CA2134101A1 - Polymeric articles and materials - Google Patents

Abstract

2134101 9322125 PCTABS00027 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

W093/22125 213 4101 PCT/GB93/~8~

POLYMERIC ARTICLES AND MATERIALS

Field of the Invention This invention relates to polymeric materials and articles made therefrom, and to methods and apparatus for 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 obtained by polymerization of vinyl acetate. This polymer i5 used for the production of polyvi~yl alcohol (PVA) by hydrolysis or alcoholysis to remove the acetyl groups from polyvin~l acetate. This removal of ace~yl - groups may be carried to partial completion so as to ~ive 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 aceta~e presen~, ~uch a copolymer is soluble in cold water and is fre~uently referr~d to as "part~ally ~ydrolyæed"
polyvi~yl alcohol. The residual vinyl aoetate content is typically about 11 wt% oo~sesponding to about 12 mol%.
If the reaotion ~s taken further, clo~e to completion, th~ crystallinity of the polyvinyl alcohol increases and the ~olubility in cold water decreases very markedly.
Material of this type is referred to as "fully hydrolysed" polyvinyl alcohol. Its contents of residual vinyl acetate is typlcally no greater than 3 mol~.

W0 92/01556 (the disclosure of wh~ch is incorporated herein by reference) describes certain degradable 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 di~ficult to SUE~STITUTE SHEET

W093/22125 2 1 3 ~ 1 l 2 - PCT/CB93/0o8~

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 produet.

It is an aim of the present invention to provide improvements in the formation o polymeric materials such as those of WO 92/0l556.

The invention is based on our surprising finding that a polymeric material of the type described in WO 92jOl556 can be prepared with æubstantial and unexpected advanta~es in terms of efficiency, speed and cost, by extruding the layers through certain particular die arrangements or by a speci~ic multistep forming process.
It is to be noted that "cast coextrusion" mentioned lS herein does not in any way resemble the non-extrusion casting/moulding processes descr~bed in WO 92/0l556, as will be expla~ned in more detail below.

Brief D~scr~ption of_~he InYention The present invention therefore prov~des in one aspect a process for preparing a composit~ polymeric article or polymsric ma~er~al compri~ing a first or~2nic polymer layer (e.g. of partially hydrolysed polyvinyl alcohol) which ~s water-solu~le at a given (~uitably low~
temperature, typically 20C, and a second organic polymer layer (e.g. fully h~drolysed polyvinyl alcohol) located ad~ac~nt to the first polymer, the second polymer being substantially less soluble than the first polymer, or insoluble, in water at the ~ame given temperature, comprising: a blown-film or cast coextrusion process in . 30 which the polymers are extruded through a die assembly in such a way th t the po}ymers 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 s parate ~ ~ WO93/22125 3 2 13 41~1 PCT~GB93/~854 polymeric layers and are ~ubsequently passed together between nipping means under conditions of temperature and nip pressure to cause the layers to laminate to~ether to form a composite polymeric material including the polymer S layers; or a ~orming and coating process in which the first polymer layer is formed by extrusion or blow-moulding and the second polymer layer subseguently applied as a coating (e.g. by spraying, dipping, painting, rolling, etc).

Where an article or material is formed using blown-film extrusion the die may comprise a f~rst 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 firs~
mandrel member being hollow along its length to encircle the second mandrel member and the arrangement being such that a first annular condu~t 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 def~ned around the outer circu~ference of ~he second mandrel member, for csnveying the sà~d other o~
the or~anic polymers over the outer surface of the second mandrel member, the arrangement further including a polymer guide channel associated with one or each o~ the condu~ts, for conveying polymer from the respective inlet port to the respective condu~t around substantially all o~ the outer circumference of the respective mandrel me~l-berr Such a die assembly for coextrusion of this material is new and constitutss a further feature of the invention.
The present invention therefore provides in a further aspect a die assambly for coextruding a compos~te polymeric article or material including first and seoond organic polymer layers a~jacent to one another, the die assembly comprising: an elongate housing having a first inlet port for receiving one of the polymers under W093/2212~ 2 13 41 01 PCr/GB93/008~ ~

