JPH07110097A - Heat insulation material - Google Patents

Abstract

PURPOSE:To improve heat insulation performance and apply heat insulation materials to rough securing places by thermoforming open cell hard polyurethane foam, covering the resultant polyurethane foam by means of a material having gas barrier characteristics, reducing the pressure in the polyurethane foam, and sealing hermetically. CONSTITUTION:An open cell hard polyurethane foam is used as a core material for a heat insulation material, and at least one of water which is chemical foaming agent, halogenated hydrocarbon which is volatile foaming agent, and hydrocarbon is used as foaming agent, and polyol and organic polyisocyanate or prepolymer are made to react under the existence of foaming agent, catalyst, and foam regulating agent. In the next step, a heat insulation material is thermoformed such that anisotropy is given to the cell diameter of at least a part of the open cell hard polyurethane foam and is contained in a material having gas barrier characteristics or resultant container and sealed hermetically with pressure reduced. Thus, the heat insulation material can be secured on a rough portion and heat insulation material having excellent heat insulation performance can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat insulating material using a rigid polyurethane foam having open cells as a core material and a method for producing the same. INDUSTRIAL APPLICABILITY The heat insulating material of the present invention is used as a heat insulating material such as a refrigerator and a freezer, and a heat insulating material such as a water heater and a pipe cover.

[0002]

2. Description of the Related Art Generally, rigid polyurethane foam is
It has closed cells, and a gas such as a halogenated hydrocarbon such as trichlorofluoromethane (hereinafter referred to as R-11) or carbon dioxide is mainly enclosed in the closed cells. Such gas has low thermal conductivity,
Therefore, the closed-cell polyurethane foam has high heat insulation. Further, the rigid polyurethane foam has excellent moldability in addition to the heat insulating property and is widely used as various heat insulating materials and structural materials.

However, conventional freon represented by R-11 is chemically stable, diffuses into the stratosphere, and causes serious environmental damage such as depletion of the ozone layer. In recent years, its use is regulated. , Or in the direction of prohibition. Therefore, various studies have been conducted on such a blowing agent which replaces CFCs, for example, 1,1-dichloro-
1-Fluoroethane (hereinafter referred to as HCFC-141b), methylene chloride and the like are listed as candidates for the substitute for R-11.

However, the thermal conductivity of the closed cell rigid polyurethane foam insulation depends on the thermal conductivity of the blowing agent gas itself enclosed in the closed cells. Therefore, it is extremely difficult to obtain a heat insulating material having a low thermal conductivity by using a substitute such as HCFC-141b having a gas thermal conductivity higher than R-11. Furthermore, the closed-cell polyurethane foam is subject to dimensional changes, deformation, warpage, etc. under conditions where the temperature changes drastically, and its use is limited.

From this point of view, there has been proposed a heat insulating material called a vacuum heat insulating material in which a core material is covered with an airtight material and the inside of the core material is depressurized and sealed. As a core material used for such a heat insulating material, an inorganic material such as powder or honeycomb pearlite is known. However, a heat insulating material using an inorganic material such as pearlite has drawbacks such as poor workability during manufacturing, high density and high cost.

A heat insulating material using an organic material such as open-celled rigid polyurethane foam as a core material has also been proposed (JP-A-57-133870, Japanese Patent Publication No. 1-41).
No. 12). Such a heat insulating material covers a rigid polyurethane foam having open cells with an airtight packaging material, and decompresses and seals the inside. However, since such a core material has a bubble diameter of 300 to 1000 μm, in order to obtain sufficient heat insulation performance as a heat insulation material,
Since the pressure must be reduced to about 001 mmHg, it has a very long exhaust time, its production efficiency is low, and it is not suitable for mass production. Further, when such a polyurethane foam core material is used, the shape of the heat insulating material is not sufficiently adapted to an electric refrigerator or the like having a large number of irregularities in the internal structure, and the place where the heat insulating material can be mounted is limited.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heat insulating material having a core material of open-cell rigid polyurethane foam which has a high heat insulating property and can be freely applied to a mounting place having many irregularities. It is in.

