JPH0710953A - Production of open-celled rigid polyurethane foam - Google Patents

Abstract

PURPOSE:To obtain the subject foam with an optimized glass transition point by reacting a specific polyol mixture with a specific polyisocyanate in the presence of water as a blowing agent under specified conditions. CONSTITUTION:This polyurethane foam is obtd. by reacting a polyol mixture having a specified OH value with a polymethylene polyphenylene polyisocyanate in the presence of a specified amt. of water as a blowing agent at a specified isocyanate index. The polyol mixture comprises a polyoxyalkylene polyol which has specified mean functionality, OH value, polyoxyethylene unit content, and primary OH content, a polyoxyalkylene polyol which has specified mean functionality and OH value and is obtd. by using a nonamine compd. as the initiator, and a polyoxyalkylene polyol which has specified mean functionality, OH value, and primary OH content and is obtd. by using a nonamine compd. as the initiator each in the specified value of the isocyanate index.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an open-cell rigid polyurethane foam, and more specifically, an open-cell foam having a glass transition point controlled within an optimum range so that it can be suitably used for thermoforming and the like. The present invention relates to a method for manufacturing a rigid polyurethane foam.

[0002]

2. Description of the Related Art Rigid polyurethane foam has hitherto been widely used as a heat insulating material and a structural material due to its excellent moldability. Generally, rigid polyurethane foam is
It has closed cells, and the inside of the closed cells is usually filled with a gas such as halogenated hydrocarbon such as trichlorofluoromethane or carbon dioxide, and such a gas has a low thermal conductivity. In order to have, a closed cell polyurethane foam has high heat insulation. This is the reason why closed-cell rigid polyurethane foam is widely used as a heat insulating material. On the other hand, the rigid polyurethane foam used for the structural material does not require particularly high heat insulation,
Conventionally, trichlorofluoromethane has been widely used as a foaming agent because it is inexpensive and easy to handle.

However, in recent years, from the viewpoint of protecting the ozone layer,
Trichlorofluoromethane (R-11, CFC-11)
The use of CFCs has come to be limited, and especially for applications that do not require CFCs, such as structural materials, it is best to refrain from using CFCs from the viewpoint of environmental protection and economy. Has been requested.

Although it is naturally possible to use a closed cell foam for a rigid polyurethane foam for a structural material, as described above, since the gas is contained in the cells, the pressure applied to the mold at the time of molding, that is, The foaming pressure is high, the jig needs strength, and there is a problem in dimensional accuracy. As mentioned above, like hard polyurethane foam for structural materials,
If heat insulation is not required so much, it is not necessary to use closed cell foam.

However, conventionally, it has been difficult to produce a relatively high-strength open-cell rigid polyurethane foam without using CFC as a blowing agent. That is, when water is used as the foaming agent, the isocyanate compound reacts with water to generate carbon dioxide, and at the same time, forms a urea bond and crosslinks, so that it is inevitably easy to form closed cells.

Therefore, various methods using a so-called defoaming agent have hitherto been proposed. For example, JP-A-63-89
As described in JP-A No. 519 and JP-A No. 61-51021, the foaming agent in each case is
CFC-11 is used. Moreover, since the obtained foam is an open-cell foam, the freon, which is a foaming agent, is released into the atmosphere without staying in the bubbles, which not only causes environmental damage but is economically unreasonable. is there.

On the other hand, regarding the method for molding polyurethane foam, thermoforming is relatively generally adopted regardless of whether it is soft or hard. In the field of hard foam, a press used for compression is heated for molding. A hot press method or a cold press method in which a foam is preheated and pressed is known. Conventionally, hard foam is also thermoformed depending on the application, and its glass transition point is T
When g, compression molding can be carried out at a temperature of about Tg to (Tg-40) ° C., so that whatever the glass transition point is, molding can be performed by devising the molding temperature. However, if the temperature exceeds 200 ° C., it is difficult to heat the foam having heat insulation property to a high temperature, and it is uneconomical. However, when the glass transition point is too low, the foam has poor heat resistance, and a practical product cannot be obtained.
Therefore, the practical molding temperature is usually 120-
It is in the range of 200 ° C., and at such molding temperature,
In order for the hard foam to have excellent thermoformability, the glass transition point is preferably in the range of 135 to 180 ° C.

