Note: Descriptions are shown in the official language in which they were submitted.
4~
The present invention relates -to various improvements in and
modifications to the earlier invention of the Applicant, describ-
ed in French patent N 75067~2 of March 4, 1975 and in the first
certificate o~ addition there-to N 7604810 of February 20, 1976.
The applicant has been able to bring out -the fact -that a
judicious choice of the thicknesses of the various layers of the
layered composi-te material described in the French patent N
7506732 and in the first certi~icate of addition N 7604810
thereto, preferably simultaneously with the selection of speci-
fic materials for constituting the various layers of this
layered composite material, allow the best conditions of fluid-
tightness, mechanical resistance and flexibility to be obtained,
as will be set ~orth later in more detail.
It will be recalled that the layered composite ma-terial
according to the French patent N 7506732 comprises at least
three continuous superposed layers or sheets of cold resisting
f1exible material, assembled together by cementing, welding or
like superficial adherent binding, and c,omprising at least one
first end layer forming a tough or mechanically resistant
suppor-t, at least one intermediate layer constituted by an
impervious film~ and at least one second end layer which may be
of the same nature às -the first end layer.
,
~k.
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It will also be recalled that, in a first form o~ embodi-
men-t, -the said firs-t end layer is of mineral ~iber, in particu~
lar glassfiber, fabric, the said intermedia-te layer is of metal
and formed par-ticularly of an aluminum or stainless-s-teel sheet,
and the said second end layer is of an elas-tomer material.
The French paten-t N 7506732 also mentions a second form
of embodimen-t in which -the said firs-t end layer is of mineral
~iber, par-ticularly glassfiber, fabric, -the said intermediate
layer is of metal and particularly formed o~ an aluminum or
s-tainless-s-teel shee-t, and -the said second end layer is of
mineral fiber, in par-ticular glassfiber, fabric, the layered
composite material having this structure being par-ticularly
usable as a secondary fluid-tight barrier in a heat-insulating
composite wall-structure for cryogenic containers.
According to a third form of embodiment described in -the
French patent N 7506732, the layered composite material is con-
stitu-ted by four layers, -the first three of which ha~e the same
structure as in the second form o:E embodimen-t men-tioned above,
the fourth layer, which covers the said second end layer, being
20 of an elas-tomer material fulfilling a function of mechanical
protection of the said second end layer, such a composite mater-
ial being particularly usable -to consti-tu-te a primary ~luid-
tigh-t barrier in a hea-t-insula-ting composi-te wall for a cryo-
genic container.
The layered composi-te material according to the present
inven-tion is of the general type described in the French patent
N~ 7506?32 and i~ the first certi~icat of addi-tion N 7604810
thereto and is characterized in tha-t its two end layers have a
thickness cf from 0.3 to 0.6 mm, the intermediate layer having
a thickness of from 0. oL~ to 0.10 mm.
In case the said layered composi-te material comprises a
~ourth layer of elastomer material covering the said second end
layer, -the -thickness of this four-th layer is comprised,
according to the present invention, between 0.3 and 1 mm.
In a first preferred form of embodiment of the present
invention, in which the layered composite material comprises
only three layers, the two said end layers, having each a thick-
ness of from 0.3 to 0.6 mm,are of fiberglass, the said interme
diate layer being preerably of aluminum or of stainless-steel,
more preferably of aluminum. The thickness of each o~ the fiber-
glass layers are then more advantageously comprised between
0.3 and 0.4 mm, whereas the intermediate layer of aluminum has
a thickness which is more advantageously comprised between 0.04
and 0.07 mm.
In another preferred form of embodiment of the present
invention, in which the layered composite material comprises
four layers, three of which, placed consecutively, possess the
10 characteristics just described hereabove in connection wit'n the
three-layered composite material according to the first preferred
form of embodiment of the inven-tion, and the fourth layer cover-
ing the said second end layer of glassfiber is of elas-tomer and
has a thickness of from 0.3 to 1 mm.
The elastomer used in the layered composite material of the
present inven-tion ,in the form of a layer the thickness of which
is comprised between 0.3 and 1 mm, is preferably selec-ted from
polyester type polyurethane, such as for example the one known
under the commercial denomination "Adipren~", polychloroprenes,
20 particularly known under the commercial denomination "Neoprene",
and'chlorosulfonated polyethylene, such as for example the one
know~ under the commercial denomination "Hypalon".
Generally, the layered composite material according to the
present invention may present, in combination with the character~
25 istics indicated abo~e, all or part of the characteristics des-
cribed and/or claimed in the French patent N 7506732 and in the
first cer-tifioate o~ addition N 7604810 thereto. Of course,
this layered composite material can be used for all the applica-
tions described in the French patent N 7506732 and the first
30 certificate of addition N 7604810 thereto.
