Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR MIXING BLOWING AGENTS WITH POLYURETHANE
RFA_GENTS FOR THE PRODUCTION OF POLYURETHANE OR
POLYISOCYANURATE FOAM BOARDS
BACKGROUND OF THE INVENTION
This invention relates to a process and apparatus for producing rigid
foams, particularly polyurethane or polyisocyanurate foam boards having cell
structures that are formed by the expansion of polyurethane reagents. Such
rigid
foam boards are often used as thermal insulators in construction.
Rigid foams based on polyurethane or polyisocyanurate are known and
are typically produced by the reaction of an isocyanate with an isocyanate-
reactive
component (polyol component), which reaction is expanded with a blowing agent
to provide a foam. The isocyanate, polyol, and blowing agent, together with
catalysts and other optional components, are all brought into contact at a
dispensing head that dispenses the foam formulation onto a laminator. The
blowing agent is typically dissolved or emulsified in the polyol component
and,
during the exothermal reaction between the polyol and isocyanate compounds,
volatizes at or above lts boiling point to produce the pore or cellular
structure of
the foam. The isocyanate is provided in what is termed an "A-side" stream of
reagents, while the polyol component is provided in a "B-side" stream of
reagents.
Foam operations typically have a low-pressure side and a high-pressure
side. The transportation of the various chemical reagents of the B-side from
one
area to another typically occurs on the low-pressure side. Mixing of the B-
side
components, including blowing agents, may also occur in these areas.
Typically,
on the low-pressure side, mixing blades are used to mix the chemicals in a
large
batch.
Due to governmental demands regarding the industrial output of ozone-
depleting compounds, foam boards are now produced using various pentane
isomers as blowing agents. Pentane isomers are normal pentane, isopentane, and
cyclopentane. Normal pentane and isopentane are the least expensive of the
isomers, but they are also the least soluble in the reagents used to make
polyurethane foams. Cyclopentane is relatively soluble in most polyurethane
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reagents, and also exhibits good initial thermal performance; however, it is
expensive and boards produced with it demonstrate poor dimensional stability
in
colder environments. Additionally, cyclopentane may contain 2,2-dimethylbutane
as a byproduct, and this byproduct is more likely to phase separate in the B-
side
stream. Blends of these various pentane isomers often are used.
One method used to dissolve pentane isomer blends into polyurethane
reagents includes the use of surfactants, emulsifiers, and/or solubilizers in
the B-
side of the foam formulation. The A-side of the foam formulation is added
after
allowing the pentane isomers within the B-side to become adequately dissolved
or
emulsified therein. To form the B-side the blowing agents are bubbled through
and/or mechanically mixed in a large tank containing the polyol component and,
optionally, other components such as catalysts, surfactants, and flame-
retardants.
Thus, the volume of blowing agent present within the B-side at any given time
is
quite large. Additionally, although surfactants, emulsifiers, and solubilizers
may
help counter-phase separation, they tend to increase the cost of foam board
production, and their presence can affect board performance as well.
In one alternative, pentane isomers are mixed into the polyol of the
foam formulation, via proprietary technology, at low-pressure, and are
retained
within a tank from which the mixture is then drawn and fed to high-pressure
pumps that bring the mixture into eontaet with the A-side stream to produce
the
foam board.
In both of the aforementioned methods, a substantial amount of
pentanes are present in a substantial volume of the B-side. Blowing agents
such as
pentanes are flammable and therefore the presence of a large amount of
pentanes
dissolved or emulsified in the B-side is a safety concern. Also, these methods
are
inefficient in cases where the pentane isomers tend to quickly phase separate
from
the other components within the B-side stream. This phase separation
negatively
impacts the properties of the foam board being produced, because the expansion
of
the board, via the pentane isomers, is less efficient.
In another alternative, the B-side stream does not contain pentane
isomers, rather, the pentanes are added as a third stream to the B-side
stream, at
high-pressure, just before impingement with the isocyanate, i.e., the A-side
stream.
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In this high-pressure mixing method, it is difficult to size a static mixer to
effectively mix the A-side, B-side, and pentane isomers at the various output
rates
that may be required for boards of different thicknesses and different
production
rate. If the static mixer is too small, backpressure within the system will
undesirably increase and the components may not be completely mixed. If the
static mixer is sized too large, the mixing efficiency will decrease for low-
output
formulations. Static mixers of different sizes may be employed, but this is
not cost
effective.
Additionally, when pentane isomers such as n-pentane or isopentane
are employed as the blowing agents, prior art processes may require
surfactants in
an amount from about 0.5 to about 5.0 pphp and emulsifiers/solubilizers in an
amount from about 0 to about 30 pphp. As mentioned surfactants, solubilizers,
and emulsifiers tend to plasticize the foam produced and, therefore, reduced
amounts of these components in the foam formulation is desirable.
Thus, a method for mixing pentane isomers with polyurethane reagents
for the production of foam boards that allows for wide flexibility in the
ratios and
amounts of pentane isomers that may be used and allows for a reduction in the
amount of flammable pentane blowing agents present within a B-side stream at
any given time is desirable. While the need particularly addressed by the
process
and apparatus of the present invention concerns the incorporation of pentane
isomers into the polyol components, it should be appreciated that the present
invention allows for the incorporation of blowing agents, other than pentane
isomers, into the polyol component.
Generally, high-pressure mixing of the A- and B-sides will produce fine
cell foam more efficiently and with better physical properties than low-
pressure
mixing of the A- and B-sides. Thus, the present invention focuses on the low-
pressure mixing of blowing agents to form the B-side stream, while maintaining
the high-pressure mixing of the A- and B-side streams.
SUMMARY OF THE INVENTION
A method for manufacturing polyurethane and polyisocyanurate foams
comprising the steps of charging at least one blowing agent and a polyol
component to an in-line continuous mixer, wherein the at least one blowing
agent
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and the polyol component are continuously charged in separate streams advanced
at predetermined flow rates chosen to bring about a desired ratio of blowing
agent
to polyol component within the in-line continuous mixer.
