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BACKGROUND OF THE INVENTION
The present invention relates to a method of producing shaped articles
having biodegradability by melt molding, in particular to a method of
producing said shaped articles by melt molding under substantially
plasticizer-free and substantially anhydrous conditions.
The invention also relates to water-soluble fibers which are useful in the
production of chemical laces or nonwoven fabrics, or as water-soluble
hot-melt adhesives.
The invention further relates to laminates comprising an oxyalkylene
group-containing vinyl alcohol copolymer film layer and a thermoplastic
resin layer an showing good degradability and interlaminar bonding.
The invention still further relates to containers for filthy waste matter,
in particular bags or pouches for collecting excreta from the artificial
anus, which have good water resistance, odor-retaining property,
flexibility and non-sound-producing property as well as favorable feel and
touch and which can be thrown into the flush toilet bowl and, after such
throwing, can be degraded so that the environmental pollution can be
minimized.
Biodegradable Shaped Articles
Waste plastic moldings, such as plastic films used as materials for
agricultural purposes, tapes and bands for binding or packaging purposes
and plastic films thrown away by routes other than regular ones, can long
retain their shape or form and are producing serious environmental
pollution problems. It is therefore desirable that such molded articles to
be possibly thrown away outdoors or in rivers, for instance, should be
degraded by microorganisms in the soil or water after achievement of their
intended purposes.
Under these circumstances, intensive studies have recently been made to
develop biodegradable moldings.
It is known that incorporation of starch or a starch-derived macromolecule
is effective in rendering plastic moldings biodegradable.
Japanese Kokai Tokkyo Koho No. 2-14228, for instance, discloses a
compounded polymer material obtained from a melt containing
water-containing degraded starch and at least one substantially
water-insoluble synthetic thermoplastic polymer. In this case, the
specification mentions that water-soluble polysaccharides, cellulosic
polymers, water-soluble synthetic polymers and the like may be used as
further additives.
U.S. Pat. No. 3,949,145 discloses a degradable multilayer film for
agricultural use which comprises a film consisting of 1 to 4 parts by
weight of polyvinyl alcohol having a saponification degree of 85 to 100
mole percent, 8 parts by weight of starch and 1 to 5 parts of glycerol and
a water-resistant coating layer made of a mixture of 0.1 to 0.2 part by
weight of a free isocyanate group-containing polyol-toluenediisocyanate
prepolymer and 1 part by weight of a vinylidene chloride-acrylonitrile
copolymer or plasticized polyvinyl chloride.
The present applicants have filed an application for patent concerning a
polyvinyl alcohol-starch film comprising polyvinyl alcohol having a
saponification degree of at least 93 mole percent and starch species and
stretched at least uniaxially (Japanese Patent Application No. 63-307225).
Film production from thermoplastic resins for general use, such as
polyolefins, with starch or a starch-derived macromolecule incorporated
therein has already put into practice. However, it is only the starch or
starch-derived macromolecule in molding that shows biodegradability.
Therefore, while the moldings may lose their film-like or other shape, the
thermoplastic resin portions, such as polyolefin portions, will remain
undegraded for a long period of time.
Meanwhile, it can be expected that films or other articles molded from a
composition comprising a water-soluble resin, such as polyvinyl alcohol,
and starch or a starch-derived macromolecule would meet strength
requirements and allow not only the starch or starch-derived macromolecule
but also the water-soluble resin (e.g. polyvinyl alcohol) portions to be
biodegraded.
However, polyvinyl alcohol intrinsically has a thermal decomposition point
close to its fusion temperature, hence can hardly be molded by melt
molding under anhydrous conditions. For smooth molding, it is necessary to
subject an aqueous solution to film casting or add a considerable quantity
of water or a plasticizer (e.g. glycerol) and carry out molding in a fused
and dissolved state. Molding a composition comprising polyvinyl alcohol
and starch or a starch-derived macromolecule has similar limitations.
Film casting using an aqueous solution of polyvinyl alcohol (or a
composition comprising the same and starch or a starch-derived
macromolecule) has drawbacks: for instance, a step is required for
preparing said aqueous solution, the rate of film formation is slow, and
long time is required for drying after film formation. The technique of
molding which comprises adding a considerable amount of water and carrying
out molding in a fused and dissolved state is also disadvantageous in that
a long drying time is required after molding. In addition, the moldings
thus obtained will lose their flexibility under low humidity conditions.
