GB2063894A - Semi-flexible polyurethane cellular foams of improved damping characteristics - Google Patents

Abstract

The damping characteristics of cellular polyurethane foam products are controlled by the level of tertiary amine catalyst present in the foam formulation. The introduction and use of significantly increased catalyst levels in the formulations reduces the individual cell size of the foam product, thereby increasing the damping characteristics thereof.

Description

SPECIFICATION Semi-flexible polyurethane cellular foams of improved damping characteristics.

The present invention pertains to cellular foam products. More particularly, the present invention concerns energy absorbing, semi-flexible cellular foam products. Even more particularly, the present invention concerns means and methods for increasing the energy absorbing properties of semi-flexible cellular foam products.

Because of energy shortages considerable efforts have been directed to creating more fuel efficient vehicles. While seeking alternate fuel sources, more efficient power plants and the like, much attention has, also, been focused on reducing the vehicle weight. By reducing the weight of the vehicle, less energy is required to drive it.

In reducing the weight of the vehicle, safety requirements cannot be compromised. Stringent Federal vehicle safety regulations and standards demand intelligent energy management systems. Quite often such systems comprise heavy metallic components, such as bumper beams, hydraulic shock absorbers and the like. Therefore, in meeting weight reduction objections, suitable lightweight plastics must be developed and strategically deployed in the vehicle.

The prior art is well acquainted with high load bearing, semi-flexible foams and their energy absorbing properties in automotive applications. Yet, because of the need to further lighten automotive vehicles improved foams having greater energy absorbing properties are constantly sought and desired. The present invention, as will subsequently be detailed, describes means and methods for improving the energy absorbing properties of semi-flexible, load bearing cellular foam products.

We have now found that the damping properties and, thus, the energy absorbing capabilities of semi-flexible cellular foam products are controlled by regulation of the individual cell sizes in the foam products. More precisely, it has been found that by reducing the cell size of the individual cells in semi-flexible cellular products the damping properties thereof are dramatically improved. The reduction in individual cell size is accomplished, in accordance with the present invention, by increasing the levels of catalyst present in the foam formulation.

According to the invention therefore there is provided a method of manufacturing a semi-flexible polyurethane cellular foam having improved damping characteristics, comprising: reacting an organic polyisocyanate and an active hydrogen-containing compound in the presence of a blowing agent and an amount of a tertiary amine catalyst in significant exess over the amount required for catalytic use alone.

It has been observed that by substantially increasing catalyst levels, e.g. to form 5 to 25 times the amount conventionally employed in semi-flexible foam formulations, the cell size is dramatically reduced.

Furthermore, further redactions in cell size may be achieved by incorporating a surfactant into the foam formulation, e.g. in a minor amount.

It is, also, contemplated herein that the damping characteristics of the foam can be further increased by filling the individual cells with a damping fluid, such as mineral oil or the like.

The catalysts used herein may be the conventional tertiary amine catalysts employed in the preparation of semi-flexible, cellular foam products.

For a more complete understanding of the present invention reference is made to the following detailed description and accompanying examples.

As noted, the present invention provides semi-flexible cellular foam products of reduced cell size. The semi-flexible polyurethane cellular products having reduced cell size are prepared by reacting the components of the polyurethane formulation in the presence of increased levels of catalyst. It has been observed that by increasing the catalyst levels the cell size of the individual cells is dramatically reduced. The reduction in cell size consequently provides cellular products with improved damping characteristics.

The smaller the cell size of the foam, the greater the resistance to air flow through the foam mass. The greater the resistance to air flow the greater the damping effect of the foam. The greater the damping effect, the greater the energy absorbing properties of the foam. Hence, by reducing the individual cell size of the semi-flexible foam, there is an increase in the energy absorbing properties thereof. The air flow resistance, it should be noted, is present even though the over-all cell structure of the foam is open or free of cell walls.

As noted hereinabove, the present invention is particularly concerned with semi-flexible cellular polyurethane foam products. Such products are, ordinarily, prepared by reacting a reactive hydrogencontaining compound with an organic polyisocyanate in the presence of a suitable catalyst and a blowing agent.

