Process for producing high resilience Polyurethane foam

Abstract: A process for producing a high resilience polyurethane foam by reacting a polyol with a polyisocyanate in the presence of a catalyst, a blowing agent, and a foam stabilizer, in which the polyisocyanate contains diphenylmethane diisocyanate, the blowing agent is water and/or a halogenated hydrocarbon and the catalyst is selected from the compounds of the general formula below: where R¹ is alkyl having 1 to 4 carbons, dimethylaminopropyl, benzyl, vinyl, or hydroxyalkyl having 1 to 3 carbons; R² is hydrogen, alkyl having 1 to 4 carbons, allyl, benzyl or phenyl, and R³ and R⁴ are independently hydrogen, alkyl having 1 to 4 carbons, or hydroxymethyl.

Description: The present invention relates to a process for producing a high resilience polyurethane foam by reacting a polyol with a polyisocyanate in the presence of a catalyst, a blowing agent, and a foam stabilizer. More specifically the present invention relates to a method for producing a high resilience flexible polyurethane foam by use of a polyetherpolyol or a mixture of a polyetherpolyol and a polymer polyol, and diphenylmethane diisocyanate and/or a derivative thereof. High resilience polyurethane foams are widely used for a variety of articles such as automotive seating, furniture, and bedding. Heretofore, in production of high resilience polyurethane foams, toluene diisocyanate (hereinafter referred to as TDI), or a mixture of TDI with diphenylmethane diisocyanate (hereinafter referred to as MDI) has been used as the starting isocyanate. However, the TDI has disadvantages of high vapor pressure high toxicity, and intolerable offensive odor, which aggravate working environments. The TDI has further a disadvantage of low reactivity with a starting polyol, which decreases the productivity and increases the plant investment. To solve the above disadvantages caused by TDI, use of MDI and/or modified MDI for high resilience polyurethane foams is disclosed in Japanese Laid-Open Patent Application Nos. 53-51299, 57-109820, 62-112616, etc. A polyurethane foam produced from MDI and/or modified MDI as the base materials is generally called "all-MDI high resilience polyurethane foam", which has excellent characteristics of superior foam properties, low toxicity to facilitate maintenance of safe working environment in a production site, high production speed to increase productivity, and so on. On the other hand, the all-MDI high resilience polyurethane formulations involve serious problems that the flow properties of the liquid system and the flowability of foams are extremely poor so that low density of the foam cannot easily be attained. Accordingly, the lowering of foam density without impairing liquid flow characteristics or foam flowability is attained by using, as a blowing agent, a halogenated hydrocarbon such as trichloromonofluoromethane (hereinafter referred to as CFC-11) in an amount of from 5 to 15 parts by weight based on the polyol. However, it is still unsatisfactory, and further improvement is desired in the starting material formulation and the production technique to attain further lower density of the all-MDI high resilience polyurethanes. Regarding the halogenated hydrocarbons, the use of chlorofluorocarbons like CFC-11 which may destroy the ozone layer surrounding the earth has been attracting world-wide concerns and has been reduced in the amount to be used, and moreover the use itself thereof is going to be regulated. In production of the all-MDI high resilience polyurethane foam, it is the latest and urgent problem to reduce the amount of a chlorofluorocarbon (hereinafter referred to as CFC) as a blowing agent and to use more water instead. On the other hand, "CFC-substituting compounds" such as methylene chloride, dichlorotrifluoroethane, and dichloromonofluoroethane (hereinafter referred to as HCFC-123, and HCFC-141b, respectively) are proposed as substitutes for the CFC compounds such a CFC-11 which may destroy the ozone layer. These CFC-substituting compounds still have implicit possibility of destroying the ozone layer, and are expensive in comparison with the conventionally used CFC compounds. Accordingly the CFC-substituting compounds cannot be used in the same level as ever, also from an economical point of view. Therefore, an improved formulation is strongly desired in which the amount of a CFC compound is decreased and instead the amount of water as a blowing agent is increased. The use of water as a blowing agent in a larger amount, however, poses several technical problems such that foams become far less stable to cause the phenomena of settling (in other words recession) and the like in the foaming process with the processing range being narrowed and with the properties of the foam being deteriorated; that a low density of the foam is attained with extreme difficulty; and that