This restricts their applications severely. The use of a plasticizer for
securing flexibility produces a new problem, namely the bleeding problem
due to the plasticizer incorporated.
The technique which comprises incorporating a considerable amount of a
plasticizer into polyvinyl alcohol (or a composition comprising the same
and starch or a starch-derived macromolecule) and carrying out molding in
a fused and dissolved state may be satisfactory from the film formation
rate viewpoint but encounters problems from the quality viewpoint, namely
bleeding due to the plasticizer incorporated or sticking together of
moldings.
Accordingly, it is an object of the invention to provide a method of
producing biodegradable shaped articles by which the problems mentioned
above can be solved.
Water-Soluble Fibers
Water-soluble polyvinyl alcohol resins are used widely in textile
processing or treatment, especially in the so-called special processing,
such as hard finishing of cloths, pigment printing, flock working, pasting
cloths together, or nonwoven fabric manufacture. Their characteristics are
well displayed particularly when used in special fields where their water
solubility should be utilized, for example when used as fibers for
chemical lace manufacture, as binders of nonwoven fabrics, or as
water-soluble fibrous binders.
In such applications, polyvinyl alcohol is eventually dissolved and removed
by washing with water. In this case, that the polyvinyl alcohol to be used
has a high water solubility is advantageous from the industrial viewpoint
since a higher water solubility leads to a higher removal efficiency,
hence to a reduction in the time required for the washing step.
However, water-soluble fibers produced from the conventional polyvinyl
alcohol species, though they have a considerable degree of water
solubility, cannot always satisfy the recent increasing demand for more
speedy processing.
Furthermore, in the production of water-soluble fibers themselves, it is
necessary to prepare an aqueous solution of polyvinyl alcohol by blending
with water and a plasticizer and subjecting the solution to dry spinning
through a nozzle. Thus a long time and a number of complicated steps are
required for the preparation of said aqueous solution of polyvinyl alcohol
treatment of the solution, such as defoaming, and for drying following
spinning, so that the productivity can hardly be said to be satisfactory
for the practice on a commercial scale. On the contrary, the melt spinning
method seems advantageous since it does not require the preparation of an
aqueous solution of polyvinyl alcohol but only requires heating polyvinyl
alcohol for melting, if necessary after admixing with a plasticizer.
However, the fusion temperature of polyvinyl alcohol is intrinsically
close to the thermal decomposition point, so that products obtained by
melt spinning tend to have been degraded or colored. The use of a
plasticizer in larger amounts in an attempt to avoid such problem will
produce other problems such as mutual adhesion of the fibers obtained to
make their handling troublesome. Fibers which can be produced by melt
spinning without concomitant use of a plasticizer in large quantities and
are higher in water solubility, if developed, would be very advantageous
from an industrial or commercial viewpoint.
The present inventors have previously proposed fibers produced from
oxyalkylene group-containing vinyl alcohol copolymers as a result of
intensive investigations to solve the problems mentioned above. The use of
oxyalkylene group-containing vinyl alcohol copolymers indeed makes it
possible to carry out melt spinning without the combined use of a
plasticizer in large amounts but does not result in a marked increase in
the water solubility of the fibers. Development of further fiber species
is needed.
As a result of intensive investigations, the present inventors found that
water-soluble fibers produced from a composition comprising an oxyalkylene
group-containing vinyl alcohol copolymer and starch or a starch-derived
macromolecule can meet the demand of the art and, based on this finding,
have now completed the present invention. Thus it is an object of the
invention to provide such water-soluble fibers.
Laminates
Oxyalkylene group-containing vinyl alcohol copolymers show improved
flexibility and mechanical strength while retaining characteristics of
vinyl alcohol polymers, for example, oxygen barrier property,
odor-retaining property and oil resistance, and therefore they are
expected to be useful in the field of packaging materials and in other
applications.
Certain laminated films comprising an oxyalkylene group-containing vinyl
alcohol copolymer film layer and a thermoplastic resin layer are known.
