Note: Descriptions are shown in the official language in which they were submitted.
3 ~3
DIRECTIONAL FLEXIBILIZATION OF EXPANDED
THERMOPLASTIC FOAM SHEET FOR LOW
TEMPERATURE INSULATION
Back~round of the Invention
Rigid closed cell thermoplastic foams have
been used extensively as thermal insulating materials
because of light weight, good compressive strength and
high insulating values. However, their rigidity and
inelasticity are adverse factors for application to
curved surfaces such as pipe lines and cylindrical or
s~herical tanks. Cutting pieces to fit or custom
molding incur added fabrication problems and costs.
Yet, if such foams are forceably applied to a curved
surface, the closed cell structure is often cracked or
broke~ resulting in loss of insulation value.
Alt~rnately, Nakamura U.S. Patent 3,159,700
describ~s a process for directional flexibili~ation of
rigid plastic foam sheets by partial compression or
crushing an expanded foam sheet in a direction generally
normal to that of desired flexibility. The process i5
dasigned to introduce wrinkles into the cell wall of
the plastic foam without rupturing the foam cell~ or
causing significant loss of compressive strength in
other diractlons. By repeating the process in a direction
C-29,668A -1-
. , ` ~
79'~
--2--
substantially at right angles to the first, two-directional
flexibilization can be achieYed giving a foam product
which can assume to a limited degree a compound curvature.
Such properties are particularly valuable for
rigid foam sheet to be used for low temperature insulation
of pipelines, tan~s, and other large vessels for the
transportation and storage of low temperature fluids.
Furthermore, such flexibilized pieces or sheets of
expanded foam are readily assembled by the spiral
generation techniques of Wright U.S. Patent 3,206,899
and Smith U.S. Patent 4,017,346.
~ owever, insulating requirements for the
transportation and storage of liquid petroleum gas
(LPG) and cryogenic fluids such as liquid nitrogen
demand even higher long term resistance to water vapor
transmission while retaining compressive strength
adequate for field application and use. Cell wall
cracking and rupture must be reduced to a minimum.
Accordingly, the present invention has for
~0 its objects providing a synthetic resin ~oam which:
(l) can be easily applied to a curved
surface and then heated to secure the
bent shape;
(2) has improved flexural wor~ability and
resistance to cracking, breaking or
tearing;
(3~ maintains effective, long term com-
pressive strength and insulating
properties necessary for low temperature
storage and transport of liquefied
natural gas and cryogenic fluids; and
C-29,668A -2-
7~4~3
-3-
(4) has high creep resistance and lastin~
crack resistance in biaxial directions
essential to tolerate heavy loads under
cryogenic storage conditions.
Summary of the Invention
It has now been discovered that flexibilized,
rigid plastic foam sheets with improved elongation and
water vapor barrier properties particularly desirable
for low temperature and cryogenic insulation can be
prepared by mechanical compression of certain expanded,
closed-cell foams having carefully s~elected structural
and physical properties including age after expansion.
More specifically the invention is an improved
process for the flexibilization of a rigid, substantially
closed-cell plastic foam sheet having a generally rec-
tangular shape defined by the three-dimensional rectangular
coordinates X (length), Y (thickness~ and Z (width) and
~he YZ, XZ and XY planes normal thereto by partial
crushing the foam sheet in a direction normal to that
of desired flexibilization. The improvement is further
ch~racterized by (A) selecting a freshly extruded foam
sheet having (1) a bulk density of ~0-100 kg/m3, (2) an
anisotropic cell structure oriented in the Y axial
direction with an average y cell size of 0.05 to 1.00
mm, and (3) a Y axial compressive strength of at least
1.8 kg/cm2; (B~ compressing said foam sheet within 0.1
to 240 hours of expansion in a short confined compres-
sion zone to form a directionally flexibilized foam;
and thereafter (C) recovering a direc~ionally flexi-
bilized foam having
(1) anisotropically wrinked cell wallstructure with wrinkles oriented in the
direction of flexibilization;
C-29,668A ~3-
7~63
(2) average cell sizes x, y and z measured in
the axial directions X, Y and Z satisfying
the following conditions;
y = 0.05 - 1.0 mm, and
y/x and y/z - 1.05;
(3) a higher elongation at rupture in the
direction of flexibilization; and
(4) a Y-axial water vapor permeability of not
more than 1.5 g/m2.hr by the water method of
ASTM C-355.
The resulting flexibilized form has improved flexural workability
and crack resistance particularly desirable for low temperature
insulation. Indeed with a substantially closed-cell polystyrene
resin foam having a bulk density of about 20 to 60 kg/m3, flexi-
bilized foam with a Y-axial water permeability of less than 1.0
g/m .hr by the water method of ASTM C-355 can be obtained which is
stable and effective for long-term insulation of cryogenic storage
tanks.
_talled Description of the In~ention
The present invention will now be further described, by -
way o~ example only, with reference to the accompanying drawings,
in which:
Figures lA, lB, lC, 2A, 2B and 2C are photomicrographs
(magnification : 50 x) of one and two-directionally flexibilized
foams of examples 123 and 223, showing a closed cell structure in
the X-, Y- and Z-axial directions,
Figure 3 illustrates the X-, Y- and Z- axial directions
.... ~ '
' ~
4~3
Figures 4 and 5 schematically illustrate the compression
equipment of flexibilizers
Figures 6A and 6B graphically illustrate the values of
Y-axial average cell sizes y and bulk densities D for a foam within
the present invention
Figure 7A graphically illustrates the relationship between
X-axial elongation at rupture Ex of flexibilized foams according to
the invention and the aging period of the initial foam sheet after
extrusion,
Figure 7B graphically illustrates the relationship between
X-axial percentage elongation at rupture Ex of two directionally
flexibilized foams and the aging time of extruded foam planks,
Figure 8A graphically illustrates the relationship between
water vapor permeability and the aging period before flexibilization,
Figure 8B graphically illustrates the relationship between
water vapor permeability Py of flexibilized foams and the aging
period of material foams after expansion,
Figure 9A graphically illustrates the relationship between
water vapor permeability and the cell shape (y/x) of material foam
plank,
Figure 9B graphically illustrates the relationship between
Y-axial water vapor permeability and axial average cell size ratios
Figure 10 is a perspective view of a pipe and flexibilized
foam board specimen arranged as a winding around the pipe for
cryogenic testing of the specimen,
Figure l.L is a perspective view of a pipe and flexibilized
foam specimen bent around the pipe with its Z-axis parallel to the
- 4a -
'
,
pipe axis for bendability testing of the specimen, and
Figure 12 is a perspective view of a pipe and flexibilized
foam specimen bent around the pipe with its Z-axis parallel to the
pipe axis for thermoformability testing of the specimen.
Referring to the drawings, Figures lA, B, C and 2A, B, C
are photomicrographs (magnification: 50x) of the one- and two-
directionally flexibilized foam of preferred Examples 123 and 223
of the present invention showing the closed cell structure as vie~ed
_
in the X-, Y- and Z- axial directions defined in Figure 3.
