JP2009114288A - Polyol composition for spray-foamed rigid polyurethane foam and process for manufacturing spray-foamed rigid polyurethane foam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyol composition which uses an HFC compound and water as foaming agents, forms a low-density rigid polyurethane foam having excellent heat-insulating properties, and has good storage stability and to provide a process for manufacturing the rigid polyurethane foam using the polyol composition. <P>SOLUTION: The polyol composition is provided in which 100 pts.wt. of a polyol compound contains 35-70 pts.wt. of an aromatic ester polyol with a hydroxyl value of 100-450 mgKOH/g and 20-50 pts.wt. of a polyether polyol with a hydroxyl value of 250-900 mgKOH/g and in which a low-molecular-weight glycol contains an ethylene glycol and a glycol containing a tertiary amino group. The content of the ethylene glycol in the low-molecular-weight glycol is 10-50 mol%. The low-molecular-weight glycol is formulated at a ratio (weight ratio) of polyol compound/low-molecular-weight glycol=98/2 to 92/8. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a spray-foamed polyol composition for rigid polyurethane foam which forms a highly heat-insulating and flame-retardant rigid polyurethane foam, and a method for producing a rigid polyurethane foam using the polyol composition.

  Rigid polyurethane foam is a well-known material as a heat insulating material, a lightweight structural material, and the like. Such a rigid polyurethane foam is formed by mixing a polyol composition containing a polyol compound and a foaming agent as essential components and a polyisocyanate component, and foaming and curing. One method for producing rigid polyurethane foam is a spray foaming method. In the spray foaming method, HCFC-141b is used in place of the CFC compound in applications that require high heat insulation (Patent Document 1).

  Although used in Patent Document 1, a spray-foamed rigid polyurethane foam using water as a foaming agent instead of HCFC-141b having an ozone layer depletion coefficient is also known (Patent Document 2).

  The rigid polyurethane foam disclosed in Patent Document 1 uses an aromatic ester polyol and a polyether polyol in combination as a polyol compound.

  The rigid polyurethane foam disclosed in Patent Document 2 aims to eliminate the side slip phenomenon that occurs when the above HCFC-141b is used as a foaming agent, and a polyol compound using ethylenediamine as an initiator is one of the polyol compounds. It is used as a component.

JP-A-8-53565 JP-A-10-87774

  However, since the rigid polyurethane foam disclosed in Patent Document 2 uses water as a foaming agent, and the polyol compound used together with the polyol compound using ethylenediamine as an initiator as the polyol compound is a polyether polyol compound, it is difficult. It is not flammable and does not clear the flame retardant grade 3 required for buildings. In addition, since water is used as a foaming agent, there are problems such as foam shrinkage and dimensional change due to aging, insufficient heat insulation performance, and insufficient adhesion to a substrate.

  On the other hand, the rigid polyurethane foam disclosed in Patent Document 1 is excellent in flame retardancy because an aromatic ester polyol is used as the main component of the polyol compound. However, when an HFC compound having a small ozone depletion coefficient is used in place of the blowing agent HCFC-141b used in Patent Document 1, the solubility of the HFC compound in polyol is inferior, and HFC-245fa has a low boiling point. In the foam formation by spray foaming, the HFC compound volatilizes in the initial stage of the reaction, and it is difficult to form a low density foam. Increasing the amount of the HFC compound as a blowing agent to reduce the density increases the cost and the vapor pressure of the polyol composition increases. Have a problem.

  The present invention uses an HFC compound such as HFC-245fa and HFC-365mfa and water as a foaming agent, can form a rigid polyurethane foam having a low density and excellent heat insulation, and has good storage stability. It is an object of the present invention to provide a simple polyol composition and a method for producing a rigid polyurethane foam using the polyol composition.

The polyol composition of the present invention is a polyol composition containing a polyol compound, a foaming agent, a foam stabilizer, a low molecular weight glycol and a catalyst, mixed with a polyisocyanate component by a spray device, and reacted to form a rigid polyurethane foam. And
The foaming agent comprises an HFC compound and water,
The catalyst contains an isocyanurate group-forming catalyst,
100 parts by weight of the polyol compound includes 35 to 70 parts by weight of an aromatic ester polyol having a hydroxyl value of 100 to 450 mgKOH / g and 20 to 50 parts by weight of a polyether polyol having a hydroxyl value of 250 to 900 mgKOH / g.
The low molecular weight glycol contains an alkylene glycol and a tertiary amino group-containing glycol, the alkylene glycol in the low molecular weight glycol is 10 to 50 mol%, and the blending amount of the low molecular weight glycol is polyol compound / low. Molecular weight glycol = 98/2 to 92/8 (weight ratio).

