CA1148699A

CA1148699A - Process for preparing a microcellular urethane foam with improved green strength

Info

Publication number: CA1148699A
Application number: CA000376269A
Authority: CA
Inventors: Robert L. Mcbrayer
Original assignee: BASF Wyandotte Corp
Current assignee: BASF Corp
Priority date: 1980-05-05
Filing date: 1981-04-27
Publication date: 1983-06-21
Also published as: GB2075531A

Abstract

PROCESS FOR PREPARING A MICROCELLULAR
POLYURETHANE FOAM WITH IMPROVED GREEN STRENGTH

ABSTRACT OF THE INVENTION

There is provided a process for preparing a micro-cellular foam with improved green strength properties comprising the step of reacting an organic polyisocyanate with polyalkylene ether polyol and from 1 to about 35 parts (by weight, per hundred parts of said polyol) of a chain extender in the presence of from about 0.1 to about 10.0 parts (by weight, per hundred parts of said polyol) of a compound selected from the group consisting of:

and wherein:
a) said polyol has an average functionality of from about 2 to about 8 and an average equivalent weight of from about 1000 to about 2700, and from about 0.8 to about 1.2 equivalents of said polyol are reacted per equivalent of isocyanate;
b) said polyurethane foam has an NCO index of from about 80 to about 130;
c) R is a divalent alkylene radical containing from about 1 to about 4 carbon atoms; and d) R1, R2, R3, and R4 are independently selected from the group consisting of hydroxyalkyl containing from about 1 to about 4 carbon atoms and from about 1 to about 2 hydroxyl groups.

Description

36`9~9 1131 PROCESS FOX PREPARING A ~IICROCELLULA~
POLYURET}~N'~ FO~I WIT!L I~IPROV~D Gr~EN Sl`~ENGTI~

BAC~CI~UND ~` T~ VENTI~N

I. Field of the Invention The present invention relates to a process for preparing a microcellular polyurethane foarn with improved green strength.

Description of the Prior Art High density microcellular polyurethane foams are 1~ used by the automotive industry to prepare such molded parts ~;~ as, e.g., fascia, air dams, fender flares, spoilers, and fender extensions. Many of these parts are quite complex in configuration; and molding of such parts can be difficult when the parts have wrap-arounds or undercuts. Problems occur on demold if the parts tear as they are pulled or ejected off of mold cores or cavities.
The propensity of a molded polyurethane par~ to show surface crackin~ if bent over sharply soon after der.lold is an indication of its green strength; the poorer the green strength of a polyurethane foam, the more likely it is that said foam will be unsuitable for producin~ complex, molded parts.
The prior art has not provided a totally satis-factory solution to this problem. Some of the relevant prior art of which the applicant is aware includes United States ~ 6~ ~

Patents Nos. 3,580,8~8; 362U,986; 33894,9`~2 and 3,922,238.
United States Patent No. 3,5S0,868 teaches that catalysts prepared by reacting dimethylamine, formaldehyde, and phenols may be used to catalyz:e tl-c polymerization of compounds which contain one or mor~ isocyanate groups in the molecule. The patentees disclosed that the prior art "...amine components used cause the isocyanate polymerization to proceed insufficiently smoothly so that the product obtained is commercially unsatisfactory in every respect." (Column 1, lines 60-64).
United States Patent No. 3,620,986 discloses certain mononuclear ~lannich bases of secondary amines, formaldehyde and phenols; it also discloses a process for the production of synthetic resins containin~ isocyanurate groups which comprises polymerizing an organic polyisocyanate in the presence of these ~lannich bases. The patentees disclose that "the use of alkoxylated condensation products of amines...
in the reaction of isocyanatesO..for the production of foams, is also known, although in these cases no substantial poly-merisation of the isocyanate groups can be observed." ~Column1, lines 39-44).
United States Patent No. 3,894,972 discloses a process for preparing rigid cellular foam compositions by condensing an organic polyisocyanate in the presence of a furfuryl alchohol and a tertiary amine.
United States Patent No. 3,922,238 discloses a process for preparing rigid cellular foam compositions by .

