EP0644823A1

EP0644823A1 - Polymeric articles and materials

Info

Publication number: EP0644823A1
Application number: EP93909387A
Authority: EP
Inventors: Paul Anthony Taylor; Kevin Mark Goninan
Original assignee: British Technology Group Inter Corporate Licensing Ltd
Current assignee: British Technology Group Inter Corporate Licensing Ltd
Priority date: 1992-04-23
Filing date: 1993-04-23
Publication date: 1995-03-29
Also published as: FI944958L; JPH07508688A; NO944003L; HUT70712A; FI944958A0; AU4021493A; CZ261594A3; KR950701272A; CA2134101A1; GB2282100A; NO944003D0; SK127794A3; HU9403063D0; WO1993022125A1; BR9306286A; GB9421384D0

Abstract

Improvements in the manufacture of multi-layer organic polymer composites are described, particularly applicable to composites including adjacent layers of a relatively water-soluble polymer (e.g. partially hydrolysed polyvinyl alcohol) and a relatively water-insoluble polymer (e.g. fully hydrolysed polyvinyl alcohol). The extruded layers are brought together within the die housing or by nipping means external to the die, or the relatively water-insoluble layer may be coated onto the relatively water-soluble layer. Specific designs of die are claimed, as are specific extrudable compositions and apparatus for conveying the same to the dies. The invention makes available for the first time a range of articles in which plastic parts are water-compatible in normal use but are completely degradable on contact with water during disposal, such as WC-disposable sanitary articles and water-degradable rigid containers for oil and petrol.

Description

POLYMERIC ARTICLES AND MATERIALS

Field of the Invention

This invention relates to polymeric materials and articles made therefrom, and to methods and apparatus for 5 forming polymeric articles and materials, more particularly polymeric articles and materials which can readily be disposed of when no longer required.

Background

Polyvinyl acetate is a water-insoluble polymer which is

10 obtained by polymerization of vinyl acetate. This polymer is used for the production of polyvinyl alcohol (PVA) by hydrolysis or alcoholysis to remove the acetyl groups from polyvinyl acetate. This removal of acetyl groups may be carried to partial completion so as to give

15 a product which is a copolymer of vinyl alcohol and vinyl acetate. If vinyl alcohol predominates, but there is still a substantial quantity of vinyl acetate present, such a copolymer is soluble in cold water and is frequently referred to as "partially hydrolysed"

20 polyvinyl alcohol. The residual vinyl acetate content is typically about 11 wt% corresponding to about 12 mol%. If the reaction is taken further, close to completion, the crystallinity of the polyvinyl alcohol increases and the solubility in cold water decreases very markedly.

25 Material of this type is referred to as "fully hydrolysed" polyvinyl alcohol. Its contents of residual vinyl acetate is typically no greater than 3 mol%.

* WO 92/01556 (the disclosure of which is incorporated herein by reference) describes certain degradable » 30 articles, typically in sheet form, in which a water- soluble PVA substrate is protected on its surface against contact with water while the article is in use by means of a polymeric composite structure. However, such structures have hitherto been relatively difficult to

SUBSTITUTESHEET form. In particular_^ we have found that the particular casting/moulding and film-blowing coextrusion processes described and claimed in WO 92/01556 do not provide a satisfactory product.

It is an aim of the present invention to provide improvements in the formation of polymeric materials such as those of WO 92/01556.

The invention is based on our surprising finding that a polymeric material of the type described in WO 92/01556 can be prepared with substantial and unexpected advantages in terms of efficiency, speed and cost, by extruding the layers through certain particular die arrangements or by a specific multistep forming process. It is to be noted that "cast coextrusion" mentioned herein does not in any way resemble the non-extrusion casting/moulding processes described in WO 92/01556, as will be explained in more detail below.

Brief Description of the Invention

The present invention,therefore provides in one aspect a process for preparing a composite polymeric article or polymeric material comprising a first organic polymer layer (e.g. of partially hydrolysed polyvinyl alcohol) which is water-soluble at a given (suitably low) temperature, typically 20°C, and a second organic polymer layer (e.g. fully hydrolysed polyvinyl alcohol) located adjacent to the first polymer, the second polymer being substantially less soluble than the first polymer, or insoluble, in water at the same given temperature, comprising: a blown-film or cast coextrusion process in which the polymers are extruded through a die assembly in such a way that the polymers are discharged from the die assembly as a composite polymeric material including the polymer layers; or an extrusion/lamination process in which the polymers are extruded through die apertures in such a way that the polymers are discharged as separate polymeric layers and are subsequently passed together between nipping means under conditions of temperature and nip pressure to cause the layers to laminate together to form a composite polymeric material including the polymer 5 layers; or a forming and coating process in which the p first polymer layer is formed by extrusion or blow- moulding and the second polymer layer subsequently applied as a coating (e.g. by spraying, dipping, painting, rolling, etc).

10 Where an article or material is formed using blown-film extrusion the die may comprise a first inlet port for receiving one of the polymers under pressure; a second inlet port for receiving the other of the polymers under pressure; and a pair of mandrel members, the first

15 mandrel member being hollow along its length to encircle the second mandrel member and the arrangement being such that a first annular conduit is defined around the outer circumference of the first mandrel member, for conveying the said one of the organic polymers over the outer

20 surface of the first mandrel member, and a second annular conduit is defined around the outer circumference of the second mandrel member, for conveying the said other of the organic polymers over the outer surface of the second mandrel member, the arrangement further including a

25 polymer guide channel associated with one or each of the conduits, for conveying polymer from the respective inlet port to the respective conduit around substantially all of the outer circumference of the respective mandrel member.

30 Such a die assembly for coextrusion of this material is new and constitutes a further feature of the invention.

The present invention therefore provides in a further „ aspect a die assembly for coextruding a composite polymeric article or material including first and second

35 organic polymer layers adjacent to one another, the die assembly comprising: an elongate housing having a first inlet port for receiving one of the polymers under pressure, a second inlet port for receiving the other of the polymers under pressure and an outlet port downstream of the inlet ports for discharging the composite polymeric material; and a pair of mandrel members provided within the housing, the first mandrel member being hollow along its length to encircle the second mandrel member and the arrangement being such that a first annular conduit is defined around the outer circumference of the first mandrel member, for conveying the one organic polymer over the outer surface of the first mandrel member towards the housing outlet port, and a second annular conduit is defined around the outer circumference of the second mandrel member, for conveying the other organic polymer over the outer surface of the second mandrel member towards the housing outlet port, the first and second conduits terminating together in such a way that the two polymers are discharged from the housing outlet port as a composite polymeric material including polymer layers; the arrangement further including a polymer guide channel associated with one or each of the conduits and preferably of relatively larger width than the respective conduit, for conveying polymer from the respective housing inlet port to the respective conduit around substantially all of the outer circumference of the respective mandrel member.

