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BACKGROUND OF INVENTION
This invention pertains to the art of packaging materials, with particular
reference to packaging films. More specifically, it relates to synthetic
polymer packaging materials made of polyvinyl alcohol used to package
materials which are sensitive to oxygen and water vapor.
Currently available synthetic polymers which are used for packaging food
stuffs, medicines and related substances, have a substantial rate of
oxygen permeability and water vapor transmission so that the foods and
medicines packaged in these materials suffer substantial degradation,
thereby losing their taste, potency or customer appeal.
Of the various polymer systems which have been considered as barrier
packaging materials, polyvinyl alcohol ranks among the best. Polyvinyl
alcohol forms tough clear films which are known for their abrasion
resistance and high tensile strength. The oxygen barrier quality of
polyvinyl alcohol is superior to all other polymers; however, this quality
has been subject to severe degradation at high humidities. Polyvinyl
alcohols presently known show a rapid loss of gas barrier performance
above 50% relative humidity. In addition, these polyvinyl alcohols
demonstrate significantly poorer barrier properties below the 95%
hydrolysis level.
In general, the use of one polymer in an extruded film does not provide
sufficiently long package life to materials susceptible to oxygen
deterioration, and multiple-ply films have been developed for these uses.
These multiple-ply products are made by post-lamination or co-extrusion
near melt temperatures of a number of different types of polymeric
materials to provide optimum life to pre-packaged goods sensitive to
oxygen deterioration. It has been conventional to laminate a polyvinyl
alcohol core between two outer layers of other polymers which provide a
structural support for the polyvinyl alcohol core which provides the gas
barrier properties.
The literature indicates that films of polyvinyl alcohol (PVOH) have
usually been produced from aqueous solutions or in the presence of some
water in conjunction with plasticizers. Conventional technology recognized
high-boiling, water-soluble organic compounds containing hydroxyl groups
as the most effective plasticizers for polyvinyl alcohol (see, e.g.
Kirk-Othmer, Encycl. of Chemical Technology, 3d ed., 1983, vol. 23, p.
854). Glycerine and various glycols are the most widely used plasticizers.
Glycerine has frequently been used with water, and water/plasticizer mixes
were the most common methods for preparing films and formed objects even
after the work of Takigawa which resulted in U.S. Pat. No. 3,607,812 in
1971, when he used glycerine in the absence of water. Even in texts
published at a later date, practical methods of fabrication involving PVOH
invariably use water as a component in addition to the plasticizer in
forming extruded products.
Melt processing additives have been used with PVOH to facilitate extrusion
because extrusion of PVOH into a usable form is impossible as a dried
powder. This inability to extrude arises from the melt temperature of PVOH
being very close to its decomposition temperature, with the rate of
decomposition being time and temperature dependent. It will decompose at
the melting temperature of about 232.degree. C., if exposed to this
temperature for a short period of time. PVOH will also decompose at lower
temperatures when left for significantly longer times, even at
temperatures as low as 180.degree. C.
It is common in the art to provide additives to decrease the melt
temperature of the PVOH system thereby avoiding or minimizing rapid
decomposition. It is also known that a PVOH which contains over 5%
unhydrolyzed polyvinyl acetate, or which contains a hydroxyl containing
plasticizer, will melt at a lower temperature. Thus, the melting
temperature of PVOH homopolymer is 232.degree.-235.degree. C. while the
melting temperature of a PVOH copolymer containing 12% unhydrolyzed
polyvinyl acetate is 195.degree. C. The addition of about 10% glycerine, a
hydroxyl containing plasticizer, to either the homopolymer or the
copolymer lowers the melting temperature 7.degree. to 10.degree. C. This
is one reason why glycerine and various glycols are the most widely used
plasticizers.
Formed products are presently fabricated using water or a water/plasticizer
combination so as to decrease the melt temperature of the PVOH and thereby
avoid or minimize rapid decomposition. Homopolymers of PVOH, copolymers
with methyl methacrylate (up to 6%), and copolymers with vinyl acetate (up
to 15%) have been extruded with water/plasticizer mixtures by removing the
water prior to the polymer leaving the die as a melt or by using a special
extrusion technique.
PVOH is prepared by the hydrolysis of polyvinyl acetate (PVAc). Until the
early 1970's, the term "polyvinyl alcohol" was used in the literature to
describe both partially hydrolyzed PVAc and PVAc which has been
substantially fully hydrolyzed to PVOH. It is now conventional to describe
materials which are at least 95% hydrolyzed as PVOH homopolymer and those
which are less than 95% hydrolyzed as PVOH/PVAc copolymer.
