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Description  |
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The present invention relates to a method for producing a skin-formed
polyurethane foam molded product.
An integral-skin polyurethane foam molded product has a skin layer
integrally formed with a foam layer and thus has excellent elasticity and
tactile properties. Therefore, it is widely used as interior parts for
automobiles, such as steering wheels, crush pads, head rests and arm
rests.
The integral-skin polyurethane foam molded product can be prepared by
controlling foaming of the polyurethane starting material at the surface
portion which is in contact with the inner wall of the molding tool when a
polyurethane foam is molded in a closed molding tool, to form an
elastomeric skin layer. The integral-skin is usually the one in which the
degree of foaming of the skin layer increases (i.e. the density decreases)
from the surface of the molded product towards the interior, and in many
cases, the boundary between the skin layer and the foam layer is not
clear.
The mechanism of formation of the integral-skin is considered to be as
follows. Namely, when expansion molding is conducted in a molding tool
using a starting material containing as a blowing agent a
chlorofluorocarbon-type blowing agent having a relatively high boiling
point, at the surface portion in contact with the inner wall of the
molding tool, the reaction heat is absorbed by the molding tool, and at
the same time, the chlorofluorocarbon-type blowing agent can not be
evaporated due to the internal pressure of the molding tool, whereby an
integral-skin layer is formed.
Accordingly, for the production of an integral-skin polyurethane foam,
selection of the blowing agent is most important, although it is of course
necessary to select the polyol and the isocyanate suitable as starting
materials. Namely, it is necessary to use a blowing agent which will not
be evaporated in the vicinity of the inner wall of the molding tool at a
temperature of from 30.degree. to 40.degree. C. a blowing agent having a
boiling point lower than the mold temperature. For this reason,
trichlorofluoromethane (R-11) has been used which is a
chlorofluorocarbon-type blowing agent.
However, the chlorofluorocarbon-type blowing agent such as R-11 is likely
to destroy the ozone layer which protects the earth, by the
ozone-destruction chain reaction, and it is desired to reduce the quantity
of its use.
Water which discharges carbon dioxide upon its reaction with an isocyanate
compound, has been used as a substitute for the chlorofluorocarbon-type
blowing agent. However, it has drawbacks such that it embrittles the
resulting foam, and the amount of the polyisocyanate compound will thereby
be increased, thus leading to an economical disadvantage. Further, for the
production of an integral-skin polyurethane foam, it has been difficult to
form an integral-skin by carbon dioxide which has a low boiling point and
which is gaseous at room temperature.
The present inventors have found it possible to produce an integral-skin
polyurethane foam molded product without using a chlorofluorocarbon-type
blowing agent such as R-11 and by using as a blowing agent water, a heat
decomposable blowing agent which generates a gas not-condensable at room
temperature, such as carbon dioxide or ammonia, upon heat decomposition,
or an inert gas such as air or nitrogen gas.
In the present invention, the integral-skin polyurethane foam molded
product is a molded product having a non-foamed skin-layer of the same
polyurethane material as the polyurethane foam, integrally formed at the
same time as the formation of the polyurethane foam at the time of molding
the polyurethane foam. Further, in the present invention, the skin means
not only the integral-skin but also a skin wherein the boundary to the
foam layer is relatively clear as compared with the integral-skin.
The above-mentioned problems have been solved by the present invention
which provides a method for producing a skin-formed polyurethane foam
molded product, which comprises reacting a high molecular weight active
hydrogen compound containing at least 80% by weight of a polyoxyalkylene
polyol having from 2 to 8 hydroxyl groups and a hydroxyl value of from 3
to 60 (mgKOH/g) and consisting essentially of from 20 to 100% by weight of
the following component (a) and from 0 to 80% by weight of the following
component (b), a chain extender and a polyisocyanate compound in a closed
molding tool in the presence of a catalyst and a blowing agent comprising
as the main component, at least one member selected from the group
consisting of water, a heat decomposable blowing agent capable of
generating a gas upon heat decomposition and an inert gas:
(a) a polyoxyalkylene polyol having from 2 to 8 hydroxyl groups and a
hydroxyl value X (mgKOH/g) of 3.ltoreq.X.ltoreq.60, provided that when
3.ltoreq.X.ltoreq.32.5, the total unsaturated degree Y(meq/g) is
Y.ltoreq.0.04, and when 32.5.ltoreq.X.ltoreq.60, X and Y satisfy the
relation of the following formula (I):
Y.ltoreq.0.9/(X-10) (1)
or a polymer-dispersed polyol having such a polyoxyalkylene polyol as
matrix,
(b) a polyoxyalkylene polyol other than the above component (a), or a
polymer-dispersed polyol having such a polyoxyalkylene polyol as matrix.
