Note: Descriptions are shown in the official language in which they were submitted.
2i0~136a v .
'W~ 92/01556 PL~'/Gg91 /0123 i
1
COMPOSITE POLYPiERIC ARTICLES
FTELD OF THE INVENTION
This invention relates to articles, and in
particular aspects to articles in sheet form, which are
composites of two organic polymers having~different
properties. Important applications of this invention
concern articles and materials which can readily be
ZO disposed-of when no longer required.
BACKGROUND OF THE TNVENTION
It has been known to make polymeric articles which,
are purposely designed to be able to be destroyed by
dissolving them, using soluble polymers such as polwinyl
alcohol.
Polyvinyl acetate is a water-insoluble polymer whic'.~.
is obtained by polymerization of vinyl acetate. This
polymer is used---for the production of polyvinyl alcohol
by hydrolysis os alcoholysis to remove the acetyl groups
from polyvinyl acetate. This removal of acetyl groups
maybe carried to partial completion so as to give a
product which is a copolymer or W nyl alcohol and vinyl
acetate. If vinyl alcohol predomrna~es,:but-there is
still a substantial quantity: of vinyl acetate present,
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such a copolymer is soluble in cold water and is
frequently referred to as "partially hydrolysed"
polyvinyl alcohol. The residual vinyl acetate content is
typically about 11 wto 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.
Material of this type is rererred to as "fully
hydrolysed" polyvinyl alcohol., Its content of residual
vinyl acetate is typically no greater than 3 mol%..
Polyvinyl alcohol can be made into film o~ sheet
form. US-A-4444839 (Hoechst describes PVA labels which
are soluble only in hot water, but which have an adhesive
fixing layer which can dissolve in cold water enabling
easy detachment cf the label. The adhesive may ba a
polyvinyl alcohol.
It is also known"to make hospital laundry bags from
partially hydrolysed polyvinyl alcohol sheet. The idea
is that such bags can be filled :with dirty iaundr.- any
20r: the entire bag with its contents can then be put into a
hospital washing mabhine where the polyvinyl alcohol will
dissolve on contact with the wash water, thus releasing
the laundry into the wash water.
In practice there is a difficult_r that the laundry
may itself be,wet and if the wet laundry contacts the
material of the bag it can dissalve it prematurely so
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VIrO 92/01556 ~ P(.'f/GB91/01237
3
that the bag falls apart. Unsuccessful attempts have
been made to rectify this by modifying the solubility
properties of the polyvinyl alcohol. For example, DE-A-
3017246 (Melchior) describes laundry bags made primarily
S of relatively insoluble PVA which will not disintegrate
except in hot water. To enable the desired emptying of
the bag in a cold wash, a subsidiary inner layer of the
bag is made of cold-soluble PVA which can form releasable
welds.
[The Invention)
Broadly, this invention provides an article or
material comprising a first organic polymer which is
water-soluble at a given temperature, typically 20°C, and
a second organic polymer located directly adjacent
thereto, which second organic polymer dissolves more
slowly or not at all in water at the same given
temperature e.g. 20°C, with the quantity by weight of. the
first (water-soluble polymer being greater Khan she
quantity of the second polymer.
It will be explained.in.more detail below that the
first, water-soluble,, polymer is preferably partially
hydrolysed polyvinyl alcohol. The water-insoluble
organic polymer may be fully hydrolysed polwinyl
alcohol. Generally bath polymers will feel dry, not
tacky, to the touch,.,.
In certain forms o° this invention the article or
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material is laminar ~:rith adjacent layers of the two
polymers. Such a form oa the invention could be polymer
film or sheet to be used ~.. industrial production
processes. Further forms of the invention are articles
., comprising pieces of such polymer sheet or film. In
particular, the pieces of polymer sheet or film may be
shaped to have curvature _:z more than one direction.
Articles and materials of this inventic: have the
property that if an e::posed surface of the first polymer
is brought into contact with water, it dissolves but
where a first polymer surface is overlaid by the second
polymer that surface is protected. The second polymer
acts as a barrier and protects the first polymer against
dissolution if the protected surface gets wet.
Usually, the two types of polymer will be
substantially co-extensive in the article c~ material
e.g. a continuous uniform multilayer laminate film, cr a
body of the soluble polymer subs~antially surrounded by a
coat of the insoluble.polymer.
The"second polymer can be a surprisingly thin layer, '
i
so thin that' it does not remain intact after the first
polymer dissolves. Thsn the first polymer is relied upon
to provide mechanical strength while the second polymer
i.
is relied on for a caster-barrier.
