Polymer foams containing blocking agents

An improved closed cell polymer foam and foaming agent involving the use of a hydrogen-containing halocarbon blowing agent (e.g., HCFC-22) in combination with an effective amount of a hydrogen bond forming blocking agent (e.g., organic ether, ester or ketone). The presence of the blocking agent is shown to significantly reduce the escape of blowing agent from and entry of air into the foam resulting in low thermal conductivity over a longer period of time and improved thermal insulation value.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to improved polymer foams and foaming agents by the 
use of blocking agents. More specifically, the invention relates to 
combinations of a hydrogen bond forming blocking agent and a 
hydrogen-containing halocarbon and a method of using the same in closed 
cell polymer foams to reduce permeation of air and/or hydrohalocarbon, 
thereby maintaining low thermal conductivity and improved thermal 
insulation value of the foam. 
2. Description of Related Art, including Information Disclosed under 
.sctn..sctn.1.97-1.99 
It is generally known and an accepted commercial practice to add a blowing 
agent to various polymeric materials during fabrication such as to produce 
a cellular (expanded foam) material. Typically, the blowing agent can be 
either a reactive solid or liquid that evolves a gas, a liquid that 
vaporizes, or a compressed gas that expands during final fabrication 
producing the desired polymeric foam. Such foams are categorically either 
closed cell (i.e., non-porous, continuous polymer phase with discontinuous 
gas phase dispersed therein) or open cell (porous) foams which are 
advantageously employed in various end use applications and exhibit 
various advantages associated with the particular type of foam produced. 
In describing the closed cell foam as involving a discontinuous gas phase, 
it should be appreciated that this description is an over simplification. 
In reality the gas phase is dissolved in the polymer phase and there will 
be a finite substantial presence of gas (blowing agent) in the polymer. 
Furthermore and as generally known in the art, the cell gas composition of 
the foam at the moment of manufacture does not necessarily correspond to 
the equilibrium gas composition after aging or sustained use. Thus, the 
gas in a closed cell foam frequently exhibits compositional changes as the 
foam ages leading to such known phenomenon as increase in thermal 
conductivity or loss of insulation value. 
Closed cell foams are usually employed for their reduced thermal 
conductivity or improved thermal insulation properties. Historically, 
insulating polyurethane and polyisocyanurate foams have been made using 
trichlorofluoromethane, CCl.sub.3 F (CFC-11), as the blowing agent. 
Similarly, insulating phenolic foam is known to be made from 
phenol-formaldehyde resins (typically via an intermediate resole mixture 
involving a phenol-formaldehyde oligomer condensate) using blends of 
1,1,2-trichlorotrifluoroethane, CCl.sub.2 FCClF.sub.2 (CFC-113), and 
CFC-11 as the blowing agent. Also, insulating thermoplastic foam such as 
polystyrene foam is commonly manufactured using dichlorodifluoromethane, 
CCl.sub.2 F.sub.2 (CFC-12), as the blowing agent. 
The use of a chlorofluorocarbon as the preferred commercial expansion or 
blowing agent in insulating foam applications is in part based on the 
resulting k-factor (i.e., the rate of transfer of heat energy by 
conduction through one square foot of one inch thick homogenous material 
in one hour where there is a difference of one degree Fahrenheit 
perpendicularly across the two surfaces of the material) associated with 
the foam produced. Thus, it is generally known and accepted that a 
chlorofluorocarbon gaseous phase within the closed cell is a superior 
thermal barrier relative to other inexpensive gases such as air or carbon 
dioxide. Conversely, the natural intrusion of air into the foam over time 
and to a lesser extent the escape of the chlorofluorocarbon from the cell 
is deleterious to the desired low thermal conductivity and high insulative 
value of the foams. Also, the escape of certain chlorofluorocarbons to the 
atmosphere is now recognized as potentially contributing to the depletion 
of the stratospheric ozone layer and contributing to the global warming 
phenomenon. In view of the environmental concerns with respect to the 
presently used chlorofluorocarbon blowing agents, it is now generally 
accepted that it would be more desirable to use hydrochlorofluorocarbons 
or hydrofluorocarbons rather than the chlorofluorocarbons. Consequently, 
the need for a method or way of inhibiting the permeation of air and 
blowing agent through the polymer phase of the polymeric foam exists and 
hopefully any such solution to the problem would be effective in 
inhibiting the permeation of the proposed alternative halocarbons. 
