METHOD OF PRODUCING POLYURETHANE FOAM

Abstract: A low-density semi-rigid polyurethane foam having excellent wear resistance, which is demolded in a short time, can be prepared by a method of producing a polyurethane foam having microcell and a density of 0.3 to 0.9/cm<3> by a reaction injection molding process, from a polyisocyanate, and a polyol mixture containing a polyol, a catalyst, a blowing agent, and optionally a cross-linking agent, an internal mold release agent, a reinforcing agent and an other aid, characterized in that a trifunctional polyether polyol having an active hydrogen equivalent of 300 to 1,000 and an ethylene oxide content of 5 to 30 % by weight is contained in an amount of at least 40 % by weight based on the polyether polyol, and the polyether polyol has an average active hydrogen equivalent of 500 to 1,200 and a viscosity of 200 to 800 mPa.s/25 DEG C.

Description: DESCRIPTION Method of producing polyurethane foam FIELD OF THE INVENTION The present invention relates to a method of producing a semi-rigid polyurethane foam having microcell, a density of 0.3 to 0.9 g/cm 3 by a reaction injection molding process in a short time, efficiently. The semi-rigid polyurethane foam having microcell has excellent touch and elasticity and can be used in an armrest, a steering wheel, a console cover, a change knob, etc. of the vehicle. RELATED ART A semi-rigid polyurethane foam is produced by adding a blowing agent to a polyisocyanate, a comparatively high-molecular weight compound having at least two hydrogen atoms capable of reacting with an isocyanate group (active hydrogen equivalent: 1000 or more, hereinafter referred to as a "polyol"), a mostly difunctional low-molecular weight cross-linking agent having an active hydrogen equivalent of 150 or less and a catalyst, and pouring the resulting mixture into a mold capable of closing by a high-pressure polyurethane foaming machine. The reaction mixture is foamed, expanded and cured in the mold, and then removed as a polyurethane molded article. The mold is made of a material having high thermal conductivity so as to control the reaction temperature. Generally, a mold made of a metal (hereinafter referred to as a "mold" ) or a mold made of a resin is used. As a blowing agent, chlorofluorocarbon (hereinafter referred to as "CFC"), particularly trichlorofluoromethane (CFC-11), has hitherto been used. A dense surface layer could be obtained by utilizing the fact that an increase in temperature due to urethane reaction heat varies from the portion in contact with the mold to the inside of the molded article, and the increase in temperature and the reaction of the portion in contact with the mold are slower than those of the inside of the product. However, it has recently been found that CFC causes depletion of an ozone layer and, therefore, use of not only CFC but also HCFC as a substitute for CFC has increasingly been limited and prohibited. In view of cost and environmental problems, a water foaming wherein foaming is conducted by using water is considered to be advantageous. Therefore, this study has widely been conducted (Japanese Patent Kokai Publication No. 339338/1993). In the production of a flexible polyurethane foam having a low density of at most 0.1 g/cm 3 , the water foaming has hitherto been conducted ( see Polyurethane Hand Book, edited by Keiji IWATA, published by Nikkan Kogyo Shinbunsha, pages 178-185). When a polyurethane foam having microcell, a density of 0.3 to 0.9 g/cm 3 is produced by the water foaming, it is very difficult to obtain a high-density skin layer, unlike the case of a conventional fluorinated hydrocarbon foaming (Urethanes Technology: Oct. /Nov. 1994, page 32). Therefore, in the application field (e.g. handle or knob) for which excellent wear resistance is required, a life of parts is liable to be deteriorated drastically as a result of wear. In order to improve the wear resistance of the polyurethane resin, for example, use of a prepolymer of polytetramethylene glycol and MDI ( Japanese Patent Kokai Publication No. 322057/1994)- and use of a polyester polyol or a high-molecular weight polyether having a molecular weight of at least 5000 as a polyol component ( Japanese Patent Kokai Publication No. 295074/1993), that is, use of a polyurethane having excellent elongation and strength is proposed, but satisfactory results are not still to be obtained. SUMMARY OF THE INVENTION The present invention relates to a method of producing a semi-rigid polyurethane foam having microcell, a density of 0.3 to 0.9 g/cm 3 and excellent wear resistance by a reaction injection molding process, from a polyisocyanate, and a mixture comprising a polyol, a catalyst, a blowing agent, and optionally a cross-linking agent, an internal mold release agent, a reinforcing agent and an other aid, without using fluorinated