A method for manufacturing polyurethane and polyisocyanurate foams
comprising the steps of charging at least one blowing agent and a polyol
component to an in-line continuous mixer, at a pressure of less than about
3,400
kPa, to form a B-side stream of polyurethane reagents contacting the B-side
stream
of polyurethane reagents with an isocyanate component at a dispensing head to
provide a foam formulation, and dispensing the foam formulation from the
dispensing head, wherein the residence time of the B-side stream of
polyurethane
reagents, from its exit from the in-line continuous mixer to its exit from the
dispensing head as part of the foam formulation, is less than about 5 minutes.
A method for manufacturing polyurethane and polyisocyanurate foams
comprising the steps of charging at least one blowing agent and a polyol
component to an in-line continuous mixer at a pressure of less than about
3,400
kPa, wherein the at least one blowing agent and the polyol component are
continuously charged in separate streams advanced at predetermined flaw rates
chosen to bring about a desired ratio of blowing agent to polyol component
within
the in-line continuous mixer, mixing the at least one blowing agent and the
polyol
component in the in-line continuous mixer to dissolve or emulsify the blowing
agent in the polyol component and thereby provide a B-side stream of
polyurethane reagents, contacting the B-side stream of polyurethane reagents
with
an isocyanate component at a dispensing head to provide a foam formulation,
and
dispensing the foam formulation from the dispensing head, wherein the
residence
time of the B-side stream of polyurethane reagents, from its exit from the in-
line
continuous mixer to its exit from the dispensing head as part of the foam
formulation, is less than about 5 minutes.
The in-line continuous mixer may be a static or dynamic mixer and, in a
preferred embodiment, the step of mixing the at least one blowing agent with
the
polyol component is carried out in an in-line dynamic mixer. The step of
mixing
the polyol and blowing agent may also be carried out in more than one in-line
continuous mixer, with one or more in-line dynamic mixer, and/or one or more
in-
line static mixer.
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In preferred embodiments, at least one pentane isomer serves as the
blowing agent for the foam manufacturing process. While the apparatus and
method of the present invention may be employed using any suitable blowing
agent, advantages of the present apparatus and method are particularly
realized
5 when blowing agents such as pentane isomers are employed because pentane
blowing agents are not very soluble in the polyol and isocyanate components
used
to produce foam boards and, thus, they tend to phase separate from these
components. The present invention more adequately mixes the blowing agents,
particularly pentane blowing agents, with the polyol and isocyanate components
to
ensure efficient expansion of the foam board. Also, the fact that an in-line
continuous mixer is employed at low-pressure allows for flexibility in the
ratios
and amounts of the various blowing agents that can be used and incorporated
into
the polyol mixture stream. Additionally, mixing in an in-line continuous mixer
may reduce the need for the use of solubilizers or emulsifiers or surfactants
that
negatively impact end product performance and inerease manufacturing costs.
The
present invention may also reduce - by about 5 % - the amount of blowing
agents necessary to produce a polyurethane foam of a desired density. The in-
line
continuous mixing of the at least one pentane isomer, at low-pressure, also
results
in smaller cells within the polyurethane or polyisocyanurate foam, thereby
yielding
foam having better insulation properties.
The present invention also provides an apparatus for manufacturing
polyurethane and polyisocyanurate foams that employ flammable blowing agents.
The apparatus includes an in-line continuous mixer having a volume in the
range
of from about 1 liter to about 40 liters. A ventilation system encloses the in-
line
continuous mixer to collect any flammable blowing agents that may escape the
in-
line continuous mixer during operation thereof. Notably, the volume of the in-
line
continuous mixer is smaller that the volume o~f prior art devices utilized to
incorporate blowing agents into the foam formulation. Therefore, the
ventilation
system is also smaller, less costly, and easier to maintain. Also, should an
accident
occur that would ignite the flammable blowing agents, the small size of these
elements of the apparatus help to minimize the damage that could occur.
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a chart depicting a preferred process according to the present
invention.
Fig. 2 is a particular embodiment of an in-line continuous mixer for use
in accordance with the present invention.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
Polyurethane and polyisocyanurate foams are produced in a continuous
manufacturing process by contacting an "isocyanate component" with a "polyol
component." The "isocyanate component" generally includes an isocyanate or
polyurethane prepolymer. "Polyol component" generally includes a polyol and/or
glycol, and, usually, small amounts of water, but "polyol component" refers to
any
isocyanate-reactive component as generally known in the art, including, for
example, noon-limiting example, diols, glycols, polyols, water, and primary
and
secondary amines. A blowing agent is typically dissolved in or emulsified in
the
polyol component. The isocyanate and polyol components are contacted and
dispensed onto a moving form, where they react and produce heat. The evolving
heat and the chemical reactions taking place serve to bring about the foaming
of
the board. Particularly, the heat causes the blowing agents, such as pentanes,
which are added as liquids, to volatize and evolve gas that becomes suspended
in
the reaction mixture to produce a foam. Water, added purposefully or as part
of
the polyol component, reacts with isocyanate to evolve carbon dioxide (C02),
which is also suspended in the reaction mixture to produce a foam.
Suitable isocyanates are generally known in the art. Useful isocyanates
include aromatic polyisocyanates such as diphenyl methane, diisocyanate in the
form of its 2,4'-, 2,2'-, and 4,4'-isomers and mixtures thereof, the mixtures
of
diphenyl methane diisocyanates (MDI) and oligomers thereof known in the art as
"crude" or polymeric MDI having an isocyanate functionality of greater than 2,
toluene diisocyanate in the form of its 2,4' and 2,6'-isomers and mixtures
thereof,
1,5-naphthalene diisocyanate, and 1,4'diisocyanatobenzene. Preferred
isocyanate
components include polymeric Rubinate 1850 (Huntsmen Polyurethanes),
polymeric Mondur 489N (Bayer), and Lupranate M70R (BASF).
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Suitable polyol components are well known in the art. The terms
"polyol component" or "polyol components" include diols, polyols, and glycols,
which may contain water as generally known in the art. As mentioned, primary
and secondary amines may be suitable "polyol components. Examples of polyols
include polyether polyols and polyester polyols. Useful polyester polyols
include
phthalic anhydride based PS-2352 (Stepen), phthalic anhydride based polyol PS-
2412 (Stepen), and teraphthalic based polyol 3522 (Kosa). Useful polyether
polyols include those based on sucrose, glycerin, and toluene diamine.
