HK1025982A - New isocyanate-terminated prepolymers - Google Patents

Description

Novel isocyanate-terminated prepolymer

The present invention relates to novel isocyanate-terminated prepolymers made from polyols having high molecular weight and to the use of such prepolymers in the preparation of flexible polyurethane foams.

U.S. Pat. No. 4,687,851 discloses the preparation of polyurethane and/or polyurea polymers which are the reaction product of a reaction mixture comprising a polyisocyanate and a polyether polyol having an equivalent weight of at least 2000 and an unsaturation level of less than 0.1 weight percent. The object of this patent is to use high molecular weight polyols with low unsaturation levels to prepare elastic and flexible materials with high resilience, good tensile properties and compression set and low glass transition temperatures. Also disclosed is the use of polyols having suitable equivalent weights (250-2000); there is no specific indication as to how such polyols are to be used, particularly with respect to the point of being non-compatible with water. All examples relate to the preparation of solid elastomers.

EP-394487 discloses the use of high molecular weight polyether polyols having a low level of unsaturation for the preparation of flexible foams having a low resonance frequency; these polyols are preferably used as a matrix for so-called polymer-dispersed polyols. EP-443614 suggests a modification of EP-394487: because of the high viscosity of the polyol, it is sometimes difficult to sufficiently mix the raw materials when preparing a polyurethane foam; to overcome this, EP-443614 has added thereto a viscosity-reducing compound having an addition-polymerizable unsaturated group, such as methacrylate compounds, vinyl ether compounds, vinyl ester compounds, alkyl ether compounds and alkyl ester compounds.

EP-422811 discloses the use of polyisocyanates for the preparation of flexible polyurethane projectiles having good elastic and elongation properties; the polyisocyanate is a prepolymer made from a polyether polyol having a high molecular weight. The prepolymer used has a rather high NCO-content, which means that the polyol content in the prepolymer is limited.

GB 2296499 discloses the use of prepolymer compositions for the manufacture of microporous moulded articles. Although polyols have been disclosed as being widely used in prepolymer compositions and resin subcomponents, there is no particular indication of the use of polyols having high molecular weights, nor of course of the use of such polyols for the preparation of water blown flexible foams. The amount of water used is low and the product obtained is a high density microcellular elastomer.

EP-420273 relates to a process for preparing flexible foams using a prepolymer composition to obtain flexible foams of low Shore A hardness. However, the problems encountered with the use of polyols having a high molecular weight are not mentioned.

EP-485953 relates to the use of prepolymers prepared using polyols having a high molecular weight and a relatively high oxyethylene content to improve the elongation properties of flexible foams.

WO 95/18163 relates to a process for the preparation of rigid polyurethane foams using prepolymers prepared by reacting polymeric MDI with polyols having a molecular weight of at least 2000 and a relatively large ethylene oxide content.

EP-392788 relates to isocyanate-terminated prepolymers and their use in the manufacture of flexible foams. The prepolymers used are prepared from polyols having a relatively low molecular weight, and in the preparation of polyurethane foams, resin auxiliary components which do not contain polyols are used.

It is known that polyols having a high molecular weight have a higher viscosity than polyols having a low molecular weight. EP-443614 suggests that such high viscosity may lead to handling difficulties; these difficulties can be alleviated by the addition of viscosity reducing compounds.

EP-111121, EP-344551, WO 95/34589, WO 95/34590 and WO95/34591 further disclose the use of prepolymers for the preparation of flexible foams; no particular indication is made as to the use of high molecular weight polyols.

