WO1998037116A1

WO1998037116A1 - Method for producing rigid polyurethane foam

Info

Publication number: WO1998037116A1
Application number: PCT/JP1998/000585
Authority: WO
Inventors: Yasuo Inazawa; Kei Odani
Original assignee: Sumitomo Bayer Urethane Co., Ltd.
Priority date: 1997-02-20
Filing date: 1998-02-13
Publication date: 1998-08-27
Also published as: JP2001524995A; JP3919824B2; AU5880098A

Abstract

A method for producing a rigid polyurethane foam, which comprises mixing (a) a polyisocyanate component with a polyol component comprising (b) a polyol mixture, (c) a catalyst and (d) a blowing agent, then foaming the mixture; wherein the polyisocyanate component (a) is polymethylenepolyphenyl polyisocyanate or a modified material thereof; the polyol mixture (b) comprises (b-1) a polyol which is produced by adding an alkylene oxide to an aliphatic amine and (b-2) an aromatic polyether polyol which is produced by using an aromatic amine, a Mannich base having an aromatic ring or a polyfunctional phenol as a starting material; the catalyst (c) is at least one metallic catalyst and the blowing agent (d) is an adduct of a primary or secondary amine compound with carbon dioxide. The method of the present invention is superior in initial activity and requires a small amount of raw materials.

Description

DESCRIPTION

Method for producing rigid polyurethane foam

FIELD OF THE INVENTION

The present invention relates to a method for producing a rigid polyurethane foam, which is superior in initial activity and requires a small amount of raw materials . The rigid polyurethane foam of the present invention can be applied by spraying in excellent workability regardless of a change in temperature throughout the four seasons. RELATED ARTS

A rigid polyurethane foam is produced by mixing a polyisocyanate component with, as a polyol component, a compound having at least two reactive groups capable of reacting with an isocyanate group (particularly polyol), a catalyst, a flame retardant, a diluent, a surfactant, a low-boiling point hydrochlorofluorocarbon such as HCFC-141b and water which reacts with the polyisocyanate to generate carbon dioxide, by a foaming machine. In case of the spray foaming in a field of construction work, it is considerably difficult to adjust the temperature of a substrate. Particularly, in winter, when the foam thickness is comparatively thin, an endothermic effect due to low-temperature of the substrate occurs so that the exothermic reaction is insufficient and the density becomes comparatively high. At the same time, since the curing at the time of foaming proceeds slowly, a lateral elongation phenomenon of the foam occurs, which results in poor adhesion to the substrate.

In order to eliminate such a phenomenon, Japanese Patent Kokoku Publication No. 99533/1994 suggests use of a specific catalyst or use of a low-boiling point blowing agent in combination with the specific catalyst. However, in case of use in combination with only the specific catalyst, the foam density becomes high when the foam thickness is comparatively thin. In order to handle the low-boiling point blowing agent of a gas at a normal temperature under a normal pressure, it is necessary to bring a cylinder into a field of foaming. Furthermore, when the metering precision of the blowing agent is not sufficiently controlled, the density becomes too high or too low. As a result, when the density becomes too high, the used amount of the raw material is increased. On the other hand, when the density becomes too low, shrinkage of the foam occurs . As another method, an attempt of increasing an initial reactivity using a foaming catalyst (catalyst which accelerates the reaction between water and isocyanate) is sometimes made, but the amount of the used foaming catalyst is limited in view of the cost, etc., as a matter of course.

Japanese Patent Kokai Publication No. 133398/1976 proposes a method for producing a flame-retardant , low-fuming polyurethane foam, which comprises blending amine carbamate of a primary or secondary amino compound having a hydroxyl group, and then foaming the blend. However, according to this method, since the reaction proceeds too slowly, the workability (e.g. instantaneous foaming and curing) required for the in-situ foaming (spray) is not satisfied. In addition, as the isocyanate, TDI (toluene diisocyanate) is used (see Examples) and is unsuitable for spray foaming.

Japanese Patent Kokai Publication No. 220512/1987 discloses a method for producing a thermally insulating polyurethane foam for refrigerator, using a special amine/carbon dioxide adduct. However, this method is not suitable for spray because of poor reactivity (long gelling time) . SUMMARY OF THE INVENTION The present invention provides a method for producing a rigid polyurethane foam which is superior in initial activity in low-temperature atmosphere and is a low-density foam.

