WO2004028772A1

WO2004028772A1 - Polymer film production

Info

Publication number: WO2004028772A1
Application number: PCT/GB2003/004182
Authority: WO
Inventors: Peter Threlfall; Alan James Clegg
Original assignee: Porvair Plc
Priority date: 2002-09-25
Filing date: 2003-09-25
Publication date: 2004-04-08
Also published as: TW200413151A; GB0222194D0; AU2003269203A1

Abstract

A process for the continuous production of polymer film in which a liquid polymer-forming composition at or in the region of room temperature is supplied to an inlet of slot die extrusion apparatus and after passing through said slot die extrusion apparatus is discharged from an outlet thereof onto a moving carrier, said polymer film forming on said carrier and being cured or allowed to cure.

Description

POLYMER FILM PRODUCTION

This invention is concerned with polymer film production. More particularly, although not exclusively, the invention is concerned with the production of hydrophilic polymer films, which are useful as functional membranes, for example breathable polymer films and composite laminates used in clothing.

Presently, there are two commercial techniques for the continuous production of hydrophilic polymer films. These are melt extrusion and solvent based casting. Both established techniques suffer drawbacks or limitations, however. Melt extrusion has limitations in that hydrophilic polymers are less thermally stable than the usual extrudable plastics materials which restricts the required properties of the films. The range of hydrophilic polymer materials which can be melt extruded is also limited, since polymer stability at melt temperature is required. Melt extrusion methods also require considerable expertise to control and balance the operating parameters.

Solvent based casting is in commercial use for the continuous production of hydrophilic polymer films, for example urethane polymer films which are widely used in functional clothing membranes. Limitations of solvent based casting reside in environmental considerations and difficulties in making cross linked polymer films. Significant quantities of solvent are used, and require recovery for re-use and to minimise environmental impact. In the production of hydrophilic polyurethane films by solvent based casting, significant volumes of the solvent dimethyl formamide (DMF) are used. The DMF solvent is extracted in water, or evaporated. It is then recovered and dried, which increases the overall cost of the production process, as well as limiting the production speed.

Accordingly it is desirable to develop an alternative continuous polymer film production technique which avoids or minimises the drawbacks and limitations of the known melt extrusion and solvent based casting techniques.

Polyurethane as an example of hydrophilic polymer, can be made by reacting liquid components in a reaction vessel. Whilst the reacting agents are liquids when mixed, at or slightly above room temperature, the resulting polymer is solid at room temperature. The reaction is therefore usually carried out in a solvent, which will permit it to be drained from the vessel as a solution below the melting point of the polymer. It is possible to carry out the above reaction to produce a very short chain polymer, which is still liquid at low temperatures without the use of solvents. Finished polymers are "end capped" in that they no longer have any reactive groups on the ends of the molecules. It is possible to make a short chain liquid polymer, which still has active end groups, and which is capable of further reaction. Such a polymer is called a pre-polymer.

A urethane pre-polymer has live isocyanate groups at the ends of the molecules. They will react with any material containing - OH groups, including water. The iso-cyanate groups are tied to the pre-polymer, and as such, most of them are not volatile. The pre- polymer is less hazardous on inhalation than un-reacted isocyanate. Such materials will be indefinitely stable, provided they are kept away from all sources of -OH groups. Accordingly such a pre-polymer can have a long or indefinite "shelf-life".

If a PU pre-polymer is mixed in exactly the correct proportion with a material whose molecules contain more than one -OH group, such as a polyol, the two agents will react to form polymer chains. A polymer can only form when the pre-polymer has at least two active isocyanates, and the polyol has at least two active OH groups. An iso- cyanate will react with an -OH group, to form a urethane group. If a molecule has two or more isocyanate groups, (such as a di-isocyanate, which has two), it can be made to react with molecules containing more than one -OH group. Reactants of this type are called polyols and form continuous chains, which consist of many urethane groups, and such materials are called polyurethanes. A pre-polymer can be made by adding an excess of di-isocyanate to a polyol, and heating the mixture in a reaction vessel. If the pre-polymer is mixed with a polyol it will react to form a polyurethane.