-- Such functionality has a wide range of applications.
In general the articles and materials of the invention
,;
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'W~ 92/Q1556 1'CT/GB91/01237
can be used where i~ can be arranged that at first the
slower-dissolving second polym2r 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
i
unprotected surface ef the water-soluble polymer is
allowed.to come into contact with water. The consequence
I
of this is that dissolution of the soluble polymer takes ,
z
place when desired but premature dissolution ._ prevented
by the second polymer.
One possibility, mentioned here as an i?lustration,
is laundry bags made from polymer film which is water-
soluble with a very thin layer of water-insoluble polymer
on the inside of the bags. wf the laundry happens to be
wet, it will not cause the bags to dissolve prematurely
because of the barrier function of the very thin
insoluble layer. :when the bags are put inzac~ into a
hospital washing machine the soluble layer is now
contacted by the wash water cn-the outside ci 4he bags .
and dissolves. The very thin insoluble layer rapidly
breaks up, releasing :,he laundry into the wash water.
The pieces of the insoluble layer are washed'into the
sewage system with-the wash water at the end of the
washing procedure.
The presence c~ insoluble polymer in the sewage
system need not be'a problem.because the preferred _.
material, namely fully hydrolysed polyvinyl alcohol, is
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bio-degradable.
Another possibility is to have a piece or layer of
the first polymer surrounded by the second polymer, so
that the article can maintain its integrity in the
S presence of water unless broken or ruptured, allowing
water to attack the first polymer.
The. preferred soluble polymer is partially
hydrolysed polyvinyl alcohol. As already mentioned above
this is a copolymer of polyvinyl alcohol with vinyl
acetate. Generally these copolymers are hydrolysed to an
extent between 75 and 95 mol%, more.commonly '~etween 80
and 90 mal%. Thus, the mol ratio of vinyl alcohol to
vinyl acetate lies between 75:25 and 95:5, more
preferably 80:20 and 90:10. Partially hydrolysed
polwinyl alcohol is fully bio-degradable. This has the
considerable benefit that ~_ the polymer is allowed to
dissolve in water which is ;:hen run to waste, the polymer
which enters_the sewage system. will degrade into
ecologically acceptable produce s. For this reason i~,. may
be desirable that the soluble polymer does not'
incorporate any other monomer although the possibility of
incorporating a further comonomer is not excluded by this ,
invention.
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 condiwi.ons,
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7
as will be mentioned below. The length oz time for this
polymer to dissolve can be chosen according to the use
envisaged for the article or material and can range from
a matter of seconds to several hours.
The speed with which partially hydrolysed polyvinyl
alcohol dissolves decreases somewhat with increasing
molecular weight of the polymer. Higher degrees of
hydrolysis (so long as the material remains only
partially hydrolysed) tend to decrease speed of solution.
Subjecting the polymer to heat during processing also
' retards the speed with which the eventual processed
polymer will dissolve.
The mare rapidly soluble polymer used in the present
invention will generally have a speed of solution such
that when a sheet of the polymer with at least one side
face of the 'sheet exposed is placed in distilled water at
20°C, the sheet dissolves sufficiently to break up wzthin
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 50um thick.
r..
The relatively less soluble polymer should of course
dissolve more slowly than the more soluble polymer. For
many applications it will be desirable that the polymer
is essentially insoluble, to the extent that if a test
r ~~heet~of the.material-with.sufficient._;thickness to be
handled, e.g. 50um, is placed in .sterile_distilled water
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8
at 20°C, the sheet remains undissolved and intact for a
period exceeding-,8~hours and perhaps more than 24 hours.
It is however possible that a soluble polymer which
dissolves slowly will provide adequate barrier protection
for a faster dissolving polymer in certain applications.
The relatively slowly dissolving polymer is
preferably fully hydrolysed polyvinyl alcohol or a
suitably insoluble pol:rvinyl alcohol copolymer. Fully-
hydrolysed PVAs are over 96 mola hydrolysed; commonly
over 98 mol%. They are in fact appreciably water-
soluble at raised temperatures, e.g. over about 50°C, and.
usually highly soluble over about 80°C, although some
special 'types can withstand such temperatures for some
time without dissolving. At about room temperature,
however, solubility is sparing and particularly so for
the more highly polymerised PVAs.
It will frequentJ.y be preferred that both polymers
are biodegradable, meaning that ;when discarded into
sewage or otherwise exposed to water and natural
bacteria, they decompose to naturally occurring chemical
species within a few months at most. Using polyvinyl
alcohol for both layers achieves this result.
