Note: Descriptions are shown in the official language in which they were submitted.
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Method of preparing rigid polyurethane foam
The present invention relates to a method of preparing a rigid polyurethane
foam and
an apparatus for preparing a rigid polyurethane foam. The rigid polyurethane
foam
S can be used as heat insulation materials for freezer, refrigerator, building
and the like.
Rigid polyurethane foams are widely used as heat insulation materials for
refrigerator-freezer, for example, refrigerators for household use, since they
have a
low product density, excellent heat insulating properties and a high
mechanical
strength.
As blowing agents for preparing the rigid polyurethane foams,
chlorofluorocarbons
(hereinafter referred to as CFCs), in particular trichlorofluoromethane (CFC-
11),
have been conventionally used.
However, since the CFC-11 blowing agent contains halogens, there is
apprehension
that it may deplete the ozone layer and cause the environmental issues such as
global
warming. For the purpose of protecting the global environment, the amounts of
production and consumption of CFCs are now under international regulations. In
Japan, the production of CFCs had been prohibited by the end of 1995. As
substitute
new blowing agents, hydrochlorofluorocarbons (HCFCs) having a low ozone
depletion potential are used. For example, HCFC-141b (1,1-dichloro-1-fluoro-
ethane), HCFC-22 (chlorodifluoromethane), HCFC-142b (1-chloro-1,1-difluoro-
ethane) have been introduced and applied as blowing agents.
However, use of HCFCs, the substitute for CFCs, are now phased down, because
they also contain chlorine atom in their molecules and therefore still retain
the
property of depleting the ozone layer although their effects on the ozone
layer are
little. Thus, in terms of global environmental protection, use of blowing
agents
having no effects on the ozone layer depletion at all was newly proposed.
Hydrocarbon-based blowing agents which contain no chlorine atom and pose no
risk
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of depleting the ozone layer, for example cyclopentane, have already been
introduced
and applied for some purposes.
However, although cyclopentane is most suitable as an earth-friendly blowing
agent,
it involves some drawbacks. In particular, gaseous cyclopentane itself has a
high
thermal conductivity and the heat insulating performance of the rigid
polyurethane
foams employing cyclopentane is therefore inferior to those employing
conventional
HCFC-141b. Accordingly, there is a need for improving the heat insulation
characteristics of such rigid polyurethane foams.
The present invention provides a method of preparing a rigid polyurethane foam
from
( 1 ) an organic polyisocyanate comprising an aromatic polyisocyanate,
(2) a polyol comprising a polyether polyol and/or polyester polyol,
(3) a blowing agent, and
(4) a surfactant, a catalyst and other auxiliaries,
characterized in that
the blowing agent (3) is cyclopentane and water,
the polyol (2) is a polyether polyol and/or polyester polyol having poor
compatibility with cyclopentane, and
cyclopentane is mixed and dispersed in a polyol premix comprising the
components (2) to (4).
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The phrase "having poor compatibility with cyclopentane" means that the
solubility
of cyclopentane in the polyol is 20 g or below, for example 10 g or below, and
particularly 5 g or below. The term "solubility" means the number of grams of
cyclopentane which are soluble in 100 g of the polyol at 25°C.
S
In order to mix and disperse cyclopentane in the polyol premix, it is
preferred to use
a stirrer of which circumferential speed is at least 5 m/s. In order to allow
the
dispersed liquid to exist stably in the tank of the foaming machine, it is
preferred to
stir the mixture at a circumferential speed of at least 0.5 m/s and circulate
the mixture
through a static mixer.
The present invention provides a composition for preparation of a rigid
polyurethane
foam, comprising
1 S { 1 ) an aromatic polyisocyanate,
(2) a polyether polyol and/or polyester polyol,
(3) a blowing agent comprising a mixture of cyclopentane and water, and
(4) a catalyst, a surfactant and other auxiliaries,
and further provides a method of preparing a rigid polyurethane foam from said
composition by mechanically disperse cyclopentane in the polyol premix
comprising
the components (2), (3) and (4).
As the aromatic polyisocyanate (1}, for example, polyisocyanates such as
tolylene
diisocyanate (TDI), diphenylmethane diisocyanate (MDI), and polymethylene poly-
phenyl polyisocyanate {polymeric MDI), or modified polyisocyanates thereof can
be
used alone or in combination with each other.
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Modified polyisocyanates, that is, products obtained by partial chemical
reactions of
organic di- and/or polyisocyanates may be used. For example, di- and/or poly-
isocyanates containing an ester, urea, biuret, allophanate, carbodiimide,
isocyanurate
and/or urethane group can be used.
The NCO content of the aromatic polyisocyanate (1) is preferably 30 to SO% by
weight, for example, 30 to 33% by weight.