The larger the amount of the high molecular weight polyol used, the more difficult the handling becomes. It has been found that when preparing water-blown flexible polyurethane foams based on MDI (diphenylmethane diisocyanate), the viscosity of the mixture of water and polyol increases when increasing the molecular weight leads to an increase in the viscosity of the polyol. Surprisingly, it has been found that the viscosity of the prepolymer does not increase by an equal amount with the viscosity of the polyol used; although the difference in viscosity between the high and low molecular weight polyols is significant, the viscosity of the prepolymer containing a significant amount of high molecular weight polyol is only slightly higher than the viscosity of the prepolymer made with a significant amount of lower molecular weight polyol. The present invention therefore relates to such prepolymer compositions and to a process for making flexible foams by reacting such prepolymer compositions with an isocyanate-reactive compound or a composition using water as blowing agent. Even in the absence of viscosity reducing agents, the treatment process has been greatly modified. The foams exhibit excellent properties, especially high ball rebound and low compression set. The present invention therefore relates to an isocyanate-terminated prepolymer composition comprising 1) a urethane containing adduct of diphenylmethane diisocyanate and a polyether polyol 1), the diisocyanate optionally containing an oligomer having an isocyanate functionality of greater than 2, the polyether polyol 1) having an equivalent weight of 2200-10000, an ethylene oxide content of from 5 to 30% by weight and a nominal hydroxyl functionality of from 2 to 4, the amount of polyether moieties being from 35 to 70% by weight, and 2) from 2 to 15% by weight of an oligomer of unreacted diphenylmethane diisocyanate having an isocyanate functionality of at least 3, and/or from 1 to 25% by weight of toluene diisocyanate, all amounts being calculated on the total weight of the composition, the composition having an NCO content of from 8 to 22% by weight, in the absence of toluene diisocyanate, when toluene diisocyanate is present, the composition has an NCO content of 8.5 to 26% by weight.

The invention further relates to a process for preparing flexible polyurethane foams by reacting the above-described isocyanate-terminated prepolymer compositions with polyether polyols 2) having an equivalent weight of from 1000 to less than 2200 and a nominal functionality of from 2 to 4 and water, optionally using chain extenders, crosslinkers, auxiliary complexing agents and additives.

The above-mentioned prepolymer compositions of the invention have an NCO content of 10 to 20% by weight when toluene diisocyanate is not present, 11 to 24% by weight when toluene diisocyanate is present, and a viscosity of up to 4500mPa · s (Brookfield) at 25 ℃. The equivalent weight of the polyol 1) is preferably 2500-; the average nominal functionality is 3 optimal.

In the context of the present invention the following terms have the following meanings:

1) isocyanate index or NCO index or index:

the ratio of NCO groups to isocyanate-reactive hydrogen atoms in the formulation, in percent, is as follows:

in other words, the NCO-index represents the percentage of isocyanate actually used in a formulation to the theoretical amount of isocyanate required to react with the amount of isocyanate-reactive hydrogen used in the formulation.

It must be noted that the isocyanate index as used herein is based on considerations related to the actual foaming process of the isocyanate component with the isocyanate-reactive component. Any isocyanate groups consumed in previous steps to make modified polyisocyanates (including prepolymers) or any active hydrogens consumed in previous steps (e.g., reacted with isocyanate to make modified polyols or polyamines) are not within the isocyanate index calculation. Only the free isocyanate groups present in the actual foaming step are counted together with the free isocyanate-reactive hydrogens, including those of the water.

2) As used herein, "isocyanate-reactive hydrogen atoms" used to calculate the isocyanate index means all of the active hydrogen atoms present in the hydroxyl and amino groups of the reaction composition; that is, when calculating the isocyanate index for an actual foaming process, one hydroxyl group is considered to comprise one reactive hydrogen, one primary amine is considered to comprise one reactive hydrogen, and one water molecule is considered to comprise two reactive hydrogens.

3) Reaction system: a combination of components wherein the polyisocyanate is placed in one or more containers separate from the isocyanate-reactive component.

4) As used herein, "polyurethane foam" refers to cellular products prepared by reacting polyisocyanates with isocyanate-reactive hydrogen containing compounds using blowing agents, and particularly cellular products comprising water as the reactive blowing agent (with the proviso that water reacts with isocyanate groups to produce urea linkages and carbon dioxide, and produces polyurea-urethane foams) and polyols, amines and/or polyamines as the isocyanate reactive compounds.