As shown in Figures l and 2, the flexibilized foams of
this invention are characterized by an anisotropic cell wall :
structure in which the wrinkles in the cell wall are directionally
oriented. Thus for the one-dimensionally flexibilized foam of
Figure l, wrinkles in the cell wall observed in the X-axial direction
- 4b -
:
7~ 3
--5--
(Figure lA) are significantly fewer than those observed
in the Y- and Z-axial directions (Figures lB and lC).
For the two-dimensionally flexibilized foam, the cell
walls are generally less wrinkled in the X-axial and
Z-axial directions (Figures 2A and 2C) than in the
Y-axial direction (Figure 2B).
Because of the small siæe and polyhedral
shape of the foam cells, it is difficult to express
thedistribution and location of such wrinkles accu-
rately in terms of cell structure. For simplicity,such distribution is parametrically observed and
described in terms of the three-dimensional coordinate
system of Figure 3. For a typical sheet of extruded
thermoplastic foam, the coordinates dimensions X, Y and
Z correspond to the length in the machine or extrusion
direction, thickness and width of the foam sheet,
respectively.
The anisotropic wrinkles in combination with
the properties of the formulated resin forming the cell
walls membranes, the cell size and shape, and the foam
density are impo~tant parameters of the flexibilized
foam. Also such physical properties as axial elongation
at rupture and water vapor permeability provide fairly
accurate indication of the type, location and distri-
bution of the anisotropic wrinkles.
Synthetic Resin Foams
The present invention is greatly influencedby tha properties of the initial expanded foam sheet or
planks. Thus the synthetic resin foams used herein
must be of s~bstantially closed-cell structure and
include foams expanded by extrusion as well as those
molded from expandable beads. However, most preferable
C~29,668A -5-
-6-
are extrusion-expanded foam boards of substantially
rigid, closed-cell structure. Also important is thelr
density, cell size, compression strength, and thermal
resistance which in turn depend on the synthetic resin
polymers used in making the initial foams.
Suitable are synthetic resins mainly composed
of styrene, vinyl chloride, vinylidene chloride, methyl
methacrylate or nylon including copolymers thereof and
physical blends of these resins. Preferable for the
present invention are resins containing as a major
component styrene or a styrenic monomer such as a-methyl
styrene and o-, m-, p-vinyltoluene and chlorostyrene.
Also usable are copolymers of styrene or styrenic
monomers and other monomers copolymeriæable therewith
such as acrylonitrile, methacrylonitrile, methyl acrylate,
methy methacrylate, maleic anhydride, acrylamide,
vinylpyridine, acrylic acid, and methacrylic acid.
However, more preferably for the present
invention are polystyrene resins consisting essentially
of only polymerized styrene and, most preferable poly-
styrene resins containing 0.3 percent by weight or less
of residual styrene monomer and 0.5 to 1.5 percent by
weight of styrene oligomers, primarily dimer and trimer.
Polystyrene resins containing such quantities of styrene
monomer and styrene trimer provide expanded foams
having particularly uniform distribution of density and
cell size as well as improved resistance to repeated
compression. Foams from such polystyrene resins are
especially well suited for one- and two-directional
flexibilization.
C-29,S68A -6-
gi3
-7-
To improve toughness, rubber may be blended
with such monomers before polymerization or added to
the system after polymerization. Further, the fore-
going resins may be blended with other polymers so long
as the desirable properties of the styrene resins axe
- not ad~ersely affected.
Selection of Foam Sheets
To achieve the desired flexibilization and
properties essential for low temperature insulation
reguires careful selection of the initial foam sheets
and control of several important properties prior to
flexibilization. Thus it has been found essential for
the present invention that the synth~tic resin foam
have (1) a bulk density of about 20 to 100 kg/m3, and
preferably about 20 to 60 kg/m3 for one-directional
flexibilizatlon (2) a Y-direction cell size of about
0.05-l.0 mm, and (3) a Y-axial compressive strength of
at least 1.8 kg/cm2.
To examine the interrelation of foam density
(kg/m3) and cell size (mm), ~spec:ially Y-axial cell
size y, a group of flexibilized foams having varied
foam densities and Y-axial cell s:izes were evaluated
for Y-axial compressive strength as a parameter of
creep resistance, X-axial and Z-axial tensile strengths
as parameters o~ breakage or rupture resistance of the
foams in use, variations in the X-axial and Z-axial
tensile strengths as parameters of the uniformity of
performance or quality, and Y-axial thermal conductivity.
Typical results given below in Tables 1 and 2
and based on an overall evaluation from a series of
tests indicate that foams of the present invention must
C-29,668~ -7-
1~'7~41~3
have a bulk density of about 20 -to 100 kg/m3, average y
cell size of 0.05 to 1.0 mm and average cell size
ratios y/x and y/z > 1.05. More preferably the foams
must be constructed substantially of cells having the
major axis thereof more definitely disposed along the
Y-axis wi~h the axial average cell axial size ratios
y/x and y/z are 1.10 to 4Ø If the average axial cell
size ratios y/x and y/z exceeds 4, the balance between
the dimensional stability, linear expansion coefficient
and the tensile strength will be lost.
Compression Flexibilization
Synthetic resin foams having the required
bulk density and anisotropic cell structure and size
can be flexibilized by compression in one or two axial
directions as described in Nakamura U.S. 3,159,700 to
provide the high water vapor barrier and other properties
desired for low temperature and cryogenic insulation.
However, carefully controlled conditions are required.
Figures 4 and 5 show schematic diagrams of
suitable compression equipment of flexibilizers. In
the flexibilizer of Figure 4, there are provided infeed
rollers 1, 2 and outfeed rollers 3, 4 spaced longitudi-
nally from each other. The flexibilizer shown in
Figure 5 is provided with infeed belts 9, 10 and outfeed
beits 11, 12 which are also spaced longitudinally from
each other. These paired rollers or belts hold the
expanded foam securely. The reference numerals 5, 6 in
Figure 5 and the reference numerals 13, 14 in Figure 4
indicate foam holding pressure means which should be
controlled accurately because the foam will undergo a
significant thicknesswise compression if the pressure
is too strong.
C-29,668A -8-
9 .
In operation the infeed rollers or belts are
driven somewhat faster than the second (outfeed~ pair
so that the foam is compressed in ~he longitudinal
direction in the gap between the infeed and outfeed
rollers or belts. According to the present invention,
the foam is normally compressed first in the longi-
tudinal ~X-axial) direction. Then if desired, the
one-directionally flexibilized sheet can be subjected
to compression in another direction at right angle to
the longitudinal d~rection, namely, in the lateral
(Z-axial) direction to provide a more flexible sheet
which can assume a compound curvature.
As noted, the flexibilization conditions must
be carefully selected and controlled. Particularly
important are:
(a) selection of expanded foam plan~ having
uniform quality throughout the sheet;
(b) minimum aging of the foam plan~s after
expansion;
(c) short compression zone; and
(d) stepwise compression~for flexibilized
foams with larger elongation.
A uniform quality for the initial expanded
foam sheet is required since the foams are mechanically
compressed for flexibilization one-direction at axis by
axis a time, e.y., X-axially first and then Z-axially,
while being held squeezedly Y-axially. Thus it is
necessary that the foams have minimum variation in
mechanical properties, especially compressive strength
throughout the sheet.