For instance, Japanese Kokai Tokkyo Koho No. 160550/89 (the applicants
being the same as in the present application) discloses containers for
filthy waste matter (ostomy bags, etc.) made of a laminated packaging
material comprising an oxyalkylene group-containing vinyl alcohol
copolymer film layer. Japanese Kokai Tokkyo Koho No. 158016/89 (the
applicants being the same as in the present invention) discloses
water-resistant flexible films made of an oxyalkylene group-containing
vinyl alcohol copolymer and showing a specific water dissolution
temperature and a specific value of Young's modulus and also refers to
lamination of this film to another substrate.
Japanese Kokai Tokkyo Koho No. 231749/87 discloses laminates having a good
gas barrier property which comprise at least a layer of an ethylene-vinyl
alcohol copolymer modified by a polyether component added terminally to
the ethylene-vinyl alcohol copolymer and a layer of another thermoplastic
resin. Japanese Kokai Tokkyo Koho No. 231750/87 also discloses laminates
having a good gas barrier property which comprise at least a layer of an
ethylene-vinyl alcohol copolymer modified by grafting a polyether
component as a branch polymer and a layer of another thermoplastic resin.
As mentioned above, several laminated films having an oxyalkylene
group-containing vinyl alcohol copolymer film layer/thermoplastic resin
layer structure are known. For any of the laminates described in the
patent publications cited above, no consideration has been given to their
degradability. To met the recent market requirement, a solution must be
found in this respect.
In the laminated films mentioned above, both the layers generally differ in
polarity in a manner as if quite opposite and, therefore, the adhesion
between both the layers tends to be insufficient not only when both the
layers are directly in contact but also when an adhesive layer lies
between both the layers. As a result, the laminated films may, in some
instances, fail to show the desired mechanical strength and/or oxygen
barrier property.
Accordingly, it is an object of the present invention to provide laminates
which have an oxyalkylene group-containing vinyl alcohol copolymer film
layer/thermoplastic resin layer construction and with which the
degradability and interlaminar adhesion problems can be solved
simultaneously.
Containers for Filthy Waste Matter
Immediately after operative treatment of diseases of tubular or cavitary
organs, such as the ileum, transverse colon, descending colon, sigmoid
colon and anal fistula, a minute opening (stoma), generally called an
artificial anus, is sometimes formed on the body surface for discharge of
filthy waste matter, such as fecal matter, pus or body fluid,
therethrough. Not only immediately after operations but also during
convalescence and even after return to work, the artificial anus is
retained in many instances.
Bags for collecting the waste matter excreted from the artificial anus are
called ostomy bags, colostomy bags, ileostomy bags and so forth depending
of the tubular or cavitary organ to which the stoma is connected.
As to the construction of bags of this kind, various proposals have so far
been made, as mentioned below.
A Japanese patent application filed under PTC and laid open under Kohyo No.
501631/82 discloses bags chiefly intended for medical use which have a
structure such that a vapor barrier layer, such as a vinylidene
chloride-vinyl chloride copolymer layer, lies between two layers made of a
blend of a chlorinated polyolefin and an olefin polymer.
Japanese Kokai Tokkyo Koho No. 1246/85 discloses non-sound-producing films
for the manufacture of ostomy bags which comprise either a layer of a
blend of an ethylene-vinyl acetate copolymer and an elastic polyolefin or
two layers of said blend and a gas/odor barrier layer of a vinylidene
chloride copolymer, an ethylene-vinyl alcohol copolymer, a vinylidene
fluoridevinyl fluoride copolymer, a polyamide or the like as interposed
between said two layers.
Japanese Kokai Tokkyo Koho No. 122527/85 discloses bags for excreta from
the human body which are made of a 3-hydroxybutyrate polymer film or a
laminate derived therefrom. As films usable for lamination to said film,
there are mentioned water-soluble polymer films, such as polyvinyl alcohol
films and polyethylene oxide films.
Japanese Kokai Jitsuyo-Shinan Koho No. 175248/85 discloses films for bags
to be attached to an artificial anus which are produced by three-layer
coextrusion of a blend of a saponified ethylene-vinyl acetate copolymer
and a partially saponified ethylenevinyl acetate copolymer (as a middle
layer) and an ethylene-(meth)acrylic ester copolymer (as sandwiching
layers).
