CA1068450A - Process for the preparation of semi-rigid polyurethane foam having exceptional shock-absorbing properties and vehicle bumpers thereof - Google Patents

Abstract

ABSTRACT OF THE DISCLOSlmE
A ___ _ _ _ A process ls provlded for produclng seml-rlgid polyurethane ioams havlng exceptional sboclc-abYorblng propert~es, even after repeated com-presslon, prepared ~y the reaction of a polylsocyanate; a polyether polyol haylng a molecubr we~ght wlthln the range trom about 2, 000 to about 10, OOO;from about 1 ~o about ~i~ by welght of water per part by we~ht of polyetber polyol;
from about 1 to about 6~c by ~velght of ~urea and/or thloures. per part by welght of polyether polyol; and a cross-1lnklng compour.d haYlng at least three actlve hydrogen atoms per molecule that are reactlve wlth lsocyanate grou~ and havlng a molecular we~ght below about 1000 ln an amount from about 5 to about 25g~ by welght per part by weight of polyether polyol; the amount of polylsocyanate belng selected to give an lsocyanate index wlthln the range from about 0. 7 to about 1. ~.
The process provldes polyurethane foams that have a cellular structure that remalns un~maged under compresslon as high as 60~ at temperatures wlthln the range from about ~ 60°C to about -40~C, and the consequent deformatlon Is 1ess than 1~ even after ten compresslons of at least 50~ In rapid succession.
Accordingly, tlle lnYention iurther pro~rides vehlcle bumpers haYing an impact-r~celvlng layer of thls polyurethane foam, and that meet th~
requlrements of FM~SS 215.