The present invention provides a method for producing a rigid polyurethane foam, which comprises mixing (a) a polyisocyanate component with a polyol component comprising (b) a polyol mixture, (c) a catalyst, (d) a blowing agent and, if necessary, a flame retardant, a diluent and a surfactant, then foaming the mixture; wherein the polyisocyanate component (a) is polymethylenepolyphenyl polyisocyanate or a modified material thereof; the polyol mixture (b) comprises: (b-1) 20 to 80 parts by weight of a polyol having a hydroxyl value of 300 to 800 mg KOH/g, which is produced by adding an alkylene oxide to an aliphatic amine;

(b-2) 20 to 80 parts by weight of at least one aromatic polyether polyol having a hydroxyl value of 170 to 600 mg KOH/g, which is produced by using an aromatic amine, a Mannich base having an aromatic ring or a polyfunctional phenol as a starting material; and

(b-3) less than 40 parts by weight of a polyol which is produced by using a compound having no aliphatic amine as a starting material, or a polyether polyol having no aromatic ring and/or an aromatic polyester polyol, and a hydroxyl value of the polyol mixture (b) is from 300 to 800 mg KOH/g; the catalyst (c) is at least one metallic catalyst, which is optionally used in combination with a tertiary amine compound; and the blowing agent (d) is an adduct of a primary or secondary amine compound with carbon dioxide, which is optionally used in combination with a low-boiling point compound and/or water.

The present invention also provides a polyol composition comprising (b) a polyol mixture, (c) a catalyst, (d) a blowing agent and, if necessary, a flame retardant, a diluent and a surfactant; the polyol mixture (b) comprises:

(b-1) 20 to 80 parts by weight of a polyol having a hydroxyl value of 300 to 800 mg KOH/g, which is produced by adding an alkylene oxide to an aliphatic amine; (b-2) 20 to 80 parts by weight of at least one aromatic polyester polyol having a hydroxyl value of 170 to 600 mg KOH/g, which is produced by using an aromatic amine, a Mannich base having an aromatic ring or a polyfunctional phenol as a starting material; and

DETAILED DESCRIPTION OF THE INVENTION The present invention will be explained in detail hereinafter.

The polyisocyanate component (a) used in the present invention is (i) polymethylenepolyphenyl polyisocyanate or (ii) a product prepared by modifying polymethylene- polyphenyl polyisocyanate and/or diphenylmethane diisocyanate (MDI) as a raw material according to a known method. The polyisocyanate component (a) is generally polymethylenepolyphenyl polyisocyanate, but a mixture of modified polymethylenepolyphenyl polyisocyanate and polymethylenepolyphenyl polyisocyanate may be used.

The modification may be urethanization, carbodiimidation, trimerization and the like. The urethanized polymethylenepolyphenyl polyisocyanate is a reaction product obtained by reacting polymethylenepolyphenyl polyisocyanate or MDI with polyol and/or monool (e.g. molar ratio of NCO to OH = 1000/1 to 10/5). The carbodiimidated polymethylenepolyphenyl polyisocyanate is a compound having a carbodiimide group and/or a uretoneimine group, which is made by carbodiimidating 0.1 to 20% by weight of isocyanate groups by using a known carbodiimidating catalyst. The trimerized polymethylenepolyphenyl polyisocyanate is a compound wherein isocyanate groups are trimerized in the amount of 1 to 20% by weight based on isocyanate groups of the starting material, which is made by a known trimerization technique. The modified material may be a mixture thereof . In the present invention, the polyol mixture (b) is used. The polyol mixture (b) is a mixture of (b-1) a polyol which is produced by adding an alkylene oxide to an aliphatic amine, (b-2) an aromatic polyether polyol and, if necessary, (b-3) a polyether polyol having no aliphatic amine or no aromatic ring and/or an aromatic polyester polyol .

Examples of the polyol (b-1) which is produced by adding an alkylene oxide to an aliphatic amine include those obtained by addition-polymerizing at least one monomer such as ethylene oxide, propylene oxide, butylene oxide, amylene oxide, glycidyl ether, methyl glycidyl ether, t-butyl glycidyl ether or phenyl glycidyl ether by a known method in the presence of at least one compound as an initiator selected from an amine compound such as ethylenediamine, propylenediamine and diethylenetriamine and/or an alkanolamine compound such as triethanolamine, diethanolamine and monoethanolamine. The polyol (b-1) may be a polyether polyol . A hydroxyl value of the aliphatic amine polyol (b-1) is from 300 to 800 mg KOH/g, preferably from 450 to 800 mg KOH/g. If the hydroxyl value is smaller than 300 mg KOH/g, the compression strength of the resulting foam is low. If the hydroxyl value is larger than 800 mg KOH/g, the viscosity of the polyol (b-1) rapidly increases, which results in high viscosity of the polyol mixture (b) .