C-29,66~ -9-
--10--
The importance of minimum foam aging after
extrusion or expansion and before flexibilization is
shown in Figures 7 and 8. As described further in
Example 3, foam samples aged for varying length of
time before flexibilization in the apparatus of Figure
5 were evaluated for water vapor barrier and foam
elongation properties particularly important in the use
of the foam for low temperature and cryogenic insulation.
These results indicate that the foam should be flexi-
bilized while fresh shortly after initial extrusion,i.e., within 10 days (240 hrs) and preferably 3 days
(72 hrs) or less. Indeed, in-line flexibilization
shortly after foam extrusion, e.g., after about 0.1
hour to allow for cooling, may be advantageous.
By control o~ the compression conditions,
foam sheets ranging from 10 mm to 300 mm in thickness
have been flexibilized without significant loss in
Y axial compressive strength, water vapor barrier
properties and other desired properties. For sheets
thicker than about 35 mm the flex:ibilizer of Figure 5
is preferred. Elongation of foam processed with this
flexibilizer can be controlled by the spacing between
the infeed and outfeed belts. For best results, the
compression distance D should be about 300 mm at the
maximum, and preferably 200 mm or less, with a com-
pression duration of at least one second. Line speeds
of 5 to 40 m/min can be achieved with good results.
For thicker insulation, flexibilized sheets
can be laminated in desired configurations using a
small amount of an adhesive applied sporadically to
minimize the effect of the adhesive on the properties
of the laminated foams.
C-29,668A -10-
63
Flexibilized Foam for Low Temperature Insulation
Flexibilization essential herein is achieved
by the controlled introduction of anisotropically
oriented wrinkles in the foam cell walls in a manner
that does not unduly weaken the integrity of the foam
or crack the cell walls and cause loss of thermal
insulation and water vapor barrier properties. Since
the foam cells are very small and have polyhedral
shapes/ it is very difficult to define the location of
such wrinkles accurately in terms of cell shape and
structure. However, the Y-axial water vapor permeability
of the flexibilized foam indicates cracking or breakage
of the cell walls. Also the percentage elongation at
rupture in the three axial directions is a measurable
parameter of the extensibility, location and distribution
of the wrinkles. Typical results are given in the
Examples, and particularly Tables 3 and 4.
From Tables 3 and 4, it will be obvious -that
the foams contemplated by the present invention must
have a Y-axial water vapor permeability Py equal to or
smaller than 1.5 g/m2 hr to prevent or minimize deteriora-
tion in thermal-insulating properties over long use.
More preferably, the water vapor permeability should be
1.0 g/m hr or less.
In addition to the Y-axial water vapor per-
meability of the flexibilized foams, the elongations at
rupture in ~he three axial directions are useful
parameters of extensibility, location and distribution
of wrinkles and suitability for applications involving
such severe conditions as encountered in liquid nitrogen
storage tanks. Evaluation of the variations in the
X-a~ial and Z-axial elongations at rupture shows the
C-29,668A -11
-12-
uniformity of the extensibility throughout th~ foam
while the change in Y-axial thermal conductivity with
time reflects loss of thermal-insulating properties
from moisture absorption after prolonged use under
Y-axial loads. Also, cryogenic tests at about -160C
and -196C show the crack resistance of the foam when
used as the~mal-insulation for liquefied natural gas
and nitrogen tanks.
The preferred polystyrene foams exhibit
excellent properties as cryogenic insulation even
without cladding reinforcement. Their bendability and
thermoformability are particularly advantageous for
ield construction. To minimize multi-axial strains of
t~e foams after application or to improve thermal
properties, two or more such foams may be bonded to
form foam logs with biaxial extensibility. Also, they
may be clad with metal foils or they may be combined
with synthetic resin films having high gas barrier
properties.
The present invention also provides improved
synthetic resin foams which can be applied to small-
-diameter pipes by adjusting the extensibility of the
~oams in the bending direction in accordance with the
pipe outside di~meter and the fo~m thickness. Other
tests with 114 mm outside diameter pipes confirmed the
applicability of the one- and two-dimensionally flexi-
~ilized foam she~t to a variety of curved surfaces
including pipes and cylindrical and spherical tanks
regardless of curvature.
Such tests are representative of the bendability,
applicability to curved surfaces, cryogenic insulating
C-29,668A -12-
7~
properties, and other characteristics re~uired ~or
practical use of such foams. Indeed, the flexibilized
foams of -the present invention are significantly improved
over prior art foam products. They are becoming increasingly
important as thermal insulation for transportation and
storage of LNG, for cold storage o.f foods, and for
e~terior walls of buildings. These foams provide
effective thermal-insulation that can be applied easily
to such structures in the field.
The present invention will be further illus-
trated by the following preferred and reference examples
using the procedures and tests described below. Unless
otherwise specified, all parts and percentages are by
weight.
PolYstyrene Resins
The polystyrene resins used for the extruded
foam sheets were selected from commercial stock after
analysis for residual volatiles (primarily styrene and
ethylbenzene) and oligomers (styrene dimer and trimer)
by gas chromatography using a flame ionization detector.
For the oligomers, the resin is dissolved in methyl
ethyl ketone, the polymer precipitated with methanol,
and the supernatant liquid analyzed. These resins had
an lntrinsic viscosity of about 0.83 measured in toluene
solution at 30C.
Extruded Foam Sheets
The polymers were expanded into a rigid, sub-
stantially closed-cell foam with an extrusion-foaming
system composed of a screw extruder, blowing agent
blending feeder, cooler and board-forming die~ More
specifically, a mechanical blend of 100 parts of the
C-29,668A -13-
~t~ 63
-14-
polystyrene resin, 2 parts of a flame retardant and
0.03 to 0~1 part of a nucleator is contlnuously fed
into the extruder with 12 to 17 parts of a 50j50 mix-
ture of dichlorodifluoromethane/methyl chloride as a
blowing agent. The thermoplastic mixture is kneaded
under pressure, cooled to an extrusion temperature of
about 90 to 118C and then extruded through a die and
expanded into a foam. The extrusion conditions were
controlled so that the foam was about 110 mm x 350 mm
in cross-section and the axial cell size ratios y/x and
y/z were about 1.1 to 1.25 and 1.1 to 1.17, respectively.
The Y-axial cell size and bulk density D were varied in
the range of 0.07 to 1.6 mm and about 21.5 to 77 kg/m3,
respectively. Foams lighter than about 21 kg/m3 were
subjected to secondary expansion by exposure to steam
at 100C for 2 to 6 minutes. The resultant foams have
a bulk density of about 15.5 to 20 kg/m3. Analysis
showed essentially no loss of residual volatiles or
oligomers in the extrusion process.
Directional Flexibilization
Skins were removed from the freshly extruded
foams to obtain skinless foam boards about 100 mm x 300
mm in cross-section and 2,000-4,000 mm in length.
These foam planks were mechanically com~ressed for
flexibilization in the of X-axial direction and then
for two-directional flexibility in the Z-axial direction
using the equipment shown in Figure 5. Typical conditions
for the compression process were:
C-29,668A -14-
3~ 3
-15-
Aging before compression: 1 day
Plank thickness: 100 mm
Infeed belt speed: 12 m/min.
