PROCESS FOR PREPARING A BLOCK OF POLYURETHANE/POLYISOCYANURATE FOAM OF A SLAB FOR HEAT-INSULATING A TANK

Abstract

The present invention relates to a preparation of a block of fiber-reinforced polyurethane/polyisocyanurate foam in which the expansion of the foam is constrained by the walls of a double belt laminator forming a tunnel, the block of fiber-reinforced polyurethane/polyisocyanurate foam being composed of cells storing a gas, advantageously having low thermal conductivity, and exhibiting a density of less than 50 kg.m.sup.−3 with a content of fibers C.sub.f representing at least 4% by weight of the block of fiber-reinforced foam, in which the impregnation time of the fibers t.sub.i is less than the cream time t.sub.c of the polyurethane/polyisocyanurate foam.

Claims

1. A process for the preparation of a block of fiber-reinforced polyurethane/polyisocyanurate foam of a thermal insulation slab of a sealed and thermally insulating tank, the block of fiber-reinforced polyurethane/polyisocyanurate foam being composed of cells storing a gas and exhibiting a density of less than 50 kg.m.sup.−3 with a content of fibers C.sub.f representing at least 4% by weight of the block of fiber-reinforced foam, the preparation process comprising the following stages: a) a stage of mixing chemical components necessary for obtaining a polyurethane/polyisocyanurate foam, said components comprising reactants for obtaining polyurethane/polyisocyanurate, optionally at least one reaction catalyst, optionally at least one emulsifier, and at least one blowing agent, b) a stage of impregnation, by gravitational flow of the abovesaid mixture of chemical components, of a plurality of fiber reinforcements chosen from fabrics of fibers and mats of fibers, said fibers having a length of at least five centimeters (cm), arranged in superimposed layers, in which the fiber reinforcements extend essentially along a direction perpendicular to the direction of said gravitational flow, these fiber reinforcements exhibiting a permeability K.sub.c to the abovesaid mixture of chemical components, expressed in m.sup.2, equal to:
K.sub.c═(r.sub.f.sup.2×p.sup.3)/(k×τ.sup.2×4×V.sub.f.sup.2), with r.sub.f=radius of the fibers, expressed in meters (m), p=porosity of the fibers (dimensionless), value between 0 and 1, k=form factor (dimensionless), dependent on the nature of the fiber reinforcement, with k=1 for a fabric of fibers, k=6 for a mat of fibers, τ=tortuosity (dimensionless), dependent on the arrangement of the fibers, V.sub.f=volume fraction of the fibers (proportion of fibers in a volume of the reinforcement), value between 0 and 1, and c) a stage of formation and of expansion of the fiber-reinforced polyurethane/polyisocyanurate foam, characterized in that the abovesaid mixture of chemical components exhibits a dynamic viscosity η, during the impregnation stage b), such that an impregnation time of the fibers t.sub.i is less than the cream time t.sub.c of the polyurethane/polyisocyanurate foam, the impregnation time of the fibers t.sub.i being equal to:
t.sub.i=(η=e.sub.m.sup.2)/(K.sub.c═ΔP),
ΔP=(M.sub.sd×g.sub.T×k.sub.p), with η=the dynamic viscosity, expressed in pascal.seconds (Pa.Math.s), e.sub.m=sum of the mean thicknesses of the fiber reinforcements, expressed in meters (m), each fiber reinforcement exhibiting a mean thickness corresponding to the mean of the distances between a plurality of pairs of local extremums of said fiber reinforcement spaced out from one another along a direction of thickness of said fiber reinforcement, ΔP=pressure gradient, expressed in pascals per meter (Pa), M.sub.sd=surface density of the abovesaid mixture of chemical components, expressed as weight per unit area (kg.m.sup.−2), g.sub.T=terrestrial gravitational force, regarded here as equal to 9.8 N.kg.sup.−1, k.sub.p=mean pressure factor, constant equal to 0.5.

2. The process as claimed in claim 1, in which the impregnation time t.sub.i observes the following formula with respect to the cream time t.sub.c of the polyurethane/polyisocyanurate foam:
0.50 <t.sub.i/t.sub.c<0.91

3. The process as claimed in claim 1, in which the expansion of the fiber-reinforced polyurethane/polyisocyanurate foam is physically constrained by the walls of a double belt laminator forming a tunnel, advantageously of rectangular section with a distance between the walls positioned laterally equal to L and a distance between the walls positioned horizontally equal to E, thus enclosing the expanding fiber-reinforced foam so as to obtain the abovesaid block of fiber-reinforced polyurethane/polyisocyanurate foam.

