Note: Descriptions are shown in the official language in which they were submitted.
WO 91/19487 PC~/GB91/00930
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POLYMERIC FILMS FOR FO MG CAPSULE SHELLS
This invention relates to polymeric films which are
suitable for forming shells or capsules for containing
various non-aqueous liquids or solids.
Depending on the various uses of the capsule shells,
the required properties may vary. At present, capsules are
usually made from gelatin. However there are various
reasons why it is sometimes undesirable to us~ a naturally
occuring material such as gelatinj for instance because of
its variable quality or because of a public pre~erence to
use a synthetic material rather than an animal-based
material. It is known to form capsules from sin~le
homopolymeric materials such as polyvinyl alcohol.
However, it is difficult with ~hese polymeric rompositions
to produce a product having all the desired properties for
each alternative use.
The walls of gel capsules must have high mechanical
strength and stability, and resistance to the substance
which will be contained in the cap~ule ~hell. It is often
necessary that the capsule shells should dissolve rapidly
. in .water. .However, the solubility properties can vary
! - considerably from one requirement .to another,~for example
the temperature of the aqueous solution:in which the shell
. must.dissolve may vary oonsidexably...',:For~example if
~25.~ capsules; ar~ filled with-pesticides -or.herbicides the
:. capsule walls must dissolve in cold .water, so that the
.. . .. .,. ~
,.~..,pesticidejmay be readily diluted:for application to the
land, whereas when the contained ~substance is.,~bath oil,
... ";.;~.;rapid solubility~,must be !achievedmfor ;warm water. In
.;..~30....~,,addition,~for..example,~if'~ the.capsule shells~are used for
containing.pharmaceutical preparations or cosmetic products
.. such .as bath joils,:,:the geljcapsule~mu~t~be'aesthetically
acceptable and.~i,therefore~ it.~ is.~,beneficial i~ the
lm-forminglpolymericl,material~.-can~be~dyed and/or can be
. ...35 ... mixed~with pearlinglagents., ~ i.c; ~ :c.~
T!~ The knownjhomopolymeric systems~for.making capsules
: .,. . have very~low controllability:and,:it.is di~ficult to vary
i
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wosl/l9487 PCT/GB91/00930
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the properties to meet the different requirements of
capsule shells for various uses. I~ particular, no
synthetic film forming system has previously been prc,posed
that provides a satisfactory combination of flexlbility and
non-stickiness in khe pr~sence o~ ambient humidity,
mechanical strength, and total rapid dissolution in water.
This invention relates to a film-forming polymeric
system suitable for preparing capsule shells which can be
varied easily according to the particular requir~ments of
lo the filling material and j especially, to a system that is
flexible, non-sticky and completely water ~oluble.
According to the present in~ention there is provided
. a polymeric composition suitable for fo~ming a capsule
- shell for con~aining a substantially non-aqueous substance
characterised in that the composition comprises a wat~r
soluble synthetic film-~orming polymeric composition of
cationic and anionic moieties.
The invention also provides a capsule shell in which
at least part of the shell is ~ormed ~rom such a
composition. For instance the total capsule may be formed
from~two shells and at least one, and preferably both, of
,;. the shells are ~ormed of~the~composition. !~ shell may be
formed of two parts,~ one-part being formed o~ the defined
- .~. composition.and tha other part being Pormed from some other
- 25 ,~ capsule-~orming~material. :-; The invention also pro~ides
.. filled capsules in which at ~least part of ;the capsule
i:- m; .-~.shell, and preferably all the capsule shell, is formed from
the compositi~n~ ?~ 5~
:: :.,^s~l s The synthetic~film~^~forming polymeric composition can
30.~J comprise'an3amphoteric pol~mér forme~ by co-polymerisàtion
P~ranionic ethylenically unsaturated~monomer with cationic
ethylenically.unsaturated monomer and, optionally, nonionic
' t '. ethylenically~unsaturated~;monomer~
,cr It!iO '~O~ .Preferably-Jthef~cationic:;and~;;anionic:moieties in the
polymeric composition~are~providèdiby a blend o~ cationic
i .. ~ . J''(~-;O polymer and;anionic polymer,':~*heiein~each-~`polymer is water :
soluble;and.--ilm;forming.~ ach `polymer is generally
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-, -.,, . .. .. . .- . .. . .. . . ..
WO91/19487 PCT~GB91/00930
~.? , ` , " 7 2 7 3
formed by polymerisation of a monomer or monomer blend
having the desired ionic character ~anionic or cationic).
If a blend is used, it may be a blend of ionic monomers of
the chosen character or a blend with a non-ionic monomer.
Each monomer.or monomer blend i5 usually water-soluble in
order to ensure that the polymer is soluble in water.
