MEMBRANE

The invention relates to a roofing membrane and a process for producing the roofing membrane. A roofing membrane and a process for producing the roofing membrane are known from EP-A-1 100844.

Roofing membranes are often applied at pitched roofs, below the roof covering, for example below tiles, slates etc. Such a roofing membrane is a barrier for water to penetrate into buildings, for example coming from leakages in the roof covering, formed by melting of fine snow that has been blown through gaps between tiles, or due to water penetration by driving rains. However, since the sheet has an adequate permeability for water vapor (also expressed as moisture vapor transmission rate), humidity that tends to accumulate in buildings is released, keeping the indoor condition dry enough to ensure the good health of people living or working in the buildings and to avoid rot in wooden structures of buildings, for example in wooden beams of the roof construction.

Roofing membranes in general comprise a layer of a fleece and a layer of a barrier film or two layers of fleece and a barrier film, the barrier film being located between the two layers of fleece. The barrier film of the roofing membrane of EP-A-1 100844 consists of a polymer composition comprising a copolyether ester.

Advantages of the barrier film of a polymer composition comprising a copolyether ester include that the film may be produced with a low thickness. This counts for both roofing membranes produced by lamination and by extrusion coating. Furthermore the copolyether ester has a good thermal stability, which is important, since the roofing membrane may be subjected to high temperatures, especially if applied below tiles. After application at the roof the sheet is occasionally exposed for several months, up to four month is a period normally accepted by roof builders, to UV radiation by sunlight, before the roof covering is applied. Also after the covering is applied exposure might continue, because of openings in the roof covering, letting rays of sunlight through. A disadvantage of the copolyether ester is the low UV-resistance. This may be solved by the addition of UV stabilizers and/or UV absorbers, as for instance disclosed in EP-A-1 100844, but especially the UV stabilizers are costly and there is still need for a further improved UV-resistance.

Furthermore the film of the polymer composition comprising the copolyether ester is slippery. Since the layer of the barrier film of the roofing membrane is often applied facing the outside of the building, the building constructors often have to walk on the film. If the film is slippery this may cause a problem with respect to safety.

It is also possible that the barrier film consists of a polymer composition comprising a thermoplastic polyurethane. Advantages of a thermoplastic polyurethane include the high level of UV-resistance obtainable with suitable UV stabilizers and/or UV absorbers and the high coefficient of friction of the surface, providing low slipperiness. A large disadvantage of the thermoplastic polyurethane is the low viscosity. Because of the low viscosity it is not possible to produce the barrier film with a low thickness, making the film from a viewpoint of costs unattractive.

Aim of the invention is to provide a roofing membrane that does not show these disadvantages and that is nevertheless cost attractive.

This aim is achieved by providing a roofing membrane comprising a barrier film that comprises a layer of a polymer composition comprising a copolyether ester and a layer of a polymer composition comprising a thermoplastic polyurethane, the roofing membrane being applied to a building, the layer of the barrier film consisting of the polymer composition comprising the thermoplastic polyurethane facing the outside of the building.

By co-extrusion of the barrier film according to the invention it is possible to apply the polymer composition comprising the thermoplastic polyurethane in a thin layer, even at high extrusion speed. Furthermore by applying the roofing membrane in such a position, that the layer of the polymer composition comprising the thermoplastic polyurethane is facing the outside of the building, low slipperiness and a good UV-resistance of the roofing membrane are obtained, even if the layer of the polymer composition comprising the copolyether ester comprises only a low amount or even no UV-stabilizers and/or UV absorbers. Furthermore the thermoplastic polyurethane may easily be colored, so that producers are able to apply distinctive marketing features to the membrane, like trademarks.

