Vapour-barrier membrane based on a PA666/EVOH blend

Abstract

The invention relates to a vapor retarder membrane, intended to be used for improving the airtightness of a building or of a room, comprising at least one active layer having a water vapor permeability which increases with the surrounding relative humidity, said active layer comprising at least 90% by weight of a blend of ethylene/vinyl alcohol (EVOH) copolymer and of a copolyamide 6-6.6 (PA666), the latter having a melting point below 210° C.

Claims

1. A vapor retarder membrane, comprising one active layer or an assembly of more than one active layer having a water vapor permeability that increases with surrounding relative humidity, wherein: said one active layer or assembly of more than one active layer comprises at least 90% by weight of a blend of ethylene/vinyl alcohol (EVOH) copolymer and of a copolyamide 6-6.6 (PA666) having a melting point below 210° C., an EVOH/PA666 weight ratio in said blend is 10/90-50/50, the total thickness of the one active layer or the assembly of more than one active layer is 20-100 μm, and the one active layer or the assembly of more than one active layer is at least 40% by weight of the vapor retarder membrane.

2. The vapor retarder membrane as claimed in claim 1, wherein the one active layer or the assembly of more than one active layer comprises at least 95% by weight of the blend of EVOH and of PA666.

3. The vapor retarder membrane as claimed in claim 2, wherein the one active layer or the assembly of more than one active layer consists essentially of the blend of EVOH and of PA666.

4. The vapor retarder membrane of claim 1, wherein the EVOH/PA666 weight ratio is 20/80-50/50.

5. The vapor retarder membrane of claim 1, wherein the membrane does not comprise another type of active layer or layers.

6. The vapor retarder membrane of claim 1, wherein an ethylene content of the EVOH is between 20 and 35 mol %.

7. The vapor retarder membrane of claim 1, wherein the PA666 is a random copolymer comprising PA6 units and PA66 units and having a PA6 unit/PA66 unit molar ratio of between 97/3 and 50/50.

8. The vapor retarder membrane of claim 1, wherein the total thickness of the one active layer or the assembly of more than one active layer is 25-80 μm.

9. The vapor retarder membrane of claim 1, further comprising a support layer or protective layer or both which is optionally peelable.

10. The vapor retarder membrane of claim 1, wherein the one active layer or the assembly of more than one active layer is more than 80% by weight of the membrane.

11. A process for manufacturing the vapor retarder membrane of claim 1, the process comprising heating and kneading, at a temperature of between 200° C. and 230° C., EVOH and PA666 until a homogeneous blend of these polymers is obtained, and forming a membrane from the homogenous blend of EVOH and of PA666.

12. The process as claimed in claim 11, wherein the forming of the membrane is by extrusion, mechanical drawing, calendering, and/or blow-molding of the polymer blend.

13. A process for improving airtightness of a building or of a room in a building, the process comprising applying the vapor retarder membrane of claim 1 to an internal face of a wall of said building or of said room.

14. The process as claimed in claim 13, wherein the applying comprises applying the membrane in an internal position relative to a thermal insulation material.

15. The vapor retarder membrane of claim 4, wherein the EVOH/PA666 weight ratio is 30/70-50/50.

16. A vapor retarder membrane, comprising an active layer having a water vapor permeability that increases with surrounding relative humidity, wherein the active layer comprises at least 90% by weight of a blend of ethylene/vinyl alcohol (EVOH) copolymer and of a copolyamide 6-6.6 (PA666) having a melting point below 210° C. wherein an EVOH/PA666 weight ratio in said blend is 10/90-50/50, and wherein the active layer is 50 μm thick, the PA666 is a random copolymer comprising PA6 units and PA66 units and has a PA6 unit-PA66 unit molar ratio of 85/15, the EVOH/PA666 weight ratio in the active layer is 30/70, and the ethylene content of the EVOH is 38 mol %.

17. The vapor retarder membrane as claimed in claim 16, wherein the active layer consists essentially of the blend of EVOH and of PA666.

18. The vapor retarder membrane as claimed in claim 1, wherein the vapor retarder membrane comprises one active layer.

19. The vapor retarder membrane as claimed in claim 1, wherein the vapor retarder membrane comprises the assembly of more than one active layer.

20. The vapor retarder membrane of claim 1, wherein the one active layer or the assembly of more than one active layer is at least 60% by weight of the vapor retarder membrane.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows the change in the S.sub.d in a wet atmosphere and in a dry atmosphere of a vapor retarder membrane with an active layer 50 m thick, as a function of the EVOH content.