[0008]

Means for Solving the Problems The inventors of the present invention have made extensive studies on the above problems. As a result, the present invention was completed with the finding that the intended purpose can be achieved by thermoforming an open-cell rigid polyurethane foam under a specific condition to obtain a desired shape and then vacuum-sealing. It was

That is, the present invention provides a heat insulating material obtained by hermetically sealing a core material of thermoformed open-cell rigid polyurethane foam in a material having a gas barrier property or in a container formed of the material under reduced pressure. The open-cell rigid polyurethane foam used as the core material is preferably a polyurethane foam obtained by using substantially only water as the foaming agent. Further, the present invention is to heat the open-cell rigid polyurethane foam to a temperature at which its storage elastic modulus is lowered or higher to thermoform it, cover the obtained polyurethane foam with a material having a gas barrier property, and seal the inside under reduced pressure. The present invention provides a method for producing a heat insulating material, characterized by

The heat insulating material of the present invention uses an open cell rigid polyurethane foam as a core material. As a foaming agent for producing open-cell rigid polyurethane foam,
It is preferred to use at least one of the chemical blowing agents water and the volatile blowing agents halogenated hydrocarbons and hydrocarbons.

The halogenated hydrocarbon has a carbon number of 1
In ~ 5, compounds are used in which at least one hydrogen is replaced by halogen, such as chlorine, fluorine and the like. Specific examples of such halogenated hydrocarbons include CFC-11 as chlorofluorocarbons, chloroform as hydrochlorocarbons, and HCFC-22 and HCFC- as hydrochlorofluorocarbons.
123, HCFC-141b and the like, and perfluorocarbons such as perfluoropentane and perfluorohexane.

As the hydrocarbon, a chain or cyclic compound having 5 to 6 carbon atoms is used. Specific examples of such hydrocarbon include n-pentane, isopentane, cyclopentane, n-hexane, isohexane, cyclohexane and the like.

When water is used as the foaming agent, the amount is 0.5 to 12 parts by weight, preferably 1 to 10 parts by weight, based on 100 parts by weight of the polyol. The amount of halogenated hydrocarbon and hydrocarbon used as the volatile blowing agent is in the range of 3 to 150 parts by weight, preferably 5 to 120 parts by weight, based on 100 parts by weight of the polyol. When the amount of these foaming agents used is small, the desired low-density foam cannot be obtained, while when it is too large, a foam having good strength cannot be obtained.

To produce an open-cell rigid polyurethane foam used as a core material for a vacuum heat insulating material, a polyol is reacted with an organic polyisocyanate or a prepolymer thereof in the presence of a foaming agent, a catalyst, a foam stabilizer and the like. Obtained by

Examples of such polyols include polyether polyols, polyester polyols and the like used in the production of ordinary rigid polyurethane foams, and phenol resins having a reactive methylol group.

Examples of the polyether polyol include polyoxyalkylene polyols having an active hydrogen-containing compound having a functional group of 2 to 8 and a hydroxyl value of 300 to 600 mgKOH / g as an initiator. Examples of the active hydrogen-containing compound include polyhydric alcohols and polyvalent amines. Examples of the polyhydric alcohol include dihydric alcohols such as propylene glycol and dipropylene glycol, glycerin,
Examples thereof include trihydric alcohols such as trimethylolpropane and trihydric or higher polyhydric alcohols such as pentaerythritol, diglycerin, methyl glucoside, sorbitol and sucrose. As the polyvalent amine, an organic compound having at least two active hydrogens derived from an amino group and at least one active hydrogen derived from a hydroxyl group, or having at least three active hydrogens derived from an amino group in the molecule. It refers to a compound, and specific examples thereof include (poly) alkylenepolyamine, alkanolamine, and aromatic polyvalent amine. Examples of the (poly) alkylene polyamine include ethylenediamine and diethylenetriamine. Examples of the alkanolamine include monoethanolamine, diethanolamine, triethanolamine, isopropanolamine and the like. Examples of aromatic polyvalent amines include tolylenediamines (2,4 / 2,
6-tolylenediamine, 2,3 / 3,4-tolylenediamine, etc.), diaminodiphenylmethanes, and polymethylenepolyphenylpolyamines. Other than these, alicyclic amines such as aminoethylpiperazine can also be used as the organic polyvalent amine compound. However, among these organic polyvalent amine compounds, ethylenediamine or tolylenediamines are particularly preferably used.

The polyether polyol can be used as a mixture of the following polyols (a), (b) and (c).