Japanese Kokai Tokkyo Koho No. 31151/86 discloses bags for receiving feces
from an artificial anus which comprise a deodorizing coagulant disposed on
the bag bottom and in the tubular section, where a readily water-soluble
paper species is used.
Bags currently in practical use for collecting filthy waste matter excreted
from an artificial anus have a three-layer construction of ethylene
vinylacetate copolymer (inside layer)/polyvinylidene
chloride/ethylenevinyl acetate copolymer (outside layer) or a four-layer
construction derived from said three-layer construction by further
lamination of a nonwoven fabric or a net-like structure.
The present applicants have filed an application for patent concerning a
container for filthy waste matter which is made of a monolayer or
multilayer packaging material having an oxyalkylene group-containing vinyl
alcohol copolymer film layer (Japanese Patent Application No. 160550/89).
Bags for collecting filthy matter discharged through the artificial anus
are required to have all the functions promoting the users' convenience,
for example, water resistance, odor barrier property (ability to prevent
odor from leaking out), non-sound-producing property or flexibility,
disposability in flush toilet, and acceptability in touch.
In addition to the above-mentioned functions, which mainly serve the
convenience of users, degradability after disposal has recently been
required as well from the standpoint of environmental pollution control.
The bags disclosed in the above-cited patent publications, namely Japanese
Kokai Tokkyo Koho No. 501631/82, No. 1246/85 and No. 122527/85, Japanese
Kokai Jitsuyo-Shinan Koho No. 175248/85 and Japanese Kokai Tokkyo Koho No.
31151/86 can indeed satisfy some of the functional requirements mentioned
above from the users'convenience viewpoint but are unsatisfactory in some
functions. No special consideration has been given to said bags from the
viewpoint of degradability after disposal. Even those bags currently in
practical use which have an ethylene-vinyl acetate
copolymer/polyvinylidene chloride/ethylene-vinyl acetate copolymer
three-layer structure or a four-layer structure derived therefrom by
further lamination of a nonwoven fabric or a net-like material have
similar problems.
No attention has been paid at all even to the bags for filthy waste matter
proposed by the present applicants (Japanese Kokai Tokkyo Koho No.
160550/89) claiming that they have the following functional
characteristics: water resistance, odor barrier property, flexibility or
non-sound-producing property, acceptability in feel and touch, and
disposability in a flush toilet.
The number of artificial anus carriers is increasing year by year, with an
increase in the number of persons who have returned to work. Under such
circumstances, it is strongly demanded that bags which not only meet the
functional requirements mentioned above from the users' convenience
viewpoint but also have degradability, namely are prevented from causing
environmental pollution, should be developed.
Accordingly, it is an object of the invention to provide containers for
filthy waste matter which meet the functional requirements from the users'
convenience viewpoint and at the same time are degradable after throwing.
SUMMARY OF THE INVENTION
The melt-molded articles of this invention are produced by melt-molding a
composition comprising an oxyalkylene group-containing vinyl alcohol
copolymer and starch or a starch or a starch-derived macromolecule.
Said melt-molded articles are preferably in the form on fibers of films.
The laminates of this invention comprise at least one film layer produced
in the above manner. The other laminating layer is preferably a
thermoplastic resin layer. One of preferred applications of said laminates
is in producing containers for filthy waste matter.
DETAILED DESCRIPTION OF THE INVENTION
Oxyalkylene Group-Containing Vinyl Alcohol Copolymer
The oxyalkylene group-containing vinyl alcohol copolymer includes products
of saponification of copolymers of an oxyalkylene group-containing,
ethylenically unsaturated monomer and a vinyl ester. Examples of the
oxyalkylene group-containing, ethylenically unsaturated monomer are
polyoxyalkylene (meth)-acrylate, polyoxyalkylene (meth)acrylamide,
polyoxyalkylene (1-(meth)acrylamido-1,1-dimethylpropyl) ester,
polyoxyalkylene (meth)allyl ether, polyoxyalkylene vinyl ether, and the
like. The oxyalkylene is, for example, oxyethylene or oxypropylene. The
number of moles of the oxyalkylene unit in the polyoxyalkylene moiety is
suitably 1 to 300, preferably 1 to 50, more preferably 5 to 50.
The oxyalkylene group-containing vinyl alcohol copolymer can be produced
also by reacting polyvinyl alcohol with an alkylene oxide or by
polymerizing vinyl acetate on polyalkylene glycol, followed by
saponification.