5) As used herein, "average nominal hydroxyl functionality" refers to the number nominal functionality (number of hydroxyl groups per molecule) of the polyol or polyol composition, assuming it is the number nominal functionality (number of active hydrogen atoms per molecule) of the initiator used in its preparation, but in practice it will generally be somewhat less because of some terminal unsaturation.

6) Unless otherwise stated, the term "average" is exponential. When the terms functionality, equivalent weight, or molecular weight are used without a "mean" or "number average" preceding them, they are still meant to be number average.

7) "polyether moiety" refers to a polyol moiety that remains in a urethane-containing adduct after the polyol is reacted with a polyisocyanate to form such adduct.

The urethane-containing adduct in the prepolymer composition of the present invention is prepared by mixing an excess of polyisocyanate with polyol 1) and reacting the mixture. Such reactions can be carried out at 60-100 ℃ and generally do not require the use of a catalyst. The relative amounts of polyisocyanate and polyol depend on the desired NCO value, the NCO value of the polyisocyanate used and the OH value of the polyol, and can be readily calculated by one skilled in the art.

The polyisocyanate used to react with the polyol 1) may be selected from diphenylmethane diisocyanate (MDI) and oligomeric blends of MDI and MDI having an isocyanate functionality of at least 3 (known in the art as crude or polymeric MDI).

The diphenylmethane diisocyanate MDI used to make the prepolymer may be selected from pure 4, 4 ' -MDI and the isomeric mixtures of 4, 4 ' -MDI and 2, 4 ' -MDI: and less than 10% by weight of carbodiimides, allophanates, isocyanurates, urethanes, allophanates, ureas or biurets of 2, 2' -MDI and modified variants thereof. The most preferred are pure 4, 4 '-MDI and isomeric mixtures of 2, 4' -MDI with preferably 5 to 50% 2, 4 '-MDI, more preferably 5 to 35% by weight 2, 4' -MDI, and MDI modified with an allophanate and/or carbodiimide and having an NCO content of at least 25% by weight, and MDI obtained by reacting excess MDI with a polyol having an average hydroxyl functionality of 2 to 6 and a number average molecular weight of 60 to 999 and an NCO content of at least 25% by weight.

As noted, the urethane-containing adduct may be prepared using a mixture of MDI and an oligomer having an isocyanate functionality of at least 3. Such mixtures are known in the art as polymeric MDI or crude MDI, more commonly polymethylene polyphenylene isocyanates, which are produced by phosgenation of a mixture of polyamines obtained by acid condensation of aniline and formaldehyde. The preparation of polyamine mixtures and polyisocyanate mixtures is well known. The condensation of aniline with formaldehyde in the presence of strong acids, such as hydrochloric acid, produces reaction products containing diaminophenylmethane with polymethylene polyphenylene polyamines of higher functionality, the precise composition of which is determined in a well-known manner by the aniline/formaldehyde ratio. The polyisocyanate is prepared by phosgenating the polyamine mixture with diamines, triamines and higher polyamines in various proportions to obtain diisocyanates, triisocyanates and higher polyisocyanates in corresponding proportions. The relative ratio of diisocyanate, triisocyanate and higher polyisocyanates in the crude diphenylmethane diisocyanate composition determines the nominal functionality of the composition, i.e. the average number of isocyanate groups per molecule. By varying the proportions of the starting materials, the nominal functionality of the polyisocyanate composition can be varied from slightly more than 2 to 3 or even higher. In fact, however, it is preferred that the isocyanate has a nominal functionality of from 2.35 to 2.9. These polymeric MDI's have NCO values of at least 30% by weight and at most 33% by weight. The composition comprises 20 to 80% by weight of diphenylmethane diisocyanate, preferably 30 to 70% by weight, the remainder being polymethylene polyphenylene polyisocyanate having an isocyanate functionality of at least 3, and by-products of the phosgenation process for making such polyisocyanates. These products are liquids, which are very convenient for the use according to the invention. The MDI optionally contains oligomers having an isocyanate functionality of 3 or more, preferably 5 to 50 wt% of 2, 4' -MDI, more preferably 5 to 35 wt%; which provides good prepolymer storage stability and low density foams with good foam stability.