Since the homopolymer and the copolymer are not equivalent in all their
properties, and in particular, demonstrate different water solubilities at
ambient temperatures and different permeabilities to gases such as oxygen
and carbon dioxide, early references to PVOH may be misleading. It is
important to identify the degree of hydrolysis of the material.
Homopolymer and copolymer cannot be treated as being equivalent.
Exemplary of the many water containing polyvinyl alcohol compositions is
Pockel, U.S. Pat. No. 2,963,461, (Dec. 6, 1960) who discloses a novel
hydroxyl containing plasticizer for polyvinyl alcohol. Primarily
interested in cast polyvinyl alcohol in which water is added to the
polyvinyl alcohol system, Pockel also discloses extrusion of polyvinyl
alcohol in systems where no water is added to the polyvinyl
alcohol/hydroxyl-containing plasticizer system. Depending on the relative
humidity of the environment, the highly hygroscopic polyvinyl alcohol used
would have contained from about 5% to about 15% water.
The following references exemplify the art relating to the extrusion of
PVOH in the absence of water.
The 1965 work, Physics of Plastics, edited by P. D. Ritchie, discloses, at
page 350, that polyvinyl alcohol is normally plasticized when used to
produce sheet and rod. It further discloses that glycerol (hydroxyl group
containing) and p-toluene sulphonamide (non-hydroxyl containing) are
suitable plasticizers. No mention is made of drying the composition before
extrusion.
The first clear description of a substantially anhydrous (less than 2%
water) system does not appear until 1971, in Takigawa et al, U.S. Pat. No.
3,607,812, (Sept. 21, 1971). A conventional polyvinyl alcohol is utilized
with a hydrolysis degree of at least 97% and a polymerization degree of
700-1500. The plasticizer is a polyhydric alcohol and the extrusion is
done at moisture contents of less than 2%.
Coker, U.S. Pat. No. 3,977,489, (Dec. 14, 1976) discloses combinations of
waxes and fatty acid derivatives to aid in the melt flow of polymers such
as those disclosed by Takigawa. Coker's melt extrudable PVOH contains:
(1) a hydrocarbon oil or wax, (2) a polyethylene wax or ethylene polymer,
and (3) optionally, a plasticizer. Hydroxyl and non-hydroxyl containing
plasticizers are disclosed and no reference is made to the presence of
water.
Yamata, Japanese Pat. No. 52-65548, (May 31, 1977) discloses a polyvinyl
alcohol composition prepared from at least 70% hydrolyzed polyvinyl
alcohol having a polymerization degree of between 500 and 3000 and a
specified plasticizer, both of which may have been dehydrated before
mixing.
Yamata's plasticizer may be non-hydroxyl containing (aromatic sulfonamides)
or hydroxyl containing (p-hydroxybenzoic acid esters) and is present in
amounts ranging from about 5% to about 67% by weight of the composition.
Yamata's plasticizer is claimed to provide a PVOH material which has
lessened solubility in water or heated water, lessened volatility during
melt molding and lessened sweating (the tendency of the plasticizer to
migrate to the surface which then becomes sticky at high temperatures and
humidities).
Three of the references discussed above disclose non-hydroxyl containing
plasticizers: Physics of Plastics in 1965, Coker in 1976 and Yamata in
1977. In each case, the reference also discloses hydroxyl containing
plasticizers and does not distinguish between the two types of
plasticizers. These references teach that there is an equivalence between
hydroxyl containing and nonhydroxyl containing plasticizers for polyvinyl
alcohol and that the two types of plasticizers are interchangeable.
Polyvinyl alcohol has been blended with copolymers to provide properties
enhanced for special applications or to solve certain problems. In all
cases, these references use conventional polyvinyl alcohols and do not
disclose the use of nonhydroxyl containing plasticizers in conjunction
with an anhydrous environment to provide enhanced gas barrier properties.
Thus, Schroeder, U.S. Pat. No. 4,254,169, (Mar. 3, 1981) discloses
multi-layer films with a core layer of polyvinyl alcohol or ethylene-vinyl
alcohol copolymer prepared by conventional means.
European patent publication No. 0,063,006 (Oct. 20, 1983) discloses
ethylene-vinyl alcohol copolymer blends and a process for manufacturing
films from such copolymers.