We have now devised polymer film forming techniques particularly suited to the production of thin hydrophilic films, involving an extrusion device, wherein a substantially solvent free polymer-forming composition is mixed and subsequently discharged from the extrusion device at or near room temperature in a continuous film- forming technique. According to one aspect of this invention there is provided a process for the continuous production of polymer film in which a liquid polymer-formmg composition at or in the region of room temperature is supplied to an inlet of a slot die extrusion apparatus and after passing through said slot die extrusion apparatus is discharged from an outlet thereof onto a moving carrier, said polymer film forming on said carrier and being cured or allowed to cure.

The polymer forming composition may be a "one-part" system, for example a polyurethane pre-polymer, which after discharge through the slot die apparatus is applied to a moving carrier and subsequently cured by passing the film (and carrier substrate) through water as a reactant. The film and substrate can be passed through one or more water baths, in similar fashion to known solvent extraction water baths, to cure the polymer film and to then be heated in an oven or by heated drums to complete the reaction.

The polymer forming composition may alternatively be a "two-part" system in which at least two reactive components are mixed and supplied to the slot die apparatus inlet as a reacting or reactive mixture wherein some polymer formation takes place before discharge onto the carrier. In such a two-part system, it is desirable to select the polymer-forming reactants in the polymer-forming composition such that the composition has a gel time of the order 5 to 10 minutes, to avoid polymer gel formation until after discharge from the slot die. Use of such a two-part system involving mixing at least two reactive components immediately before supply to the slot die inlet is conveniently referred to as reactive extrusion. The polymerisation reaction can be accelerated by heating the film in an oven after extrusion.

The present invention provides a means of eliminating or at least substantially reducing the need for environmentally undesirable solvents such as DMF. In some embodiments of the present invention, one of the components in the two part system may be solid at room temperature, in which case it is acceptable to use a small quantity of solvent to dissolve that component. Such embodiments provide a low solvent content, of the order of no more than 10% by weight but preferably less than 7% of solvent. Such levels of solvent, if used, still represent a reduction in solvent content of about 70 times below conventional solvent based casting of hydrophilic films. Whilst the present invention provides a convenient method for the continuous production of hydrophilic thin polymer films, production of hydrophobic polymer films is also contemplated and possible. Hydrophilic polymer films produced by the present process can be applied as an intermediate tie layer between a surface hydrophobic polymer and a porous substrate. This would allow deep grained surfaces to be fully filled without substantial loss of water permeability. Moreover, a similar hydrophobic two part reactive system may be used in the production of 100% solids non breathable finished films for belts, without necessarily using a corresponding supporting substrate.

It is preferred for the thin hydrophilic films produced according to the present invention to have an extruded thickness as cast in the range of 5 to 50 microns, preferably 5 to 30 microns, more preferably 10 to 20 microns.

Embodiments of thin polyurethane polymer film production using the two part reactive extrusion system may comprise the following steps:

a. reacting under an inert and moisture free atmosphere a polyfunctional isocyanate with a polyfunctional reactant comprising hydroxyl, amine or imine groups to form a reactive isocyanate-terminated pre-polymer; b. mixing the pre-polymer with a chain extender comprising hydroxyl, amine or imine groups to create the polymer forming composition; c. optionally adding a polymerisation catalyst to the composition; d. passing the polymer forming composition through the slot die at or near room temperature e. discharging from the slot die the film-forming composition on a moving carrier substrate; and f. curing of the film

The pre-polymer preferably comprises between 1 and 5 repeating units. In a preferred embodiment, the pre-polymer comprises alternating polyol units and polyfunctional isocyanate units. The molecular weight of the polyol can be between 500 and 5000. The pre-polymer may also contain a low molecular weight liquid diol, such as 1,4- butanediol. In particularly preferred embodiments, the polyol preferably comprises one or more of polypropylene glycol, polyethylene glycol or poly terra methylene glycol, but most preferably comprises polyethylene glycol or a polypropylene glycol/polyethylene glycol blend or copolymer.

h preferred embodiments of the two part reactive system, the chain extender contains reactive -hydroxyl or imine groups. In some preferred embodiments, the chain extender comprises an amine, although in other preferred embodiments the chain extender comprises an aromatic diol optionally blended with aliphatic diol. The chain extender conveniently comprises the aromatic diol Hydroquinone di-(β-hydroxyethyl) ether [HQEE]. This extender may be deployed in solution in DMF in whatever ratio is required for the desired properties.