Description

"" 1068450 SPECIFICATION
un;~ ;td~s iA The~llFederal Motor Vehicle Safety Standard FMVSS 215 establishes ``` ~ ^ requirements for safety bumpers for motor vehicles, and i.s applicable to all motor vehicles manufactured on or after September 1, 1973. The 5 objective of the standard is to prevent lo~v sl?eed collisions from impairing the safe operation of the vehicle. Certain requirements for impact resistance and the confi~uration of the front ànd rear surfaces oE the bumper system are prescribed, and the bumper must meet speciIied requirements during alld after impact by a pendlllum-type test device, followed by impact into a ~0 fixed collision barrier that is perpendicular to the line of movement of the vehicle, while the vehicle is travelling forward at a speed of five miles })er hour. The bumpe.r impact-receiving face must not have a permanent deformation greater than three-eights of an inch from its original con-figuration thirty minutes following each impact against the barrier~
15One way to meet the requirement is to incorporate a hydraulic system behind a rigid bumper structure. However, hydraulic systems are heavy, and require a considerable amount of space for proper operation.
Consequently, they are not favored by motor vehicle manufacturers.
An alternative way of meeting the requirement, interposition of à
20 shock-absorbent resin foa~ layer as the impact-receiving surface, has been the subject of considerable investi~ation. This approach contemplates a rigld bumper bar faced with a shock-absorbent layer of semi-rigid polyure-thane resin. The polyurethane resin foam layer receives and absorbs the impact~
25Prior to the promulgation of FMVSS 215, semi-rigid polyurethane foams had been in use for some time as shock~ab~orbing foams for ~068450 instrument panels, steering wheels, different types of bumpers, and shock-absorbent de~rices, as well as packing materials. These materials do not in general have the capability of resisting permanellt deformation after repeatecl compressions in excess of 50~c. Such resistance to permanent deformation or deformation set has not been a feature of polyurethane foam materials, l)ut for most purposes, where the material is not subjected to repeated compression, this has posed no problem.
The situation changed when FMV~S 215 was promulgated. Very few of the available semi-l igid polyurethane foams are capable of meeting the FM~SS 215 requirements.
The FMVSS 215 requirements are discussed in U. S. patent No.
3,q 39, 10~, ,~ 3, ~30,10~, issued February 17, 1976 to Dunleavy and Hawker. In their discussion of the art prlor to their invention, Dunleavy and Hawker point out that the polyurethane polymers providedby UO S. patent No. 3,493,257, patented February 3, 1970 to Fitzgerald, Haines, Harris and Kienle, are`
not capable of meeting the F~VSS 215 requirements. The polymers of this patent are too sensitive to temperature changes, and at cold temperatures the polyurethane foam is too hard.
Patellt No. 3, 939~106 provides an improved polyurethane foam ,~
using high molecular weight polyol starting materials. The polyurethane foam of that illvention is prepared by forming and curing a reaction mixture of: `
" a. a polymer polyol comprising a major liquid polyoxyalhylene polyol that has a molecular weig~ht of at least 1500 and a hydroxyl number from 20 to 120 and that contains therein a minor amount of film-forming organic polymer having a molecular weight of at least 5000, " b. an aromatic polyamine having at least two primary amine groups ( NH2) attached to carbon atoms of the same or different aromatic rings, at least one of such carbon atoms being adjacent to a carbon atom having a substituent other than hydrogen, '~ c. an aromatic glycol, "d. an organic polyisocyanate in an amount that provides from 0.8 to 1~ ~ (preferably from 0. 95 to 1.1) isocyanate groups per active hydrogen group in the reaction mixture, " e. a catalytic amount of catalyst for the curing of the reaction mlxture to produce the elastomer, and "f. a blowing a~ent in an amount sufficient to produce a cellular structure in the elastomer, "said reaction mixture containing from 97 to 65 (preferably from 97 to 85) parts by weight of (a) and from 3 to 35 (preferably from 3 to 15) parts by weight of (b) per 100 parts by weight of (a) and (b) and said reaction mixture containing from 1 to 35 (preferably from 1 to 20) parts by weight of (c) per 100 parts by weight of (a) and (c), with the proviso that the reaction mixture contains no more than 35 parts by weigllt of (b) and (c) per 100 parts by weight of (a), (b) and (c). "
13ven in the case of the polymers of that patent, however, the patentees point out that:
". . . a specific formulation (reaction mixture) for an energy absorb-ing impact elastomer cannot be described which would answer each and every application requirement. The reaction mixture used in a particular case will depend upon the speciEications necessary for satisfactory performance ~mder the given conditions. For e~ample, the particular operating temperature range, the final forces and deflections allowed during the impact cycle, cost requirements, processing re~uirements , etc., must be considered far each case. "
In accordance witll the invention, a series of semi-rigid polyurethane foams are provided having a high shock-absorbent capability over a wide range of temperatures, even after repeated compressions in excess of 50%, and which do not acquù e a permanent deformation or deformation set in excess of ~ ven after rapidly repeated compressions. The term "semi-rigid"
means that the polyurethane foam must be subjectecl to a pressure within the range from about 50 to about 200kPa to obtain a compression of ~k. ~, Consequently, the polyurethane foam in accordance with the invention can be used as the impact absorbent layer on bumpers which will meet the requirements of FMVSS 215.
The process for preparin~ semi-rigicl polyurethane foams of these properties in accordance with the invention comprises reacting a polyiso-cyanate; a polyether polyol having a molecular weight within the range from about 2, 000 to about 10, 000, preferably from about 3000 to about 7000; from about 1 to about 5~C, preferably from about 1. 5 to about 4~C,bY weight of water per part by weight of polyether polyol; from about 1 to about 6~k, A preferably from about 1. 5 to about~ by weight of urea and/or thiourea per part by weight of polyether polyol; a cross-linking compound having at least tbree active hydrogen atoms per molecule that are reactive with iso-cyanate groups and having a molecular weight below about 1000, preferably below about 500, in an amount from about 5 to about 25~c, preferably from :1068450 about 7 to ab~ut 20~C by weight per part by weight of polyether polyol; the amount of polyisocyanate being selected to give an isocyanate index within the range from about 0. ? to about 1. 4, preferably from about 0. 9 to about 1. 2.
The polyurethane foams obtained by this process hàve a cellular structure that remains undamaged by higll compression at temperatures within the range from about ~ 60C to about -40C, even after compressions as hi~h as 60O/C, and the consequent deformation is less than l~, even after ten compressions of at least 50~c~ in rapid succession~ ~ccordlngly, thls poly~u~ethalle foam is exceptionally suited for the manufacture of poly-urethane bumpers that meet the requirements of FMVSS 215~
The invention therefore further pro~ides a vehicle bumper ~.
comprising a bumper frame or support, and an impact-absorbing facing layer comprising a polyurethane foam of the invention having a density within the range from about 50 to about 150 g/dm3, preferably from about 70 to about 120 g/dm3, and a deformation (noted thirty minutes after compression) not e~ceeding 1~c over a temperature range from about 60 C to about -~0 C .
In the drawings:
Fi~,ures lA, lB, lC, lD and lE represent the force in kPa require~l 20 for compression and retrogression of the test foams of Example 1.
Figuxes 2~, 2B, 2C, 2D and 2E represent the force in kPa reg.uired for compression and retrogression of the test fGams of Example 2.
Fi~ure 3 represents the force ~n kPa required for compression and retrogression of the test foams of Example 3.

~068450 Fi~ure 4 represents the force in kPa required for compression and retrogression of the test foams of Example 4~
Figure 5 represents the force in kPa required for compression and retrogression of the test foams of Example 5.
Fi~u e 6 represents a view in cross-section of a motor vehicle bumper including a polyurethane foam of Example 2.
The shock-absorbellt capability of the polyurethane foam of the in~e~tion is attributed to the presence of u~ea and/or thio~u~ea, and the cross-linking compound~ In the absence of either Ol` both of these ingredients, 10 the shock-absorbing capability is greatly reduced.
The cross-linking compound can contain the active hydrogens reactive with isocyanate groups attached to nitrogen, for example, as a part of amino groups, or attached to oxygen, for example, as hydroxyl groups, or a mixture of amino and hydroxyl groups.
` Exemplary amines include ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, propylene diamine, dipropylene triamine, butylene diamine, dibutylene triamine.
Exemplary hydroxyamines include monoethanolamine, diethanol-amine, triethanolamine, monopropanolamine, dipropanolamine, dibutanol-20 amine, monobutanolamine, diiso~ropanolamine, tripropanolamine, andtributanolamine.