The articles of the invention will usually have the
"insoluble" polymer exposed to the exterior. The soluble
polymer may.also be exposed, or may be enclosed by the
insoluble polymer. However t:ne insoluble layer will
W~ 92101555 ' 2 fl 913 6 ~ PCT/GB91/01237
9
usually contact only the ex~eerior and the more soluble
polymer; not any adhesive or other type of layer.
In the article or material, 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 or three-dimensional
articles.
In an alternative preferred aspect, the less soluble
polymer covers the more soluble polymer with a general
thickness which is preferably not more than 20um, more
preferably not more than l0um, most preferably not more
than Sum. It may be as thin as 2um or thinner.
In a film product, the total film thickness may
f5 range typically from Sum to lmm, more typically from l0um
to 200um.
Each polymer may be used in admixture with other ,
substances. In particular,~a phasticiser is usuall,~
desirable to achieve a pliable film product. Glycerol,
trimethylol propane, and glycols are suitable
plasticisers. Colours and/or fillers may also be used if
desired, in one or both layers. These may be
conventional. v
Articles mav.take various forms, for example, a film
- may comprise justw two layers, one of each kind of
-polymer. -Or, the film may be a.sandwiGh.of more soluble
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iVVO 92/01556 .~ ; ' ~ ~. "1: ' ~ ~. P~'f/GB91 /0123 , '
polymer between layers of less soluble polymer.
Non-film articles may comprise a "core" of the
soluble polymer substantially or entirely covered by the '
Y.
less soluble polymer.W,.Such an article can resist attack
5 by water, but when it is broken water can dissolve the
exposed core and hence the entire article may be
disintegrated.
In another aspect, the invention provides processes
for preparing composite articles and materials as
10 described above.
There are a number of ways of forming respective
portions e.g. layers of the two polymers superimposed and
bonded together as a composite article e.g. film or
sheet. Broadly 'these are various (a) casting/moulding
and (b) extrusion processes.
A cast/mould process for film or shee'c involves
forming a first of the layers - the less soluble one if
PVA - on a flat or shaped surface and subseauently
applying the second layer on 'top of it. Application may ,
be e.g. by spraying or by a dripped feed. PVA~can be
applied with water e.g. as an aqueous solution or
dispersion optionally containing plasticisers, thickeners
etc. as appropriate, from which water is evaporated in
forming the two layers of polymer.
Extrusion preferably involves co-extrusion of the
two layers. Hlown film co-extrusion is pbeferred. '
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1~V0 92/01556 PCf/G B91 /01237
11
The process can be an adaptaticn of the known
process for forming a blown film from a single PVA
polymer. The conventional production of PVA film by
extrusion entails feeding a plasticised volume e.g. an
i
aqueous solution or dispersion of the PVA, to a die with
an annular extrusion orifice surrounding an air inlet.
I
As the plasticised polyvinyl alcohol is extruded from the
orifice it forms a tube which is blown out into a larger
diameter tube by the pressure of air introduced through
the air inlet. The blown tube is drawn off between a
pear of nip rollers which close off the air space.
A high pressure, short screw extruder is'suitable.
This usually has a smooth bush, and e.g, a vibrating
trickle feeder to avoid overloading the screw, which can .
be a problem with PVA.
A film-blowing process which is one aspect of this
invention comprises supplying an appropriate extrudable
form e.g. solution or dispersion of the polymers to
respective extrusion orifices of a die, the orifices
being annular and one within the other, so as to extrude j
tubes of the polymers from the orifices, while also '
s
. .
supplying gas pressure to the interior of the inner tube
thereby expanding both pubes and. uniting the inner tube
i
with the outer tube to form a single tube made up fram
-25 : - layers of the two palymers . .. .
The-extrusion machinery can resemble conventional
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12
machinery for forming blown films of polyvinyl alcohol
except however that its extrusion die has two annular
orifices instead of the usual single orifice and a feed
screw for each orifice with associated means for supply
to each feed screw.,. ~~° '
The gas which is blown in is suitably hot air, via
an inlet~within the inner annular slit. The heated air .
can also evaporate water From the PVA so that the film
bubble dries and can be passed through e.g. nip rollers
above the die.
Extrusion of PVA, including blown film extrusion, is
known technology and the skilled man will be~able to
select suitable conditions, for example a die temperature
in the region of 150°C, etc.