~ 9 condensing an organic polyisocyanate in the presence of a blowing agent, a polyol, and a catalyst system containing an alcohol, a ter~iary amine trimerization catalyst, and a urethane catalyst, Sur,~ary of the Invention It is an object of this invention to provide a process for preparing a microcellular polyurethane foam which has improved green strength and good physical properties.
In accordance with this invention, there is provided a process for preparing a microcellular foam with improved green strength properties comprising the step of reacting an organic polyisocyanate with polyalkylene elther polyol and from 1 to about 35 parts (by weight, per hundred parts of said polyol) of a chain extender in tl-e presence of from about 0.1 to about 10.0 parts (by weight, per hundred parts of said polyol) of a compound selected from the group con-sisting of Rl R3 / Kl N - R - N and N~---- R2 R2 ~ \ R4 \ R~
wherein:
a) said polyol has an average functionality of from about 2 to about 8 and an average equivalent weighlt of from about 1000 to about 2700, and from about 0.8 to about 1.2 equivalents of said polyol are reacted per equivalent of isocyanate;

` 3 b~ said polyurethane foam has an NC0 index of from about 80 to about 130;
c) R is a divalent alkylene radical containing from about 1 to about 4 carbon atoms; and d~ Rl, R2, R3, and R4 are independently selected from the group consisting of hydroxyalkyl contain-ing fLom about 1 to about 4 carbon atoms and from about l to about 2 hydroxyl groups.

Descri tion of the Preferred Embodiments P _ _ _ _ ; 10 In the present invention, certain compounds are used in the condensation reaction of an organic polyisocyanate with polyalkylene polyether polyol. The use of these com-pounds results in foams with improved green strengths.
In ~he process of this invention, an organic polyisocyanate is reacted with polyalkyl~ne polyether polyol in the presence of certain nitrogen compounds and a chain extender. ~ny suitable organic isocyanate may be used in the process of this invention. By way of illustration and not limitationJ some of the isocyanates which may be used in this process include, for example, aromatic isocyanates such as l-methylbenzene-2,4-diisocyanate, 1-methylbenzene-2, 6-diisocyanate, 1-methoxybenzene-2,4-diisocyanate, l-chloro~
benzene-2,4-diisocyanate, 1-benzylbenzene-2,6-diisocyanate,

2,6-diethylbenzene-1,4-diisocyanate, diisopropylbenzene diisocyanates, triisopropylbenzene diisocyanates, 1,3,-dimethoxybenzene-2,4diisocyanate, l-nitrobenzene-2,4-diiso-cyanate, technical mixtures of 2,4 and 2,6-toluene diiso-.