It is apparent from the above review of the background of the invention and
the state of the art, that completely hydrolyzed polyvinyl alcohols and
copolymers of polyvinyl alcohol with polyvinyl acetate and other
polymerizable monomers and in particular olefin modified polyvinyl
alcohols have outstanding usefulness because of their very low gas
transmission rates, at low relative humidities, particularly for gaseous
oxygen. It is well known in the packaging art that the principal cause of
packaged goods' deterioration with storage age is due to oxidative
deterioration. Thus, the art is replete with attempts to produce films and
molded articles utilizing polyvinyl alcohol as at least one layer of a
packaging material to inhibit oxygen transmission through the packaging
material at both low and high relative humidity levels.
These attempts have not been successful. There is today no satisfactory
polyvinyl alcohol homopolymer composition which can be formed by
conventional techniques and which exhibits a desirable level of
impermeability to gases at high relative humidities.
SUMMARY
The present invention overcomes the deficiencies of the prior art by
providing polyvinyl alcohol compositions which are easily extrudable and
which produce formed articles which have superior properties, including
clarity, enhanced gas impermeability at high relative humidities and
freedom from pin holes. The formed articles of the present invention are
useful as packaging materials which can be used where superior resistance
to gases, particularly at high humidities, is required. In addition, the
present invention provides a composition which can be melt extruded in a
conventional extruder used in processing well known commodity polymers,
such as nylon, polyethylene and the like. The extruder can be adapted to
the melt forming of the polymeric compositions disclosed by applicants
without extensive modification or total replacement of equipment.
In accordance with the present invention, formable polyvinyl alcohol
compositions are provided where the polyvinyl alcohol compositions
comprise a mixture of
1. a polyvinyl alcohol selected from
a. polyvinyl alcohol homopolymers; or
b. blends of polyvinyl alcohol homopolymers and polyvinyl alcohol/C.sub.2-4
polyolefin copolymers wherein
1. the polyvinyl alcohol homopolymer is at least 25% by weight of the
mixture; and
2. the polyolefin moiety in the copolymer is not more than about 45% by
weight of the copolymer; and
2. a hydroxyl-free organic plasticizer; such plasticizer
a. being substantially water insoluble;
b. having a solubility parameter greater than 10 (cal/cc).sup.1 ; and
c. having negligible vapor pressure at forming temperatures.
Polyvinyl alcohol which contains no more than 5% residual polyvinyl acetate
is known conventionally and is herein described as homopolymer; polyvinyl
alcohol with more than 5% polyvinyl acetate or which contains another
polymer is conventionally known and is herein described as copolymer.
The plasticizers of the present invention are most easily distinguished
from those which are conventionally used in that they must be free of --OH
groups. Hydroxyl-free plasticizers have been known in the art for some
time but they have always been treated as being functionally equivalent to
hydroxyl group containing plasticizers.
It is known that hydroxyl group containing plasticizers depress many of the
desirable mechanical properties of the formed article, and in particular,
lower the gas barrier properties to a substantial degree at high relative
humidity. Surprisingly, we have now discovered that non-hydroxyl group
containing plasticizers do not depress the desirable mechanical properties
of the formed article to the same extent. Most importantly, the
non-hydroxyl group containing plasticizers of the present invention, when
used in the process of this invention, provide formed articles with
superior gas barrier properties at high relative humidities.
Also provided in accordance with the present invention, is a process for
producing polyvinyl alcohol articles of manufacture possessing enhanced
gas barrier properties at high humidities. Such process comprises the
steps of mixing a polyvinyl alcohol with a non-hydroxyl group containing
plasticizer for polyvinyl alcohol, melting the mixture, forming the melted
mixture, in substantially water-free conditions, into articles of
manufacture and cooling the formed articles. Critical to the practice of
this process is a step involving heating the polyvinyl alcohol mixture or
the formed article to a temperature of at least 200.degree. C. and then
slowly cooling at a rate sufficiently slow to provide an oxygen
permeability of no more than 1 cc. mil/100 in.sup.2 24 hrs. atm at
25.degree. C. and 80% relative humidity. The heating/cooling step may be
accomplished during mixture melting and forming or it may be accomplished
by post-forming heating of the articles of manufacture.
Finally, in accordance with the present invention, there are provided
articles of manufacture formed from the disclosed compositions and having
the desired oxygen permeability characteristics.
This invention also provides a melt extrudable polymer composition of
matter which in its plural forms provides, for example, packaging
materials in several forms such as bottles and flexible films which have
exceptional resistance to the transmission of gases, particularly oxygen,
through the films or walls of such packages.
