JP2000290343A - Stock solution for hard polyurethane foam and rigid polyurethane foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide stock solution for a rigid polyurethane foam which foams using water as a major foaming agent to give a rigid polyurethane foam having a uniform cell structure and excellent heat insulation and good dimensional stability at high temperatures and under high humidity and moreover capable of being manufactured by use of a conventional foaming machine and to provide a rigid polyurethane foam using the stock solution. SOLUTION: Stock solution for a rigid polyurethane foam containing a polyol component to be reacted with an isocyante component to form a rigid polyurethane foam comprises at least a polyol component, a foaming agent containing water and a catalyst, the polyol component being a styrene oxide-containing block-copolymerized polyol having a hydroxyl value of 250 to 550 (mgKOH/g) and having a content of styrene oxide in a polyalkylene oxide of 10 to 30 mol% obtained by adding an alkylene oxide including styrene oxide to an active hydrogen-containing polyfunctional compound having an average functionality of 2 to 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rigid polyurethane foam stock solution used for producing a rigid polyurethane foam suitable as a heat insulating material and a rigid polyurethane foam produced using the same. The rigid polyurethane foam of the present invention can be used as a heat insulator for electric refrigerators, refrigerated / frozen warehouses, houses, and the like.

[0002]

2. Description of the Related Art A rigid polyurethane foam is produced by mixing and reacting a polyol component containing a polyol as a main component and a polyol component containing a catalyst, a foam stabilizer and a foaming agent with an isocyanate component containing a polyisocyanate compound as a main component using a foaming machine. Is done.

Conventionally, trichlorofluoromethane (CFC) has mainly been used as a foaming agent for rigid polyurethane foams.
-11) represented by chlorofluorocarbon (CF
The C) compounds have been used, but have been found to cause a serious environmental problem of depletion of the ozone layer, and the production and use of CFC compounds are currently prohibited.

[0004] Hydrochlorofluorocarbons (HCFCs) have been put into practical use as alternative foaming agents for CFC compounds, and HCFCs also have an ozone depletion potential (ODP).
Is not zero and its use will be regulated in the near future. Furthermore, hydrofluorocarbons (HFCs), which are considered as one of the next generation foaming agents,
Although ODP is zero, problems such as a relatively high global warming potential (GWP), many having low boiling points for use as blowing agents, and the toxicity of many of them are not yet clear. Having.

A technique has been proposed in which a hydrocarbon compound such as cyclopentane or n-pentane is used as a foaming agent instead of the above-mentioned halogenated hydrocarbon compound. However, these foaming agents are flammable and hard. There is a problem that strict explosion-proof measures are required during the production of polyurethane foam, and the equipment cost is extremely high.

On the other hand, as a foaming agent for a rigid polyurethane foam, water has been known and used in some cases. However, when an ether polyol compound obtained by ring-opening addition of propylene oxide and ethylene oxide which has been conventionally used in a system using a fluorocarbon compound as a blowing agent is used, when water is used as a main blowing agent, it becomes hard. There is a problem that the dimensional stability of the polyurethane foam, particularly the dimensional stability at high temperature and high humidity, is deteriorated.

For rigid polyurethane foams using water as the main blowing agent for the rigid polyurethane foam,
In order to improve the dimensional stability at high temperature and high humidity, problems such as a decrease in the closed cell rate and a decrease in the storage stability of the stock solution have been pointed out. As a technique for improving this, Japanese Patent Laid-Open No. 8-193117 has been proposed. It has been known.

[0008]

The problem to be solved by the present invention is disclosed in Japanese Patent Application Laid-Open No. 8-193.
No. 117 discloses that a random copolymerized polyol compound of 25 to 100 mol% of styrene oxide and another alkylene oxide is added to an added alkylene oxide in an amount of 10 to 90% of the total polyol.
Used.

However, in a polyol compound obtained by random copolymerization of styrene oxide and an addition alkylene oxide, a polyol compound containing 25 mol% or more of styrene oxide has a high viscosity of a liquid. The viscosity of the ingredient-containing stock solution increases, and when a conventional foaming machine is used, poor stirring is likely to occur, and the bubble structure is disturbed due to non-uniform reaction, and the heat insulation performance is reduced.