Historically, various methods and compositions have been proposed, with 
varying degree of success, to alleviate and/or control problems associated 
with permeation of gases into and out of polymeric foams. For example, in 
U.S. Pat. No. 4,663,361 the problem of shrinkage (lack of dimensional 
stability) associated with using any blowing agent other than 
1,2-dichlorotetrafluoroethane in the manufacture of foamed polyethylene is 
addressed. In this reference, a stability control agent is used in either 
a homopolymer or copolymer of ethylene wherein the blowing agent is 
isobutane or isobutane mixed with another hydrocarbon or a chlorocarbon, 
fluorocarbon or chlorofluorocarbon. The stability control agent is either 
partial esters of long chain fatty acids with polyols, higher alkyl 
amines, fatty acid amides, olefinically unsaturated carboxylic acid 
copolymers, or polystyrene. This reference also describes other prior art 
and is included by reference for such purpose. 
In U.S. Pat. No. 4,243,717 a Fischer-Tropsch wax is added to expanded 
polystyrene beads to produce a stable cell structure in the foam, without 
specific reference to the permeation of blowing agent or air. In Canadian 
Patent 990,900 the use of a barrier material or blocking agent is 
disclosed to alleviate the problem of gas migration through the cell wall 
specifically at the time of foaming. The particular problem addressed in 
this Canadian patent is the rupture and total collapse of the cell walls 
that frequently occur in the manufacture of closed cell polyethylene foam. 
This problem is attributed to the fact that the cell walls for such foams 
are permeable to the rapidly expanding gas under the influence of the heat 
liberated by the exothermic polymer crystallization. The specific solution 
disclosed in this reference is to use a blend of polyethylene and 
polypropylene along with a barrier resin such as an elastomer containing 
polystyrene or acrylic resin which are intended to contribute high melt 
strength to the cell wall at the foaming temperature. An inert nucleant is 
also employed along with at least two gaseous propellants of substantially 
different vapor pressures. 
In U.S. Pat. No. 4,795,763 the use of at least 2 percent carbon black as a 
filler uniformly dispersed in a polymeric foam is shown to reduce the aged 
k-factor of the foam to below the aged k-factor of the corresponding 
unfilled foam. 
SUMMARY OF THE INVENTION 
The present invention provides a method of preventing or slowing down both 
the rate of intrusion or permeation of air into the closed cells of a 
polymeric foam as well as preventing or slowing down the escape of the 
blowing agent by permeation or migration out of the polymer foam cells. 
Thus, according to the present invention the effective rate of permeation 
of air and/or hydrohalocarbon across the polymeric phase of the foam is 
substantially reduced by virtue of the presence of a blocking agent. 
Further according to the present invention a blocking agent capable of 
hydrogen bond formation with the hydrogen-containing halocarbon is 
incorporated into the polymeric foam and thus tends to form hydrogen bonds 
with the blowing agent. This in turn dramatically reduces the permeation 
rate of the hydrogen-containing blowing agent retaining it in the foam. 
The presence of the blocking agent also functions to reduce entry of air 
into the polymer foam. By reducing the entry of air into insulating foam 
and simultaneously reducing the permeation of blowing agents out of 
insulating foam, the blocking agents according to the present invention 
produce foams which better maintain their insulating characteristics 
relative to foams made without these hydrogen bond forming agents. 
Thus, the present invention provides in a closed cell thermoplastic or 
thermoset polymer foam characterized by a continuous polymeric phase and a 
discontinuous gaseous phase, the improvement comprising: (a) a gaseous 
phase comprising at least one hydrogen-containing halocarbon; and (b) an 
effective amount of a hydrogen bond forming blocking agent. Preferably the 
hydrogen bond forming blocking agent is an organic ether, ester or ketone 
and is preferably present in the range of from about 0.1 to about 20 
weight percent based on the total weight of foam. 
Since the blocking agent according to the present invention can often be 
conveniently incorporated, marketed and used in combination with the 
blowing agent, the present invention further provides an improved 
thermoplastic or thermoset polymer foaming composition comprising: 
(a) a hydrogen-containing halocarbon; and 
(b) an effective amount of a hydrogen bond forming blocking agent. 
The improved method according to the present invention involves, in a 
method of manufacturing an expanded polymeric foam wherein a blowing agent 
expands as the polymeric phase solidifies, the specific improvement 
comprising the steps of: 
(a) selecting a hydrogen-containing halocarbon as the blowing agent; and 
(b) adding an effective amount a hydrogen bond forming blocking agent to 
reduce the permeation of air into the foam or slow down the escape of 
blowing agent from of the foam. 