hydrocarbon as a blowing agent. In order to develop a semi-rigid polyurethane foam having excellent wear resistance, the present inventors have intensively studied and then found the following fact. That is, it is very difficult to improve the wear resistance of the semi-rigid polyurethane by obtaining a molded article which imparts a high breaking elongation by a combination of a polyol having a comparatively high molecular weight and a high activity hydrogen equivalent and a low-functional isocyanate (Japanese Patent Kokai Publication Nos. 295074/1993 and 339338/1993) as has hitherto been considered and, to the contrary, the wear resistance can remarkably be improved by making a molded article having a comparatively high cross-linking degree by using a polyfunctional low-molecular weight polyol having an active hydrogen equivalent of 300 to 1000. Surprisingly, it has also been found that a considerably adverse effect is exerted on the wear resistance by adding a polyether polyol having an active hydrogen equivalent of 1500 to 2000 (OH value: 28 to 35 mg KOH/g) and a molecular weight of 3000 to 6000 (Latest Polyurethane Application Technique: supervised by Keiji IWATA, CMC, p 65), which has generally been used in the semi-rigid polyurethane. It has also been found that a trifunctional polyol having an active hydrogen equivalent of 300 to 1000 in the present invention is handled easily because the viscosity is lower than that of a conventional polyol, and is superior in mixing property with an isocyanate and, therefore, defects such as crack, fracture, etc. in the molded article caused by the insufficient miscibility are remarkably improved. It has also been found that, in order to sufficiently exhibit the performance of the above polyol component, when an isocyanate containing at least 5% by weight of a polyfunctional component having a functionality of at least three is used as an isocyanate to be combined and the mixture is molded at a NCO index of at least 100, a molded article having very excellent wear resistance can be obtained. Thus, the present invention has been accomplished . The present invention provides a method of producing a semi-rigid polyurethane foam having microcell, a density of 0.3 to 0.9 g/cm 3 and Shore A hardness of 40 to 90 by a reaction injection molding process, from an isocyanate, and a polyol mixture comprising a polyether polyol, a cross-linking agent, a catalyst, a blowing agent, and optionally an internal mold release agent, a reinforcing agent and an other aid, characterized in that (A) the isocyanate contains a polyisocyanate having functionality of at least three and the content of the polyisocyanate having functionality of at least three is at least 5% by weight based on the isocyanate, (B) a trifunctional polyether polyol having an active hydrogen equivalent of 300 to 1 , 000 and an ethylene oxide content of 5 to 30% by weight is contained in an amount of at least 40% by weight based on the total polyether polyol, and the total polyether polyol has an average active hydrogen equivalent of 500 to 1 , 200 and a viscosity of 200 to 800 mPa«s/25 β C, (C) a difunctional cross-linking agent having a molecular weight of 61 to 200 is used in an amount of 2 to 20 parts by weight per 100 parts by weight of the polyether polyol , and (D) the isocyanate and the polyol mixture are molded at a NCO index of 100 to 115. DETAILED DESCRIPTION OF THE INVENTION Examples of the isocyanate used in the present invention include diphenylmethane diisocyanate, polymethylenepolyphenyl polyisocyanate, toluene diisocyanate, hexamethylene diisocyanate, isophoronediicyanate, a modified polyisocyanate obtained by urethane-modifying, carbodiimide-modifying, isocyanurate-modifying or allophanate-modifying them or a mixture thereof . In the present invention to which particularly high productivity is required, diphenylmethane diisocyanate, polymethylenepolyphenyl polyisocyanate, a modified polyisocyanate thereof or a mixture thereof is preferred. Examples of the polyisocyanate having functionality of at least three include polymethylenepolyphenyl polyisocyanate and uretoneimine-modified diphenylmethane diisocyanate. Furthermore, a desirable another type of a polyisocyanate includes a derivative of hexamethylene diisocyanate. In this case, there can be obtained a molded article which is superior in both weathering resistance and wear resistance. As the polyisocyanate having functionality of at least three, an isocyanurate modified compound of hexamethylene diisocyanate is preferred. It is more preferred in view of high productivity that a content of the isocyanurate modified compound is not less than 50% by weight based on the whole isocyanate. An amount of the polyisocyanate having functionality of at least three may be not less than 5% by weight, particularly not less than 10% by