In US 2005/0227086 a multi-layer sheet material is disclosed, comprising a polyurethane layer as fabric coating. A list of polymers that might be used for bonding the polyurethane layer to the fabric thermoplastic polyester elastomers have been suggested, however it is said that thermoplastic polyester elastomers are unsuited, since they do not provide adequate bonding. Furthermore the polyurethane layer is not used facing the outside of the building. The copolyether ester suitably contains hard segments that are built up from repeating units derived from at least one alkylene diol and at least one aromatic dicarboxylic acid or an ester thereof. As alternative to segment, also the term block is being used. The linear or cycloaliphatic alkylene diol contains generally 2-6 C- atoms, preferably 2-4 C-atoms. Examples thereof include ethylene glycol, propylene diol and butylene diol. Preferably propylene diol or butylene diol are used, more preferably 1 ,4-butylene diol. Examples of suitable aromatic dicarboxylic acids include terephthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid or combinations of these. The advantage thereof is that the resulting polyester is generally semi-crystalline with a melting point of above 150, preferably above 175, and more preferably of above 190°C. The hard segments may optionally further contain a minor amount of units derived from other dicarboxylic acids, for example isophthalic acid, which generally lowers the melting point of the polyester. The amount of other dicarboxylic acids is preferably limited to not more than 10, more preferably not more than 5 mol%, so as to ensure that, among other things, the crystallization behaviour of the copolyether ester is not adversely affected. The hard segment is preferably built up from ethylene terephthalate, propylene terephthalate, and in particular from butylene terephthalate as repeating units. Advantages of these readily available units include favourable crystallisation behaviour and a high melting point, resulting in copolyether esters with good processing properties, excellent thermal and chemical resistance and good puncture resistance.

Suitable aliphatic polyether soft segments in the copolyether ester of component (a) are flexible polyethers that are substantially amorphous and have a glass-transition temperature (T _g ) of below 0°C. Preferably, the T _g is below -20 °C, more preferably below -40, and most preferably below -50 °C. The molar mass of the segments may vary within a wide range, but preferably the molar mass is chosen between 400 and 6000, more preferably between 500 and 4000, and most preferably between 750 and 3000 g/mol. Suitable aliphatic polyethers include a poly(alkylene oxide)diol derived from an alkylene oxide of 2-6 C-atoms, preferably 2-4 C-atoms, or combinations thereof. Examples include poly(ethylene oxide)diol, poly(tetramethylene oxide)diol or poly(tetrahydrofuran)diol, poly(neopentylene oxide-co-tetramethylene oxide)diol, poly(propylene oxide)diol and ethylene oxide-terminated poly(propylene oxide)diol. High durability of the sheet according to the invention is obtained if the copolyether ester contains as polyether segments polypropylene glycol segments, polyethylene glycol segments and/or polytetrahydrofuran segments.

Polytetrahydrofuran segments provide the best durability, polyethylene glycol segments provide a combination of high durability and high vapour permeability

The copolyether ester may further contain a compound with two or more functional groups that can react with an acid- or hydroxyl-group, acting as chain extension or chain branching agent, respectively. Examples of suitable chain extension agents include carbonylbislactams, diisocyanates and bisepoxides. Suitable chain branching agents include e.g. trimellitic acid, trimellitic acid anhydride and trimethylol propane. The amount and type of chain extension or branching agent is chosen such that a block copolyester of desirable melt viscosity is obtained. In general, the amount of a chain branching agent will not be higher than 6.0 equivalents per 100 moles of dicarboxylic acids presenting the copolyether ester. The copolyether ester can further contain the usual catalysts and stabilisers.

Examples and preparation of copolyether esters are for example described in Handbook of Thermoplastics, ed. O.OIabishi, Chapter 17, Marcel Dekker Inc., New York 1997, ISBN 0-8247-9797-3, in Thermoplastic Elastomers, 2nd Ed, Chapter 8, Carl Hanser Verlag (1996), ISBN 1 -56990-205-4, in Encyclopedia of Polymer Science and Engineering, Vol. 12, Wiley & Sons, New York (1988), ISBN 0-471 -80944, p.75-1 17, and the references cited therein.

Preferably the polymer composition comprising the copolyether ester comprises at least 75 wt.% of the copolyether ester, more preferably at least 90 wt.%. Most preferably the polymer composition consists of the copolyether ester and non- polymeric additives, such as colorants, pigments, stabilizers and processing aids.