[0010] The present invention is a stock solution for forming a rigid polyurethane foam which uses water as a main component as a foaming agent, has a uniform cell structure, is excellent in heat insulation, and has good dimensional stability at high temperature and high humidity. It is an object of the present invention to provide a stock solution for a rigid polyurethane foam which can be produced with the use of a foaming machine that has been used, and a hard polyurethane foam using the stock solution.

[0011]

SUMMARY OF THE INVENTION The present invention relates to a raw rigid polyurethane foam solution containing a polyol component, a blowing agent containing water, and a catalyst, which reacts with a polyisocyanate component to form a rigid polyurethane foam. The component is a polyfunctional active hydrogen compound having an average number of functional groups of 2 to 4, that is, a hydroxyl value obtained by adding an alkylene oxide containing styrene oxide to a polyol initiator is 250.
550 (mg KOH / g), wherein the styrene oxide in the alkylene oxide is 10 to 30 mol%, and the styrene oxide and the other alkylene oxide contain a styrene oxide-containing polyol obtained by block copolymerization. It is.

In the rigid polyurethane foam stock solution of the present invention, the styrene oxide-containing polyol is
By being a block copolymer having a polymer block of the styrene oxide and a polymer block of another alkylene oxide, when the same alkylene oxide composition and the same number of functional groups and the same molecular weight, a polyol is more preferable than a random copolymer. And the viscosity of the undiluted solution using the same is suppressed to a low level, and sufficient stirring can be performed even with a conventional foaming machine (a stirrer for line production), and the generation of air bubbles can be reduced. A polyurethane foam having a uniform diameter, excellent heat insulating properties, and excellent dimensional stability at high temperature and high humidity can be obtained.

Further, if a predetermined styrene oxide-containing polyol is used, it is possible to obtain a rigid polyurethane foam having a relatively simple compounding and good appearance without blending various polyol components and adjusting the performance. Can be.

If the amount of styrene oxide in the styrene oxide-containing polyol exceeds 30 mol%, the viscosity of the polyol component becomes high, and the cell structure tends to be disordered. If it is less than 10 mol%, the dimensional stability at high temperature and high humidity decreases. A more preferable range is from 10 mol% to less than 25 mol% in that the cell structure is stable and uniform and good dimensional stability at high temperature and high humidity can be achieved.

When the average number of functional groups of the polyfunctional active hydrogen compound to which styrene oxide is added is less than 2, the physical properties of the obtained foam are deteriorated. When it exceeds 4, the viscosity of the styrene oxide-containing polyol becomes extremely high, and A problem arises in that it cannot be used for

If the hydroxyl value of the styrene oxide-containing polyol is less than 250, the physical properties of the foam also deteriorate, and if it exceeds 550, the brittleness increases, which is not preferable. The hydroxyl value of the styrene oxide-containing polyol is preferably from 300 to 500, since an excellent foam can be stably obtained.

The viscosity of the polyol is 1 at 25.degree.
The pressure is preferably 2000 mP · s or less, and if it is more than 2000 mP · s, stirring with the isocyanate compound may not be sufficiently performed depending on the capacity of the foaming machine.

Either the styrene oxide polymer block or the other alkylene oxide polymer block in the styrene oxide-containing polyol of the present invention may be on the initiator side, but other alkylene oxide polymers other than styrene oxide may be used. More preferably, the block is on the side closer to the initiator.

The above rigid polyurethane foam stock solution contains water as a main component as a foaming agent, and is used in combination with an aliphatic hydrocarbon-based foaming agent such as HCFCs, HFCs, and pentane which have little effect on other environments. Can be
The use of only water does not use a foaming agent such as HCFC or HFC, and therefore has no possibility of affecting the environment.

As is well known, water does not become a blowing agent by evaporating, but reacts with isocyanate groups to generate carbon dioxide gas, which forms bubbles.

In the rigid polyurethane foam stock solution of the present invention, the content of the styrene oxide-containing polyol in all the polyol compounds is preferably 20 to 100% by weight. If it is less than 20% by weight, the dimensional stability at high temperature and high humidity is undesirably reduced.