Infeed/outfeed speed ratio: 25/21 - 28/21
Compression distance D 200 mm
(See Figure 5):
Compression duration: 3.6 sec.
Cycles of compressions: 1 - 3
Test Procedures
The resulting flexibilized foam planks are
then evaluated by standard test procedures. Individual
test results are rated on a general scale as:
Good (G0) -- Desired or target foam quality
Passable (PA) - Conventional foam quality
Unacceptable (UN) -- Below acceptable foam quality
and then an overall composite evaluation rating is made
on the scale:
Excellent (EX) -- Rated Good in all tests
Good (GO) -- Rated Good/Passable in all tests
Passable (PA) -- Rated Passable in all tests
Unacceptable (1~) -- Rated Unacceptable in at least
one test
~1) Foam Density
Standard test samples, normally a 50 mm cube
or a 25 mm x 100 mm x 100 mm sheet are cut from the
center parts of the skinless foam board and their weight
C-29,668A -15-
-16-
(g) and volume (cm3) determined and the foam density
calculated from the average of at least three specimens.
The density variation calculated by the formula:
. Max. density - Min. density
Denslty varlatlon = x
100 Avg. density
provides a useful measure of foam uniformity:
Ratin~ Density Variation
Good -- <10% variation in density
Passable -- 10-15% variation
Unacceptable -- ~15% variation
(2) Average Cell Size and Shape
The X-axial, Y-axial and Z-axial average cell
sizes x, y and z in terms of the coordinates of Figure 3
are measured by the method of ASTM D-2842 using nine
specimens cut in the prescribed manner. Then as para-
meters of cell shape, the ratios of the Y-axial average
cell size y versus X-axial and Z-axial average cell
sizes x and z are calculated.
The average cell slze variation provides a
measure of foam uniformity on the following evaluation
scale:
- Rating Density Variation
Good -- <35% variation in cell slze
Passable -- 35-45% variation
Unacceptable -- ~45% va-iation
C-29,668A -16-
7~ ~i3
-17-
(3) Compressive Strength
A total of six to twelve 50 mm cubes are cut
from each foam in a standard pattern and each specimen
is subjected to axial compressive strength test in the
non-flexibilized direction in accord with ASTM D-1621.
The resulting average compressive strength is evaluated
on the following scale:
Ratin~ Average Compressive Strenqth (kg/cm2)
Good Y-axial: 2.2 X-axial: 1.1
Passable Y-axial: 1.8-2.2 X-axial: 0.9-1.1
Unacceptable Y-axial: <1.8 X-axial: <O.9
(4) Tensile Strength and Variation
From a skinless foam board, twelve 50 mm
cubic specimens are cut in a standard pattern. In
accordance with ASTM D-1623 B, each specimen is sub-
jected to X-axial tensile strength test with a jig or
loading fixture attached to each end. The measured
strength Sl through S12 are avera~ed and the tensile
strength variation is calculated as follows:
12
~ S.
i=l 1 2
X-axial average tensile = 12 (kg/cm 3
strength
25 Tensile strength = max. stren~th-min. strength x 100 ~)
variation average strength `
Likewise, the Z~axial average tensile strength and
~ariation thereof are measured on another twelve
~pecimens.
C-29,668A 17-
~ ~ r 7 ~
-18-
Ratinq Tensile Stren~ ~ Variation
Good 1.2 kg/cm2 <20%
Passable 1.0-1.2 kg/cm2 20-40%
Unacceptable <1.0 kg/cm2 ~40%
~5) Percent Elongation at Rupture
In accordance with ASTM D-1623B, the three
groups of 12 specimens, each a 50 mm cube, were ~ubjected
to X-axial, Y-axial and Z-axial tensile strength test,
respectively, to determine their elongations at rupture
Gx, Gy and Gz, from which the percentage elongations at
rupture Ex, Ey and Ez were calculated by using the fol-
lowing formula, respectively:
Percentage elongations = Gx, Gy, Gz (mm) x 100 (~)
at rupture tEX, Ey, Ez) 50 (mm)
Then, for the respective specimen groups, the average
percentage elongations at rupture Ex, Ey and Ez and
their variations were calculated by the following
formulas:
~ (E~, Ey, Ez)
Average percenta~e elongations
at rupture (Ex, Ey, Ez)
Variation in max. percentage min. percentage
percentage _ elongation elongation x 100 (~)
~5 elongation ~ averagP percentage
at rupture elongation (Ex, Ey, E3)
where max. and mln. percentage elongations are for each
axis.
C-29,668A -18-
~P'~ 3
--19--
% Variation in Elonqation at Rupture
Good <20%
Passahle 20-40%
Unacceptable >40%
Also, it is useful to calculate the ratios Ex/Ey and
E7/Ey as further measure of the foam quality.
(6) Thermal Conductivity
A flexibilized foam board is cut into specimens
each 200 mm square and 25 mm thick. Each specimen is
then aged in a chamber partially filled with water and
held at 27C. The specimen is secured in the chamber
about 30 mm above the water surace and a cold plate
cooled to 2~C by recirculated cooled water is brought
into tight contact with the top surface of the specimen.
After aging for 14 days, the specimen is taken out and
its surface is wiped lightly with gau2e. The thermal
conductivity A' of the aged specimen is measured in
accordance with ASTM C-518 and the ratio of A' to the
initial thermal conductivity A of the specimen before
aging is calculated.
Ratin~ Thermal Conducti~ity Chanqe (A'/A)
Good <1.07
Passable 1.07-1.12
Unacceptable >1.12
(7~ ~ater Vapor Permeability
Three circular specimens each 80 mm across
and 25 mm thick are cut from each flexibilized foam and
C-29,668A -19-
9'~3
-20-
the water v2por permeability of the specimens is measured
in accordance with ASTM C-355 using distilled water.
From the measurements, the water vapor permPability is
calculated by using the following formula:
Water vapor permeability = G (g/m2-hr)
where: G ............ ..change in specimen weight (g)
A .......... ..area subjected ~o water vapor
transmission ~m )
t .......... ..time in which the specimen weight
changes by G gram (hr)
For low temperature insulation, a water vapor
permeability of less than 1.5, and preferably less than
1.0 g/m hr, is most desirable.
(8) Cryogenic Tests
A. Three 20 mm x 100 mm x 1750 mm specimens
were prepared from a flexibilized foam board and wound
around a stainless steel pipe 3~ and thelr opposite end
faces (YZ faces) were butt-welded together as shown at
40, 41 and 42 in Figure 10. The the pipe specimens
were quickly immersed in a cryostat filled with liquid
nitrogen so that all specimens were well under the
liquid surface. After being immersed for 5 hours, they
were taken out of the cryostat and left at a room
~S temperature for 5 hours. After 4 cycles of such treat-
ment, the three specimens were carefully observed for
any visual changes including cracks, fractures or
ruptures.