Examples
of glycols include diethylene glycol, dipropylene glycol, and ethylene glycol.
Of
these, a particularly preferred glycol is diethylene glycol. Suitable primary
and
secondary amines include, without limitation, ethylene diamine, and
diethanolamine.
Suitable blowing agents are also well known in the art. Fully
halogenated chlorofluorocarbons, particularly trichlorofluoromethane (CFC-11),
have been widely used as blowing agents. However, CFC's are believed to cause
depletion of ozone in the atmosphere and are, therefore, currently being
replaced
by blowing agents having zero ozone depletion potential. These blowing agents
include alkanes and cycloalkanes such as n-pentane, isopentane, cyclopentane,
and
mixtures thereof. Pentane isomers are particularly desirable blowing agents
because they meet government mandates for the use of blowing agents having
zero
ozone depletion potential. Another alkane that meets government standards for
its
zero ozone depletion potential includes isobutane, and small amounts of
isobutane
may be employed as a blowing agent according to this invention.
As mentioned, particular advantages are realized when at least one
pentane isomer is employed as a blowing agent in the present invention. A
mixture of pentane isomers and other blowing agents may be employed. Thus, the
present method allows for the addition of auxiliary blowing agents and gases.
"Auxiliary blowing agents" as used herein include blowing agents and gases
other
than pentane isomers that may be used in a foam formulation. Other gases that
could be added include nitrogen, air, carbon dioxide, and the noble gases.
Notably, the present invention also allows for the addition of liquid carbon
dioxide,
which could eliminate the need for added water in the foam formulation. This
addition could decrease the cost of foam production by at least about 1%.
Also,
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the carbon dioxide, when it exits the mix head, as will later be described,
will tend
to froth the material and yield smaller cells, less splashing, and better
distribution
of the foam at the laminator. U.S. Patent Nos. 5,367,000, 5,444,101, and
5,866,626 are incorporated herein by reference for the purpose of disclosing
various useful pentane isomer blowing agent mixtures.
Catalysts are employed to initiate the polymerization reaction of the
isocyanate component with the polyol component. Suitable catalysts are known
in
the art. Examples include salts of alkali metals of carboxylic acids and
phenols,
such as, for example potassium octoate; mononuclear or polynuclear Mannich
bases of condensable phenols, oxo-compounds, and secondary amines, which are
optionally substituted with alkyl groups, aryl groups, or aralkyl groups;
tertiary
amines, such as pentamethyladiethylene triamine (PMDETA), triethyl amine,
tributyl amine, N-methyl morpholine, and N-ethyl morpholine; basic nitrogen
compounds, such as tetra alkyl ammonium hydroxides, alkali metal hydroxides,
alkali metal phenolates, and alkali metal acholates; and organic metal
compounds,
such as tin(II)-salts of carboxylic acids, tin(I~-compounds, and organo lead
compounds, such as lead naphthenate and lead octoate.
Surfactants, emulsifiers, and/or solubilizers may also be employed in
the production of polyurethane and polyisocyanurate foams in order to increase
the compatibility of the blowing agents with the isocyanate and polyol
components. Suitable surfactants are known in the art.
Surfactants serve two purposes. First, they help to emulsify/solubilize
all the components so that they react completely. Second, they promote cell
nucleation and cell stabilization. Typically, the surfactants are silicone co-
polymers
or organic polymers bonded to a silicone polymer. Although surfactants can
serve
both functions, a more cost effective method to ensure
emulsification/solubilization is to use enough emulsifiers/solubilizers to
maintain
emulsification/solubilization and a minimal amount of the surfactant to obtain
good cell nucleation and cell stabilization. Examples of surfactants include
Pelron
surfactant 9868, Goldschmidt surfactant B8469, and CK-Witco's L 6912. U.S.
Patent Nos. 5,686,499 and 5,837,742 are incorporated herein by reference to
show
various useful surfactants.
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Suitable emulsifiers/solubilizers are known in the art. Examples of
emulsifiers for use in the present invention include DABCO Kitane 20AS (Air
Products), and Tergitol NP-9 (nonylphenol + 9 moles ethylene oxide).
Flame Retardants are commonly used in the production of polyurethane
and polyisocyanurate foams, especially when the foams contain flammable
blowing
agents such as pentane isomers. Useful flame retardants are known in the art,
Examples of flame retardants include tri(monochloropropyl) phosphate, tri-2
chloroethyl phosphate, phosphonic acid, methyl ester, dimethyl ester, and
diethyl
ester. U.S. Patent No. 5182309 is incorporated herein by reference to show
useful
blowing agents.
As is generally known in the art, other additives may be employed in
the production of polyurethane and polyisocyanurate foams. Other additives
include, for example, dyes, fillers, fungicides, and anti-static substances.
The blowing agent preferably is mixed well with the other polyurethane
reagents. A good mix ensures an adequate and efficient expansion (foaming) and
is more likely to produce a foam that exhibits fine cell structure, good
thermal
performance, and satisfactory dimensional stability. Preferably, the blowing
agents
are solubilized or emulsified in the polyurethane reagents.
The isoeyanate component and the polyol component are maintained as
separate component streams until being brought together at a dispensing head
where they are mixed and dispensed into a moving form. They then react and
expand to produce a continuous foam product within this form. The isocyanate
component is provided in an "A-side" stream. The A-side stream typically only
contains the isocyanate component, but, in addition to isocyanate components,
the
A-side stream may contain flame-retardants, surfactants, blowing agents and
other
non-isocyanate-reactive components. The polyol component is provided in a "B-
side" stream, which may additionally contain other isocyanate reactive
compounds
(such as water), flame retardants, catalysts, emulsifiers/solubilizers,
surfactants,
blowing agents, and other ingredients as mentioned above.
"Polyol mixture" refers to a mixture containing at least a polyol
component and, optionally, any desired catalyst, surfactant,
emulsifier/solubilizer,
flame retardant, blowing agent, fillers, fungicides and anti-static
substances. "B-
side stream of polyurethane reagents" or simply "B-side" refers to a mixture
of the
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polyol mixture and the blowing agents desired for production of the foam.