The reactive hydrogen-containing compound employed herein is one which is determined by the well-known Zerewitinoff test, as described by Kohler in Journal of the American Chemical Society, 49,3181 (1927) and which is reactive with an isocyanate group. Such a compound and its method of preparation is well known. Exemplifying an active hydrogen-containing compound which is isocyanate reactive is -OH, -NH-, -COOH, and -SH.

Examples of suitable types of organic compounds containing at least two active hydrogen-containing groups which are reactive with an isocyanate group are hydroxyl terminated polyurethane polymers, polyhydric polythioethers, alkylene oxide adducts of phosphorus-containing acids, polyacetals, aliphatic polyols, aliphatic thiols including alkane, alkene and alkyne thiols having two or more --SH groups; diamines including both aromatic, aliphatic and heterocyclic diamines, as well as mixtures thereof. Compounds which contain two or more different groups within the above-defined classes may also be used in accordance with the process of the present invention such as, for example, amino alcohols which contain an amino group and a hydroxyl group.Also, compounds may be used which contain one --SH group and one --OH group as well as those which contain an amino group and aSH group.

Any suitable hydroxyl-terminated polyester may be used such as are obtained, for example, from polycarboxylic acids and polyhydric alcohols. Any suitable polycarboxylic acid may be used such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, brassylic acid, thapsic acid, maleic acid, fumaric acid, glutaconic acid, a-hydromuconic acid, ss-hydromuconic acid, a-butyl-a ethyl-glutaric acid, a,(3-diethyl-succinic acid, isophthalic acid, terephthalic acid, hemimellitic acid, and 1,4-cyclohexane-dicarboxylic acid.Any suitable polyhydric alcohol, including both aliphatic and aromatic, may be used such as ethylene glycol, propylene glycol, 1,3-propane diol, butylene glycol, 1,4-butane diol, 1,3-butane diol, 1,5-pentanediol, 1,4-pentanediol, 1,3-pentanediol, 1,6- hexanediol, 1 ,7-heptanediol, glycerol, 1,1,1 -trimethylolprnpane, 1,1,1 -trimethylolethane, hexane-1,2,6-triol, a-methyl glucoside, pentaerythritol, and sorbitol. Also included within the term "polyhydric alcohol" are compounds derived from phenol such as 2,-2-bis (4-hydroxyphenyl)propane, commonly known as Bisphenol A.

The hydroxyl-terminated polyester may also be a polyester amide such as is obtained by including some amine or amino alcohol in the reactants for the preparation of the polyesters. Thus, polyester amides may be obtained by condensing an amino alcohol such as ethanolamine with the polycarboxylic acids set forth above.

Any suitable polyalkylene ether polyol may be used such as the polymerization product of an alkylene oxide or of an alkylene oxide with a polyhydric alcohol. Any suitable polyhydric alcohol may be used such as those disclosed above for use in the preparation of the hydroxylterminated polyesters. Any suitable alkylene oxide may be used such as ethylene oxide, propylene oxide, butylene oxide, amylene oxide, and mixtures of these oxides. The polyalkylene polyether polyols may be prepared from other starting materials such as tetrahydrofuran and alkylene oxide-tetrahydrofuran copolymers; epihalohydrins such as epichlorohydrin; as well as aralkylene oxides such styrene oxide.The polyalkylene polyether polyols may have either primary or secondary hydroxyl groups and, preferably, are polyethers prepared from akylene oxides having from two to six carbon atoms such as polyethylene ether glycols, polypropylene ether glycols, and polybutylene ether glycols. The polyalkylene polyether polyols may be prepared by any known process such as, for example, the process disclosed byWurtz 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. Alkylene oxide adducts of Mannich condensation products are also useful in the invention. Polyethers which are preferred include the alkylene oxide addition products of trimethylolpropane, glycerine, pentaerythritol, sucrose, sorbitol, propylene glycol, and 2,2-bis-(4-hydroxyphenol) propane and blends thereof having equivalent weights of from 250 to 5000.

Alkylene oxide adducts of acids of phosphorus which may be used, aside from those enumerated in U.S.

Patent No. 3,639,542, include those neutral adducts prepared from the alkylene oxides disclosed above for use in the preparation of polyalkylene polyether polyols. Acids of phosphorus which may be used are acids having a P205 equivalency of from about 72% to about 95%. The phosphoric acids are preferred.

Any suitable hydroxyl-terminated polyacetal may be used such as, for example, the reaction product of formaldehyde or other suitable aldehyde with a dihydric alcohol or an alkylene oxide such as those disclosed above.