The relative rates of feed to the die arifices and
concentrations of the polymers can be adjusted to achieve
the desired ratio of thickness of the two layers.
Processing aids such as antifoamers and lubricants
may be used if desired.
In a third aspect, the invention provides a co-
extrusion apparatus adapted for producing bubble-blown
film as described above.
Particular uses envisaged for the laminar. articles
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;
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13
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.
Embodiments of the invention are now described by
way of example, with reference to the accompanying
drawings in,which:
Fig 1 is a schematic side view of a blown film co-
extrusion apparatus;
Fig 2 is a schematic top view of the apparatus;
Fig 3 is a schematic cross-section of the co-
extrusion die of the apparatus;
Fig 4 shows steps in making a baby's potty liner;
Fig 5 shows a disposable nappy.
Fig 6 shows a two layer film; '
, Fig 7 shows a three-layer laminar article, and
Fig 8 shows a three-dimensional moulded article.
Materials Used
Tn the following embodiments, both the insoluble and
soluble layers- were made from PVP: . The PVAs used were
"Mowiol" (Registered Trade Mark) obtainable from Hoechst
. '.,
~~ 9x/01556 PGT/~ B91 /012 : v
14
AC.. The soluble layers were made using Mowiol 26-88, a
partially-hydrolysed PVA having a mean molecular weight
of 103000, an 8~3 molo degree of hydrolysis and whose
viscosity, measured..as~a 4% aqueous solution, is 26
mPa.s2. The insoluble layers were made using (i) Mowiol
20-98, a fully-hydrolysed grade in which the mean
' molecular weight, viscosity and hydrolysis values are
70,000, 20 mPa.s2 and 98.4 mol% respectively, and (ii) 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.
For the cast processes, each of these was made up in
a respective aqueous composition containing,. by weight,
Z5 15~ PVA granules
5~ glycerine (plasticiser)
80~ water.
The PVA granules were added.;:o the water and glycerine
and then heated at 93°C for °ifteen to twenty minutes to
form a solution.
For the coextrusion process, the make-up~pf the
individual PVA compositions can be selected in accordance
with known criteria.
Co-extrusion Apparatus
25' An experimental apparatus caas set up as shown v
schematically in Figs l to 3. A pair of heated s~.pply
- i
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i~VO 92/01956 ' PC'f/GB91/01237
tanks 1 were provided, one for each PVA type, and
connected to respective intakes of a pair of 10 cm-long
feed screws 2. A variable electric drive 3 was connected
to drive the feed screws at predetermined proportional
5 rates. Outputs from the feed screws 2 passed in
conventional manner to respective extrusion inputs of an
upwardly opening co-extrusion die 5. This had two
circular and concentric extrusion slit openings 10,~.~.
In the experimental apparatus the outer slit 10 had a
10 diameter of 35 mm and the inner slit a diameter of 25 mm.
The width of the outer slit 10 was approximately 0.5 mm
and this was approximately four times the width of the
inner slit 11. A centrally-opening hole 15 was provided
in the die for blowing warm air up through the extrusion
15 rings in conventional manner.
Vertically above the die, a.pair of nip rollers 16
were mounted with a take off to a collecting point snot
shown) for the film produced.
Co-extrusion Process
.Aqueous extrudable PVA compositions are prepared as
described above e.g. from Mowiol 26-88 and Mowiol 20-98,
and each put in a respective heated tank 1 of the
apparatus. The tank of Mowiol 26-88 (soluble, partially
hydrolysed) composition communicates via its feed screw 2
-with thewouter, wider extrusion slit 10. ..The Mowiol 20-
98 (insoluble, fully hydrolysed) compositiow communicates
209136~;~ ~ : . . .
wo 9z/oms6 Pcz'icB9mo~z~.=;~
~,16
via its feed screca ,2,~,;~it!~ the inner , narrower extrusion
slit 11.
The die is heated to 1~0°C and the heated PVA
compositions then fed to the die by their respective
scxews 2 at rates of~e.g. .,:1 (soluble:insoluble). At
the same.time, warm air is blown to the air inlet 17 and
out through the hole in the centre of the die ~. A blown .
film bubble 20 can thereby be formed above the die, with
the thin insoluble.PVA layer on the inside. Cooling air
is blown, again in conventional manner, over the outside
of the bubble above the die. The two extruded layers ,
emerging from their respective slits 10,11 coalesce to
. form the composite film within a few millimeters of
exiting the die. '
The blown air dries the bubble rapidly to a non-
tacky state such that it can be flattened between the nip
rollers 16 and collected folded flat, to be cut open into
single sheet form subsequentl:;.
