GB2075531A - Process for Preparing a Microcellular Polyurethane Foam - Google Patents

Abstract

A microcellular polyurethane foam with improved green strength properties and an NCO index of from 80 to 130 is prepared by reacting an organic polyisocyanate with a polyalkylene ether polyol and from 1 to 35 parts by weight, per hundred parts by weight of the polyol, of a chain extender in the presence of from 0.1 to 10 parts by weight, per hundred parts by weight of the polyol, of an amino compound of the formula <IMAGE> where R is a divalent alkylene radical of 1 to 4 carbon atoms, and R<1>, R<2>, R<3> and R<4> are identical or different hydroxyalkyl radicals of 1 to 4 carbon atoms and 1 or 2 hydroxyl groups. The polyol has an average functionality of from 2 to 8 and an average equivalent weight of from 1000 to 2700, and from 0.8 to 1.2 equivalents of the polyol are reacted per equivalent of the isocyanate.

Description

SPECIFICATION Process for Preparing a Microcellular Polyurethane Foam with Improved Green Strength The present invention relates to a process for preparing a microcellular polyurethane foam with improved green strength.

High density microcellular polyurethane foams are 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 part to show surface cracking if bent over sharply soon after demold 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 producing complex, molded parts.

The prior art has not provided a totally satisfactory solution to this problem. Some of the relevant prior art of which the applicant is aware includes United States Patents Nos. 3,580,868; 3620,986; 3,894,972 and 3,922,238.

United States Patent No. 3,580,868 teaches that catalysts prepared by reacting dimethylamine, formaldehyde, and phenols may be used to catalyze the polymerization of compounds which contain one or more 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 Mannich bases of secondary amines, formaldehyde and phenols; it also discloses a process for the production of synthetic resins containing isocyanurate groups which comprises polymerizing an organic polyisocyanate in the presence of these Mannich bases. The patentees disclose that "the use of alkoxylated condensation products of amines... in the reaction of isocyanates...for the production of foams, is also known, although in these cases no substantial polymerisation of the isocyanate groups can be observed".

(Column 1, lines 39--44).

United States Patent No. 3,992,238 discloses a process for preparing rigid cellular foam compositions by condensing an organic polyisocyanate in the presence of a furfuryl alcohol and a tertiary amine.

United States Patent 3,922,238 discloses a process for preparing rigid cellular foam compositions by condensing an organic polyisocyanate in the presence of a blowing agent, a polyol, and a catalyst system containing an alcohol, a tertiary amine trimerization catalyst, and a urethane catalyst.

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 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

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.

In the present invention, certain compounds are used in the condensation reaction of an organic polyisocyanate with polyalkylene polyether polyol. The use of these compounds results in foams with improved green strengths.

