Insulating alkenyl aromatic polymer foam

Alkenyl aromatic thermoplastic synthetic resinous elongate foam bodies having a machine direction, a traverse direction and closed noninterconnecting gas-containing cells are prepared using at least 70 percent by weight of 1,1,1-trifluoroethane and or 1,1,1,2-tetrafluoroethane as a blowing agent or part of a blowing agent mixture. These foam bodies have an average cell size of 0.01 to 0.3 millimeters, a density of from about 0.75 to about 6.0 pounds per cubic foot, an absolute dimensional stability of less than 4 percent in any direction when measured by the test designated ASTM D2126/C578, and preferably a minimum cross-sectional dimension of at least 0.25 inch, a cross-sectional area of at least 8 square inches, a water vapor permeability not greater than 1.8 per inch. A cell size enlarger agent may be necessary for cell sizes in the 0.2-0.3 range.

BACKGROUND OF THE INVENTION 
This invention relates to a dimensionally stable insulating alkenyl 
aromatic polymer foam extruded in large cross sections employing specific 
blowing agents or specific blowing agent mixtures. 
One major application for alkenyl aromatic polymer foam, such as styrene 
polymer foams, is in the field of thermal insulation. Desirably a styrene 
polymer foam for thermal insulation has an average cell size of less than 
about 0.3 millimeters and excellent dimensional stability. 
One manner in which the thermal insulation value of styrene polymer foams 
is increased is by the addition of certain fully-halogenated compounds, 
such as dichlorodifluoromethane, into the styrene polymer foam as a 
blowing/insulating agent. Such a compound, when contained in the cells of 
the extruded styrene polymer foam, increases the thermal insulation value. 
Another major consideration for extruded styrene polymer foam is 
dimensional stability. Dimensional stability is particularly important 
when the extruded styrene polymer foam is employed in construction uses or 
is laminated to a cementitious layer. For most commercial applications 
regular rectangular forms are required and while a distorted shape can be 
cut into a rectangular form, considerable product is lost in cutting and 
must be discarded as scrap. Another consideration is that if an extruded 
styrene polymer foam product is not dimensionally stable, then the foamed 
polystyrene must be maintained in storage for a sufficient length of time 
until substantially all dimensional instability, such a shrinking, 
swelling, warping or bulging has stopped. 
Still another important consideration is the choice of a blowing/insulating 
agent. Certain of these agents, particularly fully-halogenated compounds 
such as dichlorodifluoromethane, when released to the atmosphere upon 
extrusion of the styrene polymer foam or upon aging of the foam are 
believed to cause harm to the atmosphere. Thus, it is desirable to reduce 
or eliminate these fully-halogenated compounds. 
Some of these considerations concerning extruded foams and their 
manufacture are discussed at great length in U.S. Pat. Nos. 2,409,910; 
2,515,250; 2,669,751; 2,848,428; 2,928,130; 3,121,130; 3,121,911; 
3,770,688; 3,815,674; and 3,960,792, the teachings of which are herein 
incorporated with reference thereto. 
Canadian Patent No. 1,086,450, hereby incorporated by reference, refers to 
this problem and proposes a variety of low permeability, 
insulating/blowing agents, or mixtures of those agents, having a 
permeability through an alkenyl aromatic resinous polymer of not greater 
than 0.017 times the permeability of nitrogen through the body, a thermal 
conductivity of less than about 0.10 British Thermal Units-inch per hour 
per square foot per degree Fahrenheit and having the following formula: 
EQU R1-CF2-R2 
herein R1 is a methyl, ethyl, chloromethyl, dichloromethyl, difluoromethyl, 
chlorofluoromethyl, fluoromethyl, or trifluoromethyl radical and R2 is 
hydrogen or a chloro, fluoro, methyl or trifluoromethyl radical with the 
further characterization that the compound contain no more than 3 carbon 
atoms and if the compound contains as halogen only 2 fluorine atoms, the 
compound must have 3 carbons. 
