Note: Descriptions are shown in the official language in which they were submitted.
~3~7,~
865~ I,SS
, c~SPEC\8654 . LSS
ICROFINE MELT FLOW RATE POLY~ER P0~1DERS AND
PROCESS FOR THEIR PREP.~RATION
The present invention relates to microfine
5 ethylene copolymer powders which are crosslinkable and
wherein the powder particles are spherical or
substantially spherically in shape. The invention also
relates to a process for producing and crosslinking the
polymer powder.
The use of thermoplastic resin powders is well
documented in the prior art. For example, powdered
thermoplastic resins in dry form have been used to coat
articles by dip coating in either a static or fluidized
bed and by powder coating. Powders can also be applied
15 in dispersed form, by roller coating, spray coating,
slush coating, and dip coating substrates such as metal,
paper, paperboard, and the like. Powders are also
widely employed for conventional powder lining and
powder molding processes, e.g., rotational molding.
20 Still other applications for powders include use as
paper pulp additives; mold release agents; additives to
waxes, paints, caulks, and polishes; binders for non-
woven fabrics; etc.
Besides the physical properties of the powder~
which are dictated by the resin being used, the size and
shape of the particles are the other major properties
which influence the selection of a powder for various
applications. These latter properties are primarily a
function of the process by which the powders are
prepared, which can include mechanical grinding,
solution processes and dispersion processes. Particle
size is determined using U.S. Standard Sieves or light
;.
'. ': '
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-2- 2 ~ 2~ J ~ 33
1 scattering techniques and, depending on the method used,
will be reported in mesh size or microns. The inverse
relationship between the sieve size (mesh number) and
particle size (in microns) is well documented and
5 conversion tables are available. The shape of the
particles is ascertained from photoimicrographs of the
powders. Particle shape has a marked influence on the
bulk density of the powder and its handling properties.
~or most effective fluidization and dry
10 spraying, it is generally considered advantageous to use
powders which have a fairly narrow particle size
distribution and wherein the particles are spherical in
shape. Powders produced by mechanical grinding or
pulverization, which are typically irregular in shape
15 and generally have quite broad particle size
distributions, are not well suited for fluidization and
dry spraying. While the particles of powders produced
by solution processes are less irregular than those
obtained by mechanical means, they are still not
20 spherical.
Powders obtained using dispersion techniques,
such as those described in U.S. Patent Nos. 3,422,049
and 3,746,681, wherein the particles produced are
spherical in shape and fall within a relatively narrow
25 size range are most advantageously employed for
~luidization and dry spraying. These processes involve
dispersing a molten synthetic organic polymeric
thermoplastic resin in about 0.8 to 9 parts by weight of
water per part of resin in the presence of from about 2
30 to 25 parts by weight per 100 parts of resin of a water-
soluble bloc~ copolymer of ethylene oxide and propylene
oxide having a molecular weight above about 3500 and
: : ~ :
~ ~ $ ~ ~ 2 ~
1 containing at least about 50~ by weight of ethylene
oxide and in the absence of an organic solvent for the
polymer. The fine dispersion which is produced is then
cooled to below the softening temperature of the resin
5 to obtain the powder.
A continuous process for the preparation of
finely divided polvmer particles is disclosed in U.S.
Patent No. 3,432,483. The process comprises the
sequential steps of feeding to the polymer, water and a
10 water-soluble block copolymer of ethylene oxide and
propylene oxide surfactant into a dispersion zone;
vigorously agitating the mixture under elevated
temperature and pressure to form a dispersion of the
molten polymer; withdrawing a portion of the dispersion
15 and coolin~ to a temperature below the melting point of
said polymer to form solid, finely divided polymer
particles in the dispersion; reducing the pressure of
said cooled dispersion to atmospheric pressure;
separating the solid polymer particles from the
surfactant solution phase and washing; drying the washed
polymer particles; and recovering dry, finely divided
powder.
While it is possible to produce a wide range
of fine powders using such procedures, the method is not
adaptable for use with all resins. As the melt index of
a resin approaches 1, it becomes increasingly difficult
to achieve the type of dispersions necessary to form
fine powders. Dispersion having droplets of the size
necessary for the production of fine powders cannot be
formed with ractional melt flow rate resins, i.e.,
resins having a melt index less than 1. This is
believed to be duer in part, to the high molecular
' :
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2~$~
l weights of such resins. The relationship of melt flow
rate to molecular weight and the inability to form
dispersions suitable for the production of fine powders
with low melt flow rate resins is discussed in U.S.
5 Patent No. 3,746,681.
It would be advantageous if fine powders o~
low melt flow rate resin powders could be produced
utilizing a dispersion process, particularly if the
particles had a relatively narrow particle size
lO distribution and were spherical in shape. Coatings
obtained using such powders would be expected to have
improved thermal stability, improved creep resistance,
improved chemical resistance and other desirable
properties.
