Note: Descriptions are shown in the official language in which they were submitted.
:~g~
~ WAT~.R SOLUBLE FILMS OF POLYVINYL
.
ALCOHOL ANDPOLYV~NYL PYRROLIDONE
BAC~GROUND OF THE INVENTION
(l~ Field of the Invention
This invention relates to water soluble films. More
particularly, this invention relates to water soluble films
useful in packaging applications~ especially for dry detergents
and similar water soluble commodities, formed from homogeneous
blends of water soluble polyvinyl alcohol and polyvinyl pyrrolidone.
!(2) Discussion of the Prior Art
Packaging materials formed from fil.l-forming ma-~erials
which are water soluble have been used for many years for
packaging water soluble or dispersible dry, solid materials
which may be toxic or otherwise harmful to th~ user or which
may be difficult to weigh out in accurate portions, or simply
for the convenience of the user. Examples of typical ma~erials
` used in aqueous environments which have been packaged or proposed
for packaging in water soluble films include,for example,
'cleaning products, such as laundry detergents, bleaches, and
caustic cleansers; pesticides, such as herbicides, fungicides,
ins~ctîcides, and nematocides which are applied as aqueous sprays;
and various other pulverulent water soluble or dispersible
chemicals, such as carbon black, pigments, dyes, etc;.food
products, and.the like.
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One of the mpst widely investigated water soluble
film-forming rnaterials used or promoted for packagin~ of sucl~
ipowdery materials is polyvinyl alcohol (i.e., partially hydrolyzed
polyvi.nyl acetate). At hydrolysis levels oE up to about 97-99%,
polyvinyl alcohol is soluble in water although the rates of
dissolution are too slow to be practical, especially in cold
water.
Many attempts have been reported in the patent litera-
ture to improve upon the properties of water soluble polyvinyl
alcohol packaging films. These cfforts have included, for
example, selection of special plasticizers, e.g., U.S. Patent
2,948,697 - J.A. Robertson and U.S. Patent 3,106,543 - J.N. Milne,
assigned to E.I. duPont de ~Jemours; U.S. Patent 3,157,611 -
M.K. Lindemann, assigned to Air Reduction Co.; U.S. Patent
3,374,195 - T.S. Bianco, et al., assigned to ~no-Sol Div. of
; Baldwin-Mon~rose Chemical Co.; modification or copolymerization
of the polyvinyl alcohol, e.g., U.S. Patent 3,300,546 ~
R.L. Baechtold, assigned to American Cyanamid, U.S. Patents
3,441,547 and 3,505,303 - M.K. Lindemann, assigned to Air
ReductionCo., U.S. Patent 3,277,009 - M. Freifeld, et al.,
assigned to General Airline & Film Corp.; and blending polyvinyl
alcohol with other polymers, e.g., U.S. Patent 2,850,541 -
I.M. Klein, U.S. Patents 3,695,989 an~ 3,892,905 - R.E. Albert,
assigned to E.I. duPont de Nemours.
The Albert patent 3-,695,989 describes cold water
soluble packages made from foamed films of polyvinyl alcohol,
polyvinyl pyrrolidone or mixtures thereof which films have
dispersed therein from 80 to 99% of the total volume of the
ilnl o~ Inn6 bubl)lcs havin~ an averagc cli.~nlcter less tllan 1/3 o~
the to~al thickness of the film. The polymers are of high
molecular weight, e.g., above about 80,000 in order to obtain
flexible packages which can dissolve rapidly in cold water.
In 3,892,905, Albert describes cold water soluble
plastic films formed from a mixture of polyvinyl alcohol and
polyvinyl pyrrolidone wherein one of the polymers has a molecular
weight average of more than 120,000 and the other has a molecular
weight aver~ge of less than 90,000.