pr~ssure, a second inlet port for recei~ing the other of the polymers under presæure and an outlet port downstream of the inlet ports for discharging the composite polymeric material; and a pair of mandrel members S 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 ls definad around the outer circumference of the first mandrel me~ber, for conveying the one organic polymer over the outer surface of the first mandrel member towards the housing outlet port, a~d a second annular conduit is defined around tha outer ¢ircumference of the second mandrel me ~ er, for conveying the other organic polymer over the outer sur~ace of the second mandrel member towards the housing outlet port, the first and second conduits terminatlng together in such a way that the two polymers are discharged from the housing outlet port ~s a composite polymeric ma~erial ineluding polym~r layers; the ~rran~ement further 20 ineluding a polymer guide ehannel associated with one or eaeh of the eonduits and preferably of relatively larger w~dth t~an the respeetive eonduit, for eo~veying polymer from the respeetive housing inlet port to the respective condult around substantially all of the outer 25 eireum~erenee of the xespective mandrel member.

Pr~ferably a gu$de channel is associated wi~h each of the conduits and mo~ preferably each guide channel provides two paths for the polymer entering ~hrough the respeotive ~let port; namely, a fir~t path to convey ~he polymPr in 30 . 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 rom the inlet port~ r The guide channels are p~eferably cut into the outer surfaces of the mandrels. The width of the guide channels preferably tapers inwards away ~rom the inlet ' ~ W093/22125 213~101 PCT/GBg3/~O~

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 gu~de channel may worm forwards (i.e. downstream) along its respective mandrel, 80 that polymer that has already travelled along the ohannel to the back of the mandrel (as viewed from the inlet port) before entering the respective conduit is substant~ally 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 xelevant inlet pOl~.

The second mandrel may con~eniently be hollow so that compressed air can be blown through the centre of t~e die to expana the fiJm as it leaves the d~e.

Where the sheet is formed by cast coextrusion or ca~t extrusion of ~eparate sheets and subsequent nip lamination, the cast die or die(s) may comprise a first 2Q inle~ port for receiving one of the pol~mers under pressure, a second inlet port for race$ving the cther of the polymers und~r pressure, and r~spe~tive elon~atP
slots in *he die(s) through which each sheet is extr~d~d.

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 a~pect a die assembly for coextruding a composite polymeric article or material including first and second or~anic polymer layers ad~acent tc one another, the die assembly co~pris~ng: a housing having a first ~nlet port for rece~ving on~ of the polymers under pressure, a second inlet port ~or receiving the other of the polymer~ under pressure and an outlet port downstream of the inlet ports for discharging the composite polymeric material: die W093/22125 - 6 - PCT/GB93/~8 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 ap~rtures terminating tog~ther 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 provlding 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 co~ventional processes for ca~t extruding a - slngle thermoplastic sh~et, e.~. a rigid polyvinyl chloride sheet, the extrudable p~lymeric composition ~s fed to a so-called "clothes-hanger" or "fish-tail" die having a ralatively large diameter antry channel which rapidly widens ~nto a manifold channel to spread the extrudable compos~tion across the mouth of the single I slot ~ie. The manifold channel is configured so as to encourage spreading of the composition towards the extremities of the slot die. ~he width of the slot is suitably ad~ustable by means of externally accessible ad~uster 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 ~ ~ W093/22125 2 13 4 1 ~ 1 ~ PCT/GB93/008~

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 $usion of the layers at the interface may not be necessary.

In the case of a fo~ming and coating process for manufacturing the desired composite polymeric art:icles 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 conventlonal manner. Spray-coat~ng of a liquid composition of the second pol~mer is particularly mentioned.

Furthermore, in a modi~ication of this aspect of the present in~ention the econd poly~er layer may be ~ubstituted by ~he dry residue of an ink which di~solves more slowly than the first polymer (or not at~all) at the given temperature (e.g. 20C). The above method is particularly sui~able for making degradabl~ rigid blow-- ~oulded con~ainers and bottles of the first (re~atively 2S water-soluble~ polymer, for holding non-a~ueous materials such a~ oil or petrol, and externally coated with the relatively lnsoluble i~k to protect against water-degradation durin~ use.
;

The articles and materials described in the preceding paragraph ar~ themselves new and they and their manufacturing processes generally constit~te further features of the present i~vention.