An amount of the used polyol (b-1) which is produced by adding an alkylene oxide to an aliphatic amine is from 20 to 80 parts by weight, preferably from 30 to 60 parts by weight, based on 100 parts by weight of the polyol mixture (b) . If the amount is smaller than 20 parts by weight, a large amount of a catalyst is necessary when adjusting to the reactivity required for performing the spray foaming, which results in high cost. If the amount is larger than 80 parts by weight, the foam does not become flat at the time of spray foaming and a problem on the finishing (e.g. bump-like portion formed by partially rising the foam from the adhesive surface, etc.) is liable to arise. The polyol mixture (b) contains the aromatic polyether polyol (b-2). The aromatic polyether polyol (b-2) is a polyether polyol produced from an aromatic amine, a Mannich base having an aromatic ring, or a polyfunctional phenol as the starting material.

The polyether polyol produced by using the aromatic amine as a starting material is a polyol prepared by adding at least one alkylene oxide such as ethylene oxide and propylene oxide to at least one aromatic polyamine such as tolylenediamine and diphenylmethanediamine .

The polyether polyol which is produced by using a Mannich base as a starting material is a polyol prepared by adding an alkylene oxide to a Mannich reduction product obtained by phenols, alkanolamine and formaldehydes. Examples thereof include DK polyol 3773 (manufactured by Dai-Ichi Kogyo Seiyaku Co., Ltd.).

The aromatic polyether polyol (b-2) may be a polyether polyol produced by using a polyfunctional phenol as the starting material . Examples thereof include resol type condensate prepared by condensing phenols with excess formaldehydes in the presence of an alkaline catalyst, a benzylic ether-type initial condensate prepared by reacting in a non-aqueous system in case of synthesizing the resol type condensate, and a novolak-type condensate prepared by reacting excess phenols with formaldehydes in the presence of an acid catalyst. A molecular weight of the condensate is preferably from about 200 to 10000. Phenols also include those wherein substituents other than the hydroxyl group is bonded to the benzene nucleus. Examples of the phenols include phenol, cresol, bisphenol A, resorcinol and the like. Examples of the formaldehydes include formalin, paraformaldehyde and the like. A hydroxyl value of the aromatic polyether polyol

(b-2) is from 170 to 600 mg KOH/g, preferably from 170 to 450 mg KOH/g. An amount of the used aromatic polyether polyol (b-2) is from 20 to 80 parts by weight, preferably from 30 to 50 parts by weight, based on 100 parts by weight of the polyol mixture (b) . If the amount is smaller than 20 parts by weight, the adhesion to the substrate is liable to be deteriorated. If the amount is larger than 80 parts by weight, the curing of the foam proceeds slowly. The polyol mixture (b) may contain (b-3) a polyol which is obtained by using a compound containing no aliphatic amine as a starting material, or a polyether polyol having no aromatic ring and/or an aromatic polyester polyol. The component (b-3) is optionally used for adjusting the viscosity and reactivity of the polyol mixture (b) . Examples of the component (b-3) include, a polyether polyol which is obtained by adding a cyclic ether, particularly propylene oxide, ethylene oxide or butylene oxide to polyhydric alcohols, saccharides and the like.

The aromatic polyester polyol (b-3) is a reaction product of a polyhydric alcohol, preferably a dihydric alcohol and/or a trihydric alcohol with a polybasic, preferably dibasic polycarboxylic acid having an aromatic ring. Examples thereof include Phantol PL-305 (manufactured by Toho Rika Kogyo Co., Ltd.).

In order to prepare the aromatic polyester polyol, a corresponding polycarboxylic anhydride or a corresponding carboxylate ester of a lower alcohol or a mixture thereof can be used in place of a free polycarboxylic acid. The polycarboxylic acid may have an aromatic ring and/or a heterocyclic ring, and it may be a polycarboxylic acid substituted with a halogen atom. Examples of the polycarboxylic acid include phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid, anhydrous phthalic acid and derivatives thereof . The polyhydric alcohol is preferably an alcohol having 3 to 9 carbon atoms, and may be anyone of a straight-chain, branched or cyclic alcohol. The polyhydric alcohol is preferably a dihydric alcohol and/or a trihydric alcohol. Examples of the dihydric alcohol include ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, cyclohexanediol and the like. Examples of the trihydric alcohol include glycerine, trimethylolpropane and the like. Those prepared by decomposing polyethylene terephthalate with various glycols may also be used.