the moldability of foam is impaired inevitably, causing blistering of foam surface and liability of void building-up. The conventionally used catalysts for all-MDI high resilience polyurethane foams are amine catalysts such as triethylenediamine as a base catalyst with bis(2-dimethylaminoethyl)ether or dimethylethanolamine as a cocatalyst. Such amine catalyst system is not capable of lowering the density of a foam which employs the present CFC compounds as the blowing agent, and will not give a practically useful high resilience polyurethane foam of low density with a blowing agent system of a decreased CFC compound and increased water. The inventors of the present invention made comprehensive studies on high resilience polyurethane systems from the viewpoint of catalysts, and have found novel facts that only the use of an amine compound having a specified chemical structure will give low density of the foam in high resilience polyurethane formulations, allowing the production of foam of lower density in the formulation of a decreased CFC compound and increased water with foam stability and improved moldability at the foaming step. Thus the inventors have completed the present invention. An object of the present invention is to provide a process for producing a high resilience polyurethane foam which enables the stabilization of the foam and the lower density thereof that have not been achieved before. Another object of the present invention is to provide a process for producing an industrially useful high resilience polyurethane foam which allows decrease of a CFC compound as a blowing agent. According to an aspect of the present invention there is provided a process for producing a high resilience flexible polyurethane foam by reacting a polyol with a polyisocyanate component containing not less than 50% by weight diphenylmethane diisocyanate or a mixture of diphenylmethane diisocyanate with a derivative thereof in the presence of (a) a blowing agent being water, or water and a halogenated hydrocarbon in amounts of not less than 2.7 parts by weight of water and not more than 20 parts by weight of the halogenated hydrocarbon based on 100 parts by weight of the polyol, (b) an amine catalyst, and (c) a foam stabilizer, wherein the isocyanate index is in the range from 70 to 120 and the amine catalyst (b) is at least one selected from the compounds represented by the general formulae (I), (II), (III), (IV) and (V) : where R 1 is alkyl having 1 to 4 carbons, dimethylaminopropyl, benzyl, vinyl, or hydroxyalkyl having 1 to 3 carbons; R 2 is hydrogen, alkyl having 1 to 4 carbons, allyl, benzyl or phenyl; and R 3 and R 4 are independently hydrogen, alkyl having 1 to 4 carbons, or hydroxymethyl; where R 5 is alkyl having 1 to 3 carbons, or dimethylaminoalkyl in which alkyl has 2 or 3 carbons; and R 6 and R 7 are respectively hydrogen or alkyl having 1 to 3 carbons; and ℓ is an integer of 2 or 3; where m and n are respectively an integer of 2 or 3; where R 8 is hydrogen, alkyl having 1 to 4 carbons, allyl, benzyl, or phenyl; and R 9 and R 10 are respectively hydrogen or alkyl having 1 to 4 carbons; and where R 11 is alkyl having 1 to 4 carbons; R 13 is -CH 2 CH(X)OH (X being hydrogen or alkyl having 1 to 4 carbons); R 12 and R 14 are respectively alkyl having 1 to 4 carbons or -CH 2 CH(X)OH (X being hydrogen or alkyl having 1 to 4 carbons), at least any one of R 12 and R 14 being alkyl; and p is an integer of 2 to 6. The catalysts which are applicable in the present invention include the imidazole compounds represented by the general formula (I) shown above, and the amine compounds having active hydrogen in the molecule thereof represented by the general formulas (II), (III), (IV), and (V). The imidazole compounds are exemplified by 1-methylimidazole, 1,2-dimethylimidazole, 1,4-dimethylimidazole, 1-methyl-2-ethylimidazole, 1,4-dimethyl-2-ethylimidazole, 1-methyl-2-isopropylimidazole, 1-methyl-2-phenylimidazole, 1-vinylimidazole, 1-benzyl-2-methylimidazole, 1-(3-dimethylaminopropyl)imidazole, 1-isobutyl-2-methylimidazole, or 1-n-butyl-2-methylimidazole. More preferable are 1-methylimidazole, 1,2-dimethylimidazole, 1-(3-dimethylaminopropyl)imidazole, 1-isobutyl-2-methylimidazole, and 1-n-butyl-2-methylimidazole. The amine compounds of the general formula (II) include N-methylpiperazine, N-(2-dimethylaminoethyl)piperazine, N-methyl-3-methylpiperazine, and N-methylhomopiperazine. The amine compounds of the general formula (III) include N,N-dimethyl-N'-(3-dimethylaminopropyl)ethylenediamine, bis(N,N-dimethylaminoethyl)amine, and bis(N,N-dimethylaminopropyl)amine. The amine compounds of the general formula (IV) include imidazole, 2-methylimidazole, 4-methylimidazole, 2-ethyl-4-methylimidazole, 2-isopropylimidazole, 2-ethylimidazole, and 2-phenylimidazole. The compounds of the general formula (V) include