(2) FIG. 2 shows the change in the S.sub.d as a function of the average humidity of the surrounding atmosphere of a PA666/EVOH membrane (O) in comparison with a Vario membrane (⋄) of the same thickness, consisting of a PA6 homopolymer.

(3) In the present invention, the term “active layer” is intended to mean a continuous layer impermeable to liquid water and to air, the water vapor permeance of which, measured according to ASTM standard E 96, is at least five times greater at an average relative humidity of 75% (wet cup) than at an average relative humidity of 25% (dry cup).

(4) This active layer preferably comprises at least 95%, in particular at least 98%, by weight of blend of EVOH and of PA666, and can even advantageously consist exclusively of such a blend.

(5) Other ingredients, such as plasticizers, lubricants, flame-retardants, biocidal or biostatic agents or reinforcing fibers, may however be present in a proportion of at most 10% by weight, preferably of at most 5% by weight and in particular of at most 2% by weight, relative to the total weight of the active layer(s).

(6) The PA666/EVOH blend-based active layer(s) is (are) advantageously the only active layer(s) of the membrane which preferably does not comprise other active layers within the meaning defined above.

(7) The active layer or the assembly of active layers advantageously has a total thickness of between 20 and 100 μm, preferably between 25 and 80 μm, in particular between 30 and 65 μm. Generally, the increase in this thickness is reflected by an increase in the resistance to the water vapor diffusion both in a wet environment and in a dry environment, without however modifying the general appearance of the curve showing the variation in S.sub.d as a function of the average relative humidity.

(8) The PA666/EVOH blend-based active layer(s) may not be the only layer(s) of the vapor retarder membrane. It may in fact be advantageous or even, in some cases, necessary to line the active layer(s) with a reinforcing or support layer, for example a textile of net or nonwoven type, attached on one side or both sides of the membrane or sandwiched between two active layers. Such a reinforcing or support layer, intended to remain in contact with the active layer throughout the lifetime of the membrane, must of course have a resistance to water vapor diffusion which is negligible compared with that of the active layer.

(9) It is also possible to envisage the use of one or two protective layers intended to be removed, generally by peeling, at the time the vapor retarder membrane is applied. These peelable protective layers may be impermeable to water and to water vapor.

(10) The active layer or the assembly of active layers preferably represents at least 40% by weight, in particular at least 50% by weight and ideally at least 60% by weight or even more than 80% by weight of the membrane.

(11) As explained in the introduction, the applicant noted that PA666, unlike PA6 homopolymer, was miscible in all proportions with EVOH, and that all the blends prepared from these two polymers made it possible to easily prepare thin, homogeneous, transparent vapor retarder membranes having a water vapor permeance which increases with the average relative humidity.

(12) The EVOH/PA666 weight ratio is consequently advantageously between 10/90 and 90/10, preferably between 20/80 and 70/30, and in particular between 30/70 and 50/50. The limitation of the EVOH content is advantageous not just from a technical point of view but from the point of view of the cost price of the raw materials. EVOH is in fact more expensive than PA666. If this situation were to change in the medium term, blends having EVOH/PA666 ratios of between 50/50 and 90/10, preferably between 60/40 and 80/20, could become very advantageous from both a technical and an economic point of view.

(13) FIG. 1 shows the change in the S.sub.d in a wet atmosphere (Δ: wet cup: average RH 75%) and in a dry atmosphere (O: dry cup; average RH 25%) of a vapor retarder membrane with an active layer 50 μm thick, as a function of the EVOH content. The EVOH used is a product sold by the company Kuraray Co. Ltd. and which has an ethylene content of 38 mol %.

(14) It is noted that the S.sub.d in a dry atmosphere continually increases, from a value of approximately 4 m for pure PA666 to more than 100 m for pure EVOH. On the other hand, in a wet atmosphere, there is only a negligible increase in this same S.sub.d value (from 0.2 m for 100% PA666 to 0.5 m for 100% EVOH). In other words, the greater the EVOH content, the greater and therefore the more advantageous the S.sub.d dry/S.sub.d wet ratio.

(15) PA666, or PA6/66, or PA6-6.6, or nylon 666 (CAS No. 24993-04-2) is a random crystalline copolymer comprising PA6 units derived from -caprolactam or from aminocaproic acid, and PA66 units derived from hexanedioic acid (adipic acid) and from hexamethylenediamine or from hexamethylenediammonium adipate. Its melting point must be sufficiently low to allow the preparation of a homogeneous blend with EVOH at temperatures where there is no risk of the EVOH being thermally degraded. Various products which have appropriate melting points are available on the market. They all have a content of PA6 units greater than the content of PA66 units. The PA6 unit/PA66 unit molar ratio of the PA666 copolyamides used in the present invention is advantageously between 97/3 and 50/50, preferably between 95/5 and 55/45, in particular between 90/10 and 60/40.