~ 9 cyanates, m- and p-phenylene diisocyanates, m-xylylene diiso-cyanate, p-xylylene diisocyanate, naphthylene-1,5-diisocyanate, diphenylmethane-4,4'-diisocyanate~ diphenylmetllane-2,2'-diiso-cyanate, diphenylmethane-4,2'-diisocyanate, 3,3'-dimethoxy-diphenylmethane-4,4'-diisocyanate, dim~thyedipllenylmethane 4, 4'-diisocyanate, 3-methyldiphenylmethane-4~4'-bipllenyl diiso-cyanate, 4,4'-diphenyl sulphone diisocyanate; aromatic diiso-cyanates which have been substituted by various substituents such alkoxy-, nitro,chloro, or bromo-, chlorophenylene-2, 4-diisocyanate, and the like. Thus, one may use aliphatic cycloaliphatic, and araliphatic isocyanates such as, tetra-methylene diisocyanate, pentamethylene diisocyanate, hexa-methylene diisocyanate, 1,3-cyclopentylene diisocyanate, 1,4-cyclohexylene diisocyanate, 1,2-cyclohexylene diiso-cyanate, hexahydroxylylene diisocyanate, 4,4'-dicyclohexyl ~; diisocyanate, 1,2-di-(isocyanatomethyl)-cyclobutane, 1,3-bis (isocyanatopropoxy)-2,2-dimethyl propane, 1,3-bis(isocyanato-propyl)-2-methyl-2-propylpropane~ 1-metllyl-2,4-diisocyanato-clohexane, l-methyl-2,6-diisocyanatocyclohexane, biso(4-iso-cyanatocyclpropyl)-2-methyl-2-propylpropane, 1-methyl-2,4-; diisocyanatocyclohexane, l-methyl-2,6-diisocyanatocyclohexane, bis-(4-isocyanatocyclohexyl)-methane, 1,4-diisocyan~tocyclo-nexane, 1,3-diisocyanatocyclohexane,isophorone diisocyanate, 2,6-diisocyanatocaproic acid ester, an isomeric mixture of 1-methyl-2,4-diisocyanatocyclohexane and 1-methyl-2,6-diiso-cyanatocyclollexane, 3,3,5-trimethyl-5-isocyanatomethylcyclo-hexylisocyanate, methyl-substituted hexamethylene- and penta-~ 99 methylene-diisocyanates~ and the like. Other organic iso-cyanates well known to those in the 3rt also may be us~ed such as mixtures of 2,2'-, 2,4'-, and 4,4'-diphenylmethane diiso-cyanates and 2,4- and 2,6-toluene diisocyanates, crude iso-cyanates from the phosgenation of toluene diamine, and the like.
It is preferred to use a diisocyanate selected fromthe group consisting of toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, and the dimethyl derivative of diphenylmethane diisocyanate. The most preferred diisocyanate is pure, modified, liquid diphenylmethane diiso-cyanate.
In one of the more pr~ferred embodiments, the poly-isocyanate used in the process of this invention is liquid.
The preferred liquid polyisocyanate is a modified diphenyl-methane diisocyanate.
In one embodiment, the polyisocyanate used in theprocess of this invention has an NCO content of from about 20 to about 31 percent. In a more preferred embodiment, said isocyanate contains from about 23 to about 31 percent of NCO
groups.
Liquid polyisocyanates may be prepared by means well known to the art. Thus, for example, liquid diphenyl-methane diisocyanates may be prepared by producing carbodiimide-modified liquid diphenylmethane diisocyanates. Alternatively, one may prepare a quasi-prepolymer by reacting liquid diphenyl-methane diisocyanate with an active hydrogen-containing com-pound.

The carbodiimide-modified diphenylmethane diiso-cyanate-may be prepared by the procedures described in United States Patent 3,152,162, in German Patent Specification N 1,092,007, in an article by T.W Campbell and K.C. Smeitz appearing in J Org. Chem., 28, ~069 tl963), and in an article by D.J. Lyman and N. Sadri appearing in Madromel. Chem., 67, 1 (1963).
The quasi-prepolymers of diphenylmethane diiso-cyanate are well known to those in the art. Thus, for example, they may be prepared by the technïques disclosed in United - States Patent 3,894,972.
In the process of this invention, the organic poly-isocyanate is reacted with a polyalkylene ether polyol. Suitable polyalkylene ether polyols which are well known to those skilled in the art may be used in this process. Thus, one may use the polymerization product of an alkylene oxide or of an alkylene oxide with a polyhydric alcohol. Any suitable polyhydric alcohol can be used such as, e.g., those disclosed in United States ~ Patent 3,894,972 for the preparation of hydroxyl-containing poly-;~ 20 esters. Any suitable alkylene oxide can be used to prepare said polyol such as ethylene oxide, propylene oxide, butylene oxide, amylene oxide, and mixtures of these oxides. The polyalkylene polyether polyol~

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-- _ -. : , ,, ~ 99 also can be prepared from other starting materials such as tetrahydrofuran and alk~Jlene oxide tetrahydrofuran copolymers.
Epihalohydrins SUCll as epichlororhydrin as well as aralkylene oxides such as styrene oxide are useful. The polyalkylene polyether polyols can have either primary or secondary hydroxyl groups and, preferably, are polyethers prepared from alkylene oxides having from two to about six carbon atoms. The poly-alkylene polyether polyols can be prepared by any known process such as, for example, the process disclosed by Wurtz in 1859 and Encyclopedia of Chemical Technolo~y, Vol. 7, pp. 257-262, published by Interscience Publishers, Inc. (1951) or in U.~.
Patent No. 1,922,459.
In the process of this invention, from about 0.8 to about 1.2 equivalents of polyol per equivalent of poly-isocyanate are used; this polyol preferably has an average functionality of from about 2 to about 8 and an average equivalent weight of from about 1000 to about 2700. It is preferred to use from about 0.5 to about 1.1 equivalents of a polyol with an average equivalent weight of from about ~ 20 1500 to about 2400.
- From about 1 to about 15 parts (by weight) of blowing agent may be uscd per 100 parts (by w~ight) of polvol.
It is preferred to use fror,l about 1 to about 4 parts (by weight) of blowing agent per 100 parts (by weight) of polyol.
In the process of this invention, the polyisocyanate is reacted with the polyol in the presence of from about 0.1 to about 10 parts (by wei~ht, per hundrcd parts of the . .