Among the oxyalkylene group-containing vinyl alcohol copolymers mentioned
above, the oxyalkylene allyl ether type vinyl alcohol copolymers are
particularly preferred, hence are mentioned below in further detail.
Said copolymers comprise a vinyl alcohol unit (A), a vinyl ester unit (B)
and an oxyalkylene allyl ether unit (C) of the formulas:
##STR1##
wherein R.sup.1 in (B) is an alkyl group; R.sup.2 and R.sup.3 in (C) each
is a hydrogen atom or an alkyl group; R.sup.4 in (C) is a hydrogen atom,
an alkyl group, a phenyl group or a substituted phenyl group; n is equal
to 1 through 300; in proportions of a mol %, b mol % and c mol %,
respectively, where
0.1.ltoreq.c.ltoreq.20 (i)
50.ltoreq.100a/(a+b).ltoreq.100 (ii)
and have a melt index of not less than 5 g/10 min. under a load of 2160 g
at a temperature of 210.degree. C.
The first expression (i) means that the proportion of oxyalkylene allyl
ether unit (C) in the copolymer must be within the range of 0.1 to 20 mol
%. The improving effect of the invention will not be sufficient if the
proportion of (C) is less than 0.1 mol %, whereas the use of (C) in excess
of 20 mol % impairs the inherent properties of polyvinyl alcohol. The
preferred range is 0.1 to 10 mol %, and the particularly preferred range
is 0.1 to 5 mol %.
The second expression (ii) means that the degree of saponification of the
vinyl ester component (B) before hydrolysis must be within the range of 50
to 100 mol %. When the degree of saponification is less than 50 mol %, the
hydrophilicity, odor barrier property, oil resistance, antistaticity,
oxygen barrier property and warmth retention property of polyvinyl alcohol
are not fully obtained. The particularly preferred range is 80 to 100 mol
%. The higher the degree of saponification, the more advantageous it is in
fully utilizing the properties intrinsic of the vinyl alcohol group.
If required, various optional monomers other than (A), (B) and (C) may be
present in a proportion not exceeding about 10 mol % provided that the
water solubility is not impaired. Such other monomers include, among
others, .alpha.-olefins such as ethylene, propylene, long-chain
.alpha.-olefin, etc. and ethylenically unsaturated carboxylic monomers
such as acrylic acid, methacrylic acid, crotonic acid, maleic acid,
fumaric acid or itaconic acid, and their half and full alkyl esters,
anhydrides, amides, imides and salts, ethylenically unsaturated sulfonic
monomers such as ethylenesulfonic acid, allylsulfonic acid or
methallylsulfonic acid, and their salts, cationic monomers such as
N-acrylamide methyl trimethyl ammonium chloride, allyl trimethyl ammonium
chloride, dimethyl diallyl ammonium chloride, diethyl diallyl ammonium
chloride, alkyl vinyl ether and so on.
The preferred unit (B) is vinyl acetate. In this case, the effect of the
invention is particularly remarkable when the oxyalkylene moiety CHR.sup.2
--CHR.sup.3 --O of unit (C) accounts for 3 to 50 weight % of the total
resin. Thus, it is important to insure not only that the proportion of (C)
in the copolymer is within the range of 0.1 to 20 mol %, preferably 0.1 to
10 mol %, more preferably 0.1 to 5 mol %, but also that the oxyalkylene
moiety accounts for 3 to 50 weight %, preferably 5 to 40 weight %, of the
total resin. In other words, for smooth melt-molding under anhydrous
conditions, there are limits to the degree of localization of the
oxyalkylene moiety within the copolymer and the length of the oxyalkylene
moiety. The range of n is 1 to 50, preferably 3 to 50 and that of the
degree of saponification is preferably 80 to 100 mol %.
The oxyalkylene group-containing vinyl alcohol copolymer to be used in the
present invention must have a melt index of not less than 5 g/10 min.
under a load of 2160 g at 210.degree. C. When this value is less than 5
g/10 min, melt-molding may not be performed as smoothly as desired even if
other conditions are fulfilled. In this specification, the melt index is
the value measured with a Toyo Seiki melt indexer with a 1 mm dia. x 10 mm
nozzle.