10684S~

Exemplary polyols include ethylene glycol, glycerol, penta-erythritol, trimethylol propane, trimethylol ethane, butanetriol, hexanetriol, arabitol,xylitol, sorbitol, mannitol,clulcitol, triethylolmethane, triethylol-ethane, and erythritol.
Also useful are the polyoxyalkylene polyols obtained by condensation of an alkylene oxide (such as ethylene oxide, propylene oxide, butylene aa~ide, and muxtures thereof) with any of the polyols just referred to above.
Illustrative aLkylelle oxide adducts of polyhydroxyall~anes include, among others, the alkylene oxide adducts of ethylene glycol, propylene glycol, 1,3-dihydroxypropane, 1,3-dihydroxybutane, 1,4-dihydroxybutane, ~,4~-, 1,5- and 1,6-dihydroYyhexalle, 1,2-,1,3-, 1,4-, 1,6- and 1,8-dihydro~yoctane, 1,10-dihydroxydecane, glycerol, 1, 2, 4-trihydroxybutane, 1, 2, 6-trihydroxyhexane, 1, 1, 1-trimethylolethane, 1, 1, 1-trimethylolpropane,pentaerythritol, caprolactone, polycaprolactone, xylitol, arabitol, sorbitol, mannitol, and the like; preferably the adducts of ethylene oxide, propylene oxide, epoxybutane, or mi~xtures thereof. A preferred class of aLkylene ~xide adducts of polyhydr~xyalkanes are the ethylene oxide, propylene oxide, butylene ~xide,or mixtures thereof, adducts of trihydroxyaLkanes.
Ethylene oxide capped (~C2H4OH terminated) propylene oxide polyols are preferred because of their increased reactivity over noncapped propylene oxide polyols thus leadin~ to decreased demold times for the molded article.
Tllustrative hydrQYyl-terminated polyesters are those which are prepared by polymerizing a lactone in the presence of an active hydrogen-containing starter as disclosed in U.S. patent No. 2,914,556.

1~6~450 Tt is important that the amount of cross-linlcing compound be at least 5~c per part by weigrht of polyether polyol. An amoullt below 5~ gives a foam whose shock absorbency is too low. On the other hand, an amount in excess o abo~lt 2~/c of cross-linking compound resùlts in a foam that is S too rigid, and insuficiently compressible to meet the FMVSS standard.
Tt is generally preferred that the cross-linking compound contains a mixture of hydroxyl and amino groups, and that at least ~~c of the cross-linking~ compound be an amine having at least one hydroxyl group, such as triethanolamille, diethanolamine, and monoethanolamine. The amino 10 alcohols have a catalytic effect on the reaction between hydroxyl groups and isocyanate groups, and therefore can replace the conventional catalysts employed in the preparation of polyurethane foams, either in whole or in part.
Resista~lce of the polyurethane foam to development of compression 15 set can be enhanced if the reaction mixture contains a small amount of a strong base, usually within the range from about 0. 001 to about 1~c by weight of the polyether polyol. Strong bases which can be used include the inorganic bases, the aLkali metal and aL~aline earth metal hydroxides, alkaline-reacting inorganic salts of tllese metals, including the alkali 20 metal and alkaline earth metal carbonates, borates, phosphates, acetates, formates and isocyanates, as well as strong organic amine bases.
Exemplary are sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide~ barium oxide, calcium oxide, strontium hydroxide, sodium carbonate, potassium carbonate, sodium acetate, potassium formate, 25 sodium borate, potassium borate, sodium phosphate, potassium phosphate, SOdiUIll ben~oate, potassium benzoate, calcium phosphate, pyridine, tributylamine, morpholine, triethylamine, ethylisopropylamine, and tripropylamine. Strong bases have the capacity of rupturing cell walls in the course of foam formation without collapsing the foam, thus resulting 5 in a foam havingahigh proportion of open cells. This is important in increasing the compressibility of the foam, since an open cell foam does not develop high internal cellular gas` pressure upon compression.
The polyether polyol is an adduct of an alkylelle oxide to a polyol havin~ at least two and preferably at least three hydroxyl ~roups with 10 reactive hydrogen atoms. The alkylene oxide can be ethylene oxide, propylene oxide~ butylene oxide, and any mixture of two or thl~ee thereof.
The polyol can have from two to si~c hydroxyl groups and from two to six carbon atoms, and includes ethylene glycol, diethylene glycol, triethylene glycol, butanediol, pentanediol, propanediol, dipropylene glycol, hexanediol, 15 glycerol, trimethyloi propane, triethylolmethane, triethylolpropane, butanetriol, hexanetriol, pentaerythritol, erythritol, sorbitol, mannitol, xylitol, arabitol, dulcitol, trimethylolethane, and triethylolethane.
Also useful compounds having reactive hydrogen atoms which form adducts with alkylene oxides include amines and aminoalcohols, including, 20 for example, aliphatic, aromatic and heterocyclic polyamines and amino-alcohols having at least one amine and one hydroxyl group or two amine groups, such as monoethanolamine, diethanolamine, triethanolamine, ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylene-tetramine, tetraetllylenepentamine, pentaethylenehexamine, dipropylene-25 triamine, and tripropylenetetramine.