The preferred cationic monomer, is diallyldimethyl
ammonium chloride or other diallyl dialkyl ammonium salt.
.Other suitable cationic monomers include dialkylaminoalkyl-
~meth)acrylate or -~meth~acrylamide, eith~r as acid salts
or, preferably, quaternary ammonium ~alts, the alkyl groups
may each contaSin 1 to 4 carbon atoms and the aminoalkyl
group may contain 1 to 8 carbon atoms. Particularly
preferred are dialkylaminoethyl (meth)acrylates,
dialkylaminomethyl (me~h) acrylamides and
dialkylamino-1,3~propyl (méth)acrylamides. These monomers
may be present as acid salts or, prefeably, quaternary
- ammonium salts~ The dialkyl group is generally dimethyl,
e.g., (meth)acrylamideopropyl trimethyl ammonium chloride.
: -20 . To make cationic polym,_rs for use in the invention the
cationic monomers.~may be homopolymerised or copolymerised
with each other;or.with:a non-ionic monomer,!preferably
~ ~ ~ (meth)acrylamide to give a~:polymer ~ormed o~ cationic
; ~ moieties~optionally with non-ionic moieti~s. :: Thus the
,;.,.25 .cationic~polymers,are usually formed fromi30 to 100% by
s ~ ~i weight cationic~monomer:with the:balance bèing~non-ionic.
The~amount of cationic monomer-is usually at~least 50% and
often~at-:least;'80% by w~ight~and !most?pre~erably 100~.
ther~suitable~cationicipolymers are.polyethylene imines
ao ~ I~;and~ polyamines;~^e.g.,~polyamine:epichlorhydrin polymers.
, r,,~ t~ The,.molecular weight~of~the~cationic polymer should
s~f:~ io ~preferably~be.such.that the polymer-hasiintrinsi~ vi~co~ity
'0 S~ u~,of~a~;;least 0sl,r~and:preferably at~least-`0.~3 ~I~g ~measured
- ek) ~jrl~ O~,.by.:~suspendad ilevel~ viscometer~}at 25C:~in~molàr aqueoussodium chloride,).~ IV can be up to~;-Yfor~ins~ance,tlOdljg or
- higher.~but is generally below 7 ~'f~most usually beslow 4 and
preferably below 2.5dllg.~-Preferred values, especially for
.
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WO 91/19487 PCT/GB91/00930
polymers of diallyl dimethyl ammonium chloride, are in the
range 0.8 to 2.4 dl/g. Such values indicate that preferred
molecular weights in the region of around 50,000 to
1,000,000 or 2,000,000 and are preferably above 200,000.
If the molecular weight is too high, the forming
composition may have an unacceptably high viscosity at
reasonable concentrations of polymer.
The anionic monomers that can be used in the invention
include acrylic acid, methacrylic acid, maleic acid,
2-acrylamido-2- methyl propane sulphonic acid (AMPS),
sodium vinyl sulphonate, or other ethylenically unsaturated
carboxylic or sulphonic acids, often as alkali or other
water soluble salts.
To make anionic polymers for use in the invention,
anionic monomers may be copolymerised with each other or
with non-ionic monomer such as (meth) acrylamide.
The proportions of anionic and nonionic monomer and
molecular weights for the anionic polymers may all be
similar to those discussed above for the cationic monomers,
although it can be desirable for the molecular weight to be
a little higher, for instance 500,000 to 10 million,
preferably 1 million to 5 million.
When the composition is based on an amphoteric
polymer, the molecular weight may be as discussed above for
cationic polymers. The amount of non-ionic monomer in the
blend is generally 0 to 50%, preferably 0 to 20%, by weight
of the total monomer blend.
The polymers must be totally soluble in water.
Accordingly, the polymers are preferably linear
homopolymers or copolymers of monoethylenically unsaturated
water soluble monomers. However, cationic polymers which
have a small degree of cross-linking or branching, or that
are formed from monomers that include a small proportion of
insoluble monomer, can also be suitable provided they do
not significantly affect solubility.
We have found that compositions formed from either
ionic type alone do not have satisfactory properties for
WO91/19487 PCT/GB9l/00930
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water soluble capsules but the use of a blend of ionic
types, and pr~ferably the u~;e o~ a blend-of counterionic
polymers, gives the opportunity of obtaining a variety of
properties that can be selected according to selection of
the ratio of cationic and anio~ic moieties.
For instance, polymers of polyvinyl pyrrolidone or
polyacrylamide or homopolymers of the anionic moieties
described abo~e tend to be too brittle when exposed to
ambient humid atmospheres. Polymers of polyvinyl alcohol
or homopolymers of the cationic moieties described above
tend to have adequate flexibility but to be too sticky when
exposed to ambient humid atmospheres. This problem of
deliquescence applies also to some of the anionic polymers,
and is particularly serious in resp~ct of capsules of, for
instance, cosmetic preparations such as bath oils.