Thus, the melt-molding under substantially plasticizer-free and
substantially anhydrous conditions is feasible with success on a
commercial scale only when the oxyalkylene group-containing vinyl alcohol
copolymer meeting the above requirements is employed.
The above oxyalkylene group-containing vinyl alcohol copolymer can be
produced by polymerizing monomers for constituting said vinyl ester unit
(B) and oxyalkylene allyl ether unit (C), if necessary, together with
other copolymerizable monomers, and then hydrolyzing the resulting
polymer. By this hydrolysis procedure, most or all of vinyl ester unit (B)
are converted to a vinyl alcohol unit.
The polymerization process that can be employed is generally solution
polymerization but depending on cases, suspension polymerization and
emulsion polymerization techniques may also be employed.
The hydrolysis can be carried out with alkali or acid.
Starch and Starch-Derived Macromolecules
As the starch and starch-derived macromolecules, there may be mentioned raw
starches such as corn starch, potato starch, sweet potato starch, wheat
starch, cassava starch, sago starch, tapioca starch, sorghum starch, rice
starch, bean starch, arrowroot starch, bracken starch, lotus starch and
water chestnut starch, physically modified starches (.alpha.-starch,
fractionated amylose, moist heat-treated starch, etc.), enzymatically
modified starches (hydrolyzate dextrin, dextrin produced by enzymatic
degradation, amylose, etc.), chemical degradation-modified starches
(acid-treated starch, hypochlorite-oxidized starch, dialdehyde starch,
etc.), chemically modified starch derivatives (esterified starches,
etherified starches, cationized starches, crosslinked starches, etc.) and
so forth. Among the chemically modified starch derivatives, the esterified
starches include, among others, starch acetate, starch succinate, starch
nitrate, starch phosphate, starch urea phosphate, starch xanthate and
starch acetoacetate, the etherified starches include, among others, allyl
etherified starch, methyl etherified starch, carboxymethyl etherified
starch, hydroxyethyletherified starch and hydroxypropyl etherified starch,
the cationized starches include, among others, the reaction product from
starch and 2-diethylaminoethyl chloride and the reaction product from
starch and 2,3-epoxypropyltrimethylammonium chloride, and the crosslinked
starches include, among others, formaldehyde-crosslinked starch,
epichlorohydrin-crosslinked starch, phosphoric acid-crosslinked starch and
acrolein-crosslinked starch.
Cellulosic macromolecules, other polysaccharide macromolecules and
proteinic macromolecules may also be used in combination with the starch
or a starch-derived macromolecule.
The cellulosic macromolecules include, among others, methylcellulose,
ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose,
hydoxyethylmethylcellulose, hydroxypropylmethylcellulose,
hydoxybutylmethylcellulose, carboxymethylcellulose, acetylcellulose and
nitrocellulose.
Other polysaccharide macromolecules include, among others, mannans, such as
ivory nut mannan, salep mannan, wood mannan, kelp mannan and yeast mannan,
fructans, such as inulin and levan, glycogen, charonin, laminaran, xylan,
chitin, chitosan, pectinic acid, hyaluronic acid, agarose, alginic acid,
heparin, chondrotin sulfate, carrageenan, gum arabic, gum tragacanth, gum
karaya, gum guaiac, locust bean gum, mesquite gum, gum ghatti, funori
(gloiopeltis glue) and agar.
The proteinic macromolecules include, among others, collagens, such as
gelatin and glue, casein, sein, gluten, blood albumin and soya protein.
Proportions
The mixing ratio between the oxyalkylene group-containing vinyl alcohol
copolymer and the starch or starch-derived macromolecule should be within
the range of 90:10 to 10:90 by weight, preferably 80:20 to 30:70 by
weight. When the starch or starch-derived macromolecule is used in a
higher proportion, the moldability is impaired and at the same time the
strength of the molded articles decreases. On the other, when said
macromolecule is used in a smaller amount, the biodegradability becomes
unsatisfactory.
Melt Molding
Prior to melt-molding, a plasticizer such as a polyhydric alcohol may be
incorporated but since sufficient flexibility can be obtained without a
plasticizer and the use of a plasticizer may rather adversely affect the
properties of the product, it is rather recommended not to use a
plasticizer. In melt molding, water may be incorporated. However, this
requires a step of drying, hence it is recommended not to use water.
