Title of Invention

HARD POLYURETHANE FOAM COMPOSITION AND HEAT INSULATOR FOR KEEPING COOLNESS

Abstract

Disclosed herein are environmentally friendly polyurethane foam compositions which are superior in flame resistancy and mechanical properties, and a heat insulator using the same. The hard polyurethane foam composition, comprising a polymeric 4,4'-diphenylmethane diisocyanate; a polyol mixture comprising (a) 20-60 wt% of polyetherpolyol, polymerized by the addition of propylene oxide and ethylene oxide to sorbitol: (b) 10-40 wt% of polyetherpolyol, polymerized by addition of propylene oxide and ethylene oxide to pentaerythritol: (c) 10-20 wt% of polyetherpolyol, polymerized by the addition of propylene oxide and ethylene oxide to sucrose: (d) 10-20 wt% of polyesterpolyol, polymerized by the addition of propylene oxide and ethylene oxide to phthalic anhydride: and (e) 1-20 wt% of polyetherpolyol, polymerized by the addition of ethylene oxide and propylene oxide to brome-substituted glycerine, the NCO/OH ratio of the composition being in the range of 1.0-2.0; and a hydrofluorocarbon lineage foaming agent selected from the group consisting of 1,3-pentafluorobutane, 1, 3-pentafluoropropane and mixtures thereof.