Next, as the polyester polyol,
Number of functional groups 2-4, hydroxyl value 250-500 mgKOH /
Examples thereof include those obtained by polycondensation of g of polyhydric alcohol and polybasic acid. Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, 1,4-butanediol, trimethylolpropane, pentaerythritol, and the like, and polybasic acids include adipic acid,
Examples thereof include succinic acid, azelaic acid, sebacic acid, maleic anhydride, and phthalic anhydride.

In particular, in order to obtain a desired foam by foaming mainly using water as a foaming agent, for example, the following (a),
It is preferred to use a polyol mixture consisting of (b) and (c).

(A) Number of functional groups 2 to 3.5, hydroxyl value 2
A polyoxyalkylene polyol having a polyoxyethylene unit content of 6 to 90 mgKOH / g and a polyoxyethylene unit content of 5% by weight or less, wherein polyoxyalkylene polyols having an amount of primary hydroxyl groups at the terminal groups of 15% or less among the hydroxyl groups. 60% by weight, (b) a polyoxyalkylene polyol having 3 to 6 functional groups, a hydroxyl value of 150 to 600 mg KOH / g, and a polyoxyethylene unit content of 5% by weight or less, of which the hydroxyl group has an end group of 1 20 to 80% by weight of a polyoxyalkylene polyol having an amount of primary hydroxyl groups of 15% or less, (c) a functional group number of 2 to 3, and a hydroxyl value of more than 600 mgKOH / g and 840 mgK.
OH / g or less polyoxyalkylene polyol 0
˜25% by weight and its hydroxyl value is 160˜
It is a polyol mixture which is 500 mg KOH / g.

In the production of open-cell rigid polyurethane foam, when the above-mentioned usual polyol for rigid polyurethane foam is used, it is preferable to use a volatile blowing agent of a hydrocarbon such as halogenated hydrocarbon or pentane together with water as a blowing agent. However, only a halogenated hydrocarbon or a hydrocarbon volatile foaming agent may be used as the foaming agent.

On the other hand, the above-mentioned polyol mixture [(a),
When (b) and (c)] are used, it is preferable that only water is used as a foaming agent for the reaction, but if necessary, a low boiling point liquid such as a halogenated hydrocarbon or pentane is used together with water as a foaming agent. You may use together.

Next, as the foam stabilizer, an organic polysiloxane copolymer generally used for soft slabs, hot molds and hard foams is preferable. Examples of such foam stabilizers include B-made by Gold Schmidt.
8404, B-8017, L-54 manufactured by Nippon Unicar Co., Ltd.
10, SZ-1127, L-582, Toray Dow Corning SH-190, SH-192, SH-193,
Shin-Etsu Chemical F-345, F-341, F-242T
Etc. can be mentioned. The amount of the foam stabilizer used is usually in the range of 0.5 to 3 parts by weight with respect to 100 parts by weight of the polyol.

As the catalyst, there are well-known amine-based catalysts, tin-based catalysts, lead-based catalysts, and isocyanurate-forming catalysts such as alkali metal carboxylate-based catalysts and strongly basic metal salt-based catalysts such as calcium hydroxide. Used. In general,
Amine-based catalysts are often used, and tertiary amines are particularly preferable. Examples of such tertiary amines include tetramethylhexamethylenediamine (TMHDA) and pentamethyldiethylenetriamine (PMDETA). These catalysts may be used alone or in combination of two or more.

As the polyisocyanate, polymethylene polyphenyl polyisocyanate (crude MDI,
(Also called C-MDI, polymeric MDI),
A prepolymer of polymethylene polyphenyl polyisocyanate and a combination thereof are preferable. The prepolymer of polymethylene polyphenyl polyisocyanate is obtained by reacting polymethylene polyphenyl polyisocyanate with a hydroxyl group-containing compound and the like, and the amine equivalent thereof is preferably in the range of 140 to 200. Examples of the hydroxyl group-containing compound include methanol, ethanol and n-
Butanol, ethylene glycol monomethyl ether,
Monoalcohols such as diethylene glycol monomethyl ether; phenols such as phenol, o-, m-, p-cresol; diols such as ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexaglycol ; In addition to triols such as glycerin and trimethylolpropane,
Examples thereof include bifunctional and trifunctional polyether polyols and polyester polyols. Furthermore, if necessary, other polyisocyanates and prepolymers thereof, for example, tolylene diisocyanate, prepolymers of tolylene diisocyanate, xylene diisocyanate (XDI), dicyclohexylmethane diisocyanate (HMDI), tetramethyl xylene diisocyanate (TMXDI), Isophorone diisocyanate (I
PDI), hexamethylene diisocyanate (HD
I), trimethylhexamethylene diisocyanate (T
MHDI) or the like may be used.