Preferably a guide channel is associated with each of the conduits and most preferably each guide channel provides two paths for the polymer entering through the respective inlet port? namely, a first path to convey the polymer in one direction around the respective mandrel and a second path to convey the polymer in the other direction around the mandrel. In this most preferred arrangement each path half-encircles the mandrel and they meet behind the mandrel (as viewed from the inlet port).

The guide channels are preferably cut into the outer surfaces of the mandrels. The width of the guide channels preferably tapers inwards away from the inlet port, most preferably down to a width identical to the conduit being supplied.

It is most preferred that each guide channel is open throughout its length to the conduit it is supplying.

As a further preference, each guide channel may worm forwards (i.e. downstream) along its respective mandrel, so that polymer that has already travelled along the channel to the back of the mandrel (as viewed from the inlet port) before entering the respective conduit is substantially at the same or similar longitudinal distance along the mandrel as polymer that has entered the conduit relatively soon after entering the assembly through the relevant inlet port.

The second mandrel may conveniently be hollow so that compressed air can be blown through the centre of the die to expand the film as it leaves the die.

Where the sheet is formed by cast coextrusion or cast extrusion of separate sheets and subsequent nip lamination, the cast die or die(s) may comprise a first inlet port for receiving one of the polymers under pressure; a second inlet port for receiving the other of the polymers under pressure, and respective elongate slots in the die(s) through which each sheet is extruded.

Such a die assembly for coextrusion is also new and constitutes a further feature of the invention. The present invention therefore provides in a further aspect a die assembly for coextruding a composite polymeric article or material including first and second organic polymer layers adjacent to one another, the die assembly comprising: a housing having a first inlet port for receiving one of the polymers under pressure, a second inlet port for receiving the other of the polymers under pressure and an outlet port downstream of the inlet ports for discharging the composite polymeric material; die means defining a first elongate slot aperture and first manifold channel means being provided to connect the first inlet port to said first slot aperture, the manifold channel means widening towards the slot aperture and being arranged to spread the polymer across the mouth of the slot aperture; die means defining a second elongate slot aperture and second manifold channel means being provided to connect the second inlet port to said second slot aperture, the manifold channel means widening towards the slot aperture and being arranged to spread the polymer across the mouth of the slot aperture; the first and second slot apertures terminating together in such a way that the two polymers are discharged from the housing outlet port as a composite polymeric material including polymer layers.

For cast extrusion of separate sheets and subsequent lamination, the die assembly used may suitably be an appropriate number of conventional cast extrusion dies providing an appropriate number of slot die apertures and feeder conduits therefor, depending upon the number of layers desired to be formed in the composite material.

Thus, in conventional processes for cast extruding a single thermoplastic sheet, e.g. a rigid polyvinyl chloride sheet, the extrudable polymeric composition is fed to a so-called "clothes-hanger" or "fish-tail" die having a relatively large diameter entry channel which rapidly widens into a manifold channel to spread the extrudable composition across the mouth of the single slot die. The manifold channel is configured so as to encourage spreading of the composition towards the extremities of the slot die. The width of the slot is suitably adjustable by means of externally accessible adjuster screws. The extruded sheet material is typically hauled off under a suitable tension and passed through conventional rollers and cutters for finishing.

Where a composite polymer is prepared by extrusion of separate layers and subsequent nip lamination, the nip lamination is suitably performed by nip rollers, and optionally at elevated temperature. Surface effects between the polymers, and/or electrostatic effects, and/or the effects of external air pressure are all believed to assist lamination, and the use of adhesives or fusion of the layers at the interface may not be necessary.

In the case of a forming and coating process for manufacturing the desired composite polymeric articles or materials, the first (relatively water-soluble) polymer layer is formed by extrusion or blow-moulding in any conventional manner and the second (relatively water- soluble) polymer layer is subsequently applied as a coating in any conventional manner. Spray-coating of a liquid composition of the second polymer is particularly mentioned.

Furthermore, in a modification of this aspect of the present invention the second polymer layer may be substituted by the dry residue of an ink which dissolves more slowly than the first polymer (or not at all) at the given temperature (e.g. 20°C). The above method is particularly suitable for making degradable rigid blow- moulded containers and bottles of the first (relatively water-soluble) polymer, for holding non-aqueous materials such as oil or petrol, and externally coated with the relatively insoluble ink to protect against water- degradation during use.

The articles and materials described in the preceding paragraph are themselves new and they and their manufacturing processes generally constitute further features of the present invention.

In a further aspect, therefore, the present invention provides a polymeric article or polymeric material comprising an organic polymer which is water-soluble at a given (suitably low) temperature, typically 20°C, wherein the surface of the article or material is wholly or partially coated with an ink which dissolves more slowly or not at all in water at the same given temperature to form a water-resistant barrier coating.

Analogously to the composites described herein, where the article or material is only partially coated with the ink, the coated portion of the surface of the article or material will suitably be all of that portion of the surface that may be expected or intended to become exposed to water during normal use of the article.

The article or material is suitably formed in any conventional manner (e.g. extrusion, moulding, blow- moulding, casting etc) from the polymer, and the ink coating subsequently applied in liquid form (e.g. by spraying, dipping, painting or rolling, for example using a conventional film printing press) and then dried.

The preferred soluble polymer is partially hydrolysed polyvinyl alcohol.

The ink coating is preferably the dry residue of a flexographic alcohol-based hydrocarbon-free liquid ink such as the commercially available inks sold for flexo- printing polyolefin films. The inks sold under the trade mark "ORION" by Coates Lorilleux Limited, Essex, England, may be particularly mentioned as examples of suitable liquid inks from which the ink coating of the present invention may be obtained.

In certain forms of this aspect of the invention the article or material is laminar. Such a form of the invention could be a polymer film or sheet to be used in industrial production processes. Further forms of this aspect of the invention are articles comprising pieces of such polymer sheet or film. In particular, the pieces of polymer or film may be shaped to have curvature in more than one direction, e.g. bottles.

If an exposed surface of the polymer is brought into contact with water, it dissolves but where a polymer surface is overlaid by the ink layer that surface is protected. The ink acts as a barrier and protects the first polymer against dissolution if the protected surface gets wet.