Ethylene/vinylalkoxysilane copolymers are
known. They are disclosed in U.S. Patent Nos. 3,225,018
and 3,392,156. In U.S. Patent No. ~,392,156 it is also
disclosed that the ethylene/vinyltrialkoxysilane
copolymers can be used in finely divided form where the
20 copolymer has an average size of less than about 1~ mesh
and preferably in the range of about 150 to 2000
microns. While the reference states that the finely
divided material may be prepared by mechanical grinding,
solution or dispersion technigues or other methods, no
25 details are provided. Furthermore, it is a requirement
of the process that the products be mechanically worked
to obtain a reduction of melt index and an increase in
stress cracking resistance. Melt indexes obtained after
mechanical workiny range from 7.95 to zero.
It would be advantageous to have a process
whereby the melt flow rate of polymer powders could be
reduced independent of the powder forming operation.
.
.
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1 This would e~able proCessQrs to "customize" the melt
flow rate of the powders to their specific application.
It could also provide better control of the
crosslinking. By having the crosslinking take place
5 outside the powder-forming reactor, fouling or corrosion
of the primary reactor caused by the presence of
crosslinking catalysts could be avoided. It would be
particularly useful if the melt flow reduction could be
performed on the powders without substantially changing
10 the particle size or particle size distribution.
Accordingly, the present invention relates to
a microfine olefin copolymer powder comprised of
particles which are spherical or substantially spherical
in shape and wherein 80 percent or more of the particles
15 range in size from 10 microns to 500 microns, said
olefin copolymer comprised of an a-olefin having from 2
to 8 carbon atoms and an unsaturated alkoxysilane of the
formula
R-Si(R-)~(Y)3_~
20 where X is an eth~lenically unsaturated hydrocarbon
radical having from 2 to 6 carbon atoms, R~ is a
hydrocarbon radical having from 1 to 10 carbon atoms, Y
is an alkoxy group having from 1 to 4 carbon atoms and n
is an integer from 0 to 2. More particularly, the
25 present invention relates to the foregoing defined
microfine olefin copolymer wherein the powder is capable
of being crosslinked and having a melt flow rate greater
than 1. -Also, the present invention relates to a
microine copolymer powder being chemically crosslinked
30 and having melt flow rate less than about 1 comprised of
particles which are spherical or substantially spherical
in shape and wherein 80 percent or more of the particles
' - ' :. '
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2 ~ 3
1 range in size from 10 microns to 200 microns, said
olefin comprised of an a-olefin having from 2 to 8
carbon atoms and an unsaturated al~;oxysilane of the
formula
R-Si(R )~(Y)3_rl
where R is an ethylenically unsaturated hydrocarbon
radical having from 1 to 10 atoms, Y is an alkoxy group
having from 1 to 4 carbon atoms and n is an integer from
0 to 2.
The particles of these fractional melt flow
rate powders are substantially spherical in shape and
fall within a relatively narrow particle distribution
range. For the process of the invention, a dispersion
is first formed using an olefin copolymer resin which
15 has a melt flow rate such that acceptable dispersions
can be produced, i.e., dispersions wherein a droplet
size necessary to produce fine powders can be formed.
More particularly, the present invention
provides for a process for producing substantially
20 spherical microfine polymer powders comprising to the
steps of: combining an olefin copolymer having a melt
index greater than 1 with 4 to 50 percent, based on the
weight of the olefin copolymer, of a nonionic surfactant
which is a block copolymer of ethylene oxide and
25 propylene oxide, and a polar liquid medium which is not
a solvent for the olefin copolymer and which does not
react with any of the foregoing ingredients under the
conditions employed, the weight ratio of the polar
liquid medium to the olefin copolymex ranging from 0.8:1
30 to 9:1; heating the mixture to a temperature above the
melting point of the olefin copolymer; dispersing the
mixture to form droplets of the desired size; cooling
. . . . . , - , . .. .
,. . . . ~, .
2~ J2
1 the dispersion to below the melting point of the olefin
copolymer; and recovering the olefin copolymer powder.
In accordance with said process, microfine
ethylene copolymer powders are produced which are
5 crosslinkable. The particles of these crosslinkable
powders are spherical or substantially spherical in
shape, typically with 80 percent or more of the
particles ranging in size from about 10 up to about 500
microns. The ability to crosslink the powders provides
10 a convenient means ~or reducing the melt ~low rate of
the powder and in those cases where it is desired, makes
it possible to produce fractional melt flow rate
powders.