The polyether polyols 1) used to prepare the urethane-containing adducts can be selected from products obtained by polymerization of ethylene oxide and other cyclic oxides, such as propylene oxide, butylene oxide or tetrahydrofuran, if the case requires, polyfunctional initiators. Suitable initiator compounds contain a plurality of active hydrogen atoms and include water, butanediol, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, ethanolamine, diethanolamine, triethanolamine, toluene diamine, diethyl toluene diamine, phenyl diamine, diphenylmethane diamine, ethylene diamine, cyclohexane dimethanol, resorcinol, bisphenol A, glycerol, trimethylolpropane, 1, 2, 6-hexanetriol, and pentaerythritol. Mixtures of initiators and/or other cyclic oxides may be used.

Particularly suitable polyether polyols include polyoxyethylene polyoxypropylene diols and triols prepared by the simultaneous and/or sequential addition of ethylene oxide and propylene oxide to di-or trifunctional initiators as detailed in the prior art. Random, block and random/block copolymers of ethylene oxide and propylene oxide having an ethylene oxide content of from 5 to 30% by weight, based on the total weight of the alkylene oxide units, are preferred, especially those having at least part, preferably all, of the ethylene oxide groups at the end of the polymer chain, so-called EO-tipped polyols. Mixtures of the diols and triols can also be used.

After the urethane-containing adduct is prepared, additional MDI may be added. After the urethane-containing adduct is prepared, polymeric or crude MDI is added to produce the isocyanate-terminated prepolymer composition of the present invention which contains from 2 to 15 weight percent unreacted oligomers of MDI having an isocyanate functionality of 3 or more, based on the total prepolymer composition. The polymeric or crude MDI used is selected from those described above. The amount added is such that the unreacted oligomer having an isocyanate functionality of at least 3 or unreacted polymethylene polyphenylene polyisocyanate is present in an amount of 2 to 15% by weight based on the total amount of the isocyanate-terminated prepolymer composition.

In addition to or instead of the addition of polymeric or crude MDI, toluene diisocyanate, which may be 2, 4-toluene diisocyanate, 2, 6 toluene diisocyanate or mixtures thereof, may be added to the urethane-containing adduct in an amount of 1 to 25% by weight, preferably 5 to 20% by weight, based on the prepolymer composition including the added toluene diisocyanate.

It should be understood that within the limits of the amount of polyol 1), the amount of MDI oligomer having an unreacted functionality of at least 3, and the amount of toluene diisocyanate, isocyanate-terminated prepolymer compositions having NCO contents outside the above ranges will still be produced; such compositions do not form part of the present invention.

The prepolymer compositions of the present invention are used to prepare flexible polyurethane foams by reacting such compositions with polyether polyols having an equivalent weight of from 1000 to less than 2200 and a nominal functionality of from 2 to 4 and water. These polyether polyols include products obtained by polymerization of cyclic oxides, such as ethylene oxide, propylene oxide, butylene oxide or tetrahydrofuran, where a polyfunctional initiator may be present if desired. Suitable initiator compounds contain a plurality of active hydrogen atoms and include water, butanediol, ethylene glycol, propylene glycol, ethanolamine, diethanolamine, triethanolamine, toluene diamine, diethyl toluene diamine, cyclohexane dimethanol, glycerol, trimethylolpropane, 1, 2, 6-hexanetriol, and other initiators as previously mentioned. Mixtures of initiators and/or cyclic oxides may be used.

Particularly suitable polyether polyols include polyoxypropylene diols and triols and polyoxyethylene polyoxypropylene diols and triols prepared by the simultaneous and/or sequential addition of ethylene oxide and propylene oxide to di-or trifunctional initiators as detailed in the prior art. Random copolymers having an oxyethylene content of 10-80%, block copolymers having an oxyethylene content of up to 50%, preferably having at least partly oxyethylene groups at the end of the polymer chain, based on the total weight of oxyalkylene units, may be mentioned. Mixtures of the diols and triols are particularly preferred.