~ 6~3 ~

polyol) of a nitrogen compound selected from the group con-sisting of Rl R3 Rl N - R - N and ~ R2 R2 / \ R4 \ ~3 wherein R is a divalent alkylene radical containing from about S 1 to about 4 carbon atoms; and Rl, R2, R3, and R4 are indepen-dently selected from the group co~isisting of hydroxy~lkyl containing from about 1 to about 4 carbon atoms and from about 1 to about 2 hydroxyl groups.
It is preferred that each of Rl, R2, R3, and R4 contain from about 2 to ~ carbon atoms and 1 hydroxyl group.
In a more preferred embodiment, each of said Rl, R2, R3, and R4 groups contains 2 carbon atoms. It is also more preferred that R contain 2 carbon atoms~
In one preferred embodiment, the polyisocyanate is reacted with the polyol in the presence of from about 0.1 to about 5.0 parts (by weight, per hundred parts of said polyol) of said nitrogen compound.
The nitrogen compound used in the process of this invention may be prepared by means well known to those in the ~0 art. Thus, e.g., it may be prepared by reacting an alkylene oxide with an alkylene diamine under suitable oxyalkylation conditions. One of the preferred compounds is prepared by reacting propyLene oxi~e with ethylene diamine. This com-pound may be mixed with the polyol at ambient temperature g ~ ~ ~8 ~9 and the mixture so formed may be reacted with the organic polyisocyanate.
In the process of this invention9 the polyisocyanate is reacted with polyalkylene ether polyol and said nitrogen compound in the presence of from about 1 to about 35 parts (by weight, per hundred parts of said polyol) of a chain extender. In a preferred embodiment, from about 10 to about 25 parts of the chain extender are used in the process of the invention.
The chain extenders known to those in the art may be used in the process of this invention. Thus~ e.g., the chain extenders described in United States Patent 2,929,800 may be used.
, It is preferrcd that the chain extender-s used in the process o~ this invention have a molecular weight of less than about 500 and are difunctional. By way of illus-tration and not limitation, some suitable chain extenders include, e.g., pentamethylenediamine, hexamethylene diamine, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, and the like. It is preferred that the chain extender be selected from the group consisting of . . , ~

X-R X' and X-R'-0-R"-X' wherein X and X' are independently selected from the group .

;. , , 10 ., ,~ ' .

~8~99 consisting of -0~1, NH, and -NH2, R is alkylene of from about L, 2 to about 10 carbon atoms, and Rt and R" are alkylene of from about 2 to about 4 carbon atoms. The most preferred chain extender is l,4-butanediol.
The preferred polyuretllane foam produced by the process of this invention has an NC0 index of from about 95 to about 120.
The present invention also contemplates the incor-poration of additional ingredients in the foam formulation to tailor the properties tllereof. Thus, e.g., one may use plasticizers such as, e.g., tris~2-chloroethyl~phosphate;
surfactants, including silicone surfactants such as, e.g., I
alkylpolysiloxanes and polyalkyl siloxanes, inorganic fill~rs, pigments, and other additives well known to those skilled in the art. These additives may b~ mixed with the polyol, and the polyol-containing mixture then reacted with the polyisocyanate. I
Following are examples which are presented to `illustrate the claimed invention and are not to be deemed limitative thereof. Unless-otherwise specified, all parts are by weight, all percentages are by weight, and all temper~
atures are in degrees centigrade.
In these Examples, the following terms are used:
Polyol 1 -- a blend of ethylene oxide capped polyols with an average hydroxyl number of about 25.
Compound A -- N ,N ,N ' ,N ' -tetrakis(2-hydroxy-propy3) etl~ylene diamine.
` .