weight, within the range where the molded article is not drastically brittle, e.g. not less than 70% by weight, based on the whole isocyanate. A content of NCO in the polyisocyanate is preferably from 17 to 29% by weight, particularly from 20 to 25% by weight . A viscosity of the isocyanate is preferably from 200 to 1200 mPa-s/25°C. The polyether polyol may be a polyol having 2 to 6 hydroxyl groups in the molecule and an average hydroxyl equivalent of 100 to 3,000, which is produced by adding an alkylene oxide (e.g. ethylene oxide, propylene oxide, etc . ) to a hydroxyl group-containing compound (e.g. propylene glycol, diethylene glycol, glycerine, trimethylolpropane , pentaerythritol, sorbitol, sucrose, etc . ) , a compound having an amino group and a hydroxyl group (e.g. triethanolamine, diethanolamine, etc.) or an amino group-containing compound (e.g. ethylenediamine, diaminotoluene, etc.). There can also be used a polymer polyol which is produced by subjecting these polyether polyols and a vinyl compound to addition polymerization. Incidentally, an amount of a polyether polyol having a hydroxyl equivalent of more than 1,500 used is preferably not larger than 30% by weight, particularly not larger than 20% by weight. It is also possible to use a polyester polyol obtained by reacting polycarboxylic acid with a low-molecular weight hydroxyl group-containing compound, a polycarbonate polyol obtained by ring opening polymerization of caprolactone or a polyether polyamine which is obtained by aminating a hydroxyl group of a polyether polyol or by hydrolyzing an isocyanate prepolymer of a polyether polyol (these polyols have an average active hydrogen equivalent of 100 to 3,000). In the present invention whose object is to improve the wear resistance, it is necessary to use a polyether polyol (namely, a trifunctional polyether polyol) having an active hydrogen equivalent of 300 to 1,000, which is produced by adding propylene oxide and ethylene oxide to a trifunctional alcohol or alkanolamine (e.g. glycerine, trimethylolpropane, triethanolamine, etc.) in an amount of at least 40% by weight based on the total amount of the polyols. It is necessary that an amount of ethylene oxide based on the trifunctional polyether polyol (the amount of trifunctional polyether polyol usually corresponds to the total amount of propylene oxide and ethylene oxide) is from 5 to 30% by weight. When the amount of ethylene oxide is less than 5% by weight, a mold is contaminated in case of removing a molded article from the mold because of insufficient reaction degree and a problem such as skin peeling arises. On the other hand, when the amount of ethylene oxide exceeds 30% by weight, cell in the molded article is a closed cell and the molded article is likely to expand in case of removing the molded article from the mold, which results in poor productivity. When a polyol having functionality of at least four and an active hydrogen equivalent within the above range or a polyol having functionality of at least three and an active hydrogen equivalent less than the above range is used in a large amount, the molded article is too brittle and is not suitable for the present invention. An amount of ethylene oxide is preferably from 5 to 25% by weight, more preferably from 10 to 25% by weight. An amount of the polyether polyol having an active hydrogen equivalent of 300 to 1,000 is preferably not less than 50% by weight, particularly not less than 70% by weight, based on the whole polyether polyol. The average active hydrogen equivalent of the polyether polyol is preferably from 500 to 1,200, particularly from 500 to 700. As the catalyst, there can be used a tertiary amine (e.g. triethylenediamine, pentamethyldiethylenetriamine, 1, 8-diazabicyclo-5,4,0-undecene-7, dimethylaminoethanol, tetramethylethylenedia ine, dimethylbenzylamine, tetramethylhexamethylenediamine, bis( 2-dimethylaminoethyl )ether, etc.) and an organic metal compound (e.g. dibutyltin dilaurate, dibutyltin dimercaptide, tin octanoate, dibutyl diacetate, etc.). As the blowing agent, a carbon dioxide adduct of a primary or secondary amine compound having an amino group, such as polyamine (e.g. ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, etc.) or alkanolamine (e.g. ethanolamine, N-methylethanolamine, diethanolamine, isopropanolamine, diisopropanolamine, etc.) (Japanese Patent Kokai Publication No. 113150/1983) is preferably used. The blowing agent can be easily synthesized in a comparatively short time when the amine compound is heated to 30 to 110"C, preferably 50 to 80°C and carbon dioxide of 1 to 5 bar is blown with stirring slowly. An amount of the carbon dioxide adduct is- preferably from 2 to 10 parts by weight based on 100 parts by weight of the polyol mixture. Another blowing agent which is preferable for use is formic acid. An amount of formic acid is preferably from 0.4 to 2.0 parts by weight based on 100 parts by weight of the polyol mixture. It is necessary that formic acid is neutralized with a tertiary amine catalyst and an organic weak base containing active hydrogen (whose equivalent is larger than that of formic acid ) in a blend polyol component and the pH of the polyol mixture is not less than 8.0. When the degree of neutralization is insufficient, a molding machine sometimes causes a problem because of corrosiveness of formic acid. In addition to these blowing agents, a low-boiling point hydrocarbon, a fluorinated hydrocarbon blowing agent, a nitrogen gas, air, etc. may be used in combination as the blowing agent. However, it is not so preferred to use water in combination as the blowing agent. As the proportion of the water foaming to the amine compound foaming increases, the foaming pressure increases and exerts an adverse effect on removal from the mold in a short time. It is difficult to avoid inclusion of water because of handling of the raw material, e.g. addition of a reinforcing agent, an amount of water must be not larger than 0.8% by weight, preferably not larger than 0.5% by weight, based on the polyol mixture. If the amount is larger than 0.8% by weight, when the molded article is removed from the mold in a short time, the foam expands and crack arises, which results in decrease in productivity of the polyurethane foam. As the cross-linking agent, a dihydric alcohol having a molecular weight of 61 to 200 (e.g. ethylene glycol, propylene glycol, butanediol, 1, 3-butanediol, hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, etc. ) and a diamine (e.g. diethyltoluenedia ine, t-butyltoluenediamine, diethylaminobenzene, triethyldiaminobenzene, tetraethyldiaminodiphenylmethane, etc. ) are optionally used, and polyether polyols prepared by adding an alkylene oxide to them can also be used (cf. Japanese Patent Kokoku Publication Nos. 17359/1979 and 34527/1989, Japanese Patent Kokai Publication No. 74325/1982, Japanese Patent Kokoku Publication No. 47726/1988, etc.). An amount of the cross-linking agent is preferably from 2 to 20 parts by weight based on 100 parts by weight of the polyether polyol . As the internal mold release agent, there can optionally be used a mixture of a carboxylic acid metal salt and an amine (Japanese Patent Kokoku Publication No. 52056/1988), a reaction product of a polysiloxane and an isocyanate (Japanese Patent Kokoku Publication No. 1139/1983), a mixture of an amine, an aliphatic carboxylate salt and a carboxylate ester ( Japanese Patent Kokoku Publication No. 42091/1980), a hardened castor oil (Japanese Patent Kokoku Publication No. 20925/1992), a transesterification product of an aliphatic polyester and a lower alkyl acetoacetate (Japanese Patent Kokai Publication No. 155969/1993), etc. Examples of the reinforcing agent include a glass, inorganic or mineral fiber (e.g. milled glass fiber, wollastonite fiber, processed mineral fiber, etc. ) or a flake (e.g. mica, glass flake, etc.), and they are optionally used. The foam can also be obtained by previously setting a glass mat, a glass cloth, etc. in a mold and pouring raw materials thereon. As the other aid, a foam stabilizer (e.g. silicone surfactant, surfactant, etc.), a weathering agent (e.g. antioxidant, etc.), an UV absorber, a stabilizer (e.g. 2, 6-di-t-butyl-4-methylphenol, tetrakis [methylene 3-( 3 ' , 5 ' -di-t-butyl-4 ' -hydroxyphenyl )propionate] methane, a colorant, etc. may optionally be used. In the production of the polyurethane foam by a reaction injection molding process, a reaction injection molding machine (e.g. a high-pressure polyurethane foaming machine manufactured by Hennecke Co., a high-pressure polyurethane foaming machine for R-RIM manufactured by Polyurethane Engineering Co., etc.) is used. In this case, it is necessary that a NCO index is within the range from 100 to 115. When the NCO index is less than 100, the wear resistance is drastically deteriorated. On the other hand, when the NCO index exceeds 115, the molded article is too soft at the time of removing from the mold and the molded article is liable to expand, which results in drastic deterioration of the- productivit . When the polyisocyanate and the polyol mixture are poured into the mold by the reaction injection molding process, using a high-pressure polyurethane foaming machine, the raw material is cured after expansion and the polyurethane foam can be removed. PREFERRED EMBODIMENT OF THE INVENTION The following Examples further illustrate the present invention in detail. In the Examples, "parts" are "by weight" unless otherwise stated. In the Examples, (a) a moldability, (b) a distance between arms, (c) physical properties and (d) a wear resistance were measured as follows. (a) Moldability It was evaluated by visually observing