Now, the present invention will be described in detail with reference to
the preferred embodiments.
It is known to produce a highly elastic polyurethane foam using a
polyoxyalkylene polyol having a low total unsaturated degree such as the
above component (a) or to produce a polyurethane elastomer molded product
by reaction injection molding, for example, as disclosed in the
applicants' Japanese Examined Patent Publications No. 31130/1986 and No.
45730/1986 and Japanese Unexamined Patent Publication No. 14812/1991.
The reason is not clearly understood as to why a skin can be formed even by
foaming by means of a non-condensable gas such as carbon dioxide when a
polyoxyalkylene polyol having a low total unsaturated degree is used in
the present invention. However, it is considered that from such phenomena
that as the unsaturated degree of the starting material polyoxyalkylene
polyol becomes low, an abrupt temperature rise occurs at a later stage of
the polyurethane foam-forming reaction, whereby the temperature difference
between the mold surface and the interior of the foam tends to be large,
and this tendency becomes remarkable when an organic metal catalyst and an
amine catalyst to accelerate resinification are used in combination,
resinification proceeds at the surface of the molding tool to form a
skin-layer and subsequently foaming and resinification will take place in
the interior to form a foam layer. Further, as the unsaturated degree of
the polyoxyalkylene polyol becomes low, the amount of an unsaturated
monool contained therein tends to be small, i.e. the true number of
average functional groups increases as compared with the one having a high
unsaturated degree. Thus, crosslinking points of polyurethane increases,
and the molecular weight increases, whereby the resin strength will
increase so that foaming in the skin-layer once formed will be suppressed.
Generally speaking, as the hydroxyl value of the polyoxyalkylene polyol
decreases (i.e. as the molecular weight increases), the unsaturated degree
increases, because as the hydroxyl value becomes low, the amount of an
oxyalkylene group having at least 3 carbon atoms, particularly an
oxypropylene group, as the main oxyalkylene group of the polyoxyalkylene
polyol, increases. Accordingly, the amount of reaction of an alkylene
oxide having at least 3 carbon atoms during its preparation tends to be
large, and consequently, a side reaction of the same alkylene oxide (the
reaction for forming unsaturated groups) tends to be substantial.
Component (a) as the essential component in the present invention is a
polyoxyalkylene polyol having a hydroxyl value of from 3 to 60 (mgKOH/g)
and a low unsaturated degree. The unsaturated degree of this component (a)
is required to be not higher than 0.04 (meq/g). Further, with the one
having a relatively high hydroxyl value, the unsaturated degree is
required to be lower. Namely, the relation between the hydroxyl value X
(mgKOH/g) and the unsaturated degree Y (meq/g) is required to be such that
when X is not higher than 32.5, Y is not higher than 0.04, and when X is
at least 32.5, the relation represented by the above formula (1) (i.e. Y
is not higher than 0.9/(X-10)) must be satisfied.
More preferably, component (a) has a hydroxyl value of from 3 to 40
(mgKOH/g) and an unsaturated degree of not higher than 0.03 (meq/g). Still
more preferably, component (a) is a polyoxyalkylene polyol having a
hydroxyl value of from 3 to 35 (mgKOH/g), and an unsaturated degree of not
higher than 0.03 (meq/g). Further, the number of hydroxyl groups (the
number of hydroxyl groups per molecule) is from 2 to 8, preferably from 2
to 6. Further, component (a) may, of course, be a mixture of two or more
polyoxyalkylene polyols. In such a case, the average unsaturated degree,
hydroxyl value and number of hydroxyl groups are within the above
identified ranges.