It is an object of the present invention to provide a blocking agent that 
when incorporated into a polymeric foam will reduce or prevent the 
intrusion of air into the foam and/or the permeation or escape of blowing 
agent from the foam. It is a further object of the present invention to 
provide such a blocking agent that is particularly useful with the 
hydrogen-containing chlorofluorocarbons and hydrogen-containing 
fluorocarbons (i.e., the HCFCs and HFCs) in that the blocking agent will 
hydrogen bond with the hydrohalomethanes and hydrohaloethanes, thus 
significantly reducing their rate of permeation and escape from a closed 
cell polymeric foam. It is an associated object of the present invention 
to provide insulating foam containing a blocking agent and a method of 
manufacturing the same that exhibits preservation of the insulating 
properties over longer periods of times relative to the absence of the 
blocking agent. Fulfillment of these objects and the presence and 
fulfillment of additional objects will be apparent upon complete reading 
of the specification and the claims. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Polymer foams typically involve a continuous or at least a contiguous phase 
in a cellular structure. This cellular structure can be either flexible or 
rigid and is categorically either an open cell structure (i.e., the 
individual cells are ruptured or open producing a soft, porous "sponge" 
foam which contains no blowing agent gas) or a closed cell structure 
(i.e., the individual cells contain blowing agent gas surrounded by 
polymeric sidewalls with minimum cell-to-cell gas flow). Thermally 
insulating foams are closed cell structures containing a blowing agent gas 
(i.e., a gas formed in situ during the foam manufacturing process). 
Preferably the blowing agent gas should have a low vapor thermal 
conductivity (VTC) so as to minimize conduction of heat through the 
insulating foam. Thus, the vapor thermal conductivities for halocarbons 
such as CFC-11, CFC-12 and hydrochlorodifluoromethane, CHClF.sub.2 
(HCFC-22), at 25.degree. C. (i.e., 45.1, 55.7 and 65.9 
Btu.ft.sup.-1.hr.sup.-1..degree.F..sup.-1 .times.10.sup.4, respectively) 
compare favorably to the VTC for air at 25.degree. C. (i.e., 150.5 
Btu.ft.sup.-1.hr.sup.-1..degree.F..sup.-1 .times.10.sup.4). From these 
data, it can readily be seen that the presence of a halocarbon blowing 
agent is required for optimum thermal insulation properties with both 
thermoplastic and thermoset foams. 
A problem with hydrogen-containing alternative blowing agent HCFC-22 is its 
rapid migration from thermoplastic foams. For example, in the case of one 
grade of polystyrene, the permeation rate at 25.degree. C. for CFC-12 vs. 
HCFC-22 was 4.2.times.10.sup.-9 g/hr vs. 6.5.times.10.sup.-8 g/hr (i.e., 
HCFC-22 diffused 15.5 times faster than CFC-12). Without some way to 
prevent or slow down the rate of HCFC-22 permeation from polystyrene foam, 
this blowing agent is unacceptable for producing good insulation foam, 
using this particular grade of polystyrene. 
HCFC-22 is also known to diffuse rapidly from some 
polyurethane/polyisocyanurate foam formulations. Techniques for 
slowing/preventing this blowing agent migration are required if the 
halocarbon is to be useful in preparing these thermoset insulating foams. 
In addition to the undesirable degradation of foam insulation value caused 
by permeation losses of blowing agent, the effect of air entry from the 
atmosphere into the foam cells is at least equally significant. As air 
enters the foam cells, the vapor thermal conductivity of the cell gas 
increases and the insulation value drops. 
The blocking agents of this invention unexpectedly function to reduce air 
entry into foams and/or to reduce the permeation of hydrogen-containing 
blowing agents such as HCFC-22 from the foam cells, thereby producing more 
effective/economical insulation foams. 
For the purposes of the present invention, the term "blocking agent" is 
used herein to denote hydrogen bond forming compounds which contain ether, 
ester or ketone groups or the like. These hydrogen bond forming compounds 
can bond or associate with hydrogen-containing halocarbon blowing agents 
such as HCFC-22 and thereby reduce their rates of permeation from the 
foam. 
