CA2280790A1

CA2280790A1 - Breathable multilayer foil

Info

Publication number: CA2280790A1
Application number: CA002280790A
Authority: CA
Inventors: Ralf Schledjewski; Dirk Schultze
Original assignee: Individual
Current assignee: Dow Produktions und Vertriebs GmbH and Co oHG
Priority date: 1997-02-19
Filing date: 1998-02-09
Publication date: 1998-08-27
Also published as: DE19706380A1; AU6621298A; JP2001512381A; WO1998036908A1; EP0963293A1; KR20000071181A

Abstract

The invention relates to a foil consisting of at least two layers and made of thermoplastic polyurethane with directional water vapour permeability. The water vapour permeability of each of said foils varies depending on which of the two outer layers of the foil faces the moisture source, when water vapour permeability as determined in accordance with DIN 53122, measured across the total density of the foil. The thermoplastic polyurethanes used for the foil are made of possibly hydrophilized rigid segments consisting of diisocyanates and low-molecular diols as chain extenders, and of soft segments consisting of bifunctional polyols, the latter being high molecular polyethers and/or polyesters.

Description

WW 5481-foreien FILE,'PtM'I#THIS Ai~fif(~
fiEX~T'~TRANSLATION Br/m/W61V26.11.1997 An actively 6reathin~ mufti-layer film The present inventian relates to mufti-layer, water-impermeable, actively breathing S films which are made of thermoplastic polyurethanes and which are produced by coextrusion, the characterising feature of which is that the film exhibits a directionally-dependent permeability to water vapour.
The present invention also relates to the use of the film according to the invention for effecting water-impermeable, actively breathing sealing of sheet-like articles such as woven goods and nonwoven fibrous webs, and relates to articles of use produced therefrom, particularly in the clothing sector, mainly relating there to workwear or rainwear.
The possibility of protecting porous, sheet-like articles from the ingress or penetration of water by means of a water-impermeable film or coating is generally known and forms part of the prior art.
For example, materials which actively breathe are frequently used in order to impart a high level of wearer comfort to articles of clothing. The actively-breathing character of the film is generally verified via its permeability to water vapour. To prevent the build-up of moisture near the wearer of articles of clothing which are finished in this manner, the permeability to water vapour has to be as high as possible.
High permeabilities to water vapour can be achieved for certain types of films, for example, by imparting microporosity as a result of biaxial stretching, as described in US 4,194,041. Microporous films of this type lead to problems in use, where they are often subjected to considerable stretching. The elbow region of outer clothing can be cited as an example of this. Enlargement of the pores can easily occur here, which results in the formation of tears and thus in the loss of impermeability to water.

Problems of this type are circumvented by the use of pore-free films having a high permeability to water vapour, such as those described in EP 0 591 782, for example.
EP 0 658 581 describes the use of hydrophilic thermoplastic polyurethanes in the sphere of actively-breathing sheet-like textile articles.
Thermoplastically processable polyurethanes are thermoplastic elastomers such as those which are described in the review article in Rubber Chemistry and Technology 62 (1989), pages 529 - 54. Commercially available thermoplastic polyurethanes are generally characterised by a cambination of good tensile strength and tear propagation resistance, together with a high level of extensibility over a broad temperature range.
A review on thermoplastic polyurethanes is given by Hepburn (editor):
Polyurethane elastomers, Applied Science Publishers, Barking (1982) pages 49 - 80. Special extruded products can be processed to form films either via a sheet extrusion die or via blown film extrusion. Further information on extrusion technology is given, for example in Kirk - Othmer: Encyclopedia of Chemical Technology, Volume 9 (1966) pages 232 - 241. Apart from single-layer films, it is also possible by employing extrusion technology to produce multi-layer films from thermoplastic polyurethanes, as is described in EP 0 603 680 for example.
As has already been described above, the wearer comfort of articles of clothing to which active breathing properties are imparted is influenced to a considerable extent by the permeability to water vapour thereof. The desired high permeability to water vapour should not, however, result in the transport of moisture from the outside to the inside. The object ofd the present invention is thus to provide a highly elastic film which is impermeable to water but which is permeable to water vapour, the permeability of which to water vapour is directionally-dependent.
This object has surprisingly been achieved by the production of a film based on thermoplastic polyurethanes ('TPUs) which is produced by coextrusion.