the presence or absence of peeling of the foam surface at the time of removing from the mold, and drastic deterioration of the surface gloss. (b) Distance between arms In order to judge the blister situation of the foam at the time of removing from the mold, the distance between portions into which a premolded horn pad is fit was measured. The portion corresponding to the root of a spoke has a large cross sectional area and, when this portion expands after removing from the mold, the distance between the root parts of the spoke to which the horn pad is mounted becomes short and it becomes impossible to mount the horn pad. ( c ) Physical properties Hardness (Shore A) The hardness was measured according to ASTM D676-59T. Tensile strength The tensile strength was measured according to JIS K-6301. Elongation The elongation was measured according to JIS K-6301. (d) Wear resistance The wear resistance was determined by vertically putting a No. 6 or No. 10 canvas (of 45 mm in width) having a weight of 100 g at the end over a molded article having a diameter of 28 mm, rubbing the upper surface under the condition of a stroke of 80 cm and a speed of 60 times/minute and measuring the number of times until a scratch is formed on the surface of the molded article. Reference Example 1 Monoethanolamine (2.39 kg), N-methylethanolamine (2.94 kg) and monoethylene glycol (2.94 kg) were charged in a 10 double jacket pressure reactor equipped with a 60 rpm rotating blade and the temperature was adjusted to 50 β C with stirring. After a carbon dioxide bomb equipped with a reducing valve was connected to this reactor, carbon dioxide having a pressure reduced to 3.0 atom was fed to the upper portion of the liquid level with stirring. The temperature raised to about 90°C in about 3 hours and then slowly decreased and returned to 50 °C. The reaction liquid was drawn from the reactor after 8 hours from the beginning of the feed of carbon dioxide, and then the amount was measured. As a result, it was 9.95 kg. This reaction liquid maintained a liquid form at a normal temperature and an abnormal evolution of carbon dioxide was not observed even if the reaction liquid was heated to 80 β C. Therefore, it could be stored as such in a 20 L tin-plated can. This reaction liquid (280 g) was charged in a 300 cc pressure vessel equipped with a pressure meter and heated to 50 °C while it was closed. As a result, the pressure became 0.17 bar. When a pressure produced by air expansion is subtracted from the above pressure, a vapor pressure of this liquid was merely 0.07 bar. Example 1 90 Parts of a polyether polyol (polyol A) having an OH value of 56 mg KOH/g (active hydrogen equivalent: 1 , 000 ) , which is prepared by adding propylene oxide and ethylene oxide in a weight ratio of 87:13 to glycerine, 6.6 parts of ethylene glycol, 3.2 parts of the amine compound obtained in Reference Example 1, 0.6 parts of a 33% ethylene glycol solution of triethylenediamine and 0.05 parts of dibutyltin dilaurate were mixed to obtain 20 kg of a polyol mixture. The property of polyol A is shown in Table I . Polymethylenepolyphenyl polyisocyanate (7.8 kg) containing 5% by weight of a polynuclear material was mixed with modified diphenylmethane diisocyanate (6 kg) containing 28% by weight of uretoneimine and the mixture was heated to 50°C. To the mixture being stirred, 6.2 kg of a polyether polyol (polyol D) having an OH value of 28 mg KOH/g (active hydrogen equivalent: 2,000), which was prepared by adding propylene oxide and ethylene oxide (a weight ratio of propylene oxide to ethylene oxide = 97/13) to glycerine, was slowly added, followed by maintaining at 80°C for 3 hours. Regarding the resulting polyisocyanate, a content of an isocyanate group was 21.0% (isocyanate A). The property of isocyanate A is shown in Table II. The respective raw materials were charged in a tank of a high-pressure polyurethane foaming machine (HK-100, manufactured by Hennecke Co . ) and then poured into an steel mold for vehicle handle warmed to 55°C under the conditions of a mixing ratio of 100:82.8 (weight ratio), a NCO index of 105, a discharge amount of 200 g/second, a mixing pressure of 160 kg/cm 2 , an injection time of 2.25 seconds . The foam was removed after 60 seconds from the beginning of the pouring of the raw materials into the mold, and then (a) the moldability, (b) the distance between arms, (c) the physical properties and (d) the wear resistance were measured. The results are shown in Table III. Example 2 In the same manner as in Example 1 except for using 90 parts of a polyether polyol (polyol B) having an OH value of 92 mg KOH/g (active hydrogen equivalent: 610), which was prepared by adding propylene oxide and ethylene oxide in a weight ratio of 75:25 to glycerine, raw materials were prepared. In the same manner as in Example 1 except for using