Full Text

HARD POLYURETHANE FOAM COMPOSITION AND INSULATOR FOR KEEPING COOLNESS USING IT TECHNICAL FIELD The present invention relates to a hard polyurethane foam composition which can be prepared into an insulator in the presence of a hydrofluorocarbon (HFC) foaming agent which is not harmful to the ozone layer, in addition to being superior in heat insulation and mechanical properties, and an insulator using the same. BACKGROUND ART Generally, hard urethane foam is prepared from diisocyanate and polyol in the presence of a foaming agent such as water, chlorofluorocarbon, hydrochlorofluorocarbon, hydrofluorocarbon, carbon dioxide, cyclopentane, etc. Widely used are toluene diisocyanate (TDI) and 4,4- diphenylmethanediisocyanate. Preferable is polymeric 4,4- diphenylmethanediisocyanate with an average functional group number of 2.7 or more. As for the polyol, it is of polyether or polyester. Polyetherpolyols are particularly widely used because they are easy to handle due to their low viscosity and stable to hydrolysis in addition to being inexpensive. Polyesterpolyols are superior in heat stability and tensile strength, but show low hydrolysis resistance. More than 90 % of polyurethane products are prepared from polyetherpolyols, while polyetherpolyols are used for special uses. Physical properties of hard polyurethane foam can be expressed in a function of density. As the density of hard polyurethane foam decreases, the thermal conductivity becomes low, so that its adiabatic performance is improved. However, physical properties, such as compression strength, are deteriorated. Thus, it is very difficult to develop hard polyurethane foam superior in heat insulation and physical properties, but both of the properties are necessary to ultra-low temperature insulators or ultra-low temperature pipe covers for liquefied natural gas storage tanks and to heat insulators for general uses. In order to improve the physical properties of polyurethane foam, the density of polyurethane foam is increased or a filler, such as glass fiber or carbon fiber, is used. However, the increase in density and the use of filler both suffer from the disadvantages of increasing the thermal conductivity to lower the heat insulation. Where polyurethane foam is used as an untra low temperature insulators, a decrease in heat insulation bears highly negative results. Therefore, there is needed an improvement in physical properties without a decrease in heat insulation. Examples of the foaming agent useful for the preparation of polyurethane foam include water, carboxylic acids, fluorocarbon foaming agents, carboxylic acid, and air. Formerly, chlorofluorocarbon was widely used because of its low thermal conductivity and high stability in the air. However, as chlorofluorocarbon was found to harm the environment, hydrochlorofluorocarbon, cyclohexane, water, hydrochlorofluorocarbon, or hydrofluorocarbon has been recently used instead. Particularly regarded as the next generation foaming agent, hydrofluorocarbon has attracted a lot of attention because it does not harm the ozone layer, shows low thermal conductivity and does not diffuse from the polyurethane foam to the air so as to make the heat insulation performance to last long. As substitutes for CPC-11 and CFC-12, HFC-365mfc (1,3- pentafluorobutane) and HFC-245fa (1,3-pentachloropropane), found to be not harmful to the ozone layer, have been under study and used, in addition to HCFC-122 (2,2-dichloro-l,1,1- trifluoroethane), HCFC-141b (1,1-dichloro-l-fluoroethane), HFC-134a (1,1,1,2-tetrafluoroethane), and HFC-152a (1,1- difluoroethane). Besides foaming agents, various additives such as catalysts, flame retardants, chain extenders, etc. are used to prepare polyurethane foam. Exemplified by low molecular weight diol or diamine, a chain extender or a crosslinking agent is used with the aim of increasing the mechanical strength of polyurethane foam. Tins and amines are useful as catalysts. The low flame retardancy of polyurethane requires the use of flame retardants, which are usually halogen, phosphorus, and inorganic compounds, being grouped into reactive and additive types. When the cells formed during foaming are small and uniform, the resultant foam is improved in heat insulation and mechanical properties. To this end, silicon surfactants are used as cell stabilizers. DISCLOSURE OF THE INVENTION With the background in mind, the intensive and thorough research into a heat insulator which is environmentally friendly as well as exhibiting superior mechanical and heat insulating properties, conducted by the present inventors, resulted in the finding that a mixture of three polyether polyols and one polyester polyol, each ranging in OH values, from 200 to 659, can be reacted with polymeric 4,4-dimethylmethanediisocyanate in the presence of an HFC lineage foaming agent which does not harm the ozone layer to give a foam with excellent mechanical and heat insulating properties. Therefore, it is an object of the present invention to provide an environmentally friendly polyurethane foam composition. It is another object of the present invention to provide a polyurethane foam composition which shows excellent mechanical and heat insulating properties. It is a further object of the present invention to provide a heat insulator which is environmentally friendly in addition to being superior in mechanical and heat insulating properties. In accordance with the present invention, the above objects could be accomplished by a provision of a hard polyurethane foam composition, comprising a polymeric 4,4'- diphenylmethane diisocyanate; a polyol mixture comprising (a) 20-60 wt% of polyetherpolyol, polymerized by the addition of propylene oxide and ethylene oxide to sorbitol: (b) 10-40 wt% of polyetherpolyol, polymerized by addition of propylene oxide and ethylene oxide to pentaerythritol: (c) 10-20 wt% of polyetherpolyol, polymerized by the addition of propylene oxide and ethylene oxide to sucrose: (d) 10-20 wt% of polyesterpolyol, polymerized by the addition of propylene oxide and ethylene oxide to phthalic anhydride: and (e) 1-20 wt% of polyetherpolyol, polymerized by the addition of ethylene oxide and propylene oxide to brome-substituted glycerine, the NCO/OH ratio of the composition being in the range of 1.0-2.0; and a hydrofluorocarbon lineage foaming agent selected from the group consisting of 1,3- pentafluorobutane, 1,3-pentafluoropropane and mixtures thereof. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is an electron microscope photograph showing the micro structure of the hard polyurethane foam prepared by use of HFC-365mfc as a foaming agent in accordance with the present invention. DETAILED DESCRIPTION OF THE INVENTION In the present invention, polyurethane foam is prepared from 4,4'-diphenylmethane diisocyanate (MDI) and a mixture of polyols in the presence of a foaming agent. The polyol mixture useful in the present invention comprises (a) 20-60 wt% of polyetherpolyol, polymerized by the addition of propylene oxide and ethylene oxide to sorbitol, (b) 10-40 wt% of polyetherpolyol, polymerized by addition of propylene oxide and ethylene oxide to pentaerythritol, (c) 10-20 wt% of polyetherpolyol, polymerized by the addition of propylene oxide and ethylene oxide to sucrose, (d) 10-20 wt% of polyesterpolyol, polymerized by the addition of propylene oxide and ethylene oxide to phthalic anhydride, and (e) 1-20 wt% of polyetherpolyol, polymerized by the addition of ethylene oxide and propylene oxide to brome-substituted glycerine. The polyol mixture ranges from 380 to 510, in average OH values. Preferably, the NCO/OH ratio of the composition comprising polymeric 4,4'-diphenylmethane diisocyanate and the polyol mixture is in the range of 1.0-2.0. As described, the polyols used in the present invention are synthesized from glycerine, pentaerythritol, sorbitol, and sucrose. Because these alcohols have three, four, six and eight functional groups, respectively, which are reactive to the diisocyanate, linear or crosslinking linkages are formed upon reaction between the reactants. According to the alcohol bases used, large differences are found in the resultant polyurethane foams. For example, the difference in compression strength between the polyurethane foams based on glycerine and sorbitol is 10 % or upward. In the present invention, the content of each polyol is optimized in sufficient consideration of the reaction time, viscosity and physical properties of the products. The use of brome-substituted polyol resides with an improvement in flame retardancy. As for a heat insulator with a low density, it is poor in flame retardancy. Thus, the brome- substituted polyol contributes to the improvement of flame retardancy. In addition to the diisocyanate and the polyols, the polyurethane foam composition of the present invention comprises a foaming agent, a catalyst, and other additives. A useful foaming agent is selected from among HFC- 365mfc (1,3-pentafluorobutane) and HFC-245fa (1,3- pentafluoropropane). HFC-365mfc and HFC245fa may be used in combination without, deteriorating the physical properties of the polyurethane foam. Therefore, HFC-245fa may be mixed in the proportions of 0-100% with HFC-365mfc. Water, if necessary, may be used as a subsidiary foaming agent. It is preferred that the organic foaming agent is used in the amount of 3-35 parts by weight based on 100 parts by weight of the polyols used. Water is preferably added in the amount of 0-7 parts by weight based on 100 parts by weight of the polyols used. In this case, the polyurethane foam obtained has a density of 30-140 kg/m3. The density can be adjusted to be below 30 kg/m3 or over 14 0 kg/m3 by controlling the amount of the foaming agent. Low evaporation temperatures of HFC-365mfc and HFC- 245fa make it easy to prepare polyurethane foam. Additionally, their low thermal conductivity contributes to the formation of high heat insulating properties in polyurethane foam. Water, used as a subsidiary foaming agent, reacts with diisocyanate to form urea and discharge carbon dioxide which is then utilized in the bubbling of the polyurethane foam. In addition, the reaction heat produced upon reaction between water and diisocyanate is used for the evaporation of HFC-365mfc and HFC-245fa. If the amount of water is over 7 parts by weight based on 100 parts by weight of the polyols used, not only is excessive heat generated by the reaction to scorch in the polyurethane foam obtained, but also excess carbon dioxide is present in the polyurethane foam, giving rise to an increase in thermal conductivity. In accordance with the present invention, hard polyurethane foam is prepared from the diisocyanate and the polyol mixture in the presence of a catalyst with the aid of a foaming agent, a bubble stabilizer and other additives. Useful to promote the reaction of the diisocyanate with the polyols are amine catalysts. In accordance with the present invention, the catalyst is selected from the group consisting of pentamethyldiethylene triamine, dimethylcycloamine, tris(3- dimethylamino)propylhexahydrotriamine, and mixtures thereof. The catalyst is preferably used in the amount of 0.1-2.0 parts by weight based on 100 parts by weight of the polyol mixture used. For example, when too little of a