In a further aspect, therefore, the present invention provides a polymeric article or polymeric material comprising an or~anic polymer which is water-soluble at WO 93/22125 213 4101 PCr/GB93/00854' a given (suitably low) temperature, typically 20C, wherein the surface of the article or material is wholly or partially coated wit~ 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 materlal will su~tably be all of that portion of the surface that may be expected or intended to become exposed to water during nor~al use of the article.

The art~cle or material ls suitably formed in any conventional manner ~e.g. extrusion, moulding, ~low-moulding, casting etc) from the polymer, and ~he ink coatiny 8ubsequently applied in liquid form ~e.g.. by spraying, dipping, painting or rolling, for example ~sing a convent1onal film pr~ nting press) and then dri~d.

Tha pre~rred 801uble polymer is partially hy~rolysed polyvinyl alcohol.

20 The ink coating is pr~ferably the dry residue of a flexographi~ alcohol-ba~ed hydros~ar~n-free liguid ir~k such as the commercially ~vailable inks sold for flexo-printlng polyolefin films. The inks sold under the trade mark "ORION" by Coates Lorllleux 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 i~vention the article or material is laminar. Such a form o the invention could be a polymer film or sheet to be used in industrial production procasses. Further forms of this aspect of the invention are articles compr~sing pieces of such polymer sheet or film. In particular, the pieces of polymer or film may be shaped to have curvature in more ~ WO93/22125 213 1101 ~ ~ PCT/GB93/0~854 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 $nk layer that surface is protected. The ~nk acts as a barrier and protects the first polymer against di~solut~on if the protected surface gets wet.

Such functionality has ~ 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 prote~ting the water-solubl0 polymer from a material which is, or might be, wet and then at a later stage an unprotected surface of the water-soluble polymer ~s allowed to come int~ cbntact with water. The consequence of ~his is that dissolution : of the soluble polym~r takes place when ~esired^ but premature dissolution is prevent2d by the ink.

Where the article comprises a polymeric film, suitably :: ~11 of one or both ~aces of the fllm is coated w~th the 29 ~nsoluble ink. The polymeric film should be s~fficiently thlck to provlde the required mechanical ~trength, ~or axample from about 5~m to ~ ~m, more typically from lO~m to 290 ~m, for example about 50~. The ~nk layer is typical~y from about l~m to 7~m in thickness, for examplP
a~out 3~m.

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 d~-~solve the exposed core and hence ~he entlre artlale may be disin~egrated.

ln accordance with a further aspect of the ~nvention, there is provided a method of forming a pol~meric article comprising an organlc polymer which is water-soluble at a given temperature, typically 20C, wherein there is WO93/22125 213 4 1 0 1 ~ PCT/GBg3/~8~

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-res~-stant 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 pr~nting 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 appearar.ce of the article. If desired, different inks may be applied sequentially to create a desired efect.
-Referring now to all aspects of the present inve~tion,and as described in W0 92/01556, th~ speed with whlch the more rapidly ~oluble (first) polymer dissolves can be altared by ~election of the polymer and also by selection of process~ng condttions. The length of~ time for this 20 polymer to dissolve can be chosen according to the use ~nvisaged for the artic:le or material an~l can range from a matter of seconds to several hour~ . The ~c: luble polymer will generally have a speed of ~olution such- that when a sheat o f the pol ymer w~ th at least one side f aae 25 o~ the sheet is exposea is placed in d1stilled water at 20C, the sheet d~ssolves suffic:iently to break up within a period of time not longer than 24 hours, usually not longer than 8 hours and possibl~ very much shorter than this e.g. less than 10 secs for a test sheet 50 ~m thick.

In the composite material described in W0 92/01556, the weight ratio of the more soluble to the less soluble polymer will preferably be at least 2:1, more preferably at léast 3:1, still more preferably at least 5:1 and perhaps above 10:1 up to even 100:1, particularly for thick articles.