An amount of the component (b-3) is less than 40 parts by weight, preferably not more than 30 parts by weight, based on 100 parts by weight of the polyol mixture (b).

The catalyst (c) is at least one metallic catalyst. The metallic catalyst may be a metal carboxylate salt. The metal carboxylate salt is represented by the general formula: R-COOX wherein R represents an alkyl, alkenyl or aryl group having 1 to 17 carbon atoms; and X represents sodium, potassium or lead.

If the number of carbon atoms of R is not smaller than 18, the catalyst is hardly dissolved in water and therefore is not suitable for practical use. The metallic catalyst is preferably potassium octanoate, lead octanoate or potassium acetate.

An amount of the solid material in the used metallic catalyst is from 0.1 to 7 parts by weight, preferably from 0.1 to 5 parts by weight, based on 100 parts by weight of the polyol mixture (b) . Those prepared by dissolving the metallic catalyst in a short chain diol may be preferably used. As the short chain diol, diethylene glycol and dipropylene glycol are preferred. Two or more types of metallic catalysts may be mixed.

The catalyst (c) may contain a tertiary amine catalyst, if necessary. As the tertiary amine catalyst, there can be used an amine catalyst which is generally known. In view of the odor and safety/hygiene, -those having low vapor pressure are preferred.

Examples of the tertiary amine catalyst include ,N,N' , ' -tetramethylhexamethylenediamine, N,N',N"- tris (dimethylaminopropyl )hexahydro-s-triazine, triethylenediamine , ,N,N' ,N' -tetramethylpropylenediamine, N,N,N' ,N'-pentamethyldiethylenetriamine, trimethyl- aminoethylpiperazine, N,N' -dimethylcyclohexylamine, bis ( 2-dimethylaminoethyl )ether, N-methylmorpholine, N-ethylmorpholine and the like. Preferred are N,N,N' ,N' -tetramethylhexamethylenediamine and triethylenediamine. An amount of the tertiary amine catalyst used may be not larger than 20 parts by weight, more preferably from 0.1 to 10 parts by weight, particularly from 2 to 5 parts by weight, based on 100 parts by weight of the polyol mixture (b) .

The blowing agent (d) is an adduct between an amine compound having a primary or secondary amino group and carbon dioxide. Examples of the amine compound include an amine compound such as butylamine, ethylenediamine, hexamethylenediamine, diethylenetriamine and triethylenetetramine and alkanolamine such as ethanolamine, N-methylethanolamine, diethanolamine, isopropanolamine and diisopropanolamine . Among them, an amine compound having a hydroxyl group is preferred. An amount of the used adduct of the amine compound having a primary or secondary amino group and carbon dioxide is from 0.1 to 30 parts by weight based on 100 parts by weight of the polyol mixture (b) .

Since the reaction solution of this adduct is liable to solidify at a normal temperature, it is preferred that a liquid polyol and/or water is previously added to the amine compound .

The blowing agent (d) may contain a low-boiling point compound and/or water, if necessary. Examples of the low-boiling point compound include hydrocarbon, halogenated hydrocarbon and the like. It is possible to use a low-boiling point compound having a boiling point within the range from -50 to 100°C (under 1 atm) . An amount of the used blowing agent (d) may be within the range from 0.1 to 80 parts by weight, for example 0.1 to 60 parts by weight based on 100 parts by weight of the polyol mixture (b) .

In the present invention, various additives such as a flame retardant, a diluent and a surfactant may be used, in addition to the components (a) to (d).

In the present invention, an isocyanate index is preferably from 60 to 180, particularly from 80 to 150.

In the present invention, it is preferred to produce a rigid polyurethane foam by a spray method. The rigid polyurethane foam may be used for thermally insulating materials in house, building, etc., for an insulated warehouse, for a bathtub, and for building interior/exterior material. PREFERRED EMBODIMENTS OF THE INVENTION

The following Examples further illustrate the present invention in detail.