Thus,
the "polyol mixture" is mixed with blowing agent to form the "B-side," and the
polyol mixture will generally not contain blowing agent. Rather, the B-side
stream
that results from mixing blowing agent with the polyol mixture will contain
the
5 desired blowing agents.
"A-side stream of polyurethane reagents" or simply "A-side" refers to a
mixture of at least an isocyanate component and, optionally, flame-retardants,
surfactants, blowing agents, and other non-isocyanate-reactive components. The
term "A-side" includes a prepolymer of isocyanate and polyol components as is
10 known in the art.
The present invention focuses on the manner in which blowing agents
are incorporated into the B-side stream and the manner in which the resultant
B-
side stream is subsequently brought into contact with the A-side stream and
dispensed to produce a foam product. A polyol mixture is provided and mixed
with desired blowing agents in an in-line continuous mixer to form a B-side
stream
of polyurethane reagents. This B-side stream is subsequently mixed with the A-
side stream of polyurethane reagents to form a polyurethane or
polyisocyanurate
foam. More particularly, the blowing agents are added to the polyol mixture at
low-pressure, and the resultant B-side stream of polyurethane reagents is
subsequently advanced, at high-pressure, to contact the A-side stream
proximate a
dispensing head. Typically, the A-side and B-side streams are mixed and
dispensed
onto a moving bottom facing sheet that carries the resultant mixture into a
restraint rise or free rise laminator in which the mixture reacts and expands
to
provide the desired foam, although they may be dispensed in another manner for
different applications. Notably, the B-side is mixed with the A-side and
dispensed
into the laminator within about 1.5 minutes from the time when the B-side
exits
the in-line continuous mixer.
This process is represented in Fig. 1 by the schematic generally
designated by the numeral 10. The various arrows represent streams of reagents
flowing through pipes in a foam forming apparatus. The reagents within the
process are identified hereinbelow with reference to the numerals drawn to
those
arrows.
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As shown in Fig. 1, the polyol mixture 12 is contacted with blowing
agent 14 in an in-line continuous mixer 16 that serves to dissolve or emulsify
blowing agent 14 within polyol mixture 12 and thereby form a B-side stream 18
of
polyurethane reagents. The resultant B-side stream 18 exiting in-line
continuous
mixer 16 is fed through heat exchanger 20 and then through precision metering
pump 22 to contact an A-side stream 24 of polyurethane reagents at dispensing
head 26. Dispensing head 26 mixes the A-side and B-side streams 24, 18 and
dispenses them into a laminator 28, where the dispensed mixture reacts and is
expanded via blowing agents 14 to provide the desired polyurethane or
polyisocyanurate foam.
Polyol mixture 12 contains polyol component and optional components
as mentioned above. The various components of polyol mixture 12 may be mixed
by conventional methods (not shown). Polyol mixture 12 is generally maintained
at a temperature of about 10°C to about 35°C and a pressure of
less than about
3400 kPa as it is advanced toward the in-line continuous mixer 16. Preferably,
polyol mixture I2 is maintained at about 15 °C to about 25 °C
and about 100 kPa to
about 860 kPa. More preferably, polyol mixture 12 is advanced a pressure less
than at about 500 kPa.
The types and amount of optional components in polyol mixture 12 that
may be useful in the production of a desired foam are well known in the art.
Generally, the amount of catalyst present in polyol mixture 12 will range from
about 0.1 to about 10.0 pphp (parts per hundred polyol). The amount of flame-
retardants will range from about 0 to about 25 pphp. The amount of water will
range from about 0.1 to about 2.0 pphp.
In the present process, blowing agent 14 is mixed with polyol mixture
I2 in such a manner that a lesser amount of surfactants and/or
emulsifiers/solubilizers will typically be required in polyol mixture 12, if
at all.
Although some amount of surfactant is needed for cell nucleation and cell
stabilization, emulsifiers, solubilizers, and surfactants tend to plasticize
the foam
produced, which reduces the compressive strength and dimensional stability of
the
foam. Various types of blowing agents may be mixed with polyol mixture 12, in
varying ratios, and still yield an emulsification, with either a lesser amount
or no
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emulsifiers/solubilizers, and the minimal amount of surfactants. Some blowing
agents, such as isopentane, may not be very soluble with the other B-side
components and, therefore, require emulsifiers/solubilizers and/or increased
levels
of surfactants to make high quality foams.
As mentioned, prior art processes may require surfactants in an amount
from about 0.5 to about 5.0 pphp and emulsifiers/solubilizers in an amount
from
about 0 to about 30 pphp. Practicing the process of the present invention may,
in
comparison, require surfactants in an amount from about 0.5 to about 3.0 pphp
and emulsifiers/solubilizers in an amount from about 0 to about 5.0 pphp.
Surfactants, solubilizers, and emulsifiers tend to plasticize the foam
produced and,
therefore, reduced amounts of these components in the foam formulation is
desirable.
The flow rate of the polyol mixture may be varied according to the
desired mix ratio of the polyol mixture to the blowing agents. More
particularly,
the mix ratio will be based upon the desired ratio of polyol components to
blowing
agent as is known in the art.
Blowing agent 14 is advanced and fed to in-line continuous mixer 16 at
a temperature of from about 10°C to about 35°C and a pressure of
less than about
3400 kPa. Preferably, blowing agent 14 is maintained at about 15°C to
about
25°C and about 100 kPa to about 860 kPa. More preferably, blowing agent
l4is
advanced at a pressure less than about 500 kPa. The flow rate of blowing agent
14
is adjusted to achieve different desired ratios of blowing agent to polyol
component within the B-side stream 18 of polyurethane reagents that is created
at
in-line continuous mixer 16.
Blowing agent 14 may be provided as a mixture of blowing agents. If a
mixture of blowing agents is desirable, the various blowing agents within
blowing
agent 14 may be mixed by conventional methods. Optionally, in order to allow
for
accurate measurement of the amount of each blowing agent added, each i blowing
agent is added to in-line continuous mixer 16 as a separate stream.