~~ WO93/22125 ~ PCT/GB93/~8 In an alternative aspect described, the less soluble polymer covers the more soluble polymer with a general thickness which is preferably not more than 20~m, more preferably not more than lO~m, most preferably not more than 5~m. It may be as thin as 2~m or thinner.

In a composite film product, the total film thiakness may range typically from 5~m to lmm, more typically from lO~m to 200~m~

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

Artiales may take various forms: for examplef a compos~te film may comprise just two layers, one of each kind of polymer. Alternatively, the composite film may~be a sandwich of more oluble polymer between layers of less soluble polymer. Layers of ot~er materials may, of course, addltionally be present~

In the processes described above, the firs~ (or only), water-æoluble, polymer is pr2ferably partially hydrolysed polyvinyl alcohol. The ~econd, relatively water insoluble, polymer may be fully hydrolys2d polyvinyl alcohol. The extrudable and bl~w-mouldable precursor compositions ar~ preferably plasticised compositions of the respect$ve polymers.

For extrusion, the plasticised composition of the first (water-soluble) polymer preferably comprises from about 1 to 60, suitably about 5 to ~5 parts (by weight or volume), more preferably from about 10 to 20 parts, most preferably about lS parts, of plasticiser per 10~ 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 .

W093/22125 2 13 4 1 01 PCT/GB93/00854 ~

to about 5, suitably about O.Ol to 5, parts (by weight or volume~, more preferably from about O.Ol to 3 parts, most preferably about 0.25 parts, of a slip agent such as powdered silica (to promote flow of the composition) per lO0 parts of polymer. Such a composition is novel and ltself 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 lO0 parts of polymer:
up to about 30, suitably about 0 to 15, more suitably about 1 to 15, parts (by weight or volume), more lS preferably from about 3 to 15 parts, most preferably about 5, suitably about 0.Ol to 5, parts, of water per 100 parts of polymer; and up to about 3 parts (by weight or ~olume), more pref~rably from a~out O.Ol to 3 parts, most preferably about 0.25 parts, of a slip agent such as powdered silica per lO0 parts of polym~r. Such a compo~ition is al80 novel and itself constitutes a further aspect of the present invent~on.

The plasticiser may ~e ~elected from any con~ent~cnal plasticiser for the polymer in qu~stin~. For polyvinyl alaohol polymers the plastioiser ~hould be a polyhydric alcohol, such as glycerol, a glycol, an alkanediol (e.g.
an ethaned$ol, propanediol, butanediol, pentanediol or hexanediol), -an alkanetrlol (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 W0 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

2 ~ 3 41~ 1 ; PCTlGB93/00854 methods, however, higher levels of water may be required.
Such ~udgements are, however, within the capacity of one of ordinary skill in this art.

The ingredients of the oomposi~ions are suitably mixed together at an elevated temperzture (e.g. about llO~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 condlttons may be selecte~ by a ~killed worker, accordt ng to the melting and degradation conditions of the polymers empl~yed.

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

Such convent~onal process features, which are within the ordinary knowledg~ of a skilled worker, can bei employed to some extent in the novel method of the present invention, and will ~ot be discussed in detail here.

However, the following particular novel preferred features of the method of the present i~vention are mentloned:

Firstly, in the case of polyvinyl alcohols, we have found that an extrusion (die) t~mperature of between about ! 25 1 190C and 240C (e.g. about 215C) gives good results.

Furthermore, each polymer composition is suitably supplied to the die by means of a short screw extruder havin~ 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 WO93/22125 213 ~ I O 1 PCT/GB93/~

significant degradation of the polymer does not take place (about 4 minute~ 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 o~ tempeiratures along its length. After the final compression zone the composition passes into the die inlet port, if necessary through a temperature-controlled adaptor to ad~ust the t~mperature 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 trudable plasticised composition of an organic polymer to an extrusion di~ in a process for formlng a composite polymeric article or material, the apparatus comprising a screw extruder having two or more compression zones in the extruder barrel a~d being vented between some or all zones, and temperature control means whereby the barrel ls capable of being maintained at a c~ntrolled temperature or series of temperatures along its leingth.