Essentially, such a thermoformed foam product does not require the use of freon or the foam to be closed cells. However, when water alone is used as a foaming agent during the production of a foam, as described above, not only can open cells not be formed, but water reacts with an isocyanate compound to form a urea bond, Since it is crosslinked, the obtained foam has a high glass transition point, which makes thermoforming difficult. As described above, conventionally, it is difficult to produce an open-cell rigid polyurethane foam that can be suitably used for thermoforming by using only water as a foaming agent.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the production of conventional open-cell rigid polyurethane foams, and uses only water as a foaming agent for thermoforming. An object of the present invention is to provide a method capable of stably producing an open-cell rigid polyurethane foam having a glass transition point controlled in an optimum range so that it can be preferably used.

[0010]

The present invention provides a method for producing an open-cell rigid polyurethane foam in which a mixture of polyols and a polyisocyanate are reacted in the presence of a blowing agent, wherein (A) a mixture of polyols is (a) an average. Number of functional groups 2-3.5,
A polyoxyalkylene polyol having a hydroxyl value of 25 to 60 mg KOH / g and a polyoxyethylene unit content of 5% by weight or less, wherein the terminal first of the hydroxyl groups is
10 to 40% by weight of a polyoxyalkylene polyol having an amount of primary hydroxyl groups of 15% or less, (b) an average number of functional groups of 2 to 4 and a hydroxyl value of 200 to 300 mgKOH / g, and a polyoxyalkylene polyol having a non-amine as an initiator 1
0 to 50% by weight, and (c) an average number of functional groups of 2 to 6 and a hydroxyl value exceeding 300 mgKOH / g, 840 mgKO
A polyoxyalkylene polyol having a H / g or less and a non-amine initiator, comprising 25 to 65% by weight of a polyoxyalkylene polyol having a terminal primary hydroxyl group content of 15% or less. And, using 100 parts by weight of the mixture of the polyol having a hydroxyl value of 200 to 500 mgKOH / g, (B) 0.5 to 5.5 parts by weight of water per 100 parts by weight of the mixture of the polyol as a foaming agent. Parts, (C) Polymethylene polyphenyl polyisocyanate is used as the isocyanate, and the isocyanate index is 70 to 1
The reaction is performed at 50.

In the present invention, the open-cell rigid polyurethane foam refers to a foam having a closed cell ratio of 10% or less. In the present invention, the isocyanate index is
(Amount of polyisocyanate actually used / theoretical amount of polyisocyanate required for the reaction of a compound having active hydrogen such as polyol, monool and water with its active hydrogen) * 100 .

According to the process according to the invention, a glass transition suitable for thermoforming is obtained by reacting a mixture of polyols having a given composition with polyisocyanate, using substantially only water as blowing agent. An open-cell rigid polyurethane foam is obtained which has points and is therefore suitable for thermoforming. The mixture of polyols used in the present invention comprises the first polyol (a), the second polyol (b) and the third polyol (c).

The first polyol used in the present invention
(a) has an average number of functional groups of 2 to 3.5 and a hydroxyl value of 25 to 60 m
gKOH / g, preferably 28-50 mgKOH / g
And a polyoxyalkylene polyol having a content of polyoxyethylene units of 5% by weight or less, wherein the amount of terminal primary hydroxyl groups among the hydroxyl groups is 15% or less. is there.

Such a polyol (a) has a hydroxyl value in the range of 25 to 60 mgKOH / g using a polyhydric alcohol having an average number of functional groups of 2 to 3.5 as an initiator. In the present invention, the polyol (a) has a polyoxyethylene content of 5% by weight or less, and a hydroxyl group of the terminal first
It is necessary that the content of the primary hydroxyl group is 15% or less.