1,1,1-trifluoroethane (HFC-143a) is specifically listed in the Canadian 
patent as being one of a number of low-permeability blowing agents useful 
in the practice of that invention and 1,1,1,2-tetrafluoroethane (HFC-134a) 
is contemplated as being within the scope of the formula defining 
low-permeability blowing agents. Also chlorodifluoromethane (HCFC-22) is 
listed as a secondary or high-permeability blowing agent useful in the 
preparation of the foam of the Canadian patent. 
However, in Table I of the Canadian patent, it can be seen that polystyrene 
foam prepared from certain of the low-permeability blowing agents, 
particularly 1,1-difluoro-1-chloroethane (HCFC-142b), have a dimensional 
stability which is excessive, although the cell size is 0.20 mm 
(millimeters) This is particularly noted in Example 16. Examples 14 and 15 
of the same Table I appear to solve the dimensional stability problem by 
using 50/50 and 40/60 (weight of each component by total blowing agent 
weight) blowing agent mixtures of 1,1-difluoroethane (HFC-152a) and 
HCFC-142b while retaining a cell sizes of 0.12 mm and 0.14 mm 
respectively. 
U.S. Pat. No. 3,960,792, previously incorporated by reference, teaches how 
to prepare a dimensionally stable expanded closed cell polystyrene foam 
body while employing as the fluid foaming agent a volatile material which 
has a diffusion rate through the polystyrene resin about 0.75 to 6 times 
the diffusion rate of air through polystyrene resin with the foaming agent 
being a mixture of at least two compounds having carbon chemically 
combined therein. 
U.S. Pat. No. 4,636,527, hereby incorporated by reference, teaches how to 
prepare an expanded closed cell polystyrene foam body while employing as 
the fluid foaming agent a mixture of carbon dioxide and ethyl chloride. 
Optionally dichlorodifluoromethane, 1,1-difluoro-1-chloroethane and 
mixtures thereof may also be included as part of the blowing agent 
mixture. 
There is a need to be able to produce a dimensionally stable extruded 
polystyrene foam body with a non-fully halogenated insulating/blowing 
agent. 
More particularly there is a need to be able to produce a dimensionally 
stable extruded polystyrene foam body with 1,1,1,2-tetrafluoroethane or 
1,1,1-trifluoroethane as the only or major insulating/blowing agent. 
SUMMARY OF THE INVENTION 
The present invention is an alkenyl aromatic thermoplastic synthetic 
resinous elongate foam body having a machine direction and a transverse 
direction with the body having a plurality of closed noninterconnecting 
gas-containing cells. 
The cells have an average cell size of from about 0.01 to about 0.3 
millimeters when measured across a minimum cross-sectional dimension of 
the body, with the body being of a generally uniform cellular structure 
without substantial discontinuities. 
The foam body has a density of from about 0.75 to about 6.0 pounds per 
cubic foot (12 to 96 kilograms/cubic meter). 
Preferably the foam body has a cross-sectional area of at least 8 square 
inches (51.6 square centimeters) with a minimum cross-sectional dimension 
of at least about 0.25 inch (6.35 millimeters), a water vapor permeability 
not greater than about 1.8 perm inch (3.02 metric perm centimeters), in 
addition to a density of from about 0.75 to about 6.0 pounds per cubic 
foot (12 to 96 kilograms/cubic meter). 
Further limitations are that the cells contain, as gas, at least 70 percent 
by weight 1,1,1,2-tetrafluoroethane or 1,1,1-trifluoroethane and that any 
change in dimension in any direction be about four percent (absolute, 
meaning a positive or negative value) or less when measured by the test 
designated ASTM D2126/C578. 
Surprisingly the use of 1,1,1,2-tetrafluoroethane or 1,1,1-trifluoroethane 
has been found to decrease cell size while still being able to maintain 
dimensional stability.