It is an object of this invention to provide new polyvinyl alcohol
packaging materials for foods, medicines and related objects such that the
superior gas barrier properties of the polyvinyl alcohol at low humidity
levels are substantially maintained at higher humidity levels.
It is another object of this invention to provide new polyvinyl alcohol
compositions with enhanced processing characteristics.
It is a further object of this invention to provide extruded, multi-layer
articles of manufacture which are suitable for use as containers for foods
and other oxygen sensitive materials.
It is yet another object of this invention to provide a process for the
manufacture of formed polyvinyl alcohol articles having an oxygen
permeability at 25.degree. C. and 80% relative humidity of not more than 1
cc mil/100 in.sup.2 24 hr. atm.
DETAILED DESCRIPTION OF THE INVENTION
It has been found that surprising enhancement of the processability of
polyvinyl alcohol compositions and of the characteristics of articles
manufactured from such compositions can be obtained through the use of the
specified polyvinyl alcohols plasticized by non-hydroxyl group containing
plasticizers, formed in a substantially water-free environment and cooled
below a critical rate.
The polyvinyl alcohols useful in this invention are those selected from
a. polyvinyl alcohol homopolymers; or
b. blends of polyvinyl alcohol homopolymers and polyvinyl alcohol/C.sub.2-4
polyolefin copolymers wherein
1. the polyvinyl alcohol homopolymer is at least 25% by weight of the
mixture; and
2. the polyolefin moiety in the copolymer is not more than about 45% by
weight of the copolymer.
Polyvinyl alcohol homopolymers having a polyvinyl alcohol content in excess
of 96% are more effective gas barriers. When the polyvinyl alcohol content
is in excess of 98% and most preferably when the polyvinyl alcohol content
is 99+%, the most outstanding gas barrier properties are obtained.
A preferred polyvinyl alcohol copolymer is an ethylenevinyl alcohol
copolymer where the olefin moiety is in the range of from about 5% to
about 40% of the copolymer.
Ethylene is a preferred olefin since ethylene-vinyl alcohol copolymers are
presently commercially available. Other useful members of this class are
described in Gardener at al, U.S. Pat. No. 3,585,177 assigned to Monsanto
Company, and contain from about 8% to about 35% of a 2-4 carbon atom
olefin modification including ethylene, propylene and isobutylene.
Physical admixtures of the polymers described may also be used and are
selected using well known criteria for quality and price variations of the
ultimate products and their specific uses and articles including
co-extruded films, laminates, injection molded articles, blow molded
articles, monofilaments and films used alone or as substrates for
packaging.
Polyvinyl alcohol polymers generally useful may vary in molecular weights
within the range of from about 22,000 to about 150,000 (polymerization
degree of from about 500 to about 3500). It is preferred to use polymers
having a polymerization degree of from about 700 to about 3400. Polymers
of varying molecular weight ranges may be co-blended to modify, regulate
and control the melt viscosity and melt temperature. It is convenient to
blend polymers with a molecular weight in the range of about 30,000 to
about 40,000 with those with a molecular weight of about 70,000 to about
140,000.
The plasticizers useful in this invention are characterized as
A. substantially water insoluble;
B. organic;
C. non-hydroxylated;
D. having a solubility parameter greater than 10 (cal/cc).sup.1/2 ; and
E. having negligible vapor pressure at forming temperatures.
We have discovered that these plasticizers do not function in the same
manner as conventionally used plasticizers. As discussed above,
conventional hydroxyl-group containing plasticizers are chosen, inter
alia, for their ability to depress the melt point of the polyvinyl
alcohol, generally in the range of 7.degree. to 10.degree. C.
Surprisingly, the plasticizers of this invention do not depress the melt
point of the polyvinyl alcohol to any great extent.
For reasons not yet fully understood, the plasticizers of the present
invention do not depress the mechanical properties of formed articles at
high relative humidities to the same extent as hydroxyl group containing
plasticizers. Surprisingly, and most importantly, the non-hydroxyl group
plasticizer containing compositions enable one, utilizing the disclosed
process, to produce articles of manufacture having substantially improved
oxygen barrier properties at high relative humidities.
Classes of compounds falling within this group include N-substitute
C.sub.10-22 fatty acid amides; aryl, alkaryl, N-alkaryl aryl, N-aryl
alkaryl, N-aryl aryl and N-alkyl alkaryl sulfonamides; aryl and alkaryl
phosphates and phosphites; sulfonated alkyl phenols; N-alkyl pyrrolidones;
alkylene carbonates and selected admixtures thereof.
