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Патент USA US2405977

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Aug. 20, 1946.
F. T. PETERS
'
2,405,977
FILM MANUFACTURE
'
Filed Sept. 2, 1943
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EaT-Lkhn Travi'is F ETEPE
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- ‘Patented
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2,405,977
rnM
Franklin Traviss Peters, Wilmington, Dei, assign
or to E. ii. du Font de Nemonrs & @ompany,
Wilmington, Del, a corporation of Delaware
i
Application September 2, 1942, Serial No. 500,989
2 Claims. (on. 18-57)
2
This invention relates to ?lm manufacture, and
and the necessity for heating the ?lm above the
more particularly to improvements in the pro
melting point before quenching.
duction of ?lms from normally solid polymers of
The above objects are accomplished‘ by a
ethylene.
method more particularly described hereinafter
The polymers of ethylene with which this in 5 which comprises casting a ?lm on a support from
vention is concerned are solid polymers obtained
a solution of the polymer of ethylene, the solu
by known procedures through the polymeriza
tion being at a temperature above the melting
tion with heat and pressure of ethylene alone or
point of the polymer and the support being at
of mixtures consisting of ethylene and another
a temperature below the melting point of the
compound containing at least one polymer form 10 polymer but not lower than 15° C. below the melt
ing unsaturated linkage. These polymers can
ing point, evaporating the solvent, and, just prior
be obtained, for example, by heating ethylene or ‘
to the time at which crystallization and haze
the mentioned mixture thereof under a pressure
formation wouldoccur, bringing the ?lm and its
above 500 atmospheres and preferably above 1000
support in contact with a non-solvent cooling
atmospheres at temperatures of from 100° to 400° 15 liquid, and then stripping the ?lm from the cast
C.. and preferably from 150° to 250° C. as de
ing surface.
scribed in United States Patents 2,153,553,
The invention will be better understood in
2,188,465, and 2,200,429. Another method of
connection with the accompanying drawing in
making these ethylene polymers consists in heat
which:
ing the ethylene alone or in admixture with an 20
Fig. 1 is a view in elevation of one form of ap
other polymerizable compound in contact with
paratus suitable for carrying out the invention,
water and a per-compound catalyst at tempera
Fig. 2 is a similar view of a modi?ed appa
tures in the range of 40° to 350° C. and at super
ratus, and
»
atmospheric pressures in excess of 3 atmos
Fig. 3 is an elevational view of a further modi
pheres. The polymers of ethylene alone are nor 25 ?ed apparatus.
mally solid, correspond in composition substan
In Figs. 1 and 2 the numeral l indicates a con?
tially to (CH2)¢, show a crystalline pattern by
X-ray diffraction analysis, and in general melt
in the range of about 100° to about 120° C. The
ventional extrusion hopper having an extrusion
lip 72 past which the ?lm 3 of polymer solution
?ows through a slot, not shown, to the casting
physical properties of the polymers of ethylene 30 drum 6. A conduit 5 passes to the interior of the
with other polymerizable organic compounds
drum in known manner at its axis of rotation to
vary depending upon the composition of the
provide means for introducing heating ?uid,
polymer and the nature of the organic compound
preferably a mixture of hot water and steam, to
polymerized with the ethylene:
the interior of the drum. A similar conduit, not
Films of the normally solid polymers of ethyl 35 shown, is provided at the other side of the drum
ene referred to above are crystalline and trans
for removal of the heating ?uid. As the ?lm is
lucent unless they are heated above the melting
stripped from the drum in Fig. 1 at the point C
point of the polymer and then shock cooled, that
it passes over a roll 6 to a drying apparatus, not
is, cooled very rapidly below the melting point.
shown, which can consist of a heated cabinet
This cooling can be effected by casting a ?lm of 40 or a series of warm rollers, etc., and is then wound
the molten polymer on a cold support, or by
quenching the molten ?lm with a cooling liquid.
The requirement that the ?lm be heated above
the melting point of the polymer before it is
up in a roll.