Thermoplastic polyurethanes may be formed by the reaction between diisocyanates, short chain doils or diamines and long chain diols or diamines.

Commonly used as diisocyanates is 4,4'-diphenylmathane diisocyanate (MDI). Short chain diols may be used as chain extenders. Examples of such short chain diols include ethylene glycol, 1 ,4 butane diol and 1 ,6-hexanediol. Preferably as long chain diols polyetherdiols or polyetherdiamines are used. As long chain diols preferably the same polyether diols or diamines are used as described above for the copolyether ester. Instead of a diol it is possible to use a corresponding diamine.

Preferably the polymer composition comprising the thermoplastic polyurethane comprises at least 75 wt.% of the thermoplastic polyurethane ester, more preferably at least 90 wt.%. Most preferably the polymer composition consists of the thermoplastic polyurethane and non-polymeric additives, such as colorants, pigments, stabilizers and processing aids.

In a preferred embodiment the film exists of the layer of a polymer composition comprising a copolyether ester and the layer of a polymer composition comprising a thermoplastic polyurethane. In a further preferred embodiment the film exists of the layer of a polymer composition comprising a copolyether ester sandwiched between two layers of a polymer composition comprising a thermoplastic polyurethane.

The roofing membrane according to the invention may contain the barrier film and at one or two surfaces of the film a fleece. As fleece normally a non- woven or needle punched fleece is used.

If one fleece is used, preferably the layer of the polymer composition comprising the polyether ester is in contact with the fleece.

In one further embodiment the roofing membrane consists of the film of the polymer composition. Such membranes are also referred to as monolithic films. The advantage of a monolithic film is that the film is easy to produce and is yet very flexible at low temperatures, making the film resistant against mechanical stresses caused by winds at low temperatures.

The barrier film of the roofing membrane according to the invention may suitable be produced in a co-extrusion process. It is possible to co-extrude a film by blow molding or to co-extrude a flat film in a first step. In a second step the roofing membrane according to the invention may be formed by adhering the film at one or both sides to the fleece by using a glue.

Preferably a flat film co-extrusion process is used, wherein the barrier film is co-extruded and wherein thereafter the barrier film is still in the molten state brought in contact with the fleece, so that after cooling of the film, the film is adhered to the fleece.

The thickness of the layer of the polymer composition comprising the polyether ester may be up to 70 μ and is preferably between 10 - 50 μ, more preferably between 12 - 40, even more preferably between 15 - 30, most preferably between 18 - 25 μ.

The thickness of the layer of the polymer composition comprising the thermoplastic polyurethane may be up to 70 μ and is preferably between 10-50, more preferably between 15 - 40, most preferably between 20 - 30 μ.

If applied to a building, the layer of the barrier film consisting of the polymer composition comprising the thermoplastic polyurethane is preferably facing the outside of the building. This is not only because if the better UV resistance. In this way it is also possible to use a copolyether ester with a high amount of the polyether soft block, without running the risk that the polyether ester swells to much because of being in direct contact with rain, the swelling causing delamination of the roofing membrane. This makes it also possible to use a thermoplastic polyether ester comprising up to 75 wt.% of poly ethylene oxide soft blocks.

The invention is further explained in the Figure, without being restricted to that.

Fig. 1 shows a membrane according to the invention consisting of a barrier film and a fleece.

Fig .2 shows a membrane according to the invention consisting of a fleece and two barrier films, one at each side of the fleece.

Fig. 3 shows a membrane according to the invention consisting of a barrier film and two fleeces, one at each side of the barrier film.

Fig. 4 shows a co-extrusion line for carrier out the preferred process of the present invention.

Fig. 1 shows a membrane (1 ) consisting of a fleece (3) and a barrier film consisting of a layer (2.1 ) consisting of a polymer composition comprising a thermoplastic polyurethane and a layer (2.2) of a polymer composition comprising a copolyether ester. After the sheet has been installed onto a building, the layer (2.1 ) is facing the outside of the building.

