Process for producing polyurethane foam

A process for producing a polyurethane foam from a foam raw material containing polyols, organic isocyanates, catalysts and blowing agents, which comprises using as the polyols a high-molecular weight polyol having a hydroxyl number lower than 100 and a low-molecular weight polyol having a hydroxyl number higher than 200 which are mixed at a ratio of 4:6 to 6:4 (by weight), and also using as the catalysts a tertiary amine alone. Polyurethane forms having good buckling performance can be obtained by the process and they are expected to be useful as a packaging material, shock-absorbing material, heat-insulating material, and so on.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process for producing a ployurethane 
foam having good buckling performance property. The polyurethane foam of 
the present invention in having this property, is useful as a packaging 
material, shock-absorbing material, heatinsulating material, and frog (for 
holding flowers in place in a bowl or base). 
2. Description of the Prior Art 
There are many instances in which foam materials are used for packaging or 
shock absorption by causing these materials to buckle. The foam materials 
for such uses have heretofore been rigid urethane foams or phenolic foams. 
These conventional foams have the following disadvantages. 
(1) They do not buckle in a neat manner. 
(2) When they are buckled, they generate powder, which adheres to the 
packaged goods and contaminates the environment. 
(3) They require a high load for buckling. 
(4) If they are to have a good buckling performance, it would be necessary 
for them to be produced batchwise from expensive raw materials. This would 
lead to their production cost being high and would limit the height of the 
foam. 
SUMMARY OF THE INVENTION 
The polyurethane foam of present invention was completed. The completed 
polyurethane foam of the present invention eliminated the above-mentioned 
disadvantages. 
Therefore, it is an object of the present invention to provide a 
polyurethane foam which has good buckling performance. 
It is another object of the present invention to provide a polyurethane 
foam which does not generate powder when it is buckled. 
To achieve the above-mentioned object, the present inventors carried out 
series of researches which led to the finding that a polyurethane foam 
having very good buckling performance can be obtained from foam raw 
material containing a polyol mixture, organic polyisocyanate, catalyst, 
and blowing agent, wherein the polyol mixture is composed of a high 
molecular weight polyol having a hydroxyl number lower than 100 and a 
low-molecular weight polyol having a hydroxyl number higher than 200 which 
are mixed in a ratio of 4:6 to 6:4 (by weight), and the catalyst is a 
tertiary amine which is used alone (not in combination with a tin catalyst 
or other catalysts). The polyurethane foam resembles a semirigid foam and 
yet has the proper hardness of a rigid foam. Despite its high degree of 
hardness, the polyurethane foam can be buckled in a neat manner under a 
comparatively low load. In addition, unlike conventional rigid foams, it 
does not generate powder when being buckled. Therefore, the polyurethane 
foam will be suitable for application in areas where it is used in a 
buckled state. The present invention was completed on the basis of this 
finding. 
Accordingly, the present invention provides a process for producing a 
polyurethane foam from a foam raw material containing polyols, organic 
isocyanates, catalyst, and blowing agents, which comprises using as the 
polyols a high-molecular weight polyol having a hydroxyl number lower than 
100 and a low-molecular weight polyol having a hydroxyl number higher than 
200 which are mixed at a ratio of 4:6 to 6:4 (by weight), and also using 
as the catalyst a tertiary amine alone (not in combination with a common 
tin catalyst). 
The above and other objects, features and advantages of the present 
invention will be more apparent from the following description.

DETAILED DESCRIPTION OF THE INVENTION 
The high-molecular weight polyol used in the present invention should have 
a hydroxyl number of lower than 100, preferably 25 to 100, more preferably 
25 to 60. Examples of such polyols include those which are formed by the 
addition polymerization of ethylene oxide, propylene oxide, butylene 
oxide, or a mixture thereof on a polyhydric alcohol such as propylene 
glycol, glycerin, diglyceride, and trimethylolpropane. These polyols 
should preferably have a molecular weight of from 2,000 to 4,000. 