The present invention relates to a rigid polyurethane foam formed by reacting an isocyanate component with a stock solution of a rigid polyurethane foam containing a polyol component, wherein the stock solution of the rigid polyurethane foam comprises a foaming agent containing at least a polyol component, water, and A hydroxyl value containing a catalyst and a polyfunctional active hydrogen compound (initiator) having an average number of functional groups of 2 to 4 and an alkylene oxide containing styrene oxide added to the polyol component is 250 to 550 (m).
gKOH / g), wherein the styrene oxide in the alkylene oxide is 10 to 30 mol%, and the styrene oxide and the other alkylene oxide contain a styrene oxide-containing polyol obtained by block copolymerization.

The styrene oxide-containing polyol is obtained by polymerizing the polyfunctional active hydrogen compound (initiator) with another alkylene oxide, and then polymerizing the styrene oxide to form a styrene oxide and another alkylene oxide. It is particularly preferable that the polymer is a polymerized block copolymer because the viscosity of the undiluted solution is suppressed to a low level, resulting in a foam having a uniform cell diameter.

In the above rigid polyurethane foam, it is particularly preferable that only water is used as a foaming agent, as described above.

As the initiator of the above-mentioned rigid polyurethane foam and the styrene oxide-containing polyol in the stock solution thereof, it is particularly preferable to use at least one of trifunctional trimethylolpropane and monoethanolamine, all of which are trifunctional. When the used polyol compound is used as a stock solution component, an excellent rigid polyurethane foam is obtained, which is preferable. These polyol initiators may be used alone or in combination with other initiators.

[0026]

DETAILED DESCRIPTION OF THE INVENTION As the polyfunctional active hydrogen compound used as a raw material of the styrene oxide-containing polyol in the present invention, that is, as a polyol initiator, conventional propylene oxide (PO), ethylene oxide (E)
The compound used for producing the polyol compound by adding O) can be used without limitation. Examples of specific compounds include glycols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,3-butanediol, 1,6-hexanediol, neopentyl glycol, trimethylolpropane, glycerin and the like. Triols, tetrafunctional alcohols such as pentaerythritol, phenols such as hydroquinone and catechol, amines such as ethylenediamine and toluenediamine, alkanolamines such as monoethanolamine and diethanolamine, pentaerythritol, sorbitol, sucrose and the like. Examples include polyhydric alcohols. These may be used alone or in combination of two or more as long as the average number of functional groups is 2 to 4.

In the present invention, as the polyol compound that can be used together with the above-mentioned styrene oxide-containing polyol, any polyol compound known in the technical field of rigid polyurethane foam can be used without any particular limitation. In particular, it is preferable to use a polyether polyol having an average number of functional groups of 2 to 8 and a hydroxyl value of 200 to 500 (mgKOH / g). In addition to the above polyfunctional active hydrogen compounds, polyfunctional polyols such as sucrose, sorbitol, etc. It is preferable to use a polyether polyol obtained by subjecting at least one of ethylene oxide and propylene oxide to a polyhydric alcohol by ring-opening addition polymerization.

In producing the rigid polyurethane foam of the present invention, a catalyst, a flame retardant, a foaming agent, a coloring agent, an antioxidant and the like well known to those skilled in the art can be used.

As a catalyst, triethylenediamine, N
Tertiary amines such as -methylmorpholine, N, N, N ', N'-tetramethylethylenediamine, N, N, N', N'-tetramethylhexamethylenediamine, DBU, dibutyltin dilaurate, dibutyltindiamine Metal-based catalysts such as acetate and tin octylate are exemplified as urethanization reaction catalysts.

In particular, when water is used as one component of the foaming agent, the use of a tertiary amine catalyst is preferred since the organotin catalyst may be hydrolyzed and deteriorated.

It is also preferable to use a catalyst which forms an isocyanurate bond which contributes to the improvement of the flame retardancy in the structure of the polyurethane molecule, and examples thereof include potassium acetate and potassium octylate. Some of the above tertiary amine catalysts also promote the isocyanurate ring formation reaction. A catalyst that promotes isocyanurate bond formation and a catalyst that promotes urethane bond formation may be used in combination.

In the present invention, it is also a preferred embodiment to further add a flame retardant.
Examples thereof include metal compounds such as organic metal complexes, halogen-containing compounds, organic phosphates, antimony trioxide, and aluminum hydroxide.

Examples of the organometallic complex include metallocenes such as ferrocene and nickelocene, metal acetylacetonates such as iron acetylacetonate, 8-oxyquinoline metal complexes such as bis (8-oxyquinoline) copper, and bis (dimethylglycol). Examples of suitable compounds include dimethylglyoxime metal complexes such as oximo) copper and the like.
More than one species can be used in combination.