N,N-diisopropanol-N′,N′-dimethylpropanediamine, N,N′-diisopropanol-N,N′-dimethylpropanediamine, N,N-diethanol-N′,N′-dimethylethylenediamine, N,N′-diethanol-N,N′-dimethylethylenediamine, and the like. Among these compounds, particularly preferable are N-methylpiperazine, N-methylhomopiperazine, N,N-dimethyl-N′-(3-dimethylaminopropyl)ethylenediamine, bis(N,N-dimethylaminopropyl)amine, 2-methylimidazole, 4-methylimidazole, N,N-diisopropanol-N′,N′-dimethylpropanediamine, N,N-diethanol-N′,N′-dimethylethylenediamine, and N,N′-diethanol-N,N′-dimethylethylenediamine. The amine catalyst of the present invention may be used combinedly with another compound having a tertiary amino group as a cocatalyst. Such compound having a tertiary amino group includes triethylamine, N,N-dimethylcyclohexylamine, N,N,N′,N′-tetramethylethylenediamine, N,N,N′,N′-tetramethylpropylenediamine, N,N,N′,N″,N″-pentamethyldiethylenetriamine, N-(3-dimethylaminopropyl)N,N′,N′-trimethylethylenediamine, N,N,N′,N″,N″-pentamethyldipropylenetriamine (PMDPTA), N,N,N′,N′-tetramethylguanidine, 1,3,5-tris(N,N-dimethylaminopropyl)hexahydro-s-triazine, 1,8-diazabicyclo[5.4.0]undecene-7, triethylenediamine, N,N,N′,N′,N″-pentamethyldiethylenetriamine, N,N,N′,N′-tetramethylhexamethylenediamine, N-methyl-N′-(2-dimethylamino)ethylpiperazine, N,N′-dimethylpiperazine, N-methylmorpholine, N-ethylmorpholine, N,N-dimethylethanolamine, dimethylaminoethoxyethanol, N,N,N′-trimethylaminoethylethanolamine, 1,3-bis(N,N-dimethylamino)-2-propanol, and bis(2-dimethylaminoethyl)ether. Preferable are triethylenediamine and/or bis(2-dimethylaminoethyl)ether. An organic carboxylate salt of the aforementioned compounds of the present invention, an organic carboxylate salt of other tertiary amines, or an organic tin compound may be optionally used as a cocatalyst within the range that the activity of the catalyst of the present invention is not impaired. The catalyst of the present invention may be prepared either from the compound of present invention singly or from a mixture thereof with other amine catalyst. In the preparation by mixing, a solvent such as dipropylene glycol, ethylene glycol, 1,4-butanediol, or water may be used, if necessary. The amount of the solvent is not specially limited, but is preferably in an amount of not more than 70 % of the total amount of the catalyst. The catalyst thus prepared may be used by adding to the polyol. Various amine catalysts may be added to the polyol separately. The amine catalyst in the present invention is used usually in an amount ranging from 0.02 to 10 parts by weight based on 100 parts by weight of the polyol. The polyol which may be used in the present invention includes known polyetherpolyols, polyesterpolyols and/or polymer polyols; preferably a polyetherpolyol, or a mixture of a polyetherpolyol with a polymer polyol. The polyetherpolyol may be produced, for example, by an addition reaction of ethylene oxide or propylene oxide to a polyhydric alcohol such as ethylene glycol, glycerin, trimethylolpropane, or pentaerythritol, according to a method, for example, described in "Polyurethane Handbook" (written by Gunther Oertel): pages 42 to 53, and in Japanese Laid-Open Patent Application No. 62-112616. The polymer polyols are exemplified by those which are produced by reacting the aforementioned polyetherpolyol with an ethylenic unsaturated monomer such as butadiene, acrylonitrile, or styrene in the presence of a radical polymerization catalyst, as described in "Polyurethane Handbook" (written by Gunther Oertel):pages 75 to 76. The polyisocyanate component used in the present invention contains not less than 50% by weight MDI or a mixture of MDI with a derivative thereof. The MDI and its derivatives include, for example, a mixture of MDI with a polyphenyl-polymethylene diisocyanate, namely a polymeric MDI, and/or diphenylmethane diisocyanate derivatives having terminal isocyanate groups. The former mixture is exemplified by a mixture of MDI and its derivative, polyphenyl-polymethylene polyisocyanate, disclosed in Japanese Laid-Open Patent Application No. 53-51299. The latter diphenylmethane diisocyanate derivatives having terminal isocyanate groups are exemplified by known isocyanate-terminated prepolymers disclosed in Japanese Laid-Open Patent Application Nos. 57-109820 and 62-112616, which are prepared by reacting MDI, polyphenyl-polymethylene polyisocyanate and/or their mixture with a polyether-diol or -triol, optionally in the presence of a catalyst, at room temperature or an elevated temperature. The halogenated hydrocarbons applicable as a blowing agent in the present invention include known halogenated methanes, halogenated ethanes, and the like, among which carbon halides and halogenated hydrocarbons such as CFC-11, HCFC-123, HCFC-141b, and the like are preferable. The amount thereof to be used is not more than 20 parts by weight based on 100 parts by weight of the