As the all~rlene oxide, ethylene oxide and propylene oxide arepreferred. Mixtures of from 5 to 60~C ethylene o~ide and from 9S to 40~C
propylene oxide (calculated on the total weight of all;ylene oxide units derived from alkylerle oxide) are preEerred. If desired, a small amount of 5 butylene oxide, up to about 20~c by weight, can also be added. Amounts of ethylene oxide in excess of 60~c give relatively hydrophilic foams, which are capable of absorbing large amounts o~ water, which may be a disadvantage.
If several alkylene oxides are used, they can be added separately, in serles, in lncrernents, alternatingly, or together as a mixture, or any 10 combination of these alternatives.
In general, the polyether polyols should have from about 2. 2 to about 3. 5 reactive hydrogens per mole. A hydroxyl number within the range from about 25 to about 40, and a primary hydroxyl number within the range from about 10 to about 80~C, and preferably from about 60 to about 80~C, 15 are prefèrred.
The organic polyisocyanate should have at least two and preferabIy three or more isocyanate groups. The aromatic isocyanates are preferred but aliphatic, heterocyclic, cycloalipllatic, and mixed aliphatic aromatic, aliphatic heterocyclic, and aliphatic cycloaliphatic polyisocyanates can 20 alsobe used.
Exemplary are tetramethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, xylene diisocyanate, phenylene diisocyanate, naphthylene diisocyanate, 1-methyl-2, 6-phenylene diisocyanate, cyclohexane diisocyanate, diphenylmethane diisocyanate, and polyphenyl-

2~ polymethylene polyisocyanate.

`` 1068450 `
Of these polyisocyanates, toluene diisocyanate is preferred, either in its isomeric 2,4-form or 2,6-form, or as mixtures of these two isomeric forms. A suitable mi~ture is composed of about 80~C 2,4 - toluene diisocyanate and 20~/c 2, 6 - toluene diisocyanate.
5Another class of suitable polyisocyanates has at least two benzene rings, with one isocyanate group per ring, the benzene rings being inter~
connectedby ether, sulfone, sulfwcide, methylene, ethylene, propylene, or carb~nyl ~roups, and having tlle g,~eneral structure:
NCO NCO NCO
10 ~-Y L-~-Y! ~ , where Y is a linking group selected from the group consisting of 15 - ~CH2-, -C2H4-~ -C~H6- and - Il-, preferably -CH~-; and O ~) O
n is a number within the range from about 0. 2 to about 1. 5, it being understood that n represents an average of the species present, and therefore need not be an integer, in which species n is an integer and can 20 range from 0 to about 10.
The amount of polyisocyanate employed is stoichiometrically equivalent to the reactive hydrogens present that are reactive with isocyanate groups, taking into account the polyether polyol, carbamine compound, water and other reactants, so that the resulting polyurethane foam has an isocyanate 106~4S0 inde~;, i. e., a ratio between isocyanate groups and isocyanate-reactive hydrogen atoms present in the mixture, witbin the range from about 0. 7 to about 1. 4, and preferably from about 0. 9 to about 1. 2.
The reaction between the polyisocyanate and the polyether polyol 5 is carried out in the presence of a catalyst, the catalyst being any catalyst l~lown to catalyze this ~olymeri~ation ~eaction. The catalyst forms no part of the installt invention.
An amine catalyst can be used, particularly tertiary amines, such as diethylene t~iamine, dimethylami1loetllanol, and tetramethyl ethylene-10 dia mlne.
Also useful are org~anometallic compounds such as lead octoate,dibutyltin dilaurate, tin octoate, tin-2-ethylhexoate, lead naphthenate and col~alt naphthenate.
Only a small amount of the catalyst is required. The amount can be 15 within the range from about 0. 01 to about 5. ~c by weight of the polyether polyol, and preferably from about 0. 05 to about 1. ~c by weight.
The blowing agent is a compound capable of generating an inert gas under the reaction conditions used, by reaction to produce a gas, or by volatilization. According to the invention the blowing agent is water. If so 20 desired the water could be combined with other blowing agents like volatile halocarbons (especially chlorocarbons and chlorofluorocarbons) such as methylene chloride, trichloromonofluoromethane, dichlorodifluoromethane, dichloromonofluoromethane, dichloromethane, trichloromethane, bromo-trifluoromethane, chlorodifluoromethane, chloromethane, 1,1-dichloro-1, 1 ~06~3450 fluoromethane, 1,1-difllloro-1, 2,2-trichloroethane, chloropentafluoroethane, 1-chloro-1-fluol~oethane, 1-chloro-2-fluoroethane, 1,1,2-trifluoroethane, 2, -chloro-1, 1, 2, 3, 3, 4, 4-heptafluorobutane, hexafluorocyclobutane and oct~fluorobutane; ancl low-boiling hydrocarbons such as butane, pentane, 5 hexane, and cyclohexalle.
The amount of blowing ag~ent is determined by the desired foam properties. From about 1 to about 5 parts by weight of water and, if so desired, 0. 3 to 0.1 paI~t by wei~m of another blowing agent per part by weight o the }~olyether polyol is generally satisfactory~
Foam stabilizers such as silicone oils can be added, to improve foam stability in the course of foam formation, and the physical strength o~ the polymer.
The density of the foam is controlled by the addition of water and the blowinD agent.
The temperature of the reaction is in no way critical. The reaction proceeds at temperatures slightly above normal room temperature, such as 30C. The maximum temperature is that which leads to undesirably rapid decomposition of the blowing agellt, and loss of control of the foam properties~ In general, the reactio~ temperature is within the range from 20 about 30 to about 130C.
A prepolymer can first be prepared by reacting the polyether polyol with a stoichiometric excess of the multifunctional polyisocyanate, or, alternatively, of the polyisocyanate with a stoichiometric excess of the polyether polyol, under circumstances such that the prepolymer 25 contains isocyanate and/or hydroxyl terminal groups~