The polyhydric alcohol having 2 to 3.5 functional groups is, for example, a bifunctional or trifunctional polyhydric alcohol such as propylene glycol, dipropylene glycol, glycerin or trimethylolpropane, either alone or appropriately. Used as a mixture or 4 such as pentaerythritol, diglycerin, methyl glucoside, sorbitol, sucrose
Or more polyfunctional polyhydric alcohols as described in 2 to 3 above.
It can be obtained by appropriately mixing it with a functional polyhydric alcohol and adjusting it so that the average number of functional groups is 3.5 or less. Further, it goes without saying that two or more kinds of the polyol (a) may be mixed and used in combination.

The hydroxyl value of the polyol (a) exceeds 60, the polyoxyethylene content exceeds 5% by weight,
Alternatively, if the terminal primary hydroxyl group exceeds 15% of the hydroxyl groups, a good open-cell rigid polyurethane foam cannot be obtained. On the other hand, hydroxyl value 25 mgK
It is difficult to produce a polyol that does not contain polyoxyethylene units below OH / g.

In the present invention, the mixture of polyols contains such polyol (a) in the range of 10 to 40% by weight, preferably 15 to 35% by weight. When the amount of polyol (a) in the mixture of polyols is less than 10% by weight, it is not possible to obtain a rigid polyurethane foam having good open cells. However, when it exceeds 40% by weight, the desired strength cannot be obtained when the thermoformed product is used as a structural material, and when a mixture of polyols is used as a premix, various components are separated. There will be problems. Particularly in the present invention, the polyol (a) is preferably a propylene oxide adduct having a polyhydric alcohol as an initiator, that is, a polyoxypropylene polyol.

In the method according to the present invention, the second polyol (b) has an average number of functional groups of 2-4 and a hydroxyl value of 200-.
It is 300 mgKOH / g and is a polyoxyalkylene polyol having a non-amine as an initiator, and preferably,
A polyhydric alcohol having an average number of functional groups of 2 to 4 is used as an initiator to which an alkylene oxide such as propylene oxide is added and polymerized so that the hydroxyl value is in the range of 200 to 300 mgKOH / g. .

The polyhydric alcohol having an average number of functional groups of 2 to 4 is, for example, propylene glycol, dipropylene glycol, glycerin, trimethylolpropane,
Bifunctional or tetrafunctional polyhydric alcohols such as pentaerythritol, diglycerin, and methylglucoside are used alone or in an appropriate mixture, or 5 or more multifunctional polyhydric alcohols such as sorbitol and sucrose are used as described above. It can be obtained by appropriately mixing with a dihydric or tetrafunctional polyhydric alcohol and adjusting the average number of functional groups to 4 or less.

Particularly in the present invention, the second polyol (b) is preferably an adduct of propylene oxide with at least one polyhydric alcohol selected from propylene glycol, glycerin and trimethylolpropane. The polyol (b) can also be used in combination of two or more kinds.

In general, the mixture of polyols does not separate in practical use, not to mention the mixture of the polyol itself, even in the premix in which the mixture of the polyol is mixed with the catalyst, the foam stabilizer, the foaming agent and the like. ,
If it does not exist uniformly and stably, it has no commercial value. The above-mentioned polyol (a) and the below-mentioned polyol (c) are
Mutual compatibility is low.

Here, in the present invention, the second polyol (b) is useful for allowing the mixture and premix of the polyol used in the present invention to be present uniformly without impairing the performance of the open cells. Further, the second polyol (b) can lower the glass transition point of the obtained rigid polyurethane foam in proportion to the blending ratio thereof, thus controlling the glass transition point of the obtained rigid polyurethane foam, Useful for lowering.

In the present invention, the mixture of polyols is
The second polyol (b) is contained in the range of 10 to 50% by weight, preferably 15 to 45% by weight. A second polyol in the mixture of polyols
When the content of (b) is less than 10% by weight, the glass transition point of the obtained rigid polyurethane foam cannot be effectively lowered, and it is difficult to obtain a polyol mixture or premix uniformly and stably. Yes, on the other hand, 5
When it exceeds 0% by weight, the obtained foam is insufficient in strength and heat resistance is also insufficient.