When the above-mentioned polyol for rigid polyurethane foam is used as the polyol in the production of the open-cell rigid polyurethane foam used for the heat insulating material of the present invention, it is necessary to add an open-cell forming agent. As such an open-cell foaming agent, an alkaline earth metal salt, a zinc salt of a saturated higher fatty acid, or a powder of a thermoplastic resin is preferable.

Examples of the alkaline earth metal salt or zinc salt of the saturated higher fatty acid include calcium stearate,
Examples thereof include magnesium stearate, strontium stearate, zinc stearate, calcium silistate, and the like. Moreover, as the powder of the thermoplastic resin, for example, a powder of polyethylene or the like can be mentioned. Such an open-celling agent is generally used in the range of 0.1 to 50% by weight, preferably 0.1 to 20 parts by weight, based on the polyol.

Further, in the present invention, if necessary,
Additives such as flame retardants, antioxidants and colorants can be used. Trischloropropyl phosphate (TCPP) is preferably used as the flame retardant.

A publicly known method can be used for producing the open-cell rigid polyurethane foam used as the core material of the vacuum heat insulating material. It may be obtained as a slab foam or a mold foam. Usually, it is preferably obtained as a slab foam. For example, the above raw materials may be uniformly mixed and foamed using a high-pressure foaming machine or the like.

Next, the obtained open-cell rigid polyurethane foam is thermoformed so as to impart anisotropy to at least a part of the cell diameter, and is housed in a material having a gas barrier property or a container formed from the material, 0.1 to 0.0
The heat insulating material can be obtained by sealing under a reduced pressure of about 1 mmHg which is industrially easy to handle.

The density of the open cell rigid polyurethane foam used is 15 to 1 in the case of foam by free foaming.
It is preferably in the range of 50 kg / m ³ . Density is 1
If it is less than 5 kg / m ³ , the strength is insufficient, while
When it exceeds 150 kg / m ³ , there is no meaning to make open cells. The foam used as the core material of the vacuum heat insulating material has a profitability of 15 to 150 kg / m ³
It is preferably in the range of.

In the present invention, the thermoforming is carried out by heating and softening the open-cell rigid polyurethane foam and forcibly applying pressure so as to give anisotropy to the cell diameter, or by vacuum suction or the like while the polyurethane foam is being softened. Form into the shape of the mold. Usually, the degree of anisotropy (major axis / minor axis) obtained here is preferably 3 to 5. As described above, when the cell diameter is anisotropy, the resistance of the heat transfer path formed by the polyurethane foam material itself is increased and the heat insulation performance is improved.
Next, the demolded foam is dried to remove adsorbed water and unreacted materials, housed in a container having a gas barrier property, depressurized inside, and sealed to obtain a heat-insulating material thermoformed into a predetermined shape. obtain.

The heat softening temperature of the rigid polyurethane foam is not lower than the temperature at which the storage elastic modulus of the foam begins to decrease and is not higher than 250 ° C., preferably,
It is desirable that the temperature is not lower than the glass transition temperature of the foam and not higher than 250 ° C. When the rigid polyurethane foam is heated to a temperature higher than 250 ° C., the rigid polyurethane foam is deteriorated by heat, and the physical properties required as the core material of the heat insulating material are lost.

The material having a gas barrier property used in the present invention is preferably a material which is flexible and can adhere to a thermoformed open-cell rigid polyurethane foam. As such a material, various packaging materials having a gas barrier property are used, and a laminate film having a heat seal property is particularly preferable. For such a film,
A composite film in which a gas barrier film and a thermoplastic film are laminated in two layers or in multiple layers is used.

As the film used for the gas barrier layer, various films vapor-deposited with aluminum, films containing a metal layer such as aluminum foil, films coated with vinylidene chloride and ethylene vinyl alcohol copolymer films (Eval :( Kuraray Co., Ltd., Sowanol: Nippon Gosei Co., Ltd., and the like.

As the film used for the thermoplastic layer, polyethylene film, polypropylene film and ethylene vinyl alcohol copolymer film (Eval:
Kuraray Co., Ltd., Sowanol: Nippon Gosei Co., Ltd., and the like.