Other polyols which may be used as polyol 2) include dispersions or solutions of addition or condensation polymers in polyols of the kind described above. Such modified polyols, often referred to as "polymer polyols", are well described in the prior art and include products obtained by in situ polymerization of one or more vinyl monomers (e.g., styrene and/or acrylonitrile) in a polymeric polyol (e.g., polyether polyol) or by in situ reaction of a polyisocyanate with an amino-and/or hydroxy-functional compound (such as triethanolamine) in a polymeric polyol. Polyoxyalkylene polyols containing from 5 to 50% by weight of dispersed polymer are particularly preferred. The particle size of the dispersed polymer is preferably less than 50 microns.

Most preferred are polyoxyethylene polyoxypropylene polyols having an equivalent weight of 1100-2100, a nominal functionality of 2-3, and an oxyethylene content of 5-30 weight percent, preferably having ethylene oxide at the end of the polymer chain.

The polyols having equivalent weights of from 1000 to less than 2200 are used in amounts of from 20 to 90 parts by weight, more preferably from 35 to 90 parts by weight, per 100 parts by weight of the prepolymer composition.

The prepolymer composition, polyol and water are subjected to a foam forming reaction at an isocyanate index of 40-120 (preferably 50-110).

The amount of water is 2 to 8 parts by weight per 100 parts by weight of the prepolymer composition. If the case requires, additional blowing agents, especially inert gases, such as CO, may be used₂And N₂。

Chain extenders and crosslinkers having equivalent weights of less than 1000, preferably selected from amines and polyols comprising 2-8 amines (preferably 2-4) and/or hydroxyl groups, such as ethanolamine, diethanolamine, triethanolamine, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, butanediol, glycerol, trimethylolpropane, pentaerythritol, sorbitol, sucrose, polyethylene glycol, and one of the other initiators, toluene diamine, diethyl toluene diamine, cyclohexane diamine, phenyl diamine, diphenylmethane diamine, alkylated diphenylmethane diamine, and ethylene diamine, may optionally be used.

If chain extenders and crosslinkers are used, up to 25 parts by weight, preferably up to 10 parts by weight, per 100 parts by weight of the prepolymer composition are employed.

Auxiliary complexing agents and additives may optionally be used, for example catalysts which enhance urea and urethane formation, such as tertiary amines and tin compounds, surfactants, stabilizers, flame retardants, fillers and antioxidants.

The flexible polyurethane foam is prepared by combining and mixing the components and foaming the mixture. The isocyanate-reactive component is mixed with the auxiliary compounding agents and additives beforehand and then mixed with the prepolymer composition in a mixing head. If desired, the components of the prepolymer composition are added separately to the mix head.

This process can be used to make slabstock or molded flexible foams. The density of the foam is generally from 15 to 80kg/m³And can be used as a cushion layer of furniture, automobile seats and mattresses.

The following examples illustrate the invention.

Example 1

The following polyoxyethylene polyoxypropylene polyols were used to prepare the isocyanate-terminated prepolymers:

polyhydric alcohols	1	2	3
				Initiator	Glycerol	Glycerol	Glycerol
Ethylene oxide content (all ends)	15％w	15％w	15％w
				Equivalent weight	1900	2400	3700
Viscosity (mPa.s) at 25 deg.C	1100	1700	3600

From these polyols, a prepolymer having an NCO value of about 7% by weight was prepared by: these polyols were reacted with 4, 4 '-diphenylmethane diisocyanate containing 10% by weight of the 2, 4' -isomer (polyol to polyisocyanate weight ratio of about 75/25) using 10ppm (calculated on MDI) of thionyl chloride at about 85 ℃ for 2.5 hours. A prepolymer having an NCO content of 12% by weight was then prepared by adding the appropriate amount of 4, 4 '-diphenylmethane diisocyanate containing 20% w of the 2, 4' -isomer.