By selecting appropriate proportions of the a~ionic
and cationic monomers (i.e., moieties~ it is possible, for
the first time, to provide a synthetic sheli that has the
optimum combination of flexibility and other properties
when exposed to an ambient atmosphere and yet'which has a
, desiredj usually very'fast,;rateiof dissolution in water.
If:tthe amount o~ cationic monomer is`too'`low'`'thenithe shell
.will,.tend to be too brittle.'~ If it` is !too high then the
: ~ shell will ,tend `:to be ~too'~'sticky in'.'the ;prèsence o~
,~. ,25 -atmospheric hu~idity. ~ :'^; ~:' ' '' ' ~ ': '
-The~-.molar '-i-ratio`-`cationic:anionic- ~moiéties is
.~ ;., ..~preferably-.about 5:1 to,1:1,'.mosti'preferably about 4:1 to
The weight ratio ~lcationic:anionic `:;mon`omers is
,~..30.i.,,rgenerally at least~l:l and can bë'up`to 8:1, but 4~i is
r~ ;iar~.o~ten sufficient.;~ ~'preferred~rang~e:is 1~`.'5~1 to'~3:1, with
~Lrbest results~.:generally at around:''2:1.''`JThèsel;values a~e
`3~ .particularly preferrediwhen the catiônic~:p'olymer is based
3;J~ tv ona'diallyl dimetXyl ammo'n'ium' chloridè (p`r`efërably as-.a
'35 ~...rhomo'poly~er).typically having molecular:'w'é'igh'~'in the range
.,.. 300,000:*o 1.5'~million,'generally`:'50'0;`000'~o'-'i,000,000 and
when the.~anionic polymer~ based on-sodium'acrylate or
,
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WO 91/19487 PCT/GB91/00930
methacrylate (generally as homopolymer) typically having
molecular weight in the range 10,000 to 5,000,000,
preferably around 50,000 to 2,000,000.
The shell-forming composition of the invention
generally contains the defined synthetic polymer or polymer
blend as the only film forming components. The
composition is normally free of natural polymers such as
gelatin.
An advantage of the invention is that the film can be
formulated wholly from reproducible synthetic polymers.
Another advantage is that it can be formulated to dissolve
rapidly and completely, without leaving a scum in the water
in which it is dissolved.
Another advantage of the invention is that the films
can be heated, for instance during drying or formation of
the capsules, without adversely affecting the properties of
the film. This is in contrast to gelatin since that is
liable to become brittle if it is heated significantly.
The capsule shell can be used to contain a variety of
substantially anhydrous fillings. The filling must be
substantially anhydrous otherwise the water in it may
weaken the shell and may even result in rupture of the
shell. Generally the water content of the filling is,
initially, below 10% and preferably below 5% and, in
particular, the total amount of water that is introduced by
the filling must be such that the resultant moisture of the
film is sufficiently low, generally below 30%, preferably
below 20% and most preferably below 10% even when exposed
to an ambient atmosphere.
An advantage of the invention is that the film can
easily be formulated to maintain structural integrity even
when it does contain these small amounts of moisture.
The filling for the capsule can be liquid or powder
and can be for instance selected from for instance
detergents, fabric softeners, fragrances, flavour oils,
hazardous chemicals such as pesticides, herbicides or other
agrochemicals, pharmaceuticals or cosmetics. It is
WO ~1/19487 P~/GB91iO0930
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7 ~0~7~-73
particularly preferred that the filling is a cosmetic, in
particular bath oil or bath grains. If 'che ~illing is a
solid, it will be in particulate form which can, typically,
be such small particle size that, if it~ was not
encapsulatad, might create a dusting hazard.
In a particularly preferred aspect of the invention a
shell is prepared that is suitable for forming a capsule
for containing a non-aqueous bath additive such as bath oil
or bath grains characterised in that the capsule comprises
a water-soluble synthetic ~ilm-forming polymeric
compositi~n of cationic and anionic moieties in which the
cationic moieties are provided by a cationic polymer and
the anionic moieties are provided by an anionic polymer and
the weight ratio of cationic to anionic polymer is ~rom 1:1
to 8:1, preferably from 1.5:1 to 3:1, and most preferably
around 2.1. The preferred po}ymers are polydiallyl
dimethyl ammonium chloride and sodium polyacrylat~ or
methacrylate, .having the preferred molecular weights
indicated above.
- - The shell capsules may be o~ any slze depending on the
requirement of the particular use. For exampl~, for
pharmaceutical preparations the capsules must be small
enough for swallowi~g and may therefore be below lcm
diameter, even below 0.5 cm diameter. Preferably the
25 capsules have a diameter above 0.2c~, less preferably they
; could be microcapsules. For use as containers for bath
oil, slightly largPr capsules, such as those having
diameter of from lcm to 5cm may be preferred.