~owever, none of these efforts have been entirely
-satisfactory in providing films which are sufficiently stable
l against degradation of physical properties when stored under
relatively low humidity/low temperature or relatively high
humidity/high temperature conditions. Thus, at low humidity/
low temperature conditions, many of the films become brittle and
lose elasticity, resulting in loss of impact resistance and
tear strength. They may also lose their clarity and heat
sealability. At high humidity/high temperature conditions
(e.g., 100F and 80% R.H.) the degree of hydrolysis of the poly-
vinyl alcohol may increase to levels at which the polyvinyl
alcohol is no lon~er water soluble or the film may simply become
too soft and tacky to be stored or handled. The films may become
- water insoluble after only 2 weeks at these conditions. For this
reason, it is usually necessary to store the films under specially
controlled atmospheric conditions or to provide special water- !
proof protective release films between plies of the water soluble
polyvinyl alcohol films, as shown, for example, in Albert - IJ.S.
Patent 3,892,905, at col. 3, line 47 - col. 4, line 4 and
col. 4, lines 44- 54. Many of the prior art films suffer from
poor aging stability when in contact with alkaline substances,
even under moderate (e.g., 50% R.H.) humidity conditions. For
example, they may become water insoluble after only 2 to 3 weeks.
Polyvinyl alcohol is not fully compatible with most
polymers and, therefore, does not form completely homogeneous
blends and, accordingly, it is difficult to form uniformly
transparent and mechanically strong films. Still further, the
prior art films do not have sufficiently high rates of dissolu-
tion in water, particularly cold water, i.e., at water temperatures
below about 60°F, especially at or near ice water conditions.
-5-
SUMMARY OF THE INVENTION
This invention is directed to providing water soluble
Eilms, useful for packaging applications, which have high rates of
solubility in both cold and hot water, and preferably water soluble
films which are insensitive to humidity, e.g., which do not become
insoluble at high relative humidity and high temperature storage
conditions.
The invention further attempts to provide water soluble
films which are clear, transparent, non-tacky, easily handleable,
heat sealable, and mechanically strong and which are inexpensive
to produce.
According to the present invention there is provided a
water soluble film comprising a uniform mixture or homogeneous
blend of water soluble polyvinyl alcohol and polyvinyl pyrrolidone
wherein both polymers are characterized by having a weight average
molecular weight in the range of about 10,000 to 50,000. ~enerally,
the polymers are blended at weight ratios ~on a dry solids basis)
of polyvinyl alcohol to polyvinyl pyrrolidone in the range of from
about 10:1 to 1:1 and more preferably about 4:1. The poly~inyl
alcohol is preferably a partially hydrolyzed polyvinyl acetate
having a degree of hydrolysis of less than about 96%.
Small amounts of plasticizers to lower the glass
transition temperature, tg, and brittle temperature, tf, and
nonionic anti-foaming agent to suppress foaming during film for-
mation are desireably included in the polymer blend. In addition,
in view of the biodegradability of the water soluble films~ a
biocide can be included in the film-casting solu~ions with the
polymers and other adjuvcmts.
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DET~ILI~D Dl~SCRIPTI~)N 01; TIIE INVENTIO~J
!
The water soluble films of this invention are especially
suitable for packaging pulverulent or powdery or other solid dry
materials which are to be dissolved or suspended in aqueous
solutions for use. These films are useful for packaging any dry
; commodities where rapid water solubility, including ice water
temperatures, is required and especially where continued stability
to aging at high and low temperatures and humidities and good
strength are required. For example, a premeasured quantity of
a powdery laundry detergent can be stored in a sealed bag made
from the water soluble films and simply dropped into ~he washing
machine. The film package will rapidly dissolve upon coming
into contact with the wash water to release the detergent. There
is no residue from the bag which could clog pipes, valves or
lS other components of the washing machine or other appara~us with
which the films are used. The polymer materials are also bio-
degradable andtherefore do not pose any environment~l pollution
problems.