polyol, preferably from 0 to 15 parts by weight. The amount of water as a blowing agent is not less than 2 parts by weight, preferably in the range of from 2.5 to 5 parts by weight based on 100 parts by weight of the polyol. If water only is used therefor, the amount is preferably not less than 3 parts by weight. The amount of water and the CFC is suitably adjusted according to the intended foam density. The isocyanate index in the present invention is within the range of from 70 to 120. A crosslinking agent or a chain extender may be added if necessary in the present invention. The crosslinking agent or the chain extender include, for example, low-molecular polyhydric alcohols such as ethylene glycol, 1,4-butanediol, glycerol, etc.; low-molecular aminepolyols such as diethanolamine, or triethanolamine, polyamines such as ethylenediamine, xylylenediamine, or methylene-bis-o-chloroaniline, secondary diamines like aliphatic and alicyclic secondary diamines, polyoxypropylene secondary diamines, or aromatic secondary diamines. Additionally, various known additives may be used such as an organic silicone compound as a surfactant, a coloring agent, a flame retardant, an age resister, and the like, if necessary. The kind and the amount of the additives are satisfactorily selected within the ranges of known types and procedures conventionally employed. The present invention has achieved low densities of high resilience polyurethane foams, which have not ever been achieved by use of a CFC as a blowing agent. Furthermore, the present invention has achieved, by employing a formulation with a reduced amount of CFC and an increased amount of water, the stabilization of foam cells and moldability of foam at a foaming process as well as the low density of the foam. The examples below are intended to illustrate more specifically characteristics and advantages of the present invention without thereby limiting it in any way. Examples 1 - 26, Comparative Examples 1 - 13 The formulations for the all-MDI high resilience polyurethane foam systems used are shown below. In the formulations, the amount of water and halogenated hydrocarbons as the blowing agent, and the kind of the catalyst were changed. The foams were prepared under predetermined foaming conditions. The evaluation was conducted on the stability of the foams during the foaming process, the moldability of the foams, and the properties of the resulting foams according to the method described below. The results are shown in Tables I, II, III and IV. a. Formulation b. Foaming conditions: Temperature of liquid starting material: 20 ± 1°C Stirring speed: 6000 rpm (5 seconds) Mold: Foamed in aluminum box (dimension: 25x25x25 cm) Mold temperature: 40°C c. Evaluated items: The items below were evaluated. Reactivity: Cream time: Time lapse before start of foaming (seconds) Gel time: Time for resinification (fiber time) (seconds) Rise time: Time lapse before the foam reaches its maximum foaming height (seconds) Settling: The stability was evaluated by the degree of recession of the foam after the rise time. Expansion ratio: The ratio (cm/g) was derived from the maximum foaming height divided by the foam weight. The larger the ratio, the higher is the foaming effect of water, and the lower can the foam density be made. Foam density: The density was measured of the test piece prepared by cutting the central portion of the foam into a size of 20x20x10 cm. Moldability: Blistering of foam and building-up of voids in the foam are observed, and evaluated in five grades. 1 : negligible 2 : slight 3 : medium 4 : considerable 5 : great As is clear from Table I and Table II,by use of an imidazole compound as the catalyst, molded foams which have stabilized cells, low density, and excellent moldability could be produced on the basis of the formulation containing a decreased amount of CFC and an increased amount of water. On the contrary, as understood from the results of Comparative Examples 1 - 7, the use of conventional catalysts such as triethylenediamine gave foams which have a high density and poor moldability giving considerable blistering of foam, which shows that with such catalyst systems, the decrease of the CFC by use of increased amount of water is impracticable. As is clear form Table III and Table IV, by use of a compound having an active hydrogen as the catalyst, molded foams which have stabilized cells, low density, and excellent moldability could be produced on the basis of the formulation containing a decreased amount of CFC and an increased amount of water. On the contrary, as understood from the results of Comparative Examples 8 - 13, the use of conventional catalysts gave foams which have a high density and poor moldability giving considerable blistering of foam, which shows that with such catalyst systems, the decrease of the CFC by use of increased amount of water is impracticable.

