CA1179463A - Directionally flexibilized expanded thermoplastic foam sheet for low temperature insulation - Google Patents

Abstract

Abstract of the Disclosure Flexibilized, rigid plastic foam sheets with improved properties particularly desirable for low temperature and cryogenic insulation can be prepared by mechanical compression of freshly expanded closed-cell thermoplastic foams. Thus an extruded foam sheet having a density of 20-100 kg/m3, a ?-axial size size of 0.05 to 1.00 mm and a ?-axial compressive strength of at least 1.8 kg/cm2 is flexibilized with 0.25 to 240 hours of expansion to give a flexibilized foam with improved elongation, workability, crack resistance and water vapor barrier properties.
C-29,668A

Description

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'~

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 (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-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 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-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-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 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 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 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-(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 (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:

~ 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 ~

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 % 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 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 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-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-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~

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-O
h ~ ~C X P~ O O O X O X O X X
~ a O ~ :"
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,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~
I O
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_~ ~> X OOOOOI~SOOOOOO U
~ N
X
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C t~ o tr1 10 o) In o ~, v.qI~ ............ ,~, o ~ ~ o o o a~ o ~o ~ ~ o co ~ P~
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s~ ~1 , ~ ~:4 O O O o o o o o O ,~
S~ X
P~ ~

C-29, 668A -26-~K O
h ~ ~ ~ F ~, O >

O
X h v~ ~ c~
~o ~
~1 r~ rl X ~ -~ ~
X ~ ~

:~ ~ ~ ~ O o o o u~ ~ N P~
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. ~Q _ N

o o a) aJ 2; . X
S: O -1 N tr7 ~ Ll~
,_1O~ OOOOOOO
m~ x l¢p:; ~q K
-C-29, 668A -27-~'7~ ~3 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 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 ~

~ O
~rl ~1 ~
X X X O O X X O X X O O

:~
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.
~ X O O O ~ ~ O O O O O
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m a~
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C~ V ~ V ~ C~
X X
i ~
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i~i O t~ C~ V P~ V
-1 1 0 U~
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~ N U) ~ ~ 1 ~ t` O ~
rt~ \ N ~1 N N ~ N ~1 N N N N ~`1 Ul ~; ~ , O ~ ~~i r-l rl ~1 ~I r-l ~I r-l ~1 rl rl ~1 1 ~1 X ~
~) ~) N N t`~ ~ ~') ~) ~ ~) ~ ~ ~i5 aJ ~ ............ 1:4 ~1 _ ~
o o o o ~n o t~ 8 X r~ N--a~ ct) co O O ~`1 N r~ O O O N
O O O ~ O O O O O O O
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C-2~, 668~ ~30~

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1~ .S-l ~1 N N N N N N
~ ' ~1 ~ ~ p~ ~ ' X
~ ~X

C- 29, 668A -31-., ~.

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 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 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-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-,1 1 O
O X ~ ~ o X o X X o X X
~-a I U~0 O~ r~ O O O O O O O O ~ O O
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S~ C) 0 v tr~
D
~,1 ~
OOOOOO(dOOOOO
X U~ O ~ ~ C~ ~ ~ ~ P~ C~

X E~ u~
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~ o o o ~ ~ o ~ o ~ o o o ~
X 1 3 11 tJ ~:
0 ~ r.q ~
~ r-l 0 ~ ~ X O Ln O Ul O 1~ t` O LO
Pq ~ ~:n o 1~ ~ O
O ~ ~ S~
a~
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h O ::1 ~:1 . . . . . . . . ,a 0 ~ ; ~ r` ao o ~ ~ o n o d' ~ ~
rl P I W ~I ~ 1 ~I M
0 ~ co co a~ 7 0 ~
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U~
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~1 \ ............ ~
V ~ ~ `1 N ~ ~ r-l ~ ~1 (~1 r 1 ~1 ~1 0 r-l ~
PC r-l N-- U~ ! ~ N ~ ~I C:l O O
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~^
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(.q~ ............ ,_, ~` ~ Lr) ~` ~D O ~D a) ~J X ~ ~ ~ ~) ~ t~ ~ ~ ~;P d1 ~) 11~ U
Q-- ~1 ~ ,1 I 0 S~ ~ ~ ~ d~ 0 1~ ~ ~ O -1 N
au ~1 ~3 0 ~ `1 ~ N ~ 7 ~11 ~ X
Pl ~ X . *