Further, component (a) is a polyoxyalkylene polyol containing mainly an
oxyalkylene group having at least 3 carbon atoms. In the case of an
oxyalkylene group having two carbon atoms i.e. an oxyethylene group, no
side reaction to form an unsaturated group takes place in the reaction for
its formation (the addition reaction of ethylene oxide). Accordingly, a
polyoxyalkylene polyol having a high proportion of oxyethylene groups, has
a low unsaturated degree. However, an integral-skin polyurethane foam
molded product obtained from a polyoxyalkylene polyol having a high
proportion of oxyethylene groups, as the starting material, does not have
practically satisfactory physical properties. Therefore, component (a) is
preferably a polyoxyalkylene polyol containing mainly oxyalkylene groups
having at least 3 carbon atoms, particularly oxypropylene groups derived
from 1,2-propylene oxide.
As component (a), a polyoxyalkylene polyol containing at least 75% by
weight of oxyalkylene groups having at least 3 carbon atoms, particularly
oxypropylene groups. It may contain oxyethylene groups, but the content of
oxyethylene groups is preferably not higher than 20% by weight. Further,
the contained oxyethylene groups are preferably located at the terminals
of the polyoxyalkylene chains. As the hydroxyl groups bonded to such
terminal oxyethylene groups are highly reactive, a polyoxyalkylene polyol
containing at least above 3% by weight, particularly at least 5% by
weight, of oxyethylene groups at the terminal, is preferred. Preferably,
component (a) is a polyoxyalkylene polyol containing mainly oxypropylene
groups, i.e. a polyoxypropylene-type polyol, having an oxypropylene group
content of at least 75% by weight and an oxyethylene group content of from
3 to 20% by weight.
Further, component (a) may be a polymer-dispersed polyol having the
above-mentioned polyoxyalkylene polyol as matrix, or a mixture of such a
polymer-dispersed polyol and the polyoxyalkylene polyol. The
polymer-dispersed polyol is a dispersion having fine particles of a
polymer such as a vinyl polymer dispersed in a polyol. For example, it may
be obtained by polymerizing a vinyl monomer such as acrylonitrile or
styrene in a polyol.
The polyoxyalkylene polyol used as a starting material for polyurethane, is
usually produced by ring-opening addition polymerization of an alkylene
oxide such as propylene oxide to an initiator such as a polyhydric alcohol
by means of an alkali catalyst such as an alkali metal hydroxide. However,
in such a process using an alkali catalyst, a side reaction to form a
monool having an unsaturated group, is likely to take place.
It may not be impossible to produce a polyoxyalkylene polyol having a low
unsaturated degree and a low hydroxyl value by means of an alkali
catalyst, (particularly by employing a mild reaction condition). However,
it is preferred to employ a polyoxyalkylene polyol produced by using other
catalysts.
As such other catalysts, a metal porphyrin (Japanese Unexamined Patent
Publication No. 197631/1986), LiPF.sub.6 (Japanese Unexamined Patent
Publication No. 197726/1985), a composite metal cyanide complex (Japanese
Examined Patent Publication No. 15336/1984 and U.S. Pat. No. 3,939,505)
and a complex of a metal with a chelating agent having at least 3 ligands
(Japanese Unexamined Patent Publication No. 197726/1985) may, for example,
be mentioned. It is particularly preferred to employ a composite metal
cyanide complex.
Component (b) is a polyoxyalkylene polyol other than the above-mentioned
polyoxyalkylene polyol of component (a), or a polymer-dispersed polyol
having such a polyoxyalkylene polyol as matrix. This polyol preferably has
from 2 to 8 hydroxyl groups and a hydroxyl value of from 20 to 110. The
total unsaturated degree exceeds the above-mentioned range for component
(a) when the hydroxyl value is not higher than 60, and it is not
particularly limited when the hydroxyl value exceeds 60. Such a
polyoxyalkylene polyol can be produced by using a common alkali catalyst.
The total unsaturated degree of this polyoxyalkylene polyol of component
(b) is usually not higher than 0.1 (meq/g).
The polyoxyalkylene polyol of component (b) is preferably a polyoxyalkylene
polyol containing mainly oxyalkylene groups having at least 3 carbon
atoms, particularly oxypropylene groups. The content of oxyalkylene groups
having at least 3 carbon atoms, is preferably at least 55% by weight. When
oxyethylene groups are contained, the content of oxyethylene groups is
preferably not higher than 40% by weight, and at least a part thereof is
preferably located at terminals of polyoxyalkylene chains. More
preferably, the polyoxyalkylene polyol of component (b) is a
polyoxypropylene-type polyol having an oxypropylene group content of at
least 55% by weight and an oxyethylene group content of from 3 to 40% by
weight.