This necessarily requires that the olefin
15 copolymer used has a melt flow rate greater than 1 since
it is not possible to adequately disperse resins having
melt flow rates lower than 1 and to produce acceptable
powders. While forming the powder having the desired
shape and size or subsequent to forming the powder, the
20 formed powder is contacted with moisture and a silanol
condensation catalyst to reduce the melt flow rate to
the desired level. The silanol condensation catalyst is
a catalyst selected from the group consisting of organic
bases, mineral or carboxylic acids, organic titanates
25 and complexes or carboxylates of lead, cobalt, iron,
nickel and tin and is usually present in an amount from
about 0.001 to 10 percent, based on the weight of the
olefin copolymer. In a particularly useful embodiment
of the invention, the crosslinking and melt flow
30 reduction are accomplished by suspending the powder in
an a~ueous medium containing the catalyst and contacting
at an elevated temperature below the melt point of the
.
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.
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l polymer for a period of time sufficient to effect the
desired degree of crosslinking and melt flow reduction.
The olefin copolymer powder is then recovered by
conventional procedures.
For the process of this invention, powders of
olefin copolymer resins which are readily dispersible
using conventional dispersion techniques, i.e., which
have melt flow rates greater than 1, are first produced.
These powders are produced using known procedures such
lO as those of U.S. Patent Nos. 3,422,049, 3,432,483 and
3,746,681, details of which are incorporated herein by
reference thereto. Olefin copolymers having an
unsaturated alkoxysilane incorporated therein by
copolymerization or grarting are employed for this
15 invention.
For the powder-forming process, the ole~in
copolymer is charged to the reactor with a polar liguid
medium, a nonionic sur~actant, and optionally a silanol
condensation catalyst and a dispersion is formed in
20 accordance with conventional dispersing procedures ~nown
to the art. The dispersing apparatus may be any device
capable of delivering su~ficient shearing action to the
mixture at elevated temperature and pressure.
Conventional propeller stirrers designed to impart h~gh
25 shear commercially available for this purpose can be
used. The reactor may also be equipped with baffles to
assist in dispersion. The particle size and
distribution of particles are dependent on the shearing
action which, in turn, is related to the stirrer design
and rate of stirring. ~gitation rates can vary over
wide limits but the speed of the stirrer will usually be
controlled so that the tip speed is between about 500
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1 and 3500 ftjmin and, more commonly, 750 and 3000 ft/min.
~ higher tip speed is generally required for batch
operation, usually 2500-3000 ft/min. Tip speeds for
continuous procedures will most generally be between 750
5 and 2500 ftlmin~
The dispersion process is typically conducted in an
autoclave since this permits the process to be conducted at
elevated temperature and pressure. In the usual batch conduct
of the process, all of the ingredients are charged to the
10 autocla~e and the mixture is heated to a temperature above the
melting point of the olefin copolymer. While the temperature
will vary depending on the specific copolymer used, it will
typically range from about 90C to 250C. Since the ~luidity
of polymers is temperature related, it may be desirable to
15 carry ou~ the process at temperatures substantially above the
melting point of the olefin copolymer to facilitate dispersion
formation. Stirring is commenced after the desired temperature
is reached. Stirring is continued until a dispersion of the
deslred droplet size is produced. This will vary depending on
the copolymer being used, the temperature and amount and type
of surfactant, and other process variables but generally will
range from about 5 minutes to about 2 hours. Most generally,
the stirring is maintained for a period from 10 to 30 minutes.
A polar liquid medium which is not a solvent ~or the
olefin copolymer is employed to form the dispersions~ These
polar mediums are hydroxylic compounds and can include water,
alcohols, polyols and mixtures thereof. The weigbt ratio o~
the polar liquid medium to olefin copolymer ranges from about
3o 0.8:1 to about 9:1 and, more preferably, from 1:1 to 5:1. It
is particularly advantageous to use water as the dispersing
medium or to use a liquid medium where water is the major
component. The pressure o~ the process is not critical so long
as a liquid phase is maintained and can range from about 1 up
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l to about 217 atmospheres. The process can be conducted at
autogenous pressure or the pressure can be adjusted to exceed
the vapor pressure of the liquid medium at the operating
temperature. Most generally, with aqueous dispersions the
pressure will range from about S to 120 atmospheres.
To obtain suitable dispersions with the olefin
copolymers, one or more dispersing agents are employed for the
process. Useful dispersing agents are nonionic surfactants
which are b~ock copolymers of ethylene oxide and propylene
oxide. Preferably, these nonionic surfactants are water-
soluble block copolymers of ethylene oxide and propylene oxide
and have molecular weights greater than about 3500. Most will
contain a major portion by weight of ethylsne oxide and are
obtained by polymerizing ethylene oxide onto preformed
polyoxypropylene segments. The amount of nonionic surfactant
employed can range from about 4 to 50 percent, based on the
weight of the olefin copolymer. Most preferably, the nonionic
~urfactant ie present from about 7 to 45 percent, based on the
weight of the polymer.