Such functionality has a wide range of applications. In general the articles and materials of the invention can be used where it can be arranged that at first the ink layer acts, as a barrier protecting the water-soluble polymer from a material which is, or might be, wet and then at a later stage an unprotected surface of the water-soluble polymer is allowed to come into contact with water. The consequence of this is that dissolution of the soluble polymer takes place when desired but premature dissolution is prevented by the ink.

Where the article comprises a polymeric film, suitably all of one or both faces of the film is coated with the insoluble ink. The polymeric film should be sufficiently thick to provide the required mechanical strength, for example from about 5μm to 1 mm, more typically from lOμm to 200 μm, for example about 50μm. The ink layer is typically from about lμm to 7μm in thickness, for example about 3um.

Non-film articles may comprise a "core" of the soluble polymer, substantially or entirely covered by the ink. Such an article can resist attack by water, but when the ink layer is broken water can dissolve the exposed core and hence the entire article may be disintegrated.

In accordance with a further aspect of the invention, there is provided a method of forming a polymeric article comprising an organic polymer which is water-soluble at a given temperature, typically 20°C, wherein there is applied to the article a whole or partial surface coating of a liquid ink and the said coating is subsequently allowed to dry to form a water-resistant ink barrier coating which dissolves more slowly or not at all in water at the same given temperature.

Where the article or material comprises a polymeric film, the liquid ink may suitably be applied initially to a blank roller of a conventional film printing press and then a film of the liquid ink rolled onto a roll of polymeric film in conventional manner.

The ink may be used in any desired colour or combination of colours to provide an attractive external appearance of the article. If desired, different inks may be applied sequentially to create a desired effect.

Referring now to all aspects of the present invention, and as described in WO 92/01556, the speed with which the more rapidly soluble (first) polymer dissolves can be altered by selection of the polymer and also by selection of processing conditions» The length of time for this polymer to dissolve can be chosen according to the use envisaged or the article or material and can range from a matter of seconds to several hours. The soluble polymer will generally have a speed of solution such that when a sheet of the polymer with at least one side face of the sheet is exposed is placed in distilled water at 20°C, the sheet dissolves sufficiently to break up within a period of time not longer than 24 hours, usually not longer than 8 hours and possibly very much shorter than this e.g. less than 10 sees for a test sheet 50 μm thick.

In the composite material described in WO 92/01556, the weight ratio of the more soluble to the less soluble polymer will preferably be at least 2:1, more preferably at least 3:1, still more preferably at least 5:1 and perhaps above 10:1 up to even 100:1, particularly for thick articles. In an alternative aspect described, the less soluble polymer covers the more soluble polymer with a general thickness which is preferably not more than 20μm, more preferably not more than lOμm, most preferably not more 5 than 5μm. It may be as thin as 2μm or thinner.

In a composite film product, the total film thickness may range typically from 5μm to 1mm, more typically from lOμm to 200μm.

Each polymer may be used in admixture with other 10. substances. For example, colours and/or fillers may be used if desired, in one or both layers. These may be conventional.

Articles may take various forms; for example, a composite film may comprise just two layers, one of each kind of 15 polymer. Alternatively, the composite film may be a sandwich of more soluble polymer between layers of less soluble polymer. Layers of other materials may, of course, additionally be present.

In the processes described above, the first (or only), 20 water-soluble, polymer is preferably partially hydrolysed polyvinyl alcohol. The second, relatively water- insoluble, polymer may be fully hydrolysed polyvinyl alcohol. The extrudable and blow-mouldable precursor compositions are preferably plasticised compositions of 25 the respective polymers.

For extrusion, the plasticised composition of the first (water-soluble) polymer preferably comprises from about 1 to 60, suitably about 5 to 35 parts (by weight or volume), more preferably from about 10 to 20 parts, most 30 preferably about 15 parts, of plasticiser per 100 parts of polymer; up to about 30, suitably about 0 to 15, more suitably about 1 to 15, parts (by weight or volume), more preferably from about 3 to 15 parts, most preferably about 5 parts, of water per 100 parts of polymer; and up to about 5, suitably about 0.01 to 5, parts (by weight or volume), more preferably from about 0.01 to 3 parts, most preferably about 0.25 parts, of a slip agent such as powdered silica (to promote flow of the composition) per 100 parts of polymer. Such a composition is novel and itself constitutes a further aspect of the present invention.

For extrusion, the plasticised composition of the second polymer preferably comprises from about 1 to 80, suitably about 5 to 60 parts (by weight or volume), more preferably from about 15 to 35 parts, most preferably about 25 parts, of plasticiser per 100 parts of polymer; up to about 30, suitably about 0 to 15, more suitably about 1 to 15, parts (by weight or volume), more preferably from about 3 to 15 parts, most preferably about 5, suitably about 0.01 to 5, parts, of water per 100 parts of polymer; and up to about 3 parts (by weight or volume), more preferably from about 0.01 to 3 parts, most preferably about 0.25 parts, of a slip agent such as powdered silica per 100 parts of polymer. Such a composition is also novel and itself constitutes a further aspect of the present invention.

The plasticiser may be- selected from any conventional plasticiser for the polymer in question. For polyvinyl alcohol polymers the plasticiser should be a polyhydric alcohol, such as glycerol, a glycol, an alkanediol (e.g. an ethanediol, propanediol_Λ butanediol, pentanediol or hexanediol), an alkanetriol (e.g. a hexanetriol or trimethylol propane), a fatty acid monoglyceride, or a mixture thereof.

The extrudable compositions described above are generally solid and granular, in contrast to the aqueous compositions indicated for extrusion in WO 92/01556. It is to be noted particularly that the compositions of the present invention employ significantly less water than comparable known compositions. For other forming methods, however, higher levels of water may be required. Such judgements are, however, within the capacity of one of ordinary skill in this art.

The ingredients of the compositions are suitably mixed_ together at an elevated temperature (e.g. about 110°C), but this is not essential, and lower temperatures may be used for the mixing, which will result in a longer mixing time.

The extrusion is performed under pressure and suitably at elevated temperature. The precise pressure and temperature conditions may be selected by a skilled worker, according to the melting and degradation conditions of the polymers employed.

Processing aids such as antifoamers and lubricants may be used if desired.

Such conventional process features, which are within the ordinary knowledge of a skilled worker, can be employed to some extent in the novel method of the present invention, and will not be discussed in detail here.