.

~.. ;;

~ . . .
, Compound B -- Triethanolamine.
Compound C -- Dimethylethanolamine.
Isocyanate 1 -- a ~nodified, liquid polyiso-cyanate based on pure diphenylmetlhane diisocyanate with a 5 free NCO content of 25 percent.
Isocyanate 2 -- a modified polyisocyanate based on pure diphenylmethane dii~ocyanate with a free NC0 content of 26 percent.
The physical properties of the foams prepared in these ~xamples were evaluated by standard tests known to those skilled in the art. The following tests were used:
` Density A.S.T.M. D-792 Tensile strength, tensile A.S.T.i~l. D-412 modulus, and elongation Split tear A.S.T.~I. D-1938 ; Shore D hardness A.S.T.M. D-2240 ~- Flexural modulus A.S.T.M. D-790 Flexural recovery Materials Standard ~GTZ 22003 Chevrolet `~ 20 Motor Standard, G.~l.C.
Heat sag ~laterial Standard #CTZ22006 Chevrolet ~lotor Standard, G.~.C.

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Examples 1-3 In these Examples, large molded pl~ques were pre-pared on a high pressure foam machine equipped with an 18 millimeter x 90 millimeter head; 40 degree centigrade component temperatures were used. The total output was about 3.3 pounds per second. The initial mold temperature was 145 degrees Fahrenheit. The mold was an aluminum plaque which measured 36" x 36" x 1/8", and demold time was 1 minute. The samples were post cured for 45 minutes at a temperature of 250 degrees ~ahrenheit.
The formulations used in these Examples contained 100 parts (by weight) of polyol 1, 22.5 par~s (by weight) of 1,4-butanediol, 0.5 parts (by weight) of triethylene diamine, 0.0~ parts ~by wcight) of dibutyltin dilaurate, and ~.24 p~rts (by weignt) of compound A. The isocyanate 1 was used at indices of 102, 105 and 108 Lor Examples 1, 2, and 3, respec-tively.
The green strength of the molded polyurethane plaques was determined by bending over the corners of the molded plaques immediately upon demold and observing whether there was any cracking of the pad~ No cracking was observed in any of the plaques of these examples.
The polyurethanefoam samples prepared in these Examples had the following properties:

- .

xam~e 1 E~ple 2 ~ensity, pcf. 65.8 65.6 65.7 Tensile strength, p.s.i. 1770 1961 2043 Elongation, percent 209 212 227 Split tear, p.i. 112 134 150 Die C Tear, p.i. 4~5 470 4~3 Shore "D" Hardness 49-45 52~48 54-50 Heat Sag, in. 1.04 U.78 0.~9 Flex Recovery 15l9 l~llU 15/10 Tangent al ~lodulus, p.s.i.
`. x 10 -20F. 8/.9 ~4.~ 101.0 72F. 24.8 24.7 27.7 1~8F. 5.8 6.5 8.2 ~lodulus Ratio 15.10 12,99 12.35 Comparative Example 4-6 The procedure described for Examples 1-3 was repeated with the exception that Compound A was not used in these ex-periments and 24.5 parts of 1,4-butanediol were used. The isocyanate 1 indices were lU2, 105 and 108 for Examples 4, 5 and 6, respectively.
The green strengths of the molded polurethane -~ plaques were determined by bending over the corners of the molded plaques immediatcly upon demold and observing whether there was any cracking of the pad. All of the molded plaques of these examples exhibited cracking.
The physical properties of the polyurethaneplaques `,~ -' ~