Useful nonionic surface active agents of the above
type are manu~actured and sold ~y BASF Corporation, Chemicals
Division under the trademark Pluronic. These products are
obtained by polymerizing ethylene oxide on the ends of a
preformed polymeric base o~ polyoxypropylene. Both the
molecular weight of the polyoxypropylene base and the
polyoxyethylene segm~nts can be varied to yield a wide variety
of products. one such compound found to be suitable for the
practice of the process of this invention is the product
designated as F-98 wherein a polyoxypropylene of average
molecular weight of 2,700 is polymerized with ethylene oxide to
give a product of molecular weight averaging about 13,500. This
product contains 20 weight percent propylene oxide and 80
weight percent ethylene oxide. Other effective Pluronic~
surfactants include F-88 (M.W. 11,250, 20S propylene oxide, 80%
- - ,
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'
.
- 1 1--
l ethylene oxide), F-108 (M.W. 16,250, 20~ propylene oxide, 80
ethylene oxide), and P-85 (M.W. 4,500, 50% propylene oxide, 50
ethylene oxide). These compounds, all containing at least
a~out 50 weight percent ethylene oxide and having molecular
weights of at least 4,500, are highly effective as dispersing
agents for the aforementioned oleEin copolymers.
It is also possible to employ products sold under the
trademark T~tronic which are prepared by huilding propylene
oxide block copolymer chains onto an ethylenediamine nucleus
and then polymerizing with ethylene oxi~e. Tetronic~ 707 and
Tetronic~ 908 are most effective for the present purposes.
Tetronic~ 707 has a 30 weight percent polyoxypropylene portion,
of 2,700 molecular weight, polymerized with a 70 weight percent
oxyethylene portion to give an overall molecular weight of
12,000. Tetronic~ 908, on the other hand, has a 20 weight
percent polyoxypropylene portion, of 2,gO0 molecular weight,
polymerized with an 80 weight percent oxyethylene portion to
give an overall molecular weight of 27,000. In general,
useful Tetronic0 surfactants have molecular weights above
10,000 and contain a major portion by weight o ethylene oxide.
- ~ The powder-forming p~ocess may also be conducted ln a
continuous manner. If continuous operation is desired, the
lngredients are continuously introduced to the system while
removing the dispersion from another part of the system. The
ingredients may be separately charged or may be combined,for
introduction to the autoclave.
.
` `: ` :
-12- 2~ J~
Olefin copolymers containing randomly copolymerized
or grafted unsaturated alkoxysila~e is necessarily employed to
obtain the crosslinkable powders of the invention. More
specifically, the olefin copolymers are comprised of ~-olefins
having from 2 to 8 carbon atoms and unsaturated alkoxysilanes
of the formula
R -si (R*)o(Y)3o
where R is an ethylenically unsaturated hydrocarbon radical
havlng from 2 to 6 carbon atoms, R* is a hydrocarbon radical
having from 1 to lO carbon atoms, Y is an alkoxy group having
from 1 to 4 carbon atoms and n is an integer from Q to 2. The
olefin copolymers must be readily dispersible in the liquid
medium employed for the process. The olefin copolymers will
therefore have melt flow rates greater than 1, and more
typically g~eater than about 3. While the melt index may range
as high as 500, it generally does not exceed about 300 and,
more preferably, will ba less than 100.
Random copolymers of ethylene and unsaturated
20 al~oxysilanes, such as vinyltrialkoxysilanes, are known. Such
copolymers can be obtained in accordance with any of the
recognized procedures such as those described in U.S. Patent
.. _ ....... . . . . . .
Nos. 3,225,018 and 3,3~2,15~. Generally, these copolymeriza-
tions are carried out at high pressure and temperature in the
25 presence of a free radical initiator. Copolymers wherein an
unsaturated alkoxysilane is grafted onto an olefin polymer
backbone are also known and can ~e prepared in accordance with
conventional procedures. Free radical initiators, such as
peroxides, are generally used to facilitate grafting alkoxy-
3 silanes onto the polyolefins.
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-13- ~3~
The unsaturated alkoxysilane will constitute from
about 0.25 to 20 percent ~y weigllt and, more preferably, from
about 0.5 to lo percent by weight of the ole~in copolymer. In
a highly useful embodiment of th:is invention, the unsaturated
alkoxysilane is a vinyltrialkoxysilane, i.e., where R is a
vinyl group and n is o. It is especiaily advantageous to
utilize vinyltrimethoxysilane or vinyltriethoxysilane, i.e.,
where R is a vinyl group, n=o and Y is methoxy or ethoxy,
respectively. Olefin copolymers derived from C23 ~-olefins are
especially useful. Minor amounts of higher olefins may be
present, particularly if the unsaturated alkoxysilane is
grafted. ~hile polyethylene is-most commonly grafted,
copolymers of ethylene with propylene, butene-1 and hexene-l
are also suitable. When the ~-olefin and unsaturated alkoxy-
silane are copolymerized, ethylene is preferably e~ployed
particularly when the alXoxysilane is vinyltrimethaxysilane or
vinyltriethoxysilane. When the olefin copolymer is comprised
of an ~-ole~in and unsaturated alkoxysilane only, the ~-olefin
will constitute from 80 to 99.7S weight percent and, more
preferably, 90 to 99.5 weiqht percent of the polymer.