Accordingly, the present invention relates to a TPU film which comprises at least two layers and to the use thereof for the production of actively-breathing, water-impermeable sheet-like articles which exhibit a directionally-dependent permeability to water vapour, characterised in that the films exhibit a different permeability to water vapour when a different one of the two outer layers of the film according to the invention faces the source of moisture when the permeability to water vapour is determined according to one of the customary standard methods of measurement.
Customary methods of determining permeability to water vapour are described in DIN
53122 or ASTM E9(~ for example. These methods of determination are based on the penetration of water vapour from a source to a sink. The water vapour source is formed by a climatic chamber, a climatic solution or a defined vapour phase, etc. The sink is generally formed by a drying agent. The films according to the invention preferably consist of different TPU resin formulations in the different layers. The essential concept of the invention is to employ what is a preferential transport of moisture from the layer which exhibits the higher permeability to water vapour to the layer which is provided with a lower permeability to water vapour.
This object has been achieved by a multi-layer film which is characterised in that the individual layers are built up from linear, thermoplastically processable, segmented polyurethane molecules. The polyurethanes, which are comparatively hydrophilic, are formed from alternating blocks of soft and hard segments, wherein the soft segments are formed from difunctional polyols A) which are synthesised from polymerised ethers and/or esters, and the hard segments are formed from the reaction products of a low molecular weight diol B), i.e. from the chain extender, and a diisocyanate C).
These blocks are advantageously linked to each other so that the hard segment forms the two ends of the molecular chain in each case, and so that the reactive cyanate groups situated at the ends of the linear molecule can optionally be capped by alcohols D).
The thermoplastic polyurethanes are preferably linear block copolymers which always comprise a certain i:raction of branches due to the allophanate-forming secondary ' ' CA 02280790 1999-08-16 WW 5481-foreien reaction which occurs during the reaction to form the urethane. The average molecular weight of suitable thermoplastic polyurethanes is preferably between 10,000 g/mol and 250,000 g/mol.
Difunctional compounds, i.e. compounds which advantageously contain two terminal hydroxyl groups, are preferably used for the soft segment A). Compounds which are particularly preferred in this respect are ethylene oxide polymers and/or copolymers, which are also often termed polyoxyethylene glycols and/or polyethylene oxide glycols, the monomer unit of which is characterised by the structure (-O-CHz-CHZ-) and-which have an average molecular weight of at least 400 g/mol and at most g/mol. In one particularly preferred embodiment, the average molecular weight is between 800 g/mol and 1200 g/mol. These compounds are further characterised by a weight ratio of carbon to hydrogen which is at least 1.3 and which is at most 2.5. The proportion by weight of the soft segment A) to the thermoplastic elastomer which forms the film according to the invention ranges between 35 % and 60 %, and is preferably between 40 % and 50 %, with respect to the total weight of thermoplastic polyurethane in each case. The tendency of the soft segments to crystallise can be reduced, and the breathing activity can optionally be increased, by copolymerisation of the ethylene oxide with other cyclic ethers, for example propylene oxide or tetrahydrofuran.
The constituents of the hard segments can be selected from isocyanate and diol components which are known for the production of film raw materials from thermoplastic polyurethanes.
Short-chain, bifunctional substances, the molecular weight of which is between 18 and 350 g/mol, are used as diol component B). Examples thereof in the form of dihydric alcohols include ethylene glycol, 1,2-propylene glycol, 1,4-butylene glycol, which is also known as tetramethylene glycol, 2,3-butylene glycol, 1,5-pentanediol, 1,6-hexanediol and 1,8-octanediol, as well as diethylene glycol, triethylene glycol, tetraethylene glycol and higher polyethylene glycols with molecular weights up to 350 ' ' CA 02280790 1999-08-16 g/mol, dipropylene glycol and higher polypropylene glycols with molecular weights up to 350 g/mol, and also include dibutylene glycol and higher polybutylene glycols with molecular weights up to 350 g/mol.
Other low molecular weight diols B) with molecular weights up to 350 g/mol which are suitable for the production of the polyurethanes used according to the invention are ester diols of general formula HO-(CHZ)y CO-O-(CHZ)X OH
---and HO-(CHZ)x O-CO-R-CO-O-(CHZ)X-OH, wherein R denotes an alkylene radical comprising 1 to 10, preferably 2 to 6, C atoms or a cycloalkylene or arylene radical comprising 6 to 10 C atoms, x is 2 to 6, and y is3to5, e.g. adipic acid-bis-(~i-hydroxyethyl) ester and terephthalic acid-bis-([3hydroxyethyl) ester.
Suitable isocyanates C) comprise aliphatic, cycloaliphatic, aromatic and heterocyclic diisocyanates which ~~re described by the formula OCN-Q-NCO