A nozzle 1 is placed to direct a
spray of cold water against the ?lm at the point
B within the required period of time before crys
tallization and haze formation would occur. The
quenched prevents the use of a heated conven 45 point A indicates the point on the drum where
tional casting drum as a support for the molten
haze formation would occur had not the ?lm been
?lm during quenching since a greater di?‘erential
rapidly chilled at the proper time before that
point is reached. The position of the point A
is required than can be maintained between two
on the drum, and hence that of point B where
points on the periphery of the drum.
50 the cooling liquid is applied will depend on par
This invention has as an object to provide a
ticular conditions of operation, as will be further
new and improved method for obtaining clear
referred to later.
ethylene polymer ?lms. A further object is a
In Fig. 2 the spray of water is replaced with
method for casting these ethylene polymer ?lms
a stream of water which ?ows through a shallow
which avoids the disadvantages of melt casting 55 tank 8 and against a small area of the underside
between the casting and quenching temperatures
2,405,977
3
of the drum. The point D on the drum corre
sponds to the point A in Fig. 1 and the water
likewise contacts the ?lm within the required
polymer melting at 105° C. and one part of alumi
num palmitate are dissolved in 399 parts of hot
xylene. This solution is heated to a temperature
time before haze formation would occur. The '
in the range from 110° ‘to 120° C. and ?owed
?lm, after being stripped from the drum by pass
from an extrusion hopper or suitable spreader
ing over a roller 9 mounted in the tank 8, is led
blade on a rotating hollow casting drum such as
under a second roller l0 and then to suitable
that shown in Fig. 1 of the drawing. The drum
wind up mechanism not shown.
is maintained at 94° to 98° C. by circulating
In Fig. 3 the ?lm of ethylene polymer solution
through its interior a mixture of hot water and
is ?owed on a ?lm casting surface or ?at plate 10 steam. The rate of solvent evaporation from the
II by a spreader blade or other means to obtain
liquid ?lm is controlled by circulation of heated
the desired ?lm thickness. This ?lm casting
air above the ?lm surface. The rate of evapo
surface is the upper side of a hollow steel box I2
ration is thus regulated and the speed of the
and is heated by means of a stream of hot water
rotation of the drum is also regulated so that
entering the box at i3 and leaving by the outlet
the ?lm becomes substantially solvent-free, solid,
M. This steel box I2 is enclosed in a larger box
and crystalline when it reaches point A in Fig. 1.
IS on the bottom of which the steel box 12 rests
However, as soon as these adjustments have been
on supports l6. Box I5 is provided with a. re-'
made so that crystallization occurs at the point
movable lid I‘! having a window l8 to observe the
A, a spray of cold water is directed against the
condition of the ?lm. Warm air is passed 20 ?lm at point B on the drum’s periphery,. thus
through the box from an inlet l9 to an outlet 20
causing it to solidify without crystallization and
to control the evaporation rate of the solvent
haze formation. The ?lm is stripped from the
from the ?lm. The ?lm is quenched at the proper
drum back to the point C, where it leaves the
time by removing the lid and applying water to
water spray. As the drum rotates and casting
the ?lm.
continues, the ?lm is drawn off the drum at
The time at which crystallization and haze
this point as described in connection with Fig. 1.
The evaporated xylene can be recovered for re
formation would occur and therefore the time
just prior to this condition when the shock cool
use by passing the vapors through a conventional
ing isapplied, is determined empirically for the
solvent recovery system.
particular casting equipment and evaporation 30
Although the spray of cold water tends to re
conditions used. This interval which exists be
duce the drum temperature, the desired range
tween the ?rst moment at which the non-solid
of 94° to 98° C., as measured at the point of cast
?lm can be quenched to a clear solid ?lm and
ing, can be maintained by increasing the tem
the moment it will crystallize and become trans
perature and rate of flow of the inlet water and
lucent if not quenched may be referred to as the 35 steam used to heat the drum. The water cling
ing to the drum’s surface above the point of
critical time interval, which varies somewhat in
magnitude with a number of other variables. If
quenching and stripping is removed, as by blow
quenching is carried out before this interval the
ing it off with a blast of hot air, before the point
of casting is reached on the next cycle. The rate
liquid ?lm will be converted to a weak, opaque,
white film‘. Quenching is, of course, useless after 40 of solvent evaporation and rotation of the, drum
can also be adjusted so that if no shock cooling
this time.