To sum up, in the practice of the invention, it is desirable to carry out
melt-molding under substantially plasticizer-free and substantially
anhydrous conditions (at a moisture content of not more than about several
percent by weight, preferably not more than 1% by weight, more preferably
not more than 0.5% by weight). It is one of the characteristic features of
the invention that smooth melt-molding can be performed even under such
conditions. In melt molding, various additives, such as fillers,
colorants, stabilizers, antioxidants, ultraviolet absorbers, flame
retardants and water resistance-imparting agents, and functional agents,
such as fertilizers, agrochemicals, enzymes, biocides, deodorants and
perfumes, as well as other water-soluble or water-insoluble resins can be
incorporated in the molding compounds.
The melt-molding process may be any of injection molding, extrusion
molding, transfer molding and other techniques.
Extrusion molding includes blow molding, inflation molding, coextrusion
molding and extrusion coating as well. In extrusion molding, the die
temperature is preferably set at 150.degree. to 300.degree. C. and the
temperature of the screw compression zone is at a temperature higher by
5.degree. to 30.degree. C. than the temperature of the discharge zone.
The preferred injection molding conditions are: cylinder temperature
150.degree. to 250.degree. C., mold temperature 30.degree. to 100.degree.
C. and injection pressure 500 to 2000 kg/cm.sup.2. It is surprising that
the polymer compositions having water solubility or hydrophilicity a used
in the practice of the invention can be injection-molded under
plasticizer-free and substantially anhydrous conditions.
By such melt-molding, moldings having any form and shape as desired can be
obtained, for example fibrous moldings (fibers, monofilaments, etc.), and
film-like moldings (films, sheets, tapes, tubes, bottles, trays, etc.).
The moldings obtained may be further subjected to secondary treatment or
processing, such as weather resistance-imparting treatment, stretching or
drawing, fiber splitting, or bag manufacture.
Effects
In accordance with present invention, the moldings, or shaped articles, are
produced by melt-molding a composition comprising an oxyalkylene
group-containing vinyl alcohol copolymer and starch or a starch-derived
macromolecule and therefore show sufficient strength and other
characteristics when they are used for their intended purposes whereas,
after achievement of said purposes, they are rapidly degraded under the
action of microorganisms in the soil and/or water.
Furthermore, said melt-molding can be performed under substantially
plasticizer-free and substantially anhydrous conditions. This is a very
advantageous feature of the invention from the commercial productivity
viewpoint. The freedom from the use of any plasticizer means that neither
plasticizer bleeding from the molding nor adhesion between the moldings
occurs.
In particular, the use of a vinyl alcohol copolymer of the oxyalkylene
allyl ether type mentioned above as the oxyalkylene group-containing vinyl
alcohol copolymer is preferable. This is because, in the saponification
reaction for the production of said copolymer, the oxyalkylene group in
the oxyalkylene allyl ether unit (C) will not be eliminated and because,
in said copolymer, the vinyl alcohol unit (A) and the oxyalkylene allyl
ether unit (C) are distributed in an appropriate ratio and the weight
proportion of the oxyalkylene unit in unit (C) is controlled within the
specific range mentioned above, so that the degree of localization of the
oxyalkylene unit and the length of the oxyalkylene unit are well balanced
and well suited for melt-molding. Therefore, the compositions comprising
this copolymer and starch or a starch-derived macromolecule can be
smoothly molded in a commercially acceptable manner even under
substantially plasticizer-free and substantially anhydrous conditions.
The resulting shaped article is not only water-soluble or water-dispersible
and flexible but has an odor trapping property, oil resistance, chemical
resistance, antistaticity, oxygen barrier property and warmth retention
property, all of which are derived from the vinyl alcohol unit (A).
Fibrous moldings
As a particular case of the above-mentioned melt-molding, the production of
fibrous shaped articles is described below in further detail.
Any melt-molding method suited for melt spinning may be employed, for
example the extrusion molding method. The extruder is not limited to any
particular type but conventional melt molding machines for thermoplastic
resins can be used for fiber production, with a nozzle attached thereto.
The nozzle may have any desired form unless inappropriate. In the practice
of the inventi | | |