catalyst is used, the reaction rate becomes so slow as to produce incomplete hard polyurethane foam which is poor in physical properties. On the other hand, if the amount of the catalyst exceeds 2.0 parts by weight, the reaction rate and physical properties are not improved to the same degree. The silicon surfactant polysiloxane ether is useful as a bubble stabilizer in the present invention. The foaming agent is vaporized by the heat generated during the reaction between diisocyanate and polyol, forming bubbles to foam the polyurethane reactants. When the bubbles gather together into larger ones due to their internal pressures, the polyurethane foam has poor heat insulating properties and weak mechanical strength. The silicon surfactant provides charges on the surface of the bubbles so that the bubbles become repulsive to each other by the electrostaticity. As a result, the polyurethane foam retains small and uniform cells. Preferably, the amount of the bubble stabilizer falls into the range of 0-2.0 parts by weight based on 100 parts by weight of the polyols used. If the bubble stabilizer is used in an amount larger than 2.0 parts by weight, the polyurethane foam becomes poor in compression strength and load resistance. To provide the polyurethane foam with flame retardancy, a flame retardant may be added. Useful are phosphorus flame retardants, exemplified by tricresyl phosphate. The amount of the flame retardant preferably ranges from 5 to 15 parts by weight based on 100 parts by weight of the polyols used. For example, if the flame retardant is used in an amount smaller than 5 parts by weight, satisfactory flame retardancy is not obtained. On the other hand, if the amount of the flame retardant is over 15 parts by weight, there is only a slight increase in flame retardancy obtained and the productivity becomes low. In accordance with the present invention, a crosslinking agent may be used to reinforce the strength of the polyurethane foam, as well as shortening the curing time. Optionally, other additives which are used in urethane chemistry, such as fillers, stabilizers, e.g., anti-oxidants and UV light absorbers, and colorants, etc. may be added. The polyurethane foam may be prepared in various methods, such as a one-shot method, a prepolymer method, etc. According to the one-shot method, all reactants including isocyanate and polyol are simultaneously fed to a reaction tank. The one-shot method is simple and easy, but suffers from the disadvantage of finding difficulty in controlling reaction rates and producing a large quantity of reaction heat to cause cracks in the foam. On the other hand, isocyanate is partially reacted with polyol in advance and the remaining reactants are added to the prepolymers synthesized according to the prepolymer method. This method enjoys the advantage of showing high reaction rates as the reactants relatively slowly reacted and of allowing the foam to fill every nook and corner of complicate structures as the viscosity of the foam is slowly increased. However, the prepolymer method is disadvantageous in that the production procedure is so lengthy as to increase the production cost. In the present invention, the one-shot method is adopted in consideration of productivity, workability, and production cost. However, the addition of polyols and additives are under control lest scorch and cracks attributed to a large reaction heat are caused. High or low pressure foaming machines as usually used in the polyurethane industry may be used. A better understanding of the present invention may be obtained in light of the following examples which are set forth to illustrate, but are not to be construed to limit the present invention. EXAMPLE 1 To a polyol mixture comprising 35.0 g of the polyol polymerized by the addition of propylene oxide and ethylene oxide to pentaerythritol, 25.0 g of the polyol polymerized by the addition of propylene oxide and ethylene oxide to sucrose, 10.0 g of the polyol polymerized by the addition of propylene oxide and ethylene oxide to phthalic anhydride, 30.0 g of the polyol polymerized by the addition of propylene oxide and ethylene oxide to sorbitol, and 30.0 g of the polyol polymerized by the addition of propylene oxide and ethylene oxide to glycerine, 2.0 g of polysiloxane ether, a catalyst mixture comprising 0.3 g of pentamethyldiethylenetriamine, 0.8 g of dimethylcycloamine, and 0.3 g of tris(3-dimethylamino)propylhexahydrotriamine, a flame-retardant mixture comprising 10.0 g of tricresyl phosphate and 0.4 g of water, and 8.0 g of HFC-365mfc were added to form a resin solution. 140.0 g of 4,4- dimethylmethanediisocyanate was mixed with the resin solution to prepare polyurethane foam. The polyurethane foam was measured for physical properties and the results and test methods are given in Table 1, below. The closed cell content has an influence on the thermal conductivity, vapor transmittance, and water absorption. Accordingly, the closed cell content may be used as a barometer for controlling the quality of polyurethane foam. The polyurethane foam of this example is found to be high in the closed cell content as compared with the usual polyurethane foam which has a closed cell content of 90 %. The microstructure of the polyurethane foam prepared in the example was observed with the aid of an electron microscope. The foam is based on the cells produced by the bubbling of the polymer. As seen in Fig. 1, the polyurethane foam of the present invention contains small and uniform cells. EXAMPLE 2 To a polyol mixture comprising 25.0 g of the polyol polymerized by the addition of propylene oxide and ethylene oxide to pentaerythritol, 45.0 g of the polyol polymerized by the addition of propylene oxide and ethylene oxide to sucrose, 13.0 g of the polyol polymerized by the addition of propylene oxide and ethylene oxide to glycerine, 14.0 g of the polyol polymerized by the addition of propylene oxide and ethylene oxide to phthalic anhydride, and 4 g of the polyol polymerized by the addition of propylene oxide and ethylene oxide to brome-substituted glycerine, 2.0 g of polysiloxane ether, a catalyst mixture comprising 0.4 g of pentamethyldiethylenetriamine and 0.8 g of dimethylcyclohexylamine, a flame-retardant mixture comprising 3.0 g of tricresyl phosphate and 1.1 g of water, and 26.5 g of HFC-365mfc were added to form a resin solution. 