Any suitable aliphatic thiol including alkane thiols containing at least two --SH groups may be used such as 1 ,2-ethane dithiol, 1 ,2-propanedithiol, 1 ,3-propanedithiol, and 1 ,6-hexane dithiol; alkene thiols, such as 2-butene-1,4-dithiol, and alkyne thiols such as 3-hexyne-1,6-dithiol.

Any suitable polyamine may be used including aromatic polyamines such as methylene dianiline, polyaryl-polyalkylene polyamine (crude methylene dianiline), p-aminoaniline, 1,5-diaminonaphthalene, and 2,4-diaminotoluene; the condensation products of aniline and formaldehyde; aliphatic polyamines such as methyl amine, ethylene diamine, 1,3-propylenediamine; 1,4-butylenediamine, and 1,3-butylenediamine, as well as substituted secondary derivatives thereof, such as triisopropanolamine, as well as mixtures thereof.

In addition to the above hydroxyl-containing compounds, other compounds which may be employed include graft polyols. These polyols are prepared by the in situ polymerization product of a vinyl monomer in a reactive polyol medium and in the presence of a free radical initiator. The reaction is generally carried out at a temperature ranging from about 40"C to about 150"C.

The reactive polyol medium generally has a molecular weight of at least about 500 and a hydroxyl number ranging from about 30 to about 600. The graft polyol has a molecular weight of at least about 1500 and a viscosity of less than 40,000 cps. at 10% polymer concentration.

A more comprehensive discussion of the graft polyols and their method of preparation can be found in U.S. Patent Nos. 3,383,351; 3,304,273; 3,652,639 and in U.S. Patent No. 3,823,201,the disclosures of which are hereby incorporated by reference.

Also, polyols containing ester groups can be employed in the subject invention. These polyols are prepared by the reaction of an alkylene oxide with an organic dicarboxylic acid anhydride and a compound containing a reactive hydrogen atom. A more comprehensive discussion of these polyols and their method of preparation can be found in U.S. Patent Nos. 3,585,185; 3,639,541 and 3,639,542.

The organic polyisocyanate used to prepare the foams hereof correspond to the formula: R" (NCO)z Wherein R" is a polyvalent organic radical which is either aliphatic, aralkyl, alkaryl, aromatic or mixtures thereof, and z is an integer which corresponds to the valence of Rand is at least two.Representative of the organic polyisocyanates contemplated herein includes, for example, the aromatic diisocyanates, such as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, mixtures of 2,4- and 2,6-toluene diisocyanate, crude toluene diisocyanate, methylene diphenyl diisocyanate, crude methylene diphenyl diisocyanate and the like, the aromatic triisocyanates such as 4,4', 4"-triphenylmethane triisocyanate, 2A,6-toluene triisocyanates; the aromatic tetraisocyanates, such as 4,4'-dimethyldiphenylmethane-2,2'-5, 5'-tetraisocyanate, and the like; arylalkyl polyisocyanates, such as xylylene diisocyanate; aliphatic polyisocyanates, such as hex amethylene-1 ,6-diisocyanate, lysine diisocyanate methylester and the like, and mixtures thereof.Other organic polyisocyanates include polymethylene polyphenylisocyanate, hydrogenated methylene diphenylisocyanate, m-phenylene diisocyanate, naphthalene-1 ,5-diisocyanate, 1 -methoxyphenyl-2,4-disocyanate, 4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenyl diisocyanate, 3,3'-dimethyl-4,4'-biphenyl diisocyanate and 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate.

These polyisocyanates are prepared by conventional methods known in the art such as the phosgenation of the corresponding organic amine.

Still another class of organic polyisocyanates contemplated for use herein are the so-called "quasiprepolymers". Three quasi-prepolymers are prepared by reacting an excess of organic polyisocyanate or mixtures thereof with a minor amount of an active hydrogen containing compound such as those described hereinabove.