The polyol (2) is a polyether polyol and/or polyester polyol.
The polyether polyol may be obtained by addition polymerization of propylene
oxide
and/or ethylene oxide using a polyhydric alcohol such as ethylene glycol,
propylene
glycol, glycerine, trimethylolpropane, pentaerythritol, sorbitol, sucrose, or
bisphenol
A, an aliphatic amine such as triethanolamine or ethylenediamine, or an
aromatic
amine such as toluenediamine or methylenedianiline (NiDA) as a starting
material.
The polyether polyol may be obtained by a known method, for example, by
anionic
polymerization of an alkylene oxide using a starting material containing 2 to
8,
preferably 3 to 8, reactive hydrogen atoms in its molecule, with using an
alkali
hydroxide such as potassium hydroxide or sodium hydroxide or an alkali
alcoholate
such as potassium methylate or sodium methylate as a catalyst. Alternatively,
the
polyether polyol may also be obtained by cationic polymerization of an
alkylene
oxide using a Lewis acid such as antimony pentachloride or boron fluoride
etherate
as a catalyst.
Suitable alkylene oxides are tetrahydrofuran, ethylene oxide, 1,3-propylene
oxide,
1,2- or 2,3-butylene oxide, 1,2-propylene oxide, and styrene oxide. Ethylene
oxide
and 1,2-propylene oxide are particularly preferred. These alkylene oxides may
be
used alone or a mixture thereof.
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Examples of the reaction starting material are polyhydric alcohols such as
ethylene
glycol, propylene glycol, glycerin, trimethylolpropane, pentaerythritol,
sorbitol,
sucrose, and bisphenol A, or alkanolamines such as ethanolamine,
diethanolamine,
N-methyl- and N-ethyl-ethanolamine, N-methyl- and N-ethyl-diethanolamine, tri-
ethanolamine, and ammonia.
In addition, aliphatic amines and aromatic amines may be used as the reaction
starting material. Examples are ethylenediamine, diethylenetriamine, 1,3-
propylene-
diamine, 1,3- or 1,4-butylenediamine, 1,2-, 1,3-, 1,4-, 1,5-, and 1,6-
hexamethylene-
diamine, phenylenediamine, o-toluenediamine, m-toluenediamine, methylenedi-
aniline (MDA), and polymethylenedianiline (P-MDA).
The polyether polyol preferably contains 3 to 8, especially preferably 3 to 6,
functional groups, and those having a hydroxyl value of 300-800 mg KOH/g, more
preferably of 300-500 mg KOH/g, are suitable.
As the polyester polyol, a polyester polyol prepared from a polycarboxylic
acid and a
polyhydric alcohol, such as polyethylene terephthalate, can be used. A
suitable
polyester polyol may be prepared from an organic carboxylic acid (particularly
dicarboxylic acid) having 2-12 carbon atoms and a diol preferably having 2-12
carbon atoms, especially preferably 2-6 carbon atoms.
Examples of such organic carboxylic acid are succinic acid, glutaric acid,
adipic acid,
suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, malefic
acid, phthalic
acid, isophthalic acid, and terephthalic acid. Instead of a free carboxylic
acid,
corresponding carboxylic acid derivatives, for example dicarboxylic acid
monoester
or diester of an alcohol having 1-4 carbon atoms or dicarboxylic anhydride,
may also
be used.
As the diol, ethylene glycol, diethylene glycol, 1,2- or 1,3-propanediol,
dipropylene
glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, or 1,10-decanediol
may be
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used, and glycerine or trimethylolpropane may be used as a triol. Similarly,
lactone-
based polyester polyols may also be used.
The polyester polyol preferably contains 2 to 3, especially preferably 2,
functional
groups, and those having a hydroxyl value of 200-600 mg KOH/g, preferably of
350-
450 mg KOH/g, are suitable.
It is preferred that at least part of the polyol, in particular at least 10%
by weight of
the polyol, for example at least 30% by weight, is a polyether polyol prepared
by
addition polymerization of ethylene oxide and propylene oxide to an initiator
such as
sorbitol.
As the blowing agent (3), a combination of cyclopentane and water is used. The
amount of water used herein is 0.1 to 5 parts by weight, preferably 0.1 to 1
part by
weight, per 100 parts by weight of the polyol. The amount of cyclopentane is
preferably 5 to 30 parts by weight, more preferably 10 to 25 parts by weight,
per 100
parts by weight of the polyol.
As the catalyst, the surfactant and other auxiliaries, those conventionally
known may
be used. Amine catalysts or metal catalysts may be used as the catalyst.
As the amine catalyst, a tertiary amine such as triethylenediamine,
tetramethylhexa-
methylenediamine, pentamethyldiethylenetriamine, or methylmorpholine can be
used.