Blowing agent 14 is advanced through heat exchanger 30 to low-
pressure pump 32. Low-pressure pump 32 pumps blowing agent 14 through flow
meter 34 toward three-way valve 36. Three-way valve 36 may be operated to
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either allow blowing agent 14 to advance toward in-line continuous mixer 16 or
to
direct blowing agent 14 through a recycle line indicated at numeral 38, which
reconnects to the system at a position before heat exchanger 30. If blowing
agent
14 is being recycled through this closed loop, check valve 40 is closed. Heat
exchanger 30 is employed to prevent the buildup of heat within the stream of
blowing agents 14 during recycling.
Three-way valve 36 is operated to force blowing agent 14 through
recycle line 38 whenever a foam board is not being produced. When a foam board
is to be produced, three-way valve 36 is opened to allow blowing agent 14 to
~ advance through line 39 toward in-line continuous mixer 16.
Flow meter 34 measures the mass flow rate of blowing agent 14. This
mass flow rate will be directly related to the ratio of blowing agent 14
within B
side stream 18 and, thus, measurement of the mass flow rate, via flow meter
34,
allows for adjustment of the amount of blowing agent 14 within the B-side
stream
18. This will be described more fully hereinbelow.
The ratio of polyol components to blowing agents to be mixed in in-line
continuous mixer 16 will depend upon the desired properties of the foam to be
produced. Generally, when greater amounts of blowing agents are employed, the
foam produced will be lower in density, while, when lesser amounts of blowing
agents are employed, the foam produced will be higher in density. Those of
ordinary skill in the art will appreciate what types and amounts of blowing
agents
are useful in the production of a desired foam product. The blowing agent to
polyol component mass ratio will preferably range from 1:10 to 1:4, more
preferably, from 1:7 to 1:5.
Blowing agent 14 is typically introduced to in-line continuous mixer 16
as a liquid. The preferred blowing agents include at least one pentane isomer
and,
optionally, may contain auxiliary blowing agents as defined above. Notably,
auxiliary blowing agents are typically added to in-line continuous mixer 16 as
a
separate stream from the pentane isomer. A particularly useful auxiliary
blowing
agent is carbon dioxide (C02). By adding C02 as an auxiliary blowing agent,
the
amount of water present in the polyol mixture may be decreased. Water is
usually
added because it forms C02 through reaction with the other foam forming
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14
reagents, thus, the addition of C02 as an auxiliary blowing agent decreases
the
need for water, decrease production costs.
Polyol mixture 12 and blowing agent 14 are contacted and mixed
within in-line continuous mixer 16. An "in-line continuous mixer" refers to a
mixer
that allows for the continuous introduction and removal of components
therefrom
so as to realize no substantial net gain or loss of volume within the mixer.
That is,
the volumetric flow rate of components entering the in-line continuous mixer
is
substantially equal to the volumetric flow rate of the mixture exiting the in-
line
continuous mixer. "In-line continuous mixers" to preferably emulsify and blend
polyol mixture 12 and the blowing agent 14. Additionally, during production of
a
foam board, in-line continuous mixer 16 does not serve as a general supply
tank
for B-side stream 1S, but rather continuously creates B-side stream 1S from
polyol
mixture 12 and blowing agent 14 as they are advanced through the process.
These
mixers are distinguishable from batch mixers.
In-line continuous mixer 16 is preferably employed to mix polyol
mixture 12 and blowing agent 14 at the low-pressure side of the process, i.e.,
before precision metering pump 22. Employment of in-line continuous mixer 16
on the low-pressure side allows for easier adjustment in the ratios and
amounts of
blowing agents used in relation to the ingredients within the polyol mixture
stream
12. In-line continuous mixer 16 may be employed on the high-pressure side, but
this is not preferred. It has been found that good mixing and accurate mix
ratios
are more difficult and less precise in high-pressure mixing operations, and,
additionally, mixers in high-pressure systems must be more structurally sound
and
are thus more expensive. By using an in-line continuous mixer 16, and
employing
this mixture on the low-pressure side of the system, the mix ratios of the
ingredients can be easily adjusted, through the use of flow meters, in a
continuous
process.
Suitable in-line continuous mixers include dynamic mixers. Generally,
dynamic mixers employ moving blades or impellers to impart motion to the
fluids
within the mixer and thereby produce the mixing effect. Useful dynamic mixers
include pin-impeller mixers, turbine mixers, double helix mixers, and radial
axial
mixers. Suitable in-line continuous mixers also include static mixers.
Generally,
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static mixers consist of a pipe containing a series of specially shaped
stationary
blades, which divide and twist the flowing stream of fluid within the pipe so
that
mixing proceeds by a distributive process.
Preferably, the volume of the in-line continuous mixer 16 is from about
5 1 liter to about 40 liters. More preferably, the volume of the in-line
continuous
mixture is generally from about 3.5 liters to about 7.5 liters. In-line
continuous
mixer 16 is of relatively small volume as compared to apparatus used in the
prior
art for mixing blowing agents with polyol components. The small volume of in-
line continuous mixer 16 is beneficial because, as will be described below,
when
10 flammable blowing agents such as pentane isomers are employed, in-line
continuous mixer 16 may be enclosed within a ventilation system that exhausts
any flammable blowing agent that escapes from the system.
The use of an in-line continuous mixer provides advantages in a
polyurethane or a polyisocyanurate foam board production process.
Particularly,
15 the flow rate of the polyol mixture and blowing mixtures may be varied
according
to the desired mix ratio of the polyol mixture to the blowing agents. Also,
with
proper mixing, the amount of surfactants, emulsifiers, and solubilizers
required to
assure adequate mixing of blowing agents, particularly pentane isomers, with
the
polyol mixture can be reduced. Additional safety features can also be added to
the
process due to the fact the in-line continuous mixer is relatively smaller
than the
mixing apparatus of the prior art, and the in-line continuous mixer can be
enclosed
in a ventilation system.
Adequate mixing of the polyol mixture with the blowing agents, i.e.,
mixing that deters phase separation, can be empirically determined through
experimental runs without undue experimentation. Notably, for achieving
desired
foam board properties, the empirical method will be appreciated by those of
ordinary skill in the art.