Unexpectedly, HCFC-22, difluoromethane (CH.sub.2 F.sub.2, HFC-32), 
1,1,1-trifluoro-2,2-dichloroethane (CHCl.sub.2 CF.sub.3, HCFC-123), 
1,1,2-trifluoro-1,2-dichloroethane (CHClFCClF.sub.2, HCFC-123a), 
1,1,1,2-tetrafluoro-2-chloroethane (CHClFCF.sub.3, HCFC-124), 
pentafluoroethane (CHF.sub.2 CF.sub.3, HFC-125), 1,1,2,2-tetrafluoroethane 
(CHF.sub.2 CHF.sub.2, HFC-134), and 1,1,1,2-tetrafluoroethane (CH.sub.2 
FCF.sub.3, HFC-134a) have been observed to associate or hydrogen bond with 
compounds containing ether, ester or ketone groups. Glycols and other 
polyhydroxy compounds tend to form intra- or inter-molecular hydrogen 
bonds with themselves and thus do not associate strongly with HCFC-22. 
HCFC-22, with hydrogen bonding esters, ketones or ethers, exhibits 
dramatically reduced vapor pressure as a result of the association. 
Furthermore, when these hydrogen bonding compounds are present in 
thermoplastic polymers such as polystyrene, the permeation of HCFC-22 is 
reduced/slowed as the result of the mutual association which occurs 
between these compounds. The hydrogen bond forming agents additionally 
function to improve the solubility of blowing agents such as HFC-134a in 
thermoplastic polymers such as polystyrene. 
Also, the mutual solubility of HCFC-22 and HCFC-123 or the like with 
several hydrogen bond forming compounds further provides evidence of an 
unexpected association between these materials. CFC-12 does not share this 
unexpected solubility characteristic. Because of the solubility of many of 
the hydrogen bond forming compounds in HCFC-22, these compounds are 
suitable for dissolving in HCFC-22 and, thus, can be made commercially 
available in this convenient form. 
For purposes of the present invention and as previously mentioned, the 
blocking agent can broadly be any compound that contains either an ether, 
ester or ketone group or combinations of the same and is capable of 
hydrogen bonding or the equivalent strong association or complexing with 
hydrogen-containing halocarbons. For example, but not by way of 
limitation, the following table lists examples of ether, ester or ketone 
groups containing compounds which associate or hydrogen bond with 
hydrogen-containing halocarbons such as HCFC-22. 
HYDROGEN BONDING AGENTS 
(1) Polyethylene oxide polymers 
(2) Ethylene oxide/propylene oxide copolymers 
(3) Polypropylene oxide polymers 
(4) Polyethylene glycol mono- and dioleates 
(5) Polyethylene glycol monostearates 
(6) Alkylphenoxy polyethoxy ethanols 
(7) Polyethylene oxide sorbitan monostearates and tristearates 
(8) Polyethylene oxide fatty acid amides 
(9) Primary and secondary alcohol ethoxylates 
(10) Glyme, diglyme, triglyme and tetraglyme 
(11) Mono-, di- and tripropylene glycol methyl ethers and ether acetates 
(12) Dimethyl adipate, succinate and glutarate 
(13) Ethylene oxide/propylene oxide adducts with a sucrose 
(14) Ketones and polyketone polymers. 
The use of hydrogen-containing blowing agents such as HCFC-22 with ether, 
ester or ketone hydrogen bond forming compounds in polymer foams does not 
preclude the simultaneous incorporation of blowing agents such as 
1,1-dichloro-1-fluoroethane (CCl.sub.2 FCH.sub.3, HCFC-141b), 
1-chloro-1,1-difluoroethane (CClF2CH.sub.3, HCFC-142b), 
1,1,1-trifluoroethane (CF.sub.3 CH.sub.3, HFC-143a), 1,2-difluoroethane 
(CH.sub.2 FCH.sub.2 F, HFC-152), and 1,1,-difluoroethane (CHF.sub.2 
CH.sub.3, HFC-152a) which do not tend to form strong hydrogen bonds. It 
should be further appreciated that various CFCs may also be present as a 
component of a blowing agent mixture useful according to the present 
invention and that the present invention is applicable when CO.sub.2, 
hydrocarbons or methyl formate are components of the blowing agent gas. 
Similarly, various additives such as stabilizers, dyes, fillers, and the 
like can be present in the blowing agent. 
In addition to reducing the entry of air into and/or the migration of 
hydrogen-containing blowing agents such as HCFC-22 from thermoplastic 
foams, the hydrogen bond forming agents may provide other functions to the 
foam manufacturing process. For example, compounds such as the 
polyethylene oxide polymers may provide lubricity and thereby increase the 
extrusion throughput or production rate. Furthermore, these compounds are 
contemplated as potentially useful as polymer plasticizers and may 
contribute advantageously to other properties. 