Advantages of using a liquid chain extender such as a butane diol reside in a beneficial balance of properties. Liquid chain extenders may impart desirable characteristics of a 100% solid, essentially solvent-free system, and may further confer a beneficial balance of substantial "pot-life" and an acceptably low cure time. In such "two-part" reactive systems, it is desirable to achieve the longest pot life commensurate with the most rapid cure time within an oven. A polymerisation catalyst, preferably a blocked such catalyst which is catalytically functional only at temperatures significantly greater than room temperature [25 C, RT"], can be used in the polymer forming composition to accelerate cure time without adverse effect upon pot life. The polymer forming compositions may further comprise, if required, a silicone diol as a release agent, to aid release of a film from the surface onto which it was cast. It also provides anti-block characteristics, and improves surface wetting of the carrier.

Embodiments of the present invention provide hydrophilic polymer films, preferably polyurethane films suitable for fabric lamination, whereby a fabric laid onto a polyurethane film, during its curing stage, permits fibres of said fabric to become bonded into the film during the curing process. For example, a reacting polymer can be extruded as a film and laminated, whilst still wet, with a fabric or other film. If the laminating material is permeable to water vapour as will be the case for most commercially useful laminating materials, the prepolymer film is able to cure in the presence of water or water vapour.

Further embodiments of the present invention reside in composite laminates of hydrophilic polymer films and a different plastics material such as microporous poly(tetrafluoroethene). This provides a breathable plastics membrane.

The polymer is formed as a film, and as such, it can react vigorously with -OH groups which form part of a fabric. Both one part and two part systems permit "one shot" production of laminated fabrics, which are probably bonded by chemical reaction. A further important property of these reacting films is that they do not shrink significantly upon setting, because there is no loss of solvent. They are thus ideally suited to making reasonably "flat" one-shot laminates, where the lamination process, and film curing are carried out simultaneously. Any laminated product made by coagulating or evaporating a film onto a laminatable layer will show severe curl. All lamination is thus carried out in two stages at present, i.e. film production, followed by separate lamination.

We have found that hydrophilic polymer films produced by the present methods can bond very effectively with PTFE, by encapsulating the surface fibres, enabling production of flat PTFE laminates. These laminates are regarded as difficult to achieve, but both the one part and the two part systems are well suited to producing such laminates.

At least three embodiments of polymer forming compositions useful in the present invention will now be described by way of non-limiting example only.

Initially a low molecular weight pre-polymer is made. This pre-polymer is then mixed with a chain-extender in a static mixer and the polymer forming composition is passed through a slot die as a film- forming liquid and applied to a moving carrier such as a web of release paper. The film which forms is then cured and the carrier may be removed.

The pre-polymer preferably consists of between 1 and 5 repeating units and is typically a soft (or liquid) material with a low melting point. The pre-polymer typically comprises a series of alternating polyfunctional alcohols (polyols) and polyfunctional isocyanates which are joined by a urethane linkage. The urethane linkage is very stiff due to the usually aromatic nature of the isocyanate and forms crystalline regions within the material, commonly called 'hard blocks' which form extremely tough local nodules within the soft polyol. These stiffen the polymer and lend rigidity.

The pre-polymer may, if required, comprise only 1 to 2 polyol molecules. At this length, the pre-polymer has a low melting point and may easily be brought into liquid form.

During formation of polyurethane pre-polymer, for example, an excess of isocyanate is typically used to ensure that the terminal residues of the pre-polymer are isocyanate residues. By adjusting the molar reacting ratio of polyol to isocyanate, the length of the pre-polymer molecule may be controlled.

In order to allow the hardness of the film to be varied, additional low molecular weight diol can be added to the polyol. The resultant diol/isocyanate link will provide short chains of hard blocks.

Typically, the polyol may comprise polyester or polyether. If a polyester is used, its constituents can be varied to alter the hardness of the film. A number of different polyethers are suitable for use as preferred polyols. For example, polyethers based on propylene glycol (polypropylene glycol, PPG), ethylene glycol (polyethylene glycol, PEG) or tetra methylene glycol (poly terra methylene glycol, PTMEG) may all be used and will confer different properties on the finished product. For example, PPG provides an economic soft film, PEG gives the most hydrophilic film whilst PTMEG gives the toughest polymeric film. In general, the film properties affected by the polyol type include rebound, abrasion resistance, modulus, breathability, and solvent resistance. To produce moisture vapour permeable polymeric films, PEG or PPG/PEG blends are most preferred as the polyfunctional alcohol.