The present invention also relates to a method of surface
assembling of the sheets of the said composite material compris-
ing two end layers of glassfiber, -the said method being charac-
terized in that the adjacent sheets are so arranged that -their
35 peripheral edges are superposed, an adhesive composition being
placed between the two fibrous end layers in mutual contact,
pertaining to the said superposed edges, so as to penetrate '
between the fibers of the said two fibrous end layers and thus
ensure a very strong bond between the said adJacent sheets.
* Trade Mark
44
Other purposes, characterizing features, or advantages of
the present invention, especially in i-ts preferred forms of
embodiment, are se-t forth ~ereafter.
The form of embodimen-t in which the two ~nd layers of -the
layered composi-te material are glassfiber layers produces
surpri:sing effects due to -the fact -that -the material allows. a
par-ticularly fluid-tight cryogenic-container coating to be ob-
tained extremely easily? as indicated previously, by ~urface-
j ux-taposing of -the sheets of the said material and by binding
them together along their peripheral edges overlapping one
ano-ther in superposition, by means of an adhesive, withoùt it
being necessary -to apply pressure, the assembling process being
effected at room temperature. ~-
This remarkable advantage is essentially due to the sym~et-
rical structure of the layered composite material according tothis form of embodiment,since -this structure allows the mutual
con-tac-t of two rough-surfaced layers formed of fibers, under
such conditions that the binding streng:th is maximum on the one
hand because precisely of the non-smooth surface of the two
mutually confron-ting layers, -thus allowing the two layers to
perfectly cling together along the peripheral edges of the layer-
ed composite material sheets, and on the o-ther hand, owing to
the penetration of the adhesive composition into each of -the said
two layers, on ei-ther side of its interface , which is allowed
precisely by the porous structure of the layers.
Under such conditions, a highly satisfactory binding can
be ob-tained without applying external pressure and without heat-
ing, since the assembling of the said sheets can be easily
performed by hand.
Moreover, the risks of cleavage inherent in the cementing
of sheets with smooth .outer surfaces are avoided by the use of
the said layered composite materialf
TheA pplicant will now set forth the critical character of
the various above-indicated thicknesses, insof~r as it is desir-
ed to obtain excellent flexibili-ty, mechanical resistance and
fluid-tightness characteristics of the layered composite material
according to the present invention.
In the first place, the use of glassfiber layers of smaller
1~4
-thickness -than 0.3 mm would impar-t thereto a tensile streng~h
insufficient -to withstand -the tensile stresses occurring at the
joints between the heat-insulating panels of a heat-insulating
composi-te wall on which the layered composite material of the
presen-t invention, forming a primary or a secondary fluid-tight
barrier, is placed, such stresses being due -to the thermal con-
tractions undergone by the said panels. Moreover, such glass-
fiber layers would no-t be capable o~ withstanding the stresses
or forces caused by casual breakage or ~racking of a panel of
the subjacent heat-insulating bed.
On the other hand, -the thickness of the said glassfiber
layers must not exceed about 0.6 mm, because ? if thicknesses
exceeding tha-t value are used, the -tensile stresses due to the
thermal contraction of -the material may lead to ruptures of -the
insula-tion at the dihedral angle of the heat-insulating wall,
where the fastenings allowing the said membrane to be secured
and -the stresses due to -the thermal contrac~ion to be -taken up
or compensa-ted for are located. In other words, the limita-tion
c~ the thickness of each of the said layers a-t that value allows
the layered composi-te material according -to the invention to be
imparted sufficien-t flexibility -to withs-tand withou-t rupture the
said stresses or forces.
The use of an intermedia-te layer of excessive thickness,
exceeding about 0.10 mm, wo;lld lead to stresses due to -thermal
contraction, which might result in insulation ruptures in the
dihedral angles. Moreover, such a thickness ~ould lead in in-
creased rigidity of -the composite material and would render i.ts
use less easy.
On the other hand, the use of an intermediate layer of a
thickness smaller than abou-t 0.04 mm would involve a serious
risk of formation of porosity in the said layer, resulting in a
loss in fluid-tightness of the layered composite material as a
whole.
Also to be pointed out is the fact that, in case the said
intermediate layer is of aluminum, the aforementioned thickness
range allows large-siæe a].uminum sheets, having for example a
thickness up to 1.50 m, to be obtained by rolling, thus permitt-
ing large-surfac~ sheets for the layered compositematerial of
the invention -to be obtained.