However, the following particular novel preferred features of the method of the present invention are mentioned:

Firstly, in the case of polyvinyl alcohols, we have found that an extrusion (die) temperature of between about 190°C and 240°C (e.g. about 215°C) gives good results.

Furthermore, each polymer composition is suitably supplied to the die by means of a short screw extruder having a trickle feeder to prevent blockage. The extruders should be arranged to avoid excessive shearing forces on the compositions while delivering the compositions to the die inlet under the desired compression and within a sufficiently short time so that significant degradation of the polymer does not take place (about 4 minutes under normal extrusion conditions for PVA compositions).

We have found that such a requirement can suitably be achieved by using for each composition a screw extruder having two or more compression zones in the extruder barrel, vented between zones for the release of steam and the barrel being at a carefully controlled temperature or series of temperatures along its length. After the final compression zone the composition passes into the die inlet port, if necessary through a temperature-controlled adaptor to adjust the temperature of the composition to the die temperature.

According to a further aspect of the present invention, therefore, there is provided an apparatus for delivering an extrudable plasticised composition of an organic polymer to an extrusion die in a process for forming a composite polymeric article or material, the apparatus comprising a screw extruder having two or more compression zones in the extruder barrel and being vented between some or all zones, and temperature control means whereby the barrel is capable of being maintained at a controlled temperature or series of temperatures along its length.

The extrusion die may be a coextrusion die for receiving both polymers or may comprise dies having separate apertures for extruding each polymer separately and nipping means provided downstream of the die apertures to laminate the polymer layers after extrusion. In these cases, each polymer is preferably delivered via its own screw extruder as described above. Still further, however, the die may be a single die for extruding only a relatively water-soluble polymer for subsequent coating.

The positions of the compression zones along the barrel are chosen to suit the particular composition being carried. It is preferred that the first compression zone is far enough down the barrel so that the composition has achieved significant momentum before entering the compression zone, for ease of feeding and to prevent blockage (to further reduce the possibility of blockage in the compression zone, and to reduce shear of the composition, the compression on the composition suitably increases gradually into the compression zone). The final compression zone, before the composition enters the die, may similarly be arranged so that the compression on the composition increases gradually into the zone (in addition to reducing shear, this prevents back-flow of composition out of the vent in the region of substantially zero compression immediately before the final compression zone).

The compression ratio, screw barrel diameter and screw speed of the screw extruder are also chosen to suit the particular polymer composition being carried. Thus, for example, plasticised insoluble PVA composition may suitably be delivered under a compression ratio of from 1.1:1 to 5.6:1 (more preferably about 2.15:1) whereas plasticised soluble PVA composition may suitably be delivered under a compression ratio of from 1.5:1 to 6:1 (more preferably about 3:1). Plasticised insoluble PVA composition is desirably delivered to the coextrusion die at a relatively high screw speed and low barrel diameter, compared with plasticised soluble PVA composition. More particularly, plasticised insoluble PVA may be delivered at a screw speed of about 70 rpm through a screw barrel of 18mm diameter, and plasticised soluble PVA at a screw speed of about 50 rpm through a screw barrel of 25mm diameter.

As stated above, the temperature conditions along the barrel are controlled. The temperature of each successive portion of the barrel may increase, remain substantially constant or decrease towards the die. We have found that it is preferred that, for a screw carrying plasticised insoluble PVA composition, the temperature of each successive third of the barrel should increase towards the die, suitably in the steps 180 ± 30°C, 230 ± 30°C and 250 ± 30°C; and for a screw carrying plasticised soluble PVA composition, the temperature of each successive third should remain substantially constant or decrease slightly towards the die, suitably in the steps 203 ± 30°C, 202 ± 30°C and 199 ± 30°C.

Industrial Application

Particular uses envisaged for the laminar articles prepared by means of the present invention include disposable packaging material and barrier layers in sanitary products e.g. nappies and bed-pan liners. These need to be able to withstand wetness on one side; by using film embodying the present invention they can after use be dropped, with their contents, into a WC bowl to disintegrate. The whole can then be flushed away. The advantage in terms of convenience is apparent, while from the environmental point of view PVA is not only biodegradable to harmless C0₂ and water, but also has no known toxicity and hence does not present a risk before chemical degradation.

A further application lies in water-disintegratable containers, e.g. rigid oil containers. These can suitably be formed by blow-moulding the water-soluble first polymer into container form in conventional manner, and applying an external coating of the water-soluble second polymer or of a water-insoluble ink (e.g. by spraying).

Brief Description of the Drawings

Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings in which: Fig. 1 shows a longitudinal sectional view of a coextrusion die assembly;

Fig. 2 shows a top view of the die assembly of Fig. 1; Fig. 3 shows (a) a top view and (b) a longitudinal sectional view of a lower housing block part of the assembly of Fig. 1;

Fig. 4 shows (a) a bottom view and (b) a front view of a first mandrel part of the assembly of Fig. 1; Fig. 5 shows a side view of the mandrel part of Fig. 4 (b) looking down from the left;

Fig. 6 shows (a) a bottom view and (b) a front view of a second mandrel part of the assembly of Fig. 1;

Fig. 7 shows a side view of the mandrel part of Fig. 6 (b) looking from the right;

Fig. 8 shows (a) a top view and (b) a longitudinal sectional view (with a detail enlarged) of a top housing block part of the assembly of Fig. 1;

Fig. 9 shows a longitudinal sectional view of a die bush part of the assembly of Fig. 1;

Fig. 10 shows (a) a top view and (b) a front view of a pin part of the assembly of Fig. 1;

Fig. 11 shows (a) a top view and (b) a longitudinal sectional view of a clamp ring part of the assembly of Fig. 1;

Fig. 12 shows a semi-schematic vertical sectional view of a cast coextrusion die assembly;

Fig. 13 shows a sectional view of the die assembly of Fig. 12, taken along the line AA looking in the direction of the arrows;

Fig. 14 shows a schematic view of a first coextrusion apparatus;

Fig. 15 shows a schematic view of a second coextrusion apparatus; Fig. 16 shows a side view of a screw part of an extruder for use in the apparatus of Fig. 14 or 15;

Fig. 17 shows in cross-section a film protected by an ink barrier^' layer on one side; and

Fig. 18 shows in cross-section a film protected by an ink barrier layer on both sides.