the same isocyanate as in Example 1 under the conditions of a mixing ratio of 100:94.9 (weight ratio), a NCO index of 105, a discharge amount of 200 g/second, a mixing pressure of 180 kg/cm 2 and an injection time of 2.25 seconds, a molded article was prepared and then evaluated. The results are shown in Table III. Example 3 In the same manner as in Example 1 except that the polyol mixture shown in Example 2 was mixed with polymethylenepolyphenyl polyisocyanate (8.2 kg) containing 5% by weight of a polynuclear material and modified diphenylmethane diisocyanate (6.4 kg) containing 28% by weight of uretoneimine and the mixture was heated to 50°C. To the mixture, 5.4 kg of a polyether polyol (polyol B) having an OH value of 92 mg KOH/g (active hydrogen equivalent: 610), which was prepared by adding propylene oxide and ethylene oxide (a weight ratio of propylene oxide to ethylene oxide = 75/25) to glycerine, was slowly added and an isocyanate (isocyanate B, content of an isocyanate group: 21.0%) was used in combination under the conditions of a mixing ratio of 100:94.9 (weight ratio), a ratio), a NCO index of 105, a discharge amount of 200 g/second, a mixing pressure of 180 kg/cm 2 and an injection time of 2.25 seconds. A molded article was prepared and then evaluated . The results are shown in Table III. Example 4 In the same manner as in Example 3 except for using the same raw materials as in Example 3 under the conditions of the mixing ratio of 100:99.4 (weight ratio) and the NCO index of 110, a molded article was prepared and then evaluated. The results are shown in Table III. Example 5 In the same manner as in Example 1 except for replacing 45 parts out of 90 parts of the polyether polyol (polyol A) used in Example 1 having an OH value of 56 mg KOH/g (active hydrogen equivalent: 1,000), which was prepared by adding propylene oxide and ethylene oxide in a weight ratio of 87:13 to glycerine, with a polyether polyol (polyol F) having an OH value of 112 mg KOH/g (active hydrogen equivalent: 500) under the conditions of the mixing ratio of 100:92.2 (weight ratio) and the NCO index of 105, a molded article was prepared and then evaluated. The results are shown in Table III. Example 6 90 Parts of a polyether polyol (polyol B) having an OH value of 92 mg KOH/g (active hydrogen equivalent: 610), which was prepared by adding propylene oxide and ethylene oxide in a weight ratio of 87:13 to glycerine, 6.6 parts of ethylene glycol, 0.5 parts of formic acid, 1.5 parts of diethanolamine, 0.6 parts of a 33% ethylene glycol solution of triethylenediamine and 0.05 parts of dibutyltin dilaurate were mixed to obtain 20 kg of a polyol mixture. In the same manner as in Example 1 except for using this polyol mixture in combination with isocyanate A under the conditions of the mixing- ratio of 100:88.1 (weight ratio) and the NCO index of 105, a molded article was prepared and then evaluated. The results are shown in Table III. Example 7 90 Parts of a polyether polyol ( polyol B ) having an OH value of 92 mg KOH/g (active hydrogen equivalent: 610), which is prepared by adding propylene oxide and ethylene oxide in a weight ratio of 87:13 to glycerine, 6.6 parts of 1, 3-butanediol, 3.2 parts of the amine compound obtained in Reference Example 1 and 0.5 parts of dibutyltin dilaurate were mixed to obtain 20 kg of a polyol mixture. In the same manner as in Example 1 except for using this polyol mixture in combination with Desmodur TPLS2025/1 (isocyanate C, manufactured by Bayer AG), which is prepared by isocyanurate-modifying hexamethylene diisocyanate, under the conditions of the mixing ratio of 100:70.1 (weight ratio) and the NCO index of 105, a molded article was prepared and then evaluated. The results are shown in Table III. Example 8 90 Parts of the polyether polyol (polyol B) used in Example 7, 9.0 parts of 1, 3-butanediol, 3.2 parts of the amine compound obtained in Reference Example 1 and 1.0 part of dibutyltin dilaurate were mixed to obtain 20 kg of a polyol mixture. In the same manner as in Example 1 except for using this polyol mixture in combination with isocyanate E, which was prepared by mixing- an experimental product (isocyanate D) of a low-viscosity isocyanurate modified material prepared by partially allophanate-modifying hexamethylene diisocyanate with isocyanate C used in Example 7 in a ratio (isocyanate D : isocyanate C) of 30:70, under the conditions of the mixing ratio of 100:81.3 (weight ratio) and the NCO index of 105, a molded article was prepared and then evaluated. The results are shown in Table III. Example 9 In the same manner as in Example 1 except for replacing 45 parts out of 90 parts of the polyether polyol (polyol B) used in Example 8 having an OH value of 92 mg KOH/g (active hydrogen equivalent: 610), which was prepared by adding propylene oxide and ethylene oxide in a weight