The compositions can contain; for instance, dyes
30 and/or pearling agents.
c A variety o~.polymeric films suitable for making
capsules were formed from various polymer solutions by
drying, and the resulting films were evaluated for
35 characteristics of appearance and stability of ~ilms,
water-solubilities at temperatures of from 35-45~,
mech~nical strength, and resistance to non-aqueous oils.
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WO 91/194B7 PCI'/GB91/0093û
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The results are given in Tables 1 and 2.
TA~
POLYMER POLYMER '~FIG~T RATE O~
FILM TYPE RATIO DISSOLUTION AT
. 43-45C (y/~ec~
A_ Polv DADMAC - O 005
Poly DAD~AC/
B Poly~odium acrylat~ 3:1 0.009
_ -~ Pearlinq aa~nt 3:1 _ 0.003
Poly DAD~AC/ inco~plete
C Poly~odium acrylate 2:1 ~olubil$ty
_+ Pearlinq,agent _ 2:1
PolyDADMAC/
D Poly Sodium
Methac~ylate 3:1 0.003_
PolyDADMAC/
E Poly Sodium
UethacrYlate2:1_ 0.004
PolyDADMAC/
_ F Polv asrylic acid 2:1 _OOQ07
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7f '~ O .~ rJ ~ J~ f~ ~ f 7~ '!7r;-~ ~ .. '.il ii ~ .; :~ s~ i ~ C . i-~
.~"J '~ 'r~ 3'~ ir' ~ f?~ '3~ ~'3~t~ '.'~ f~ fir?
SU13~TIll~UTE SHEE~
WO91/19487 PCT/GB91/00930
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TABLE 2
POLYMEiR ~ SICAL_. STRENGTH
60~ REL._ HUMDIITY _ 30~6 REL. HUMliDITY
Elongation Ma~.~oad Elongation , Mi~x ~oad
At ~r~ak At BrQak At Break Load at
Point Point Point Break ~ -
Point
A X 2 12N X 1!2 150N
_ . _ - 1
B X 2 20N X 1/3 84N
B I
PearlLng
Agent 1/7 4N ~ 1/10 69N
1 X 1/7 6N X 1/3 }07N
+
P~arl~ng . ---
20 A~ent 1/7 ~3N X 1/10 60N
D X 2 16N X 1/3 150N
. . . _ . I
- X 2 12N X 1/3 110N
~: 25
,,.~ X 3 - . ~ 3N ~ X.1/10 . ;:.~.. 98N
The ~echanical strength tests were carried out at 22C
30 on pol~m~ric film sampleæ having thickness,of from 0.4 to
O.5m~. ~ .
A subjective assessment was made of various films.
PolyDADMAC having moleaular weight around IV2 gives a tough
opaque flexible film that is very sticky in humid
. 35 . atmospheres, whilst polyDADNAC having lower molecular
4 weight forms a weaker ~ilm, that is again sticky in humid
,~ ~atmospheres. Polyacrylic acid (as the ~ree acid) ~of
:. molecuIar weight of around 2,000,000 gives a hard brittle
ilm that is slightly sticky~in a humid atmosphere whilst
40 its sodium salt gives a brittle film that is slightly less
~ticky in humid at~osphexes. Polyacrylamide gives an
inflexibls clear film.
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WO91/19487 PCT/GB91/00930
~o87i73 lo
Mixtures of two or three parts by weight polyDADMAC
with one pa~t by weigh~. sodium acrylate or methacrylate
homopolymer give flexible opaque ~ilms that are only
slightly sticky when wet and which dissolve rapidly a~d
fully in warm water. ~hen the film is ~ormed from two
parts polyDADMAC and one part polyacrylic acid homopolymer
(as free acid) the film is rather brittle.
Capsules may ~e formed for instance from the
exemplified polymer compositions or other compositions of
the invention by conventional capsule forming methods,
including sachet folding or casting. For example using
casting, the polymer solution may be cast into
semi-spherical shapes and this is followed by sealing two
semi-spheres together, for example using aqueous based
lS adhesive or by moistening the edges of the ~emi-spherical
shells and sealing them together by drying.
Capsules can a}so be prepared by ~aving for example a
semi-sphere of water-soluble shell adhered to a non
water-insoluble hemisphere. Thus, the capsules do not have
to be entirely water-soluble, but may comprise a wall which
is partly formed of the water-soluble. synthetic
. film-forming polymeric composition according to the
.invention.
The non-aqueous filling can be ~illed inside the shell
capsules by known techniques, for instance injection into
a ~ully ~o~med, sealed shell capsule or by incorporation
into the capsule during casting or other manu~acturing
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