DETAILED DISCUSSION OF ILLUSTRATIVE EMBODIMENTS 
The volatile fluid foaming agents used to prepare the foams of the present 
invention are those having at least 70 percent by weight 
1,1,1,2-tetrafluoroethane or 1,1,1-trifluoroethane based on total blowing 
agent mixture weight. More preferably the blowing agent is at least 80 
percent HFC-134a or HFC-143a. Most preferably the blowing agent is 100 
percent HFC-134a or HFC-143a. Any remaining part of the blowing agent 
mixture can be any other chemical or physical blowing agent. Preferably 
the remaining part of the blowing agent mixture is water (H.sub.2 O), 1 to 
4 carbon aliphatic hydrocarbons, such as ethane, chlorodifluoromethane 
(HCFC-22), or carbon dioxide (CO.sub.2). Other combinations include a 
chemical blowing agent mix of sodium bicarbonate and boric acid (or citric 
acid) and mixtures of the above, including specifically CO.sub.2 and 
H.sub.2 O, 1 to 4 carbon aliphatic hydrocarbons and CO.sub.2 and a 
chemical blowing agent mix of sodium bicarbonate and boric acid (or citric 
acid) and CO.sub.2. 
Preferably the blowing agents and their mixtures (weight percent based on 
total blowing agent mixture weight) are as follows: 
1. 100% HFC-134a; 
2. 100% HFC-143a; 
3. 94-100% HFC-134a/0-6% CO2; 
4. 94-100% HFC-143a/0-6% CO2; 
5. 70-100% HFC-134a/0-30 HCFC-22, preferably 80-100% HFC-134a/0-20 HCFC-22; 
6. 70-100% HFC-143a/0-30 HCFC-22, preferably 80-100% HFC-134a/0-30 ethane; 
and 
7. 70-100% HFC-134a/0-30 ethane; and 
8. 70-10% HFC-143a/0-30 ethane. 
The amount of blowing agent or blowing agent mixture added to the alkenyl 
aromatic synthetic resin to produce a foam is about 3 to about 18 weight 
parts per hundred parts of resin by weight. 
The term `alkenyl aromatic synthetic resin` refers to a solid polymer of 
one or more polymerizable alkenyl aromatic compounds. The polymer or 
copolymer comprises in chemically combined form, at least 60 percent by 
weight of at least one alkenyl aromatic compound having the general 
formula 
##STR1## 
wherein Ar represents an aromatic hydrocarbon radical, or an aromatic 
halo-hydrocarbon radical of the benzene series, and R is hydrogen or the 
methyl radical. Examples of such alkenyl aromatic resins are the solid 
homopolymers of styrene, alpha-methylstyrene, o-methylstyrene, 
m-methylstyrene, p-methylstyrene, ar-ethylstyrene, ar-vinylstyrene, 
ar-chlorostyrene or ar-bromostyrene: and the solid copolymers of two or 
more of such alkenyl aromatic compounds with minor amounts of other 
readily polymerizable olefinic compounds such as, for example, 
methylmethacrylate, acrylonitrile, maleic anhydride, citraconic anhydride, 
itaconic anhydride, acrylic acid, and rubber reinforced (either natural or 
synthetic) styrene polymers. 
The preparation of alkenyl aromatic resinous polymer foams in accordance 
with the present invention is most conveniently done in a known manner 
wherein the alkenyl aromatic synthetic resin is heat-plastified within an 
extruder. From the extruder the heat plastified resin is passed into a 
mixer, for example a rotary mixer wherein a studded rotor is enclosed 
within a housing which has a studded internal surface which intermeshes 
with the studs on the rotor. The heat-plastified resin and a volatile 
fluid foaming agent are fed into the inlet end of the mixer and discharged 
from the outlet end, the flow being in a generally axial direction From 
the mixer, the gel passes through coolers and from the coolers to a die 
which extrudes a generally rectangular board. 