As the metal catalyst, an organic metal compound such as stannous octoate,
dibutyltin dilaurate, or lead octylate can be used. The amount of the catalyst
is
preferably 0.01 to 5 parts by weight, more preferably 0.05 to 2.5 parts by
weight, per
100 parts by weight of the polyol.
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As the surfactant, usual organic silicone-based compounds may be used. For
example, L6900, SZ-1684, SZ-1689 or the like manufactured by Nihon Unicar
Company Limited, F395 or the like of Shin-Etsu Chemical Co., Ltd., or B8465,
B8474 or the like available from Goldschmidt may be used. The amount of the
surfactant is 0 to 5 parts by weight, preferably 0.5 to 3 parts by weight, per
100 parts
by weight of the polyol.
In the present invention, other auxiliaries such as foaming stabilizers, foam
controlling agents, fillers, dyes, pigments, flame retardant additives, anti-
hydrolysis
agents may be used in appropriate amounts.
For preparation of polyurethane foam, the polyisocyanate and the polyol premix
are
injected into a mold to harden using a high pressure foaming machine. The NCO
index of the polyisocyanate and the polyol premix may be 90 to 150, for
example,
IS 110 to 130.
Preferably, the high pressure foaming machine has a circulating line (for
example, a
high pressure circulating line) and a polyol tank.
The polyol premix is a mixture prepared by adding cyclopentane to a mixture of
the
polyol, the surfactant, the catalyst, water as a blowing agent and other
auxiliaries, and
mechanically mixing and dispersing them.
Although the stirrer for mechanically stirring the polyol premix may be any of
usual
stirrers, those having a circumferential speed of at least 5 m/s is preferred.
For example, cyclopentane may be mechanically mixed and dispersed by a stirrer
having stirring wings of 7 cm in diameter at 1700 rpm (circumferential speed:
6 m/s),
and fed into the polyol tank of a cyclopentane-compatible high pressure
foaming
machine having a static mixer in the high pressure circulating line.
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A commercially available static mixer is sufficient for this purpose, and for
example,
a 1 inch x 8 blocks static mixer available from SULZER Corporation may be
used.
On the other hand, the polyol dispersion liquid can stably exist by reasons
that the
circumferential speed of the stirrer of the polyol tank is at least 0.5 m/s
and the
circulating line of the high pressure foaming machine contains the static
mixer.
By using such high pressure foaming machine, rigid polyurethane foams may be
prepared by a prepolymer process or a one-shot process using a batch method or
a
continuous method. One particularly preferred method is a method of processing
conducted according to a two-components process (Component A: isocyanate,
Component B: polyol premix).
Components A and B are mixed at a temperature in the range of 15 to
35°C, and
injected into a mold thermoregulated at 20 to 60°C (for example, 35 to
45°C), and
foamed to give a rigid polyurethane foam.
The rigid polyurethane foam may be used as heat insulation materials for
freezer,
refrigerator, building and the like.
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The present invention is further demonstrated by the following Examples and
Comparative Examples.
Cyclopentane Compatibility
Into a test tube, 100 g of a polyol is placed, a given amount of cyclopentane
is added,
and stirred and mixed thoroughly. After allowing to stand for one day, it is
observed
whether the mixture is clear, cloudy or separated. When the mixture is clear,
the
evaluation is "soluble". When the mixture is cloudy or separated, the
evaluation is
"insoluble".
Compression Strength
The measurement is conducted using a universal tester (TCM 1000 manufactured
by
Minebea Co., Ltd.) according to TIS-A-9514.
Core Foam Density
The core foam density refers to the density at the central part of the foam,
and is
calculated by measuring the weight down to 0.01 g and measuring the volume
down
to 0.1 cm' by a water displacement method.
Thermal Conductivity
The measurement is conducted on a 200 mm x 200 mm x 25 mm sample cut from
the core of the foam, using a thermal conductivity tester (Auto Lambda
manufactured
by EIKO Instruments Trading, Co.) according to ASTM-C-518.
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Example 1
A polyol mixture liquid was prepared by adding an amine catalyst (1.8 parts by
weight of tetramethylhexamethylenediamine plus 1.0 part by weight of
pentamethyl-
S diethylenetriamine plus 0.5 part by weight of trisdimethylaminopropyl-s-
triazine), 2
parts by weight of a surfactant (L6900 manufactured by Nihon Unicar Company
Limited), and 0.5 part by weight of water to 30 parts by weight of Polyol A,
25 parts
by weight of Polyol B, 20 parts by weight of Polyol C, 20 parts by weight of
Polyol
D, and 10 parts by weight of Polyol E.