However, in these flame retardants, for example, when an organic phosphoric acid ester is excessively added, the physical properties of the obtained rigid polyurethane foam may be deteriorated, and a metal compound powder such as antimony trioxide is excessively added. This may cause problems such as affecting the foaming behavior of the foam, and the amount of addition is limited to a range that does not cause such problems.

The rigid polyurethane foam of the present invention includes:
It is preferable to use a plasticizer as needed. Such plasticizers also preferably contribute to flame retardancy, and halogenated alkyl esters of phosphoric acid, alkyl phosphates, aryl phosphates, phosphonates, and the like can be used. Specifically, tris ( β-chloroethyl) phosphate (TCEP, manufactured by Daihachi Chemical),
Tris (β-chloropropyl) phosphate (TMCP
P, manufactured by Daihachi Chemical Co., Ltd.), tributyl phosphate, triethyl phosphate, cresyl phenyl phosphate, dimethyl methyl phosphonate and the like, and one or more of these can be used. The added amount of the plasticizer is preferably 5 to 30 parts by weight based on 100 parts by weight of the polyol component. If the ratio exceeds this range, problems may occur such that a sufficient plasticizing effect cannot be obtained or physical properties of the foam deteriorate.

The rigid polyurethane foam of the present invention is molded into a shape suitable for the application by a generally known polyurethane foaming / molding apparatus. For example, in a manufacturing plant, a laminate is formed into a panel shape or other shape using a mixed foaming device such as a high-pressure foaming machine, and is foamed while supplying a slab foam manufacturing device using a low-pressure foaming machine or the like and various face materials. Board materials are manufactured by a board manufacturing apparatus, manufactured by a spray foaming apparatus at a construction site or the like, and rigid polyurethane foam as a heat insulating material of an electric refrigerator is manufactured by an injection molding machine or the like.

When the rigid polyurethane foam of the present invention is used as a heat insulating board, it is preferable to use a face material, and any known face material can be used without particular limitation. Specifically, paper, aluminum foil,
A steel plate is exemplified. In particular, since the paper surface material is soft, the adhesive strength is reduced if the foam flyability is high. Therefore, the use of the rigid polyurethane foam stock solution of the present invention is preferred.

[0038]

Embodiments of the present invention will be described below. (Polyol synthesis example) [Polyol A] Glycerin (GLY) 20 as an initiator in a 1-liter autoclave equipped with a stirrer
0 g and 2 g of the catalyst, and while the mixture was heated to 120 ° C. and stirred, 501 g of propylene oxide (PO) was added dropwise in a nitrogen stream to carry out ring-opening addition polymerization.
After completion of the dropwise addition of styrene, 334 g of styrene oxide (SO) is added dropwise to carry out ring-opening addition polymerization, and the ring-opening polymerization is carried out by heating to 120 ° C. to obtain a styrene oxide-containing polyol compound having an SO polymer block and a PO polymer block. Was. This polyether polyol compound is referred to as polyol A.

[Polyol B] Using 200 g of trimethylolpropane (TMP) as an initiator,
A styrene oxide-containing polyol compound was obtained in the same manner as in polyol A except that 6 g and 310 g of PO were used. This polyether polyol compound is converted to polyol B
And

[Polyol C] Trimethylolpropane (200 g) was used as an initiator, SO was added at 130 g, and PO was added.
Styrene oxide-containing polyol compound was obtained in the same manner as in polyol A except that 388 g of styrene oxide was used. This polyether polyol compound is referred to as polyol C.

[Polyol D] Using 100 g of monoethanolamine (MEA) as an initiator,
g, PO except that 602 g of PO was used to obtain a styrene oxide-containing polyol compound in the same manner as in polyol A. This polyether polyol compound is converted to polyol D
And

[Polyol E] A styrene oxide-containing polyol compound was obtained in the same manner as in polyol A, except that 100 g of monoethanolamine was used as the initiator, 257 g of SO and 413 g of PO were used. This polyether polyol compound is referred to as polyol E.

[Polyol F] A styrene oxide-containing polyol compound was obtained in the same manner as in polyol A, except that 200 g of monoethanolamine was used as the initiator, 320 g of SO and 482 g of PO were used. This polyether polyol compound is referred to as polyol F.