The pre-polymer melting temperature typically depends on the polyol used and its molecular weight: PPG gives a thick liquid, polyester gives thicker liquids and PTMEG and PEG give solids which melt at approximately 50°C. Pre-polymer viscosity is rapidly reduced by heat and by solvents; alternatively, extra liquid isocyanate can be added to reduce viscosity (quasi pre-polymers). The low melting temperature of the pre- polymer means that it can be made, handled and mixed without using temperatures of above 100°C. This reduces risk of degradation from thermal instability of, for example, the ether links in a PEG-based polyol.

The terminal isocyanate groups of the pre-polymer can be further reacted (or chain extended) by a chain extender containing 2 or more groups that react with isocyanates such as hydroxyl groups and/or imine groups. The chain extender may comprise an amine. Suitable commercially available amine chain extenders include, for example, Ethacure 100, Ethacure 300 and Unilink 4200.

Alternatively, water can be used as a chain extender with a pre-polymer containing methyl-diisocyanate (MDI). The water reacts with the MDI end groups to give the corresponding amine and this, in turn, reacts with more MDI to form urea groups which give an exceptionally tough hard block which increases the tear strength, elasticity and Young's modulus of the final polymer film. If such a polyurethane pre-polymer is extruded into water or a water vapour atmosphere, it reacts to form an elastomeric hydrophilic polymer with commercially desirable properties. The resulting polymer is a poly-urea-urethane, which can be highly breathable and suitable for use in functional clothing membranes.

The pre-polymer is typically in liquid form, allowing easier handling of the reactants. The "two-part" system (pre-polymer and chain extender) should be thoroughly mixed without entraining air before extrusion through the slot die as an equal number of isocyanate and reactive groups must be available to provide complete chain extension. Optionally, the mixing of the pre-polymer and the chain extender may be carried out by metered pumps to ensure the chosen reacting ratios. Typically, mixing of the two components triggers the reaction to produce the end polymer. In-line mixing of the reactants in the selected polymer forming composition immediately before passage into the slot die allows for rapid cure and thus faster line speeds, leading to lower production costs.

Polymer structure may be varied in other ways. For example, by varying the choice of pre-polymer or chain extender, or by using mixtures of reactants for this reaction, the overall structure, chain-length and physical and chemical properties of the resultant polymer material may further be adapted. In particular, it is possible to use a polyol or isocyanate with more than two functional groups, for example, a tri-functional -OH polyol to create a cross linked material. Such cross-linked polymers may not be so pliable or physically flexible as non-cross-linked polymers but are often more chemically resistant, a desirable property for use in some applications of the present invention. In particular, such cross-linked films may be resistant to DEET (N,N - diethyl -3- methylbenzamide or diethyltoluamide which has a similar structure to DMF) and other organic solvents.

The final polyurethane polymer cured film may consist of 50-500 repeating units, depending on the polyol size and the hard block content. The rate of reaction of the pre- polymer and the chain extender depends on the type of isocyanate and the chemical nature of the -OH or =NH group. Aliphatic isocyanates react more slowly than aromatic ones.

The rate of chain extension can thus be varied from instantaneous reaction at ambient temperature to slow reaction, even at elevated temperatures. It is also possible to blend chain extenders, giving a stepped cure. In the case of the two part reactive polymer forming composition, one extender may be used to react rapidly to provide increased melt strength, and a second slower extender may allow time to apply the liquid to the release surface. The reactions between pre-polymer and chain extender are potentially highly exothermic. Resultant excess heat may cause side reactions which result in unwanted cross-linking and gelling. Thorough mixing and dissipation of heat during pre-polymer production and application after mixing with the chain extender are therefore most preferred. It can also be advantageous to slow the rate of reaction whereby heat produced is more easily manipulated, and the temperature of the reactants can be more finely controlled.

Typically, for the production of hydrophilic thin film by two-part reactive extrusion the polymer forming composition is passed through the slot die and discharged onto a moving carrier, for example a wound roll of release paper, or other suitable low energy surface. To provide some resistance to blocking of the final film, the casting substrate surface should have a fine but rough profile. It is preferred that the polymer forming composition is passed through slot die extrusion apparatus constructed and arranged to allow a uniform film coating to be applied onto a moving substrate, with controllable thickness of application.