Third polyol used in the present invention
(c) has an average number of functional groups of 2 to 6 and a hydroxyl value of 300 mg
A polyoxyalkylene polyol which exceeds KOH / g and is 840 mgKOH / g or less and which has a non-amine as an initiator and whose primary hydroxyl group content is 15% or less among the hydroxyl groups. Therefore, the third polyol (c) contains dipropylene glycol and tripropylene glycol.

The third polyol (c) is preferably a polyhydric alcohol having an average number of functional groups of 2 to 6 as described above, for example, propylene glycol, dipropylene glycol, glycerin, trimethylolpropane,
Using pentaerythritol, diglycerin, methyl glucoside, sorbitol, sucrose, etc. alone or as an appropriate mixture as an initiator, the hydroxyl value is 300 mg.
It is obtained by addition-polymerizing alkylene oxide such as propylene oxide so as to be in the range of 840 mgKOH / g or less in excess of KOH / g.

In particular, according to the invention, a third polyol
(c) is preferably 550 mgKOH having an average number of functional groups of 2.5 to 6 and a hydroxyl value of more than 300 mgKOH / g.
/ G or less, a polyoxyalkylene polyol having a non-amine as an initiator, wherein
A polyoxyalkylene polyol having a primary hydroxyl group content of 15% or less, preferably a polyoxypropylene polyol.

It is preferable to use a polyoxypropylene polyol having sorbitol or glycerin as an initiator as the polyol (c) from the viewpoint of suppressing scorch during the formation of foam. Most preferably, according to the present invention, the third polyol (c) has an average functionality of 2.5 to 6 and a hydroxyl value of 300 mgK.
OH / g is exceeded and 550 mgKOH / g or less,
Polyoxyalkylene polyol using a polyhydric alcohol as an initiator, particularly polyoxypropylene polyol,
Mixtures with dipropylene glycol or tripropylene glycol are used. Thus, the polyol (c)
The use of dipropylene glycol or tripropylene glycol as part of the is useful in increasing the compatibility and stability of the polyol mixture.

In the present invention, the mixture of polyols contains such polyol (c) in the range of 25 to 65% by weight, preferably 25 to 55% by weight. In a mixture of polyols, when the amount of polyol (c) is less than 25% by weight, the obtained foam is inferior in strength,
If it exceeds 5% by weight, good open cells cannot be obtained.

In the present invention, the mixture of polyols comprises such polyols (a), (b) and (c) and has an average hydroxyl value of 200 to 500 mgKOH / g.
It is necessary to be in the range of
It is preferably in the range of mgKOH / g. The average hydroxyl value of this polyol mixture is 500 mg KOH / g
When it exceeds, it is not possible to obtain good open cells,
On the other hand, when it is less than 200 mgKOH / g, the strength required as a structural material cannot be obtained even if the foam density is increased.

According to the present invention, an open-cell rigid polyurethane foam is obtained by reacting such a mixture of polyols with polyisocyanate using water as a blowing agent. Here, the amount of water as a foaming agent is 0.5-5.
It is in the range of 5 parts by weight, and preferably in the range of 1.0 to 4.5 parts by weight. When the amount of water used is small, it is difficult to obtain the desired open-cell foam, and the density of the obtained foam becomes too high to obtain a foam having a low specific gravity. On the other hand, if the amount of water as the foaming agent is too large, the density will be too low, and it will be difficult to obtain a compressive strength of 1 kg / cm ² or more (at 10% compression) even if molded. Further, since the glass transition point of the obtained foam rises according to the amount of water, when the amount of water is too large, the effect of lowering the glass transition point of the above-mentioned polyol (b) is lowered to lower the glass transition point. Can even exceed 200 ° C. Such a foam having a high glass transition point is unsuitable for use in thermoforming.

In the present invention, it is preferable that only water is used as the foaming agent for the reaction, but if necessary, a halogenated hydrocarbon, pentane or the like may be used in combination with water as a foaming agent in a low boiling point liquid. .