ratio of 87:13 to glycerine, with a polyether polyol (polyol H) having an OH value of 112 mg KOH/g (active hydrogen equivalent: 500) and using the polyether polyol in combination with isocyanate E under the conditions of the mixing ratio of 100:84.4 (weight ratio) and the NCO index of 105, a molded article was prepared and then evaluated. The results are shown in Table III. Comparative Example 1 In the same manner as in Example 1 except for replacing 90 parts of the polyether polyol (polyol A) used in Example 1 having an OH value of 56 mg KOH/g (active hydrogen equivalent: 1,000), which was prepared by adding propylene oxide and ethylene- oxide in a weight ratio of 87:13 to glycerine, with 90 parts of a polyether polyol (polyol D) having an OH value of 28 mg KOH/g (active hydrogen equivalent: 2,000) and using the polyether polyol in combination with isocyanate A under the conditions of the mixing ratio of 100:73.4 (weight ratio) and the NCO index of 105, a molded article was prepared and then evaluated. The results are shown in Table III. Comparative Example 2 In the same manner as in Example 1 except for replacing 90 parts of the polyether polyol used in Example 1 having an OH value of 56 mg KOH/g (active hydrogen equivalent : 1 , 000 ) , which was prepared by adding propylene oxide and ethylene oxide to glycerine in a weight ratio of 87:13, with 90 parts of a polyether polyol (polyol E) having an OH value of 35 mg KOH/g (active hydrogen equivalent: 1,600) and using the polyether polyol in combination with isocyanate A under the conditions of the mixing ratio of 100:75.8 (weight ratio) and the NCO index of 105, a molded article was prepared and then evaluated. The results are shown in Table III. Comparative Example 3 In the same manner as in Example 1 except for replacing 90 parts of the polyether polyol used in Example 7 having an OH value of 92 mg KOH/g (active hydrogen equivalent: 610), which was prepared by adding propylene oxide and ethylene oxide in a weight ratio of 87:13 to glycerine, with 90 parts of a polyether polyol (polyol G) having an OH value of 28 mg KOH/g ( active hydrogen equivalent: 2,000) , which was prepared by adding propylene oxide and ethylene oxide in a weight ratio of 80:20 to propylene glycol, and using the polyether polyol in combination with isocyanate C under the conditions of the mixing ratio of 100:50.9 (weight ratio) and the NCO index of 105, a molded article was prepared and then evaluated. The results are shown in Table III. Comparative Example 4 90 Part of polyol E used in Comparative Example 2, 10 parts of 1 , 3-butanediol, 3.2 parts of the amine compound obtained in Reference Example 1 and 1.0 part of dibutyltin dilaurate were mixed to obtain 20 kg of a polyol mixture. In the same manner as in Example 1 except for using this polyol mixture in combination with isocyanate D under the conditions of the mixing ratio of 100:95.3 (weight ratio) and the NCO index of 105, a molded article was prepared and then evaluated. The results are shown in Table III. Comparative Example 5 In the same manner as in Example 1 except for replacing 90 parts of the polyether polyol used in Example 1 having an OH value of 56 mg KOH/g (active hydrogen equivalent: 1,000), which was prepared by adding propylene oxide and ethylene oxide in a weight ratio of 87:13 to glycerine, with 90 parts of a polyether polyol (polyol C) having an OH value of 178 mg KOH/g (active hydrogen equivalent: 315) and using the polyether polyol in combination with isocyanate C under the conditions of the mixing ratio of 100:124 (weight ratio) and the NCO index of 105, a molded article was prepared and then evaluated. The results are shown in Table III. Comparative Example 6 In the same manner as in Example 1 except for using the same raw materials as in Example 3 under the conditions of the mixing ratio of 100:81.3 (weight ratio) and the NCO index of 90, a molded article was prepared and then evaluated. The results are shown in Table III. Comparative Example 7 In the same manner as in Example 1 except for using the same raw materials as in Example 3 under the conditions of the mixing ratio of 100:108 (weight ratio) and the NCO index of 120, a molded article was prepared and then evaluated. The results are shown in Table III. Table 1 Property of used polyol Table 2 Property of used isocyanate Type of A B C D E isocyanate NC0% 21 21 23.5 20 22 Viscosity 400 450 1,000 200 650 (mPa- s/25°C) Table III Example Example Example Example Example Example Example Example Example 1 2 3 4 5 6 7 8 9 Polyol A 90 - - - 45 - - - - Polyol B - 90 90 - 90 45 Polyol C - - - - - - - - - Polyol D - - - - - - - - - Polyol E - - - - - - - - - Polyol F - - - - 45 - - - - Polyol G - - - - - - - - - Polyol H - - - - - - - - 45 MEG 6.0 «_ * . - - 6.6 - , - - Amine 3.2 - - - 3.2 compound 1.3BD - - - - - - 6.6 9.0 - DELA - - - - - 