Other methods of preparing alkenyl aromatic resinous polymer foams are 
known and include systems which the foam is extruded and foamed under 
sub-atmospheric, atmospheric and super-atmospheric conditions. One such 
sub-atmospheric (vacuum) extrusion method useful in preparing the foams of 
the present invention is detailed in U.S. Pat. No. 3,704,083. This type of 
vacuum system does not require a low-permeability/high-permeability 
blowing agent mixture, due to the influence of the vacuum on the foaming 
process. 
In the preparation of foams generally, it is often desirable to add a 
nucleating agent such as, for example talc, calcium silicate, or indigo to 
reduce the cell size. 
However in the preparation of the foams in accordance with the present 
invention, little or no nucleating agent should be required when using 
HFC-134a or HFC-143a due to the unexpected nucleating action of these 
blowing agents. In fact, the exact opposite may be required to achieve 
specific desired cell sizes, an additive or agent which increases cell 
size may be required, for example, polyethylene or other waxy materials 
known in the art. 
So depending on the cell size desired In the preparation of foams in 
accordance with the present invention, it may be desirable to add no or 
only a small amount of nucleating agent such as, for example talc, calcium 
silicate, or indigo to regulate the cell size or it may be desirable to 
add an additive which increases cell size. 
Other type of ingredients which may be included are fire retardants, for 
example hexabromocyclododecane or monochloropentabromocyclohexane, 
extrusion aids, for example barium stearate or calcium stearate, and acid 
scavengers, for example magnesium oxide or tetrasodium pyrophosphate may 
also be added. 
EXAMPLES 
The following examples in Tables 1 are prepared from polystyrene having a 
weight average molecular weight of about 200,000, calcium stearate (in 
amounts ranging from about 0.00 to about 0.08 weight parts per hundred 
based on resin weight, but generally about 0.05) and the blowing agents 
identified in Table 1. 
These ingredients are added to an extruder and melted at a temperature of 
about 220.degree. C and a pressure of about 2000 psi (pounds per square 
inch). 
This mixture of heat-plastified ingredients and the volatile blowing agent 
mixture (having at least about 70 weight percent by total blowing agent 
weight HFC-134a or HFC-143a) is then introduced into the inlet end of the 
mixer where the mixture is thoroughly mixed. 
Generally for forming a foam board, the mixture is then cooled to a foaming 
temperature, extruded through a slit die and expanded between a pair of 
substantially parallel plates to form a foam board having a rectangular 
cross-section of at least 8 square inches (51.6 square centimeters) with a 
minimum cross-sectional dimension of at least about 0.25 inch (6.35 
millimeters). 
For the purposes of Table 1, the mixture is then cooled to a foaming 
temperature, extruded through a slit die and expanded to a round shape 
(continuous cylindrical shape) having a diameter of about 1/2 inch to 
about 3/4 inch. 
For the dimensional stability testing the specimens in Tables 1 are 
prepared according to ASTM D-2126/C578. After conditioning the dimension 
of the extrusion axis of the specimens is taken to the nearest .+-.0.1%. 
Cell sizes may be measured by any known method, such as for example those 
methods detailed by ASTM. 
The specimens are then exposed to a temperature of 70.degree..+-.2.degree. 
C. (158.degree..+-.4.degree. F.) and a relative humidity of 97.+-.3% for a 
period of 7 days. After cooling at room temperature for 2 hours the 
dimensions of the three principal axes (vertical, horizontal and 
extrusion) of the specimens are again taken to the nearest .+-.0.1%. The 
percentage dimensional change in the extrusion axis, positive or negative, 
is then determined to the nearest 0.1%. 