The extrusion die may be a coextrusion die for receiving both polymers or may comprise dies having separate apertures for extruding each polymer s~iparately and nipping means provided downstream of the die apertuxes to laminate the polymer layers after extrusion. In these cases, eaah 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.
~ .
~35 The positions of the compression zones along the barrel ~WO93/22125 2 13 4 ~ O 1 ~` ~ PCT/GB93/~8~

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 zons, 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). ~he final compression zone, before the composltion enters the die, ~ay similarly be arran~ed 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 b~fore the final compre~sion zone).

The compression ra~io, screw barrel diame~er and~screw speed of th~ ~crew extruder are also chosen to suit the partic~lar polymer composition being carried. Thus, for example, plasticised insoluble PVA composition may sultably 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 rat~o of from 1~5:1 to 6:1 (more prefer3bly about 3:1). Plasticised insoluble PVA
composition is desirably deliv~red to the coextrusion die a~ a rela~ively high screw speed and low barrel diameter, compared with plasticised soluble P~A composition. More particularly, plastici~ed insoluble PV~ may be delivered at a screw speed of about 70 rpm ~hrough a screw barrel of 18mm diameter, and plaæticised soluble PVA at a screw speed of about 50 rpm through a screw barrel of 25mm diameter.

As stated above, the temperature condition-~ along the barrel are controlled~ The temperature of each successive portion of the barrel may increase, remain substantially cor.stant or decrease towards the die. We WO93/22125 213 41 01 PCT/GB93/~

have found that it is preferred that, for à 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 +
30C, 230 + 30C and 250 ~- 30C; and for a screw carrying plasticised soluble PVA composition, the temperature of each success~ve third should remain substantially constant or decrease slightly towards the die, suitably in the steps 203 + 30C, 202 + 30C and l99 + 30C.

Industrial Ap~lication 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 wlthstand wetness on one side; by using film embodying the present ~nvention they can after use be dropped, wlth their contents, into a WC bowl to disintegrate. The whole can then be 1ushed away. The advantage in terms of convenience is apparent, while from the env~ronmental point of view PV~ is not only biode~radable to harmless CO2 and wat~r, but also has no kn~wn toxlclty and hence d3es not present a risk befora chemical degradation.

A further application lies in water-dislntegratable containers, e.g. rigid oil containers. These can su$tably be formed by blow-moulding the water-soluble first polymer into container form in conventional manner, ! and applyin~ an external coating of the water-soluble second polymer or of a water-insoluble ~nk (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:
: .
, ~ ~ W093/22125 213~ 01 - 17 - PCT/GB93/~8~

Fig. 1 shows a longitudinal sectional view of a coextrusion die assembly;
Fig. 2 shows a top view of the die assembly of Fig.
l;
Fig. 3 shows (a~ a top view and ~b) a longitudinal sectional view of a lower housing block part of the assembly of Fig. l;
. Fig. 4 shows ~a~ a bottom view and (b) a fron~ view of a first mandrel part of the assembly o~ ~ig. l;
- Fig. 5 shows a side view of the mandrel part of Fig.
4 ~b~ looking down from the left;
Fig. 6 ~hows ~a) a bo*tom view and (b~ a front view of a second mandrel part of the assembly of Fig. l;
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 en12rg~d~ of a top housing block part of the assembly of Fig. l;
F$g. 9 hows a longitudinal sectlonal view of a die bush part of the assenbly of Fig~ l;
Fig. 10 shows ~a) a top view and (~) a front view of a pin part of the assembly o~ Fig. 1: ~
Fig. 11 shows (a) a top ~ew and (b) a longitudinal seational vlew of a clamp ring part of the assembly of ~i~. 1;
Fig. 12 ~hows a semi-~chematic vertical sectional v~ew of a cast coextrusion die as-~e~bly~
Fig. 13 shows a sectional view of ~he die assembly of Fig. 12, taken alo~g the line AA looking in the direction of the arrows;
Fig. ~4 shows a schematic view of a first coextrusion apparatus;
Fig. 15 shows a schematic vi~w of a second coextrusion apparatus;
Fig. 16 shows a s~de view o~ 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 barrie~ layer on one side; and Fig. 18 shows in cross-section a film protected by WO93/22125 2 1 3 41 01 PCT/GB93/008~ ~

an ink barrier layer on both sides.