Claims: A process for producing a high resilience flexible polyurethane foam by reacting a polyol with a polyisocyanate component containing not less than 50% by weight diphenylmethane diisocyanate or a mixture of diphenylmethane diisocyanate with a derivative thereof in the presence of (a) a blowing agent being water, or water and a halogenated hydrocarbon in amounts of not less than 2.7 parts by weight of water and not more than 20 parts by weight of the halogenated hydrocarbon based on 100 parts by weight of the polyol, (b) an amine catalyst, and (c) a foam stabilizer, wherein the isocyanate index is in the range from 70 to 120 and the amine catalyst (b) is at least one selected from the compounds represented by the general formulae (I), (II) , (III), (IV) and (V) : where R 1 is alkyl having 1 to 4 carbons, dimethylaminopropyl, benzyl, vinyl, or hydroxyalkyl having 1 to 3 carbons; R 2 is hydrogen, alkyl having 1 to 4 carbons, allyl, benzyl or phenyl; and R 3 and R 4 are independently hydrogen, alkyl having 1 to 4 carbons, or hydroxymethyl ; where R 5 is alkyl having 1 to 3 carbons, or dimethylaminoalkyl in which alkyl has 2 or 3 carbons; and R 6 and R 7 are respectively hydrogen or alkyl having 1 to 3 carbons; and ℓ is an integer of 2 or 3; where m and n are respectively an integer of 2 or 3; where R 8 is hydrogen, alkyl having 1 to 4 carbons, allyl, benzyl, or phenyl; and R 9 and R 10 are respectively hydrogen or alkyl having 1 to 4 carbons; and where R 11 is alkyl having 1 to 4 carbons; R 13 is -CH 2 CH(X)OH (X being hydrogen or alkyl having 1 to 4 carbons); R 12 and R 14 are respectively alkyl having 1 to 4 carbons or -CH 2 CH(X)OH (X being hydrogen or alkyl having 1 to 4 carbons), at least any one of R 12 and R 14 being alkyl; and p is an integer of 2 to 6. The process of Claim 1, wherein the polyol is a polyetherpolyol or mixture of a polyetherpolyol with a polymer polyol. The process of Claim 1 or 2, wherein the halogenated hydrocarbon is selected from trichloromonofluoromethane (CFC-11), dichlorotrifluoroethane (HCFC-123), and dichloromonofluoroethane (HCFC-141b). The process of Claim 1, wherein the compound of the general formula (I) is at least one selected from 1-methylimidazole, 1,2-dimethylimidazole, 1-(3-dimethylaminopropyl)imidazole, 1-isobutyl-2-methylimidazole, and 1-n-butyl-2-methylimidazole. The process of Claim 1, wherein the compound of the general formula (II) is N-methylpiperazine, N-methylhomopiperazine, or N-(2-dimethylaminoethyl)piperazine. The process of Claim 1, wherein the compound of the general formula (III) is N,N-dimethyl-(3-dimethylaminopropyl)ethylenediamine, or bis(N,N-dimethylaminopropyl)amine. The process of Claim 1, wherein the compound of the general formula (IV) is 2-methylimidazole or 4-methylimidazole. The process of Claim 1, wherein the compound of the general formula (V) is N,N-diisopropanol-N',N'-dimethylpropanediamine, N,N'-diisopropanol-N,N'-dimethylpropanediamine, N,N-diethanol-N',N'-dimethylethylenediamine, or N,N'-diethanol-N,N'-dimethylethylenediamine.

Inventors: ARAI SHOJI, OKUZONO SHUICHI, YOSHIMURA HIROYUKI, ARAI, SHOJI, OKUZONO, SHUICHI, YOSHIMURA, HIROYUKI
Applicants: TOSOH CORP, TOSOH CORPORATION
Application year: 1990
Main classification: C08G18
IPC codes: C08G18