Specific examples of the laminated film include aluminum vapor-deposited polyester film / polyethylene film, polyester film / aluminum foil / polypropylene film, vinylidene chloride-coated polyester film / polyethylene film and the like. Of these, the laminate film preferably has an aluminum vapor-deposited polyester film / polyethylene film structure. The heat insulating material thus obtained may be further deformed by applying heat to have a shape corresponding to the place of use.

According to the method of the present invention, the open-cell rigid polyurethane foam used as the core material is thermoformed so as to be deformed in a uniaxial direction, and then coated with a material having a gas barrier property to give 0.1 to 0.1. By sealing under a reduced pressure of about 01 mmHg which is industrially easy to handle, it is possible to mount even on a portion having a large number of irregularities and to obtain a heat insulating material having excellent heat insulating performance. Since the heat insulating material thus obtained has a low thermal conductivity and can be attached to an uneven surface, it can be used as a heat insulating material such as a refrigerator, a freezer or the like, a water heater, a pipe cover or the like.

[0039]

EXAMPLES Next, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these. In addition, a part shows a weight part.

The polyols used in the examples and comparative examples are as follows. Polyol A: Glycerin-based polyether polyol with a hydroxyl value of 34 Polyol B: Aromatic polyether polyol with a hydroxyl value of 450 Polyol C: Sugar glycerin-based polyether polyol, hydroxyl value of 450 Polyol D: Ethylenediamine-based polyether polyol, hydroxyl group Value 400

In the following, the abbreviations mean the following. CT: The time (seconds) from the start of mixing the reaction solution to the time when the reaction mixture starts to rise like a cream. GT: The time (seconds) from the start of mixing the reaction solution to the time when thickening occurs and gel strength starts to appear. DPG: Dipropylene glycol B-8017: Silicon-based foam stabilizer manufactured by Gold Schmidt SH-193: Silicon-based foam stabilizer manufactured by Toray Dow Corning TE-30: Tetramethylhexanediamine (TMHD)
A) / bis (2-dimethylamine) ethyl) ether (70
/ 30) mixed catalyst No. 1: Tetramethylhexanediamine (TMHD
A, Kaolizer No. 1, Toyocat MR) Millionate MR-200: Polymethylene polyphenyl polyisocyanate manufactured by Nippon Polyurethane Co., Ltd. Sumidule 44V-10: Polymethylene polyphenyl polyisocyanate manufactured by Sumitomo Bayer Urethane Co., Ltd.

The following physical properties of the foam were measured as follows. Thermoformability: The foam was heated to about 200 ° C., compressed by 50% with a cold press, cooled and demolded, and the dimensional change of the foam was measured. Cell size: The next day after free foaming, it was cut, and the average of the major axis direction and the minor axis direction of the foam was taken as the average cell size, which was determined from an electron micrograph. Compressive strength: The strength at 10% compression in the foam rising direction (P) and in the foam rising direction and the vertical direction (V) was measured. Further, regarding foams having a free foaming density of 30 kg / m ³ or less, thermocompression was performed and the compression strength of the foam compressed by 50% was measured. Dimensional stability: -30 ° C x 2 in foam before and after thermoforming
Measure the dimensional change after 4 hours and 80 ° C x 24 hours, and
% Or less was considered good. Glass transition temperature: The temperature at which tan δ (= E ″ / E ′) shows a maximum in the viscoelasticity chart of temperature dispersion of polymer materials, where E ′ is the storage elastic modulus and E ″ is the loss. Is the elastic modulus.

Moldability of heat insulating material: The next day after free foaming, it was cut in parallel with the foaming direction, heated to about 200 ° C., compressed by 50% with a cold press, cooled, and then demolded at 120 ° C. It is heated for about 2 hours to remove adsorbed water and unreacted materials, and then housed in a container made of a metal-plastic laminated film having a laminated structure of an aluminum vapor-deposited polyester film and a polyethylene film,
The inside was depressurized to 0.05 mmHg and sealed to obtain a vacuum heat insulating material. Then, with the dimension of the foam compressed by 50% + the thickness of the metal-plastic laminate film as the standard dimension, the rate of dimensional change after forming the vacuum heat insulating material was measured, and 0 to 1
% Was considered good. Thermal conductivity: About this vacuum insulation material, manufactured by Vacuum Riko Co., Ltd.
It measured by K-Matic at the average temperature of 24 degreeC. For the comparative example, the thermal conductivity was measured by the vacuum heat insulation obtained by the above method without thermoforming.