is carried out the crystallization takes place just
By operating at a temperature below the melt
beyond the lowest point on the drum’s periphery,
ing point of the polymer (de?ned herein as the
as at the point D in Fig. 2 where the water spray
temperature at which the haze disappears from
a crystalline solid ?lm as it is subjected to grad 45 is replaced by a stream of water ?owing against
a small area of the under side of the drum.
ually increasing temperature, for example, at
The invention is further illustrated by the
the rate of 1° C. per minute), but not more than
following examples in which the parts are by
15° C. below, it is possible to maintain a time
weight.
~
interval de?ned above within which the quench
Example I
.ing can be applied to'yield clear ?lms and the 50
method conducted as a continuous process.
The
most favorable operating conditions with regard
to temperature are from 7° C. to 15° C. below the
melting point of the polymer. Within the above
mentioned temperatures the critical time interval
does not vary signi?cantly with the tempera
ture except as temperature a?ects evaporation
To 1500 parts of an ethylene polymer having
a melting point of 105° C. is added 15 parts of
aluminum palmitateand the mixture is dissolved
in 6000 parts of xylene by heating and stirring
together under re?ux at about 120° C. This
solution at 120° C. is extruded, by means of an
extrusion head having a slot ori?ce with a clear
ance of 0.010" between the lips, on the surface
of a rotating hollow stainless steel casting drum
rate of the solvent. The rate of solvent evapora
tion from the liquid ?lm ?owed out from the
polymer solution, however, has a marked effect 60 (6 feet in diameter) at the highest point of the
on the critical time interval, which decreases
drum’s periphery. The drum is rotated at a
as the rate of solvent evaporation is increased.
peripheral speed of 20 feet per minute and is
Solvent evaporation so rapid that this interval
heated to 94° to 98° C. by circulating a mixture
is too short for the quenching process to be con
of water and steam through its interior. After
trolled is therefore avoided. At a given tem 65 the liquid ?lm is formed the xylene is evaporated.
perature the rate of solvent evaporation can be
At a point about 1 foot beyond the lowest point
controlled by regulating the rate of air flow used
of the drum’s periphery, that is, at point B in
to remove solvent vapor above the ?lm.
Fig. 1, the drum is sprayed with water at 10° C.,
A valuable embodiment of this invention re
whereupon a self-supporting ?lm is formed.
sides in the increased critical time interval which 70 The ?lm is stripped at the point (C in Fig. 1) at
can be obtained by incorporating with the poly
which it leaves the water spray. As the process
mer solution aluminum soaps and related ma
continues the ?lm is led away over rollers and
terials which are referred to in more detail here
wound up on a roll. The temperature at the
inafter.
surface of the drum, at the point of casting, is
In a typical procedure 100 parts of an ethylene 75 maintained at 94° to 98° C. by adjusting the
5
‘2,405,077
?ow of steam and water through its‘ interior.
The ?lm'obtained by this process is transparent,
of a plus b is equal to the valence of X. In this
de?nition the ammonium ion and alkyl substi~
tough, and ?exible. It has a tensile strength of
1800 lbs./s‘q. in. and an elongation at the break
tuted ammonium ions are regarded as metals.
Comparative critical time intervals for ethyl
one polymer ?lms containing various modifyingv
agents of the kind referred to above are shown
in the following table:
ing point of 250%.