The process was repeated using the blend of Mowiol
56/98 and 28/99 in place of the Mowiol 20/98, to produce
a still less soluble protective thin layer in the film.: '
Mould Process
This process was used to make a liner for a child's
potty: - A conve.x~. mould surface 2~ ( see Fig 4a i was
i
v prepared, made from.a, shaped metal sheet.., This had a hat
...-. -.shape, with an upwardly-projecting central portion 26 and
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~'~ 92/01556 PCT/G1391/01237
17
a surrounding bottom rim 27 for forming the rim of the
liner. '
An insoluble PVA layer was formed by spraying a
solutian of Mowiol 20-98 onto the outer, convex mould
surface. The solution was as described previously under
'°Materials Used", but with the substitution of 10~
cellulose ether thickener ("Tylose" (Registered Trade
Mark)) for 10~ of the water to improve adhesion of the.
PVA layer to the sloping sides of the mould 25. This
first layer was then dried to tackiness by blowing it
with warm air, and a second layer of a corresponding
thickened aqueous solution of Mowiol 2588 was sprayed
over it to a considerably greater thickness. In
particular, a pronouncedly thick layer was formed on the .
brim 27 of the former, to strengthen the rim oø the
liner.
After drying the water from this second coat using
warm air blowers, the basic composite PVA liner 30 was
lifted from the mould 25. An absorbent pad 31 of
cellulose wadding was placed in its base, and the flat
upper surface of the rim was given a coating of PVA
adhesive 32 which was then covered by a ring of
siliconised release paper 33.
' In use, the insoluble inner layer of the liner was
~ able to contain the potty contents for an extended period
without leaking. -To dispose of both liner and contents
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'W~ 92/01556 PCf/GB91 /0123-: - '
18
the release paper 33 was lifted off and two opposing
sides of the rim stuck together face-to-face using the
PVA adhesive coat 32, so as to form a sealed bag
completely enclosing the contents. The whole was then
taken to a WC and dropped into the water where after
about ten seconds it had already broken up so much as to
be fully flushable.
Again, the process.was repeated using instead the
56/98 and 28/99 blend to form the insoluble layer.
Improved resistance to water was noted.
Disposable Nappy
A backing sheet 40 for a disposable nappy was made
by sequential spraying and drying of two different PVA
layers as described above for the liner, but~this time on
a flat steel surface and without the Tylose thickener.
The thicker, soluble layer formed the outside of the
nappy and the thin, insoluble layer the inside (uppermost
in Fig 5). ~In the cast sheet; the more soluble layer may_
be about 0.1 mm thick and the less soluble layer about
0...02 mm, but these can be adjusted according ~o the
required strength. A conventional cellulosic absorbent
pad 41 was affixed to the thin insoluble layer using a
aommercial PVA adhesive.
In an experiment,- aqueous liquid was poured onto the
:- 25 padding and the nappy was then ralled up. After being
left for eight hours, the nappy. was still intact and
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'NVO 92/01556 PCT/GB91/01237
19
there was no leakage. However, on putting the rolled-up
nappy into a bowl of water, it broke up in seconds and
dispersed.
Figures 6 to 8 illustrate schematically various
forms of article embodying the invention.
Figure 6 shows a two-layer flexible film comprising
a layer.50 of fully-hydrolysed PVA, 3~am thick,
superimposed on a layer~~l of partially-hydrolysed
(soluble) PVA 25~am thick.
Figure 7 shows a disposable drinking cup.made from a
three layer laminar product. This has a thick
intermediate layer 61 of partially-hydrolysed PVA,
perhaps 0.5mm thick, giving mechanical strength to the
cup. The inner and outer surfaces of the cup have a
thin, Sum coating 60 of fully-hydrolysed PVA which
prevents outside moisture, and liquid in the cup, from
attacking the intermediate layer 61. To render the cup
disposable it need only be torn up, whereupon the
intermediate layer is exposed and can be dissolved.
20. Fig. 8 shows a moulded golf tee having a central
core 7l of partially-hydrolysed PVA forming the basic
shape of the tee. Sum coating 70 of insoluble PVA covers
the tea. The coating may be applied to the moulded
"soluble" tee by conventional methods. The tee can
a
withstand normal use. If it is lost, any natural wear or
damage will allow natural moisture to destroy it quickly
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WO 92/01556 PCd'/GB91/0123 ~
and hence avoid a litter problem.