In the process of this invention, an organic polyisocyanate is reacted with polyalkylene polyether polyol in the presence of certain nitrogen compounds and a chain extender. Any suitable organic isocyanate may be used in the process of this invention. By way of illustration and not limitation, some of the isocyanates which may be used in this process include, for example, aromatic isocyanates, such as 1 -methylbenzene-2,4-diisocyanate, 1 -methylbenzene-2, 6-diisocyanate, 1 -methoxybenzene-2,4- diisocyanate, 1 -chlorobenzene-2,4-diisocyanate, 1 -benzylbenzene-2,6-diisocyanate, 2,6- diethylbenzene-1 ,4-diisocyanate, diisopropylbenzene diisocyanates, triisopropylbenzene diisocyanates, 1 ,3-dimethoxybenzene-2,4-diisocyanate, 1 -nitrobenzene-2,4-diisocyanate, technical mixtures of 2,4 and 2,6-toluene diisocyanates, m- and p-phenylene diisocyanates, m-xylylene diisocyante, p-xylene diisocyanate, naphthylene-1 ,5-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane2,2'-diisocyanate, diphenylmethane-4,2'-diisocyanate, 3,3'-dimethoxydiphenylmethane-4,4'- diisocyanate, dimethyldiphenylmethane-4,4'-diisocyanate, 3-methyldiphenylmethane-4,4'-biphenyl diisocyanate, 4,4'-diphenyl sulphone diisocyanate; aromatic diisocyanates which have been substituted by various substituents such alkoxy-, nitro, chloro, or bromo-, chlorophenylene-2,4diisocyanate, and the like.Thus, one may use aliphatic cycloaliphatic, and araliphatic isocyanates such as, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 1,3- cyclopentylene diisocyanate, 1,4-cyclohexylene diisocyanate, 1,2-cyclohexylene diisocyanate, hexahydroxylylene diisocyanate, 4,4'-dicyclohexyl diisocyanate, I ,2-di-(isocyanatomethyl)- cyclobutane. 1 ,3-bis(isocyanatopropoxy)-2,2-dimethyl propane, 1 ,3-bis(isocyanatopropyl)-2-methyl-2 propylpropane, 1 -methyl-2,4-diisocyanatoclohexane, 1 -m ethyl-2, 6-diisocyanatocyclohexane, bis-(4 isocya natocycipropyí )-2-methyl-2-propyí 1 -methyl-2,4-diisocyanatocyclohexane, 1-methyl- 2,6-diisocyanatocyclohexane, bis-(4-isocyanatocyclohexyl)-methane, 1 ,4-diisocyanatocyciohexane, 1 ,3-diisocyanatocyclohexane, isophorone diisocyanate, 2,6-diisocyanatocaproic acid ester, an isomeric mixture of 1 -methyl-2,4-diisocyanatocyclohexane and 1 -methyl-2,6-diisocyanatocyclohexane, 3,3,5- trimethyl-5-isocyanatomethyl cyclohexylisocyanate, methyl-substituted hexamethylene- and pentamethylene-diisocyanates, and the like. Other organic isocyanates well known to those in the art also may be used such as mixtures of 2,2'-, 2,4'-, and 4,4'-diphenyimethane diisocyanates and 2,4- and 2,6-toluene diisocyanates, crude isocyanates from the phosgenation of toluene diamine, and the like.

It is preferred to use a diisocyanate selected from the 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 diisocyanate.

In one of the more preferred embodiments, the polyisocyanate used in the process of this invention is liquid. The preferred liquid polyisocyanate is a modified diphenylmethane diisocyanate.

In one embodiment, the polyisocyanate used in the process 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 diphenylmethane diisocyanates may be prepared by producing carbodiimide-modified liquid diphenyimethane diisocyanates. Alternatively, one may prepare a quasi-prepolymer by reacting liquid diphenylmethane diisocyanate with an active hydrogen-containing compound.

The carbodiimide modified diphenyl methane diisocyante may be prepared by the procedures described in United States Patent 3,152,1 62; in German Patent Specification No. 1,092,007; in an article by T. W. Campbell and K. C. Smeltz appearing in J. Org. Chem., 28, 2069 (1963); and in an article by D. J. Lyman and N. Sadri appearing in Madromel. Chem., 67, 1(1 963). Each of the patents and publications referred to in this paragraph is hereby incorporated by reference into this specification.

The quasi-prepolymers of diphenylmethane diisocyanate are well known to those in the art. Thus, for example, they may be prepared by the techniques disclosed in United States Patent 3,894,972; the disclosure of this Patent is hereby incorporated by reference.

In the process of this invention, the organic polyisocyanate 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 polyesters; the disclosure of said patent is hereby incorporated by reference. Any suitable aikylene 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 polyols also can be prepared from other starting materials such as tetrahydrofuran and alkylene oxide tetrahydrofuran copolymers. Epihalohydrins such 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 polyalkylene polyether polyols can be prepared by any known process such as, for example, the process disclosed by Wurtz in 1859 and Encyclopedia of Chemical Technology, Vol. 7, pp. 257-262, published by Interscience Publishers, Inc. (1951) or in U.S. 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 polyisocyanate 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 0.9 to about 1.1 equivalents of a polyol with an average equivalent weight of from about 1500 to about 2400.

From about 1 to about 1 5 parts (by weight) of blowing agent may be used per 100 parts (by weight) of polyol. It is preferred to use from 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 weight, per hundred parts of the polyol) of a nitrogen compound selected from the group consisting of

wherein R is'a divalent alkylene radical containing from about 1 to about 4 carbon atoms; and 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.

It is preferred that each of R1, R2, R3, and R4 contain from about 2 to 3 carbon atoms and 1 hydroxyl group. In a more preferred embodiment, each of said R1, 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 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 oxide with ethylene diamine. This compound may be mixed with the polyol at ambient temperature and the mixture so formed may be reacted with the organic polyisocyanate.