Detailed Des$ription o$ the_Drawings Mater~als Used In the following embodiments, both the insoluble and S 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 ~ol% degree of hydrolysls ~nd whose viscosity, measured as a 4~ aqueous solution, is 26 mPa. S2 . rhe ~nsoluble layers were made using a 50:50 blend of Mowiol 56/98 and Mowiol 28/99 which are fully-hydrolyæed grades having viscosities and hydrolysis ~alues substantially as indicated by their respective specification numbers, as before.

The plaQt~cised Mowiol 26-88 composition had ~he following composition ~proportions are parts ~y weight per 100 parts o~ Mowiol 26-88): ~
. .
Mowiol 25-88 ~100) Glyc~rina (plast~ciser) 15 Distilled Water 5 Powdered Silica R972 0.25 The powdered silica R972 was present as a slip agen~, manufactured by Aerosil.

The ~ngredients w~re all placed initially into a Baker Perkins High Speed Mixer (manufactured by Baker Perkins Limited), which was preheated to 110C. The mixer was then run at approx~mately~600 rpm for about 6 minutes, wh~reupon the material began to li~t on the side of the mixer. The composition was then dumped into a cooler for approximately 15 minutes or until the temperature fell below 40C.

~ W093/22125 2 13 41 0 i 19 - PCT/GB93/~8~

In the mixing process the glycerine plasticiser and the silica slip agent coat the Mowiol granules and the distilled water is absorbed lnto the Mowiol granules.
The process is accompanied by a rise in te~perature.

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

Mowiol 56-g8 (50) Mowiol 28-99 (50) Glycerine (plasticiser) 25 Water 5 Powdered Silica R972 0.25 The ingredients were placed initially into a Baker Perkin~ Hi~h Speed Mixer which was preheat~d to 110C.
The mixer was run at 8pproximately 600 rpm for 30 sêconds ~nd then at lQ00-1200 rpm for approximately 15-17 minut~s, whereupon the material began to lift on the side of the mixer. The compo~ition was then dumped into a cooler for approximately 15 minutes or until the temperature fell below 40C.

The liquid i~k used was an alcohol-based and hydrocarbon-free flexographic ink old for printing polyolefin films, having the ~rade mark ~ORION" (Coates Lorilleux Lim~ted, Essex, England). Such inks have low odour and solvent xetention, are relati~ely quick drying when app~ied to a polymeric surface, with good adhesion ~o the surface, are resistant to freezing t~mperatures and show accep~able anti-statlc and slip properties. The liguid 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 WO93/2212S ~13~ PCT/GBg3/008~;~ ~i - 2~ -21 3 ~ ~1 0 1block part 1 surrounded by an electrical heating ~acket (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 cylindricai in form and is provided near its base with a palr 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 recei~e bolts 12 for securing the top block S to the lower blook l; a similar number o~ holes are provided in the bottom face of the block 1 to receive bolts 14 or securing a base portion 15 of ~nner mandrel 4 in 1~ position.

Each lnlet port 9,10 is provided with an adaptor piece 16,17 to connect the wider diameter 8crew 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 heat~ng jackets 18 which enable their temperature to be controlled. Most typica~ly the temperature maintained by heating jackets 2 and 18 w~ll be substantially the same, ~h9 adaptors - 16,17 thereby also ~unctioning as reg~lators of-the temperature of the incoming polymer compositions.

The first ~outer~ mandrel 3 is generally cyli~drical in form, being arranged to fit snugly within the housing block 1 and having itself a hollow central channel 1~ to receive the second (inner ? mandrel 4, as will be de8cribed in greater detail below.

The outer mandrel 3 is formed of metal and has machined into its external surface by means of a bull-n~se cutter a polymer guide channel 20 which ~tarts relatively near the base of the mandrel, at a point adjacent the inlet

3~ port 9 of the housin~, and worms up and around the .

