 is simultaneously used. In this manner, the compression stress values can be reduced by more than 40% while still maintaining such values at an excellent level. In addition, foams of excellent resilience are produced.
A surprising observation in the comparison with Examples A and B
herein where a normal isocyanate index is used, is the fact that resilience is even further increased by use of the special polyether mixture according to the invention (Examples B and E). The prior art discloses that high quantities of water and low indices produce inelastic, or "tired" foams.
More particularly, the present invention is directed to a process for the preparation of resilient, flexible, open cell polyurethane foams comprising reacting a) polyisocyanates, b) a polyether mixture comprising:
1 ) from 5 to 10% by weight, based on 100% by weight of b) the polyether mixture, of a polyether i) having a molecular weight of from 3000 to 5000, ii) containing three hydroxyl groups, and iii) having an oxyethylene group content of more than 70% by weight, based on 100% by weight of alkylene oxide present in polyether b)1), and Mo3847 2) from 95 to 80% by weight, based on 100% by weight of b) the polyether mixture, of a polyether i) produced by the addition of one or more alkylene oxides to glycerol, ii) having a molecular weight of from 3000 to 5000, and iii) having an oxyethylene group content of 13% by weight or less, based upon 100% by weight of alkylene oxide present in polyether b)2), c) water, and optionally organic blowing agents, d) catalysts, e) optionally, compounds having at least two hydrogen atoms capable of reacting with isocyanate groups, and having molecular weights of from 32 to 399, and f) optionally, surface-active or flame-retardant additives, whereby the reaction is conducted in an isocyanate index range of from 95 to 110, and preferably from 98 to 100.
It is particularly preferred that anionic, cationic or nonionic emulsifying agents, and preferably alkane sulphonates as emulsifying agents, are used, and that water is used as blowing agent in a quantity of from 2 to 15 wt-%, based upon the amount of component b).
Substantially any isocyanates may be used in order to prepare the foams herein. Aliphatic, cycloaliphatic, aromatic and heterocyclic polyisocyanates, as described for example by Mo3847 _4_ W. Siefken in Justus Liebigs Annalen der Chemie, 562, pages 75 to 136 can be used. More specifically, isocyanates of the following formula are suitable herein:
Q(NCO)n s where n a 2 to 4, and preferably 2 t~ 3, and Q represents an aliphatic hydrocarbon radical having from 2 to 18 (and preferably from 6 to 10) carbon atoms, a cycloaliphatic hydrocarbon radical having from 4 to 15 (and preferably from 5 to 10) carbon atoms, an aromatic hydrocarbon radical having to from 6 to 15 (and preferably from 6 to 13) carbon atoms or an araliphatic hydrocarbon radical having from 8 to 15 (and preferably from 8 to 13) carbon atoms. Specific isocyanates are known in the art and are described, e.9., in German Offenlegungsschrift 2,832,253, pages 10 to 11. Particularly 1s preferred are aromatic polyisocyanates, and particularly the technically readily available aromatic polyisocyanates, e.g.
2,4- and 2,6-toluylene diisocyanate, and mixtures of such isomers ("TDI"); polyphenyl-polymethylene polyisocyanates, as prepared by condensing aniline with formaldehyde and subsequent 2o reaction with phosgene ("crude MDI"); and polyisocyanates containing carbodiimide groups, urethane groups, allophanate groups, isocyanurate groups, urea groups or biuret groups ("modified polyisocyanates"), especially such modified polyisocyanates as are derived from 2,4- and/or 2,6-toluylene 2s diisocyanate or 4,4'- and/or 2,4'-diphenylmethanediisocyanate, respectively.
Component b) comprises a mixture of 1. from 0.5 to 20 wt-% of a polyether containing at least two hydroxyl groups, having an oxyethylene so group content greater than 50 wt-% (calculated on total alkylene oxide), and having an average molecular weight of from 400 to 10,000; the polyether polyol contains predominant amounts of primary OH
groups; it is preferred that from 5 to 10 wt-% of a triol of an average molecular weight of from 3,000 to Mo3847 _5_ 5,000 and comprising more than 70 wt-% oxyethylene groups (calculated on total alkylene oxide) is used;
and 2. from 99.5 to 80 wt-% of a polyether produced by the addition of alkylene oxide to glycerol or a mixture of glycerol and ethylene glycol, having an average molecular weight of from 400 to 10,000, and preferably from 3,000 to 5,000, and comprising a maximum of 20 wt-% oxyethylene groups (calculated on to total alkylene oxide), preferably having an oxyethylene group content of up to 13 wt-%
(calculated on total alkylene oxide); this polyether contains predominant amounts of secondary OH groups;
Catalysts of the type known in the art in guantities of up 15 to 10 wt-%, based upon the amount of component b) are also used.