In the present invention, as the foam stabilizer, an organic polysiloxane copolymer which is generally used for soft slabs, hot molds and hard foams is preferably used. Examples of such a foam stabilizer include B-8404 and B-8017 manufactured by Gold Schmitt, L-5410, L-5420 and SZ-1 manufactured by Nippon Unicar.
127, L-582, SH-made by Toray Dow Corning
190, SH-192, SH-193, Shin-Etsu Chemical F-
345, F-341, F-242T and the like. Such a foam stabilizer is usually used in the range of 0.2 to 10 parts by weight, preferably 0.5 to 3 parts by weight, based on 100 parts by weight of the mixture of polyols.

A catalyst may be used in the present invention. Well-known amine-based, tin-based, and lead-based catalysts are used as such catalysts. In general, amine-based catalysts are often used, and tertiary amines are particularly preferably used. As such a tertiary amine, for example, tetramethylhexadiamine (TMHD
A, Kaolizer No.1 (made by Kao), Toyocat MR
(Manufactured by Tosoh), pentamethyldiethylenetriamine (PMDETA, Kaolizer No. 3 (manufactured by Kao)), Dubco 33LV (manufactured by Air Products), bis (2-dimethylaminoethyl) ether (Toyocat ET (manufactured by Tosoh)), etc. Can be mentioned. These may be used alone or as a mixture. In particular, a mixture of TMHDA / bis (2-dimethylaminoethyl) ether (7/3) (hereinafter, TE-30) is preferably used in the present invention. In the present invention, the catalyst is usually used in the range of 0.01 to 20% by weight based on the polyisocyanate.

As the polyisocyanate, polymethylene polyphenyl polyisocyanate (crude MDI,
It is also called C-MDI or polymeric MDI. )
Is preferred, and in particular, polymethylene polyphenyl polyisocyanate having a viscosity of 200 millipascal · second (centipoise) or less at 25 ° C. is preferably used.
As described above, when the viscosity at 25 ° C. is 200 millipascal · sec or less, compatibility with the polyol mixture is good, and open cells are easily formed as compared with the case where it is not. Such a polymethylene polyphenyl polyisocyanate has an isocyanate index of 70-
It is used in the range of 150, preferably 80 to 130. When the isocyanate index is too high, the hardness of the obtained foam is high, but it becomes easy to form closed cells, while when the isocyanate index is too low,
The obtained foam is inferior in strength.

Specific examples of such polymethylene polyphenyl polyisocyanate include commercially available products of luplanate M-20S (viscosity at 25 ° C .: 180 millipascal seconds (centipoise)), luplanate M-12.
S (viscosity at 25 ° C: 120 millipascal-seconds (centipoise)) (Takeda Birdishe Urethane Industry Co., Ltd.)
Manufactured by Mitsubishi Kasei Co., Ltd.), Millionate MR-200 (manufactured by Nippon Polyurethane), Sumidule 44V-20, 44V-10 (manufactured by Sumitomo Bayer Urethane), Papi-135 (manufactured by Mitsubishi Kasei Dow) and the like.

Further, in the present invention, if necessary,
Additives such as flame retardants, antioxidants and colorants can be used. As the flame retardant, trischloropropyl phosphate (TCPP) is preferably used. In the present invention, in the premix of the mixture of polyols,
Thickeners can also be used. Examples of such a viscosity reducer include propylene carbonate. Furthermore, if necessary, a small amount of low-viscosity diol or monool can be used.

The density of the open-cell rigid polyurethane foam obtained according to the present invention is preferably in the range of 33 to 150 kg / m ^{3 in} the foam obtained by free foaming.
When the density is less than 33 kg / m ³ , the strength is not sufficient, and when it exceeds 150 kg / m ³ , there is no meaning to make open cells.

[0038]

According to the method of the present invention, as described above,
By using a mixture of polyols having a predetermined structure and composition, an open-cell rigid polyurethane having a glass transition point suitable for thermoforming by using only water without using a halogenated hydrocarbon as a blowing agent. You can get the form. However, the open-cell rigid polyurethane foam according to the present invention can be used as a structural material or a general heat insulating material, if necessary.

[0039]

EXAMPLES The present invention will be described below with reference to comparative examples and examples, but the present invention is not limited to these examples. Parts indicate parts by weight. The polyols used in the following comparative examples and examples are as follows. In the following, the hydroxyl value is described by omitting the unit (mgKOH / g).