In the process of this invention, 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; the disclosure of said patent is hereby incorporated by reference.

It is preferred that the chain extenders used in the process of this invention have a molecular weight of less than about 500 and are difunctional. By way of illustration 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-H-X' and X-H'-O-H"-X' wherein X and X' are independently selected from the group consisting of---OH, --NH, and NH2, R is alkylene of from about 2 to about 10 carbon atoms, and R' and R" are alkylene of from about 2 to about 4 carbon atoms. The most preferred chain extender is 1,4-butanediol.

The preferred polyurethane foam produced by the process of this invention has an NCO index of from about 95 to about 120.

The present invention also contemplates the incorporation of additional ingredients in the foam formulation to tailor the properties thereof. Thus, e.g., one may use plasticizers such as, e.g., trips(2 chloroethyl)phosphate; surfactants, including silicone surfactants such as, e.g., alkylpolysiloxanes and polyalkyl siloxanes, inorganic fillers, pigments, and other additives well known to those skilled in the art. These additives may be mixed with the polyol, and the polyol-containing mixture then reacted with the polyisocyanate.

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 temperatures 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-hydroxypropoxy) ethylene diamine.

Compound B-Triethanolamine.

Compound C-Dimethylethanolamine.

Isocyanate 1-a modified, liquid polyisocyanate based on pure diphenylmethane diisocyanate with a free NCO content of 25 percent.

Isocyanate 2-a modified polyisocyanate based on pure diphenylmethane diisocyanate with a free NCO content of 26 percent.

The physical properties of the foams prepared in these Examples 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 modulus, and A.S.T.M. D-41 2 elongation Split tear A S.tM. D-1938 Shore D hardness A.S.T.M. D-2240 Flexural modulus A.S.T.M. D-790 Flexural recovery Materials Standard &num;CTZ 22003 Chevrolet Motor Standard, G.M.C.

Heat sag Material Standard #CTz 22006 Chevrolet Motor Standard, G.M.C.

Examples 1-3 In these Examples, large molded plaques were prepared on a high pressure foam machine equipped with an 18 millimeterx 90 millimeter head; 400C component temperatures were used. The total output was about 1.5 kg per second. The initial mold temperature was 630C. The mold was an aluminum plaque which measured 91.4x91.4x0.32 cm (36"x361'x1/8"), and demold time was 1 minute. The samples were post cured for 45 minutes at a temperature of 1 21 OC.

The formulations used in these Examples contained 100 parts (by weight) of polyol 1,22.5 parts (by weight) of 1,4-butanediol, 0.5 parts (by weight) of triethylene diamine, 0.03 parts (by weight) of dibutyltin dilaurate, and 3.24 parts (by weight) of compound A. The isocyanate 1 was used at indices of 102, 105 and 108 for Examples 1,2, and 3, respectively.

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 obsereved in any of the plaques of these examples.

The polyurethane foam samples prepared in these Examples had the following properties: Example 1 Example 2 Example 3 Density, g/ccm 1.054 1.051 1.053 Tensile strength, kg/cm2 124.4 137.8 144.0 Elongation, percent 209 212 227 Split tear, p.i. 112 134 150 DieCTear,p.i. 435 470 493 Shore "D" Hardness 49-45 52-48 54-50 Heat Sag, cm 2.64 1.98 1.75 Flex Recovery 15/9 16/10 15/10 Tangential Modulus, kg/cm2x 103 -29"C 6.15 5.92 7.07 220C 1.74 1.73 1.73 700C 0.41 0.45 0.57 Modulus Ratio 15.10 12.99 12.35 Comparative Example 46 The procedure described for Examples 1-3 was repeated with the exception that Compound A was not used in these experiments and 24.5 parts of 1,4-butanediol were used. The isocyanate 1 indices were 102, 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 immediately 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 polyurethane plaques are shown below.