Detailed Description of the Drawings

Materials Used

In the following embodiments, both the insoluble and soluble layers were made from PVA. The PVAs used were "Mowiol" (Registered Trade Mark) obtainable from Hoechst AG. The soluble layers were made using Mowiol 26-88, a partially-hydrolysed PVA having a mean molecular weight of 103000, an 88 mol% degree of hydrolysis and whose viscosity, measured as a 4% aqueous solution, is 26 mPa.s². The insoluble layers were made using a 50:50 blend of Mowiol 56/98 and Mowiol 28/99 which are fully- hydrolysed grades having viscosities and hydrolysis values substantially as indicated by their respective specification numbers, as before.

The plasticised Mowiol 26-88 composition had the following composition (proportions are parts by weight per 100 parts of Mowiol 26-88):

Mowiol 26-88 (100) Glycerine (plasticiser) 15

Distilled Water 5

Powdered Silica R972 0.25

The powdered silica R972 was present as a slip agent, manufactured by Aerosil.

The ingredients were all placed initially into a Baker Perkins High Speed Mixer (manufactured by Baker Perkins Limited), which was preheated to 110°C. The mixer was then run at approximatel 600 rpm for about 6 minutes, whereupon the material began to lift on the side of the mixer. The composition was then dumped into a cooler for approximately 15 minutes or until the temperature fell below 40°C. In the mixing process the glycerine plasticiser and the silica slip agent coat "he Mowiol granules and the distilled water is absorbed into the Mowiol granules. The process is accompanied by a rise in temperature.

The plasticised 50:50 Mowiol 56-98:Mowiol 28-99 composition had the following composition (proportions are parts by weight per 100 parts of Mowiol mixture):

Mowiol 56-98 (50)

Mowiol 28-99 (50) Glycerine (plasticiser) 25

Water 5

Powdered Silica R972 0.25

The ingredients were placed initially into a Baker Perkins High Speed Mixer which was preheated to 110°C. The mixer was run at approximately 600 rpm for 30 seconds and then at 1000-1200 rpm for approximately 15-17 minutes, whereupon the material began to lift on the side of the mixer. The composition was then dumped into a cooler for approximately 15 minutes or until the temperature fell below 40°C.

The liquid ink used was an alcohol-based and hydrocarbon- free flexographic ink sold for printing polyolefin films, having the trade mark "ORION" (Coates Lorilleux Limited, Essex, England). Such inks have low odour and solvent retention, are relatively quick drying when applied to a polymeric surface, with good adhesion to the surface, are resistant to freezing temperatures and show acceptable anti-static and slip properties. The liquid ink may be admixed with conventional additives, diluents, colouring agents or solvents if desired.

Coextrusion Die —

Referring firstly to Figs. 1 to 11 of the drawings, a coextrusion die assembly is shown, having a lower housing block part 1 surrounded by an electrical heating jacket (approx. 600W; 240V) 2; a first (outer) mandrel part 3; a second (inner) mandrel part 4 located within a hollow interior of the first mandrel 3; a top housing block part 5; a die bush part 6; a pin 7 located within the die bush 6; and a top clamp ring part 8.

The metal housing block 1 is cylindrical in form and is provided near its base with a pair of inlet ports 9,10 angled at approximately 120° to each other. The top face of the block is provided with six tapped holes 11 to receive bolts 12 for securing the top block 5 to the lower block 1; a similar number of holes are provided in the bottom face of the block 1 to receive bolts 14 for securing a base portion 15 of inner mandrel 4 in position.

Each inlet port 9,10 is provided with an adaptor piece 16,17 to connect the wider diameter screw extruders (discussed in more detail below with reference to Figs. 12 and 13) to the inlet ports. The adaptor pieces are of metal and are provided with electrical heating jackets 18 which enable their temperature to be controlled. Most typically the temperature maintained by heating jackets 2 and 18 will be substantially the same, the adaptors 16,17 thereby also functioning as regulators of the temperature of the incoming polymer compositions.

The first (outer) mandrel 3 is generally cylindrical in form, being arranged to fit snugly within the housing block 1 and having itself a hollow central channel 19 to receive the second (inner) mandrel 4, as will be described in greater detail below.

The outer mandrel 3 is formed of metal and has machined into its external surface by means of a bull-nose cutter a polymer guide channel 20 which starts relatively near the base of the mandrel, at a point adjacent the inlet port 9 of the housing, and worms up and around the mandrel in both the clockwise and the anticlockwise directions, tapering inwards in width as it does so, to terminate on the opposite side of the mandrel.

In use, a polymer composition entering the die through inlet port 9 encounters the relatively wide portion 21 of guide channel 20 and divides its flow to follow the guide channel in both its directions.

As more polymer enters the inlet port the polymer spills out of the guide channel over a relatively smaller diameter upper portion 22 of the mandrel. This upper section 22 of the mandrel, being spaced somewhat away from the neighbouring upper portion 23 of the interior of the housing block 1, defines therewith a first annular conduit 24 which receives polymer from the guide channel 20 and inlet port 9 for conveying the polymer over the mandrel 3.

The channel 20 markedly assists in achieving an even circumferential distribution of the polymer around the mandrel 3.

The mandrel 3 is provided in its wall near its base with a radial hole 25 for communicating between the second inlet port 10 and the second (inner) mandrel 4, as will be described in greater detail below. Furthermore, the base of the outer mandrel 3 is provided with six holes 26 to receive bolts for securing the base portion 15 of the inner mandrel 4 in position.

The second (inner) mandrel 4 is also generally cylindrical in form, but smaller than the first mandrel 3, being arranged to fit snugly within the central channel 19 of the first mandrel. The second mandrel 4 also has a central channel 27, however, for conveying compressed air in the extrudate blowing stage, as will be described in more detail below. The inner mandrel 4 is of generally similar form and function to mandrel 3, having a similar polymer guide channel 28 cut into the mandrel 4 for conveying polymer, from the second housing inlet port 10 and the hole 25 of mandrel 3, circumferentially around the mandrel 4 to spill out into a second annular conduit 29 defined by the upper portion 30 of the interior wall of the first mandrel 3 and the upper portion 31 of the second mandrel, which is of somewhat reduced diameter and is therefore spaced apart from the upper portion 30 of the interior wall of the first mandrel. The guide channel 28 tapers inwardly in width away from the inlet port 10 and follows a two-directional worm path over the mandrel 4, analogously to guide channel 20 of mandrel 3.

The base portion 15^~Of inner mandrel 4 is provided with a radially outer set of six holes 31 to receive bolts 14 for securing the mandrel 4 to the housing block 1. The base portion 15 is also provided with a radially inner set of six holes 32 to receive bolts for securing the mandrel 4 to the outer mandrel 3.