4. The process as claimed in claim 3, in which the positioning of the walls of the tunnel of the double belt laminator is defined so that the constraint on the expansion of the fiber-reinforced polyurethane/polyisocyanurate foam results in a volume of fiber-reinforced polyurethane/polyisocyanurate foam, at the outlet of the double belt laminator, representing between 85% and 99%, preferably between 90% and 99%, of the expansion volume of this same fiber-reinforced polyurethane/polyisocyanurate foam in the case of free expansion, without the constraint of the walls of such a double belt laminator.

5. The process as claimed in claim 1, in which the expansion of the fiber-reinforced polyurethane/polyisocyanurate foam is free, i.e. without the constraint exerted by a volume of closed section.

6. The process as claimed in claim 5, in which, following the stage of free expansion of the fiber-reinforced polyurethane/polyisocyanurate foam, said fiber-reinforced foam is cut in order to obtain the abovesaid block of fiber-reinforced polyurethane/polyisocyanurate foam.

7. The process as claimed in claim 1, in which the dynamic viscosity η of the abovesaid mixture of components is between 30 mPa.Math.s and 3000 mPa.Math.s, preferably between 50 mPa.Math.s and 1500 mPa.Math.s, under standard temperature and pressure conditions.

8. The process as claimed in claim 1, in which at least 60% of the abovesaid cells storing a gas, advantageously having low thermal conductivity, exhibit a shape elongated or stretched along an axis parallel to the axis of a thickness E of the block of fiber-reinforced polyurethane/polyisocyanurate foam.

9. The process as claimed in claim 1, in which at least 80%, preferably at least 90%, of the abovesaid cells storing a gas, advantageously having low thermal conductivity, exhibit a shape elongated or stretched along an axis parallel to the axis of a thickness E of the block of fiber-reinforced polyurethane/polyisocyanurate foam.

10. The process as claimed in claim 1, in which the long to continuous fibers consist of glass fiber, of carbon fiber or any other organic or inorganic material, preferably of glass fiber.

11. The process as claimed in claim 1, in which the fiber reinforcements are positioned over an entire width L and stage b) of impregnation of the fibers by the mixture of components, in order to obtain a fiber-reinforced polyurethane/polyisocyanurate foam, and of a blowing agent is carried out, via a controlled liquid dispenser, simultaneously over the entire width L.

12. The process as claimed in claim 1, in which the blowing agent consists of a physical and/or chemical expanding agent, preferably a combination of the two types.

13. The process as claimed in claim 12, in which the physical expanding agent is chosen from alkanes and cycloalkanes having at least 4 carbon atoms, dialkyl ethers, esters, ketones, acetals, fluoroalkanes, fluoroolefins having between 1 and 8 carbon atoms and tetraalkylsilanes having between 1 and 3 carbon atoms in the alkyl chain, in particular tetramethylsilane, or a mixture of these.

14. The process as claimed in claim 12, in which the chemical expanding agent consists of water.

15. The process as claimed in claim 13, in which, during stage a) of mixing chemical components, nucleating gas is incorporated in at least one polyol compound, preferably using a static/dynamic mixer under a pressure between 20 and 250 bar, the nucleating gas representing between 0% and 50% by volume of polyol, preferably between 0.05% and 20% by volume of the volume of polyol.

16. The process as claimed in claim 1, in which, during stage a) of mixing the chemical components, the temperature of each of the reactants for obtaining polyurethane/polyisocyanurate is between 10° C. and 40° C., preferably between 15° C. and 30° C.

17. The process as claimed in claim 1, in which there is additionally added to the mixture, in stage a), an organophosphorus flame retardant, advantageously triethyl phosphate (TEP), tris(2-chloroisopropyl) phosphate (TCPP), tris(1,3-dichloroisopropyl) phosphate (TDCP), tris(2-chloroethyl) phosphate or tris(2,3-dibromopropyl) phosphate, or a mixture these, or an inorganic flame retardant, advantageously red phosphorus, expandable graphite, an aluminum oxide hydrate, an antimony trioxide, an arsenic oxide, an ammonium polyphosphate, a calcium sulfate or cyanuric acid derivatives, or a mixture of these.