-`` 10684S0 The amounts of polyether polyol and polyisocyanate are so chosen that the isocyanate index is within the range from about 1. 5 to about 3, when the prepolymer contains isocyanate terminal gl`OUpS, and within the range from about 0.1 to about Q. 7, when the prepolymer contains hydroxyl 5 terminal groups.
The reactive prepolymer is then mixed with the remaining polyol Ol` polyisocyanate, cross-linking compound, carbamide compound, catalyst, foam stabilizer, filler, pigment, and any other reactant com~onent, and introduced into a mold.
It is also possible to mix all of the reactants together, and allow the reaction to proceed with this reaction mixture. This can be done by first mixing polyether, polyol, cross-linking agent and catalyst, and then adding polyisocyanate. It is also possible first to react polyisocyanate and the carbamide compolmd, and then add the remaining ingredients.
The following Examples in the opinion of the inventor represent preferred embodiments of the invention.

Five polyurethane foams were prepared, in accordance with the following procedure. The polyether polyol ~sed was prepared by 20 addition to glycerol of,first,propylene oxide, to a molecular weight of about 4300, and then ethylene oxide, to a molecular weight of about 5000.
The formulations ~ each of these polyurethane foams were as follows:

TABLE I
Exam~le No. lA lB lC _ lD _ lE
Ingredients Parts by Weight Polyether polyol 100 100 100 100 100 Triethanolamine 15 15 15 15 15 Water 3.0 3.0 3.0 3.0 3.0 Dimethylamilloethanol 0. 25 0. 25 0. 25 0. 25 0. 25 Polyphenylpolymethyle~le polyisocyanate (functionallty 2. 5) 95. 9 95. 9 95. 9 95. 9 95. 9 lû Urea 0 1 2 3 4 Isocyanate Index 1 0. 95 0. 91 0. 87 0. 84 The reaction mixture was prepared by mixing together:
(1) polyether polyol and triethanolamine;
(2) water, dimethylaminoethanol, and urea; and

(3) polyphenylpolymethylene polyisocyanate.
Each of the reaction mixtures was poured into a mold 1800 mm x 150 mm x 120 mm and allowed to react for 0. 5 hour. After conditioning for 24 hours at room temperature and 50~c relative ~lumidity, 50 mm x 50 mm samples of each test foam lA to lE were taken~ The samples were com~
pressed at a rate of 150 mm per minute to a compression of 70~c. Com-pression was then released, at the same rate. The force in KpA required for compression and retro,,ression was registered by a recorcler, resulting in the dia~ams lA, lB, lC, lD and lE of the drawing. -~068450 It is apparent from the diagrams that the polyurethane foams in accordance with the invention, Examples lB, lC, lD and lE, have a very high shock-absorbing capability. The polyurethane foam lA without the urea was quite unsatisfactory in this respect.
Samples of foams lA to lE were àlso subjected to a dynamic impact test. Each of the test foam specimens was subjècted to a 60~/c compression at 25~C, the compression and retrogression being completed within this tin~e interval. The foams were then allowed to stantl for 30 minutes. Tn each case, the deformation remailling after this time was less than 1~ .
It is apparent that the polyurethane foams in accordance with the invention have a high shock~absorbent capability, together with an absence of deformation set.