A particularly useful in-line continuous mixer is a dynamic pin-impeller
mixer. A cross-sectional view of a pin-impeller mixer that may be employed for
in-
line continuous mixer 16, is provided in Fig. 2, and designated generally by
the
numeral 100. Pin-impeller mixer 100 includes a chamber 102 to which polyol
mixture 12 and blowing agent 14 are introduced. Chamber 102 includes pin
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16
protrusions 104, which extend inwardly from its outer walls, and impeller 106
having pin protrusions 108 that extend outwardly from impeller 106 between pin
protrusions 104. A motor 110 is operatively connected to impeller 106, and
serves
to rotate impeller 106. Polyol mixture streams 12, and blowing agent 14 added
to
chamber 102 are subjected to high amounts of shear by the rotation of motor
110
and, as a result, blowing agent 14 is mixed with polyol mixture 12 to a
greater
extent than heretofore realized in the art.
Pin-impeller mixer 100 preferably has a volume of from about liters to
about 40 liters, and, more particularly, from about 3.5 to about 7.5 liters.
The
contents of the pin-impeller mixer 100, i.e., blowing agent 14 and polyol
mixture
12 are preferably kept at a temperature of from about 10°C to about
35°C, and,
more preferably, from about 15°C to about 25°C. Motor 110
rotates impeller 106
at a speed of about 500 to about 3,600 revolutions per minute (rpm), and, more
preferably, at a speed of about 1,000 to about 2,500 rpm.
The mixing that occurs in in-line continuous mixer 16 may alternatively
be earried out in multiple in-line continuous mixers. That is, polyol mixture
12
and blowing agent 14 may be first introduced to in-line continuous mixer 16
and
mixed therein, and, thereafter, may be advanced to a second in-line continuous
mixer (not shown). Third and fourth in-line continuous mixers may also be
employed. Multiple in-line continuous mixers may be arranged in series and
serve
to increase the effectiveness of the mixing function. After mixing, whether in
a
single or multiple in-line continuous mixers, the resultant B-side stream 18
is
quickly advanced to and dispensed from dispensing head 26 along with A-side
stream 24. Particularly, the residence time of B-side stream 18, from its exit
from
in-line continuous mixer 16 to its exit from dispensing head 26, is less than
about
1.5 minutes. This will be disclosed more fully below.
Polyol mixture 12 and blowing agent 14, when mixed by impeller mixer
100, provide the B-side stream 18. B-side stream 18 exits pin-impeller mixer
100
at outlet 112. B-side stream 18 exits at a flow rate that is dependant upon
the
entering flow rates of polyol mixture 12 and blowing agent 14. As mentioned,
the
flow rates of polyol mixture 12 and blowing agent 14 depend upon the desired
ratio of blowing agent to polyol component.
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17
During foam board production, in-line continuous mixer 16 constantly
receives polyol mixture 12 and blowing agent 14 and mixes them to form B-side
stream 18 and constantly advances this B-side stream to the high-pressure side
of
the system. Referring now back to Fig. 1, the B-side stream 18 exits in-line
continuous mixer 16 and is fed to heat exchanger 20. Heat exchanger 20
preferably has a volume of from about 7.5 liters to about 75 liters, and, more
preferably, from about 7.5 to about 20 liters.
From heat exchanger 20, B-side stream 18 is fed to precision metering
pump 22. Precision metering pump 22 advances B-side stream 18 through flow
meter 42, and thereafter through three-way valve 44. As shown in Fig. l, three
way valve 44 may be operated to allow B-side stream 18 to advance to
dispensing
head 26 or, in the alternative, may be operated to force B-side stream 18 back
to
in-line continuous mixer 16 through a recycle line indicated at numeral 46. As
with three-way valve 36, the direction that B-side stream takes through three-
way
valve 44, whether for advancement of B-side stream 18 to dispensing head 26 or
for the recycling thereof to in-line continuous mixer 16, depends upon whether
or
not a foam board is being produced. When a board is being produced, B-side
stream 18 is directed toward dispensing head 26. When a board is not being
produced, B-side stream 18 is directed through recycle line 46.
Precision metering pump 22 operates to advance B-side stream 18 at a
set flow rate regardless of the backpressure within the system. Thus, when
three-
way valve 44 is open so as to permit B-side stream to advance towards
dispensing
head 26, B-side stream 18 advances at a pressure of between about 6,800 kPa to
about 20,000 kPa, and, more preferably, at a pressure between about 13,500 kPa
to about 17,000 kPa. This large pressure is due to the amount of backpressure
encountered in bringing A-side stream 24 and B-side stream 18 together at
dispensing head 26 and dispensing them into laminator 28. Despite this
backpressure, precision metering pump 22 advances B-side stream at a constant
flow rate and therefore the pressure increase is realized. The B-side is said
to be
advanced through the high-pressure side of the system. When three-way valve 44
is open so as to force B-side stream to recycle, precision metering pump 22
feeds B-
side stream 18 at the same set flow rate; however, there is little back
pressure, and
B-side stream recycles at low-pressure, at from about 100 kPa to about 3400
kPa.
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1$
Flow meter 42, together with flow meter 34, facilitates the adjustment
of the mix ratio of the blowing agent within the B-side stream. Particularly,
flow
meter 42 measures the mass flow rate of the B-side stream 18 flowing
therethrough, and, based upon the mass flow rate across flow meter 42, the
flow
rate of blowing agent 14 across flow meter 34 can be adjusted accordingly to
provide the desired end ratio of blowing agent within the B-side stream.
In an alternative embodiment, B-side stream 18 is split into multiple
streams after exiting heat exchanger 20. Each stream includes a precision
metering pump, flow meter, three-way check valve, and recycle line as
described
above. The various recycle lines would preferably join together before being
introduced back into the in-line continuous mixer as one stream. In such an
embodiment, the A-side stream 24 would also be split into an equal number of
streams such that each separate B-side stream, when advanced at high-pressure
toward contact with an associated A-side stream, would advance to a separate
dispensing head. This embodiment is useful when, due to the dimensions of the
laminator, multiple dispensing heads must be used to fill the laminator.