18. The process as claimed in claim 1, in which the content of fibers C.sub.f represents between 7% and 15% by weight of the block of fiber-reinforced foam.

19. A block of fiber-reinforced polyurethane/polyisocyanurate foam of a thermal insulation slab of a sealed and thermally insulating tank, directly obtained by virtue of the process as claimed in claim 1, the block of fiber-reinforced polyurethane/polyisocyanurate foam being composed of cells storing a gas, advantageously having low thermal conductivity, and exhibiting a density of less than 50 kg.m.sup.−3 with a content of fibers C.sub.f representing at least 4% by weight of the block of fiber-reinforced foam, p1 characterized in that the fibers are distributed uniformly in the block of fiber-reinforced polyurethane/polyisocyanurate foam, in such a way that the content C.sub.f varies only by +/− 35%, preferably by +/− 20%, in all the zones or portions of said block of fiber-reinforced polyurethane/polyisocyanurate foam.

20. A sealed and thermally insulating tank, said tank consisting of: a tank integrated in a supporting structure comprising a sealed and thermally insulating tank comprising at least one sealed metal membrane composed of a plurality of metal strakes or metal plates which can comprise corrugations and a thermally insulating slab comprising at least one thermally insulating barrier adjacent to said membrane, or a tank of type B or C according to the definition given by the IGC Code comprising at least one thermally insulating slab, characterized in that the thermally insulating slab comprises the block of fiber-reinforced polyurethane/polyisocyanurate foam as claimed in claim 19.

21. A ship for the transportation of a cold liquid product, the ship comprising at least one hull and a sealed and thermally insulating tank as claimed in claim 20, positioned in the hull.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0122] The description which will follow is given solely by way of illustration and without limitation, with reference to the appended figures, in which:

[0123] FIG. 1 is a diagrammatic view illustrating the different stages of the preparation process according to the invention

[0124] FIG. 2 is a diagrammatic representation of an embodiment of a controlled liquid dispenser according to the invention

[0125] FIG. 3 is a diagrammatic view of two sets of thermal insulation panels, fixed one to the other, respectively forming a primary insulation space and a secondary insulation space for a tank, these panels being formed by a plurality of blocks of fiber-reinforced polyurethane/polyisocyanurate foam according to the invention

[0126] FIG. 4 is a cutaway diagrammatic representation of a tank of an LNG tanker, in which tank are installed the two sets of thermal insulation panels of the type of those represented in FIG. 3, and of a loading/unloading terminal for this tank

DESCRIPTION OF THE EMBODIMENTS

[0127] Preferably, the preparation of the fiber-reinforced PUR/PIR according to the invention is carried out in the presence of catalysts making it possible to promote the isocyanate/polyol reaction. Such compounds are described, for example, in the document of the state of the art entitled “Kunststoffhandbuch, Volume 7, Polyurethane”, published by Carl Hanser, 3.sup.rd edition, 1993, Chapter 3.4.1. These compounds comprise amine-based catalysts and catalysts based on organic compounds.

[0128] Preferably, the preparation of the fiber-reinforced PUR/PIR according to the invention is carried out in the presence of one or more stabilizers intended to promote the formation of regular cellular structures during the formation of the foam. These compounds are well known to a person skilled in the art and, by way of example, mention may be made of foam stabilizers comprising silicones, such as siloxane-oxyalkylene copolymers and other organopolysiloxanes.

[0129] A person skilled in the art knows the amounts of stabilizers, between 0.5% and 4% by weight of the PUR/PIR foam, to be used depending on the reactants envisaged.

[0130] According to one possibility offered by the invention, during stage a), the mixture of chemical components can include plasticizers, for example polybasic esters, preferably dibasic esters, of carboxylic acids with monohydric alcohols, or can consist of polymeric plasticizers, such as polyesters of adipic, sebacic and/or phthalic acids. A person skilled in the art, depending on the reactants used, knows what envisaged amount of plasticizers, conventionally from 0.05% to 7.5% by weight of the polyurethane/polyisocyanurate foam.

[0131] Organic and/or inorganic fillers, in particular reinforcing fillers, can also be envisaged in the mixture of chemical components, such as siliceous minerals, metal oxides (for example kaolin, titanium or iron oxides) and/or metal salts. The amount of these fillers, if they are present in the mixture, is conventionally between 0.5% and 15% by weight of the PUR/PIR foam.