Reference Example 1

Production of blowing agent: N-methylethanolamine (6.57 kg) and water (1.50 kg) were charged in a 10 L pressure reactor equipped with a rotating blade, followed by stirring. After a carbon dioxide cylinder equipped with a pressure reducing valve was connected to this reactor, carbon dioxide having a pressure reduced to 2 atm was fed to the liquid part with stirring. The temperature raised to about 90°C in about 3 hours and then slowly decreased. 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 9.8 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°C. Therefore, it could be stored as such in a 20 L tin-plated can. This reaction liquid was used as the blowing agent. Reference Example 2 Production of blowing agent: In the same manner as in Reference Example 1, N-methylethanolamine (3.90 kg) was charged, followed by stirring. After 1 hour from the beginning of the feed of carbon dioxide, the temperature raised to about 90°C and then slowly decreased. The reaction liquid was drawn from the reactor after 4 hours from the beginning of the feed of carbon dioxide, and then the amount was measured. As a result, it was 4.8 kg. This reaction liquid maintained a liquid form at a normal temperature after drawing but it solidified with heat revolution after standing at a normal temperature. When the reaction liquid (100 g) and a polyether polyol (400 g) having a hydroxyl value of 500 mg KOH/g, which is produced by adding ethylene oxide to monoethylamine, were mixed with heating to 60°C, the solid was converted into a liquid. This liquid was used as the blowing agent . Reference Example 3 Production of blowing agent:

The reaction liquid (4.8 kg) obtained by operating in the same manner as in Reference Example 2 was mixed with previously warmed ethylene glycol (14.4 kg). The resulting mixed 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°C. Therefore, it could be stored as such in a 20 L tin-plated can. This mixed solution was used as the blowing agent .

Reference Example 4 Production of blowing agent:

In the same manner as in Reference Example 1, dimethylaminopropylamine (3.5 kg) and water (0.9 kg) were charged, followed by stirring. The liquid temperature raised to about 90°C in about 10 minutes and then slowly decreased. 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 4.9 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°C. Therefore, it could be stored as such in a 20 L tin-plated can. This mixed liquid was used as the blowing agent.

Examples 1 to 7 and Comparative Examples 1 to 3 A polyol, a catalyst, a flame retardant, a diluent and a surfactant, a blowing agent (those obtained in Reference Examples and fluorinated hydrocarbon) and, if necessary, water were mixed to obtain a polyol component. The polyol component and isocyanate were sprayed on a substrate by a spray foaming machine (PF-1600, manufactured by Higaki Machinery Co . ) equipped with a D gun manufactured by Gasmer Co. to form a rigid polyurethane foam. The ingredients of the sprayed composition are shown in Table 1.

The spray foaming conditions were as followings. Spray foaming conditions

Liquid temperature 45 °C

Air pressure 5 kg/cm²G

Ejection pressure 70 kg/cm G (initial setting)

The following evaluations were conducted. Cream time (initial activity) [Test A]

At the ambient temperature of room temperature (about 30°C), a spray liquid was instantaneously sprayed on an aluminum plate having the temperature controlled to 0°C, and then the time required for the spray liquid to turn white on the aluminum plate (cream time) was measured.

Spray pattern, froth-state, lateral elongation, core density and dimensional stability [Test B]

A releasing agent was applied and dried on a veneer plywood of 90 cm x 90 cm x 12 mm, and then a spray liquid was sprayed on the veneer plywood in the atmosphere at 0°C so that the thickness of the primary spray layer was about 2 mm. After 30 seconds, the spraying was conducted so that the final thickness of a sprayed foam layer was about 30 mm to form a sample. At that time, the situation of spraying from the gun to the veneer plywood was observed. Then, it was visually evaluated whether the spray pattern extends in a round shape (good), or does not extend or is divided into two parts (poor). Furthermore, it was visually evaluated whether the spray pattern becomes a frothy (good) or not (poor). Furthermore, it was observed whether the foam overflows the veneer plywood or not, and then the presence or absence of the lateral elongation of the foam was evaluated.

The upper and lower skins were removed from the resulting sample and the core density was measured. In order to compare the dimensional stability of the foam, the core density was measured and the sample was allowed to stand for 24 hours under the conditions of -30°C, 100°C and 70°C x 95% R.H. and the amount of deformation ( (V_x - ^vo)/^vo ^x 100) (wherein V₀ represents a volume before exposing to each condition and V_x represents a volume after exposing to each condition) was determined. Amount of used raw materials [Test C]

In the atmosphere at 0°C, a primary spraying was conducted on a slate plate of 50 cm x 50 cm x 6 mm in a thickness of about 2 mm, followed by spraying so that the total thickness of the foam was 10 mm. Then, the thickness of the resulting foam was measured (average value (n = 10) was determined) and the amount of raw materials used per 1 m was determined. Table 1