Polyol (a) Polyol A: Propylene oxide is added to glycerin and has a hydroxyl value of 34, which is within the range specified in the present invention. Polyol B: Propylene glycol is added to propylene glycol and has a hydroxyl value of 37, which is within the range specified in the present invention. Polyol K: Propylene oxide is added to glycerin, and then ethylene oxide is added, and the hydroxyl value is 35, the polyoxyethylene content is 14% by weight, and the primary hydroxyl group content of the hydroxyl groups is 70%. It is not within the range specified in the present invention.

Polyol (b) Polyol M: Propylene oxide is added to propylene glycol and has a hydroxyl value of 280, which is within the range specified in the present invention. Polyol N: Propylene oxide is added to glycerin and has a hydroxyl value of 250, which is within the range specified in the present invention.

Polyol (c) Polyol H: Propylene oxide is added to a mixture of sorbitol and glycerin (average functional group 4.5) and has a hydroxyl value of 370, which is within the range specified in the present invention. Polyol L: 1 mole of trimethylolpropane to which 5.45 moles of ethylene oxide are added, and a hydroxyl value of 45
0, the content of ethylene oxide is 64% by weight, and the amount of primary hydroxyl groups among hydroxyl groups is 100%, which is not within the range specified in the present invention. Dipropylene glycol: It has a hydroxyl value of 837 and is in the range specified in the present invention.

In the following, the abbreviations mean the following. CT: Time (seconds) from the start of mixing the reaction solution to the time when the reaction mixture starts to rise in a creamy state. 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 TCPP: trischloropropyl phosphate TE-30: tetramethylhexanediamine (TMHD)
A) / bis (2-dimethylamino) ethyl) ether (70/30) mixed catalyst luplanate M-12S: polymethylene polyphenyl polyisocyanate manufactured by Takeda Bardish Urethane Co., Ltd. (viscosity at 25 ° C. 120 millipascals. Second (centipoise)) Luplanate M-20S: Polymethylene polyphenyl polyisocyanate manufactured by Takeda Birdiche Urethane Co., Ltd. (viscosity at 25 ° C. 180 millipascal second (centipoise))

Further, among the physical properties, the following physical properties are
It measured as follows. Compressive strength: The strength during compression in the rising direction of the foam was measured. Unless otherwise specified, it means the strength at 10% compression. Dimensional stability: Dimensional changes after -30 ° C x 24 hours and 80 ° C x 24 hours were measured, and 1% or less was regarded as good. Glass transition point: When the viscoelastic chart is measured at a temperature rising rate of 3 ° C./min in a tensile mode using a viscoelastic spectrometer (manufactured by Iwamoto Seisakusho), and tan δ (= E ^" / E ^' ) shows a maximum. indicated by the temperature. However, E ^'is the storage modulus,
^" E ^" is the loss modulus.

Further, among the physical properties, the following physical properties are
It measured as follows. Dimensional stability: Dimensional changes after -30 ° C x 24 hours and 80 ° C x 24 hours were measured, and 1% or less was regarded as good.

Example 1 A three-fold amount (g) of the amount shown in Table 1 as Example 1 was mixed with a polyol, a foam stabilizer, water and a catalyst to prepare a premix in a 2-liter polyethylene beaker. This premix was transparent and uniform. Next, this premix in a polyethylene beaker was adjusted to a temperature of 25 ° C., and separately adjusted to 25 ° C., 3 times the amount of luplanate M-12S shown in Table 1 was weighed into the beaker and immediately homogenized with a homodisper 3000 to 3000. A mixture was prepared by stirring at 5000 rpm for 5 seconds, and the mixture was poured into a 25 cm square wooden box into which release paper was folded to produce a free foam foam. Table 1 shows the reactivity of the foam, the density, the closed cell ratio, the compressive strength, the dimensional stability, the glass transition point and the appearance of the cell of the obtained foam.

According to the present invention, the glass transition point is 130 to
An open-cell rigid polyurethane foam having a compressive strength in the range of 170 ° C. and a strength of 1 kg / cm ² or more can be obtained.