[0132] It should be noted that the present invention is not intended here to add technical teaching to the formation of a PUR/PIR foam, both in terms of the nature of the essential chemical components and of the optional functional agents and their respective amounts. A person skilled in the art knows how to obtain different types of fiber-reinforced PUR/PIR foam and the present preparation relates, from a specific choice of the permeability characteristics of the fiber reinforcements and from a just as specific choice of viscosity of the foam during its impregnation of said reinforcements, considering moreover a relatively high or high content of long to continuous fibers, in such a way that the impregnation time t.sub.i is just less, or only just less, than the cream time t.sub.c of the polymer foam under consideration.

[0133] Thus, the present invention, as set out here, is not in the first place targeted at a new chemical preparation of fiber-reinforced PUR/PIR foam but rather at a new preparation of a block of fiber-reinforced PUR/PIR foam in which these particular characteristics of permeability of the fiber reinforcements and of viscosity/cream time of the PUR/PIR foam are defined so as to follow the rule t.sub.i<t.sub.c, and preferably:

0.50<t.sub.i/t.sub.c<0.91   [Math 1]

[0134] or in other words t.sub.i+0.1t.sub.i<t.sub.c<2t.sub.i, the impregnation of the fibers by the foam being carried out by pouring.

[0135] Thus, as can be seen in FIG. 1, a plurality of fiber reinforcements 10 are unwound and brought along a parallel alignment with one another onto or above a conveyor belt 11 intended to carry these reinforcements 10 and the components forming the PUR/PIR foam. This is because the impregnation of the fiber reinforcements 10 is carried out, in the context of the present invention, by gravity, that is to say that the mixture 12 of chemical components, blowing agent(s) and optional other functional agents used to obtain the PUR/PIR foam is poured, from a liquid dispenser located above the fiber reinforcements 10, directly onto the fibers 10.

[0136] Thus, the abovesaid mixture 12 has to impregnate all of the fiber reinforcements 10, whether it concerns, for the latter, one or more mats or one or more fabrics, in a very homogeneous manner, during the cream time t.sub.c so that the start of the expansion of the PUR/PIR foam takes place after or at the earliest just at the moment when the fiber reinforcements 10 are definitely all impregnated by the mixture 12. On doing this, by virtue of observing the characteristics for the fiber reinforcements and the PUR/PIR foam which are defined according to the invention, the expansion of the PUR/PIR foam is carried out while maintaining perfect homogeneity of the fibers 10 in the volume of the block of PUR/PIR foam.

[0137] In the context of the invention, the cream time of the components of the mixture 12 in order to form the PUR/PIR foam is known to a person skilled in the art and chosen in such a way that the conveyor belt 11 brings the assembly formed from the mixture 12 of components, blowing agent and fibers 10, for example, up to a double belt laminator, not represented in the appended figures, while the expansion of the foam has just started, in other words the expansion of the PUR/PIR foam then ends in the double belt laminator.

[0138] In such an embodiment with a double belt laminator (DBL), a pressure system, using one or two rollers, is optionally positioned before the double belt laminator, i.e. between the zone for impregnation of the mixture on the fibers and the double belt laminator. In the case of the use of a DBL, the expansion of the volume of the foam is carried out in the laminator when the expansion volume of this foam reaches between 30% and 60% of the expansion volume of this same foam when the expansion is left free, i.e. without any constraint. On doing this, the double belt laminator will be able to constrain the expansion of the PUR/PIR foam in its second expansion phase, when the latter is close or relatively close to its maximum expansion, that is to say when its expansion brings the foam close to all of the walls, forming a tunnel of rectangular or square section, of the double belt laminator. According to a different way of presenting the specific choices of the preparation according to the invention, the gel point of the mixture of components, that is to say the moment when at least 60% of the polymerization of the mixture of components is achieved, in other words 70% to 80% of the maximum volume expansion of the mixture, obligatorily takes place in the double belt laminator, possibly in the second half of the length of the double belt laminator (i.e. closer to the outlet of the laminator than to the inlet of the latter).