WO93/22125 2 13 ~ 1 01 21 - PCT/GB93/008~4 mandrel in both the clockwise and the anticlockwise directions, tapering inwards in width as it does so, ~o 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 gu~de channel 20 and divides its flow to follow the guide channel in both its direct~ons.

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 inle~ port 9 for conveying the polymer over the mandrel 3.

The channel 2Q markedly ~ssists 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 por~ lO and the second (inner) mandr~l 4, as will be describ~d in yreater detail b~low. Furtha~more, the base of the outer mandr~l 3 is prvvlded 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 flt snugly within the central channel l9 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.

WO93/22125 213 4101 PCT/GB93/~8~ !

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 lO and the hole 25 of mandrel 3, circumferentially around the mandrel 4 to spill out ~nto 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 ~herefore 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 $nlet port lO and follows a two-directional worm path over the mandrel 4, . analogously to guide channel 20 of mandrel 3.

~he 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 l: The base portion 15 is also provided with a radially inner set of six holes 32 to rec~ive bolts for securing the - 20 mandrel 4 to the outer mandrel 3.

At the upper ends of each conduit 24,29 are provided constrictions 33,34 which adiust the thickne~s and evenness of each polymer f~lm prior to the f$lms ~eeting and adher~ng toge~her to form th~ desired bilayer.

In the case of the first conduit 24, constriction 33 is provided by a bulbous portion 35 prov~ded on an interiox portion of the cylindrlcal 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 cons~riction 33 radially inwards to meet the other polymer emerging from the second conduit 29 via constriction 34.
.
Block 5 i9 bolted to the top of housing block l~ via ~ix holes 37, six sma~ler holes 38 also being provided in the upper rim of block 5 to receive bolts for securing the ; W093~22l2~ ~13a~ D 1 PCT~GB93/~8 clamp ring 8 to the block 5, as will be described in more detail below.

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

The die bush 6 is of hollow ~ylindrical construction having an internal surface tapering outwards in the up direction to form a chamber 40 w~ich 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 i~ner mandrel 4 to secure the pin in position. The central channel 27 and the central channel of the hollow bolt tog~ther provide a passage through the centre of the die assembly to permit the passage of compressed air ~hrough the die a8semb1y. The p~n 7 has an outwardly tapering outer surface which gNides the composita polymeric film out of the die housing through an ex~ port 41 ~o a film blowing region above the assembly.

Around th~ base of the pin 7 is provided an annular rib 42 by which the above mention~d constri~tlon 34 in second conduit 29 is obtained when the rib 42 is ln position near the upper port~on 30 of the interior wall of the ~5 first mandr~l 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 S through six holes 44 in the clamp ring 3 (only one such hole i8 shown ln the sectional view of Fig. ll(b), for clarity). The top block S is then suitably surrounded by an electric heating ~acket 45.

Referring now to Figs. 12 and 13 of the drawings, a two-slot cast coextrusion die assembly i5 shown, having two WO93/22125 213 410 1 PCI`/GB93/0085 housin~ 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 5 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 al~er ~he width of the respective slot by means of conventional adjusting screws 56,57.

As shown in more detail in Figure 13 (which shows s~hematically a top vlew of the conduit available to extrudable composition following through the upper die 51 - the lower die 52 corresponds analogously), composition initially enters the hous~ng through ~nlet port 58 which enlarges laterally to form a manifold channel 59 which ~uides 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 mani~old channel 59 tapers inwards in diameter and turns somewhat forwards (in the directton of the fl~w of - ~xtrudable compo~ttion) towards its ~xtremities (the dotted ellipses ~n F~g. 13 represent the changing profile of the manifold channel) and by this means spreads the composition across the upstream mou~h of the slo~ conduit 60 formed in the housing block 50a, 50bo Viewed from above as in Fig. 13 the upstream edge of this conduit is arcuate in shape, as indicated by line 61, so that eomposition 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-ad~ustable restrictor bar 63 (adjustable by means of a screw 64) may if desired constrict the width of the zone to control the flow.