1)4'~
As regards the elastomer layer used as a covering layer on
a fibrous end layer in a four-layered material, it should be
noted that a thickness smaller than 0.3 mm would not allow the
said elastomer layer to fulfill its mechanical protection func-
tion. In particular, in the case where this elastomer layercovers a fibrous layer, such as for example a glassfiber layer,
a -thickness smaller than about 0.3 mm would not allow an ade-
quate abrasion resis-tance to be obtained, for the following
reason. Owing to the irregularities of the fibrous layer -
elastomer layer interface, the elastomer layer is necessarilyvariable in thickness, the said thickness being minimum at the
bosses or peaks of the fibrous layer surface, so that the mech-
anical protection is poor in local regions, the elastomer being
more or less rapidly eliminated by abrasion in those regions,
thus denuding the glassfibers, and resulting in a risk of rupture
therein. On the contrary, when the thickness of the elastomer
layer is comprised between 0.3 and 1 mm, all the regions of the
subjacent fibrous layer are perfec-tly protected and there is no
risk of rupture in -this last layer.
The use of glassfiber in preference to other types of fib-
ers is justified by the high mechanical resistance of -the glass-
~ibers compared with those other fibers, with the exception of
aromatic polyamide or aramide fibers, such as for example those
known under the coMmercial denomina-tion ~Kevla~" manufactured
by Dupont de NEMOURS. However, even thovgh the last-named f~bers
exhibit higher mechanical resistance than glassfibers do, they
suffer from the disadvantage of a much higher Young's modulus
and coefficient of thermal expansion than fibe~glass, resulting
in thermal stresses much greater than those prodllced by the_
thermal contraction of glassfiber when the layered composi-te
material of the present invention constitutes a f1uid-tight
barrier covering a bed of heat-insulating panels of a composite
heat-insulating wall of a cryogenic container, right above or
below the joints between the said panels. Consequently, the
glassfibers offer a set of optimum characteristics which render
their use highly preferable in the constitution of the composite
material according to the present invention.
Of course, the glassfiber layer or layers of the layered
-,
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-~ * Trade Mark
composite rnaterial according -to the present invention may have
different structures or specific te~tures, a preferred texture
being that of a woven glassfiber fabric because of its much
higher mechanical resistance or s-trength. '
It should also be pointed out that the composite ~aterial
according to the present invention displays an excellent cyclic
fatigue behavior and that its imperviousness to liquids and gases
is very considerably improved compared with the other fleY~ible
membranes used in the composite heat-insulating walls for cryo-
genic containers according to the prior art. Thus, with a
difference in pressure of 1 bar between the two sides of -the
membrane, the fhllowing results are obtained, for a leakage rate
D, in the case of a membrane according to the presen-t invention,
with t~o end ].ayers of glassfiber fabric and one intermediate
layer of aluminum, on the one hand, and in the case of membranes
of, respectively, "Myla~" (commercial denomination 'of a product
manufactured by Dupont de NEMOURS), of elastomer silicone, and
of butyl rukber, on the other hand, :
- material according to the inven-tion : D = 6x10-3 cm3/j.m2
- "Mylar membrane : D = 12 cm3/j.m
-elastomer silicone membrane : D = 3,9x105cm3/j.m2
- butyl rubber membrane D = 1.9x103cm3/j.m2
It should also be pointed out 'that the known membranes
~u~t me~tioned are difficul-t to use, ~ the assembling of sheets
of the corresponding materials to constitute a continuous membrane
requires a welding or cementing process with the applicatDn o~
press~re, which is not the case with the material of the present
invention, as mentioned earlier.
In the following table are given the tensile streng'th char-
acteristics of the layered composite material of the presentinvention, in the form of embodiment corresponding to the use of
two end layers of glassfiber fabric and one intermediate layer
constituted by an aluminum sheet, each o~ the glassfiber layers
having a thickness of 0.3mm and the thickness of the aluminum
sheet being 0.04 mm:
* Trade Mark
~,,,~ .
~4i~444
. . ,.. _ .. ". _ _ _ _.. , . . _ .~ ~ . _, .
i Test -tempera-ture
Tensile streng-th -------------~ - --------
20C ~196~C
. .
Force required to break : :
1 meter of membrane : 15 tons : 26 tons
---- .
Brea~ingstress- , 3000 bars , 5250 bars
:
Of course, -the presen-t invention is by no means limited
to the forms of embodiment described. In particu:Lar, it comprises
all means constituting technical equivalents to the means des-
cribed, as well as their combinations, should the latter be
carried out according to i-ts gist and used within the scope of
the following claims.