As the polyoxyalkylene polyol of component (b), various polyoxyalkylene
polyols other those mentioned above, may be employed. For example, a
polyoxyalkylene polyol having a higher hydroxyl value, a polyoxyalkylene
polyol having a higher oxyethylene group content, a polyoxyalkylene polyol
containing no oxyethylene group and a polyoxyalkylene polyol containing
mainly oxyalkylene groups having at least 3 carton atoms other than
oxypropylene groups may be used. When these polyoxyalkylene polyols are
used, their amount is preferably smaller than the above-mentioned
polyoxypropylene-type polyol. It is usually preferred that these polyols
are used in combination with the above-mentioned polyoxypropylene-type
polyol. The amount of these polyols, if used, should preferably be not
higher than 30% by weight relative to the total polyoxyalkylene polyols.
The polyoxyalkylene polyols of component (a) and (b) are usually prepared
as follows. Namely, they are prepared by adding at least one type of
alkylene oxides to a polyvalent initiator in the presence of a catalyst.
As the alkylene oxides, alkylene oxides having at least 2 carbon atoms,
specifically, ethylene oxide, 1,2-propylene oxide, 1,2-butylene oxide,
2,3-butylene oxide and styrene oxide, may, for example, be mentioned. It
is preferred to use at least one member selected from the group consisting
of 1,2-propylene oxide, 1,2-butylene oxide and 2,3-butylene oxide or to
use at least one such member and ethylene oxide in combination.
The polyvalent initiator useful for the preparation of the above
polyoxyalkylene polyols includes a polyhydric alcohol, a polyhydric
phenol, a polyamine and an alkanol amine. For example, ethylene glycol,
diethylene glycol, propylene glycol, dipropylene glycol, neopentyl glycol,
1,4-butanediol, 1,6-hexanediol, glycerol, trimethylolpropane,
pentaerythritol, diglycerol, dextrose, sucrose, bisphenol A, ethylene
diamine and polyoxyalkylene polyols having lower molecular weights than
the desired product obtainable by adding alkylene oxides thereto, may be
mentioned. These initiators may be used alone or in combination as a
mixture of two or more of them. A particularly preferred polyvalent
initiator is a polyhydric alcohol.
The hydroxyl groups in the above polyoxyalkylene polyols preferably contain
highly reactive hydroxyl groups i.e. primary hydroxyl groups in a high
proportion. Especially in order to conduct a reaction injection molding
method in which it is necessary to use a highly reactive starting
material, it is usually required that oxyethylene groups are present at
terminals of molecular chains of polyoxyalkylene polyols.
Such polyoxyalkylene polyols can be obtained by adding ethylene oxide after
adding an alkylene oxide having at least 3 carbon atoms such as
1,2-propylene oxide to a polyvalent initiator. Oxyethylene groups may also
be present in the polyoxyalkylene chains. In a case where oxyethylene
groups are provided at the terminals of polyoxyalkylene chains for the
purpose of improving the reactivity, the content of oxyethylene groups is
usually required to be at least 3% by weight, preferably at least 5% by
weight.
The higher the content of oxyethylene groups in the polyoxyalkylene
polyols, the higher the hydrophilic nature of the resulting integral-skin
polyurethane foam. In a case of a molded product used outdoors such as an
air spoiler for automobiles, if the hydrophilic nature is too high, the
water absorptivity will be high, and the dimensional stability tends to
deteriorate. Accordingly, the content of oxyethylene groups in all
polyoxyalkylene polyols is preferably not larger than 35% by weight, more
preferably not larger than 25% by weight. Further, in such case, it is
preferred that majority of oxyethylene groups are present at the terminal
portions of molecular chains. In a case where the hydrophilic nature of
the integral-skin polyurethane foam is not required to be low, the upper
limit of the oxyethylene group content may not be so limited.
As mentioned above, components (a) and (b) in the present invention may be
polymer-dispersed polyols having the above-mentioned polyoxyalkylene
polyols as matrix. Further, they may be a polymer-dispersed polyol
produced by using a mixture of polyoxyalkylene polyols of components (a)
and (b) as matrix. A polymer-dispersed polyol is a dispersion having fine
polymer particles dispersed in a stabilized condition in such matrix, and
the polymer may be an addition-polymerized polymer or a polycondensation
polymer.
