CA2026033A1

CA2026033A1 - Process for the preparation of heat curable flexible molded polyurethane foams

Info

Publication number: CA2026033A1
Application number: CA002026033A
Authority: CA
Inventors: Martin Brock
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1989-10-12
Filing date: 1990-09-24
Publication date: 1991-04-13
Also published as: EP0422471A2; DE59004885D1; ES2050325T3; EP0422471B1; DE3934098C1; EP0422471A3; JPH03152118A; ATE102636T1

Abstract

PROCESS FOR THE PREPARATION OF HEAT CURABLE
FLEXIBLE MOLDED POLYURETHANE FOAMS
ABSTRACT OF THE DISCLOSURE
The present invention relates to a process for the preparation of heat curable flexible molded polyurethane foams comprising reacting in a closed mold (a) polyisocyanates of the diphenylmethane diisocyanate type containing no more than 80%
by weight of monomeric diphenylmethane diisocyanate as the 4,4'-isomer, with (b) compounds containing at least two isocyanate-reactive hydrogen atoms and having a molecular weight of from 400 to about 10,000, and, optionally, (c) chain lengthening and/or crosslinking agents containing at least two isocyanate-reactive hydrogen atoms and having a molecular weight of from 32 to 399, in the presence of (d) water as blowing agent.

Description

2~2~
M~3463 PROCESS FOR THE PREPARATION OF HEAT CURABLE - -FLEXIBLE MOLDED POLYURETHANE FOAMS

BACKGROUND OF THE INVENTION
Heat curable nexib]e pol~urethane that means hot molded or slabstock foams are widely used, inter alia, for the manufacture of seating upholstery, back rests, and head rests in the automotive and f urn i ture i ndustr i es .
Products having widely differing physical properties, such as gross density and cDmpression resistance, must be produced for the different uses. The wide product spectrum has previously been encompassed entirely by reaction products of toluene diisocyanates with polyether or polyester polyols, chemical and physical blowing agents, and, optionally, other auxiliary agents (for example, catalysts, stabilizers, emulsifiers, and crosslinking agents).
It has now surprisingly been found that isocyanates of the diphenylmethane diisocyanate ("MDI") type may also be I - -usefull~ employed in the preparation of heat curable foams. MDI
has previousl~ been used onl~ for the preparation ol high resilient or cold ~ ~-~; 20 molded foams or under extreme conditions.
- ~ The process of the invention now enables high quality foams to be produced with the aid of special polyisocyanates based on MDI. Foaming can be carried out using conventional ` formulations used for the preparation of heat curable flexible foams.
SUMMARY OF THE INVEN~JON
The present invention relates to a process for the preparation of heat curable flexible polyurethane foams compri s i ng react i ng (a) polyisocyanates of the diphenylmethane diisocyanate type ~ ~ containing no more than 80% by weight of monomeric - diphenylmethane diisocyanate as the 4,4'-isomer, ; ~ wi th ; ~j,75~S~

2 2 ~
(b) compounds containing at least two isocyanate-reactive hydrogen atoms and having a molecular weight of from 400 to about 10,000, and, optionally, (c) chain lengthening and/or crosslink.ing agents containing at least two ;socyanate-reactive hydrogen atoms and having a molecular weight of from 32 to 399, in the presence of (d) water as blowing agent, and, optionally, (e) other blowing agents, catalysts, and other known auxiliary o agents and addit~ves.
DETAIL~D DESCRIPTION OF THE INVENTION