On the other hand, the low-molecular weight polyol used in the present 
invention should have a hydroxyl number of higher than 200, preferably 
200 to 600. Examples of such polyols include those which are formed by the 
addition polymerization of ethylene oxide, propylene oxide, butylene 
oxide, or a mixture thereof on a hydroxyl compound such as glycerin and 
trimethylolpropane or a polyhydric alcohol such as glycerin, 
pentaerythritol, sorbitol, sucrose, and .alpha.-methyl glucoside, and 
trimethylolpropane, or those which are formed by the addition 
polymerization of ethylene oxide, propylene oxide, butylene oxide, or a 
mixture thereof on an amine compound such as tolylenediamine, 
ethylenediamine and diethylenetriamine. These polyols should preferably 
have a molecular weight of from 200 to 800. 
The two polyols should be used in combination in a mixing ratio of from 4:6 
to 6:4 by weight. With a mixing ratio outside this range, the polyurethane 
foam obtained is not satisfactory in buckling performance. 
As mentioned above, the process of the present invention employs a tertiary 
amine alone as the sole catalyst. Examples of the tertiary amine catalyst 
include aliphatic tertiary amines such as triethylenediamine, 
triethylamine N,N, N',N'-tetramethyl methyl-1, 3-butanediamine, 
dimethylethanolamine, ethyldiethanolamine, N, N-dimethylcyclohexylamine, 
N-ethylmorpholine, N-methylmorpholine, 1,8-diazacyclo (5. 4. 0) 
undecene-7, bis(2-dimethylaminoethyl)ether, trimethylaminoethyl 
piperagine, methylhydroxyethyl piperazin, N, N, N', 
N',-tetramethylhexamethylenediamine, N, N, N', 
N'-tetramethylpropylenediamine, N, N, N', N', 
N''-pentamethyl-diethylenetriamine, N-trioxyethylene-N,N-dimethylamine, 
and N, N, N'-trimethylaminoethyl ethanolamine. They may be used 
individually or in combination with one another. 
These tertiary amines should be used in a catalytic amount which is not 
specifically limited. The preferred amount is 0.1 to 3 parts by weight for 
100 parts by weight of the total amount of polyols used. 
The organic isocyanate that can be used in the present invention is one 
which is commonly used for the production of polyurethane foams. It 
includes, for example, m-phenylenediisocyanate, p-phenylenediisocyanate, 
2,4-tolylene-dissocyanate, 2,6-tolylenediisocyanate, 
chlorophenylene-2,4-diisocyanate, and crude diphenylmethane diisocyanate 
and a mixture thereof. The organic isocyanate should be used in an amount 
of 20 to 70 parts by weight for 100 parts by weight of the total amounts 
of polyols used. 
The blowing agent that can be used in the present invention includes water 
and common halogenated hydrocarbons such as monofluorotrichloromethane, 
difluorodichloromethane, dichloromethane, 
2,2-dichloro-1,1,1-trichloroethane, and 1,1-dichloro-1-fluoroethane. The 
blowing agent may be used in an effective amount. Preferably, when water 
is used, it may be present in amount of 1 to 6 parts by weight for 100 
parts by weight of the total amount of polyols used, and when halogenated 
hydrocarbon is used, it may be present in amount of 1 to 30 parts by 
weight for 100 parts by weight of the total amount of polyols used. 
The above-mentioned raw materials may further contain a flame retardant, 
pigment, inorganic filler, and the like. 
The foaming of the above-mentioned raw materials can be accomplished by 
either a one-shot process or prepolymer process under various foaming 
conditions. In the one-shot process, a polyol, isocyanate, water, amine 
catalyst and, if necessary, an auxiliary agent are independently 
introduced into a mixing room. Then the components are mixed and the 
mixture is provided on a conveyor belt and allowed to foam. In the 
prepolymer process, a prepolymer having an isocyanate terminating group is 
prepared by reacting a polyol with an excess of an isocyanate, and the 
thus prepared prepolymer is used as an isocyanate in the one-shot process. 