WW 5481-foreign wherein Q denotes an aliphatic hydrocarbon radical comprising 2 to 18, preferably 6 to 10, C atoms, a cycloaliphatic hydrocarbon radical comprising 4 to 15 C atoms, or an aromatic hydrocarbon radical comprising 6 to 15, preferably 6 to 13, C
atoms.
Examples of diisocyanates such as these include 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, cyclohexane 1,3- and 1,4-diisocyanate and any mixtures of these isomers, naphthalene 1,5-diisocyanate, 2,4- and 2,6-diisocyanatotoluene and any mixtures of these isomers, and diphenylmethane 2, 4'- and/or 4,4'-diisocyanate.
Suitable alcohols D) which can be used as capping reagents include low molecular weight alcohols with a molecular weight of at least 32 g/mol and at most 100 g/mol.
Suitable capping reagents not only include monofunctional alcohols, but also include di-, tri- or higher polyols. Aliphatic short chain alcohols with a molecular weight of at least 32 g/mol and at most 400 g/mol are preferred.
According to the invention, polyurethane elastomers which exhibit different degrees of hydrophilic character or permeabilities to water vapour are used for the individual layers of the film. This can be achieved by the use of different soft segments and/or modified hard segments of the polyurethanes in the individual layers. For the soft segments, for example, there is an increase in hydrophilic character in the sequence:
polyester < polytetrahydrofuran < polyethylene oxide.
Modifications can be used for the hard segments, for example, such as those which are sold by Bayer AG, Leverkusen and which are known as dual hydrophilic Impraperm~
types (EP 0 525 567 and DE 4 236 569).

WW 5481-foreien _7_ In one preferred embodiment, all the layers of the film are based on thermoplastic polyurethane elastomers, the longer chain diol components of which are essentially formed from polyethers. Structures which are particularly preferred in this respect are those in which all the layers of the film are formed from different thermoplastic polyurethanes which ~~re used to build up polyether soft segments.
In one particularly preferred embodiment, the polyurethane elastomer resins which form the different layers of the film according to the invention have different Shore hardnesses. In this respect, whilst optionally retaining the same soft segment structure, the-soft segment content of the layers which form the film according to the invention is varied, so that the resins which form the individual layers exhibit different permeabilities to water vapour.
The thermoplastic polyurethanes which are used preferably have a Shore hardness of 75 - 95 A, most preferably 85 - 95 A, as determined according to DIN 53 505.
Examples of thermoplastic polyurethanes which are suitable according to the invention are those which are obtainable under the trade names of Desmopan~, Elastollan~, Estane~, lmpraperm~, Pellethane~, Morthane~ or Texin~.
In one suitable embodiment of the film according to the invention the individual layers additionally contain customary additives from the group comprising:
I. anti-seizing agents, inorganic or organic separators, II. internal lubricants or demoulding agents, III. pigments or fillers, and IV. stabilisers.
The total content of said additives I to IV is preferably between 1 % by weight and 30 by weight.