The isocyanates used according to 1he inven~on (component a)) contain generally from about 1 to about 80% b.w., preferably from about 5 - 70% b.w.,more preferably from about 10 - 65% b.w. of 4,4'-diisocyanato diphenylmethane.
Preferred polyisocyanates (a) include monomeric diphenylmethane diisocyanates containing at least 2%byweight (preferably at least lOX by weight and more preferably at least 25% by weight) of the 2,4'-isomer. It is also preferred to use ~ -toluene diisocyanate ("TDI") in addition to polyisocyanate (a) and to use divalent and/or higher valent organometallic compounds (preferably tin(II) salts of higher carboxylic acids) as crosslinking catalysts.
The flexible polyurethane foams prepared according to the invention have numerous unexpected advantages.
First, such foams are distinguished by their excellent recovery from pressure deformation. This physical property is particularly important with respect to the quality of products used for seating upholstery and cushions.
Furthermore, it has been found that when a polyisocyanaté (a) according to the invention is mixed with TDI, the rigidity of the foams is significantly affected. This effect may be an advantage for the preparation of foams having regions of differing hardness. It has previously been necessary to prepare such foams by adding polyethers as fillers. The polyether fillers may, however, give rise to processing problems because of their high viscosity and high reactivity. The addition of MDI provides a comparatively simple procedure that does not suffer from such problems.
Mo3463 2~2~`3 Processing polyisocyanates according to the invention has the further advantage of increasing the useful range of isocyanate indexes to about 80 to 120. In the preparation of ~exiblefoams, the indexes have in practice previously been limited to about 100 (~ 4). Deviations from this value gave rise to production problems and, therefore, increased cost.
The increased range of indexes obtained by using MDI according to the invention provides for greater processing reliability.
Moreover, the rigidity of the foams may be influenced by varying the index, thereby providing an enormous technical advantage for the preparation of products having varying degrees of rigidity.
The following starting components are used according to the invention for the production of the heat curable flexible - polyurethane foams. ~-Suitable polyisocyanates (a) of the diphenylmethane diisocyanate type include monomeric diphenylmethane diiso-cyanate ("MDI") containing no more than 80% by weight of the 4,4'-isomer and preferably ccntaining at least 2 % by weight of 20..... the 2,4'-isomer (advantageously at least 107O by weight or more preferably at least 25% by weight of the 2,4'-isomer);
polyphenylpolymethylene polyisocyanates (obtained by aniline-formaldehyde condensation followed by phosgenation and known as "crude MDI"); polyisocyanates of the diphenylmethane diiso-cyanate type modified by carbodiimide groups, urethane groups, allophanate groups, isocyanurate groups, urea groups, or biuret groups; and alkyl substituted MDI derivatives in which the monomeric diphenylmethane diisocyanate has the composition indicated above.
The listed isocyanate type can also be used as a prepolyrner or as any rnixture of prepolyerised MDI and non-prepolymerised MDI.
It is particular1y advantageous to use such MDI polyisocyanates as rnixtures with toluene diisocyanate ("TDI") containing TDI in arnounts of up to 98% by weight (preferably up to 80% by weight) based on the total mixture of isocyanates.
Forms of TDI that can be used include toluene diisocyanate as a mixture of the 2,4- and 2,6-isomers in a ratio of 80:20 ("~
Mo3463 - 2~2~a33 80"); toluene diisocyanate as a mixture of the 2,4- and 2,6-isomers in a ratio of 65:35 ("T 65"); and toluene diisocyanate as a prepolymer.
Suitable compounds containing at least two isocyanate-reactive hydrogen atoms and having a molecular weight of from 400 to about 10,000 include not only compounds containing amino groups, thiol groups, or carboxyl groups but preferably also compounds containing hydroxyl groups (in particular two to eight hydroxyl groups), especially those lo compounds having molecular weights of from about 1000 to about 6000 (preferably from 2000 to 6000). Examples of such compounds include polyethers, polyesters, polycarbonates, and polyester amides containing at least two (generally two to eight and preferably 2 to 6) hydroxyl groups, such as the compounds known for the preparation of both homogeneous and cellular polyurethanes and described, for example, in German Offenlegungsschrift 2,832,253, pages 11-18. These isocyanate-reactive compounds preferably have OH numbers of from 28 to 80.