When the blowing agents employed are flammable blowing agents, such
as pentane isomers, in-line continuous mixer 16 is preferably enclosed by a
ventilation system, generally represented in Fig. 1 by the numeral 50.
Ventilation
system 50 serves to collect any flammable blowing agent that may escape from
the
system so as to minimize any safety concerns. As can be seen, ventilation
system
50 includes an enclosure 52, generally represented by the dashed lines in Fig.
1.
Enclosure 52 completely encloses the majority of the process components that
contain the flammable blowing agents, although the blowing agents are
initially
introduced from a position outside enclosure 52, and B-side stream 18, which
contains the flammable blowing agents, ultimately exits enclosure 52 to
advance to
dispensing head 26. Enclosure 52 is air tight and preferably explosion proof
for
added safety. One or more exhaust fans 54 communicate with the interior of
enclosure 52 and are connected to exhaust duct 56. Fans 54 and duct 56 serve
to
collect and remove any flammable blowing agents that may escape from the
system and into enclosure 52.
Notably, in-line continuous mixer 16 is of much smaller volume that the
tanks and other apparatus of the prior art used for incorporating blowing
agents
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19
into a polyol mixture. Therefore, the use of a ventilation system 50 is very
practical, because it will not have to be of a large size. The present
apparatus and
process is safer than prior art processes in that the amount of flammable
blowing
agent present in a B-side stream of polyurethane reagents at any given time is
much smaller than the amount generally present in prior art processes.
A-side stream 24 is fed through a heat exchanger 58 to high-pressure
pump 60. High-pressure pump 60 advances A-side stream 24 through flow meter
62, and thereafter through three-way valve 64. As can be seen in Fig. 1, three-
way
valve 64 may be operated to allow A-side stream 24 to advance to dispensing
head
26 or, in the alternative, may be operated to force A-side stream 24 back to a
position before heat exchanger 58 through a recycle line indicated at numeral
66.
As with three-way valve 36, the operation of three-way valve 64, whether for
advancement of A-side stream 24 to dispensing head 26 or for the recycling
thereof, depends upon whether or not a foam board is being produced. When a
board is being produced, three-way valve 64 is opened to allow A-side stream
24 to
advance to dispensing head 26. When a board is not being produced, three-way
valve is opened to force A-side stream 24 through recycle line 66.
When producing board, A-side stream 24 of polyurethane reagents is
advanced through high-pressure pump 60 and flow meter 62, and brought into
contact with B-side stream 18 on the high-pressure side of the process at
dispersing
head 26. A-side stream 24 is preferably maintained at a temperature of from
about
15°C to about 45°C and a pressure from about 6,800 kPa to about
20,000 kPa.
Mare particularly, the temperature is maintained at about 25 ° C to
about 40 ° C and
a pressure from about 13,500 kPa to about 17,000 kPa. The flow rate for A-side
stream 24 is chosen based upon the desired ratio of polyol components to
isocyanate in the end product dispensed to the laminator. As mentioned with
respect to the amounts of blowing agent and polyol components employed, the
ratio of polyol components in the B-side to isocyanate components within the A-
side will depend upon the desired properties of the foam to be produced.
The ratio of the equivalence of NCO groups (provided by the isocyanate
or "A-side") to all polyol components is called the index. When the NCO
equivalence to the polyol equivalence is equal, then the index is 1.00 or 100,
and
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the mixture is said to be stoiciometrically equal. As the ratio of NCO
equivalence
to polyol equivalence increases, the index increases. Above an index of about
150
the material is generally known as a polyisocyanurate foam, even though there
are
still many polyurethane linkages. When the index is below about 150, the foam
is
5 generally known as a polyurethane foam even though there may be some
isocyanurate linkages.
An isocyanurate is a trimeric reaction product of three isocyanates
forming a six-membered ring. Isocyanurates are characterized by their good
thermostability and excellent dimensional stability. However, they also tend
to be
10 friable when used at high indexes, hence index ratios of 200 to 350 are
preferred
for isocyanurate foams.
A-side stream 24 is brought into contact with B-side stream 18 at
dispensing head 26. Dispensing head 26 is typically an impingement mixer,
wherein A-side stream 24 and B-side stream 18 forcefully contact one another,
at
15 high-pressure, and are thereafter dispensed from dispensing head 26 and
into
laminator 28. At laminator 28, the foam formulation of the various components
of
A-side stream 24 and B-side stream 18 interact to produce a foam board as
commonly known in the art.
As mentioned, A-side stream may be split into multiple streams when
20 multiple dispensing heads are necessary. The A-side stream is split before
the
high-pressure pump, and each separate A-side stream has its own high-pressure
pump, flow meter, check valve and recycle line, and each A-side stream
advances
towards contact with an associated B-side stream at an associated dispensing
head.
To ensure that the blowing agents do not phase separate from the other
components within the B-side stream, and more particularly, from the polyol
components within the B-side stream, the residence time of the B-side stream,
from
its exit from the in-line continuous mixer to its impingement with the A-side
stream at the dispensing head, is preferably controlled. Particularly, the
residence
time of the B-side stream within the process is preferably less than 5 minutes
from
its exit from the in-line continuous mixer to its introduction to the
laminator. In
other words, the residence time of the B-side stream of polyurethane reagents,
from it exit from the in-line continuous mixer to its exit from the dispensing
head
as part of a foam formulation is preferably less than 5 minutes. More
preferably,
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21
this residence time is less than 1.5, even more preferably less than 60
seconds, and
even more preferably less than 30 seconds.
In order to demonstrate the practice of the present invention, the
following examples have been prepared and tested. The examples should not,
however, be viewed as limiting the scope of the invention. The claims will
serve to
define the invention.