Examples 2 to 4 and Comparative Examples 1 to 3 Using the formulations shown in Tables 1 and 2, in the same manner as in Example 1,
A mixture of polyol, a foam stabilizer, water, a catalyst and, if necessary, a flame retardant were mixed to prepare a premix. The mixture of all polyols was transparent and uniform, and the premixes were both transparent and uniform.

Next, in the same manner as in Example 1, the above premix and polymethylene polyphenyl polyisocyanate were mixed and hand-mixed and foamed to produce a free-foamed foam. Tables 1 and 2 show the reactivity of the foam, the density, the closed cell ratio, the compression strength, the dimensional stability, the glass transition point, and the appearance of the cell of the obtained foam.

[0051]

[Table 1]

[0052]

[Table 2]

According to the present invention, the glass transition point is 135 to
An open-cell rigid polyurethane foam having a compressive strength in the range of 170 ° C. and a strength of 1 kg / cm ² or more can be obtained. From Examples 1 to 3 and Comparative Example 1, it is shown that the polyol (b) has a great effect on lowering the glass transition point of the obtained foam. However, in Comparative Example 1, since the polyol (a) is not within the range specified in the present invention, the obtained foam is substantially closed cells.

In Comparative Example 2, since the polyol (b) was not used, the obtained foam was a substantially closed cell hard foam although the glass transition point was relatively low. Comparative Example 1
As in 2 and 2, the closed cell foam has a large dimensional change at high temperature, and cannot be a practical product. In Comparative Example 3, the amount of the polyol (b) used was too large, and the obtained foam had a too low glass transition point,
Poor heat resistance and dimensional stability at high temperatures.

Claims (6)

[Claims] 1. A method for producing an open-cell rigid polyurethane foam, which comprises reacting a mixture of polyols with a polyisocyanate in the presence of a foaming agent, wherein the mixture of (A) polyol comprises (a) an average number of functional groups of 2 to 3.5,
A polyoxyalkylene polyol having a hydroxyl value of 25 to 60 mg KOH / g and a polyoxyethylene unit content of 5% by weight or less, wherein the terminal first of the hydroxyl groups is
10 to 40% by weight of a polyoxyalkylene polyol having an amount of primary hydroxyl groups of 15% or less, (b) an average number of functional groups of 2 to 4 and a hydroxyl value of 200 to 300 mgKOH / g, and a polyoxyalkylene polyol having a non-amine as an initiator 1
0 to 50% by weight, and (c) an average number of functional groups of 2 to 6 and a hydroxyl value exceeding 300 mgKOH / g, 840 mgKO
A polyoxyalkylene polyol having a H / g or less and a non-amine initiator, comprising 25 to 65% by weight of a polyoxyalkylene polyol having a terminal primary hydroxyl group content of 15% or less. And, using 100 parts by weight of the mixture of the polyol having a hydroxyl value of 200 to 500 mgKOH / g, (B) 0.5 to 5.5 parts by weight of water per 100 parts by weight of the mixture of the polyol as a foaming agent. Parts, (C) Polymethylene polyphenyl polyisocyanate is used as the isocyanate, and the isocyanate index is 70 to 1
A method for producing an open-cell rigid polyurethane foam, which comprises reacting at 50. 2. The method for producing an open-cell rigid polyurethane foam according to claim 1, wherein the polyol (a) is a propylene oxide adduct having a polyhydric alcohol as an initiator. 3. The method for producing an open-cell rigid polyurethane foam according to claim 1, wherein the polyol (b) is a propylene oxide adduct having glycerin or propylene glycol as an initiator. 4. The open-cell rigid polyurethane foam according to claim 1, wherein the polyol (c) is a polyoxypropylene polyol having an average number of functional groups of 2.5 to 6 and a hydroxyl value of 300 to 550 mgKOH / g. Production method. 5. The method for producing an open-cell rigid polyurethane foam according to claim 1, wherein a part of the polyol (c) is dipropylene glycol or tripropylene glycol. 6. The method for producing an open-cell rigid polyurethane foam according to claim 1, wherein the polymethylene polyphenyl polyisocyanate has a viscosity of 200 millipascal · second or less at 25 ° C.