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~ 69 are sho~ below.
Example 4 Example 5 Example 6 Density, pcf. 64.2 ~4.~ 64.8 Tensile strength, p.s.i.167~ 1735 1848 Elongation, percent 305 308 290 5plit tear, p.i. 154 185 209 Die C tear, p.i. 516 548 558 Shore "D" hardness 47-44 49-45 50-46 Heat Sag, in. 0.46 0.59 0.56 Flex Recovery 12/7 13/7 12/7 Tangent al Modulus, p.s.i.
x 10 -20F. 5~.2 ~3.4 6~.4 72F. 18.3 20.2 21.8 158F. 8.5 3.6 10.7 : Modulus ~atio 6.67 6.64 6.51 Examples 7-18 A resin masterbatch was prepared for the experiments described in these Examples~ This masterbatch contained 100 .
~ 20 parts (by weight) of polyol 1, 2 parts (by weight) of a 1:3 : mixture (by weight~ of triethylene diamine and 1,4-butanediol, and 0.0~ part (by weight) of dibutyltin dilaurate, as a catalyst.
~` The formulation used in these Examples contained 102.03 parts (by weight) of the resin masterbatch, a specified amount of 1,4--butanediol, 100.2 parts (by weight) of isocyanate 2, and a specified amount of compound A. In Examples 7-9, 23.~ parts of 1,4-butanediol and 1.62 parts of compound A
: ~' `; 15 ' ' ~

~B~99 w~re used. In Examples 10-1~, 22.0 parts o~ 1,4-butanediol and 1.62 parts of compound A were used. In Examples 13-15, 21.0 parts of 1,4-butanediol and 3.24 parts of compound A
were used. In Examples 16-18, 20.0 parts of 1,4-butanediol and 4.86 parts of compound A were used.
In each o these experiments, the components were maintained at ambient temperatur~es, the mold temperatures were 130-139 degrees Fahrenheit, the in-mold time was 3 min-utes, and the samples were post cured for 30 minutes at a temperature of 250 degrees FahrPnheit.
The green strengths of these samples were determined by bending over the corners of thc molded plaques immediately on demold and observing whether cracking occurred. Cracking was observed for each of the pads produced in Examples 7, 8 . , .
and 9. No cracking was observed for the pads of Examples 10-18.
The properties of the foams of these Examples were determined. They are shown in Table 1 and Table 2.

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~ 9 9 Additional experiments were conducted in substantial accordance with the procedure ~escribed in Example 1. How-ever, comparable amounts of Compound C or Compound B were substituted for the Compound A used in Example 1.
It was found that the Compound B did improve the green strengtn of the foams of these experime~ts. However, the use of the Compound C did not cause any substantial improvement in the green strength of the foams.
Many other modifications and ramifications will suggest themselves to those skilled in the art) they are ; intended to be comprehended within the scope of this inven-: tion.

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Claims

The embodiments of this invention in which an exclusive property or privilege is claimed are as follows:

1. A process for preparing a microcellular foam with improved green strength properties comprising the step of reacting an organic polyisocyanate with polyalkylene ether polyol and from 1 to about 35 parts (by weight, per hundred parts of said polyol) of a chain extender in the presence of from about 0.1 to about 10.0 parts (by weight, per hundred parts of said polyol) of an amine selected from the group consisting of N,N, N1, N1 - tetrakis - (2 -hydroxypropyl) ethylene diamine, triethanolamine and mixtures thereof, wherein:
a) said polyol has an average functionality of from about 2 to about 8 and an average equivalent weight of from about 1000 to about 2700, and from about 0.8 to about 1.2 equivalents of said polyol are reacted per equivalent of isocyanate; and b) said polyurethane foam has an NCO index of from about 80 to about 130.

2. The process of claim 1, wherein said polyurethane foam has an NCO index of from about 95 to about 120.

3. The process of claim 2, wherein said polyol has an average equivalent weight of from about-1500 to about 2200.

4. The process of claim 3, wherein from about 0.9 to about 1.1 equivalents of said polyol are reacted per equivalent of isocyanate.

5. The process of claim 1, wherein said chain extender is 1,4-butanediol.

6. The process of claim 4, wherein said chain extender is 1,4-butanediol.

7. The process of claim 1 wherein said amine is N, N, N1, N1 - tetrakis (2-hydroxypropyl ethylene diamine.

8. The process of claim 7, wherein said chain extender is 1,4-butanediol.

9. The process of claim 1, wherein said poly-isocyanate and said polyol and chain extender are reacted in the presence of from about 0.1 to about 5.0 parts (by weight, per hundred parts of said polyol) of said amine.

10. The product of the process of claim 1.