The polyol composition having such a structure uses an HFC compound and water as a foaming agent, can form a rigid polyurethane foam having low density, excellent heat insulation and dimensional stability, and good storage stability. It is a composition. When the polyol composition of the present invention is used, a rigid polyurethane foam having a density of 26 kg / m ³ or less can be formed.

  When the blending ratio of polyol compound / low molecular weight glycol is larger than 98/2 and the blending ratio of low molecular weight glycol is small, it is difficult to form a low density foam, and the blending amount exceeds 92/8 and the low molecular weight glycol If the blending ratio is too large, the adhesiveness between the foam and the substrate is lowered. From the viewpoint of flame retardancy, the blending amount of the aromatic ester polyol is more preferably 40 parts by weight or more, and further preferably 45 parts by weight or more.

  In the polyol composition for spray foamed rigid polyurethane foam, the polyether polyol is a Mannich polyol having a hydroxyl value of 250 to 550 mgKOH / g, a functional group number of 2 to 4, and an aliphatic amine polyol having a hydroxyl value of 600 to 900 mgKOH / g. Yes, the Mannich polyol / aliphatic amine polyol (weight ratio) is preferably 5/1 to 2/1.

  A rigid polyurethane foam formed by spray foaming using a polyol composition having such a structure is low in density and conforms to flame retardant grade 3 and has excellent adhesion to a substrate.

In another aspect of the present invention, a polyol composition containing a polyol compound, a foaming agent, a foam stabilizer, a low molecular weight glycol and a catalyst and a polyisocyanate component are mixed by a spray device to form a reactive composition, and the reactive composition is foamed. , A method for producing a rigid polyurethane foam that is cured to form a rigid polyurethane foam,
The foaming agent comprises an HFC compound and water,
The catalyst contains an isocyanurate group-forming catalyst,
100 parts by weight of the polyol compound includes 35 to 70 parts by weight of an aromatic ester polyol having a hydroxyl value of 100 to 450 mgKOH / g and 20 to 50 parts by weight of a polyether polyol having a hydroxyl value of 250 to 900 mgKOH / g.
The low molecular weight glycol contains an alkylene glycol and a tertiary amino group-containing glycol, the alkylene glycol in the low molecular weight glycol is 10 to 50 mol%, and the blending amount of the low molecular weight glycol is polyol compound / low. Molecular weight glycol = 98/2 to 92/8 (weight ratio).

According to the manufacturing method having such a configuration, it is possible to form a rigid polyurethane foam having a low density and excellent heat insulation and dimensional stability by using an HFC compound and water as a foaming agent. According to the production method of the present invention, a rigid polyurethane foam having a density of 26 kg / m ³ or less can be produced.

  In the method for producing a spray foamed rigid polyurethane foam, the polyether polyol constituting the polyol composition is composed of a Mannich polyol having a hydroxyl value of 250 to 550 mgKOH / g, a functional group number of 2 to 4, and a hydroxyl value of 600 to 900 mgKOH / g. g aliphatic amine polyol, and the Mannich polyol / aliphatic amine polyol (weight ratio) is preferably 5/1 to 2/1.

  According to the method for producing a rigid polyurethane foam having such a configuration, it is possible to produce a rigid polyurethane foam that is low in density and conforms to flame retardant grade 3 and has excellent adhesion to a substrate.

  In the manufacturing method of the above-mentioned spray foaming rigid polyurethane foam, it is preferable that the equivalent ratio of NCO group / OH group in mixing of the said polyol composition and a polyisocyanate component is 1.5-2.5.

  According to the manufacturing method having such a configuration, an isocyanurate bond is formed in the molecule of the hard polyurethane to be formed, the flame retardancy of the foam is improved, and a rigid polyurethane foam that more reliably meets the flame retardancy class 3 is manufactured. be able to.