At the upper ends of each conduit 24,29 are provided constrictions 33,34 which adjust the thickness and evenness of each polymer film prior to the films meeting and adhering together to form the desired bilayer.

In the case of the first conduit 24, constriction 33 is provided by a bulbous portion 35 provided on an interior portion of the cylindrical top block part 5 of the assembly. The block 5 has an inner wall 36 which tapers inwards towards the top, so guiding the extruded polymer passing through the constriction 33 radially inwards to meet the other polymer emerging from the second conduit 29 via constriction 34.

Block 5 is bolted to the top of housing block 1, via six holes 37, six smaller holes 38 also being provided in the upper rim of block 5 to receive bolts for securing the clamp ring 8 to the block 5, as will be described in more detail below.

Block 5 is also provided with four side holes 39a through its upper portion, to receive bolts 39b for securing the die bush 6 in position within the hollow interior of block 5, as will be described in more detail below.

The die bush 6 is of hollow cylindrical construction having an internal surface tapering outwards in the up direction to form a chamber 40 which houses the pin 7. The pin 7 is hollow to receive a hollow bolt (not shown) which passes down through the pin and into a widened top portion of the central channel 27 of the inner mandrel 4 to secure the pin in position. The central channel 27 and the central channel of the hollow bolt together provide a passage through the centre of the die assembly to permit the passage of compressed air through the die assembly. The pin 7 has an outwardly tapering outer surface which guides the composite polymeric film out of the die housing through an exit port 41 to a film blowing region above the assembly.

Around the base of the pin 7 is provided an annular rib 42 by which the above mentioned constriction 34 in second conduit 29 is obtained when the rib 42 is in position near the upper portion 30 of the interior wall of the first mandrel 3.

The die bush 6 is retained to the top block 5 by means of a top clamp ring 8 overlying both the top block 5 and a shoulder 43 of the die bush 6 and bolted to the top block 5 through six holes 44 in the clamp ring 8 (only one such hole is shown in the sectional view of Fig. 11(b), for clarity). The top block 5 is then suitably surrounded by an electric heating jacket 45.

Referring now to Figs. 12 and 13 of the drawings, a two- slot cast coextrusion die assembly is shown, having two housing block parts 50a,50b including conventional heating means (not shown); an upper slot die 51 having associated adjuster and feed means as described in more detail below; and a lower slot die 53 having similar associated adjuster and feed means.

Each slot die 51,52 is defined by respectively an upper 53 and lower 54 variable lip spaced apart from a fixed central double-edged lip 55, each variable lip being moveable to and fro with respect to the fixed lip 55 to alter the width of the respective slot by means of conventional adjusting screws 56,57.

As shown in more detail in Figure 13 (which shows schematically a top view of the conduit available to extrudable composition following through the upper die 51 - the lower die 52 corresponds analogously), composition initially enters the housing through inlet port 58 which enlarges laterally to form a manifold channel 59 which guides the composition laterally outwards into the mouth of an elongate and relatively narrow slot conduit 60 which constitutes the exit from the manifold channel.

The manifold channel 59 tapers inwards in diameter and turns somewhat forwards (in the direction of the flow of extrudable composition) towards its extremities (the dotted ellipses in Fig. 13 represent the changing profile of the manifold channel) and by this means spreads the composition across the upstream mouth of the slot conduit 60 formed in the housing block 50a,50b. Viewed from above as in Fig. 13 the upstream edge of this conduit is arcuate in shape, as indicated by line 61, so that composition which has already passed laterally outwards along the manifold channel has correspondingly less distance to travel through this conduit 60 before exiting the conduit into a pre-entry zone 62 in which a flex- adjustable restrictor bar 63 (adjustable by means of a screw 64) may if desired constrict the width of the zone to control the flow. 5

- 25 -

The dotted straight lines in Fig. 13 represent the width of the conduit 60 and pre-entry zone 62 (as illustrated the width is constant and somewhat narrower than the manifold channel, but nevertheless wider than the final die exit at lips 53,54 and 54,55).

From the pre-entry zone 62 the composition passes to the upstream mouth of each slot die at lips 53,54 and 54,55 and then out through the die, forming thereby a coextrusion in the form of a laminate of cast coextruded sheets to be processed through rollers, cutters and haul- off systems in conventional manner.

Coextrusion Apparatus

Referring now to Figs. 14 and 15, a coextrusion apparatus are shown schematically, comprising respectively a die assembly 70 of the form shown in Figs. 1 to 11 and a die assembly 71 of the form shown in Figs. 12 and 13 and described above.

The first inlet port of the die assembly 70 is supplied with the plasticised composition of a soluble polyvinyl alcohol previously described, through first adaptor piece 16 by means of a 25mm barrel diameter medium compression extrusion screw 72 connected between a first heated supply chamber 73 and the adaptor piece 16.

The second inlet port of the die assembly 70 is supplied with the plasticised composition of an insoluble polyvinyl alcohol previously described, through second adaptor piece 17 by means of an 18mm barrel diameter low compression screw 74 connected between a second heated supply chamber 75 and the adaptor piece 17.

The upper inlet port of the die assembly 71 is supplied with the plasticised composition of a soluble polyvinyl alcohol previously described, through first adaptor piece 80 by means of a 25mm barrel diameter medium compression extrusion screw 72 connected between a first heated supply chamber 73 and the adaptor piece 80.

The lower inlet port of the die assembly 71 is supplied with the plasticised composition of an insoluble polyvinyl alcohol previously described, through second adaptor piece 81 by means of an 18mm barrel diameter low compression screw 74 connected between a second heated supply chamber 75 and the adaptor piece 81.

As shown in more detail in Fig. 16, the extrusion screw 72 was a Betol short screw having a length/diameter ratio (L/D) of 25:1 and a compression ratio of 3:1. The screw had two compression zones 76,77 separated by a zone 78 in which no compression of polymer composition took place and in which a vent 79 in the barrel wall allows the escape of steam. The screw operated at a speed of 53-54 rpm.

The extrusion screw 74 was of generally similar construction to the screw 72, although it had an L/D ratio of 18:1, a compression ratio of 2.15:1 and a screw speed of 71.4 rpm.

In the blown-film extrusion case illustrated in Fig. 14, a pair of nip rollers 83 were mounted a distance of about 0.75 to 1 metre vertically above the die, with a take off to a collecting point (not shown) for the film produced. In the cast extrusion case illustrated in Fig. 15, the extruded film is taken up by conventional haul-off apparatus, rollers and cutters for finishing (not shown).

The screw flights continue along the entire length of the extruder, although for simplicity only the first and last few flights are illustrated in Fig. 16.

