Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~090~
VINYLIDENE CHLORIDE POLYMæR LATEX
This invention relates to polymer latex
coating composi~ions and, more particularly, to latices
of vinylidene chloride polymers.
In recent years, vinylidene chloride polymer
latices have been widely used, particularly in the food
industry, as coatings for plastic films, cellophane,
paper, and like packaging materials due to their high
resistance to chemicals and oils, low temperature heat~
-sealing properties, and excellent resistance to the
transmission of oxygen and moisture vapor. However, it
has also been recognized thzt such coatlngs tend to be
generally deficient in a number of properties demanded
by advanced packaging techniques. ~'or instance, such
coatings should have a lower dynamic coef~icient of
friction to permit faster packaging speeds. They should
also be capable of forming low temperature heat-seals
having higher strength to withstand the stresses inhe~-
ent in such packaging speeds. Further, they should have
reduced blocking tendencies to permit rapid feed ng from
aged rolls of coated packaging material without breaking
or dest~oying the coatings.
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I~ is generally considered that heat-sealing
properties are incompatible with antiblocking and slip
properties. Accordingly, the methods chosen to modify such
coatings typically have focused on improving only a limited
number of properties at one time to the detriment of other
properties, thereby inherently restricting the resulting
coatings to specific end-uses.
For example, one method consists of increasing
the vinylidene chloride content of the latex polymer to
improve crystallinity and reduce the tendency for block-
ing. Due to such increased crystallinity, however, this
method undesirably reduces the heat-sealing properties.
Another method employs a suitable amount of
an additive, such as talc, wax, silica, or the like, to
reduce blocking and increase slip properties. Such addi-
tives are typically incompatible with the latices and,
accordingly~ have a tendency to affect latex stability
and reduce the transparency of the resulting coatings.
A further method has consisted of blending a
latex having reduced blocking tendencies but poor heat-
-sealing properties with one or more latices having good
heat-sealing properties but high blocking tendencies to
achieve a suitable balance in overall performance prGp-
erties. Although this method has proven to be generally
successful in its results, it is nevertheless disadvan-
tageous inasmuch as it necessitates preparing several dif-
ferent but compatible latices and requires careful control
of the proportions of each during blending.
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The present invention provides a vinylidene
chloride polym~r latex which can be used to form coatings
having improved slip properties and reduced blocking
tendencies without sacrificing the low temperature heat-
-sealing properties.
More particularly, he invention provides 2
polymer latex coating composition comprising the product
obtained by emulsion polymerizing a monomer mixture con-
sisting essentially of (a) 50 to 95 parts by weight of
vinylidene chloride; (b) 0.5 to 30 parts by weight of
propylene; (c) 4.5 to 20 parts by weight of at least one
comonomer selected from alkyl esters of acrylic and
methacrylic acids, glycidyl esters of acrylic and meth-
acrylic acids, nitriles of ethylenically unsaturated
carboxylic acids, vinyl chloride, and styrene; and,
optionally, (d) not more than 5 parts by weight of at
least one polar comonomer selected from unsaturated
carboxylic acids, unsaturated amides, ar.d hydroxyalkyl
esters of unsaturated carboxylic acids. The preferred
monomeric mixture consists essentially of (a) 77 to 82
parts by weight of vinylidene chloride; (b) 13 to 17 parts
by weight of propylene; (c) 4.5 to 5 parts by weight of
methyl methacrvlate; and (d) less than 2 parts by weight of
acrylic acid.
The novel vinylidene chloride polymer latices
of the present invention can be prepared by free radical
initiated emulsion polymerization processes well known
to those skilled in the art.
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Suitable emulsifiers which can be employed,
either singly Oî in combination, in the preparation of
the present latices include anionic emulsifying agents,
such as alkyl aryl sulfonates, alkyl sulfates, alkyl
sulfonates, and the like, as well as non-ionic emulsi-
fying agents, such as polyoxyethylene-monofatty acid
esters, sorbitan-monofatty acid esters, and the like.
Suitable free radical initiating catalysts which can
be used include peroxides, such as hydrogen peroxide,
tertiary butyl hydroperoxide, and the li~e; persulfates,
such as potassium persulfate, a~monium persulfate, and
the like; and redox systems such as an alkali metal
bisulfite in combination with a peroxide or persulfate.