Good ............ No visible fractures or cracXs
Unacceptable .... cannot wind without fracturing
C-29,668A -20-
-~'7~ 3
-21-
B. In another test, flexibilized foam speci-
mens 50 mm thick, 170-270 mm wide and 300 mm long were
smoothed by machining the top and bottom surfaces.
After mar~ing the X and Z axes on the çdses, each piece
was covered top and bottom with 12 mm thic~ plywood
(conforming to Japanese Agricultural Standard) using a
commercial cryogenic polyurethane adhesive (Sumitac
EA90177 produced by Sumitomo Bakelite Co., Ltd., Japan)
to the joint surfaces. The adhesive was cured by placing
the test panel under pressure of 0.5 kgjcm2 for 24 hours
at 23C.
1. Cryogenic Test at -160C
Each cryogenic test panel 34 is placed in a
liouid nitrogen cooled cryostat box having an internaI
temperature controlled to -160C ~ 5C by controlled
addi~ion, gasifica~ion and diffusion of liguid nitrogen.
~fter 5 hours, thP test panel is quickly removed and
left at room temperatures for about 1 hour. This pro-
ces~ is repeated 4 cycles. After the last cycle, the
test panel i~ visually checked for cracks in the four
exposed faces of the foam specimen. Then one hour after
removal from the cryostat, the plywood covers are removed
wi-~h a slicer. Then a 10 mm thick slice of the foam is
cut from the top surface and a mixture of a surfactant
and colorant in water is applied to the sur~aces of
- the cut foam to show any crac~s formed therein.
2. Cryogenic Test at -196C
For this test, a cryogenlc box partially filled
with a liquid nitrogen is used. The plywood faced test
panels are submerged in the li~uid nitrogen and placed
on triangular steel supports fixed to the bottom of
the box. A steel weight precooled in liguid nitrogen
C-29,668A -21-
-22
is placed on thP test panel top, and the panel held
immersed for 30 minutes. Then the test panel is taken
out and left at room temperature for one hour under
forced ventilation. After repeating the foregoing pro-
cess for four or more cycles, check is made for surfaceand internal cracks in the manner described above in
test B(1).
Rating Obser~ation
Good No visible damage or crac~s
10 Passable Fine cracks
Unacceptable Ruptures or large cracks
(9) Cryogenic Pipe Insulation
A. Bendabillty Three pieces of flexibilized
foam 200 mm wide, 500 mm long and 25, 37.5 and 75 mm
thick are bent to the curvature of a steel pipe 54
about 114 mm in outside diameter by applying a bending
stress Y-axially thereto with its Z-axis disposed in
parallel with the axis of the pipe 54, as shown in Fig-
ure 11. The specimen is ~ent until it is brought into
close contact with the outer periph~ral surface of the
pipe over an area exceeding the outer surface area of a
semicylindrical half section of the pipe (the section
above the center line A - A shown in Figure 11).
Ratinq Observation
25 Good Bends easily without cracks
Passable Bends with careful attention
Unacceptable Breaks
C-29,668A -22-
-23-
B. Thermoformabili~y The flexibilized foam
pieces are bent to the outside curvature of the steel
pipe 54 about 114 mm in outside diameter with its
Z-axis disposed along the axis of the pipe. Markings
are put on the cut edge of the pipe 54 diameterically
oppositely along the center line A - A shown in Figure
12. The bent specimen 56 is then totally covered with
a galvanized, 0.3 mm thick sheet iron 55 and the opposite
side ends of the foam specimen held with tensioning
bands 57. Then the covered specimen 56 is placed in a
hot-air oven with the tensioning bands 57 down and
heated at 85C for 45 minutes. After being remove~
from the oven, the specimen is cooled at room tempera-
ture for two hours. Then, the galvanized cover 55 is
removed and the gaps 58 and 59 from the outer ends of
the foregoing markings to the intersections of the
center line A - A and the inner wall of the specimen 56
are measured and rated as follows:
Good Average gap ~5 mm
Passable Average gap 5--10 mm
Unacceptable Average ~ap >10 mm
C. Thermal Insulation Test Pieces of flexi-
bilized foam cut to a 37.S mm x 200 mm ~ S00 mm size
are thermoformed as above in two layers and then cut
Z-axially to provide inner and outer semicylindrical
thermal insulation covers for a 114 mm o.d. pipe. The
test cover pieces are then fit to a 114 mm o.d. stain-
less steel pipe about 800 mm long with flanges at each
end and secured with a cryogenic polyurethane adhesive.
The joints of the outer covers are staggered from those
C-29,668A -23-
~'7~3~
-24-
of the inner cover. The entire section is then coated
with a 2.5 mm t~ick waterproof layer of polyurethans
mastic. After 4 days aging, the covered pipe is connected
to a cryogenic test line and filled with liquid nitrogen.
The interior of the stainless steel pipe is maintained
at -196C for 6 hours. Thereafter, the liquid nitrogen
is discharged and the covered pipe left for 12 hours at
23C and 80% R.~. The foregoing test cycle is repeated
four times while observing the surface conditions of
the water-proof layer 66 including water condensation
and icing~
The results are evaluated as follows:
Good No visible surface change
Passable Brief spots of moisture condensation
Unacceptable Icing or extensive condensation
Immediately after the above tests, the water-
proof coating and foam insulation layers are carefully
removed and visually examined for cracks using a colorant ,
solution if necessary.
Good No visible d~lage or cracks
Passable Fine cracks
Unacceptable Ruptures or large cracks
Example 1 One-Direction Flexibilization
Using a commercial polystyrene resin containing
0.20 weight percent residual volatiles including styrene
monomer and 0.87 weight percent oligomers including
styrene trimer (herein PS Resin A), a variety of foam
planks were prepared for one-directional flexibilizatlon.
C-29,668A -24-
.
~ -25-
The extrusion conditions were controlled to give a foam
sheet about liO mm x 350 mm in cross-section with a
bulk density of about 21.5 to 60 kg/m3. Skins were
removed from each of the foams and the resulting foam
board was cut into three smaller planks each 100 mm
syuare and ~,000 mm long.
Preferred Exam~les 101-112; Reference Examples R101-107
After aging one day, the foam planks were
flexibilized by compression in the machine direction
(X-axis) using the eyuipment of Fig. 5 and the typical
conditions described in the procedures above. The
flexibiliz~d foam planks of the preferred Examples
101-112 were evaluated for density, Y-axial cell sizes,
cell shapes represented by y/x and y/z, compression
strengths (Y-axial and Z-axial), X-axial tensile
strengths and elongation at rupture with the results
shown in Table 1. In these examples, the axial cell
size ratios y/z were in the range of 1.00 to 1.25.
For comparison other foams expanded from PS
Resin A but lacking in desired foam characteristics
were flexibilized in a similar manner with results
shown in Table 1 as Reference Examples.
C-29,668A -2S-
-26-
O
h ~ ~C X P~ O O O X O X O X X
~ a
O ~ :"
,C O
,1
1 ~
o o o ~ 0 0 1~ 0 0 0 0
C~ ~ ~ V ~ 1~ V
'~ ~
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) ~
ri ~ 0 O O O ~ 5 o ~ o ~ o o
x e~ ,, c~ ~ ~ p~ ~ p., ~ ~ o P~ v
h Q~
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~1 ~ ~, h ~1
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d ~-) (~ C~ V ~
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C t~ o tr1 10 o) In o
~, v.qI~ ............ ,~,
o ~ ~ o o o a~ o ~o ~ ~ o co ~ P~
rl r-l N ~ L0 0 c~ 0 a~ o t~ ~1 0 0
X ~ rl ~
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ul~ .......... ,, .