  In the polyol composition for rigid polyurethane foam and the method for producing the rigid polyurethane foam of the present invention, 100 parts by weight of the polyol compound constituting the polyol composition is 35 to 70% by weight of an aromatic ester polyol having a hydroxyl value of 100 to 450 mgKOH / g. Part and 20 to 50 parts by weight of a polyether polyol having a hydroxyl value of 250 to 900 mgKOH / g.

  The aromatic ester polyol is an aromatic dicarboxylic acid glycol ester, and at least one selected from terephthalic acid, phthalic acid, and isophthalic acid, and ethylene glycol, diethylene glycol, 1,4-butanediol, 1,6-hexanediol, Examples include ester polyols having a hydroxyl group terminal based on glycol with glycol such as polyoxyethylene glycol having an average molecular weight of 150 to 500.

  When the hydroxyl value of the aromatic ester polyol is less than 100, the brittleness of the resulting rigid polyurethane foam increases, and when it exceeds 450, the flame retardancy is increased even if the blending amount in the polyol composition is 70 parts by weight or more. May not be enough. The hydroxyl value of the aromatic ester polyol is more preferably from 100 mgKOH / g to 400 mgKOH / g.

  As the polyether polyol, a polyether polyol known in the field of rigid polyurethane foam can be used. Among these known polyether polyols, it is preferable to use a Mannich polyol having a hydroxyl value of 250 to 550 mgKOH / g and a functional group number of 2 to 4 and an aliphatic amine polyol having a hydroxyl value of 600 to 900 mgKOH / g. The aliphatic amine polyol (weight ratio) is preferably in the range of 5/1 to 2/1.

  If the blending ratio of Mannich polyol is too large, the blending ratio of aliphatic amine polyol may be too small and the adhesion between the foam and the substrate may decrease, and if the blending ratio of aliphatic amine polyol is too large, flame retardancy will occur. May decrease.

  Mannich polyol is obtained by subjecting an active hydrogen compound obtained by the Mannich reaction of phenol and / or its alkyl-substituted derivative, formaldehyde and alkanolamine, or ring-opening addition polymerization of at least one of ethylene oxide and propylene oxide to this compound. It is a polyol compound having a hydroxyl value of 250 to 550 mgKOH / g and having 2 to 4 functional groups. As a commercial item of such a polyol compound, for example, there is DK-3810 (Daiichi Kogyo Seiyaku) and can be used. The hydroxyl value of Mannich polyol is more preferably 250 to 450 mgKOH / g.

  Examples of the aliphatic amine polyol include alkylene diamine polyols and alkanol amine polyols. These polyol compounds are polyfunctional polyol compounds having a terminal hydroxyl group obtained by ring-opening addition of at least one of ethylene oxide and propylene oxide using alkylene diamine or alkanol amine as an initiator. As the alkylene diamine, known compounds can be used without limitation. Specifically, use of alkylene diamine having 2 to 8 carbon atoms such as ethylene diamine, propylene diamine, butylene diamine, hexamethylene diamine, and neopentyl diamine is preferable. In the alkylene diamine-based polyol, the alkylene diamine as the initiator may be used alone or in combination of two or more. Examples of the alkanolamine include monoethanolamine, diethanolamine, and triethanolamine. The number of functional groups of the polyol compound using alkylene diamine as the initiator is 4, and the number of functional groups of the polyol compound using alkanolamine as the initiator is 3. Among these, use of a polyether polyol (EDA polyol) having ethylenediamine as an initiator is preferable because the adhesiveness between the base and the foam to be formed is good.

  The low molecular weight glycol constituting the polyol composition for rigid polyurethane foam of the present invention contains alkylene glycol and tertiary amino group-containing glycol. The alkylene glycol has a molecular weight of 120 or less and may have a side chain, and specific examples thereof include ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, and hexanediol. Among these, the use of ethylene glycol is most preferable. As the tertiary amino group-containing glycol, N-alkyl dialkanolamine having a molecular weight of 170 or less is used. As the N-alkyl dialkanolamine, it is preferable to use at least one of N-methyldiethanolamine and N-ethyldiethanolamine.

  You may mix | blend a crosslinking agent with the polyol composition for rigid polyurethane foams of this invention as needed. Such cross-linking agents include non-aromatic polyhydric alcohols such as triethanolamine, glycerin, and trimethylolpropane, bishydroxyethoxybenzene, bishydroxyethyl terephthalate (BHET), and bisphenol A with 2 to 6 moles of ethylene oxide or propylene oxide. And aromatic polyhydric alcohols such as xylylene glycol. Among these, the use of aromatic polyhydric alcohol is preferable.