TABLE 1 
______________________________________ 
Cell size and Dimensional Stability 
Examples with HFC-134a and HFC-143a 
and Comparative Examples with CFC-12 
Blowing Agent 
Foaming 
Type and Temper- Cell Dimensional 
Amount (pph).sup.1 
ature Density Size Stability 
and Ratio.sup.3 
.degree.C..sup.1 
pcf.sup.1 
mm.sup.1,4 
%.sup.2 
______________________________________ 
(12.3) CFC-12* 
122 2.79 0.148 3.06 
(12.3) CFC-12* 
124 2.46 0.144 1.14 
(13.1) CFC-12* 
127 2.21 0.224 2.74 
(12.0) CFC-12* 
118 3.56 0.600 5.62 
(9.6) HFC-134a 
133 2.55 0.1 -0.30 
(9.6) HFC-134a 
133 2.71 0.1 -0.65 
(9.9) HFC-134a 
118 2.81 0.1 -1.29 
(8.7).sup.1 HFC-134a 
124 3.23 0.112 -0.63 
and HCFC-22 
(83.3/16.7).sup.3 
(8.5) HFC-134a 
122 3.62 0.1 0.80 
and HCFC-22 
(83.3/16.7) 
(10.4) HFC-134a 
124 2.12 0.130 -0.66 
and HCFC-22 
(83.3/16.7) 
(10.0) HFC-134a 
118 5.57 0.1 0.61 
and HCFC-22 
(83.3/16.7) 
(10.1) HFC-134a 
118 3.99 0.138 0.56 
and CO.sub.2 
(90.9/9.1) 
(10.1) HFC-134a 
117 2.50 0.197 0.61 
and CO.sub.2 
(90.9/9.1) 
(10.1) HFC-134a 
117 2.53 0.230 1.36 
and CO.sub. 2 
(90.9/9.1) 
(8.6) HFC-134a 
125 2.40 0.1 -0.44 
and ETHANE 
(83.3/16.7) 
(8.4) HFC-134a 
125 2.46 0.1 -0.19 
and ETHANE 
(83.3/16.7) 
(9.0) HFC-134a 
118 3.23 0.1 -1.87 
and ETHANE 
(83.3/16.7) 
(8.6) HFC-143a 
120 3.24 0.151 -1.29 
(8.6) HFC-143a 
121 2.80 0.131 -1.29 
(8.9) HFC-143a 
117 4.14 0.1 0.61 
and HCFC-22 
(83.3/16.7) 
(8.9) HFC-143a 
116 3.89 0.1 0.61 
and HCFC-22 
(83.3/16.7) 
(8.7) HFC-143a 
121 2.50 0.176 0.61 
and HCFC-22 
(83.3/16.7) 
______________________________________ 
*Not examples of the present invention. 
.sup.1 pph = weight parts per hundred weight parts of resin; .degree.C. = 
degrees centigrade; pcf = pounds per cubic foot; mm = millimeters; 
.sup.2 As measured by ASTM D2126/C578 in the extrusion direction 
.sup.3 Weight percent ratio based on total blowing agent weight 
.sup.4 Cell sizes were not measured below 0.1 due to test limitations 
As can be seen in the in Table 1, not only is it possible to obtain small 
cell sizes with HFC-134a or HFC-143a and certain mixtures having at least 
70 weight percent of these blowing agents, it is also possible to obtain 
dimensional stability, even when using HFC-134a or HFC-143a alone as a 
blowing agent. 
This unexpected and valued combination of small cell size (less than about 
0.30 mm) and dimensional stability is clearly shown in Table 1 for 
HFC-134a or HFC-143a. 
Foams of the present invention, using HFC-134a or HFC-143a or specified 
mixtures having at least 70 weight percent of HFC-134a or HFC-143a based 
on total blowing agent mixture weight, will have a fine cell structure of 
less than about 0.3 mm, preferably less than about 0.25 mm and most 
preferably less than about 0.1 mm and a dimensional stability in any 
direction about four percent or less when measured by the test designated 
ASTM D2126/C578. The foam will also have a five year k-factor of at least 
0.03 British Thermal Units-inch/hour-square foot-degree Fahrenheit lower 
than that of a foam with only air in the cells. 
As is apparent from this specification, the present invention is 
susceptible of being embodied with various alterations and modifications 
which may differ in some respect from those examples described in this 
specification and description. For this reason it is to be fully 
understood that this specification and description is intended to be 
merely illustrative and is not to be construed or interpreted as being 
restrictive or otherwise limiting of the present invention.