; The films can be simply prepared by forming an aqueous
solution of the polyvinyl alcohol and polyvinyl pyrrolidone and
laying down the solution on a smooth casting surface. A doctor's
blade or other means can be used to obtain the desired film
thickness. Upon evaporation of the aqueous solvent, a clear
;transparent and uniformly thin film of the polymer blend is left
which can be easily stripped from the casting surface.
The casting surface can be any smooth, hard material
such as steel, aluminum, glass or polymer, e.g., polyolefin,
polyester, polyamide, polyvinyl chloride, polycarbonate, poly-
halocarbons, etc. Tlle rate o~ evaporation of the aqueous solvent
' , ;
--7--
can be increased by heating the casting surface or by exposing
the deposited coating solution to, for example, heated air or
infrared rays. The casting surface may be flat or the films may
be made on standard (drum type) industrial film casting machinery
followed, for example, by oven drying.
The aqueous coating or casting solution can be formed
by any desired means. For example, the polyvinyl alcohol can
first be dissolved in water and the polyvinyl pyrrolidone added
to this solution.
The polyvinyl alcohol can be added to a solution of
polyvinyl pyrrolidone. Alternately, the two polymers can first
be blended together and then added to water. The choice of any
particular method will generally be dictated by the form of the
commercial source of the respective polymers.
However, it has been found that with a typical commer-
cially available granular, partially hydrolyzed polyvinyl alcohol,
the best results are achieved by preparing the polymer blend
casting solution by first dissolving the granules in water by a
two-step procedure: adding the granules to cold to room
temperature or warm water to form a dispersion, and then heating
the solution at an elevated temperature in the range of about
150°F to 250°F, preferably 180°F to 200°F, with vigorous agitation.
To prevent foaming with possible occulation of air bubbles in the
cast film, an anti-foam agent is preferably added to the solution
before raising the temperature and agitating.
Any anti-foam agent which will not adversely effect the
water-solubility of the film can be used. Non-ionic surfactants
are useful anti-foam agents. For example, the polyalkylene
oxide condensates of alkylphenols and alkylene oxide condensates
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~ ~'9~
witll a hydrophobic base are suitable classes of nonionic sur-
factants. As typical examples of the former class, mention can
! be made of the condensation products of alkyl phenols having an
alkyl group containing from about 6 to 12 carbon atoms in either
a straight chain or branched chain configuration, with about
5 to 25 moles of ethylene oxide per mol of alkyl phenol. A
typical example of the latter class is a condensation product
of ethylene oxide and/or propylene oxide with propylene glycol.
The water soluble condensation products of aliphatic
alcohols having from 8 to 22 carbon atoms, in either straight
chain or branched chain configuration, with alkylene oxide,
e.g., a coconut alcohol-ethylene oxide condensate having from
about 5 to about 30 mols of ethylene oxide per mol of coconut
alcohol (e.g., C]o~ C14 alcohol fraction), are also useful non-
ionic surfactant anti-foaming agents.
Specific examples of non-ionic anti-foaming agents
include ethoxylated octyl and nonyl phenol containing 5 to 12 mols
ethylene oxide and available commercially under such tradenames
as Triton CF-32, Triton X-100, Triton X-45, Stearox DJ, and
Igepal; and the polyoxyalkylene alcohols such as ~hose sold
commercially under the Pluronic trademark.
In addition, the silicone emulsion anti-foaming agents,
such as Antifoam AF, and others, available from Dow Chemical
Company, can be used.
, The amount of the anti-foam agen~ is not especially
critical and generally only that amount which is effective to
suppress foaming of the polyvinyl alcohol during ~le preparation
of the film casting solution will be used. Amounts in the range
of from about 0.005 to 1.0%, preferably from about 0.05 to 0.5%
* Trade Mark
_9_
~9~
by weig~lt, I)ased ol-l polyvinyl ~nlcollol solids, is satisfacl:ory.
~or ex~ e, wiLI-l 'r-r~ on C1'-32, about 0.1% of anti-foam agent is
sufficient.