Five polyurethane foams were prepared in accordance with the following procedure. The polyether polyol used was prepared by addition to glycerol of, first, prowlene oxide to a molecular weight of about 4300, and then, ethylene oxide to a molecular weight of 500~. The formulations of each of these polyurethane foams were as follows:

TABLE II

Example No. 2A 2B 2C 2D 2E
.
dients Parts by Weigllt Polyether polyol 95.9 100 103.6 107.3 110.9 Triethanolamine 15 15 15 15 15 Water 3~0 3.0 3.0 3.0 3.0 Dimethylaminoethanol 0. 25 0. 25 0. 25 0. 25 0. 25 Polyphenylpolymethylerle 95- 9 95- 9 95- 9 95- 9 95- 9 polyisocyanate (futlctiouality 2.5) Thiourea 0 1 2 3 4 _ Isocyanate Index 1 1 1 1~ 1 The reaction mixture was prepared by mixing together:
(1) polyether polyol and triethanolamine;
(2) water, dimetllylaminoethanol, and thiourea; and (3) polyphenylpolymethylene polyisocyanate.
- Each of these mixtures was poured into a mold 1800 mm x 150 mm x 120 mm and allowed to react for 0. 5 hour. After conditioning for 24 hours at room temperature and 50~C ~elative humidity, 50 mm x 50 mm samples of 20 each test foam were taken. The samples were thell compressed at a rate of 150 mm per minute to a com~ression o~ 70~c. Compression was then released at the same rate. The force requirecl for compression and retrogression was re~isterecl by a recorder, resulting in the diagrams shown as 2A, 2B, 2C, 2D and 2E in the drawing.

106~450 It is a~parena rom tlle diagrams that the polyurethane foams in accordallce with tlle invention,Examples 2B, 2C, 2D and 2E:,have a very high shock-absorbing capability. The polyurethane foam without the thiourea (2A) was quite unsatisfactory in this respect.
Samples of the differellt polymers were also subjected to a dynamic impact test. Each of the test foam specimens were subjected to a 60~C
compression at 25~C~ the compression and retrogression belng completed within this time interval. The foams were then allowed to stand for 30 mil~uaes. In each case, the deformation remaining after this time was less than l~c-It is apparent that the polyurethane foams in accordance with the invention have a high shocl~-absorbent capability, together with an absence of deformation set.
EXA~IPLE 3 ~ polyurethane foam was prepared in accordance with the following procedure. The polyether polyol used was prepared by addition to glycerol of, first, propylene oxide to a molecular weight of about 4300, alld then, ethylene o~ide to a molecular weic~,ht of 5000. The formulation of the poly~ethane foam was as ollows:

106~3450 T~BLE III

In~Jredients Parts by Wei~t Polyether polyol lO0 Triethanolamine 15 Water 3~ 0 Dimetllylaminoethallol 0. 25 Polyphellylpolymetllylene polyisocyanate (functionality 2. 5) 106. 5 Urea 2. 0 10 Isocyanate Index ~ . .
The reaction mixture was prepared by mixing together:
(l) polyether polyol and triethanolamine;
(2) water, dimethylaminoethanol, and urea; and (3) polyphellylpolymethylene polyisocyanate.
The reaction mixture was poured into a mold 1800 mm x 150 mm x 120 mm and allowed to react for 0. 5 hour. After conditioning for 24 hours at room temperature and 50~0 relative humidity, a 50 mm x 50 mm sample of the foam was tak~n. The sample was canpressed at a rate of 150 mm per minute to a compression of 70~Zo. Compression was then released at the same - 20 rate. The force required for compression and retrogression was registered by a recorder, resulting in the diagram 3 shown in the drawing.

It is app.~rent from the dia~ram that the polyurethane foam in accordance with the invention has a very high shock absorbent capability.
The sample was also subjected to a dynamic impact test. The test foam specimen was subjected to a 609ro compression at 25C, 5 the compression and retrogression being completed within this time interval. The foam was then allowed to stand for 30 minutes. The deformation`re~aining after this time was less tllan 1qb.
It is apparent that the polyurethane foa~n in accordance with the invention has a high shock-absorbent capability, together with an absence 10 of defol~n~ation set.