  The blowing agent used in the method for producing the polyol composition and the rigid polyurethane foam of the present invention is an HFC compound. As the HFC compound, at least one of HFC-245fa and HFC-365mfc can be used. By using such a foaming agent, a rigid polyurethane foam having excellent heat insulation can be obtained. It is also preferable to use HFC-245fa and HFC-365mfc in combination. In the case of using HFC-245fa and HFC-365mfc together, the ratio of HFC-245fa / HFC-365mfc is preferably 95/5 to 60/40. The amount of HFC compound added is preferably 20 to 50 parts by weight and more preferably 20 to 45 parts by weight with respect to 100 parts by weight of the total polyol compounds.

  Further, it is preferable to add water as a foaming agent. By adding water, the vapor pressure of the blowing agent of the polyol composition can be reduced. The amount of water added is preferably 0.5 to 5 parts by weight, more preferably 0.5 to 3 parts by weight, based on 100 parts by weight of the polyol compound.

  In the present invention, the vapor pressure lowering agent of HFC-245fa, which is a low-boiling foaming agent, has a boiling point of 100 ° C. or higher, more preferably 120 ° C. or higher, no active hydrogen groups, and 100 parts by weight of water. It is preferable to add to the polyol composition a hydrophilic organic solvent that dissolves at 40 parts by weight or more, more preferably 50 parts by weight or more, and even more preferably a free ratio. According to such a configuration, it is possible to form a rigid polyurethane foam having a stable density even in the construction in summer. Examples of the hydrophilic organic solvent include polyethylene glycol (average molecular weight 150 to 800) dimethyl ether, ε-caprolactone, diethylene glycol monoethyl ether acetate, N-methylpyrrolidone and the like which are liquid at normal temperature. The addition amount of the hydrophilic organic solvent is preferably 5 to 40 parts by weight with respect to 100 parts by weight of HFC-245fa.

  As the catalyst, at least an isocyanurate group forming catalyst is used. Examples of the isocyanurate group-forming catalyst (trimerization catalyst) include alkali metal salts of organic carboxylic acids having 1 to 20 carbon atoms such as potassium acetate, potassium propionate, potassium 2-ethylhexanoate (potassium octylate), and N- (2-hydroxypropyl) -N- (2-hydroxyethyl) -N, N-dimethylammonium octylate, tetraalkylammonium monocarboxylate, N-hydroxyalkyl-N, N, N-trialkylammonium salt Etc., at least one compound selected from compounds disclosed in JP-A-9-104734 and quaternary ammonium salt catalysts such as Dabco TMR, Dabco TMR-2 (Air Products) is used.

  In the polyol composition for rigid polyurethane foam and the method for producing the rigid polyurethane foam of the present invention, a tertiary amine catalyst is used in addition to the isocyanurate bond-forming catalyst. The tertiary amine catalyst is a urethane bond forming catalyst or a foaming catalyst. Specifically, N, N, N ′, N′-tetramethylethylenediamine or N, N, N ′, N′-tetramethylhexamethylene is used. N-alkyl polyalkylene polyamines such as diamine (kaolyzer No. 1), N, N, N ′, N ′, N ″ -pentamethyldiethylenetriamine (kaolyzer No. 3), diazabicycloundecene (DBU), N , N-dimethylcyclohexylamine (Polycat-8), triethylenediamine, N-methylmorpholine, and the like can be used.

  In the production of the rigid polyurethane foam of the present invention, in addition to the above components, foam stabilizers, flame retardants, colorants, antioxidants and the like well known to those skilled in the art can be used.

  As the foam stabilizer, known foam stabilizers used in the technical field of rigid polyurethane foam can be used without limitation. Specifically, foam stabilizers such as B-8465 (Gold Schmidt), SH-192, SH-193, S-824-02, SZ-1704 (Toray Dow Corning Silicon) can be used. Two or more foam stabilizers may be used.

  In the present invention, addition of a flame retardant is also a preferred embodiment, and examples of suitable flame retardants include metal compounds such as halogen-containing compounds, organophosphates, antimony trioxide, and aluminum hydroxide. .