Fine polymer particles in the polymer-dispersed polyol may be composed of
an addition-polymerized polymer such as a homopolymer or copolymer of
acrylonitrile, styrene, methacrylate, acrylate or other vinyl monomer, or
a polycondensation polymer such as polyester, a polyurea, a polyurethane
or a melamine resin. By the presence of such fine polymer particles, the
hydroxyl value of the entire polymer-dispersed polyol is usually lower
than the hydroxyl value of the matrix polyol. Accordingly, the overall
hydroxyl value of the polymer-dispersed polyol having the polyoxyalkylene
polyol of component (a) as matrix is preferably at most 60, more
preferably from 3 to 35.
The content of fine polymer particles in the polymer-dispersed polyol or in
a mixture thereof with the above polyoxyalkylene polyol, is usually at
most 60% by weight, preferably at most 40% by weight. The amount of fine
polymer particles is not necessarily be large, but a large amount may be
used without any particular problem except for economical disadvantage. In
many cases, an amount of not higher than 20% by weight is sufficiently
effective. The presence of fine polymer particles in the polyoxyalkylene
polyols is not essential, but the presence is effective for improvement of
the hardness, air permeability and other physical properties of the
resulting foam.
The polyoxyalkylene polyol in the present invention consists essentially of
the above component (a) or the above components (a) and (b). The
combination is such that it comprises from 20 to 100% by weight of
component (a) and from 0 to 80% by weight of component (b), based on the
total amount of components (a) and (b). More preferably, it comprises from
50 to 100% by weight of component (a) and from 0 to 50% by weight of
component (b). More preferably, it comprises from 70 to 100% by weight of
component (a) and from 0 to 30% by weight of component (b). The average
hydroxyl value of the mixture of the two [hereinafter represented by
(a+b)] is required to be from 3 to 60 (mgKOH/g). More preferably, the
average hydroxyl value of (a+b) is from 3 to 40 (mgKOH/g). Further, as
mentioned above, the average oxyethylene group content of (a+b) is
preferably not higher than 35% by weight, particularly not higher than 25%
by weight.
The high molecular weight active hydrogen compound as one of the main
starting materials for polyurethane is a compound having at least two
active hydrogen-containing groups reactive with isocyanate groups, such as
hydroxyl groups, primary amino groups, secondary amino groups, etc. In the
present invention, this high molecular weight active hydrogen compound is
a compound having a molecular weight of at least 600. The high molecular
weight active hydrogen compound in the present invention contains at least
80% by weight of (a+b). It may contain other high molecular weight active
hydrogen compound, but the amount of such an additional compound is at
most 20% by weight.
In the present invention, a high molecular weight polyol or other high
molecular weight active hydrogen compound may be incorporated as an
optional component in addition to the polyoxyalkylene polyols (a+b) as
essential components. However, its use is not essential, but it may be
used for the purpose of improving the physical properties of the
integral-skin polyurethane foam or for other purposes. For example, to
reduce the hydrophilic nature of the integral-skin polyurethane foam, it
is preferred to employ a highly hydrophobic high molecular weight polyol
such as a hydroxyl group-containing polybutadiene.
As such a high molecular weight polyol, a polyol having an average
molecular weight per hydroxyl group of at least 40, particularly at least
800 and an average number of hydroxyl groups per molecule of from 1.6 to
4, is preferred. The average molecular weight per hydroxyl group is
preferably not higher than 10000. Such a high molecular weight polyol may,
for example, be a hydroxyl group-containing hydrocarbon type polymer such
as a hydroxyl group-containing polybutadiene, a polyester polyol or a
polyoxytetramethylene polyol.