The polyurethane foam obtained by the process of the present invention 
resembles a semirigid foam and yet has the proper hardness of a rigid foam 
and good buckling performance. It buckles in a neat manner, with no powder 
generated, under a comparatively low load. Therefore, it can be buckled 
without routing in the manner of a flexible foam, and it can be fitted to 
a complex shape. Because of these characteristic properties, it is useful 
as a packaging material (for foods, cosmetics, and stationery), shock 
absorbing material, heat insulating material (for pipers), frog (for 
natural flowers and artificial flowers), decorating material, medium for 
hydroponic culture, wadding, and mold, which are buckled or cut to form a 
shape when used. 
As mentioned above, the process of the present invention permits the 
production of a polyurethane foam which can be buckled in a neat manner to 
a desired shape, without powdering. The polyurethane foam can be produced 
from less expensive raw materials than those used for the production of 
conventional rigid foams. In addition, it can be buckled without routing 
in the manner of a flexible foam. 
The present invention will be explained in more detail with reference to 
the following examples and comparative examples, which are not intended to 
limit the scope of the invention. In the examples "parts" means "parts by 
weight." 
[EXAMPLE1 AND COMATIVE EXAMPLES 1 to 5] 
Polyurethane foams were prepared according to the formulation and 
conditions shown in Table 1. A mixture of a high-molecular weight polyol 
and a low-molecular weight polyol, an organic isocyanate, a mixture of 
amine catalyst, foam stabilizer and water, freon, and stannous octoate (if 
used) were introduced into a mixing room at the predetermined flow rate 
(the flow rate of polyol is 3.5 kg/cm.sup.3). Then the components were 
mixed at a high agitation speed of 4000 rpm and the mixture was provided 
into a cubical box (600 mm.times.600mm.times.600mm to prepare a 
polyurethane foam. The resulting foams were tested for foaming performance 
and buckling performance. The results are shown in Table 1. 
The foaming performance was evaluated according to the following criteria. 
A:Excellent 
No cracks, no constriction due to the formation of closed cells and no foam 
down occurred. 
B:Good 
No cracks and no foam down occurred. Closed cells are slightly produced. 
C:Fair 
No cracks and no foam down occurred. The constriction due to the formation 
of closed cells slightly occurred. 
D:Poor 
No constriction due to the formation of closed cells occurred. Cracks and 
foam down occurred. The buckling performance was tested and evaluated 
according to the following method and criteria. 
TEST METHOD 
As shown in FIG. 1, a test sample 10 (polyurethane foam) having a thickness 
of 50 mm, a length of 200 mm and a width of 200 mm was pressed by an steel 
cylinder 20 having a diameter of 57 mm in the vertical direction to the 
surface of sample at a compression speed of 100 mm/min so that the center 
portion of the sample 10 was compressed at a 70% compression rate. 
Thereafter the sample 10 was unloaded to obtain a hysteresis curve as 
shown in FIG. 2. The buckling performance was evaluated from the residual 
strain rate "a" which is the value when the stress becomes zero after the 
unloading. 
CRITERIA 
A:Excellent 
The sample can be buckled in a neat manner to a desired shape. The residual 
strain rate is more than 65%. 
B:Good 
The sample can be buckled, but not in a neat manner. The residual strain 
rate is 50 to 65%. 
C:Fair 
The sample can be somehow buckled, but in a rough manner. The residual 
strain rate is 35 to 50%. 
D:Poor 
The sample cannot be buckled. The residual strain rate is less than 25%. 
TABLE 1 
______________________________________ 
Exam- 
ple Comparative Examples 
Formulation (parts) 
1 1 2 3 4 5 
______________________________________ 
High-molecular 
60 30 10 70 90 50 
weight polyol 
Low-molecular 
40 70 90 30 10 50 
weight polyol 
Organic isocyanate 
97 97 97 97 97 97 
Amine catalyst 
0.45 0.45 0.45 0.45 0.45 0.45 
Water 2.0 2.0 2.0 2.0 2.0 2.0 
Stannous octoate 
-- -- -- -- -- 0.1 
Foam stabilizer 
0.48 0.48 0.48 0.48 0.48 0.48 
Freon 7.0 7.0 7.0 7.0 7.0 7.0 
Evaluation 
Foaming A C C D D B 
performance 
Buckling A C C D D D 
performance 
______________________________________ 
Notes to Table 1 
*.sup.1 OH number: 56, molecular weight: 3000 (Voranol 3022J; a product o 
Dow Chemical) 
*.sup.2 OH number: 570, molecular weight: 400 (CA 203; a product of Sanyo 
Kasei Co., Ltd.) 