  Organophosphates are suitable additives because they also have an action as a plasticizer and thus have an effect of improving the brittleness of rigid polyurethane foam. It also has the effect of reducing the viscosity of the polyol composition. Examples of the organic phosphate esters include halogenated alkyl esters of phosphoric acid, alkyl phosphate esters, aryl phosphate esters, phosphonate esters, and the like. Specifically, tris (β-chloroethyl) phosphate (CLP, Daihachi Chemical), Tris (β-chloropropyl) phosphate (TMCPP, Daihachi Chemical), Tributoxyethyl phosphate (TBXP, Daihachi Chemical), Tributyl phosphate, Triethyl phosphate, Cresyl phenyl phosphate, Dimethyl methylphosphonate Etc., and one or more of these can be used. The addition amount of the organic phosphates is 40 parts by weight or less, preferably 5 to 40 parts by weight, based on 100 parts by weight of the total polyol compound.

  The polyisocyanate compound that forms a rigid polyurethane foam by mixing and reacting with the polyol composition is easy to handle, fast in reaction, excellent in the physical properties of the resulting rigid polyurethane foam, and low in cost. For this reason, liquid MDI is used. As liquid MDI, Crude MDI (c-MDI) (Sumijoule 44V-10, Sumijoule 44V-20, Sumijoule H-420, etc. (manufactured by Sumika Bayer Urethane Co., Ltd.), Millionate MR-200 (Nippon Polyurethane Industry)) Uretonimine-containing MDI (Millionate MTL; manufactured by Nippon Polyurethane Industry Co., Ltd.), prepolymer-modified polyisocyanate compounds obtained by adding polyol compounds to these polyisocyanate compounds and reacting them or adding separately prepared prepolymers, etc. Select used. In addition to liquid MDI, other polyisocyanate compounds may be used in combination. As the polyisocyanate compound used in combination, a polyisocyanate compound known in the technical field of polyurethane can be used without limitation.

  In the method for producing the rigid polyurethane foam, the isocyanate group / active hydrogen group equivalent ratio (NCO index) in the mixing of the polyol composition and the polyisocyanate component is 1.0 to 4.0, more preferably 1.5. It is -3.5, More preferably, it is 1.5-2.5. More preferably, the NCO index is 1.5 or more, and the catalyst contains a trimerization catalyst.

(Polyol composition)
A polyol composition was prepared with the composition described in the upper part of Table 1. The contents and characteristics of the raw materials used are as follows.
a) Polyol A
Ester polyol produced by a known method using terephthalic acid as the acid component and diethylene glycol as the glycol component (Toho Rika);
Hydroxyl value = 250 mgKOH / g
b) Polyol B
DK-3810 (Daiichi Kogyo Seiyaku); hydroxyl value = 315 mgKOH / g
c) Polyol C
Polyether polyol compound (made by Asahi Glass Urethane) using ethylenediamine as an initiator;
Hydroxyl value = 600 mgKOH / g
d) Low molecular weight glycol ethylene glycol (EG)
N-methyldiethanolamine (MDA)
e) TMCPP: Phosphorus flame retardant (plasticizer) (Daihachi Chemical Industry)
f) Foam stabilizer SZ-1704 (Toray Dow Corning Silicon)
g) Polyisocyanate component: Sumidur 44V-20 (Sumika Bayer Urethane).

(Examples and comparative examples)
In Examples and Comparative Examples, a polyol composition was prepared by blending a polyol compound described in the upper part of Table 1. The compound other than the polyol compound and the catalyst is 20 parts by weight of the flame retardant TMCPP (Daihachi Chemical Industry) with 100 parts by weight of the total amount of the polyol compound, and the HFC compound of the blowing agent is HFC-245fa / HFC-365mfc = 80. / 20 (weight ratio). The rigid polyurethane foam is prepared by mixing a polyol composition and a polyisocyanate component at a volume ratio shown in Table 1 with a laboratory stirrer and pouring it into a 200 mm × 200 mm × 200 mm mold laid with kraft paper as a face material. Molded to produce a foam. The evaluation described below was performed, and the results are shown in the lower part of Table 1.