Compounds having at least two hydrogen atoms capable of reacting with isocyanate groups arid having molecular weights of from 32 to 399 are optionally used. These include compounds 2o containing hydroxyl groups and/or amino groups and/or thiol groups and/or carboxyl groups, preferably compounds containing hydroxyl groups and/or amino groups, which compounds serve to increase chain length or serve as cross-linking agents. The compounds generally contain from 2 to 8, and preferably from 2 25 to 4, hydrogen atoms which are capable of reacting with isocyanates. Examples of such compounds are described in German Offenlegungsschrift 2,832,253, pages 19 to 20.
Additional materials may also be included in the reaction mixture. Such materials include surface-active additives such 3o as emulsifying agents and foam stabilizers; porosity regulators of the type known in the art (such as paraffins or fatty alcohols or dimethyl polysiloxanes); pigments or dyes and flameproofing agents of the type known in the art, e.g.
trischloroethyi phosphate, triscresyl phosphate; stabilizers to guard against the effects of ageing and weathering;
Mo3847 21~884~4 plasticizers and substances having a fungistatic and bacteriostatic action; and fillers such as barium sulphate, diatomaceous earth, carbon black or prepared chalk. These additional substances and additives which may be added are described, for example, in German Offenlegungsschrift 2,732,292, pages 21 to 24. Further examples of surface-active additives and foam stabilizers, cell regulators, reaction retardants, stabilizers, flame-retardants, plasticizers, dyes and fillers, plus substances having fungistatic and io bacteriostatic action, any of which may also be used according to the invention, and details regarding the method of use and the mode of action of these additives are described in the Kunststoff-Handbuch (Manual of Plastics), Vol. VII, edited by Vieweg and Hbchtlen, and published by Carl-Hanser-Verlag, 15 Munich 1966, e.g. on pages 103 to 1I3.
According to the invention the reaction components are reacted by the one-shot process, the prepolymer process or the semi-prepolymer process, which processes are known in the art.
Mechanical equipment is frequently used, e.g. such as that 2o described in U.S. Patent 2,764,565. Details concerning processing equipment which may also be used for the invention, are described in the Kunststoff-Handbuch, Vol. VII, edited by Vieweg and Hochtlen, and published by Carl-Hanser-Verlag>
Munich 1966, e.g. on pages 121 to 205.
2s All components are reacted according to the invention at an isocyanate index of from 95 to 110, and preferably at an index of from 98 to 100. The isocyanate index, a concept which is frequently used in the preparation of polyurethane foams, is indicative of the degree of cross-linking of a foam. It is customary to regard a foam as having been produced at an index 30 of 100 if the actual quantity of isocyanate equivalents is equal to the theoretical quantity of isocyanate equivalents necessary to react with all the active hydrogens present. It is therefore possible with the aid of the index to define more Mo3847 2~~88~14 _,_ precisely the degree of under- or over-cross-linking. The index is calculated by the following general formula:
Index a isocyanate quantity (actual equivalents) isocyanate quantity (theoretical) x 100 The flexible polyurethane foams which may be obtained according to the invention find applications as, for example, furniture for reclining and for seating, and as seats in passenger vehicles and, automobiles.
1o The invention is further illustrated but is not intended to be limited by the following examples in which all parts and percentages are by weight unless otherwise specified.
EXAMPLES
In the examples, all the components listed below were mixed together intensively and expanded in a manner which is known per se.
Foams were prepared by the following handmix procedure:
200g of polyol were weighed together with all other ingredients 2o except isocyanate and tin catalyst in a papex cup and premixed with a Pendraulik 7~M 34 stirrer for 5 seconds at 3000 rpm.
After adding the required amount of tin catalyst and another 5 seconds of stirring the isocyanate is added under continously mixing . 8 seconds later the mixture is poured into a 12x12x25 cm open papex box.
When rising of the mixture has completed, the fresh foam is transferred to a microwave oven (Panasonic NE 1440) and cured for 25 3 minutes with an irradiation power of 340 W Afterwards the foam is cured for further 45 minutes in a conaentional oven at 110 Degr. Celsius.
Physical properties of the foams were determined 3 days after preparation.
Mo3847 2~D~8~~.4 _g_ Examples A B C
(control) (control) Polyol A 100 90 100 Polyol B 10 Water 4.5 4.5 4.5 Foam stabilizer 1.0 1.5 1.0 OS 20 (Bayer AG) Dimethylethanolamine 0.3 0.3 0.3 Tin(II)-octoate 0.2 0.2 0.35 TDI*) 54.2 54.1 46.4 io Isocyanate index 107 107 92 Apparent density (kgm 3) 23 23 23 1) Tensile strength (kPa) 2) 124 102 25 Elongation at break (%) 3) 214 165 54 Compression stress (kPa) 3.5 3.4 2.0 4) value (40%) DVR (90%a) (%) 5) 6.2 4.9 adheres Ball rebound resilience (%) 6) 42 44 39 *isomer mixture of 2,4- and 2,6-toluylenediisocya nate in an 80/20 weight ratio Test methods according to:

1 ) DIN 53420 2) DIN 53571 3) " ., 4) DIN 53577 5) DiN 53572 6) In house method:

2xH

30 according ~
The resilience is calculatedto the formula:

1 ()D

H is the return height of diameter;
a steel ball (14 mm 13.6 g weight) falling from a height of 50 cm on a foam (8 x 8 x 5 cm) sample.

20~~~14 _g_ Examples D E F
(control) Polyol A 100 90 90 Polyol 8 10 10 Water 4.5 4.5 4.5 Foam stabilizer 1.0 1.5 1.5 OS 20 (Bayer AG) Dimethylethanolamine 0.3 0.3 0.3 Tin(II)-octoate 0.28 0.24 0.22 TDI~) 47.9 47.8 49.4 Isocyanate index 95 95 98 Apparent density (kgm 3) 23 23 23 Tensile strength (kPa) 79 94 118 Elongation at break (%) 189 249 282 Compression stress (kPa) 2.7 2.0 2.6 val ue (40fo) DVR (90%) (%) 5.5 4.3 4.2 Ball rebound resilience (%) 40 46 44 Polyol A: adduct of PO/EO and a mixtureof glyceroland ethylene glycol having an oxyethyl ene contentof about 2o and having wt-%, predominantly secondary an OH (>97%) end groups average molecular weight of about3,500.

Polyol B: adduct of PO/E0 and glycerolcontainingabout 72 wt-oxyethylene groups, pred ominantlyprimary (85%)groupsand lar ,700.
having an average molecu weight of about Mo3847

Claims

1. A process for the preparation of resilient, flexible, open cell polyurethane foam comprising reacting:
a) one or more polyisocyanates, b) a polyether mixture comprising:
1) from 5 to 10% by weight, based on 100% by weight of b) said polyether mixture, of a polyether triol having a molecular weight of from 3000 to 5000 and containing more than 70% by weight of oxyethylene groups, based on 100% by weight of oxyalkylene groups present in said polyether b)1);
and

2) from 95 to 90% by weight, based on 100% by weight of said polyether mixture, of a polyether produced by the addition of one or more alkylene oxides to glycerol, having a molecular weight of 3000 to 5000, and containing no more than 13% by weight of oxyethylene groups, based on 100% by weight of oxyalkylene groups present in said polyether b)2);
c) water, d) catalysts, whereby the reaction is conducted in an isocyanate index range of from 95 to 110.

2. The process of Claim 1, wherein said isocyanate index range is from 98 to 100.

3. The process of Claim 1, wherein said reaction mixture additionally comprises one or more organic blowing agents.

4. The process of Claim 1, wherein the reaction mixture also contains emulsifying agents, and said water is used in a quantity of from 2 to wt-%, based upon the amount of component b).

5. The process of Claim 1 wherein e) compounds having at least two hydrogen atoms capable of reacting with isocyanates, having a molecular weight of from 32 to 399, are included in the reaction mixture.