[Polyol G] Using 100 g of ethylenediamine (EDA) as an initiator, 290 g of SO,
A styrene oxide-containing polyol compound was obtained in the same manner as in polyol A except that 677 g of PO was used. This polyol compound is referred to as polyol G.

[Polyol H] A styrene oxide-containing polyol compound was obtained in the same manner as in polyol A, except that 300 g of trimethylolpropane was used as an initiator, 310 g of SO, and 465 g of ethylene oxide (EO) were used. This polyether polyol compound is referred to as polyol H.

[Polyol I] A styrene oxide-containing polyol compound was obtained in the same manner as in polyol A, except that 100 g of monoethanolamine was used as an initiator, 275 g of SO and 413 g of EO were used. This polyether polyol compound is referred to as polyol I.

[Polyol J] Using 80 g of monoethanolamine as an initiator, 409 g of SO and 6 g of PO were used.
A styrene oxide-containing polyol compound was obtained in the same manner as in polyol A except that 14 g was used. This polyether polyol compound is referred to as polyol J. This polyol compound has a hydroxyl value of less than 200.

[Polyol K] A styrene oxide-containing polyol compound was obtained in the same manner as in polyol A, except that 300 g of monoethanolamine was used as the initiator, 388 g of SO and 584 g of PO were used. This polyether polyol compound is referred to as polyol K. This polyol compound has a hydroxyl value exceeding 550.

[Polyol L] Using 300 g of trimethylolpropane as an initiator, 116 g of SO and PO
Styrene oxide-containing polyol compound was obtained in the same manner as in polyol A, except that 660 g of was used. This polyether polyol compound is referred to as polyol L. This polyol compound has less than 10 mol% of SO.

[Polyol M] Using 100 g of ethylenediamine as an initiator, 483 g of SO and 48 g of PO were used.
A styrene oxide-containing polyol compound was obtained in the same manner as in polyol A except that 4 g was used. This polyether polyol compound is referred to as polyol M. This polyol compound contains more than 30 mol% of SO.

[Polyol N] Using 300 g of trimethylolpropane as an initiator, not using SO,
Propylene oxide-added polyol compound was obtained in the same manner as in polyol A, except that 776 g of was used. This polyether polyol compound is referred to as polyol N.

[Polyol O] Using 200 g of trimethylolpropane as an initiator, 206 g of SO and PO
Was used in the same manner as in polyol A, except that these were mixed and subjected to ring-opening addition polymerization to obtain a propylene oxide-added polyol compound which is a random polymer of SO and PO. This polyether polyol compound is referred to as polyol O. The polyol O is a compositionally identical random copolymer to the polyol B.

For the above polyols A to O, Table 1 summarizes the mol% of the alkylene oxide used, the hydroxyl value, and the viscosity at 25 ° C.

[0054]

[Table 1] (Production Example of Rigid Polyurethane Foam) A rigid polyurethane foam was prepared using the above-mentioned polyol compound as a polyol component (indicated as R component) and formulated as shown in Table 2, and evaluated.

The other raw materials used are as follows.
Note that the NCO index, that is, the NCO / active hydrogen group equivalent ratio, was calculated and displayed using water as a bifunctional active hydrogen compound. Foam stabilizer: Silicon-based foam stabilizer SH-193 (manufactured by Dow Corning Toray Co., Ltd.) Flame retardant plasticizer: tris (β-chloropropyl) phosphate (TMCPP, manufactured by Daihachi Chemical Co.) Catalyst: N, N, N ', N'-tetramethylhexamethylenediamine (Kaolyzer No. 1 manufactured by Kao Corporation) Isocyanate compound (indicated as P component): Crude MD
I (MR-200 manufactured by Nippon Polyurethane Industry Co., Ltd.) A rigid polyurethane foam is obtained by weighing and mixing the ingredients of the R component, stirring using a homogenizer,
The components were added, mixed with a homogenizer, poured into a mold, reacted, and foamed.

[0056]

[Table 2] Table 3 shows the composition of the comparative example. Form production
This was performed in the same manner as in the example.

[0057]

[Table 3] (Evaluation) 1) Measurement of closed cell ratio Using a rigid polyurethane foam sample cut into a size of 20 × 20 × 25 mm, the measurement was performed using an air comparison specific gravity meter Model 930 (manufactured by Beckman).