160.0 g of 4,4-dimethylmethanediisocyanate was mixed with the resin solution to prepare a hard polyurethane foam. The polyurethane foam was measured for physical properties and the results and test methods are given in Table 2, below. EXAMPLE 3 Hard polyurethane foam was prepared in a manner similar to that of Example 2, except that 22.0 g of HFC- 245fa was used instead of HFC-365mfc. After its surface was removed, the hard polyurethane foam was measured for physical properties, and the results are given in Table 3, below. In the presence of hydrofluorocarbon compounds which are not harmful to the ozone layer, as described hereinbefore, hard polyurethane foam is obtained which is superior in mechanical strength while retaining excellent heat insulating properties. Therefore, using the polyurethane foam composition of the present invention, an environmentally friendly heat insulator which exhibits heat insulation and mechanical properties can be prepared in a conventional method. The present invention has been described in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. 1. A hard polyurethane foam composition, comprising: a polymeric 4,4'-diphenylmethane diisocyanate; a polyol mixture comprising (a) 20-60 wt% of polyetherpolyol, polymerized by the addition of propylene oxide and ethylene oxide to sorbitol: (b) 10-40 wt% of polyetherpolyol, polymerized by addition of propylene oxide and ethylene oxide to pentaerythritol: (c) 10-20 wt% of polyetherpolyol, polymerized by the addition of propylene oxide and ethylene oxide to sucrose: (d) 10-20 wt% of polyesterpolyol, polymerized by the addition of propylene oxide and ethylene oxide to phthalic anhydride: and (e) 1-20 wt% of polyetherpolyol, polymerized by the addition of ethylene oxide and propylene oxide to brome-substituted glycerine, the NCO/OH ratio of the composition being in the range of 1.0-2.0; and a hydrofluorocarbon lineage foaming agent selected from the group consisting of 1,3-pentafluorobutane, 1,3-pentafluoropropane and mixtures thereof. 2. The hard polyurethane foam composition as defined in claim 1, wherein the composition ranges, in average OH values, from 380 to 510 and, in average NCO%, from 29 to 32. 3. The hard polyurethane foam composition as defined in claim 1, wherein the hydrofluorocarbon lineage foaming agent is used in the amount of 3-35 parts by weight based on 100 parts by weight of the polyol mixture. 4. The hard polyurethane foam composition as defined in one of claims 1 to 3, further comprising a phosphorus flame retardant in the amount of 5-30 parts by weight based on 100 parts by weight of the polyol mixture. 5. The hard polyurethane foam composition as defined in one of claims 1 to 3, further comprising an amine catalyst in the amount of 0.1-2.0 parts by weight based on 100 parts by weight of the polyol mixture. 6. The hard polyurethane foam composition as defined in one of claims 1 to 3, further comprising polysiloxane in the amount of 0-2.0 parts by weight based on 100 parts by weight of the polyol mixture. 7. The hard polyurethane foam composition as defined in claim 3, further comprising water as a subsidiary foaming agent. 8. A heat insulator, prepared from the urethane foam composition of claim 1. Disclosed herein are environmentally friendly polyurethane foam compositions which are superior in flame resistancy and mechanical properties, and a heat insulator using the same. The hard polyurethane foam composition, comprising a polymeric 4,4'-diphenylmethane diisocyanate; a polyol mixture comprising (a) 20-60 wt% of polyetherpolyol, polymerized by the addition of propylene oxide and ethylene oxide to sorbitol: (b) 10-40 wt% of polyetherpolyol, polymerized by addition of propylene oxide and ethylene oxide to pentaerythritol: (c) 10-20 wt% of polyetherpolyol, polymerized by the addition of propylene oxide and ethylene oxide to sucrose: (d) 10-20 wt% of polyesterpolyol, polymerized by the addition of propylene oxide and ethylene oxide to phthalic anhydride: and (e) 1-20 wt% of polyetherpolyol, polymerized by the addition of ethylene oxide and propylene oxide to brome-substituted glycerine, the NCO/OH ratio of the composition being in the range of 1.0-2.0; and a hydrofluorocarbon lineage foaming agent selected from the group consisting of 1,3-pentafluorobutane, 1, 3-pentafluoropropane and mixtures thereof.

Documents:

396-kol-2003-granted-abstract.pdf

396-kol-2003-granted-claims.pdf

396-kol-2003-granted-correspondence.pdf

396-kol-2003-granted-description (complete).pdf

396-kol-2003-granted-drawings.pdf

396-kol-2003-granted-examination report.pdf

396-kol-2003-granted-form 1.pdf

396-kol-2003-granted-form 18.pdf

396-kol-2003-granted-form 2.pdf

396-kol-2003-granted-form 26.pdf

396-kol-2003-granted-form 3.pdf

396-kol-2003-granted-form 5.pdf

396-kol-2003-granted-priority document.pdf

396-kol-2003-granted-reply to examination report.pdf

396-kol-2003-granted-specification.pdf