Such slot die apparatus preferably comprises a die block having within it an internal cavity, which internal cavity widens into a slot through which the polymer forming composition may be pumped; and said apparatus being distinguishable from an extrusion die apparatus, in that it further comprises a dry lip held in contact with the substrate, and a wet lip to facilitate distribution of the polymer film forming composition upon the moving carrier.

Closed-loop control of casting thickness, optionally facilitated by an automatically- dilatable slot gap, may be incorporated into the slot die.

It is most preferred that the reaction rate and temperature are carefully controlled. The rate should be sufficiently slow to allow time for complete mixing and application to carrier before gelling, but fast enough to allow complete reaction in a continuous process. The reaction rate can be varied by varying the types of polyols, isocyanates and chain extenders used, and may be varied by catalyst type and level.

The film of reacting pre-polymer and chain extender is cured after application to the carrier surface. A commercial aromatic amine chain extender such as Ethacure 100 will give gel times of between 2 and 5 minutes under ambient conditions or between 5 and 20 seconds at 50 to 60°C, with a corresponding reduction in cure time compared with butane diol extrusion. By using alternative materials, for example, Ethacure 300 and Unilink 4200, variations in cure time of between 3 and 10 times slower can be achieved.

As an alternative to amine chain extenders, it is possible to use a diol with a catalyst. This can provide a better pot life without compromising a desirable cure time of about 1 minute.

The method of the present invention allows hydrophilic thin films to be cast at high speed, for example at casting speeds of greater than 10 metres of film per minute, hi conventional solvent casting, the rate-limiting step is the removal of the solvent. The substantial or complete absence of solvent in embodiments of the present invention contributes towards this increased line speed.

EXAMPLE 1 - basic linear pre-polymer resin capable of subsequent chain extension

An example of this product consists of a pre-polymer made by reacting MDI (4,4^Λ methylene bis phenyl isocyanate) with a 2000 MWT polyethylene glycol and 1,4 - butanediol as a chain extender.

The materials are reacted at 45-70°C under dry Nitrogen until all the hydroxyl functionality has reacted with isocyanate.

A minor addition of DMF (79 gm) made to this formulation will ensure that it is liquid at 25 °C to allow simpler handling if required.

Once the reaction is complete, the isocyanate content is measured, usually by titration with DNB (di-n-butylamine). The material is then mixed rapidly with the required amount of chain extender and cast as a thin film onto a release paper. The mix has a gel time of about 20 sees at ambient temperature in the case of Ethacure 100 as a chain extender. To complete the reaction, the film/carrier is heated prior to removing the film. EXAMPLE 2 - High solids reactive extrusion pre-polymer

Materials 1. 2000 M Wt Polyethylene glycol, PU grade ex Uniqemi. This high molecular weight polyol enhances breathability.

2. HQEE [Hydroquinone bis-(2-Hydroxy Ethyl) Ether] ex Arch Chemical. This aromatic diol forms hard nodules in the film to enhance antiblocking.

3. Desmodur 44M flake ex Bayer, stored at -15 to -20°C in a sealed metal container (isocyanate).

4. Di Methyl Formamide ex Wliyte Chemicals (solvent).

5. Para-Toluene Sulphonic Acid (pTSA) ex BDH (neutraliser - to neutralise amines in the DMF).

6. Irganox 245 ex Ciba Additives (anti-oxidant heat stabiliser). 7. Tinuvin 326 ex Ciba Additives (UN absorber).

8. Methylene Chloride ex Albion Chemicals (formerly Hays) (solvent for (6) and (7).

9. Ninyzene ex Rohm Haas (biocide).

10. Polycat SAl/10 ex Air Products (blocked catalyst - to provide long pot life but short cure time). 11. 0. IN Hydrochloric acid ex BDH ) (for determining

12. Tetrahydrofuran ex BDH ) isocyanate

13. 0. IN Di Ν-butylamine solution in Tetrahydrofuran ) concentration)

14. Supply of dry Nitrogen gas (to exclude moisture).

15. Felix Scholler 051 casting paper. 16. Industrial Methylated spirits )

17. Distilled water ) (solvent for

18. Bromophenol Blue indicator solution, 0.2gms per ) indicator), litre of 50/50 IMS/distilled water )

Equipment

1. Colette model MP 20 planetary mixer.

2. 25ml burette

3. 10ml pipette 4. 2 1 steel tin with lid. 5. Laboratory oven, ambient to 200°C.