In the present invention, if the vinylidene
chloride content of the polymer exceeds 95 parts by
weight, the crystallization speed, the ~ilm-forming tem-
perature, and heat-sealing temperature will be undesirably
increased and, at the same time, the shelf li e of the
latices is shortened to such an extent that the resultant
coated materials cannot be put to practical use. Further-
more, if the vinylidene chloride content goes below 50
parts by weight, the highly advantageous barrier properties
of vinylidene chloride polymers will be diminished. As
to propylene, if its content exceeds 30 parts by weight,
the polymerization productivity goes down to a practically
unacceptable level due to very poor reactivity between
the vinyl comonomers and vinylidene chloride. On the
other hand, if the propylene content is reduced below 0.5
part by weight, the improvement in the antiblocking and
slip properties cannot be expected.
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The comonomers which are copolymerizable with
vinylidene chloride according to the present invention
include the alkyl esters of acrylic and methacrylic acids
such as methyl acrylate, ethyl acrvlate, propyl acrylate,
butyl acrylate, octyl acrylate, methyl methacrylate, ethyl
methacrylate, propyl methacrylate, butyl mRthacrylate,
octyl methacrylate, and the like; glycidyl esters of
acrylic and methacrylic acids such as glycidyl meth-
acrylate; nitriles of ethylenically unsaturated carboxylic
aci~ds such as acrylonitrile and methacrylonitrile; and
Yinyl monomers such as vinyl chloride and styrene.
The polar comonomers which can be used include
unsaturated carboxylic acids, e.g., ethylenically unsatu-
rated mono- and dicarboxylic acids such as acrylic acid,
methacrylic acid, itaconic acid, fumaric acid, and the
like; hydroxyalkyl esters of unsaturated hydrocarbons,
e.g., the glycol monoesters of acrylic and methacrylic
acids such as hydroxyethyl acrylate, hydroxyethyl meth-
acrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate,
and the like; and unsaturated amides, e.g., amides of
ethylenically unsaturated carboxylic acids such as
acrylamide and crotonamide.
The resulting latices of the present invention
can also contain, if desired, various conventional addi-
tives including lubricants, antiblocking agents, and thelike.
The latices are coated on a suitable substrate
by methods well known in the art. Exemplary substrates
include plastic films, such as those prepared from poly-
propylene, polyamide, and polyester; paper; cellophane;and like packaging materials.
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-6-
The following specific examples further illus-
trate the invention. Parts and percentages are by weight
unless otherwise indicated.
The latices used and the performance of film
substrates coated therewith were evaluated by the fol-
lowing methods:
Coating ~ethod
A urethane anchor agent was first coated by
means of a Mayer rod onto a biaxially oriented polypro-
pylene film having the surfaces thereof previously sub-
jected to a corona discharge treatment. The prime-coated
film was dried at 105C for 15 seconds in a box dryer
with internal hot-air circulation. Thereafter, the film
was coated with a latex having a solids content of about 40
percent by means of a Mayer rod (at a coating weight of
about 3 g/m2) and the resultant coated film was dried at
105C for 30 seconds in the box dryer with internal hot-air
circulation.
Blocking Tendency
Specimens taken from the film to be examined
were superimposed so as to bring the coated surfaces
together and the specimens were placed under a load of 5
kg/cm for 24 hours in an atmosphere of 90 percent rela-
tive humidity at 40C. Thereafter, the specimens were
pulled apart and the blocking tendency was qualitatively
evaluated according to the following scale:
(1) specimens that smoothly separated with-
out any resistance;
(2) specimens that smoothly separated with
slight resistance;
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(3) specimens that separated with some
resistance, but without damaging the
coatings;
(4) specimens that had the coatings thereof
damaged when separated; or
(5) specimens that would not separate with-
out force and without tearing the sub-
strate.
eat-Sealing Properties
Immediately after coating a film with a latex
or after aging the coated film at 40C for two days,
samples measuring 5 cm x 5 cm were cut therefrom and the
coated surfaces thereof were heat-sealed for 0.5 second at
80 to 110C under a load of 1 kg/cm2 by means of a bar-type
heat-sealer. Then, the samples were cut along the direc-
tion perpendicular to the heat-sealing surface to
obtain three heat-sealing strength test specimens 15 mm
wide and 50 mm long each. Thereafter, the specimens were
subjected to the measurement of heat-sealing strength at a
tension speed of 30 cm/min by using a Tensilon tensile
tester. The average heat-sealing strength for the three
specimens was recorded.