X ~ ~1 ~ ~ O O ,~ O u~ ~ o ~o
.
O t~
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s~ ~1 ,
~ ~:4 O O O o o o o o O ,~
S~ X
P~ ~
C-29, 668A -26-
--2 7--
~K O
h ~ ~ ~ F ~,
O >
0
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X h v~ ~ c~
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X ~ -~ ~
X ~ ~
:~ ~ ~ ~ O o o o
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O V~ X ~ ~ ~ O O O O
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. ~Q _ N
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m~ x
l¢p:; ~q K
-
C-29, 668A -27-
~'7~ ~3
-28-
Based on results as shown ln Table 1, the
foam bulk densities were plotted on the chart Fig. 6A
against the Y-axial average cell sizes y. The coordinates
representing the foam specimens satisfying the objects
of the present invention are marked with o, while those
representing the specimens not satisfying the objects
of the present invention are marked with X.
As seen in Fig. 6A, the foams as intended by
the present invention must have such Y-axial average
cell sizes y and bulk densities D that fall in the
pentagonal domain defined by five coordinates (1.0,
43), (1.0, 20), (0.05, 24), (0.05, 60) and (0.1, 60)
and, more preferably, in the tetragonal domain defined
by the coordinates (0.8, 42), (0.8, 23), (0.07, 26) and
lS (0.07, 57). The bulk densities D and Y-axial cell
sizes y of these foams satisfy the following formula:
-17 Qog y + a3 _ D > -3 ~og y + 20
(where 20 s D s 60 and 0.05 s y s 1)
and more preferablyi
-15 Qog y + 40 > ~ > -3 Qo~ y ~ 23
Iwhere 20 ~ D ~ 60 and 0.07 s y ~ 0.8).
Exam~le 2 Two-Direction Flexibilization
Using the same commercial polystyr~ne resin A
and procedures of Example 1, a variety of foam planks
25 were prepared about 110 mm x 350 mm in cross-section,
axial cell size ratios y/x and y/z about 1.1 to 1.25
and l.l to 1.17, respectively, while the Y-axial cell
size and bulk density d are varied in the range of 0.07
to 1.6 mm and 21.5 to 77 kg/m3, respectively. Those
foams lighter than about 21 kg/m3 are subjected to
secondary expansion by exposing them to steam at
C-29,668A -28-
~l~'7~i3
-29-
100C for 2 to 6 minutes resulting in a bulk density of
about 15.5 to 20 kg/m3. Skins are removed from each of
the foams to obtain a skinless foam board of about 100
mm x 300 mm in cross-section and 2,000 mm in length.
These resultant foam planks are mechanically compressed
for flexi~iliæation in the direction of X-axis first
and then Z-axially by using the equipment as shown in
Fig. 5 and the typical conditions described above
including aging for one day after extrusion.
Preferred ExamPles 201-212; Reference Examples R201-206
As a result of the compression process,
flexibilized foam planks of the Preferred Examples
201-212 and Reference Examples R201-206 having almost
constant cell shapes with the axial cell size ratios
y/x and y/z ranging from 1.2 to 1.4 are obtained. Then
these flexibilized planks are evaluated by the standard
procedures with typical results shown in Table 2.
C-29,668A -29-
~ 3L 7 ~
--30--
~ O
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X X X O O X X O X X O O
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V ~ ~ V C~ V ~ ~ V
O
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o~ ~ v
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C~ V ~ V ~ C~
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i~i O t~ C~ V P~ V
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C-2~, 668~ ~30~
~'7~3
--31--
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C- 29, 668A -31-
.,
~.
-32-
Based on typical results as shown in Table 2,
the bulk densities D are plotted on the chart of Fig.
6B against the Y-axial averaga cell sizes y, in which
the coordinates representing the foam specimens evaluated
as excellent and good in Table 2 are marked with 0 and
o, respectively, while those evaluated as unacceptable
being marked with X.
As seen in the chart of Fig. 6B, the foams as
intended by the present invention must have such y-axial
average cell sizes y in mm and bulk densities D in
kg/m3 that fall in the pentagonal domain defined by
five coordinates (1.0, 55), (0.25, 100), (0.05, 100),
(0.05, 26.5) and (1.0, 20) and, more preferably, in the
pentagonal domain defined by five coordinates (0.8,
55), (0.25, 93), (0.07, 93), (0.07, 28.5) and (0.8,
23.5)-
In other words, the foams contemplated by the
present invention must have such a foam density D
(kg/m3~ and Y-axial average cell size y (mm) that
satisy the following formula:
-75 Qog y + 55 ~ D ~ -5 Qog y + 20
(where about 20 ~ D _ about 100, 0.05 ~ y < 1)
or more preferably;
-75 Qog y + 48 > D ' -5 Qog y + 23
~where about 23 S D ~ about 93, 0.07 ~ y ~ 0.8).
Example 3 Flexibilization Time
In normal practice, rigid thermoplastic foam
sheets are aged for at least saveral weeks before use
to stabilize tha foam structure. During the development
C-29,668A -32-
, .
~.~t7~ 3
-33-
of the flexibilized foam for cryogenic insulation, it
was discovered that the age of the extruded foam at the
time of compression flexibilization profoundly influenced
the resulting foam properties.
Using foam sheet extruded from polystyrene
resin A and cut to standard 25 mm and 100 mm thick
pieces, the effect of flexibilization time was examined
for both one- and two-direction flexibilization.
Typical results are shown graphically in Figures 7 and
8 with the A series being one~directional (X-axial)
flexibilization and the B series being two-directional
(X-axial, then Z-axial) flexibilization.
A. One-Directional Flexibilization
Figure 7A shows the relation between X-axial
elongation at rupture Ex of the fle~ibilized foams and
the aging period of the initial foam sheet after extru-
sion, while Fi~lre 8A shows the relation between water
vapor permeability and the aging period be~ore flexi-
bilization. It is evident that to o~tain the irnproved
elongation and water vapor barrier properties intended
by the prese~t invention, it is necessary that the
aging period for the foams prior to compression flexi-
bili2ation be not more than 10 days (240 hrs) and more
preferably, 3 days (72 hrs) or less.
B. Two-Directional Flexibilization
Figure 7B shows a relation ~etween the X-axial
percentage elongation at rupture Ex of two-directionally
flexibilized foams and the aging time of the extruded
foam planks. Note that aging a fects the X-axial and
Z axial percentage elonga-tions at rupture substantially
equally. The initial fresh foam planks had a density
C-29,668A -33
''3'~3
-34-
of about 27 kg/m3, thickness o~ about 100 mm, and 2, Y-
and Z~axial average cell sizes of about 0.55 mm, 0.72
mm and 0.58 mm, respectively. After being cut to a
thickness of 25 mm, the foams were subjected to one
cycle of 37 percent compression X-axially first and
then Z-axially at varied aging times. The Z-axial
percentage elongations at rupture Ez ranges from about
80 to 90 percent of the X-axial percentage elongation
at rupture Ex. In Fig. 7B, the axial percentage elonga-
tions at rupture are representatively given as theX-axial percent-elongation at rupture Ex.