6. Pressure regulating valve for Nitrogen supply.

7. Laboratory temperature controlled circulator, Techne C-85A.

8. Laboratory balances, 200gm x O.OOOlgm and 16000gms x 0. lgm. 9. Werner-Mathis lαiife coating equipment or suitable hand coating Icnife ex Sheen Instruments. 10. 2 1 reaction vessel equipped with power driven stirrer paddle and Nitrogen bleed. 11. 1 litre volumetric flask. 12. 50ml Quickfit conical flasks & stoppers. 13. Water bath with circulator controlling to 0.1 °C.

14. Brookfield LVT viscometer with No 4 spindle and extrusion.

Method

Determination of free isocyanate concentration.

1. Accurately weigh the conical flask and stopper.

2. Add c. lgm of pre-polymer to conical flask, and re-weigh.. 3. Add 1 Omls of THF and 1 Omls of 0. IN DNB solution using a pipette.

4. Stopper flask and shake to dissolve.

5. Add a few drops of Bromophenol Blue solution

6. Titrate against 0.1N Hydrochloric acid to a green yellow end point, noting the volume of HC1 solution used. 7. Repeat the above procedure using a blank test with no pre-polymer.

8. Calculate the isocyanate content as follows:

. , .„. . , . , (Blank HCl - titreHCl) x 0.1

Isocyanate concentration (milh equivalents/gm) =

Sample weight

Pre-polymer manufacture

3.0% Nitrogen 100% solids pre-polymer

Formulation: Polyethylene glycol 2000PU 1344gm HQEE 32gm MDI 624gm 1. Dissolve the HQEE in the polyethylene glycol at 130°C for c. 45 minutes in the steel tin fitted with lid. Shake container occasionally to dissolve.

2. Once fully dissolved, allow mix to cool to c. 60°C. 3. Set Colette water jacket temperature to 50°C

4. Transfer PEG/HQEE to the mixing bowl of the Colette mixer, and purge vessel with Nitrogen.

5. Once the temperature has stabilised to 50°C, add the MDI flakes. Mix at high speed for 10 minutes until all MDI has dissolved. 6. Reduce stirrer speed, set temperature to 60°C. React for a further 3 hours, or until a constant isocyanate concentration is obtained.

7. Measure the free isocyanate concentration of the pre-polymer.

8. Transfer pre-polymer into an air-tight container or applicator, and label with the measured NCO value. The pre-polymer has reactive isocyanate terminated groups and should be kept away from air and moisture.

Chain extender

1. The required weight of HQEE is calculated as follows:

Weight of HQEE = 0.95 x (NCO concentration in milliequivalents/gm) x Batch weight in gms x 99

1000

2. Dissolve HQEE in DMF to give a 60% solids solution 3. Store at 40°C to prevent HQEE from precipitating.

Stabilisers

1. Prepare stock solution 1 by mixing :

Tinuvin 326 8.0gms

Irganox 245 32.0gms

Methylene Chloride 140gms 2. Prepare stock solution 2 by mixing:

Ninyzene 20.0gms DMF 80gms

Preparation of coating mix

1. Weigh out lOOgms of 3.0% Nitrogen pre-polymer.

2. To each lOOgms of pre-polymer add 5.625gms of stabiliser solution 1 and 5.0% of stabiliser solution 2.

3. To each 1 OOgms of pre-polymer add the required weight of HQEE/DMF.

4. To each lOOgms of pre-polymer add 0.25gms Polycat SAl/10.

5. Mix thoroughly and de-gas under vacuum for 2 mins.

Production of films

1. Knife-coat a suitable thickness of mixed pre-polymer onto the release paper.

2. Cure film at 150°C in the drying oven for 1 minute.

3. Allow to cool and remove from paper.

By using reactants which are independently stable the need for large volumes of solvents and all of the secondary processes which their use involves can be significantly reduced or substantially eliminated, thereby conferring environmental and economic as well as practical advantages.