Slip Properties
Using a tack strength tester, dynamic coeffi-
cients of friction observable between overlapped film
surfaces coated with a latex were measured in an atmos-
phere of 20C and 55 percent relative humidity in accord-
ance with the method of ASTM D-1894-63.
Antistatic Properties
~ . ........ ._ . . .
A rotary static tester developed by the Chem-
ical Research Laboratory of Kyoto University, was used
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to measure the static voltage generated on a coated film
surface rl~bed at 400 rpm with a flannel cloth for 40
seconds in an atmosphere of 20C and 55 percent relative
humidity. The value for antistatic properties was deter-
mined relative to the charged voltage on an uncoatedspecimen.
Polymer Composition
In the examples described herein, the polymer
composition was determined in the following manner: a
sample of the latex was isolated and salted out with meth-
anol and the resultant precipitated resin was analyzed.
Vinylidene chloride content was determined by Schoniger's
oxygen flask combustion method and methyl acrylate
content was determined by means of an infrared spectro-
photometer calibrated with a vinylidene chloride-methyl
acrylate copolymer having a known composition. The
methyl acrylate content was corrected by determining
its weight ratio to vinylidene chloride from a standard
curve of absorbance ratio and by using the actual vinyli-
dene chloride content obtained from the Sch~niger's oxy-
gen flask combustion method. The propylene content was
determined by calculation. Acrylic acid content was
determined by dissolving 0.5 g of the dried resin in 70 g
of dimethylformamide and subjecting the resulting solution
to conductimetric titration with a 0.1N solution of
Co(CH3COO)2.
Example 1
One hundred parts of deionized water, 3 parts
of sodium dodecylbenzenesulfonate, 0.1 part of potassium
persulfate, 0.3 part of disodium hydrogen phosphate, and
0.5 part of sodium sulfate were placed in a stainless
steel autoclave provided with an agitator. Subsequently,
the air contained in the autoclave was fully substituted
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_g_ -
with nitrogen gas and the autoclave was closed. Then, the
internal temperature of the autoclave was raised while agi-
tating the contents therein. When ~he internal tempera-
ture reached 30C, the internal pressure of the autoclave
was reduced to 160 mm Hg. Thereafter, 78 parts of vinyli-
dene chloride (VDC), 5 parts of methyl acrylate (MA),
and 17 parts of propylene (P) were further charged in the
autoclave and mixed therein for 30 minutes~ Then, the
internal temperature was further raised to 50C and the
mixture was allowed to polymerize for 20 hours. At the end
of that period, the internal temperature of the autoclave
was cooled to 25C and the residual unreacted monomers were
slowly vented. Sodium dodecylbenzenesulfonate was added to
the resultant latex to adjust its surface tension to 40
dyne/cm. This latex was designated as Latex A.
For comparison, 90 parts of vinylidene chloride
and ]0 parts of methyl acrylate were polymeriæed in
the same manner as used for the Latex A. To the result-
ant latex, sodi~m dodecylbenzenesulfona~e was added to
adjust its surface tens on to 40 dyne/cm. This latex
was designated as Latex B.
Varying amounts of a carnauha wax emulsion and
a silica lubricant were added to some samples of the A
and B latices.
The so-formed latices were coated on biaxially
oriented polypropylene films in the manner earlier described
and the resultant films, all of which were haze-free,
were tested for physical properties~ The results of
these tests are reported in Table I.
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1090~3~
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As clearly seen from Table I, the latices which
include propylene provide coatings having improved anti-
static and slip properties in addition to good heat-sealing
properties at lower temperatures and reduced blocking
tendency.
Example 2
In the manner of Example 1, Latices C, D, E,
and F were prepared by using varied proportions of charged
monomers. Each of the resultant latices were mixed with
1 percent, based on the weight of latex solids, of a car-
nauba wax emulsion and 0.2 percent, based on the weight
of latex solids, of silica lubricant. The treated
latices were then coated on biaxially oriented polypropy-
lene films and physical properties of the resultant
coated films, all of which were haze-free, were
measured. The results of these tests are shown in
Table II.
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109093t~
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1(~905~3~
-13-
The results shown in Table II again highlight
the improved properties of coatings prepared from latices
of the present invention. These results also demonstrate
the enhanced heat-sealing properties obtained when the
present latices include a minor amount of a polar comono-
mer such as acrylic acid.
27,722-F