Fig. 8B shows a relationship between the
water vapor permeability Py of flexibilized foams and
the aging period of the material foams after expansion
thereof. The foam planks have the same density and
axial average cell sizes as those above. Test pieces
about 25 mm thick were cut and subjected to 20-37
percent compression applied one to three times in each
direction. The resulting foams had an X-axial porcentage
elongation at rupture Ez of about 20 percent and Z-axial
percentage elongation at rupture E:z of about 16 percent.
Again it is clear that to obtain desired pro-
perties, the foam should be flexibiiized while fr~sh,
i.e., within 10 days or more preferably 3 days of
extrusion and/or expansion. This applies especially to
relatively thin foams as represented by the 25 mm thick
samples used in the preceding experiments. The optimum
time within the range of about 0.25-240 hours will, of
course, depend on the specific properties of the initial
foam and the desired results.
C-29,668A -34-
-35-
Exam~le 4 Water Vapor Permeability
Critical for low temperature insulation is
the ability of the foam to be an effective barrier to
the transfer of water vapor from the outer to inner
surface of the insulation.
A. One Directionally Flexibilized Foam: Preferred
Examples 1~1-132 ~ Reference Examples R121-126
Using the same equipment and methods, flexi-
bilizable foam planks were expanded from ~S Resin A
under controlled conditions so that the resultant foams
had densities D in the range of about 22.5 to 51 Xg/m3,
Y-axial cell sizes y in the range of about 0.07 to 1.0
mm and axial cell si~e ratios y/x and y/z of about 1.35
to 2 and about 1.1-1.3, r~spectively. Then the resultant
foam planks were cut to 100 mm square and 4,000 ~m long
and after aging for one day were compressed X-axially.
Typical properties including water vapor permeability
for these flexibilized foams are given in Table 3.
C-29,668A -35-
36--
,1 1
O
O X ~ ~ o X o X X o X X
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C-29, 668A -36-
--37--
*
~1 0
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~ L R :~ ~ ~ V
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y
C-29, 668A -37-
:
l~ t~ ;3
Based on such typical results as shown in Table 3, the
flexibilized foam of the present invention must have a water vapor
permeability of 1.5 g/m .hr or lower as determined by the water
method of ASTM C-355.
Figures lA, B and C are photomicrographs (magnlfication:
50x) of the polystyrene foam of the preferred example 123 showing
closed cells distributed as viewed in the X-, Y- and Z-directions
shown in Figure 3. Note that the flexibilized foams of the present
invention have a unique structural anisotropy in which wrinkles in
the cell walls observed in the YZ-plane (Figure lA) are significantly
fewer than those observed in the XZ- and XY planes (Figure lB and lC).
Since the foam cells are very small and have polyhedral shapes, it
is very difficult to express the distribution and locations of such
wrinkles accurately. However, considering the relations between Ex,
E and the Y-axial water vapor permeability Py with reference to
Figure 1, these relationships provide fairly accurate structural
parameters of the wrinkles including their type, location and
distribution. Also as shown in Figure 9A by the plot of water vapor
permeabilit~ and cell shape of the foam, it is desired that the
cells be oriented along the Y-axis, preferably with a ratio of
average y/x cell size of 1.2 to 3.
B. Two-Directionally flexibilized ~oam: Preferred
Examples 221-227 ~ Ref. Examples R221-225
Using the same PS Resin A, equipment and methods of
Example 1 foam planks having the same cross-sections were extruded
and expanded with a density of 27 kg/m3 or 50 kg/m3 and Y-axial
average cell size of 0.61 mm or 0.11 mm with y/x of 1.20 or 1.15
and y/z of 1.25 to 1.20. These foam planks were compressed for
flexibilization X-axially first and then Z-axially by
- 38 -
!`
. .,
1,
-39-
using the equipment as shown in Fig. 5. Then the foam
densities D and other properties including the Y-axial
water permeability Py of the thus biaxially-flexibili2ed
foams are measured. Also, the changes in Y-axial
thermal conductivity as well as the X-axial and Z-axial
cryogenic resistance at -160C and -196C are observed.
Typical results are shown in Table 4.
C-29,668A -39-
.~ 3
--40--
O ,~
~ u~ ~1 ~ oo In o
:~ ,CI N 11~ ~Ç) t` r~ D N t~ 1~
s~ aJ \ o o o ,~ ,~ o ,~ o ,~ ,~ o o
3 Pl
::~ N t` ~` 0r` ~ N -1
~ N ~D CO ~O O D t` O O r~ tr)
--1:~ N N N ~) r`tr) t~ ~i CO ~i r~ r~
_ 7~ N ~` I` ~0 N d~ N ~D O 11'~ ~D
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r1 ~1
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C-29, 668A -40-
~1:3'7~
~41--
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*
C-29, 668A -41-
.
-42-
Table 4 shows that the foams of this invention
must have a Y-axial water ~apor permeability Py equal
to or smaller than 1.5 g/m2 hr ~o prevent or minimize
deterioration in thermal-insulating properties over a
long period of use. More preferably, the water vapor
permeability should be 1.0 g/m2 hr or smaller to secure
a higher level of thermal insulation.
For applications involving such severe con-
ditions as encountered in liguid nitrogen gas tanks and
for ensuring improved heat-insulating properties over a
longer period, the preferred foams of the present
invention must also satisfy the following conditions:
Ez s 52 - Ez
8.3 ' Ex/Ey > 1.8, 8.3 >- Ex/Ey A 1.8
Ex + Ez < 12 Ey
where 40 > Ex '- 12 and 40 ~ Ez ' 12; and
Py ~ 1.0
Fig. 2A, B and C are photomicrographs (magni-
fication: 50x3 of the flexibilized polystyrene foam of
Prèferred Example 223 showing the closed cells viewed
in the X, Y and Z directions shown in Fig. 3. Note
that the ~oam is characterized by structurally aniso-
tropic cell walls. Those visible in the Yz and XY
planes shown in Fig. 2A and 2C are generally wa~ only
in one direction, namely in the Z-axial and X-axlal
directions respectively, but not in the Y-axial
direction.
Such aniso-tropically distributed cell wall
wrinklPs in combination with the foam density as well
as with the siz~s and shapes of cells are important
C-29,668A -42-
9~3
structural parameters of the foams of the present invention, in view
of the aforementioned relationship between Ex and Ez, the ratios of
axial percentage elongations at rupture (Ex/Ey, Ez/Ey) and Y-axial
water vapor permeability that represent the distribution and
directions of such wrinkles. Also as shown in Figure 9B by the plot
of water vapor permeability and cell shape of the foam, it is
desired that the cells of the foam be disposed along the Y-axis,
preferably with an average axial cell size ratio y/x and y/z of 1 or
more.