Example 1 These raw materials were heated to 25 ± 1 ° C. according to the foaming recipe shown in Table 1 and then freely foamed by a urethane high-pressure foaming machine to obtain a continuous foamed rigid polyurethane foam. After leaving it for 1 day, it is cut in parallel with the rising direction of the foam, heated to about 200 ° C., compressed by 50% with a cold press, cooled, and the demolded foam is heated at 120 ° C. for about 2 hours to absorb moisture Unreacted material was removed and the product was placed in a container made of a metal-plastic laminate film having a laminated structure of aluminum vapor-deposited polyester film and polyethylene film, and the inside was 0.05 m.
The pressure was reduced to mHg and sealed to obtain a vacuum heat insulating material.

Examples 2 to 7 and Comparative Examples 1 to 5 In the same manner as in Example 1, according to the foaming formulation shown in Table 1, free foaming was carried out by a urethane high pressure foaming machine, and after thermoforming,
A vacuum insulation material was obtained. Comparative Examples 1 to 5 also produced free-foamed foams in the same manner as in Examples according to the formulations shown in Table 2.

[0046]

[Table 1]

[0047]

[Table 2]

Comparative Example 1 has a high closed cell rate and cannot be thermoformed into a predetermined shape. In Comparative Examples 2 to 5, since the open-cell rigid polyurethane foam was used as a vacuum heat insulating material without being thermoformed, its thermal conductivity was 80 × 10 ^{−4 to} 90 × 10 ⁻⁴ Kcal.
Although it has fallen to / mhr ° C, it is still not enough for practical use.

[0049]

EFFECTS OF THE INVENTION The heat insulating material of the present invention is made of open-celled rigid polyurethane foam as a core material, has a high heat insulating property, and can be freely applied to a mounting place having many irregularities.

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Claims (10)

[Claims] 1. A method for producing a heat insulating material, comprising thermoforming an open-cell rigid polyurethane foam, covering the obtained polyurethane foam with a material having a gas barrier property, and hermetically sealing the inside under reduced pressure. 2. The method according to claim 1, wherein at least some of the cells of the polyurethane foam have anisotropy. 3. The method according to claim 1 or 2, wherein the polyurethane foam is thermally deformed at a temperature higher than the temperature at which its storage elastic modulus starts to decrease. 4. The method according to claim 3, wherein the upper limit of the heat distortion temperature is 250 ° C. 5. The method according to claim 1, wherein the polyurethane foam is formed by using substantially only water as a blowing agent. 6. The process according to claim 1, wherein the polyurethane foam is obtained by reacting a polyol mixture with an organic polyisocyanate. 7. The polyol mixture comprises (a) a functional number of 2 to 3.5 and a hydroxyl value of 26 to 90 mg.
A polyoxyalkylene polyol having a KOH / g and polyoxyethylene unit content of 5% by weight or less, and 10 to 60% by weight of the hydroxyl groups of the polyoxyalkylene polyol having a primary terminal hydroxyl group content of 15% or less. %, (B) Number of functional groups 3 to 6, hydroxyl value 150 to 600 mg
Polyoxyalkylene polyol having a KOH / g and polyoxyethylene unit content of 5% by weight or less, and 20-80% by weight of polyoxyalkylene polyol having 15% or less of the primary hydroxyl groups of the terminal groups among the hydroxyl groups. %, And (c) the number of functional groups is 2 to 3, and the hydroxyl value is 600 mgK.
Composed of 0 to 25% by weight of a polyoxyalkylene polyol having an OH content of 840 mgKOH / g or less, and
The method according to claim 6, wherein the hydroxyl value is 160 to 500 mgKOH / g. 8. The method according to claim 6, wherein the organic polyisocyanate is polymethylene polyphenyl polyisocyanate, a prepolymer thereof or a mixture thereof. 9. The method according to claim 1, wherein the material having a gas barrier property comprises a laminate film including a gas barrier layer and a thermoplastic film. 10. A heat insulating material obtained by vacuum-sealing a core material of thermoformed open-cell rigid polyurethane foam with a material having a gas barrier property.