'I`l~e so~ o~ g content or th~ aqueous coating solu-
tion will. be s~lecte(:L bssecl on ,he desirecl viscosi.ty and on the
cles:ired film thickness. Gellerally, solid contents in the range
of from aboll~ 5~/O to ahout 30~/O, ~refe-rc~hly from about 8% to about
20%, more preLe~ l`rc)rll about 10% to about 15~/~, and film
thicknesses in the range of from about 0.0005 to about 0.0l0 inch,
preferably from about 0.001 to about 0.005, more preferably from
about 0 001 to about 0.002, are satisfactory. Naturally, it is
preferable to minimize the amount of solvent as much as possible
so that the time requirecl for drying the deposited film will be
minirnized.
Any of the commercially available forms of water
soluble (i.e., partially hydrolyzed) polyvinyl alcohol are
suitable for use in the invention. Generally, degrees of hydrol
ysis wherein 99% or more of the acetate groups of polyvinyl
acetate are replaced hy hydroxyl groups are not water soluble,
while above 96% hydrolysis, the rates of solub.~lity may be too
;low or solubility in colcl water may be impaired. On the other
hand, at hydrol.ysis levels below about 85~/c, especially below
about 79%, the polyvinyl alcohol is not suf.fic:iently soluble.
Accordingly, partially hydrolyzed polyvinyl alcohol having a
degree o:f hydrolysis of from about 79% to about 95%, preferably
from about 85% to 90%, especially preferably from about 86~/~ to
89% is used as the water soluble polyvinyl alcohol component of
the polymer blend.
10-
to be compatible with and form homogeneous solutions and blends
with polyvinyl alcohol.
To achieve the desired degree of solubility in cold
and hot water, the rate of solubility and resistance to aging,
the polyvinyl pyrrolidone has a molecular weight in the range of
from about 10,000 to about 50,000, preferably from about 20,000
to about 50,000, especially from about 30,000 to about 48,000.
The polyvinyl alcohol and polyvinyl pyrrolidone are
blended with each other to provide weight ratios (on a dry matter
basis) in the range of from about 10:1 to about 1:1, preferably
from about 6:1 to about 2:1, more preferably from about 5:1
to 3:1 and especially about 4:1.
The properties of the water soluble films of the inven-
tion can be further improved by incorporating any of the known
plasticizers for polyvinyl alcohol into the aqueous casting
solution. In particular, the glass transition temperature, tg,
and brittle temperature, tf, is lowered so that the impact
strength of the film, and hence packages produced therefrom,
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~ ~3.~
WlliC~ l`C .su~ ct to low ter~ er<ll~sres and h~ idit-ies are great]y
improved. The preferred plas~icizers include polymerized glycerol
(e.g., Dow Cl~emic~ll (`o.'s Polyglycerol W-~ and glycol ethers,
(c g , tetrae~ ylelle ~lycol). O~:her s~ able plasticizers
inc:Lude, Eor exa~)le, gLycerol, cliettlylelle glycol, triethylene
glycol, poLyethylene glycol, alld o~her e~-hec polyols, triethanol-
amine, 1,3-butalledioL, Car[)owax~2000, triethanolamlne acetate,
ethanol acetamide, as well as the plasticizers mentioned in any
of the above-lr!entioned patenl:s. Mixtures of plasticizers can
also be used.
The amount of the plasticizer can vary wldely.
Generally, the plasticizer will be added to the aqueous casting
solution in amounts sufficient to provide about 0.5% to about 5%,
preferably about 1% to about 4%, more preferably about 2% to 3%
by weight, based on the weight o:E the entire cssting solution.
In terms of total polymer ~polyvinyl alcohol plus polyvinyl
pyrrolidone) content o:E the water soluble film, the amount of
the plasticizer in the Eilm is preferably from about 10% to 30%,
more preferably from about 15% to about 25% by weight.