WW 5481-foreien _g_ The customary additives which the film according to the invention may contain are described, for example, by Gachter and Muller in: Kunststoff Additive, Carl Hanser Verlag Munich, 3rd F;dition (1989).
The films which are preferred according to the invention are those which have a total thickness between 5 ~m and 500 Vim, most preferably between 5 ~m and 50 Vim.
According to the invention, the thickness of each of the individual layers can vary within the range from 10 % to 90 % of the total thickness. A structure is particularly preferred in which thc: thinner layer corresponds to a proportion between 10 %
and 49 % ef the total thickness.
In very thin actively-breathing structures, an additional backing layer, e.g.
a layer based on polyethylene, can be used according to the invention to impart better handling, e.g. for stiffening. In a film such as this, the thickness of the layers) of thermoplastic polyurethane(s;) is preferably between 5 ~m and 25 Vim, and the thickness of the backing layer is preferably between 5 ~.m and 100 Vim.
Customary thermal shaping procedures for the processing of plastics to form multi-layer sheet-like articles are pwticularly suitable for the production of the mufti-layer film according to the invention. One such procedure which should be mentioned here is production by coextrusion, which is preferably effected by the blown film process.
On account of the better composite bonding which can be achieved, coextrusion is the particularly preferred process of those which are suitable for the production of multi-layer thermoplastic sheet-like articles.
Moreover, coextrusian is preferable to the coating processes from a melt or solution which are known in the art, since only one pass through the machine is necessary.
According to the prior art, the melt is distributed circularly for mufti-layer blown film dies by means of designs which comprise sleeves, ribbed mandrel holders, spiral distributors or sandwich dies (e.g. the Bramton Engineering design). Circular distribution of the melt based on the spiral distributor principle is preferred according to the present invention.
The surface properties of the films according to the invention can be modified on one or both sides by means of known physical and chemical methods of treatment, such as corona, flame, plasma or fluorine treatment for example.
On account of their properties according to the invention, the films described here are particularly suitable as membrane films, especially those which are used in the clothing sector. They are particularly suitable for use in the sphere of workwear or working clothes, which are often worn for long periods. In the leisurewear sector, they are particularly suitable for use as a wind- and weatherproof, rain-resistant outdoor membrane.
The films according to the invention are also suitable for applications in the fields of medicine and medical technology. Coverings for wounds, active ingredient patches, anti-allergic mattress covers and operating theatre protective clothing should be explicitly mentioned here.
In a most preferred embodiment, the films according to the invention are used as laminated composites with woven textile goods, knitted goods or nonwoven webs, or with wovens and nonwovens in general.
The films which are described in the context of the following examples and comparative examples were produced by blown film coextrusion. The construction of endless screw tooling which is suitable for the digestion of thermoplastic resins is described, for example, by Wortberg, Mahlke and Effen in: Kunststoffe, 84 (1994) 1131-1138, by Pearson in: Mechanics of Polymer Processing, Elsevier Publishers, New York, 1985 or by the Davis-Standard company in: Paper, Film & Foil Converter 64 (1990) pages 84 - 90. Dies for shaping the melts into films are described by lU
Michaeli in: Extrusions-Werkzeuge, Hanser Verlag, Munich, 1991, amongst other references.