one or more other monomers may be included with
~-olefin and unsaturated alkoxysilane. Such comonomers include
vinyl esters of C2~ aliphatic carboxylic acids, C~ alkyl
acrylates, and Cl~ alkyl methacrylates. The comonomers can be
copolymerized with the unsaturated alkoxysilane and ~-olefin or
the unsa~urated alkoxysilane can be grafted onto a copolymer
form by copolymerizing an ~-ole~in and the comonomer. When
comonomers are present, the olefin copolymer will comprise 55
30 to 99.5 percent ~-olefin, 0.25 to 20 percent unsaturated
alkoxysilane and 0.25-to 4s percent comonomer(s~. More
commonly, the copolymers will contain 55 to 99 percent
~ olefin, O.S to 40 percent unsaturated alkoxysilane and 0.5 to
. .
-14- 2~2~,3
1 40 percent comonomer. Preferred vinyl esters of c~ aliphatic
carboxylic acids include vinyl acetate and vinyl butyrate.
Ethyl acrylate and n-butyl acrylate are particularly useful C~b
alkyl acrylate comonomers. Ethyl methacryla~e is a
5 particularly useful cl~ alkyl methacrylate comonomer.
The microfine olefin copolymer powders obtained Wi
have 80 percent or more of the particies ranging in size from
1~ microns to 500 microns. In an especially useful embodiment,
the particle size will range from 20 to 300 microns. To
produce powders of the desired particle size, a dispersion
having droplets of the desired size must be formed. This
requires proper selection of the operating conditions, such as,
temperature and agitation, as well as proper selection of the
dispersing agent (surfactant) to coat the droplets. The
temperature of the dispersion is then lowered to oelow the
melting temperature of the olefin copolymer and the polymer is
separated from the liquid phase by filtration, centrifugation,
decantation' evaporation, or the like. In a highly useful
. . ...
embodiment of the invention, the temperature of the dispersion
is lowered to below the boiling point of the water or other
liquid medium and the finely di~ided polymer is recovered by
atmospheric or vacuum-assisted filtration. The cooling may be
accomplished by removing the heating source and allowiny the
mixture to cool or the hot dispersion may be rapidly quenched
by mixing with cold liquid which is not a solvent for the
polymer. This liquid may be the same or different than that
employed as the dispersing medium. ~ater is preferably used
for this purpose.
.
: ; : - ,
-15~ ?J3
1 The polym~r powder may be washed and/or dried before
being subjected to the crosslinking operation; however, this is
not necessary. The powder may be crosslinked as it i5 obtained
from the powder-forming process. For example, if the powder is
recovered using the quenchin~ procedure, it may be
advantageously crosslinked while suspended in all or a portion
of the quenching medium.
To crosslink the result:ing olefin copolymer powders
and effect reduction of the melt flow rates, the powders are
contacted with water in the presence of a silanol condensation
catalyst. If the powders are dried after the powder-forming
operation, they are suspended in an aqueous medium containing
the condensation catalyst. If, however, the powder is used
directly as it is obtained from the quenching step, the
catalyst may simply be added to this mixture and additional
water added if desired.
The amount of water required for crosslinking can be
varied over wide limlts. Small amounts of water may be used
since, in theory, each molecule of water can produce one
crosslink site. on the other hand, large excesses on the order
of 100 or mdre parts water per part olefin copolymer can be
used. Such large volumes of water are not necessary, however,
and can present handling and disposal problems. Generally, the
weight ratio water to olefin copolymer powder will range from
25 0.001:1 to 20:1 and, more preferably, from 0.01:1 to S:1. One
or more other organic liquids may be included with the water.
~ These organic liquids should be miscible with water and cannot
; be a solvent for the polymer. Such iiquids include alcohols,
polyols, ketones, aldehydes, carboxylic acids, carboxylic acid
3lesters and the like. If a carboxylic acid is employed with
water as the suspending medium, it can also serve as the
crosslinking catalyst. The organic liquids should not
,
:
- . . ~ : :
-16-
2~2~'~
1 excessively swell or soften the powders as this will cause the
powder particles to agglomerate. As a practical matter, the
organic liquid will also generally have a boiling point above
the operating temperature used for the crosslinking. If an
organic liquid is present with the water, the ratio of water to
organic liquid can range from about 99:1 to about 1:99.