(16) By way of examples of PA666 available on the market, mention may be made of the products Ultramid® C33 01, Ultramid® C33 LN 01 and Ultramid® C4001 sold by the company BASF, or the products UBE Nylon of the 5000 series (5024, 5033B, 5034B, 5024FDX57, 5033FDX27, 5033FDS, 5034FDX40, 5034FDX17, 5034MTX1) sold by the company UBE.

(17) Similarly, there is a wide range of ethylene/vinyl alcohol random copolymers (CAS No. 26221-27-2) on the market, sold for example by the company Kuraray under the trade name EVAL®. The ethylene content of the EVOHs used in the present invention is preferably between 20% and 50% by weight, in particular between 25% and 45% by weight. Higher ethylene contents are, a priori, less advantageous for the application as vapor retarder membrane since they contain fewer hydrogen bonds, which are known to be essential for obtaining good vapor retarder properties.

(18) By way of examples, mention may be made of the products EVAL M (24 mol % of ethylene); EVAL L (27 mol % of ethylene); EVAL F, T or J (32 mol % of ethylene); EVAL C (35 mol % of ethylene); EVAL H (38 mol % of ethylene); EVAL E (44 mol % of ethylene); EVAL G (48 mol % of ethylene);
all sold by the company Kuraray Co. Ltd., first and foremost as polymers which have an excellent barrier effect against oxygen diffusion. A range of products which are similar and just as suitable is sold under the trade name Soarnol® by the company Nippon Gohsei.

(19) A subject of the present invention is also a process for manufacturing the membranes described above, comprising the preparation of a homogenous blend of the two polymers, followed by a step of forming the membranes.

(20) More specifically, the process for preparing the vapor retarder membranes of the present invention comprises the following successive steps:

(21) the heating and kneading, at a temperature of between 200° C. and 230° C., preferably between 205° C. and 225° C., of EVOH and of PA666 until a homogeneous blend of these polymers is obtained, and

(22) the forming of a membrane from the homogenous blend of EVOH and of PA666 thus obtained.

(23) The heating and kneading step can be carried out in a known manner in an extruder.

(24) The step of forming the membrane is preferably carried out by extrusion, mechanical drawing, calendering and/or blow-molding of the polymer blend.

(25) The vapor retarder membranes thus prepared, consisting only of the active layer, can subsequently be applied, for example under pressure and/or with heating, or by means of a suitable adhesive, to the optional support or protective layers.

(26) The vapor retarder membranes of the present invention can be used in exactly the same way as known vapor retarder membranes, for example the Vario KM and Vario KM Duplex membranes made of PA6, for improving the airtightness of buildings or rooms. Their water-permeability properties mean that they are particularly well-suited to wetter and colder climates rather than moderate climates for which the polyamide 6 membranes are commonly used.

(27) During this use, the membranes are generally applied to the internal face of the walls of the building or of the room to be made leaktight. The expression “to the internal face” encompasses in particular the application of the membranes to other coatings and layers already present on said wall, in particular any type of thermal insulation materials, for example based on mineral wool.

(28) The vapor retarder membrane is then applied in an internal position relative to the thermal insulation material, preferably in direct contact therewith.

(29) FIG. 2 shows, by way of example, the change in the S.sub.d (logarithmic scale) as a function of the average humidity of the surrounding atmosphere, determined according to standard EN ISO 12572; 2001, of a PA666/EVOH membrane (O) according to the invention (thickness 50 μm, 70/30 PA666/EVOH, ethylene content of the EVOH used: 38 mol %; 85/15 PA6 units/PA66 units) in comparison with a Vario membrane (⋄) of the same thickness, consisting of a PA6 homopolymer.

(30) It can be noted that, in a wet atmosphere (75% RH), the two membranes advantageously exhibit a high water vapor permeance, i.e. their equivalent air thickness is low, about 0.2 to 0.3 m. At low relative humidity (27.5%), the equivalent air thickness of the membrane according to the invention (S.sub.d=12 m) is four times higher than that of the known membrane (S.sub.d=3 m). The membrane according to the invention differs, moreover, from the known membrane in that the equivalent air thickness varies greatly over a very narrow humidity range, growing from a value of approximately 0.2 for 75% RH to a value of approximately 2.7 for 68% RH.