The catalysts which are employed in preparing the semi-flexible, cellular products are the well known tertiary amine urethane catalysts. Any such tertiary amine catalyst can be used herein. Representative of such catalyst is, for example, triethylenediamine, triethylamine, diethylcyclohexylamine, dimethylethanolamine, N-methyl morpholine, trimethylpiperazine, N-ethylmorpholine, diethyl-ethanolamine, 2,4,6-tris (dimethylolmethyl) phenol, 1 -methyl-4-dimethylamine, ethyl piperazine, 3-methoxy-N-dimethyl propyl amine, N-dimethyl-N-methyl isopropyl propylene diamine, N,N-diethyl-3-diethylaminopropylamine, dimethyl benzyl amine and the like, as well as mixtures thereof.

Water is conventionally employed as the blowing agent. However, fluorocarbon blowing agents or methylene chloride can be used either alone or in combination with water.

In a preferred embodiment of the present invention, the reactive hydrogen-containing compound is a polyhydroxyl-containing compound or mixtures thereof and the organic polyisocyanate is crude methylenediphenyldiisocyanate.

As is known to those skilled in the art to which the present invention pertains, the amine catalyst is conventionally employed in an amount ranging from about 0.01 parts to about 1 part thereof per 100 parts, by weight, of active hydrogen-containing compound. In accordance herewith the catalyst is employed in an amount ranging from about 1 to 10 parts by weight thereof per 100 parts by weight of active hydrogen-containing compound. Preferably, the catalyst is present in an amount ranging from about 2 to 7 parts by weight thereof per 100 parts of active hydrogen-containing compound. By operating within the prescribed range shrinkage of the foam is not encountered. Greater levels of catalyst, if employed, may result in shrinkage of the foam.

The present invention, also, contemplates the use of a surfactant in the foam formulation. The surfactant contributes to reduction in cell size. Although optional, where used, the surfactant is employed in an amount ranging from about 0.5 to about 5 parts by weight, per 100 parts by weight of polyol and, preferably, from about 0.2 to about 2.5 parts by weight thereof per 100 parts by weight of polyol. The surfactants contemplated for use are the silicone surfactants, such as alkyl polysiloxane and polyalkylsiloxanes.

The improvement in damping effect attributable to cell size reduction because of catalyst levels can be still further enhanced, if desired. By saturating the cellular product of reduced cell size with a suitable damping fluid, the cells become filled with the fluid. Filling the cells in this manner further increases the resistance to air flow of the mass. Suitable damping fluids include mineral oil, and other viscous materials which are non-reactive with the foam. The damping fluid is employed by immersing the foam product therewithin or by any other suitable mode. Where used, the foam is preferably subsequently encapsulated to prevent loss of the fluid.

In preparing foams in accordance herewith, ordinarily, the active hydrogen-containing compound, catalyst, blowing agent and surfactant, if any, are blended together. Then, the isocyanate is admixed therewith to commence the reaction. Ordinarily, the reaction is carried out at ambient conditions. If desired, the foam produced thereby can, then, be saturated with a damping fluid in the manner described above.

For a more complete understanding of the present invention reference is made to the following specific example thereof. In the example, which is to be construed as iilustrative and not limitative of the invention, all parts are by weight absent indications to the contrary.

Example To test the efficacy of the present invention a series of semi-flexible polyurethane foams were prepared by the following procedure: Into one-quart capacity mixing cups, at room temperature was added a blend of (a) a polyol blend, (b) water as a blowing agent, (c) a silicone surfactant, where used, and (d) dimethylethanolamine, as a catalyst.

The mixture was stirred with a light duty bench top drill press equipped with a 11/4 inch diameter shrouded mixing blade. The stirring was timed by a stop watch. Mixer speed was 3400 rpms. The stop watch and mixer were started simultaneously and the mixture was stirred initially for 30 seconds. While mixing, to the container was, then, added quickly crude methylene diphenyldiisocyanate (MDI) as the isocyanate reactant.

After the isocyanate was added, mixing continued for about 5 to 10 seconds. The foam compositions were then poured into a 9" x 9" x 12" aluminum molds pretreated with a release agent and were retained in the mold for twenty-five minutes to ensure complete reaction. The foams were, then, removed from the mold and tested for physical properties.

The following table sets forth the ingredients and their respective amounts, the processing conditions and the physical tests and the results thereof carried out on the sample foams.

TABLE Sample A. Ingredient amt, pbw 1 2 3 polyol(1) 100. 100. 100.

Water 2.2 2.2 2.2 Dimethylethanolamine 0.125 2.5 2.5 Surfactant2 ---- ---- 1.0 Crude MDI 45.0 45.0 45.0 Isocyanate Index 103. 90. 90.