While the olefin copolymer powders can be crosslinked
under ambient conditions it is more customary to carry out the
crosslinking at an elevated temperature. The temperature can
range up to just below the melt point of the olefin copolymer;
however, if the temperature is above the boiling point of water
or other liquids present, use o~ a con~enser or pressure vessel
is necessary. Generally, the crosslinking and melt flow
reduction will be carried out at a temperature fro~ ambient up
to about 110C and, more preferably, from 50C to 100C.
While it is not necessary to employ a surlact~nt in
the crosslinking step, surfactants or dispersants may be
included in the aqueous medium if desired. If a surfac~ant is
used it may be the same or different than the surfactant used
in tha powder-forming operation. Residual surfactant resulting
from the powder-forming operation can be utilized for this
purpose or dther surfactants may be employed. In continuous
processes, the first wash of the powder produced in the powder-
2, forming step which will contain the bulk of the surfactant maybe recycled and the powder and any residual surfactant can be
fed to a downstream vessel where the crosslinking reaction will
be carried out. After crosslinking, the powder can be washed
to then remove final traces of surfactant and catalyst
3~ residues.
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` -17- 2~ 23
l A silanol condensation catalyst is necessarily
employed to crosslink the powders. These catalysts generally
include organic bases, mineral ac:ids, c~22 carboxylic acids or
anhydrides, organic titanates and complexes or carboxylates of
lead, cobalt, iron, nic~el, zinc and tin. Lauryl amine, acetic
acid, azelaic acid, lauric acid, palmitic acid, stearic acid,
maleic acid, maleic anhydride, dibutyltin dilaurate, dibutyltin
maleate, dibutyltin diacetate, dibutyltin dioctoate, stannous
acetate, stannous octoate, lead naphthenate, zinc caprylate,
and cobalt naphthenate are illustrative of the catalysts which
can be used. Dialkyl tin carboxylates, especially dibutyltin
dilaurate and dibutyltin maleate, and Ct~l aliphatic
monocarboxylic acids, especially acetic acid and stearic acid,
are highly effective crosslinking catalysts for this invention.
The amount of catalyst used can vary over wide limits
depending on the catalyst and ole~in copolymer used and ~ince,
in some instances, the catalyst can also serve as the
suspending medium. Where the catalyst also functions as the
suspending medium, such as in the case of certain carboxylic
acids, it can constitute up to as high as 90 percent of the
total suspension mixture. In most instances where the catalyst
is not part of the suspending medium, the catalyst will
typically constitute from 0.01 percent up to about 5 percent of
the total mixture. More commonly, the silanol condensation
catalysts comprise from about 0.1 to 1 percent of the
suspenslon.
The following examples illustrate the process of the
invention and the crosslinkable powders obtained therefrom more
3 fully. As will be apparent to those skilled in the art,
numerous variations are possible and are within the scope of
the invention. In the examples all parts and percentages are
given on a weight basis unless otherwise indicated.
' ` -18- ~ 3
l The powders produced in khese examples were analyzed
using laser light scattering to determine average particle size
and particle size distribution. ~ Model 2600C Malvern Particle
Size Analyzer with the proper lens configuration for the
expected particle size to be measured and equipped to
automatically calculate the distribution curve and average
particle size was used. For the analysis, water is charged to
the water bath and circulated th;roug~ the sample measuring
chamber. After obtaining the baseline measurement, the
agitator and sonic vibrator are turned on and powder is added
to the water bath until the obscuration reading is 0.3. Mixing
and circulation are controlled to obtain acceptable dispersion
without excessive foaming. A drop of liquid detergent is added
to facilitate dispersion. After eight minutes a~itation,
- measurements are taken over a period of time and the
distribution curve and average particle size are calculated.
Duplicate runs are made for each powder sample. The particle
size reported in the examples is the number average particle
size D(v, 0.5). The range reported for the particle size
distribution in the examples is for 80 percent of the
distribution curve, i.e., 10 percent of the powder particles
will ~all below the lower limit of the recited distribution and
10 percent will be larger than the upper recited particle size
distribution limit.
Melt flow rates provided in the examples were
measured in accordance with ASTM D1238-89 at 190C with a
~inius Olsen Extrusion Plastometer. Melt flow rates are
expressed in grams per 10 minutes.
3o
. .. . .
.
2~$~?J2~
E~:HPI.~B I
To demonstrate the improved process of the invention
whereby fractional melt flow rate microfine powders are
produced, 340 parts random copolymer of ethylene and vinyltri-
ethoxysilane having a melt flow rate of 4.8 and containing 4.0%
vinyltriethoxysilane was charged to a reactor with 810 parts
deionized water, 97.2 parts nonionic.surfactant (Pluronic~ F-98
- a block copolymer of ethylene oxide and propylene oxide of
molecular weight 13500 and containing 20~ propylene oxide3, and
7 parts polyethylene grafted with 2% maleic anhydride ~MFR 10).