Further, as other high molecular weight active hydrogen compound, a high
molecular weight active hydrogen compound having at least one primary
amino group or secondary amino group may be used in combination. As such
an active hydrogen compound, an amino group-containing polyoxyalkylene
compound having a molecular weight of at least 600 and having at least two
functional groups selected from the group consisting of hydroxyl groups,
primary amino groups and secondary amino groups, at least one of which is
a primary amino group or a secondary amino group, is preferred. Such an
amino group-containing polyoxyalkylene compound may, for example, be a
compound obtained by converting a part or all of hydroxyl groups of a
polyoxyalkylene polyol having a molecular weight of at least 600 to
primary amino groups, secondary amino groups or organic groups having such
amino groups. Particularly preferred is an amino group-containing
polyoxyalkylene compound obtained by converting a part or all of hydroxyl
groups of a polyoxypropylene polyol to primary amino groups. Further, a
compound obtained by hydrolyzing isocyanate groups of a prepolymer having
terminal isocyanate groups obtained by the reaction of a polyoxyalkylene
polyol with an excess equivalent amount of a polyisocyanate compound, to
convert them to amino groups, may also be employed.
The molecular weight per functional group of such a high molecular weight
active hydrogen compound is preferably at least 400, particularly at least
800, and the number of functional groups per molecule is preferably from 2
to 8. The molecular weight per functional group is preferably not higher
than 10000.
In the present invention, the chain extender is a compound having a
molecular weight of less than 600 having at least two active
hydrogen-containing groups reactive with isocyanate groups, such as
hydroxyl groups, primary amino groups, secondary amino groups, etc.
Particularly preferred is a compound having a molecular weight of not
higher than 400 and having at least two functional groups selected from
the group consisting of hydroxyl groups, primary amino groups and
secondary amino groups. Such chain extenders may be used alone or in
combination as a mixture of two or more of them. The chain extender is
used usually in an amount of from 1 to 30 parts by weight, preferably from
1 to 15 parts by weight, per 100 parts by weight of the high molecular
weight active hydrogen compound.
The polyol-type chain extender having hydroxyl groups, preferably has from
2 to 4 hydroxyl groups. This polyol-type chain extender includes typical
chain extenders such as ethylene glycol and 1,4-butanediol. Further, other
polyhydric alcohols as well as polyols such as a low molecular weight
polyoxyalkylene polyol obtained by adding an alkylene oxide to a
polyhydric alcohol or a polyol having tertiary amino groups, may be
mentioned.
The polyol-type chain extender includes the following compounds:
ethylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol,
diethylene glycol, triethylene glycol, dipropylene glycol,
triethanolamine, an N-alkyldiethanol and a bisphenol A-alkylene oxide
adduct. However, the polyol-type chain extender is not limited to such
specific examples. Preferred are ethylene glycol and 1,4-butanediol.
It is also possible to use as a chain extender a compound having one amino
group selected from the group consisting of a primary amino group and a
secondary amino group and at least one hydroxyl group. As such a chain
extender, monoethanolamine, diethanolamine or monoisopropanolamine may,
for example, be mentioned. An amine-type chain extender having at least
two amino groups selected from the group consisting of primary amino
groups and secondary amino groups, may, for example, be an aromatic
polyamine, an aliphatic polyamine and an alicyclic polyamine.
As the aromatic polyamine, an aromatic diamine is preferred. As the
aromatic diamine, an aromatic diamine having at least one substituent
selected from the group consisting group of alkyl groups, cycloalkyl
groups, alkoxy group, alkylthio groups and electron attracting groups, on
the aromatic ring to which amino groups are bonded, is preferred.
Particularly preferred is a diaminobenzene derivative. In the case of the
above substituents except for the electron attracting groups, from 2 to 4
of them are preferably bonded to the aromatic ring to which amino groups
are bonded, and it is particularly preferred that at least one is bonded
to the o-position to the position to which the amino group is bonded, more
preferably they are bonded on all positions.
In the case of the electron attracting groups, one or two are preferably
bonded on the aromatic ring to which amino groups are bonded. It is of
course acceptable that an electron attracting group and other substituent
are bonded to one aromatic ring. The carbon number of the alkyl group, the
alkoxy group and the alkylthio group is preferably not more than 4, and
the cycloalkyl group is preferably a cyclohexyl group. The electron
attracting group is preferably a halogen atom, a trihalomethyl group, a
nitro group, a cyano group and an alkoxycarbonyl group. Particularly
preferred are a chlorine atom, a trifluoromethyl group and a nitro group.
As the aliphatic polyamine, a diaminoalkane or a polyalkylene polyamine
having at most 6 carbon atoms, or a polyamine obtained by converting a
part or all of the hydroxyl groups of a low molecular weight
polyoxyalkylene polyol to amino groups, may, for example, be mentioned.