(Evaluation)
1) Foam density (kg / m ³ )
A foam sample of 100 mm × 100 mm and thickness 100 mm was cut out from the core layer excluding the skin layer from the rigid polyurethane foam obtained by free foaming using a mold of 200 mm × 200 mm, depth 200 mm, and weighed. The density (kg / m ³ ) was calculated.

2) Flammability (flame retardant evaluation)
Flame retardant evaluation was performed in accordance with JIS A 1321. The evaluation results are indicated as “◯” when the classification is flame retardant class 3 and conforming to the determination of the surface test, and “X” is not conforming.

3) Adhesiveness to the face material As shown in FIG. 1, a notch with a width of 5 cm is formed in the face material, and the face material from which the end has been peeled is pulled in the direction of the arrow (W) with a spring balance to increase the peel strength. It was measured.

From the results shown in Table 1, the spray foamed rigid polyurethane foam using the polyol composition of the present invention has a low density of 26 kg / m ³ or less and satisfies the flame retardant grade 3 standard according to the evaluation of JIS A 1321. Met. Moreover, it was excellent also in adhesiveness with a base material. On the other hand, although the foam of the comparative example had a low density, it did not clear the flame retardant grade 3, and the adhesion to the face material was not sufficient.

Claims (5)

A polyol composition comprising a polyol compound, a foaming agent, a foam stabilizer, a low molecular weight glycol and a catalyst, mixed with a polyisocyanate component by a spray device and reacted to form a rigid polyurethane foam,
The foaming agent comprises an HFC compound and water,
The catalyst contains an isocyanurate group-forming catalyst,
100 parts by weight of the polyol compound includes 35 to 70 parts by weight of an aromatic ester polyol having a hydroxyl value of 100 to 450 mgKOH / g and 20 to 50 parts by weight of a polyether polyol having a hydroxyl value of 250 to 900 mgKOH / g.
The low molecular weight glycol contains an alkylene glycol and a tertiary amino group-containing glycol, the alkylene glycol in the low molecular weight glycol is 10 to 50 mol%, and the blending amount of the low molecular weight glycol is polyol compound / low. Molecular weight glycol = 98/2 to 92/8 (weight ratio), A polyol composition for spray foamed rigid polyurethane foam.   The polyether polyol is a Mannich polyol having a hydroxyl value of 250 to 550 mgKOH / g and a functional group number of 2 to 4 and an aliphatic amine polyol having a hydroxyl value of 600 to 900 mgKOH / g, and the Mannich polyol / aliphatic amine polyol (weight ratio). The polyol composition for spray-foamed rigid polyurethane foam according to claim 1, wherein the ratio is 5/1 to 2/1. A polyol composition containing a polyol compound, a foaming agent, a foam stabilizer, a low molecular weight glycol and a catalyst and a polyisocyanate component are mixed by a spray device to form a reactive composition, and the reactive composition is foamed and cured to be hard. A method for producing a rigid polyurethane foam as a polyurethane foam,
The foaming agent comprises an HFC compound and water,
The catalyst contains an isocyanurate group-forming catalyst,
100 parts by weight of the polyol compound includes 35 to 70 parts by weight of an aromatic ester polyol having a hydroxyl value of 100 to 450 mgKOH / g and 20 to 50 parts by weight of a polyether polyol having a hydroxyl value of 250 to 900 mgKOH / g.
The low molecular weight glycol contains an alkylene glycol and a tertiary amino group-containing glycol, the alkylene glycol in the low molecular weight glycol is 10 to 50 mol%, and the blending amount of the low molecular weight glycol is polyol compound / low. Molecular weight glycol = 98 / 2-92 / 8 (weight ratio), The manufacturing method of the spray foaming rigid polyurethane foam characterized by the above-mentioned.   The polyether polyol constituting the polyol composition is a Mannich polyol having a hydroxyl value of 250 to 550 mgKOH / g, a functional group number of 2 to 4, and an aliphatic amine polyol having a hydroxyl value of 600 to 900 mgKOH / g, and the Mannich polyol / The method for producing a spray-foamed rigid polyurethane foam according to claim 3, wherein the aliphatic amine polyol (weight ratio) is 5/1 to 2/1.   The spray foamed rigid polyurethane foam according to claim 3 or 4, wherein an equivalent ratio of NCO group / OH group in mixing of the polyol composition and the polyisocyanate component is 1.5 to 3.0. Method.