Based on the weight of the copolymer, the amount of surfactant
and catalyst used was 28% and 2~, respectively. The reactor
was sealed and the mixture heated for 52 minutes at 216C ~nder
400 psi pressure. Agitation was commenced and maintained for
15 minutes. The stirrer speed was maintained at 3000-3300 rpm
(tOp speed 2350 to 2590 ft/min) during the 15 minute interval.
The contents of the reactor were then emptied into a stainle~s
steel tank containing approximately 5 liters cold water to
precipitate the copolymer. The resulting ethylene-
vinyltriethoxysilane copolymer powder was recovered by
filtration and dried. The powder had a melt flow rate of 0.14,
number average particle size of 62 um and the particle size
distribution ranged from 28 to 161 um. Micro-~copic examination
f the powder particles showed them to be spherically shaped.
-. . ' . .. ` :
.'. : ~ .- : -
: - - ., ,
:.
` -20
1 EgAHPL~
Example I was repeated except that a dif f erent
catalyst was used to brinq about the melt flow reduction. The
amount o~ copolymer, water and sur.Eactant used was identical to
Example I. Five parts acetic acid (1.44~ based on the
copolymer) was used as the catalyst. The resulting powder had
a melt flow rate of 0.11, an average particle size of 56 um and
particle size distrib~tion ranging from 25 to 145 um.
, -21- ~ ?~3
1 E~A~P~B III
Following the procedure of Example I an experiment
was conducted using stearic acid as the catalyst. The amount
of copolymer, water and surfacta:nt used was the same as in that
example except that 0.2 parts stearic acid (0.06~ based on the
weight of the copolymer) was useld. The resulting microfine
powder particles were spherically shaped, had a melt flow rate
of 0.01, an average size of 76 um and size distribution of 37-
148 um.
.
. .. - . .
::
-22- 2~8~223
CO~SPAR~TIVE Ea~lPL}: A
To demonstrate the need to use a catalyst for the
process of the invention, Example I was repeated except that
the polyethylene grafted with mal~eic anhydrids was omittad from
the reaction. The reactant chargle and reaction condi~ions wer~
otherwise identical, While a fine powder was produced (average
particle sizs 55 um and particle ~size distribution 27-108 um),
the melt flow rate of the resultin~ ethylene-vinyltriethoxy-
silane powder was 4.6.
-
.
~:
, . . - ,.. : , . : .` : .
-23- 2~122~
COHPAR~TIyE E~.H2~E E3
To demonstrate the ina~ility to disperse fractional
melt flow rate polymers, 347 parts polyethylene having a melt
index of o. 17 was charged to the reactor with 49 parts
surfactant (Pluronic~ F-98) and and.810 parts water. The
mixture was heated for 52 minutes at 216C under 400 psi
pressure and then agitated for 15 minutes at the same rate as
used for Example I. When the reactor contents were discharged,
essentially all of the polymer re~ained in the reactor.
Dlsassembly and inspection of the reactor revealed that the
polymer was agglomerated on the agitator blades. Increasing
the surfactant ~oncentration, up to as high as equal parts
surfactant based on the resin, still did not produce acceptable
dispersions capable of yielding f ine powders.
- .~. : .:: , , . ~ :: - ~
.
, -24- 2~ 2~
1 E~AHP~E IV
To demonstrate the ability to use other ethylene-
vinyltriethoxysilane copolymers, in the process of the
invention, the following experiment was carried out. For the
reaction, 350 parts ethylene-~inyltriethoxysilane copolymer
having a melt index of 5 and containing 1.9 weight percent
copolymerized vinyltriethoxysilane was charged to a reactor
with 810 parts water. Twenty-eicJht percent surfactant
(Pluronic~ F-98), based on the we.ight of the copolymer, and
o.06~ stearic acid, based on the weight of the copolymer, were
also charged to the reactor. The materials were then dispersed
and the copolymer recovered in accordance with the procedure of
Example I. The resulting powder comprised of spherical
particles had a melt flow rate of 0.17. The average partlcle
size of the powder was 53 um and the particle size distribution
was 27-96 um.
When the above procedure was repeated, except that
the amount of stearic acid used was doubled, comparable
fractional melt flow ra~e microfine powders were produced. The
powders had no measurable flow rate, an average particle size
of 77 um and particle size distribution ranging from 47 to 140
um.
3o
- -: : . , , ~ ' ~ :
.
-~5-
2~3~w23
E~A~PLE V
Example IV was repeated using ethylene-vinyltri-
Pthoxysilane copolymer having 0.8 weight percent vinyltri-
ethoxysilane copolymerized. The copolymer had a melt index of
6. When 0.12% stearic acid based on the amount of the
copolymer was employed, the resu:Lting spherical powder had a
melt index of 0.44, an average particle size of 42 and particle
size distribution of 21-72 um. Xncreasing the catalyst
(stearic acid) level to 0.23~, based on the weight of the
copolymer, yielded a powder of melt index 0.25, average
particle size of 51 um and particle size distribution ran~ing
from 25-125 um.