*.sup.3 A 80:20 mixture of 
##STR1## 
(TDI KZ; a product of Takeda Chemical Industries, Ltd.) 
*.sup.4 A dipropylene glycol solution containing 33% of 
##STR2## 
(DABCO 33LV; a product of Toso Co., Ltd.) 
*.sup.5 Polyoxyalkylene-silicone copolymer (L520; a product of Nippon 
Unicar Co., Ltd.) 
*.sup.6 F-11, CCl.sub.3 F (a product of Asahi Glass Co., Ltd.) 
It is noted from Table 1 that the polyurethane foam obtained according to 
the process of the present invention has superior foaming performance and 
buckling performance. 
[EXAMPLE 2 AND COMATIVE EXAMPLE 6 AND 7] 
Polyurethane foams were prepared in the same procedure as in Example 1 
according to the formulations and conditions shown in Table 2 except that 
the polyol was introduced as an independent stream into the mixing room 
when the high-molecular weight polyol or the low-molecular weight polyol 
was used alone in Comparative Examples 6 and 7. The resulting foams were 
tested for performance as a packaging material and frog. The results are 
shown in Table 2. 
The performance as a packaging material was ranked according to the 
following criteria in the case where an object is pushed against the 
polyurethane foam for packaging by buckling. 
A:Easily buckled without great resistance and spring-back. 
B:Buckled with some resistance, but not in a very neat manner. 
C:Unsuitable for packaging due to complete spring-back. 
The performance as a frog was ranked according to the following criteria. 
A:Can hold many flowers firmly. 
B:Cannot hold flowers firmly; easily broken when many flowers are thrusted 
in. 
C:Cannot hold flowers at all. 
TABLE 2 
______________________________________ 
Comparative 
Example 
Examples 
Formulation (parts) 
2 6 7 
______________________________________ 
High-molecular weight 
50 -- 100 
polyol*.sup.1 
Low-molecular weight 
50 -- -- 
polyol*.sup.2 
Low-molecular weight 
-- 100 -- 
polyol*.sup.7 
Organic isocyanate*.sup.3 
93 -- 105 
Organic isocyanate*.sup.8 
-- 108 -- 
Amine catalyst*.sup.4 
0.45 -- 0.45 
Water 2.0 0.5 3.5 
Stannous octoate -- -- 0.20 
Foam stabilizer*.sup.5 
0.48 -- 1.0 
Foam stabilizer*.sup.9 
-- 0.5 -- 
Freon*.sup.6 7.0 30.0 5.0 
Dimethylcyclohexylamine*.sup.10 
-- 1.5 -- 
Evaluation 
As a packaging material 
A B C 
As a frog A B C 
______________________________________ 
Comparative Example 6: Conventional formulation for rigid foam. 
Comparative Example 7: Conventional formulation for flexible foam. 
Notes to Table 2 
*.sup.7 OH number: 450, molecular weight: 600 (SANNIX HS 209; a product o 
Sanyo Kasei Co., Ltd.) 
*.sup.8 Represented by the formula below. (MDI KZ; a product of Sumitomo 
Bayer Co., Ltd.) 
##STR3## 
- 
*.sup.9 Polyoxyalkylene-silicone copolymer (L5420; a product of Nippon 
Unicar Co., Ltd.) 
*.sup.10 Represented by the formula below. (a product of Toso Co., Ltd.) 
##STR4## 
It is noted from Table 2 that the polyurethane foam obtained according to 
the process of the present invention has such superior buckling 
performance that it is suitable for use as a packaging material and frog.