Example 5 Cryogenic Insulation
A. One-Directionally Flexibilized Foam
Surprisingly, an experiment has revealed that when wound
around a steel drum and heated at about 80C foams having the desired
improved elongation properties and water vapor barrier properties can
be shaped to the drum curvature and can be fixed to that shape. Still
the winding requires no large force and en-tails only a minimum re-
duction in the thermal-insulating properties.
Table 5 shows the results of experiments on still another
group of the preferred examples of the present invention and several
reference foams. Since these evaluation items are substantially
representative of the bendability, applicability to curved surfaces,
adhesion workability, cryogenic insulating properties and other
characteristics practically required to such foams, Table 5 does
give overall evaluation for practical applicabilities of such foams.
Further, to minimize multi-axial strains of the foams after
application or to improve the thermal-insulating properties effect-
ively, two or more such foams may be bonded so that the resultant
- 43 -
~,. ..
.
. ~
~ ,
.
~ 7t~ ,3
foam logs show biaxial extensibility or they may be clad with
metal foils or they may be combined with synthetic resin films
having high gas barrier properties.
- 43a -
--44--
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C-29, 668A -44-
.
7~
--45--
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C-29, 668A -45-
7~
-4~-
B. Two-Directionally Flexibilized Foam
To determine the applicabllity to curved sur-
faces such as pipings, cylindrical or spherical tanks,
workability including bendability and formability, and
performance as cryogenic thermal~insulating materials,
selected foams, namely the foams of preferred examples
222-225 and of the references R221, R223-225 are appplied,
respectively, onto a steel pipe of about 114 mm in out-
side diameter as a typical representative of cylindrical
pipes having a very large curvature. The foams were
sliced to a thickness of 25, 37.5 or 75 mm and applied
in one, two or three layers to obtain an overall thick-
ness of 75 mm. The longitudinal and circumferential
seams of the semicylindrical foams sections applied in
layers are butt~d, while those of the foam sections 77
mm thick are shiplapped.
The bendability, thermoformability to the
bent forms, cryogenic heat-insulating properties and
crack resistance thereof are tested and typical results
are given in Table 6.
C-29,G68A -46-
--47--
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C 29, 668A -47-
~7~3
--48--
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r-l ~J ~ -~ O 4-1 (~1 N N ~ ~`1 N N ~ N ~ N N N ~`3 C`l ~1 11~2 O Ul tl~ Z; (I) 1~1 ~ ~ N C`l ~ 1 ~1 p~
ta ~. ~ x h ~ X
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C-29, 668A -48-
-49-
The synthetic resin foams of the present
invention having larger extensibility in two axial
directions show excellent bendability, thermoformability
and applicability to pipes having small diameters.
They can be easily applied to such small-diameter pipes
and can be easily thermoformed to their bent shapes.
Further, becausP of substantial freedom from crack
formation in bending operation or under cryogenic
conditions, the synthetic resin foams according to the
present invention can provide excellent cryogenic
thermal-insulating materials free from moisture con-
densation even at -196C which are generally applicable
to pipes, cylindrical and spherical tanks.
Althou~h the reference foams compressed only
X-axially or Z~axially have satisfiable bendability and
thermoformability, they are not entirely satisfactory
as cryogenic thermal-insulation because they m~y break
under cryogenic conditions due to cracks spreading
circumferentially of the pipe or in other directions.
Such cracks form because these oams do not have suf-
ficient extensibility to absorb st:resses generated bv
sudden changes between the room and cryogenic temperatures.
Example 6 Thermoplastic Resin Foams
The improved flexibilization process is
applicable to a variety of thermoplastic resin foams,
both extruded and expanded.
A. Commercial PS Resin A is a thermally
polymerized polystyrene resin having an intrinsic
viscosity of about 0.83 dissolved in toluene at 30C
and containing 0.20 weight percent residual volatiles
C-29,668A -49-
7~
-50-
including styrene monomer and 0.87 weight percent
oligomers including styrene -trimer. Blends with other
polystyrene resins richer in residual styrene monomer
and trimer were flexibilized with typical results shown
in Table 7. For such thermally polymerized polystyrene
resins, preferred resins for the flexibilized foams are
those containing 0.3 weight percent or less of residual
volatiles including styrene monomer and 0.5-1.5 weight
percent of styrene oligomers including trimer.
C-29,668A -50-
i ~ 7 ~ 3
--51--
N O
rl
X C~ ~ ~0 g
O
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~ O
~ O O O O
N . ~ ~ V C~
U~
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x 1-1 u) In Ll'~
l~ ..... ...
00000 000 11
O al
F: O ~ ~
In ~ o
I~ ~ ~ .~ . ',i ,~ .
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. ~ .~ V V P~ P~ U P
~' ~; ~ I p, .
~-1 . . U~ 11
.
a~ ~1~ ~` ~o o ~ N l` O ~ (~ .
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N N N N N N N N > O
Il
- O
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t~ ~ o o o ~ ~ a~
.,1 ~ ~ ~ Ln U~ U ~ ~ U~ `
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U~ ~ N N N O ~ dl ~ ~1 ~ 1:~
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X Q ~1 U~ ~I r~
C-29, 668A -51-
-S2-
B. Instead of the polystyrene foams used in
the foregoing examples, two commercially-available
polyvinyl chloride foams (Klegecell~ 33 produced by
Kanegafuchi Chemical Co., Ltd. and Rockecell Board~
produced by Fuji Kasei Co., Ltd.) and a methyl meth-
acrylate resin foam (made experimentally by Asahi-Dow
Limited) cut to 50 x 600 x 900 (mm), 25 x 600 x 900
(mm) and 50 x 300 x 900 (mm), respectively, are com-
pressed under conditions typically given above.
The resultant flexibilized foams are tested
and evaluated with typical results shown in Table 8.
Thus, the present invention is applicable also to foams
expanded from polyvinyl chloride resins including
blends thereof with inorganic materials, methyl
methacrylate and the like resins other than polystyrene,
and the resulting flexibilized foams ~atisfy the
reguirements of the present invention.
C. A batch of prefoamed polystyrene beads
having a bulk density of 11.6 kg/m3 is placed in a
mold, and steam is heated for about 40 seconds under
pressure of 3 kg/cm . The resulting foam was aged at
about 70C for 12 hours. It`had a density of 10.9
kg/m3 with x of 0.33 mm, y of 0.31 mm and z of 0.32 mm.
Three 350-mm cubes are cut out from its central portion
by means o~ an electrically-heated wire cutter.
One sample was flexibilized X-axially by com-
pression to 90 percent of its original volume by applying
40 kg/cm2 pressure with a 50~ton press. The compression
was repeated continuous six times by relieving the
pressure immediately after its application. The com-
pressed foam has the size of 350 x 350 x 262 (mm) with
a density of 14.5 kg/m3.
C-29,668A -52-
- :~.1'7~4~
-53-
The other samples were similarly flexibilized
in two- and three- directions. All were subjected to
the standard tests and failed to meet one or more of
the desired results contemplated by the present inven-
tion. Note also that none had the re~uisite initial
~oam density.
C-29,668A -53-
'54--
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C-29, 668A -55-
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C-29, 668A -56-
`