1.5 - - - Formic acid - - - - - 0.5 - - - DABCO/EG 0.6 - - - - DBTD 0.05 - - 0.5 1.0 - Isocyanate 100/ 100/ - - 100/ 100/ - - - A 82.8 94.9 92.2 88.1 Isocyanate - - 100/ 100/ - - - - - B 94.9 99.4 Table III (continued) Example Example Example Example 4 Example Example Example 7 Example Example 9 1 2 3 5 6 8 Isocyanate C - - - - - - 100/ - - 70.0 Isocyanate D - - - - - - - - - Isocyanate E - - - - - - - 100/ 100/ 81.3 84.4 NCO-Index 105 110 105 - Cure time 60 - •»— (sec) a) No - Brittle No •— Moldability problem problem b) Distance 194.65 194.78 194.74 194.32 194.25 193.85 194.12 194.35 194.95 between arms (mm) c) Physical Properties 0.65 Density - - - - - - (g/cm 3 ) Hardness 70 - 74 70 - 73 73 - 75 72 - 75 68 - 71 68 - 73 73 - 85 72 - 77 66 - 69 (Shore A) Tensile 58 52 73 79 35 48 33 30 35 strength (kg/cm 2 ) Elongation 135 110 150 120 100 120 40 60 80 (Z) d) Wear resistance No. 6 Canvas 5,000 8,000 25.000 50,000 < 8,000 10,000 50,000 < 40,000 50,000 < No. 10 10,000 10,000 50,000 100.000 < 10,000 12,000 100,000 < 50,000 100,000 < Canvas Table III (continued) Comparative Comparative Comparative Comparative Comparative Comparative Comparative Example 1 Example.2 Example 3 Example 4 Example 5 Example 6 Example 7 Polyol A - - - - - - - Polyol B - - - - - 90 - Polyol C - - - - 90 - - Polyol D 90 - - - - - - Polyol E - 90 - 90 - - - Polyol F - - - - - - - Polyol G - - 90 - - - - Polyol H - - - - - - - MEG 6.6 - - 6.6 - - Amine 3.2 - - compound 1.3BD - - 6.6 10 - - - DELA - - - - - - - Formic acid - - - - - - - DABCO/EG 0.6 - - - 0.6 DBTDL 0.05 0.5 1.0 0.05 Isocyanate A 100/ 100/ - - 100/ - - 73.4 75.8 124 Isocyanate B - - - - - 100/ 100/ 81.3 108 Table III (continued ) Comparative Comparative Comparative Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Isocyanate C - - 100/ - - - - 50.9 Isocyanate D - - - 100/ - - - 95.3 Isocyanate E - j j - - - NCO-Index 105 90 120 Cure time 60 120 60 (sec) a) No problem 4— No elasticNo problem Blister Moldability ity b) Distance 194.30 194.66 194.50 195.80 194.15 195.35 192.44 between arms (mm) c) Physical Properties 0.65 Density - - - - (g/cm 3 ) Hardness 59 - 72 70 - 75 65 - 75 50 - 52 90 < 60 - 62 79 - 85 (Shore A) Tensile 43 36 55 25 70 48 110 strength (kg/cm 2 ) Elongation 140 125 90 60 75 220 70 (Z) d) Wear resistance No. 6 Canvas 500 1,000 2,000 1,000 50,000 < 5,000 50,000 < No. 10 Canvas 1,000 2,000 3,000 2,000 100,000 < 10,000 100,000 < EFFECT OF THE INVENTION According to the present invention, it is possible to demold a low-density semi-rigid polyurethane foam having excellent wear resistance in a short time. In the present invention, it is not necessary to use chlorofluorocarbon or chlorocarbon as a blowing agent.

Claims: CLAIMS 1. A method of producing a semi-rigid polyurethane foam having microcell, a density of 0.3 to 0.9 g/cm 3 and Shore A hardness of 40 to 90 by a reaction injection molding process, from an isocyanate, and a polyol mixture comprising a polyether polyol, a cross-linking agent, a catalyst, a blowing agent, and optionally an internal mold release agent, a reinforcing, agent and an other aid, characterized in that (A) the isocyanate contains a polyisocyanate having functionality of at least three and the content of the polyisocyanate having functionality of at least three is at least 5% by weight based on the isocyanate, (B) a trifunctional polyether polyol having an active hydrogen equivalent of 300 to 1,000 and an ethylene oxide content of 5 to 30% by weight is contained in an amount of at least 40% by weight based on the total polyether polyol, and the total polyether polyol has an average active hydrogen equivalent of 500 to 1 , 200 and a viscosity of 200 to 800 mPa»s/25°C, (C) a difunctional cross-linking agent having a molecular weight of 61 to 200 is used in an amount of 2 to 20 parts by weight per 100 parts by weight of the polyether polyol, and (D) the isocyanate and the polyol mixture are molded at a NCO index of 100 to 115. 2. The method of producing a semi-rigid polyurethane foam according to claim 1, wherein the isocyanate is diphenyl methane diisocyanate, polyphenylmethane polyisocyanate or a modified substance thereof and a NCO % of the isocyanate is from 17 to 29% by weight. 3. The method of producing a semi-rigid polyurethane foam according to claim 1, wherein the isocyanate is a modified substance of hexamethylene diisocyanate and at least part of the modified substance is an isocyanurate modified substance, and the viscosity of the isocyanate is from 200 to 1200 mPa»s/25°C-

Inventors: NISHIKAWA SHINJI, YOKOTA HIROSHI, NISHIKAWA, SHINJI, YOKOTA, HIROSHI
Applicants: NISHIKAWA SHINJI, SUMITOMO BAYER URETHANE CO, YOKOTA HIROSHI, NISHIKAWA, SHINJI, SUMITOMO BAYER URETHANE CO., LTD., YOKOTA, HIROSHI
Application year: 1997
Main classification: C08G18
IPC codes: C08G18, C08G101, C08J9, C08K3, C08K5, C08L75