Example II
To 1500 parts of an ethylene polymer having
a melting point of 110° C. is added 15 parts of
Critical time
interval in
seconds
Composition
magnesium stearate and the mixture dissolved
in 6000 parts of toluene by heatingand stirring
together under re?ux at 120° C. This solution
is ?owed out with a spreader blade having a
clearance of 0.012" on the ?lm casting surface
or ?at plate H shown in Fig. 3 which is heated
to 100° C. by hot water ?owing through the
steel box [2, as previously described. A current
Unmodi?ed ethylene polymer. .
1% aluminum palmitate _ . . _ . _ _ _
l5
_ . _ . . . __
120
1
_
180
magnesium stearate..__
1 a titanium tetrastearate__
90
60
1% sodium oleate ________ __
17 ammonium stearate ____ __
__-
1% potassium naphthenate ________________________ __
of warm air passing from the inlet 19 through
2/40
.
10% titanium tetrastearate.
the outlet 20 circulates through the chamber
formed by the box l5 containing the casting 20
surface and removes the toluene vapor formed
_
1% aluminum stearate _____ ._
1% Zinc tomato
_________ __
1% palmitic acid
30
30
30
45
30
The per cent of each modi?er indicated in the
above table is calculated on the weight of ethylene
polymer used. All solutions used for casting the
the ?lm has dried for about 3 minutes, cold
?lms were in xylene and contained 10% of an
water (about 20° C.) is poured onto a portion 25 ethylene polymer having a melting point at 105°
of the ?lm. Heating of the plate is continued
C. The ?lms were all cast at 100° C. under a
by circulating a stream of water at 100° C.
spreader blade having a clearance of 0.0127.
through the interior of the steel box. After about
The evaporation conditions were the same'for all
another 3 minutes the portion of the ?lm which
the ?lms and were such that the unmodi?ed ?lm
has not been wet with water becomes hazy and 30 was
substantially solvent-free and crystallized 4
crystalline. The portion that is wet with water
minutes after casting. More rapid evaporation
remains clear and non-crystalline. The steel
. will shorten the critical time interval for each of
casting box is cooled to about 80° C. and the
the compositions indicated in the table. Con
?lm is stripped. The portion of the ?lm which
versely, slower evaporation will lengthen the crit
has been Wet with water remains transparent 35
as the ?lm dries. The condition of the ?lm can
be observed through a window in the lid. After
ical time intervals. However, the ratio between
and non-crystalline; the part that has not been
wet with water remains hazy and crystalline.
The clear ?lm has substantially the same tensile
strength and elongation as that described in Ex
ample I.
the critical time intervals of two different com
positions is substantially independent of the evap
oration rate.
Thus, it will be seen that the proc
40 ess is more easy to control if ‘a modifying agent
The following experiment, which is illustrative
of the value of the classof modifying agents used
for increasing the critical time interval, compares
the results obtained from ?lms made from two
solutions of the polymer each of which is com 45
of the kind pointed out above is used. The pre
ferred modifying agent is aluminum palmitate.
Aluminum salts of other long chain aliphatic
acids and magnesium salts of these acids also are
very effective modifying agents. Similar salts of
alkaline earth metals, alkali metals, ammonia
. posed of 1500 parts of the polymer (melting point
and amines, as well as the, long chain acids them
105° C.) dissolved in 6000 parts of xylene, but
selves, also are operable, but do not increase the
only one of which contains aluminum stearate
critical time intervals as markedly as the alumi
(15 parts). A ?lm from each solution was flowed
num salts. Effective concentrations of these
out at 100° C. These ?lms were flowed, simul 50 modifying agents, based on the ethylene polymer,
taneously and under opposite sides of the same
are from about 0.1% to about 10%.
spreader blade having a clearance of 0.012," on
The critical time interval will vary appreciably
the casting plate I I described in connection with
with the solvent used. Aliphatic hydrocarbons
Fig. 3, and the behavior of the two ?lms was
having boiling points above about 100° C. also
observed through the window l8. Pouring cold 55 are suitable. Chlorinated hydrocarbons having
water on the ?lm not containing the aluminum
boiling points above about 100° C. are also oper
soap within the time interval of from about 4
able but have substantially smaller critical time
to, 4.25 minutes after casting sets the ?lm to a
intervals.