C-29, 668A -36-*
~1 0 O
I ~3 ~ aJ
O rl~ ~ O O O ~ O
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V ~.~
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r~-rl L O O O 1;1 0 X ~ ~ r~
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0-~ 3 F~l V ~ ~ ~ V g X ~ ~rl U) 1 3 ~4~ ~ o ~ ~-i ~ (~ L~
~ ;1 t~- o 1~ ~ ~n o u~ o o o co o ,n ~:1 ~ j ~ N

0~ N
~ ~ O O O ~I N ~1 .U~
r-l C~ I ~
r-l _ ~ 1 N 11~ ~1 X N-- O O O O O r-i ~

R ;~ R
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C~--~ 0 ~ .
~ l ~
~I t:: ~ O ~ N ~J ~ ~ ~1 X
o a) (li Z
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 !`
. ., 1, 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 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
;~1 N `D O Lr)r~ O t:O C;~ In ~O
h X N N d~ 7 r; ~ 0 u~
::1 ~1 O~ R
~1 1~(~ :~ ~ U') dl N~ O ~ C() ~ ~
N O ~ ~ PC ~ ~ Lt) t` ~ ~ ~ ~r) CO 1` ~D U) r1 ~1 rl ,~ o o n In ~ O U~ ~ O t' rl rl ~ N
~ I rl ~ CO N Ll~ ~D N N O ~ d~ I` t`
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E-~ ;:~ I ~1 ~ 0 N N O ~1 N O t` ~ N 0 0 O ~ X~1 ~ ~ ~ ~1 ~~ ~D ~ ~
r~ d' ~ O O O 00 ~ o o co ~1 0 I N N N ~ ~ t` ~ ~1 0 N N ~1 ~ . . . .
,C I ~ ~ 1 ~ r~ I r~ r~
O U~
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r l I N N ~ ~ ~ rl Ln N LO CJ~
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1~
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~3 ~rl t` ~ ~1 ~ ~ 1~ r l d~ I` N 0 O ~: t;l O r; Lt) Lt') 0 0 0 a~ r` ~ ~ N
,Y 0 ~ Ll' N 111 d~
~_ ~ ~
r~ S I ~ rl N ~) ~ Ul ~ ' O ~I N ~ d~ 1/') ~D t~ ~1 N N N N N
El O ~1 N N N N N N N O N N N N N
~Z; N N N N N N N ~1 ~; 1~; ~ ~;
~1 ~4 P:

C-29, 668A -40-~1:3'7~
~41--o ,1 ,~
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~ ~ o X X o o X o s~ ~ ~ W ~ ~ V
o ~

xl ~oooooo ~o~
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o ~ ~OOOOOO ~dOOOO

C~~ ~ ~ X
~1 ~1 O ~--1 N ~ ~ U ) p~ O -1 N ~ 1 ~ N N N N X
~1 13 0 ~ N N N N N N N O ~ N N ~ N ~1 .q X ~) N tN N ~ ~ N N 4-1 ~
*

C-29, 668A -41-.

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 ~,. ..

.

. ~
~ , .

~ 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.

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C-29, 668A -44-.

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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.

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C-29, 668A -48-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~

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.

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C-29, 668A -51-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~

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.