The hydrogen bond forming agents of this invention are suitable for use 
with thermoplastics such as polystyrene, polyethylene, polypropylene, 
polyvinyl chloride, and the like to prevent loss of hydrogen-containing 
blowing agents; however, they can also be used with thermoset polymer 
foams such as polyurethane, polyisocyanurate, and phenolic resin foams. 
Since these hydrogen bond forming agents associate with blowing agents 
such as HCFC-22, they will function to reduce/prevent permeation of the 
blowing agent in any compatible polymer foam system. Furthermore, these 
hydrogen bond forming agents will function in the presence of other 
additives normally used in polymer foams, such as stabilizers, dyes, 
fillers, and the like. 
The blowing agent concentration used to prepare most conventional 
thermoplastic and thermoset polymer foams is generally in the range of 
about 5 weight percent to about 30 weight percent (based on total weight 
of the foam). To reduce migration of hydrogen-containing blowing agents 
such as HCFC-22, the effective use concentration of hydrogen bond forming 
agent is at least about 0.1 weight percent and preferably from about 1.0 
to 20 weight percent (based on total formulation weight), most preferably 
about 0.5 weight percent to about 10 weight percent. Typically, the 
improved polymer foaming composition will contain from 1 to 100 parts by 
weight hydrogen bond forming blocking agent for every 100 parts of 
hydrogen-containing halocarbon blowing agent. 
The actual method by which the blocking agent according to the present 
invention is to be incorporated into the closed cell foam can vary 
according to the specific application and composition being employed. In 
the broadest sense, the blocking agent can be treated as any other foam 
additive as generally known in the art. As previously stated, the blocking 
agent in certain applications imparts beneficial effects to the polymer 
phase in addition to reducing permeability and in such cases the blocking 
agent can be added to the polymer. Since the blocking agent is 
categorically a hydrogen bond forming compound, it may be advantageously 
added to the blowing agent or preblended into the polymer (e.g., 
polystyrene) prior to extrusion or other method of fabrication. In the 
case of thermoset foams (e.g., polyurethane/polyisocyanurate foams) the 
hydrogen bond forming agents can be added to the foam in the isocyanate 
(A-side) or the polyol (B-side) or added with the blowing agent at the 
mixing head where the A-side and B-side are combined (i.e., 
third-streamed). For purposes of the present invention the term "A-side" 
is used to specify the isocyanate containing component of a conventional 
two component precursor foam system. The term "B-side" is used to specify 
the polyol containing component. It should be appreciated that this 
nomenclature may be reversed particularly in certain European literature. 
It should be further appreciated that these precursor components to foams 
typically contain other ingredients, additives, agents, diluent and the 
like all as generally known in the art. Thus for example, but not by way 
of limitation, the B-side will typically contain, in addition to the 
polyol, a surfactant, a catalyst and one or more blowing agents. If the 
hydrogen bond forming agent used contains free hydroxyl groups, this must 
be taken into account when calculating the hydroxyl equivalent for the 
B-side system. In the case where the blocking agent is preferentially more 
soluble in one of the foam components, it is preferably added to that 
component. For example, addition of the blocking agent to the polyol 
component of two-component thermoset resin is preferred. Of course, the 
addition to more than one component or either component is also 
contemplated. In the case of phenolic foams, the hydrogen bond forming 
agents can be added to the foam by preblending into the resole or added 
separately at the mixing head prior to the foam laydown. The most 
preferred method of adding the blocking agent is to mix it with the 
blowing agent and as such the admixture of HCFC or HFC and blocking agent 
is contemplated as being a commercially attractive product, per se. Again, 
since the blocking agent is categorically a hydrogen bond forming 
compound, in the case of the thermoset foams (e.g., 
polyurethane/polyisocyanurate foams) not only can a polyol be added as the 
blocking agent but the polyol (B-side) can be viewed as the blocking 
agent. Thus, as previously stated if the hydrogen bond forming agent used 
contains free hydroxyl groups they must be taken into account when 
calculating the hydroxyl equivalent for the B-side system. Conversely, the 
ether and ester groups of the polyol found in the B-side should also be 
view as contributing as the hydrogen bond forming blocking agent. As such, 
in cases where there are ether and/or ester groups present in the polyol, 
the polyol should be considered as a blocking agent.