A polyurethane foam ~vas prepared in accordance with the following procedure. The polyether polyol used was prepared by addition to glycerol oE, first, propylene oxide to a molecular weight of about 5000 and then, ethylene oxide to a molecular weight of 6000. The formulation of the polyurethane foam ~vas as follows:
TABLE IV
In~edients Parts by Weight Polyether polyol ` 100 ~:q :
Triethanolamine 15 Water 3. 0 Dimethylaminoethanol 0. 25 Polyphenylpolymethylene polyisocyanate (functionality 2 . 5) 105 . 2 Urea 2.0 25 Isocyanate Index The reaction mixture was prepared by mixing together:
(1) polyether polyol and triethanolamh~e, (2) water, dimethylaminoethanol, and urea; and (3) polyphenylpolymetllylene polyisocyanate.
The r eaction mi~;ture was poured into a mold 1800 mm x 150 mm x ~20 mm and allowed to react for 0. 5 hour. After conditiorling for 24 hours at room temperature and 50~c relat~re humidity, a 50 Irlm x 50 mm sample of the foam was taken. The sample was compressed at a rate of 150 mm per minute to a compression of 70/~c. Compression was then released at the same rate. The force reqLuired for compression and retrogression was registered by a recorder, resulting in the diagram ~ shown in the drawing.
It is apparent from the diagram that the polyurethane foam in accordance with the invention has a very high shock-absorbent capability.
The sample was also subjected to a dvnamic impact test. The test foam specimen was subjected to a 60~k compression at 25C, the compression and retrogression being completed within this time interval. The fo~m was then allowed to stand for 30 minutes. The deformation remaining after this time was less than l~c.
It is apparent that the polyurethane foam in accordance with the invention has a high shock-absorbent capability, together with an absence of deformation set.
.

A polyurethane foam was prepared in accordance with the following procedure. The polyether polyol used was prepared by addition to glycerol of, first, propylelle oxide to a molecular weight of about4300, 5 and then, ethylene o2~ide to a molecular weight of 5000. The formulation of the polyurethane foam was as follows:
TABLE V
ngredients P rts by Wei~t Polyether polyol 100 Triethanolan~ e 10 Water 4 0 Diethanolamine 2. 0 NaOH 0. 1 Polyphenylpolymethylene polyisocyanate (functionality 2. S) 115. 0 Glycerol 2. 0 Urea 3 0 . . . _ . _ . . .
Isocyanate Index o. go .. .. . ~
The reaction mixture was prepared by mixing together:
(1) polyether polyol and triethanolamine;
(2) water, diethanolamine, Na~H, glycerol, and urea; and (~) polyphenylpolymethylene polyisocyanate.
The reaction mixture was poul~ed into a mold 1800 mm x 1500 mm x 120 mm and allo~ved to react for 0. 5 hour. After conditioning for 24 hours at room temperature and 50/c relative humidity, a 50 mm x 50 mm sample of the foam was taken. The sample was compressed at a rate of 150 mm per minute to a compression of 70/c. Compression was then released at the same rate. The force required iOl' compression and retrogression was registered by a recorder, resulting in the diagram 5 shown in the drawing.
It is apparent from the diagram that the polyurethane foam in accordance with the inventioll has very higll shock absorbent capability.
The sample was also subjected to a dynamic impact test. The test oam specimen ~vas ~ubjected to a 60~ compression at 25C, the compression and retrogression being completed within this time interval. The foam was then allowed to stand for 30 minutes. The deformation remaining after this time was less than 1~
The bumper shown in Figure 6 has a frame 1 and an impact-receiving facint, layer 2 of polyurethane foam mounted in the frame. The foam layer 2 has a density of 50-150 grs/dm and a remaining deformation of at most 1'~c at a dynamic compression of 60~c within the temperature range from -40C to +60C after 30 minutes. The bumper according to the invention can easily be given such dimensions that it complies with the ~n ~t~ s+Qt~5 "~ requirements oftFederal ~otor Vehicle Security Standard 215 (~MVSS 215).For a heavy vehicle, a polyurethane foam of a somewhat higher density is normally preferred to a lighter one.
The polyurethane foam layer 2 is attached to the frame 1 by a number of assembly screws 3 (of which only one screw is shown) which thread into a perforated aluminum sheet 4 molded in situ in the polyurethane foam layer. A protective cover 5 of a thin hydrophobic plastic film material such as polypropylelle or polyethylene keeps out moisture and dirt from the polyurethane foam layer 2.
The polyurethane foam was made of the same formulation as Example 2C, injected into a mold 14 cms ~16 cms x 172 cms. The mold 5 was closed, and the ~eaction mi.;t~u~e allowed to react at a mold tempera-t~u~e of ~0C. The ~olyurethane foam had a density of 96 grs/dm~. Further-more, before the casting of the polyurethane in the mold a perforated alumlnum sheet with assembly screws 3 and a cover 5 had previously been inserted, arranged in such a way that after the casting and assembling 10 of a frame, the structure shown in Figuxe 6 was obtained. The bumper was testèd accoxding to F~aVSS 215, and found to meet all requirements of the specification.