[0139] As regards the function of simultaneous dispensing of the mixture 12 of chemical components and of blowing agent over the entire width L of the fiber reinforcements 10, it is provided here by a controlled liquid dispenser 15, visible in FIG. 2. Such a dispenser 15 comprises a feed channel 16 for the assembly formed of the mixture 12 of chemical components and at least blowing agent from the reservoir forming a reactant mixer, not represented in the appended figures, in which, on the one hand, all the chemical components and the blowing agent are mixed and, on the other hand, in particular the nucleation, indeed even the heating, of such a mixture is carried out. This liquid assembly formed of the mixture 12 of chemical components and of the blowing agent is then distributed, under pressure, in two channels 17 extending transversely to respectively end in two identical dispensing plates 18, extending along the width L (each having a length substantially equal to L/2), comprising a plurality of nozzles 19 for the flow of said mixture 12 over the fiber reinforcements 10. These flow nozzles 19 consist of orifices of calibrated section exhibiting a predetermined length. The length of these flow nozzles 19 is thus predetermined so that the liquid leaves with an equal flow rate between all the nozzles 19 in order for the impregnation of the fiber reinforcements 10 to take place at the same time, or simultaneously, over the section of width L of the fiber reinforcements 10, and for the surface density of liquid deposited at right angles with each nozzle to be equal. On doing this, if a section of width L of the fibers 10 is considered, the latter are impregnated concurrently so that the impregnation of the layers of fibers 10 by the mixture 12 is carried out, at all points of this section, in an identical manner, which contributes to obtaining, at the outlet of the double belt laminator, a block of fiber-reinforced foam which is perfectly homogeneous.

[0140] The controlled liquid dispenser 15 shown in this FIG. 2 is an exemplary embodiment in which two identical dispensing plates 18 are used but it will be possible to envisage a different design, insofar as the function of simultaneous dispensing of liquid over the width section of the fibers 10 is achieved. Of course, the main technical characteristic used in this instance lies in the different lengths of the flow nozzles 19, which are longer or shorter depending on the route, or path, of the liquid mixture 12 from the feed duct 16 of the dispenser 15 as far as the flow nozzle 19 under consideration.

[0141] One of the aspects of importance for achieving a good impregnation of the fiber reinforcements 10 just before the cream time t.sub.c of the PUR/PIR foam lies in the choice of a specific viscosity of the liquid (consisting of the mixture 12 of chemical components and of the blowing agent) to be linked with the specific characteristics of the fiber reinforcements. The viscosity range chosen as well as the permeability characteristics of the fiber reinforcements have to make possible good penetration of the liquid into the first layers of fibers 10, in order to reach the following ones down to the final layer (the lower layer of fibers 10, i.e. that located lowest in the stack of the fiber reinforcements), so that the impregnation time t.sub.i of the fibers 10 is carried out within the time period given by the chemical components corresponding substantially to (but always less than) the cream time t.sub.c. The viscosity of the mixture 12 of components is chosen, for example by heating, additions of plasticizers and/or by a greater or lesser nucleation, so that the impregnation of all the fibers 10 by the mixture 12 chemical and of the blowing agent, over a section of width L, is obtained just before the cream time, that is to say before or just before the start of the expansion of the PUR/PIR foam.

[0142] The block of fiber-reinforced foam is intended to be used in a very particular environment, and thus has to guarantee specific mechanical and thermal properties. The block of fiber-reinforced foam obtained by the preparation according to the present invention thus conventionally forms part of a thermal insulation slab 30, i.e., in the example used in FIG. 3, in an upper or primary panel 31 and/or a lower or secondary panel 32 of such an insulation slab 30 of a tank 71 intended to receive an extremely cold liquid, such as an LNG or an LPG. Such a tank 71 can equip, for example, a ground tank, a floating barge or the like (such as an FSRU “Floating Storage Regasification Unit” or a FLNG “Floating Liquefied Natural Gas”) or else a ship, such as an LNG tanker, transporting this energetic liquid between two ports.

[0143] With reference to FIG. 4, a cutaway view of an LNG tanker 70 shows a sealed and insulating tank 71 of prismatic general shape, mounted in the double hull 72 of the ship. The wall of the tank 71 comprises a primary sealed barrier intended to be in contact with the LNG contained in the tank, a secondary sealed barrier arranged between the primary sealed barrier and the double hull 72 of the ship, and two insulating barriers arranged, respectively, between the primary sealed barrier and the secondary sealed barrier and between the secondary sealed barrier and the double hull 72.

[0144] In a way known per se, loading/unloading pipes 73 positioned on the upper deck of the ship can be connected, by means of appropriate connectors, to a shipping or harbor terminal, in order to transfer a cargo of LNG from or to the tank 71.