EXAMPLES
Example 1
Formulation
Polyol Mixture
Stepan Polyol 2352 (pbw) 100
Pelron Catalyst 9540A (Potassium Octoate) (pbw) 4.4
Pelron Amine Catalyst 9529 (pbw) 0.55
Goldschmidt Surfactant B8469 (pbw) 3
Rhodia Flame Retardant AB 80 (FBP) (pbw) 12.5
Water (pbw) 0.5
Blowing A
Exxsol Pentane Blend 1600 (pbw) 25.4
A-Side
Total Huntsman Polyurethanes Rubinate 1850 (pbw) 212.08
Index 300
A/B ratio 1.45
Processing Variables
No. mixheads 2
Top laminator temperature (°F) 140
Bottom laminator temperature (°F) 133
A-Side temperature (°F) 88
B-side temperature (°F) 82
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22
Line speed (ft./min.) 93.2
A-Side pressure (psi) 2000
B-Side pressure, high-pressure side (psi) 1737
B-Side, low-pressure side (psi) 60 (approx)
A-Side per mixhead (lbs./min) 26.1
B-Side per mixhead (lbs./min) 18.2
In-line mixer setting 50%
rpms 1830
Machine Reactivi
Cream time (sec) 5
Gel time (sec) 13
Tack free time (sec) 37
End of rise time (sec) 58
Physical Properties of Board
Board Thickness (inches) 1.50
Core density (pcf) 1.69
Initial k-factor (Bru in./h ft2 F) 0.14
Compressive Strength (psi) 23.2
Huntsman Dimvac test at -25C (14 days)
Width -0.5
Length -0.3
Closed cell content (%) 90.9
Average cell size, ~,m n/a
Butler Chimney test weight retained (%) 90.3 - 91.4
Example 2
Formulation
Polyol Mixture
Stepan Polyol 2352 (pbw) 100
Pelron Catalyst 9540A (Potassium Octoate) (pbw) 4.6
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Pelron Amine Catalyst 9529 (pbw) 0.55
Goldschmidt Surfactant B8469 (pbw) 3
Rhodia Flame Retardant AB 80 (FBP) (pbw) 12.5
Water (pbw) 0.5
Blowing Agent
Phillips Petroleum Isopentane 25.1
A (1!
Total Huntsman Polyurethanes Rubinate 1850 206.2
(pbw)
Index 300
A/B ratio 1.41
Processing Variables
No. mixheads 3
Top laminator temperature (F) 145
Bottom laminator temperature (F) 153
A-Side temperature (F) 89
B-side temperature (F) 75
Line speed (ft./min.) 89.4
A-Side pressure (psi) 2217
B-Side pressure, high-pressure side (psi) 2164
B-Side pressure, high-pressure side (psi) 60 (approx.)
A-Side per mixhead (lbs./min) 22.8
B-Side per mixhead (lbs./min) 16.1
In-line mixer setting 25%
rpms 925
Machine Reactivity
Cream time (sec) 0
Gel time (sec) 14
Tack free time (sec) 24
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24
End of rise time (sec) n/a
Physical Properties of Board
Board Thickness (inches) 2.10
Core density (pcf) 1.68
Initial k-factor (Bru in./h ft2 °F) 0.149
Compressive Strength (psi) 18.8
Huntsman Dimvac test at -25 °C (14 days)
Width -1.0
Length -0.3
Closed cell content (%) 90.9
Average cell size, ~,m 0.16 - 0.19
Butler Chimney test weight retained (%) 90.3 - 91.4
In Example 1 the pentane blend used was Exxsol 1600, which is
approximately 70% cyclopentane and 30% isopentane. This blend is relatively
soluble in the B-side. B-sides blends made with Exxsol 1600 can be processed
in a
number of methods including the method described in this invention. However,
there are a number of combinations of polyol type, flame-retardants, level of
Exxsol 1600 and processing temperatures that could increase the probability of
phase separation or large cell structure in the foam. The advantage of the
method
described in this invention is that, as compared to other methods, it is much
less
likely to either result in phase separation or yield large cells.
The foams board produced in Example 1 had excellent strength
(compressive strength: 23.2 psi), low thermal conductivity (0.14 Btu-
in./hft2°F),
and was dimensionally stable as measured by the Huntsman Dimvac test in the
two
critical directions. In the Dimvac test the foam sample was put into a vacuum
to
remove any carbon dioxide formed primarily from the reaction of water with
isocyanate. This reduced the cell pressure and made it more susceptible to
cold
age shrinkage. The sample was then put in the freezer at -25°C for 14
days and
then dimensional changes were measured. This test reproduced unrealistic
conditions for the board, such that, if a board passes this test, the board
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manufacturer can be confident that it will perform in the field. It has been
determined that if a linear change in this test on small samples is less than -
5%,
then the board will be dimensionally stable in the field. The percent linear
change
in the length and width were well below -1.0%. thus excellent boards were made
5 from Example 1.
Isopentane is not very soluble in the B-side and will phase separate
much more readily. Additionally, the use of isopentane will produce a thick
emulsion, which requires efficient mixing in a timely manner. Isopentane will
phase separate or produce large cells unless emulsifiers are used in many
10 processing methods. For example, in a batch process it would require a long
time
with vigorous mixing to obtain an emulsion and, over a short period of time,
the
isopentane would start to phase separate. The process described in this
invention
circumvents these problems.
Example 2 illustrates that, even in this highly stressed formulation, with
15 isopentane, the method described in this invention mixed the blowing agents
very
well and produced a high quality foam. The foam was strong with a low thermal
conductivity and was dimensionally stable. The small cell size confirmed that
the
isopentane was well mixed. Isopentane requires a lot of energy to mix
thoroughly
with the polyol mixture and then stay in an emulsion long enough to make
20 excellent foam. The method described in this invention facilitates the
mixing of
isopentane with the polyol mixture and doesn't allow the components to phase
separate.
It is important to note the high output of the A-side and B-side and the
large amount of pentane blowing agent used in both examples. The higher the
25 output the more stress is put on the method to efficiently mix the pentane
blowing
agent with the polyol mixture and the higher the pentane blowing agent level
in
the B-side the harder it is to keep in solution. This further demonstrates the
wise
utility of the method in this invention.
Thus, it should be appreciated that the present disclosure provides
advancements in the art of polyurethane and polyisocyanurate foam board
production. Various modifications and alterations that do not depart from the
scope and spirit of this invention will become apparent to those skilled in
the art.
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This invention is not to be duly limited to the illustrative embodiments set
forth
herein. The claims will serve to define the proper scope of the invention.