2a~

Claims (23)

Having regard to the foregoing disclosure, the following is claimed as the inventive and patentable embodiments thereof:

1. A process for preparing semi-rigid polyurethane foam having a high shock-absorbent capability over a wide range of temperatures, even after repeated compressions in excess of 50%, and which do not acquire a permanent deformation or deformation set in excess of 1% even after rapidly repeated compressions, which comprises reacting a polyisocyanate;
a polyether polyol having a molecular weight within the range from about 2000 to about 10, 000; from about 1 to about 5% by weight of water per part by weight of polyether polyol; from about 1 to about 6% by weight of at least one member selected from the group consisting of urea and thiourea per part by weight of polyether polyol; and a cross-linking compound having at least three active hydrogen atoms per molecule that are reactive with isocyanate groups and having a molecular weight below about 1000 in an amount from about 5 to about 25% by weight per part by weight of polyether polyol; the amount of polyisocyanate being selected to give an isocyanate index within the range from about 0.7 to about 1.4 at a temperature at which reaction proceeds within the range from about 30 to about 130°C until a polyurethane foam is produced.

2. A process according to claim 1, which comprises first preparing a prepolymer by reacting the polyether polyol with a stoichiometric excess of the polyisocyanate to form a prepolymer containing isocyanate terminal groups.

3. A process according to claim 1, which comprises first preparing a prepolymer by reacting the polyisocyanate with a stoichiometric excess of the polyether polyol to form a prepolymer containing hydroxyl terminal groups.

4. A process according to claim 1 in which the member is urea.

5. A process according to claim 1 in which the member is thiourea.

6. A process according to claim 1 in which the cross-linking compound contains the active hydrogens reactive with isocyanate groups attached to nitrogen as a part of amino groups.

7. A process according to claim 1 in which the cross-linking compound contains the active hydrogens reactive with isocyanate groups attached to oxygen as a part of hydroxyl groups.

8. A process according to claim 1 in which the cross-linking compound contains the active hydrogens reactive with isocyanate groups attached to nitrogen and oxygen as a mixture of amino and hydroxyl groups.

9. A process according to claim 1 in which the cross-linking compound is a polyol.

10. A process according to claim 1 in which the cross-linking compound is a polyoxyalkylene polyol obtained by condensation of an alkylene oxide with polyol.

11. A process according to claim 1 in which the reaction mixture also contains an amount of a strong base within the range from about 0. 001 to about 1% by weight of the polyether polyol.

12. A process according to claim 11 in which the base is selected from the group consisting of the alkali metal and alkaline earth metal hydroxides, alkaline-reacting inorganic salts of these metals, and organic amine bases.

13. A process according to claim 1 in which the polyether polyol is an adduct of an alkylene oxide to a polyol having at least two hydroxyl groups with reactive hydrogen atoms, the alkylene oxide having from two to four carbon atoms and the polyol having from two to six hydroxyl groups and from two to six carbon atoms.

14. A process according to claim 1 in which the polyether polyol is an adduct of an alkylene oxide to an amine or aminoalcohol having at least one amine and one hydroxyl group or at least two amine groups.

15. A process according to claim 1 in which the organic poly-isocyanate has at least two isocyanate groups and is selected from the group consisting of aliphatic, heterocyclic, cycloaliphatic, and mixed aliphatic aromatic, aliphatic heterocyclic, and aliphatic cycloaliphatic polyisocyanates.

16. A process according to claim 15, in which the polyisocyanate is toluene diisocyanate.

17. A process according to claim 15, in which the polyisocyanate has at least two benzene rings, with one isocyanate group per ring, the benzene rings being interconnected by a member selected from the group consisting of ether, sulfone, sulfoxide, methylene, ethylene, propylene, and carbonyl groups, and having the general structure:

where Y is a linking group selected from the group consisting of -O-, -?-, -?-, -CH2-, -C2H4-, -C3H6- and -?-; and n is a number within the range from about 0.2 to about 1.5 representing an average of the species present.

18. A process according to claim 1 in which the reaction between the polyisocyanate and the polyether polyol is carried out in the presence of a catalyst.

19. A process according to claim 18 in which the catalyst is an amine.

20. A process according to claim 18 in which the catalyst is an organometallic compound.

21. A process according to claim 1 in which the reaction mixture also includes a blowing agent capable of generating an inert gas under the reaction conditions used.

22. A polyurethane foam obtained by the process of claim 1, having a cellular structure that remains undamaged by high compression at temperatures within the range from about + 60°C to about -40°C, even after compressions as high at 60%, and a consequent deformation of less than 1%, even after ten compressions of at least 50%, in rapid succession.

23. A vehicle bumper comprising a bumper support, and an impact-absorbing facing layer comprising a polyurethane foam of claim 22, having a density within the range from about 50 to about 150 g/dm3 and a deformation (noted thirty minutes after compression) not exceeding 1%
over a temperature range of from about + 60°C to about -40°C.