Table 2

Isocyanate: Sumidur 44V10 (manufactured by Sumitomo Bayer Urethane Co . , Ltd . ) NCO content: 31.6%, viscosity: 110 mPa»s/25°C Polyol A: polyol having a hydroxyl value of 760 mg KOH/g and a viscosity of 50000 mPa»s/25°C, which is produced by adding propylene oxide to ethylene diamine

Polyol B: polyol having a hydroxyl value of 470 mg KOH/g and a viscosity of 1200 mPa»s/25°C, which is produced by adding ethylene oxide and propylene oxide to ethylenediamine

Polyol C: polyol having a hydroxyl value of 320 mg KOH/g and a viscosity of 2100 mPa«s/25°C, which is produced by adding ethylene oxide and propylene oxide to tolylenediamine

Polyol D: DK polyol 3773 (manufactured by Dai-Ichi Kogyo Seiyaku Co . , Ltd . ) polyether polyol having a hydroxyl value of 470 mg KOH/g and a viscosity of 11000 mPa«s/25°C, which is produced by adding an alkylene oxide to a Mannich reaction product having an aromatic ring

Polyol E: polyether polyol having a hydroxyl value of 280 mg KOH/g and a viscosity of 12000 mPa«s/25°C, which is produced by adding ethylene oxide to bisphenol A

Polyol F: polyether polyol having a hydroxyl value of 250 mg KOH/g and a viscosity of 250 mPa»s/25°C, which is produced by adding propylene oxide to glycerine

Polyol G: Phantol PL-305 (manufactured by Toho Rika Kogyo Co . , Ltd . ) polyester polyol having a hydroxyl value of 315 mg KOH/g and a viscosity of 2600 mPa»s/25°C, which is a product of the reaction between a polyhydric alcohol and a polybasic polycarboxylic acid having an aromatic ring

Catalyst A: mineral spirits solution of lead octanoate (lead content: 20% by weight)

Catalyst B: dipropylene glycol solution of triethylenediamine (TEDA) (TEDA content: 33% by weight)

Catalyst C: UL-28 (manufactured by Witco Co. ) Catalyst D: bis ( 2-dimethylaminoethyl )ether Flame retardant: tris ( β-chloropropyl )phosphate Diluent: dibutyl phthalate Surfactant: F348 manufactured by Shinetsu Kagaku

Kogyo Co . , Ltd .

R-141b: dichlorofluoroethane

Table 3

Table 4

EFFECT OF THE INVENTION According to the method of the present invention, there can be produced a rigid polyurethane foam in a state of high initial activity without causing a lateral elongation of the foam, in good workability and a small amount of raw materials, even if the temperature of a substrate is low such as 0°C in the atmosphere at 10°C or less .

Claims

1. A method for producing a rigid polyurethane foam, which comprises mixing (a) a polyisocyanate component with a polyol component comprising (b) a polyol mixture, (b) a catalyst, (d) a blowing agent and, if necessary, a flame retardant, a diluent and a surfactant, then foaming the mixture; wherein the polyisocyanate component (a) is polymethylenepolyphenyl polyisocyanate or a modified material thereof; the polyol mixture (b) comprises:

(b-1) 20 to 80 parts by weight of a polyol having a hydroxyl value of 300 to 800 mg KOH/g, which is produced by adding an alkylene oxide to an aliphatic amine; (t>-2) 20 to 80 parts by weight of at least one aromatic polyether polyol having a hydroxyl value of 170 to 600 mg KOH/g, which is produced by using an aromatic amine, a Mannich base having an aromatic ring or a polyfunctional phenol as a starting material; and (b-3) less than 40 parts by weight of a polyol which is produced by using a compound having no aliphatic amine as a starting material, or a polyether polyol having no aromatic ring and/or an aromatic polyester polyol, and a hydroxyl value of the polyol mixture (b) is from 300 to 800 mg KOH/g; the catalyst (c) is at least one metallic catalyst, which is optionally used in combination with a tertiary amine compound; and the blowing agent (d) is an adduct of a primary or secondary amine compound with carbon dioxide, which is optionally used in combination with a low-boiling point compound and/or water.

2. A polyol composition comprising (b) a polyol mixture, (c) a catalyst, (d) a blowing agent and, if necessary, a flame retardant, a diluent and a surfactant; the polyol mixture (b) comprises:

(b-1) 20 to 80 parts by weight of a polyol having a hydroxyl value of 300 to 800 mg KOH/g, which is produced by adding an alkylene oxide to an aliphatic amine;