Preferred classes include N-substituted C.sub.10-22 fatty acid amides,
alkaryl and N-alkyl alkaryl suldonamides, sulfonated alkyl phenols,
N-alkyl pyrrolidones, alkaryl phosphates, alkylene carbonates and selected
admixtures thereof.
Specific members of the above classes which are readily available from
commercial sources include the following preferred plasticizers:
para-toluene sulfonamide, sold under the trademark "Santicizer 9"; a
mixture of ortho-and para-isomers of N-ethyl toluene sulfonamide, sold
under the trademark "Santicizer 8", both available from Monsanto Company;
sulfonated alkyl phenols sold under the trademark "MESAMOLL", available
from Mobay Chemical Company; (isopropyl phenyl) di-phenyl phosphate, sold
under the trademark "KRONITEX 50", available from FMC Corporation;
dimethyl amides of oleic acid, sold under the trademark "HALLCOMID M
18-OL", available from C. P. Hall Company; N-cyclohexyl pyrrolidone,
available from GAF Corporation; and ethylene or propylene carbonate,
available from the Texaco Company.
In its most preferred embodiment, this invention contemplates the use of a
mixture of an N-alkyl alkaryl suldonamide and a sulfonated alkyl phenol as
the plasticizer.
The polyvinyl alcohol composition contains from about 4% to about 30% by
weight of the composition of the plasticizer. It is preferable to employ
from about 5% to about 20% and most preferable to employ from about 7.5%
to about 12.5% plasticizer.
The polyvinyl alcohol and plasticizer may be formulated in advance of the
forming operation or may be formulated just prior to and directly in
commercial forming operations. The polyvinyl alcohol and plasticizer
should preferably be substantially water free (less than 2% water) at the
time of formulation and most preferably should be anhydrous to minimize
post formulation drying procedures. Regardless of the water content at the
time of formulation, the mixture must be substantially water free and most
preferably anhydrous when the forming operation takes place.
The compositions of the present invention may be formed by any conventional
means such as drawing, coining, or impact forming, and it should be
understood that the following discussions, describing forming by
melt-extrusion, are non-limiting and that the discussion applies, mutatis
mutandis, to other forming methods.
The use of the substantially water free compositions of this invention in a
readily feedable particulate form is advantageous in melt extrusion, blow
molding and injection molding operations. Availability of such forms of
the invention would assist in the manufacture of articles as described by
Schroeder in U.S. Pat. No. 4,254,169, Mar. 3, 1981, and Ortolani et al in
British Pat. No. 1,544,780, without the requirement of proportionate
feeding equipment and other equipment essential to pre-blending.
A drying step before melt extrusion is desirable as polyvinyl alcohol in
all its forms is hygroscopic, acting as a dessicant for water, and
production worthy products may be obtained only on using the dry materials
of this invention.
The melt extrusion of the above polyvinyl alcohol polymeric compositions
under substantially water free, preferably anhydrous, conditions produces
clear, bubble free films characterized by extremely low gas transmission
rates, particularly oxygen. Water may be removed from the composition at
any time prior to exit from the extrusion die.
Extrusion is accomplished in a conventional manner, in conventional
equipment when the composition has been previously dried. The extrusion
temperature will be in the range of from about 210.degree. C. to about
250.degree. C., preferably from about 220.degree. C. to about 235.degree.
C., and most preferably from about 228.degree. C. to about 233.degree. C.
It is important to the practice of the present invention that the polyvinyl
alcohol compositions, having gone through a heat forming step or where the
compositions have otherwise been heated to a temperature of above
200.degree. C., are then allowed to cool at a rate sufficiently slow to
allow the formation of enhanced gas barrier properties. Most
advantageously, the slow cooling step will be accomplished immediately
after the heat forming step in which the polyvinyl alcohol composition
will have been heated to above 200.degree. C. The slow cooling step may
also be accomplished after the formed articles have been otherwise cooled.
In this case, the formed articles are quickly heated to about 200.degree.
C. and then slowly cooled.
The time necessary for cooling, and the rate of cooling varies with
different forming processes, the temperature at which forming took place,
the specific PVOH used and the ratio of plasticizer to polymer. In
general, it can be said that the enhanced properties will be obtained if
the polyvinyl alcohol compositions are allowed to cool without the
application of cooling means. Commercially, however, it is desirable to
cool the material relatively quickly by application of cooling means to
maintain equipment through-put.