[0145] FIG. 4 represents an example of a shipping terminal comprising a loading and unloading station 75, an underwater pipeline 76 and a land-based installation 77. The loading and unloading station 75 is a fixed offshore installation comprising a mobile arm 74 and a tower 78 which supports the mobile arm 74. The mobile arm 74 carries a bundle of insulated hoses 79 which can be connected to the loading/unloading pipes 73. The swiveling mobile arm 74 fits all sizes of LNG tankers. A linking pipeline (not represented) extends inside the tower 78. The loading and unloading station 75 allows the LNG tanker 70 to be loaded and unloaded from or to the land-based installation 77. This installation comprises liquefied gas storage tanks 80 and linking pipelines 81 connected via the underwater pipeline 76 to the loading or unloading station 75. The underwater pipeline 76 allows the transfer of liquefied gas between the loading or unloading station 75 and the land-based installation 77 over a great distance, for example 5 km, which makes it possible keep the LNG tanker 70 at a great distance from the coast during the loading and unloading operations.

[0146] To generate the pressure required for the transfer of the liquefied gas, on-board pumps in the ship 70 and/or pumps equipping the land-based installation 77 and/or pumps equipping the loading and unloading station 75 are used.

[0147] As was stated above, the use or the application of the subject matter of the present invention, namely in the case in point the block of fiber-reinforced polyurethane/polyisocyanurate foam, is not intended to be limited to an integrated tank in a supporting structure but it is also provided for tanks of type B and C of the IGC Code in force at the date of filing of the present patent application, but also for the future versions of this Code unless these very substantial modifications apply thereto for these tanks of type B and C, it being furthermore understood that other types of tanks might, under this assumption of a modification of the IGC Code, become applications which can be envisaged for the block of fiber-reinforced PUR/PIR foam according to the present invention.

[0148] In the continuation, a part of the experiments and tests carried out by the applicant company to allow it to assess the subject matter of the invention and its scope are presented, it being considered that other tests/experiments have been carried out and will be liable to be provided subsequently, if necessary/required.

[0149] A polyurethane foam composition, incorporating fibers in the form of mats, is used to demonstrate the invention, these fibers always being provided as long to continuous; more precisely, the lengths of these fibers are exactly the same in the compositions according to invention and those according to the state of the art. The applicant company has in particular tested the subject matter of the invention with fibers provided in the form of fabric and the results obtained are equivalent or virtually similar to those obtained with a mat of fibers, as presented below.

[0150] For each of these PUR foams, the fiber reinforcements exhibit characteristics which are either those defined as meeting the present invention (visible in bold type in the table of results presented below) or characteristics not meeting the definition of the invention; more precisely, in the latter case, the impregnation time for the fibers t.sub.i is greater than the cream time t.sub.c of the PU foam. It will be noted here that the case where the impregnation time for the fibers t.sub.i is much less than the cream time t.sub.c, in other words the cream time t.sub.c would be more than twice the impregnation time for the fibers t.sub.i (t.sub.c>2t.sub.i), is excluded because, in this case, the preparation process obviously cannot have any industrial reality.

[0151] Thus, in order to make quite sure that only the combination of particular characteristics of impermeability of the fiber reinforcements with the choice of a PUR foam exhibiting a particular cream time, or one suited to the characteristics of said fiber reinforcements, no other parameter of the preparation of a block of PUR foam is modified or different between the preparations in accordance with the invention and those in accordance with the state of the art. As nonexhaustive examples, mention may be made of the fact that the nucleation, the amounts of blowing agents, the reaction temperatures, nature and amounts of the mixture of chemical components, pouring process, distance between the pouring of the mixture of chemical components and the DBL or the device making possible the free expansion, if appropriate, are strictly identical in the cases according to the invention and the cases according to the state of the art.

[0152] Of course, it has been chosen in this instance to illustrate the invention using a PIR foam for the sake of clarity and conciseness but equivalent or virtually similar results have been obtained with PUR foams as well as PUR/PIR mixtures.

[0153] Likewise, the preparations of fiber-reinforced foam, the results of which are presented below, use the free expansion technique but the applicant company has shown that equivalent or virtually similar results, from the viewpoint of fiber-reinforced foams according to the invention and fiber-reinforced foams according to the state of the art, have been obtained using a DBL.

[0154] Furthermore, it is understood that all the compositions tested in the continuation are considered under conditions of identical density, it being understood that this parameter of the density is involved in the assessment of the performance qualities in terms of compressive strength.