Further, a polyamine having an aromatic ring such as an aromatic compound
having at least two aminoalkyl groups, an aromatic compound having a total
of at least two aminoalkyl groups or such an aromatic compound having the
above-mentioned substituents, may also be used. As the alicyclic
polyamine, a cycloalkane having at least two amino groups and/or amino
alkyl groups, may be mentioned.
Specific examples of the amine-type chain extender will be given below:
1-methyl-3,5-diethyl-2,4-(or 2,6)-diaminobenzene,
monochloro-p-diaminobenzene, 1-methyl-3,5-dimethylthio-2,4-(or
2,6)-diaminobenzene, 1-trifluoromethyl-3,5-diaminobenzene,
1-trifluoromethyl-4-chloro-3,5diaminobenzene, 2,4-toluenediamine,
2,6-toluenediamine, bis(3,5-dimethyl-4-aminophenyl)methane,
4,4-diaminodiphenylmethane, ethylenediamine, 1,4diaminohexane,
1,3-bis(aminomethyl)cyclohexane and isophoronediamine. However, the
amine-type chain extender is not limited to such specific examples.
Particularly preferred is a diaminobenzene derivative such as a
diethyltoluenediamine [one of or a mixture of
1-methyl-3,5-diethyl-2,4-diaminobenzene and
1-methyl-3,5-diethyl-2,6-diaminobenzene], dimethylthiotoluenediamine,
monochlorodiaminobenzene or trifluoromethyldiaminobenzene.
Another main starting material for polyurethane is the polyisocyanate
compound. As the polyisocyanate compound, an aromatic, alicyclic or
aliphatic polyisocyanate having at least two isocyanate groups, a mixture
of two or more such polyisocyanates, and a modified polyisocyanate
obtained by the modification thereof, may be mentioned. Specifically,
polyisocyanates such as tolylene diisocyanate (TDI), diphenylmethane
diisocyanate (MDI), polymethylenepolyphenyl diisocyanate (so called crude
MDI), xylylene diisocyanate (XDI), isophorone diisocyanate (IPDI) and
hexamethylene diisocyanate (HMDI) and prepolymer-type modified products,
nurate-modified products, urea-modified products and carbodiimide-modified
products thereof, may be mentioned.
A preferred polyisocyanate compound is the MDI-modified product, the crude
MDI or a mixture of aromatic polyisocyanates containing one of them as the
main component.
The polyisocyanate compound is used usually in an amount of at least 0.8
time in equivalent, relative to the total equivalent of the high molecular
weight active hydrogen compound and the chain extender. The upper limit is
usually 1.5 times in equivalent, preferably 1.3 times in equivalent, when
an isocyanate group-providing catalyst is not used. In the present
invention, a preferred amount of the polyisocyanate compound to be used is
from 0.8 to 1.3 times in equivalent, relative to the total equivalent of
the high molecular weight active hydrogen compound and the chain extender.
The blowing agent to be used in the present invention is a blowing agent
containing as the main compound at least one member selected from the
group consisting of water, a heat decomposable foaming agent capable of
generating a gas upon heat decomposition and an inert gas. Water generates
carbon dioxide when reacted with a polyisocyanate compound. The gas
generated by the heat decomposition of the heat decomposable blowing agent
may, for example, be carbon dioxide, ammonia or nitrogen gas. The inert
gas may, for example, be air or nitrogen gas. Such water, a heat
decomposable blowing agent and an inert gas may be used alone or in
combination. Otherwise, they may be used in combination with other blowing
agent. In the case of the combined use with other blowing agent, the
amount of the gas (volume) generated by the blowing agent of the present
invention is preferably larger than the amount of the gas generated by
such other blowing agent.
As the heat decomposable blowing agent in the present invention, a compound
capable of discharging carbon dioxide or ammonia upon heat decomposition,
is preferred. Such a heat decomposable blowing agent generates a gas when
thermally decomposed under a high temperature atmosphere by the reaction
heat during the formation of a polyurethane foam. The heat decomposition
temperature is preferably from 40.degree. to 100.degree. C., particularly
from 50.degree. to 80.degree. C. Specific compounds include, for example,
am | | |