Formation of thin hydrophilic polymer films by a solvent-free or substantially solvent- free method which does not require a melting process allows a degree of cross-linldng within the film to impart solvent resistance to the film (a melt-based process or a solution based process could not allow such cross-linldng), with the economic and environmental benefits associated with a largely solvent-free method. EXAMPLE 3 - Solution-based hydrophilic high polymers

Materials

As EXAMPLE 2. Equipment

As EXAMPLE 2.

Polymer manufacture

3.0%o Nitrogen polymer

Formulation: PEG 2000PU 178.56gm

HQEE 38.58gm

MDI 82.9gm

DMF 700.03gm

PTSA 0.045gm

1. Charge the reaction vessel with PEG2000, HQEE and DMF.

2. Set water bath temperature to 50°C, and set up a slow Nitrogen purge.

3. Leave under constant stirring until the temperature is uniform. 4. Add the MDI, increase stirrer speed.

5. Once MDI has dissolved, reduce stirrer speed.

6. Leave 15 mins, then increase temperature to 60°C.

7. Allow to react for 2 hours, then measure isocyanate concentration.

8. Leave 15 mins then re-measure isocyanate concentration. 9. If the NCO concentration is dropping, leave for a further 15 mins and re-measure. Continue this procedure until the value stabilises. Otherwise take the average of the first two values.

Correction stage: 1. Using the measured isocyanate concentration, add butane diol chain extender calculated as below. 2. Weight of diol = (isocyanate concentration) x batch wt in gms x 45 1000

3. Dilute diol with an equal amount of DMF, add to the reaction and stir at 60°C.

4. Measure viscosity every 30 mins

5. When viscosity reaches 300Poise, add 5gm diol in an equal amount of DMF to cap the reaction. Stir vigorously to disperse the diol and decant into sealed metal cans.

Reference is now made to the accompanying drawings, in which:

FIGURE 1 is a sectional view through a suitable form of slot die, wherein a dry lip engages the carrier surface;

FIGURE 2 is a view of one suitable form of static mixer for a reactive two-part system, to be affixed to a slot die;

FIGURE 3 a shows a suitable one part polymer film casting unit;

FIGURE 3b shows the remainder of the apparatus from Figure 3 a; and

FIGURE 4 shows one form of polymer film production apparatus suited to the two part reactive systems described above.

Referring firstly to Figure 1, a schematic illustration of a suitable form of slot die is shown. The die has a die body (1) with a dry lip engaging and depressing the moving carrier web (6) and a wet lip (4) adjacent the dry lip (2), which assists in spreading the applied composition, which becomes the polymer film (9) coated on the web material. The web path is deliberately deflected by the die. The carrier web is shown in a manner supported by a pair of moving rollers (7, 8) which form part of the production equipment described subsequently.

The selected polymer-forming composition is fed to an inlet of the slot die at feed (3). This is particularly adapted to the 'one part' system in which the polymer composition, for example mainly comprising a polyurethane pre-polymer (having a long or almost indefinite pot life) is supplied to the inlet of the slot die without use of an associated mixer or blender.

The composition enters a die cavity (10) before being compressed through a narrow channel defining the slot, whereafter the composition is applied to the carrier web. The thickness of the applied coating is adjusted by means of lip bolts (5) which are connected to the wet lip (4).

Referring to Figure 2, a static mixer (11) is shown in which the two reactive components namely the metered pre-polymer (12) and metered chain extender (13) of the two part system can be fed, preferably through accurate metering, for thorough mixing and blending immediately before supply to the slot die, through feed (15). A sweep facility (14) is provided to sweep the polymer in the event of processing shut down. The static mixer can be affixed to the slot die such that the reactive mixture is fed from feed (15) to the die inlet without entraining air or moisture.

Figure 3a shows a one part polymer film casting unit adapted to use the 'one part' polymer forming compositions.

A support web (16) continuously feeds a carrier substrate such as polyester film (6) towards the support rollers (7, 8) between which the slot die (1) is located in a manner to apply the polymer composition to the carrier whereby polymer film (9) is formed upon the carrier. Optionally, a web (17) of laminatable material is included in line to feed that material directly onto the film or composition.

Via an arrangement of rollers, the substrate/film is supplied to a water bath (19) having submerged rollers (20). A section (21) of the casting unit has controlled humidity to start the polymer curing process. There is an approximate residence time of the order 2 minutes within the controlled humidity section.