In view of the biodegradability of the polyvinyl alcohol
and polyvinyl pyrrolidone components, it is often desirable to
include one or more biocides, especially bactericides, in the
,water soluble film. Generally, the biocide will be the last
'component added to the casting solution. The amount of biocide
is not particularly critical and will depend on the amounts of
the polymers an~ on the particular bioci.de. Generally, amounts up
to about 0.l%, based on the amount of the polyvinyl alcohol
solids will be sufficient.
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*
Trade Mark
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Any convelltiol-lal bacterici(ie can be selected so long
as it is compatible witll the polymer blend. The biocide should
be non-toxic to humans, especial:l.y for those appli.cations of the
water solub:le .f~ ns, SUCII as paclcagi.ng filnls :Eor detergents and
~ other cleaning agents, or for foodstuffs, where there is a
possibi:Lity that the components of ~he .E:ilm, when dissolved, will
come into con~act, directly or indirect:Ly, with the skin, or may
even be consu[ned Examples of suitable biocides include the
quaternary ammonium sal.ts, Alkyl (C8-Cl8) di lower alkyl benzyl
arnmonium chlorides, Di-isobutyl phenoxy ethoxy et-nyl dimethyl
. benzyl ammonium chloride, monohydrate, Alkyl (C9-C15) tolyl
methyl trimethyl ammonium chlor.ides, Cetyl pyridinium chloride or
bromide, N-myristyl benzyl-N,N-die-thyl-N-ethanol ammonium
chloride, Alkyl (C8-C18)dimethyl ethyl. benzyl an.,lonium chlorides,
Lauryl isoquinolinium bromide, Alkeny]. dimethyl ethyl ammonium
bromides, N(methyl heptyl-colamino-formyl-methyl) pyridinium
chloride, Cetyl dimethyl ethyl ammonium bromide, Lauryl pyridinium
chloride, Cetyl ethyl dimethyl a-mmonium bromlde, Tridecyl benzyl
hydroxy ethyl imidazolinium chloride, Dodecyl acetamido dimethyl
benzyl ammonium chloride, Polyalkyl naphthalene methyl pyridinium
chloride, Dialkyl dimethyl ammonium chloride, Dialkyl dimethyl
ammonium bromide, Myristamido propyldimethyl benzyl arnmonium
chloride, Myristyl-Y-picoliniurll chloride, N-N-N'-N'-tetramethyl
N-N'-didodecyl-~-hydroxy-propylene diammonium bromi.de, benzalkoniun
quaternary compounds, halogenated salicylonilides, hexa-
chlorophene, neomycin sulfate, bithionol, 3,4,4'-trichlorocarb-
. anilide, and the like. '~
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Al.thougll no~ wishing to be bound by any particular
theory, it is believed that the improved aging characteristics
of the water soluble films of this invention result from the
h:igll mol.ccu:lar comp(-lLibi.lity be~ween tlle polyvinyl alcoho] and
po:Lyvinyl pyrroli.done, and more particularly, because of the
abil:ity o:E the polyv:i.nyl pyrroli.done to interfere with the
inllerent tendency of the partially hydrolyzed polyvinyl alcohol
to undergo further hydrolysis (e.g., 96% or more) and become
insoluble. This pro tective mechanism appears to be a preferential
H-bonding o.E the polyvinyl. alcohol with carbonyl sites Erom the
polyvinyl pyrrolidone. This is macle possible because of the
compat:ibility of the two polymers, viz. the polyvinyl pyrrolidone
fits into the molecular lattice of the polyvinyl alcohol and,
thus, prevents further crystallization by spoiling the molecular
symmetry or per:Fection.
On a molecular scale, hydrolysis of partially
hydrolyzed polyvinyl alcohol can be represented by the :Eollowing
formula:
_ _ High Temperature,
~ i ~ ~ high R H. ~ .