~ W093/22125 2 1 3 ~ 1 0 I - PCT/GB93/00854 The dot~ed straight lines in Fig. 13 represent the width of the conduit 60 and pre-entry zone 62 (as illustrated the wid~h is constant and somewhat narrower than the manifold channel, but nevertheles~ 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 coe~truded sheets to be processed ~hrough rollers, cutters and haul-off systems in conventional manner.

oextrus~on 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 Fig~. 1 to ~1 and â die assembly 71 of the form shown in Fi~s. 12 and 13 and described above.

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

The second inlet port of the die assembly 70 i5 supplied with the plas~icised composit~on of an insoluble polyvinyl alcohol previously descri~ed, through second adaptor piece 17 by means of an 18mm barrel diameter low compression screw 74 connected b~tween 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 WO93/221~ 21 3 ~ 1 01 PCT/GB~3/~8~ 1 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 composltion of an insoluble S polyvinyl alcohol previously de~cribed, through second adaptor piece 81 by means of an 18mm barrel diameter low compress~on screw 74 connected between a second heated supply chamber 75 and the adaptor piace 81.

As shown in more detail in Fig. 16, the extrusion screw 72 was a Betol short sCrew havin~ a length/diameter ratio (L/D3 of 25:1 and a compression ratio of 3~ he screw had two compression zones 76,77 separated by a zone 78 in wh$ch no compress~ on of polymer composition took place and in which a vent 79 in the barrel wall allows the 15 escape of ste~m. The screw operated at a speed of 53-S4 rpm.

The extrusion screw 74 was of generally similar construction to the screw 72, although it had an L/D
ratlo of 18:1, a compression ratio of 2.1~:1 and a screw speed of 71.4 rpm.

In the blown~ilm extrusion case illustrated in Fig~ 14, - a pair of nip rollers 83 were mounted a di~tance of about 0.75 to 1 metre vertically above the die, w~th a take off to a collectin~ point (not shown) for the f~lm produced.
In the cast ext~usion case illustrated in Fig~ 15, the extruded film is taken up by conventional haul-off apparatus, rollers and cu~ers for finishing (not shown).

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

Coextrusio~ Process ?he Mowiol compositions were prepared as described abo~e . ~ W093/22125 213 410 1 27 - PCT/GB93/~8~

and dumped the respective hoppers 90,9l 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 S region 92 and passes into the barrel of the extruder. In this region the barrel temperature is maintained at about 203 + 30C in the case of the soluble polymer and about 180 + 30C in thè 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 the~ 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, tne barrel temperature is mainta~ned at about 202 ~ 30C in the case of the soluble p~lymer and about 230 + 30 in the corresponding case of the ~nsoluble po~ymer.

Immediately there~fter the root diameter reduces markedly and compression is thereby released ~ragion 95). Steam vents through an aperture 79 in the barrel~

The compression is then repeated in region 96 of the ~xtruder, before passing into the adaptor piece and the die. In this xegio~ (region 96~ the barrel temperature is maintained at about l99 l 30C in ~e case of the ~oluble polymer and about 250 ~ 30 in the case of the insoluble polymer.

Temperature regulation ~s performed by means of conventional electric ~ ackets.

In each case the dies 70,71 are heated to 214C and the heated PVA compositions then fed to the die by their respective screws at rates of e.g. 5:l (soluble:insoluble). In the case of the blown-film 2 13 ~ 1 0 1_ 28 -extr~sion ~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 lQ state such that it can be flattened between the nip rollers 83 and collected folded flat, to be cut open into single æheet form subsequently.

Referring particularly ~o Figure 17, there is shown a flexible polymeric film comprising a substrate layer 10J
of partially-hydrolysed (soluble) PVA having a relatively thin coating ~02 on one face, fo~med 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 ~oating ~02 is applied ~to both sides of the substrate 101~ In both cases the coating 102 is applied as a liquid by co~ventional ink printing methods and subsequently allowed to dry in air.

The i~k coating is applicable to all types of polymeric articles but is particularly useful in the case of th~n-walled or film articles. After the useful life of the article is completed, sim~le 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 me~hanical strength.

Claims (40)

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 form 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 polymeric material 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 17 to 19, 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.

WO 93/22125 PCT/GB93/0085?

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.