Figure 3b shows the remainder of the one part forming unit commencing in Figure 3 a. After the water bath treatment, the substrate/film is directed over heated drums (21) at about 110°C whereafter separation of film/substrate takes place at final rollers (22,23). Separated film is collected at product winder (24) whilst the carrier substrate is collected at substrate web winder (25). There is an approximate residence time of the order 7 minutes from the slot die applicator to the heated drums.

Finally, Figure 4 shows one suitable production apparatus for making polymer film from two part reactive polymer compositions. Where appropriate, the same reference numerals have been used to identify parts equivalent to the arrangement in Figures 3a and 3b. Thus, a substrate web (16) continuously feeds a carrier substrate (6) over support rollers (7, 8) between which the slot die (1) is positioned, in the manner depicted in Figure 1. If desired, a web (17) of laminatable material (18) is included in line for film lamination between pinch rollers. The film/substrate is passed to an oven (26) having a primary heating zone (27) at about 100°C and a secondary heating zone (28) at about 150°C. The approximate residence time within the oven is about 1 minute. Separation of film from substrate takes place at rollers (22,23) in similar manner to Figure 3b, using product winder (24) and substrate web winder (25).

The arrangement can provide a fast line speed and avoid the need for significant quantities of solvent in the polymer forming composition and the disadvantage of a curing in water phase. It will be appreciated that the particular arrangements shown in Figures 1 to 4 are embodiments depicted by way of non-limiting example only, since other arrangements are possible, for example, a radio frequency oven could be used because the polymer systems presently demonstrated would be heated by RF energy.

Claims

1. A process for the continuous production of polymer film in which a liquid polymer- forming composition at or in the region of room temperature is supplied to an inlet of slot die extrusion apparatus and after passing through said slot die extrusion apparatus is discharged from an outlet thereof onto a moving carrier, said polymer film forming on said carrier and being cured or allowed to cure.

2. A process as claimed in claim 1, in which the polymer forming composition is solvent- free, substantially solvent- free or largely solvent-free.

3. A process as claimed in claim 2, in which the solvent content of the polymer forming composition is less than 10% by weight, based on the total weight of the composition.

4. A process as claimed in any preceding claim, in which the polymer film formed is a thin polymer film with a thickness in the range of 8 to 50 microns.

5. A process as claimed in claim 4 in which the thickness of the film formed is in the range of 10 to 20 microns.

6. A process as claimed in any preceding claim, in which the polymer-forming composition is such as to produce a hydrophilic polymer film.

7. A process as claimed in claim 6 in which the polymer film comprises polyurethane or poly-urea-urethane.

8. A process as claimed in any preceding claim, in which the liquid polymer- forming composition comprises a one-part system based on a pre-polymer such as a polyurethane pre-polymer.

9. A process as claimed in any one of claims 1 to 7, in which the liquid polymer forming composition comprises a two-part system based on at least two reactive components.

10. A process as claimed in claim 9, in which the reactive components comprise a pre-polymer and a chain extender.

11. A process as claimed in claim 10, in which the pre-polymer comprises isocyanate-terminated reactive polyurethane pre-polymer, and the chain extender comprises reactive hydroxyl, amine or imine groups.

12. A process as claimed in any preceding claim, in which the slot die apparatus is fitted at its inlet end with a static mixing device adapted to receive and blend within the mixer, two or more reactive components which, when mixed, provide said liquid polymer-forming composition.

13. A process as claimed in any preceding claim, wherein an additional layer of material is applied to the polymer film to become laminated therewith.

14. A process as claimed in claim 13 in which the additional layer is fed in line to contact the polymer film or film forming composition.

15. A process as claimed in claim 13 or 14 in which the additional layer comprises fabric material or polytetrafluoroethylene (PTFE).

16. A process for the continuous production of polymer film as claimed in any preceding claim substantially as herein described, exemplified or illustrated.

17. Apparatus constructed and arranged to continuously produce polymer film in accordance with a method as claimed in any preceding claim, which apparatus comprises a slot die extrusion apparatus adapted to supply said liquid polymer- forming composition to said moving carrier.

18. Apparatus as claimed in claim 17 incorporating a web of laminatable material arranged to supply said material in line to the polymer film or polymer film forming composition.

19. Apparatus as claimed in claim 17 or 18 substantially as herein illustrated in any Figure of the accompanying drawings.