,' ~ ~ OCi~3"/x\ 0~1 JY of inlkpresence OH
(I) (I-A)
x ~5 to 20 mole %
y ~80 to 95 mole %
yl~96 to >99 mole %.
The mechanism of aging st~biliz.~tion flgl~inst f~lrther
hydrolysis can be represented by ~he following formula:
[t~+ ,~ ged as ab ~
-' ¦m
(III)
where formula (III) shows the interference ~-bonding between the
,polyvinyl pyrrolidone and polyvinyl alcohol. The hydrogen bonded
structure (III) interferes sterifially and electronically with
continuing hydrolysis (as well as internal ~-bonding) of the
polyvinyl alcohol (I) which thereby prevents the conformational
perfection of structure (I-A) which would result in high order
crystallinity and insolubilizatio~.
In any case, by whatev~ mechanism, it has been found
that the water soluble films of ~is invention exhibit superior
resistance to aging in low temp~ature/~ow humidity and high
temperature/high humidity condi~ions, i.e,, remain soluble in
icold water, do not become soft ~r tacky, retain high mechanical
strength, etc., as compared to a~nventiQnal water soluble films
,based on polyvinyl alcohol.
,i The water soluble films are heat sealable and are
readily formed into packages. For ins~a~ce,~two sheets of water
soluble ril~ call be placcd OllC oVer ~lle ~ r and lleaL scaled
along three edges. The dry, water-soluble commodity, e.g., dry
laundry powder, is loaded into the package through the remaining
,l open edge which can then also be heat sealed. It is a particular
advantage of the invention that even after storage of tlle water
soluble films for extended periods at low temperature/low humidity
and/or high temperature/high humidity conditions, the heat seal-
ability of the films are not adversely effected. The elasticity,
strength, clarity, as well as high rate of solubility, even in ice
cold water conditions~ of the films also withstands any adverse
effects from the ambient conditions.
The invention will now be illustrated by specific
embodiments in the following non-limiting examples, in which all
"parts" and "percents" are "by weight" unless otherwise noted.
Example_l
An aqueous casting solution is prepared by first forming
a 10~/o solids solution of polyvinyl alcohol (88% hydrolyzed,
molecular weight in the range of 22,000 to 31,000) by forming a
disp~rsion of thepolymer in cold water, adding about 0.1% of
nonionic anti-foam agent (Triton CF-32) to the dispersion, and
then solubilizing by heating the dispersion to a temperature of
180F to 220F with vigorous stirring. To eighty parts of the
polyvinyl alcohol solution (10% solids), 2.5 parts of tetra-
~ethylene glycol plasticizer is added. 6.65 parts of a commer-
cially available aqueous solution (30% solids) of polyvinyl
pyrrolidone (PVP K-30, molecular weight 40,000) is added to
the plasticized polyvinyl alcohol solution. The casting solution
is adjusted to 100 parts with water (10.85 parts water) to form
an aqueous casting solution containing 12.5 parts (12.5%) of
-16-
nctive inr,re(lien~s, i.c., p(-lylllers an(l plasti.ci~.er. To-this
casting solution, about 0.5% biocide/perservative (GIV-GARD DXN,
a product of Givaudan Corp.), based on the amount of polyvinyl
alcohol solids, is added. All ingredients are blended using
S vigorous agitation to assure homogeneity.
From the aqueous casting solution, films are prepared
with both a 4-inch and 8-inch Gardener film casting knife using
a blade clearance of 22~24 mils. The casting solution is
,deposited on either Mylar polyester or plasticized polyvinyl
chloride sheets as the casting surface. After drying in air
overnight, clear films are obtained having a thickness of
0.0015 inches.
IExample 2
Example 1 is repeated except that 3.~5 parts of
polyglycero]. (75% solids) is used as plasticizer in place of
2.5 parts of tetraethylene glycol and the amount of water is
; adjusted from ln.85 parts to lO.0 parts to again give a casting
sol~tion with 12.5% of active solids.
. .
; * Trade Mark
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