WW 5481-foreien A film was produced by means of a double-layer blown film extrusion die. Layer (1) of the film, which had a thickness of 20 Vim, was produced from a thermoplastic polyurethane of Shore hardness 90A according to DIN 53505, which exhibited an MFR of 27 g/10 minutes as measured at 190°C using a test mass of 10 kg , and which was essentially synthesised from components comprising diphenylmethane 4,4'-diisocyanate as the hard segment, polyethylene oxide as the soft segment and 1,4-butanediol as the chain extender. 4 % by weight, with respect to the total weight of co~rrponents used for film processing, of a natural hydrated silica with a particle size between 3 ~.m and 7 ~.m, and 1 % by weight of an amide wax were added in order to adjust the processing properties.
The substances used in layer (2), which had a thickness of 10 Vim, comprised a thermoplastic polyurethane of Shore hardness 85A according to DIN 53505, which exhibited an MFR of 25 g/10 minutes as measured at 190°C using a test mass of 10 kg, and which was essentially synthesised from components comprising diphenylmethane 4,4'-diisocyanate as the hard segment, polytetrahydrofuran as the soft segment and 1,4-butanediol as the chain extender. Amounts of hydrated silica and amide wax were added which were the same as those used in layer ( 1 ).
The materials were each processed to form a film, in a single-screw extruder comprising a flanged-on blown film extrusion die. Increasing temperatures of 190°C were set at the; extruders, which had a diameter of 45 mm. The extrusion die temperature was 190°C.
xa le 2 A film was produced by means of a double-layer blown film extrusion die. Layer ( 1 ) of the film, which had a thickness of 20 Vim, was produced from a thermoplastic polyurethane of Shore hardness 82A according to DIN 53505, which exhibited an ' ' CA 02280790 1999-08-16 WW 5481-foreien MFR of 26 g/10 minutes as measured at 190°C using a test mass of 10 kg, and which was essentially synthesised from components comprising diphenylmethane 4,4'-diisocyanate as the hard segment, polyethylene oxide as the soft segment and 1,4-butanediol as the chain extender. 4 % by weight, with respect to the total weight of components used for film processing, of a natural hydrated silica with a particle size between 3 ~m and 7 um, and 1 % by weight of an amide wax were added in order to adjust the processing properties.
The substances used in layer (2), which had a thickness of 10 ~.m, comprised a thermoplastic polyurethane with a Shore hardness of 85A according to DIN
53505, which exhibited an MFR of 25 g/10 minutes as measured at 190°C using a test mass of 10 kg, and which was essentially synthesised from components comprising diphenylmethane 4,4'-diisocyanate as the hard segment, polytetrahydrofuran as the soft segment and 1,4=butanediol as the chain extender. Amounts of hydrated silica and amide wax were added which were the same as those used in layer ( 1 ).
The materials were each processed to form a film, in a single-screw extruder comprising a flanged-on blown film extrusion die. Increasing temperatures of 190°C were set at the extruders, which had a diameter of 45 mm. The extrusion die temperature was 190°C.
A film was produced as in Example 2, using a double-layer blown film extrusion die.
Layer (1) of the film had a thickness of 36 ~m and layer (2) thereof had a thickness of 10 Vim.
A film was produced using a three-layer extrusion die. Layer (1) of the film, which had a thickness of 10 Vim, was produced from a thermoplastic polyurethane of Shore WW 5481-foreign hardness 82A according to DIN 53505, which exhibited an MFR of 26 g/10 minutes as measured at 190°C using a test mass of 10 kg, and which was essentially synthesised from components comprising diphenylmethane 4,4'-diisocyanate as the hard segment, polyethylene oxide as the soft segment and 1,4-butanediol as the chain extender. 4 % by weight, with respect to the total weight of components used for film processing, of a natural hydrated silica with a particle size between 3 pm and 7 p,m, and 1 % by weight of an amide wax were added in order to adjust the processing properties.
The--substances used in layer (2), which had a thickness of 10 Vim, comprised a thermoplastic polyurethane of Shore hardness 85A according to DIN 53505, which exhibited an MFR of 25 g/10 minutes as measured at 190°C using a test mass of 10 kg, and which was essentially synthesised from components comprising diphenylmethane 4,4'-diisocyanate as the hard segment, polytetrahydrofuran as the soft segment and 1,4-butanediol as the chain extender. Amounts of hydrated silica and amide wax were added which were the same as those used in layer ( 1 ).
In layer (3), which had a thickness of 20 pm, a polyethylene was used which exhibited an MFR of 3 g/10 minutes as measured at 160°C using a test mass of 2.16 kg.
The materials were each processed to form a film, in a single-screw extruder comprising a flanged-on blown film extrusion die. Increasing temperatures of 190°C were set at the extruders, which had a diameter of 45 mm. The extrusion die temperature was 190"C.
om~arative example 1 A film was produces! using a single-layer extrusion die. Layer (1) of the film, which had a thickness of 50 pm, was produced from a thermoplastic polyurethane of Shore hardness 90A according to DIN 53505, which exhibited an MFR of 27 g/10 minutes as measured at 190°C using a test mass of 10 kg, and which was essentially WW 5481-foreign synthesised from components comprising diphenylmethane 4,4'-diisocyanate as the hard segment, polyethylene oxide as the soft segment and 1,4-butanediol as the chain extender. 4 % by weight, with respect to the total weight of components used for film processing, of a natural hydrated silica with a particle size between 3 pm and 7 p.m, and 1 % by weight of an amide wax were added in order to adjust the processing properties.
The material was processed to form a film, in a single-screw extruder comprising a flanged-on blown film extrusion die. Increasing temperatures of 160-190°C were set at tie extruders, which had a diameter of 45 mm. The extrusion die temperature was 190°C.
Unitsxample xampleExample ExampleComparative 1 2 3 4 example ilm thickness pm 30 30 45 20 50 ermeability to g/
water apour (source 130 720 650 1400 350 of oisture facing (mz layer .
(1)) d) ermeability to g/
water apour (source 90 700 470 1200 350 of oisture facing (mz layer .
d) 2)) It can be seen from Table 1 that the films according to the inventions exhibit a directionally-dependent permeability to water vapour, whereas this is not observed for the film from the comparative example. It can be seen from a comparison of Example 2 and Example 3 in particular that the degree of directional-dependency of the permeability to water vapour can be adjusted in a targeted manner by the variation according to the invention of the layer thicknesses.
Determination of the permeability to water vapour:
The permeability to water vapour was determined according to DIN 53122. This was performed at a temperature of 23°C and at a relative atmospheric humidity of 85%. In Example 4, the permeability t:o water vapour was determined after separating the PE
backing film or layer (3).