Coextrusion Process

The Mowiol compositions were prepared as described above and dumped the respective hoppers 90,91 of the extruder supply chamber 73,75. A trickle feeder is used to prevent blockage of the hopper mouths.

The composition is taken up by the first screw portion in region 92 and passes into the barrel of the extruder. In this region the barrel temperature is maintained at about 203 ± 30°C in the case of the soluble polymer and about 180 ± 30°C in the corresponding case of the insoluble polymer.

A short distance down the extruder the root diameter of the screw begins to taper outwards towards the barrel wall (region 93) and then remains parallel with the barrel wall for a distance about equal to the distance of taper. In this region (region 94) the composition is compressed. Here, the barrel temperature is maintained at about 202 ± 30°C in the case of the soluble polymer and about 230 ± 30° in the corresponding case of the insoluble polymer.

Immediately thereafter the root diameter reduces markedly and compression is thereby released (region 95). Steam vents through an aperture 79 in the barrel.

The compression is then repeated in region 96 of the extruder, before passing into the adaptor piece and the die. In this region (region 96) the barrel temperature is maintained at about 199 ± 30°C in the case of the soluble polymer and about 250 ± 30° in the case of the insoluble polymer.

Temperature regulation is performed by means of conventional electric jackets.

In each case the dies 70,71 are heated to 214°C and the heated PVA compositions then fed to the die by their respective screws at rates of e.g. 5:1 (soluble:insoluble). In the case of the blown-film extrusion (Fig. 14), at the same time, warm air is blown through the hole in the centre of the die 70. A blown film bubble can thereby be formed above the die, with the thin insoluble PVA layer on the inside (or optionally on the outside, depending on which inlet port of the die is supplied with which polymer). Cooling air is blown, again in conventional manner, over the outside of the bubble above the die.

The blown air dries the bubble rapidly to a non-tacky state such that it can be flattened between the nip rollers 83 and collected folded flat, to be cut open into single sheet form subsequently.

Referring particularly to Figure 17, there is shown a flexible polymeric film comprising a substrate layer 101 of partially-hydrolysed (soluble) PVA having a relatively thin coating 102 on one face, formed of the dried insoluble residue of the ORION ink described above. Figure 18 shows a modification of the film of Figure 17 wherein the ink coating 102 is applied to both sides of the substrate 101. In both cases the coating 102 is applied as a liquid by conventional ink printing methods and subsequently allowed to dry in air.

The ink coating is applicable to all types of polymeric articles but is particularly useful in the case of thin- walled or film articles. After the useful life of the article is completed, simple tearing or other damage to the protective ink coating will lead to dissolution of the polymer by water and subsequent breaking down by the natural action of microorganisms and the ink coating which is present in much lower amounts than the polymer, will also disperse naturally as the polymer breaks down, since the ink coating itself has no inherent mechanical strength.

Claims

1. A process for preparing a composite polymeric article or polymeric material comprising a first organic polymer layer which is water-soluble at a give temperature and a second organic polymer layer located adjacent to the first polymer, the second polymer being substantially less soluble than the first polymer, or insoluble, in water at the same given temperature, comprising: a blown-film or cast coextrusion process in which the polymers are extruded through a die assembly in such a way that the polymers are discharged from the die assembly as a composite polymeric material including the polymer layers; or an extrusion/lamination process in which the polymers are extruded through die apertures in such a way that the polymers are discharged as separate polymeric layers and are subsequently passed together between nipping means under conditions of temperature and nip pressure to cause the layers to laminate together to orm a composite polymeric material including the polymer layers; or a forming and coating process in which the first polymer layer is formed by extrusion or blow- moulding and the second polymer layer subsequently applied as a coating.

2. A process according to claim 1 for preparing a composite polymeric article or material using blown-film extrusion, wherein the blown-film die comprises a first inlet port for receiving one of the polymers under pressure; a second inlet port for receiving the other of the polymers under pressure; and a pair of mandrel members, the first mandrel member being hollow along its length to encircle the second mandrel member and the arrangement being such that a first annular conduit is defined around the outer circumference of the first mandrel member, for conveying the said one of the organic polymers over the outer surface of the first mandrel member, and a second annular conduit is defined around the outer circumference of the second mandrel member, for conveying the said other of the organic polymers over the outer surface of the second mandrel member, the arrangement further including a polymer guide channel associated with one or each of the conduits, for conveying polymer from the respective inlet port to the respective conduit around substantially all of the outer circumference of the respective mandrel member.

3. A process according to claim 2, wherein a guide channel is associated with each of the conduits of the die assembly.

4. A process according to claim 2 or 3, wherein the or each guide channel provides two paths for the polymer entering through the respective inlet ports namely, a first path to convey the polymer in one direction around the respective mandrel and a second path to convey the polymer in the other direction around the mandrel.

5. A process according to any one of claims 2 to 4, wherein each guide channel is cut into the outer surface of the mandrel.

6. A process according to claim 5, wherein the width of each guide channel tapers inwards away from the inlet port.

7. A process according to claim 1 for preparing a composite polymeric article or material by cast coextrusion or cast extrusion of separate layers and subsequent nip lamination, wherein the cast die or dies comprise(s) a first inlet port for receiving one of the polymers under pressure; a second inlet port for receiving the other of the polymers under pressure; and respective elongate slots in the die(s) through which each layer is extruded.

8. A process according to claim 7, wherein at least one of the inlet ports feeds into an entry channel which then widens into a manifold channel to spread the polymer across the mouth of a slot die.

9. A process according to any one of the preceding claims for preparing a composite polymeric article or material by extrusion of separate layers and subsequent nip lamination, wherein the nip lamination is performed between nip rollers.

10. A process according to claim 1 for preparing a composite polymeric article or material by an extrusion or blow-moulding process for forming the first polymer layer and subsequent application of the second polymer layer as a coating, wherein the coating is effected by spraying.

11. A modification of the process according to claim 1 for preparing a composite article or material by an extrusion or blow-moulding process for forming the first polymer layer and subsequent coating, wherein the second polymer coating is replaced by the dry residue of a liquid ink which dissolves more slowly than the first polymer (or not at all) at the given temperature.

12. A process according to claim 11, wherein the ink is a flexographic alcohol-based hydrocarbon-free liquid ink.

13. A process according to any one of the preceding claims, wherein the first polymer is extruded from a plasticised composition thereof comprising from about 1 to 60 parts of plasticiser per 100 parts of polymer; up to about 30 parts of water per 100 parts of polymer; and up to about 5 parts of a slip agent per 100 parts of polymer.