To the polyol mixture liquid, 21 parts by weight of cyclopentane (blowing
agent),
was added, and mechanically mixed and dispersed by.a stirrer having 7-cm
stirring
wings at 2,000 revolutions/min (circumferential speed: 7 m/s) to prepare the
final
polyol mixture. The polyol mixture liquid was fed into a high pressure foaming
machine equipped with a static mixer (a 1 inch x 8 blocks mixer manufactured
by
SULZER Corporation), and mixed by circulating it at high pressure for a while.
The
solubility of cyclopentane was 5 g or below per 100 g of the polyols.
According to the mixing ratio shown in Table 1, the polyol mixture and
polymeric
MDI were mixed and foamed. The urethane feedstocks were adjusted at the
temperature of 20°C, and injected into a 600 mm x 400 mm x 50 mm
aluminum
mold adjusted at 45°C, and the molded product was demolded from the
mold after 7
minutes. Physical properties of the molded product are shown in Table 1.
Examples 2 and 3
A polyol mixture liquid was prepared according to Table 1. As a silicone-
containing
surfactant, 2 parts by weight of F395 manufactured by Shin-Etsu Chemical Co.,
Ltd.
was used. The other procedures were the same as those described in Example 1.
Physical properties of the molded product are shown in Table 1.
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Comparative Examples 1 and 2
As in Example 1, a polyoi mixture liquid was prepared according to Table 1.
The
mixture liquid was then mixed with cyclopentane, and fed into the high
pressure
foaming machine, and the molded product was obtained in the same manner as in
Example 1. The difference between these Comparative Examples and Examples 1-3
is in that the polyol mixture liquid in these Comparative Examples was a
liquid in
which cyclopentane was completely dissolved. Physical properties of the molded
product are shown in Table 1.
Polyol A:
A polyol obtained by addition of EO (ethylene oxide) and PO (propylene oxide)
to
sorbitol as a starting material, having a hydroxyl value of 550 mg KOH/g
Polyol B:
A polyol obtained by addition of PO to glycerin as a starting material, having
a
hydroxyl value of 520 mg KOH/g
Polyol C:
A polyol obtained by addition of EO to trimethylolpropane as a starting
material,
having a hydroxyl value of 550 mg KOH/g
Polyol D:
A polyol obtained by addition of PO to trimethylolpropane as a starting
material,
having a hydroxyl value of 865 mg KOH/g
Polyol E:
A polyester polyol derived from polyethylene terephthalate, having a hydroxyl
value
of 315 mg KOH/g
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Polyol F:
A polyol obtained by addition of EO to ethylene glycol as a starting material,
having
a hydroxyl value of 374 mg KOH/g
Polyol G:
A polyester polyol derived from phthaIic acid and diethylene glycol, having a
hydroxyl value of 420 mg KOH/g
Polyol H:
Glycerin
Polyol J:
A polyol obtained by addition of PO to glycerin as a starting material, having
a
hydroxyl value of 390 mg KOH/g
Polyol K:
A polyol obtained by addition of PO to toluenediamine/diethanolamine as
starting
materials, having a hydroxyl value of 450 mg KOH/g
Polyol L:
A polyol obtained by addition of PO to sugar/propylene glycol as starting
materials,
having a hydroxyl value of 380 mg KOH/g
Polyol M:
A polyol obtained by addition of PO to propylene glycol as a starting
material,
having a hydroxyl value of 500 mg KOH/g
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Table 1
ExampleExample Example ComparativeComparative
1 2 ~3 Example Example
I 2
Polyol A 30 3S 30 - -
Polyol B 25 - 25 -
Polyol C 2S - - - _
Polyol D 10 - - -
Polyol E 10 - _ - -
Polyol F - 20 20 - -
Polyol G - 20 20 1S -
Polyol H - S S - -
Polyol J - 20 - - -
Polyol K - - - 40 50
PolyoiL - - - 4S 40
Polyol M - _ _ - 10
Cyclopentane 21 21.5 21.5 15.5 11.2
water O.S 0.5 0.6 1.3 2.0
Polymeric MDI 170 130 130 123 140
Compressive strength2.0 1.S 1.6 1.5 2.0
(kg/emz)
Core foam 3S 32 32 32 35
density (kg/m')
Thermal conductivity
x 10'' 163 161 162 163 173
(kcal/mhC)
25C 154 15S 156 1S8 168
10C 150 151 1S2 156 166
0C
Pentane compatibilityInsoluble,Insoluble,Insoluble,Soluble Soluble
(solubility: g) 55 g 55 g <S g
According to the present invention, a rigid polyurethane foam having a low
thermal
conductivity and excellent heat insulating properties can be prepared by using
polyols having poor compatibility with cyclopentane.