Claims

1. A film comprising at least two layers which is made of thermoplastic polyurethane and which exhibits a directionally-dependent permeability to water vapour, characterised in that said film comprising at least two layers exhibits a different permeability to water vapour when a different one of the two outer layers of the film faces the source of moisture when the permeability to water vapour is determined according to DIN 53122 and is measured over the total thickness of the film comprising at least two layers, the thermoplastic polyurethanes which are used therefor are built up from hard segments, which are optionally rendered hydrophilic, consisting of diisocyanates in combination with low molecular weight diols as chain extenders, and from soft segments comprising difunctional polyols, wherein the latter comprise high molecular weight polyethers and/or polyesters.

2. A film according to claim 1, characterised in that the different layers thereof are synthesised from thermoplastic polyurethanes with different resin formulations.

3. A film according to claims 1 or 2, characterised in that all the layers of the film consist of thermoplastic polyurethane comprising polyether-based soft segments.

4. A film according to claims 1 to 3, characterised in that different types of ethers are used in the soft segments in the different layers.

5. A film according to any one of claims 1 to 4, characterised in that the layer with the highest permeability to water vapour comprises a soft segment based on ethylene oxide.

6. A film according to claims 1 to 5, characterised in that a hard segment which has been rendered hydrophilic is used in at least one layer.

7. A film according to claims 1 to 3, characterised in that the layers which make up the film have different hardnesses.

8. A film according to at least one of claims 1 to 7, characterised in that the film has a thickness between 5 µm and 500 µm.

9. A film according to at least one of claims 1 to 8, characterised in that the film has a thickness within the range from 5 µm to 50 µm.

10. A film according to at least one of the preceding claims, characterised in that the individual layers of the film have different thicknesses and the thinner layer constitutes a proportion between 10 % and 49 % of the total thickness.

11. A film according to claim 10, characterised in that the thinner layer has a lower water absorption capacity.

12. A film according to any one of claims 1 to 11, characterised in that it comprises a peelable backing film.

13. A film according to at least one of claims 1 to 12, characterised in that the film is produced by means of a coextrusion process.

14. A film according to at least one of claims 1 to 12, characterised in that the film is manufactured as a blown film by means of a coextrusion process.

15. A film according to any one of claims 1 to 14, characterised in that at least one additive from the group comprising:

I. anti-seizing agents, inorganic or organic separators, II. internal lubricants or demoulding agents, III. pigments or fillers, and IV. stabilisers, is used in at least one layer in a proportion from 1 % to 30 %.

16. A film according to at least one of claims 1 to 15, characterised in that the film is physically or chemically pretreated on at least one side.

17. The use of a film according to at least one the claims 1 to 16 as a membrane film.

18. The use of a film according to at least one of claims 1 to 16 in the clothing sector.

19. The use of a film according to at least one the claims 1 to 16 in the workwear sector.

20. The use of a film according to at least one of claims 1 to 16 in the rainwear sector.

21. The use a film according to at least one of claims 1 to 16 in the medical domain.