,
clear solid ?lm. This ?lm or that containing the
The quenching liquid is preferably water hav
aluminum soap cannot be quenched before about 60 ing a temperature of from 0° to 10° C. _ The
4 minutes without becoming opaque, white and
temperature of the water can, however, be con
weak, but the ?lm containing the aluminum soap
siderably higher, and temperatures as high as 70°
can be quenched to a clear non-crystalline ?lm
C. can be used if the water is kept ?owing rapidly.
at any time during the much longer period of
The
higher temperatures are less desirable be
from 4 to 8 minutes after casting.
cause of greater tendency toward partial crystal
The modifying agents used to increase the crit
lization and slight haze formation. The water
' ical time interval are of the formula X(R)a(Y)b,
should ?ow against and then away from the ?lm
in which X is a member of the class consisting
so that it does not become stagnant and heated
of hydrogen and metals, R is a member of the
at the point where it contacts the ?lm. In place
class consisting of carboxylic and sulfonic acid 70 of
water various other quenching liquids, such
radicals containing from 6 to 30 carbon atoms
as
alcohols, esters and ethers, which are non--’
and preferably from 10 to 30 carbon atoms, Y is
an hydroxyl group, a is an integer ranging from 1
solvents for the polymer can be used.
The temperature of the ethylene polymer solu
tion from which the ?lm is formed is not particu
.
to the valence of X, b is an integer ranging from
0 to one less than the valence of X, and the sum 75 larly important, except that as in any solution
2,405,977
7
8
casting process it should be below the boiling
point but somewhat higher than the temperature
of the casting support in order to prevent the
I claim:
1. A process for preparing transparent ?lms
from a normally solid polymer of ethylene which
melts at a temperature of from 100° C. to 120° C.,
formation of vapor bubbles in the ?lm, The con
centration of the ethylene polymer in the solu
tion is preferably about 25% by weight,but can
range from 5% to‘ 40%.
Although the present process is most ad
vantageously carried out on a drum as the casting
said process comprising casting a ?lm on a cast
ing support from a liquid composition, the tem
perature of said liquid composition being above
the melting point of said polymer, and the tem—
perature of said support being below the melting
support, other types of casting supports, such as 10 point of said polymer but not more than 15° C.
an endless belt, can be used. This invention is
below the melting point of said polymer, said
also applicable to coating of various substrates,
liquid composition comprising a modifying agent
including paper, cloth, and the like.
and a solution of said polymer, maintaining the
The transparent ?lms prepared by the process
film in contact with said support until substan
of this invention are characterized by high ?exi 15 tially all of the solvent is evaporated from the
bility, high resistance to tearing, retention of
?lm, quenching the ?lm by contacting it with a
toughness at very low temperatures, and excel
non-solvent cooling liquid at a temperature of
lent waterproofness and moisture impermeability.
from 0° C. to 70° C. just prior to crystallization
Because of these properties they are well adapted
and haze formation in the ?lm, and then strip~
as protective wrappings for food, tobacco, medic
ping from the casting support the'transparent
inal products, clothing and the like. They are
?lm thus obtained, said modifying agent being
also useful as protective coatings for paper, card
present in amount of from 0.1% to 10% of the
board, fabrics. and other ?exible materials, to
weight of the ethylene polymer in said solution
which they may be laminated by heat or pressure
or with an adhesive.
The unsupported ?lms or -
laminated articles are particularly useful as elec
trical insulating materials.
'
As many apparently widely di?‘erent embodi
ments of this invention may be made without de
parting from the spirit and scope thereof, it is to
be understood that I do not limit myself to the
speci?c embodiments thereof except as de?ned in
the appended claims.
and consisting of a substance selected from the
group consisting of fatty acids containing from 6
to 30 carbon atoms, and salts of said acids.
2. The process set forth in claim 1 in which
said small amount of substance contained in said
solution of ethylene polymer is aluminum palmi
tate.
FRANKLIN TRAVISS PETERS.
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