[0155] For the compositions according to the state of the art, the characteristics of permeability of the fiber reinforcements and of cream time t.sub.c of the PIR foam are as follows:

TABLE-US-00001 TABLE 1 Content (relative share Commercial of the different reference of the Type of product components) Description product Polyol 1 60-70 190-230 mg KOH/g aromatic polyester polyol Polyol 2 15-25 295-335 mg KOH/g aromatic polyester polyol Flame retardant 10-20 triethyl phosphate Isocyanate 240-290 30-31.5% NCO polymeric MDI isocyanate of Voracor CM 388 type Water (chemical blowing 0.5-0.7 agent) Physical blowing agent 20-24 Mixture of isomers of pentane: cyclo- and isopentane Silicone surfactant 0.5-1.5 PEO/PPO-grafted silicone Catalysts .sup. 1-1.6 Voracor CM639 0.4-0.7 Voracor CM420 Additives 1-2 Voratherm CN821 K.sub.c = 5.2 × 10.sup.&.sup.−9 m.sup.2 with r.sub.f = 16 μm; p = 0.978; k = 6; τ = 2; V.sub.f = 0.022 t.sub.i (impregnation time) = 41 s (seconds) with η = 0.45 Pa .Math. s; e.sub.m = 2.4 mm; ΔP = 5140 Pa; M.sub.sd = 4.2 kg/m.sup.2 t.sub.c (cream time) = 15 s

[0156] For the compositions according to the invention, the characteristics of permeability of the fiber reinforcements and of cream time t.sub.c of the PIR foam are as follows:

TABLE-US-00002 TABLE 2 Content (relative share Commercial of the different reference of the Type of product components) Description product Polyol 1 60-70 190-230 mg KOH/g aromatic polyester polyol Polyol 2 15-25 295-335 mg KOH/g aromatic polyester polyol Flame retardant 10-20 triethyl phosphate Isocyanate 240-290 30-31.5% NCO polymeric MDI isocyanate of Voracor CM 388 type Water (chemical blowing 0.5-0.7 agent) Physical blowing agent 20-24 Mixture of isomers of pentane: cyclo- and isopentane Silicone surfactant 0.5-1.5 PEO/PPO-grafted silicone Catalysts .sup. 1-1.6 Voracor CM639 0.4-0.7 Voracor CM420 Additives 1-2 Voratherm CN821 K.sub.c = 3 × 10.sup.−8 m.sup.2 with r.sub.f = 106 μm; p = 0.94; k = 6; τ = 2; V.sub.f = 0.057 t.sub.i = 11 s with η = 0.45 Pa .Math. s; e.sub.m = 3 mm; ΔP = 4116 Pa; M.sub.sd = 4.2 kg/m.sup.2 t.sub.c = 15 s

[0157] It is noted that the cream time t.sub.c for the PIR foams used is logically the same, because the foam used is identical, whatever the case, according to the state of the art and according to the invention.

[0158] Subsequent to carrying out the tests, some results are presented below, in a simplified manner, in order to illustrate the discoveries of the applicant company, in the case where the fiber reinforcements are provided in the form of at least one mat of glass fibers.

[0159] As is seen with the results presented in the table above, with regard to the three criteria considered in order to compare the fiber-reinforced foams obtained, those in accordance with the invention exhibit results which are very significantly better than those of the fiber-reinforced foams according to the state of the art.

[0160] Furthermore, it should be noted that the fiber-reinforced PUR/PIR foams according to the invention do not exhibit any significant deterioration in their property relating to the (very low) thermal conductivity. Thus, by way of example, for the fiber-reinforced foam having 10% of fibers by weight according to the invention, the following values of thermal conductivity are obtained:

TABLE-US-00003 TABLE 4 Thermal conductivity (mW/m .Math. K) at −160° C. at −120° C. at +20° C. 10-14 11-16 23-27

[0161] Although the invention has been described in connection with several particular embodiments, it is quite obvious that it is in no way limited thereto and that it comprises all the technical equivalents of the means described as well as their combinations, if these come within the scope of the invention.

[0162] The use of the verb “to comprise” or “to include” and of its conjugated forms does not exclude the presence of other elements or of other stages than those set out in a claim.

[0163] In the claims, any reference sign in brackets should not be interpreted as a limitation on the claim.