In a preferred embodiment of the present invention, the PVOH is formed into
a film by a chill roll melt-extrusion process. In this process for
extruding plastic film, it is conventional to immediately advance the
extruded and still plastic film onto a metal take-off roll which
immediately cools the film to the temperature of the roll by absorbing the
heat content of the film. This tends to raise the temperature of the roll.
The absorbed heat is removed by circulating a cooling means through the
rolls at a rate or at a temperature sufficient to maintain the rolls at an
elevated temperature.
Unlike the prior art, where the rolls are maintained at a temperature
substantially below that of the still plastic extruded material, in the
process of the present invention, the rolls are maintained at a
temperature just below the point at which the extruded material begins to
stick to the roll. This temperature will provide a rate of cooling
sufficiently slow to allow maximum gas barrier properties to develop while
maintaining acceptable production rates. Once the extruded material has
passed over the rolls and solidified, the rate of cooling is not as
critical and further cooling to ambient temperatures may be accomplished
by any conventional means.
Other cooling means may be used as, for example in blown film extrusion
where an air stream flowing across the surface of the formed article is
the cooling means. The temperature and flow rate of the air stream are
interdependent and are in turn dependent on the shape of the formed
article and on the temperature and rate of extrusion.
If the rate of cooling is too fast, the gas barrier properties of the
formed article will not be obtained. For example, if the material, having
just been extruded at about 230.degree. C. is brought into immediate
contact with a roll maintained at 45.degree. C. the rate of cooling is so
fast that the desired gas barrier properties will not be achieved. Once
the forming process and the specific PVOH compositions within the scope of
the present invention have been chosen, it is a simple matter for a
skilled artisan to arrive at appropriate processing temperatures and time.
The slow cooling step of this invention will provide articles having an
oxygen permeability of 1 cc mil/100 in.sup.2 24 hr. atm or less when used
with the polyvinyl alcohol compositions described in this specification.
The slow cooling step, used with PVOH compositions outside the scope of
the present invention, will not provide the desired gas permeability
properties.
Articles manufactured in accordance with this invention will have oxygen
permeabilities (in cc. mil/100 in.sup.2 24 hr. atm., at a temperature of
25.degree. C. and at an eighty (80) percent relative humidity) of no
greater than about 1. It is preferred to select combinations of polyvinyl
alcohols, plasticizers and processing parameters such that the oxygen
permeability is less than about 0.5. For many applications, oxygen
permeabilities of about 0.25 or below are preferred. Suitable selection of
components following the teaching of this disclosure will allow one
skilled in the art to achieve a most preferred embodiment where the oxygen
permeabilities are about 0.1 or below.
Oxygen permeabilities as used herein are measured on an Ox-Tran instrument
supplied by Modern Controls, Inc., Minneapolis, MN. This instrument
consists of a means for securing the test specimen, an oxygen specific
coulometric detector, an oxygen injector and bubblers for humidifying
gases.
EXAMPLES
The following examples illustrate actual reduction to practice of the
invention and establishment of utility thereof.
EXAMPLE 1
One hundred parts by weight of a 99% hydrolyzed polyvinyl alcohol
homopolymer having a weight average molecular weight of about 100,000
(Elvanol 71-30) after drying at 160.degree. F. for 16 hours was intermixed
with 20 parts of p-toluene sulfonamide (Santicizer 9), 10 parts of a
mixture of the ortho and para isomers of N-ethyl toluene sulfonamide
(Santicizer 8) and 2 parts of zinc stearate as lubricant. After extensive
blending at high shear rate, the mixture was extruded through a 3/4"
extruder equipped with a three inch slot die and placed immediately after
exit onto a roll that was maintained at a temperature just below the
temperature where the web would start to adhere to the roll. The extruder
had a temperature profile of 150.degree., 195.degree., 227.degree. C. from
the throat to the metering section with a die temperature of 215.degree.
C. Extruded films drawn to a thickness of two mils extruded well, were
clear of surface defects and bubbles and indicative of commercially
acceptable quality.
EXAMPLE 2
Ninety parts by weight of a fully hydrolyzed polyvinyl alcohol homopolymer,
having a molecular weight of about 35,000 (Elvanol 90-50), ten parts by
weight of a mixture of the ortho and para isomers of N-ethyl toluene
sulfonamide (Santicizer 8), and two parts stearamide were thoroughly mixed
and dried for 2.5 hours at 80.degree. C. The mixture was intensively mixed
and fed into an extruder with a temperature profile of 150.degree.,
195.degree., 238.degree. | | |