Fig. 2 shows a membrane (1 1 ) according to the invention consisting a fleece (3) and of two barrier films, one at each side of the fleece. The barrier films consist of a layer (2.1 ) consisting of a polymer composition comprising a thermoplastic polyurethane and a layer (2.2) of a polymer composition comprising a copolyether ester.

Fig. 3 shows a membrane (21 ) according to the invention consisting of two fleeces (3.1 ) and (3.2) and a barrier film, consisting of a layer (2.1 ) consisting of a polymer composition comprising a thermoplastic polyurethane and a layer (2.2) of a polymer composition comprising a copolyether ester. The fleeces are each located at one side of the barrier film.

Fig. 4 shows a co-extrusion line for producing the membrane according to the invention. The co-extrusion line comprises an extruder (20.1 ) for delivering a molten polymer composition comprising a thermoplastic polyurethane and an extruder (20.2) for delivering a molten polymer composition comprising a copolyether ester to a co-extrusion die head (30). The barrier film consisting of a layer (2.1 ) of a polymer composition comprising a polyether ester (2.1 ) and a layer (2.2) consisting of a polymer composition comprising thermoplastic polyurethane is after leaving the die head brought in contact with the fleece (3) so that after cooling down the film adheres to the fleece.

The invention will further be elucidated with reference to the following examples and comparative examples, without being limited hereto

Materials used

EM400: Arnitel® EM400 , a copolyether ester delivered by DSM Engineering Plastics. VT3104: Arnitel® VT3104, a copolyether ester delivered by DSM Engineering Plastics. VT3108: Arnitel® VT3108, a copolyether ester delivered by DSM Engineering Plastics. E2-UV: masterbatch Arnitel® E2-UV, a masterbatch of COPOLYETHER ESTER, comprising UV stabilizers, delivered by DSM Engineering Plastics.

MVT 75AT3: Estane MVT 75AT3 a thermoplastic polyurethane elastomer (TPU) delivered by Lubrizol Advanced Materials.

6-BK-20: masterbatch BLK MB 6-BK-20, a masterbatch of TPU, comprising UV stabilizers, available from Lubrizol Advanced

Fleece: Polypropylene non-woven available from RKW in Gronau

Preparation of roofing membranes

The roofing membranes were produced at an extrusion coating machine from the company SML (Austria). The machine was fitted with 2 extruders making it possible to prepare a co-extrusion coating film on top of the fleece material. The extruders where fitted with barrier screws, melt sieve and a gear pump. The copolyether ester and TPU resins were dried before use and a two layer barrier film was extruded on top of the fleece, the copolyether ester layer being brought in contact with the fleece. Thereafter the film was cooled down, the film being bonded to the fleece. The structure is further explained in Figure 1.

Sample compositions of Examples 1 -4 and Comparative Examples A&B are listed in table 1 . The examples 1 -4 are directed to sheets according to the invention, comprising barrier film of a copolyether ester layer and a TPU layer as explained above. Comparative examples A & B are directed to single layer barrier films comprising either copolyether ester or TPU. Table 1. Compositions of examples and comparative examples according the invention.

The sample compositions as listed in table 1 are processed at different extrusion speeds. The extruder setting were such that the output of both extruders is equal. This results in a multi-layer coating comprising a copolyether ester and a TPU layer of comparable thickness. Coating thickness was determined by weight. The target layer thickness for all extrusion conditions was 40 grams per square meter. The different extrusion conditions are listed in table 2.

Table 2. Extrusion speed versus coating thickness.

Not Processable

The comparative examples A&B show the difference in processability of the copolyether ester composition compared to the TPU composition. The copolyether ester composition can be produced in thin layers at 80 meters per minute line speed without any problems to provide a 40 grams per square meter film. The TPU composition on the other hand can't be processed at speeds as of 60 meters per minute if a coating thickness of 40 grams per square meter is demanded. Examples 1 - 4 show that it is possible to increase the line speed of the machine up to 80 meters per minute when a coextrusion film out of a layer comprising a copolyether ester is combined with a layer comprising a TPU.