Example 2

Molded flexible polyurethane foams were prepared from these prepolymers having an NCO content of 12% by weight. In many experiments, polymeric MDI (NCO: 30.7% w; isocyanate functionality: 2.7; diisocyanate content: 38% w, the remainder being polyisocyanates having an isocyanate functionality of 3 or more and a 2, 4' -MDI content: 2% w) was mixed with the prepolymer beforehand; in other experiments, the polymeric MDI and TDI (2, 4/2, 6 ═ 80/20 w/w) were mixed with the prepolymer beforehand. 100 parts by weight of these prepolymer compositions are mixed with a polyol composition and poured into a mold to be reacted. The polyol composition comprises 65 parts by weight (pbw) of polyol 1, 2 or 3; 0.5pbw B4113 of a silicone surfactant from Goldschmidt: 0.5pbw of X8154, a catalyst from Air Products; 0.05pbw of NiaxA1, a catalyst from Union Carbide; 3pbw of triethanolamine; 3pbw of water; and 3pbw of ethoxylated sorbitol having a molecular weight of about 1800.

Additional details are shown in the following table. Measuring the properties of the foam after demolding; the results are also shown in the following table:

experiment of	1*	2	3	4*	5*	6*	7	8*
									Prepolymer from polyol (pbw) polymeric MDI, pbw TDI, pbw polyol in a polyol composition	1(81)19-1	2(81)19-1	3(81)19-1	2(81)19-2	3(81)19-3	1(78)10121	3(78)10121	3(78)10123
Core density kg/m3(ISO/DIS845)	62	61	59	60	61	58	54	53
									CLD，40％，kPa(ISO3386)	5.7	5.4	4.4	5.3	3.5	6	4.4	3.3
Ball rebound resilience% (TSM 7100-4.7)	65	69	70	72	74	69	74	78
									Compression set dry and wet (TSM 7100-4.8 and 4.9)	34.5	2.55	34	24	24	36	25.5	24
Machining	+	+	+	-	-	+	+	-

^*Control experiment

Processing + means: easy mixing; a smoothed product distributed in the mold; there are no problems associated with the fluidity of the reaction mass.

Processing-means: difficult to mix; a significant lack of flowability.

TSM：^ToyotaStandard methods

Claims (8)

1. An isocyanate-terminated prepolymer composition comprising 1) a urethane comprising an adduct of diphenylmethane diisocyanate and a polyether polyol 1), said diisocyanate optionally comprising an oligomer having an isocyanate functionality of greater than 2, said polyether polyol 1) having an equivalent weight of 2200-10000, an ethylene oxide content of 5-30% by weight and a nominal hydroxyl functionality of 2-4, the amount of polyether moieties being 35-70% by weight, and 2) 2-15% by weight of an oligomer of unreacted diphenylmethane diisocyanate having an isocyanate functionality of at least 3, and/or 1-25% by weight of toluene diisocyanate, all amounts being calculated on the total weight of the composition, the composition having an NCO content of 8-22% by weight when toluene diisocyanate is not present, when toluene diisocyanate is present, the composition has an NCO content of 8.5 to 26% by weight.

2. The composition according to claim 1, wherein the equivalent weight is 2500-.

3. The composition according to claims 1 and 2, wherein the equivalent weight is 3000-7000.

4. A composition according to claims 1-3, wherein the viscosity of the composition is lower than the viscosity of the polyol.

5. A process for preparing a flexible polyurethane foam comprising reacting a composition according to claims 1-4 with a polyether polyol 2) having an equivalent weight of 1000 to less than 2200 and a nominal hydroxyl functionality of 2-4 and water, and optionally using chain extenders, crosslinkers, auxiliary complexing agents and additives.

6. The process according to claim 5, wherein the amount of polyol 2) is from 20 to 90 parts by weight per 100 parts by weight of the prepolymer composition.

7. The process according to claim 6, wherein the amount is from 35 to 90 parts by weight.

8. The process according to claims 5-7, wherein the amount of water is from 2 to 8 parts by weight per 100 parts by weight of the prepolymer composition and wherein the isocyanate index is from 50 to 110.