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C-29, 668A -56-`

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a process for flexibilization of a rigid, substantially closed-cell plastic foam sheet having a generally rectangular shape defined by the three-dimensional coordinates X (length), Y (thickness), Z (width) and the YZ, XZ and XY planes normal thereto by partial crushing of the foam sheet in a direction normal to the direction of desired flexibility, the improvement characterized by A. Selecting a freshly expanded foam sheet of a resin selected from the group comprising styrene, vinyl chloride, vinylidene chloride, methyl methacrylate or nylon including copolymers and physical blends thereof and having (1) a bulk density of 20 to 100 kg/m3, (2) an anisotropic cell structure oriented in the ?-axial direction with an average ? cell size of 0.05 to 1.00 mm and (3) ?-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 compression zone to form a directionally flexibilized foam; and thereafter C. Recovering of a directionally flexibilized foam having (1) anisotropically wrinkled cell wall structure with wrinkles in the direction of flexibilization;
(2) average cell sizes ?, ?, and ? measured in the axial directions ?, ? and ? satisfying the following conditions:
C-29,668A -57-? = 0.05 - 1.0 mm, and ?/? and ?/? ? 1.05;
(3) a higher elongation at rupture in the direction of flexibilization; and (4) a ?-axial water vapor permeability of not more than 1.5 g/m2?hr by the water method of ASTM
C-355.

2. The process of Claim 1 wherein the foam sheet is flexibilized within 72 hours of its expansion.

3. The process of Claim 1 wherein the foam sheet is compressed in a confined compression zone not more than 300 mm long.

4. The process of Claim 1 wherein the thermoplastic resin is polystyrene.

5. The process of Claim 4 wherein the poly-styrene resin contains 0.3 percent by weight or less of residual volatiles including styrene monomer and 0.5 to 1.5 percent by weight of styrene oligomers.

6. The process of Claim 4 wherein the poly-styrene resin foam is successively compressed in the longitudinal (?-axial) and lateral (?-axial) directions to give a two-directionally flexibilized polystyrene foam sheet.
C-29,668A -58-

7. A one-directionally flexibilized, substantially closed-cell polystyrene resin foam having a generally rectangular shape defined by the three dimensional coordinates X, Y and Z and an anisotropically wrinkled cell wall structure formed by partial crushing of the foam in a direction normal to the direction of flexibility further characterized by having (1) a bulk density of 20 to 60 kg/m3, (2) an anisotropic cell structure oriented in the ?-axial direction with an average ? cell size of 0.05 to 1.00 mm, (3) average axial cell sizes ?, ?, ? satisfying the conditions:
?/? and ?/? ? 1.05; (4) a ?-axial elongation at rupture (Ex) of 7-70 percent, and (5) a ?-axial water vapor permeability (Py) of not more than 1.0 g/m2?hr by the water method of ASTM C-355.

8. A two-directionally flexibilized, substantially closed-cell thermoplastic resin foam of a resin selected from the group comprising styrene, vinyl chloride, vinylidene chloride, methyl methacrylate or nylon including copolymers and physical blends thereof and having a generally rectangular shape defined by the three-dimensional coordinates X, Y, Z and an anisotropically wrinkled cell wall structure more highly wrinkled in the ?? plane further characterized by having (1) a density of 20 to 100 kg/m3;
(2) average axial cell sizes ?, ?, ? measured in the axial directions X, Y, Z satisfying the following conditions:
? = 0.05 - 1.0 mm, and ?/? and ?/? ? 1.05;
(3) The axial elongations at rupture (Ex, Ey, Ez) satisfy the conditions: EX > 1.8 Ey and Ez <
8.3 Ey; and (4) a ?-axial water vapor permeability of not more than 1.5 g/m2?hr by the water method of ASTM C-355.
C-29,668A -59-

9. The flexibilized thermoplastic resin foam of Claim 8 wherein the resin is polystyrene.

10. The flexibilized polystyrene resin foam of Claim 7 or 9 wherein the polystyrene resin contains 0.3 percent by weight or less of residual volatiles including styrene monomer and 0.5 to 1.5 percent by weight of styrene oligomers.
C-29,668A