B. Processing Conditions Cream Time, sec. 40. 10. 10.

Free-rise time, sec. 400. 60. 60.

C. Properties Density, pof 6.99 6.99 7.12 ILD, lb.1 sq. in.

25% 45.3 37.1 48.8 65% 62.1 53.4 58.8 25% return 5.6 6.2 6.4 SAG factor (4) 1.38 1.44 1.20 Guide factor (5) 6.50 5.3 6.9 Recovery, % (6) 12.4 16.7 13.0 Decreasing Cell Size ') a polyol blend of (a) triol-based styrene-acrylonitrile graft polyol having an OH No. of about 23, (b) an ethoxylated and propoxylated glycerine-based polyol having an OH No. of about 35, and (c) an ethoxyiated and propoxylated ethylenediamine having an OH No. of about 450, the polyols (a), (b) and (c) being present in a, respective, weight ratio of 4:1 :0.263.

(2) a silicone surfactant sold under the name NIAX Surfactant L-5302 (3) each sample property based on an average of three foams per sample (4)defined as the ratio of 65% ILD/25% ILD (5) defined as the ratio of 25% ILD/density (6) defined as the ratio of 25% return I LD/25% ILD It is to be observed from the Table that the load bearing level of the smaller cell sized foams are equivalent to those of the larger cell sized foams (Sample 1), even though the isocyanate index for the smaller cell sized foams is lower than that of SAMPLE 1. Ordinarily, the lower the isocyanate index the softer the foam.

Claims (13)

1. A method of manufacturing a semi-flexible polyurethane cellular foam having improved damping characteristics, comprising: reacting an organic polyisocyanate and an active hydrogen-containing compound in the presence of a blowing agent and an amount of a tertiary amine catalyst in significant excess over the amount required for catalytic use alone.

2. A method as claimed in claim 1 wherein the catalyst is used at a level of from 5 to 25 times the amount conventionally employed in semi-flexible foam formulations.

3. A method as claimed in claim 1 or 2 wherein the catalyst is employed in an amount from 1 to 10 parts by weight per 100 parts by weight of active hydrogen-containing compound.

4. A method as claimed in claim 1 or 2 wherein the catalyst is employed in an amount from 2 to 7 parts by weight per 100 parts by weight of active hydrogen-containing compound.

5. A method as claimed in any of claims 1 to 4 wherein triethylenediamine, triethylamine, diethylcyclohexylamine, dimethylethanolamine, N-methyl morpholine, trimethylpiperazine, N-ethylmorpholine, dieth ylethanolamine, 2,4,6-tris(dimethylaminomethyl)phenol, 1-methyl-4-dimethylamine, ethyl piperazine, 3- methoxy-N-dimethyl propyl amine, N-dimethyl-N'-methyl isopropyl propylene diamine, N,N-diethyl-3diethyl aminopropylamine, dimethyl benzyl amine, or a mixture of two or more thereof is used as catalyst.

6. A method as claimed in any of claims 1 to 5 wherein the resulting foam is saturated with a damping fluid to fill the cells of the foam therewith.

7. A method as claimed in claim 6 wherein the saturated foam is encapsulated to prevent the loss of damping fluid.

8. A method as claimed in any of claims 1 to 7 wherein the organic polyisocyanate has the formula: R" (NCO)z where R" is a polyvalent organic radical which is either aliphatic, aromatic, aralkyl, alkylaryl or mixtures thereof and z is equal to the valence of R".

9. A method as claimed in any of claims 1 to 8 wherein the reaction between the organic polyisocyanate and the active hydrogen-containing compound in the presence of a catalyst is carried out in the presence of a surfactant in addition.

10. A method as claimed in claim 9 wherein the surfactant is employed in an amount of from 0.2 to 2.5 parts by weight per 100 parts by weight of the active hydrogen-containing compound.

11. A method as claimed in claim 9 or 10 wherein the surfactant is an alkylpolysiloxane or a polyalkylsiloxane.

12. A method of manufacturing a semi-flexible polyurethane cellular foam carried out substantially as described in the foregoing Example.

13. Semi-flexible polyurethane cellular foams when manufactured by a process as claimed in any of claims 1 to 12.