14. A process according to any one of the preceding claims other than 11 or 12, wherein the second polymer is extruded from a plasticised composition thereof comprising from about 1 to 80 parts of plasticiser per 100 parts of polymer; up to about 30 parts of water per 100 parts of polymer; and up to about 5 parts of a slip agent per 100 parts of polymer.

15. A process according to any one of the preceding claims, wherein the first, water-soluble, polymer is partially hydrolysed polyvinyl alcohol and the second, relatively water-insoluble, polymer (where present) is fully hydrolysed polyvinyl alcohol.

16. A process according to any one of the preceding claims, wherein the or each polymer composition is supplied to the die(s) via a screw extruder having two or more compression zones in the extruder barrel, vented between zones for the release of steam and the barrel being maintained at a controlled temperature or series of temperatures along its length.

17. A polymeric article or polymericmaterial comprising an organic polymer which is water-soluble at a given temperature, wherein the surface of the article or material is wholly or partially coated with an ink which dissolves more slowly or not at all in water at the same given temperature to form a water-resistant barrier coating.

18. An article or material according to claim 17, wherein the given temperature is about room temperature (about 20°C).

19. An article or material according to claim 17 or 18, wherein the ink coating extends over all of that portion of the surface that is expected or intended to become exposed to water during normal use.

20. An article or material according to any one of claims M to (9, wherein the organic polymer is partially hydrolysed polyvinyl alcohol.

21. An article or material according to any one of the preceding claims, wherein the ink coating is the dry residue of a flexographic alcohol-based hydrocarbon-free liquid ink.

22. A method of forming a polymeric article or material as defined in claim 17, wherein there is applied to the organic polymer a whole or partial surface coating of a liquid ink and the said coating is subsequently allowed to dry to form a water-resistant ink barrier coating which dissolves more slowly than the polymer, or not at all, in water at the given temperature.

23. A method according to claim 22, wherein the liquid ink is applied initially to a blank roller of a conventional film printing press and then a film of the liquid ink is rolled onto a film of the organic polymer.

24. A die assembly for coextruding a composite polymeric article or material including first and second organic polymer layers adjacent to one another, the die assembly comprising: an elongate housing having a first inlet port for receiving one of the polymers under pressure, a second inlet port for receiving the other of the polymers under pressure and an outlet port downstream of the inlet ports for discharging the composite polymeric material; and a pair of mandrel members provided within the housing, the first mandrel member being hollow along its length to encircle the second mandrel member and the arrangement being such that a first annular conduit is defined around the outer circumference of the first mandrel member, for conveying the one organic polymer over the outer surface of the first mandrel member towards the housing outlet port, and a second annular conduit is defined around the outer circumference of the second mandrel member, for conveying the other organic polymer over the outer surface of the second mandrel member towards the housing outlet port, the first and second conduits terminating together in such a way that the two polymers are discharged from the housing outlet port as a composite polymeric material including polymer layers; the arrangement further including a polymer guide channel associated with one or each of the conduits and preferably of relatively larger width than the respective conduit, for conveying polymer from the respective housing inlet port to the respective conduit around substantially all of the outer circumference of the respective mandrel member.

25. A die assembly for coextruding a composite polymeric article or material including first and second organic polymer layers adjacent to one another, the die assembly comprising: a housing having a first inlet port for receiving one of the polymers under pressure, a second inlet port for receiving the other of the polymers under pressure and an outlet port downstream of the inlet ports for discharging the composite polymeric material; die means defining a first elongate slot aperture and first manifold channel means being provided to connect the first inlet port to said first slot aperture, the manifold channel means widening towards the slot aperture and being arranged to spread the polymer across the mouth of the slot aperture; die means defining a second elongate slot aperture and second manifold channel means being provided to connect the second inlet port to said second slot aperture, the manifold channel means widening towards the slot aperture and being arranged to spread the polymer across the mouth of the slot aperture; the first and second slot apertures terminating together in such a way that the two polymers are discharged from the housing outlet port as a composite polymeric material including polymer layers.

26. An apparatus for delivering an extrudable plasticised composition of an organic polymer to an extrusion die in a process for forming a composite polymeric article or material, the apparatus comprising a screw extruder having two or more compression zones in the extruder barrel and being vented between some or all zones, and temperature control means whereby the barrel is capable of being maintained at a controlled temperature or series of temperatures along its length.

27. An apparatus according to claim 26, wherein the die is a coextrusion die as claimed in claim 24 or claim 25.

28. An apparatus according to claim 26 or 27, wherein the screw extruder is adapted to deliver composition under a compression ratio of from 1.1:1 to 5.6:1.

29. An apparatus according to claim 26 or 27, wherein the screw extruder is adapted to deliver composition under a compression ratio of from 1.5:1 to 6:1.

30. An apparatus according to any one of claims 26 to

29, wherein the temperature control means are arranged so that the temperature of each successive third of a barrel increases towards the die.

31. An apparatus according to any one of claims 26 to 29, wherein the temperature control means are arranged so that the temperature of each successive third of a barrel remains substantially constant or decreases slightly towards the die.

32. A plasticised composition of partially hydrolysed polyvinyl alcohol, comprising from about 1 to 60 parts of plasticiser per 100 parts of polymer; up to about 30 parts of water per 100 parts of polymer; and up to about 5 parts of a slip agent per 100 parts of polymer.

33. A plasticised composition of fully hydrolysed polyvinyl alcohol, comprising from about 1 to 80 parts of plasticiser per 100 parts of polymer; up to about 30 parts of water per 100 parts of polymer; and up to about 5 parts of a slip agent per 100 parts of polymer.

34. An article or material formed by a process as claimed in any one of claims 1 to 16, 22 and 23.

35. An article or material according to claim 27 in sheet form.

36. An article or material according to claim 27 in the form of a container.

37. A WC-disposable sanitary product wherein substantially all plastic parts are made from a sheet according to claim 35, the water-soluble layer being outermost in normal use to avoid contact with water until disposal is required.

38. A container for non-aqueous materials (e.g. oil or petrol), wherein substantially all of the container is made from a polymeric material according to claim 36, the water-soluble layer being innermost in normal use to avoid contact with water until disposal is required.

39. A WC-disposable sanitary product comprising an absorbent portion and a plastic barrier backing portion, wherein substantially all plastic parts are completely water-degradable on WC-disposal.

40. A degradable oil/petrol container which completely degrades but only upon introduction of water to the interior of the container.