Example 4 Example 5 Example 6 Density, g/ccm 1.029 1.030 1.038 Tensile strength, kg/cm2 117.1 121.9 129.9 Elongation, percent 305 308 290 Split 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, cm 1.17 1.50 1.42 Flex Recovery 12/7 13/7 12/7 Tangential Modulus, kg/cm2x 103 -29"C 3.93 4.44 4.86 220C 1.28 1.41 1.53 700C 0.59 0.67 0.75 Modulus Ratio 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 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 0.03 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, 1 00.2 parts (by weight) of isocyanate 2, and a specified amount of compound A. In Examples 7-9, 23.0 parts of 1,4-butanediol and 1.62 parts of compound A were used. In Examples 10-12, 22.0 parts of 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 16-1 8, 20.0 parts of 1,4-butanediol and 4.86 parts of compound A were used.

In each of these experiments, the components were maintained at ambient temperatures, the mold temperatures were 54.5 to 59.50C, the in-mold time was 3 minutes, and the samples were post cured for 30 minutes at a temperature of 121 OC.

The green strengths of these samples were determined by bending over the corners of the 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.

Table 1 Example No. 7 8 9 10 11 12 Density g/ccm 0.964 0.947 0.945 0.971 0.953 0.950 Tensile Strength, kg/cm2 141.0 125.1 140.3 153.6 141.0 148.0 Elongation, % 120 100 120 110 70 110 Graves Tear, pi. 350 325 350 325 325 337 Shore "D" Hardness, inset. 5 Sec. 49 46 48 49 48 47 Tangential Modulus, kg/cm2 -290C 3277 3063 3103 4002 3421 3500 220C 1043 1124 1216 1194 1248 1253 700C 650 714 736 734 773 783 Modulus Ratio 5.0 4.3 4.2 5.5 4.4 4.5 Table 2 Example No. 13 14 15 16 17 18 Density, g/ccm 0.939 0.953 0.944 0.948 0.936 0.931 Tensile Strength, kg/cm2 134.0 134.0 142.4 148.0 141.0 141.0 Elongation, % 60 70 60 60 50 60 Graves Tear, pi. 312 325 300 300 312 287 Shore "D" Hardness, Inst. 5 Sec. 49 47 47 48 49 48 Tangential Modulus, kg/cm2 -290C 4696 3927 4001 4900 4503 4641 22"C 1312 1289 1254 1501 1514 1220 700C 678 612 663 681 791 595 Modulus Ratio 6.9 6.4 6.0 7.2 5.7 7.8 Additional experiments were conducted in substantial accordance with the procedure described in Example 1. However, 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 strength of the foams of these experiments. 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 invention.

Claims (9)

Claims

1. A process for preparing a microcellular polyurethane foam with improved green strength properties and an NC0 index of from 80 to 1 30, comprising reacting an organic polylsacyanate with from 0.8 to 1.2 equivalents per equivalent of isocyanate of a polyalkylene ether polyol having an average functionality of from 2 to 8 and an average equivalent weight of from 1000 to 2700, and from 1 to 35 parts by weight per hundred parts by weight of the polyol of a chain extender in the presence of from 0.1 to 10 parts by weight per hundred parts by weight of the polyol of an amino compound of the formula

where R is a divalent alkylene radical of 1 to 4 carbon atoms, and R', R2, R3 and R4 are identical or different hydroxyalkyl radicals of 1 to 4 carbon atoms and 1 or 2 hydroxyl groups.

2. A process as claimed in claim 1, wherein the polyurethane foam has an NCO index of from 95 to 120.

3. A process as claimed in claim 1 or 2, wherein from 0.9 to 1.1 equivalents of polyol are reacted per equivalent of isocyanate.

4. A process as claimed in any of claims 1 to 3, wherein the polyol has an average equivalent weight of from 1 500 to 2200.

5. A process as claimed in any of claims 1 to 4, wherein the chain extender is 1,4-butanediol.

6. A process as claimed in any of claims 1 to 5, wherein the polyisocyanate and the polyol and chain extender are reacted in the presence of from 0.1 to 5.0 parts by weight of the amino compound per hundred parts by weight of the polyol.

7. A process as claimed in any of claims 1 to 6, wherein R1, R2, R3 and R4 in the formula of the amino compound each contain 2 or 3 carbon atoms and 1 hydroxyl group.

8. A process for preparing a microcellular foam as claimed in claim 1 and carried out substantially as described in any of the foregoing Examples.

9. A microcellular polyurethane foam when prepared by a process as claimed in any of claims 1 to 8. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~