The optional compounds containing at least two isocyanate-reactive hydrogen atoms and having a molecular weight of from 32 to 399 include, as above, compounds containing hydroxyl groups, amino groups, thiol groups, and/or carboxyl groups (preferably hydroxyl groups and/or amino groups) and serve as chain lengthening agents or crosslinking agents. These compounds generally have from 2 to 8 (preferably 2 to 4) isocyanate-reactive hydrogen atoms. Examples are described in German Offenlegungsschrift 2,832,253, pages 10-20.
Water is used as blowing agent in a quantity of from about 1 to about 15 parts by weight (preferably 3 to 5 parts by weight) per 100 parts by weight of the "basic pclyol" component (b)-Optional auxiliary agents and additives include (i) readily volatile organic substances as additional blowing agents, (ii) known reaction accelerators (i.e., catalysts) and reaction retarders in the usual quantities, and (iii) surface-Mo3463 2g~2~3 active additives such as emulsifiers and foam stabilizers, as well as known cell regulators (such as paraffins, fatty alcohcls, dimethyl polysiloxanes), pigments, dyes, known flame-retardants (such as tris(chloroethyl) phosphate or tricresyl phosphate), stabilizers against ageing and weathering, plasticizers, fungistatic and bacteriostatic substances, and fillers (such as barium sulfate, kieselguhr, carbon black or whiting). These optional auxiliary agents and additives have been described, for example, in German o Offenlegungsschrift 2,732,292, pages 21-24. Other examples of optionally used surface-active additives and foam stabilizers, such as cell regulators, reaction retarders, stabilizers, flame retardants, plasticizers, dyes, fillers, and fungistatic and bacteriostatic substances, as well as details concerning the use and mode of action of these additives, may be found in Kunststoff-Handbuch, Volume VII, published by Vieweg and Hochtlen, Carl-Hanser-Verlag (Munich, 1966), for example, on pages 103-113.
Among the particularly preferred auxiliary agents and additives are crosslinking catalysts, such as divalent and/or higher valent organometallic compounds. Suitable organo-metallic crosslinking catalysts include tin(II) salts of higher carboxylic acids (preferably C8 20 alkanoic acids), such as tin(II) octoate, tin(II) ethylhexoate, and tin(II) laurate.
When carrying out the process according to the invention, the components are reacted together by the known (preferred) one-shot process, the prepolymer process, or the semiprepolymer process. It is often possible to use mechanical devices such as, for example, those described in U.S. Patent 2,764,565. Details concerning processing apparatus suitable for the purpose of this invention are given in Kunststoff-Handbuch, Volume VII, published by Vieweg and Hachtlen, Carl-Hanser-Verlag (Munich, 1966), for example, on pages 121-205.
In the process according to the invention, all the components are generally reacted together at an isocyanate Mo3463 ~ ; " -: 292~33 index of from 80-120. The isocyanate index, a term frequently used in connection with the preparation of polyurethane foams, gives an indication of the degree of crosslinking of a foam.
It is customary to consider a foam as having an index of 100 if it has been prepared with the stoichiometric or theoretically required quantity of ;socyanate. The index may thus be used to define the degree of under-crosslinking or over-crosslinking.
The isocyanate index is calculated from the following formula:
o Isocyanate index s Quantitv of isocYanate (actual) x 100 Quantity of isocyanate (theoretical) The preparation of flexible polyurethane foams is hlown (see Kunststoff-Handbuch, Volume 7, polyurethane foams is known (see Kunststoff-Handbuch, Volume 7, "Polyurethane", by Gunter Oertel, Carl-Hanser-Verlag, Munich (Vienna, 1983), in particular the chapter entitled "Weichelastische PUR-Formschaumstoffe" ("Flexible Elastic PUR
Molded Foams") on pages 212-235.
Foaming according to the invention is carried out preferab~ in closed molds. The reaction mixture is introduced into a mold made of a metal, such as aluminum, or a synthetic resin, such as an epoxide resin. The foamable reaction mixture foams up inside the mold to form the molded product. The process of the invention may be carried out either by introducing just enough foamable reaction mixture to fill the mold with foam or by introducing a larger quantity of reaction mixture into the mold. The latter procedure is known as overcharging, and has been described, for example, in U.S. Patents 3,178,490 and 3,182,104.
The heat curable flexible molded polyurethane foams ob~ainable according to the invention may be used, for example, for dashboards, arm rests (e.g., in passenger cars), beds, seats, sofas, head rests, and seats in public or private conveyances, especially in motor vehicles.