2) Measurement of compressive strength Measured according to JIS A 9514. 50x50
Using a rigid polyurethane foam sample cut to a size of × 50 (mm), the compressive strength was measured by a 4301 type universal testing machine (manufactured by Instron). The compressive strength in the vertical method in the free foaming of the foam was expressed as compressive strength (⊥), and the compressive strength in the parallel direction in the free foaming of the foam was expressed as compressive strength (‖).

3) Measurement of Thermal Conductivity The measurement of the thermal conductivity was performed according to ASTM C-177-63. Using a rigid polyurethane foam sample cut to 200 × 200 × 30 (mm), the upper plate temperature was set to 10 ° C. and the lower plate temperature was set to 27.5 ° C. using a thermal conductivity measuring device TCA8 (manufactured by Anacon). It was measured. 4) Evaluation of dimensional stability at high temperature and high humidity The evaluation of dimensional stability at high temperature and high humidity was performed according to ASTM D-2126.
Performed according to -66. A rigid polyurethane foam sample cut to 100 × 100 × 25 mm was heated at 70 ° C.
Cured under 95% RH condition for 48 hours, and measured the dimensional change rate in the foaming direction of the foam (vertical method in free foaming) and the dimensional change rate in the direction perpendicular to the foaming direction of the foam (horizontal direction in free foaming). The dimensional change rate (⊥) and the dimensional change rate (‖) are shown.

The evaluation results are shown in Table 4.

[0061]

[Table 4] From these results, the rigid polyurethane foam of the present invention is:
The closed cell rate is high, the cells are uniform and the appearance is good, and the compressive strength and the heat insulation are excellent.However, when a polyol that does not use SO is used, the heat insulation is reduced, and the hydroxyl value of the SO-containing polyol is too low. It can be seen that the appearance of the foam decreases, and if it is too high, the foam becomes brittle and the compressive strength decreases. Also S
When the ratio of O is low, the heat insulating property and the compressive strength are lowered, and when it is too high, the foam itself cannot be formed well. Further, it can be seen that a block copolymer of SO and another alkylene oxide is more suitable than a random copolymer with the same alkylene oxide composition and a lower viscosity.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Riichiro Ohara 1-17-18 Edobori, Nishi-ku, Osaka-shi, Osaka Toyo Tire & Rubber Co., Ltd. F-term (reference) 4J034 BA03 DB03 DB04 DB05 DB07 DC02 DG02 DG03 DG04 DG18 DG12 DG18 HA06 KA01 KB02 KC17 KD12 NA03 QC01 QD03 RA10 RA15

Claims (5)

[Claims] 1. A rigid polyurethane foam stock solution containing a polyol component, a foaming agent containing water, and a catalyst, which reacts with a polyisocyanate component to form a rigid polyurethane foam, wherein the polyol component has an average number of functional groups of 2 to 2. The hydroxyl value obtained by adding an alkylene oxide containing styrene oxide to the polyfunctional active hydrogen compound of No. 4 is 250 to 550 (mg)
KOH / g), a rigid polyurethane foam stock solution containing a styrene oxide-containing polyol in which the styrene oxide content in the alkylene oxide is 10 to 30 mol% and the styrene oxide and another alkylene oxide are block-copolymerized. . 2. The rigid polyurethane foam stock solution according to claim 1, wherein only water is used as the foaming agent. 3. The content of the styrene oxide-containing polyol in all polyol compounds is 20 to 100% by weight.
The rigid polyurethane foam stock solution according to claim 1 or 2, 4. A hard polyurethane foam formed by reacting a polyisocyanate component with a stock solution of a rigid polyurethane foam containing a polyol component, wherein the stock solution of the rigid polyurethane foam is a foaming agent containing at least a polyol component, water, and a catalyst. Having a hydroxyl value of 250 to 550 (mg KOH) obtained by adding an alkylene oxide containing styrene oxide to a polyfunctional active hydrogen compound having an average functionality of 2 to 4 as the polyol component.
/ G), a rigid polyurethane foam having a styrene oxide content of 10 to 30 mol% in the alkylene oxide and containing a styrene oxide-containing polyol obtained by block copolymerizing the styrene oxide and another alkylene oxide. 5. The rigid polyurethane foam according to claim 4, wherein only water is used as the foaming agent.