Mo3463 ` 202~3~

The following examples further illustrate details for the process of this invention. The invention, which is set ~ -forth in the foregoing disclosure, is not to be limited either in spirit or scope by these examples. Those skilled in the art 5 will readily understand that known variations of the conditions of the following procedures can be used. Unless otherwise noted, all temperatures are degrees Celsius and all percentages are percentages by weight.
EXAMPLES
lo Examples 1 to 6 The following compositions are used in Examples 1-6:
Polyether A A trifunctional, long-chained propylene-oxide/
ethylene-oxide ("PO/EO") polyether (about 4% EO) started on glycerol (OH number 50, molecular weight 3900) Catalyst 1 Bis(N,N'-dimethylaminoethyl) ether (30%)~
dipropylene glycol (70~0) Catalyst 2 Tin(II) dioctoate Stabilizer Polysiloxane foam stabilizer (product of 05 32 Bayer AG) T 80 Toluene diisocyanate, mixture of 2,4- and 2,6-isomers in a 80:20 ratio by weight T 65 Toluene diisocyanate, mixture of 2,4- and 2,6-isomers in a 65:35 ratio by weight M 50 Diphenylmethane diisocyanate, mixture of 2,4'-and 4,4'-isomers in a 50:50 ratio by weight M 6 Crude diphenylmethane diisocyanate containing 60% by weight of 4,4'-diphenylmethane diiso-cyanate and 25X by weight of 2,4'-diphenyl-methane diisocyanate All the components are vigorously mixed together and foamed up inside a closed mold (22 x 22 x 7 cm). The physical data of the resultant foams are shown in the following Table.

Mo3463 . ': i ::: ' : i i , .. . . .

-8- 2 0 ~ ~ 0 3 3 ID U~
8 ~ u~ o _, o ~ ~ o o o ~ o , 0 U- , ~ ~ ' ' U~
o _ o o ~ 8 ~ --' o ' OD ~ ~ ~
U~
o ~ o o ~ ~ o o ~ _, oo U~ . 0 o o _ U~ o o ~ o o ~ o , o , o oo O 0 0 N ~ ~

O -- _ O ,~'.
_ o ~ o o _ o :'~ O O O '~
~ r~
.~ ' . ..
_ ~ .
i ~ ~, . !.0 '~ `
~J X
~ O C
_ e~ O G O
: .. ~ ~ ~ ~ ~ a~ V al ~ ~ I ~0 ~ s ~, ~ Y ~ E m E ~ ~ ~ c~ o u~ _ o ~ _ ~ ~ ~ o 0 ~o m ~ o E il~

. , .

Claims

1. A process for the preparation of heat curable flexible polyurethane forms comprising reacting (a) a polyisocyanate of the diphenylmethane diisocyanate type containing no more than 80% by weight of monomeric diphenylmethane diisocyanate as the 4,4'-isomer, with (b) a compound containing at least two isocyanate-reactive hydrogen atoms and having a molecular weight of from 400 to 10,000, and, optionally, (c) a chain lengthening and/or crosslinking agent containing at least two isocyanate-reactive hydrogen atoms and having a molecular weight of from 32 to 399, in the presence of (d) water as blowing agent.

2. A process according to Claim 1 wherein the polyisocyanate of the diphenylmethane diisocyanate type contains at least 2% by weight of monomeric diphenylmethane diisocyanate as the 2,4'-isomer.

3. A process according to Claim 1 wherein the polyisocyanate of the diphenylmethane diisocyanate type contains at least 10% by weight of monomeric diphenylmethane diisocyanate as the 2,4'-isomer.

4. A process according to Claim 1 wherein the polyisocyanate of the diphenylmethane diisocyanate type contains at least 25% by weight of monomeric diphenylmethane diisocyanate as the 2,4'-isomer.

5. A process according to Claim 1 wherein polyisocyanate (a) is used as a mixture with up to 98 % by weight, based on the mixture of isocyanates, of toluene diisocyanate.

6. A process according to Claim 5 wherein the toluene diisocyanate is a mixture of 2,4- and 2,6-isomers in a ratio of 80:20 or in a ratio of 65:35.

7. A process according to Claim 1 additionally comprising (e) other blowing agents, catalysts, and auxiliary agents and additives.

8. A process according to Claim 7 wherein the catalyst is a divalent or higher valent organometallic compound.

9. A process according to Claim 7 wherein the catalyst is a tin(II) salt of a C8-20 alkanoic acid.

10. A process according to Claim 7 wherein the catalyst is tin(II) octoate, tin(II) ethylhexoate, or tin(II) laurate.