.. . ..
. -26-
2 ~
1 E~AMPIE VI
The versatility of the present process is further
illustrated by the following example wherein a fractional melt
flow rate powder of an ethylene-vinyl acetate copolymer grafted
wlth vinyltriathoxysilane is produced. The EVA resin contained
9~ vinyl acetate and was gra~ted with 0.9~ vinyltriethoxy-
silane. The graft copolymer had a melt flow rate of 23. For
this example, 350 parts gr~ft copolymer, 810 parts water, 10
parts acetic acid and 97.2 parts surfactant (Tetronic~ 908)
were used. After sealing the reactor, the mixture was heated
for 50 minutes at 210C at 350 psi pressure and then agitated
for 15 minutes. The stirrer speed was maintained at 3500 rpm
(tip speed 2750 ft~min). The reactor contents were then
discharged into water and the resulting powder recovered by
filtration and dried overnight in a hood. The melt flow rate
of the polymer was reduced to O.OS as a result of the
treatment. The powder consisted of spherically shaped
particles having an average particle size of 69 um and particle
size distribution ranginy from 25 to 135 um.
.... .
: :: . :' ~ - . : . , ~ .
,. . . ~ . ~ . . .
. -27~ 2~
E~HPLE VII
The procedure of Exa~ple V.L was repeated except that
lauryl amine was used as the catalyst in place of the acetic
acid and Pluronic~ F-98 was substituted for Tetronic~ 908. The
melt flow rate of the polymer powcler produced was O.OS. The
number average particle size of the powder was 43 um and
particle size distribution was 18--95 ym.
-28-
2 ~ 2 ~
1 E2AXPL~ VIII
Example VI was repeated except that a different graft
copolymer was employed. For this reaction, an EvA copolymer
(9% VA) grafted with 0.3% ~inyltrimethoxysilane was used. The
EVA resin had a melt flow rate of 20. one part acetic acid and
97.2 parts Pluronic0 F-98 surfactant were used for this
reaction. The powder produced had a melt flow rate of 0.3~,
average particle size of 9S um and particle size distribution
lO from 65 to 142 um.
..
. -29- 2~22,~
1 ! EXnHP~E IX
Preparation of ethylen~v~nyltriethoxy~llane
copolym~r powder: A crosslinkable microfine powder was
produced in accordance with the dispersion procedure descri~ed
in U.S. Patent No. 784,862. To produce the powder, an
electrically heated two-liter Paar reactor equipped with a
thermowell and thermocouple connected to a digital display was
used. The reactor was equipped with an agitator haYing three
six-bladed impellers driven by a drill press equipped with a 2
HP DC varia~le speed motor. Three hundred and forty seven
parts of a random copolymer of ethylene and vinyltriethoxy-
silane having a melt flow rate of 4.1 and containing 4.1%
vinyltrieth~xysilane was charged to ~he autoclave with ~lO
parts deionized water and 97.Z parts nonionic surfactant. The
nonionic surfactant employed was Pluronic~ F-9~ - a block
copolymer of ethylene oxide and prop~^lene oxide of molPcular
weight 1350 and containing 20~ propylene oxide. The autoclave
was sealed and heated over a period of 45 minutes up to 222C
wh~ch resulted in a pressure of 340 psi. Agitation was
commenced and maintained for 15 minutes at 3300 rpm (tip speed
2750 ft/min). The contents of the reactor were then rapidly
discharged thraugh a Strahman valve into a stainless steel ~an~
containing 5 liters of cold water to precipitate the polymer.
The resulting,,e,thylene-vinyltriethoxysilane copolymer powder
was washed several times with water, collected by filtration
and drled. 'The powder had a melt flow rate of 3.0fi and number
average particle size of 141 microns. The particle size
distribution ranged from 83 to 258 microns. Microscopic
examination of the powder showed the powder particles to be
spherically shaped.
-30- ~ 3
1 E~HPhEiX_
To demonstrate the ability to crosslink the olefin
copolymer powders of the invention to reduce the melt flow
ra~e, lOo parts of the dry powder o ethylene-vinyltriethoXy
silane copolymer powder produced in.ExampleIX was combined wlth
300 parts deionized water and ~5 parts glacial acetic acid.
The powder was suspended in the liquid medium by stirring with
a magnetic stirrer while heating the mixture at 70c for
1-1/2 hours. After this period, the polymer was recovered by
filtra~ion, washed several times with water and dried. The
melt flow rate of the dried powder was reduced from 3.06 to
~.66 as a result of this treatment.
,
. .
. : : ., . ., - .
~ 31- 2~ 2~
1 E~HPLE_XI
To further illustrate the ability to crosslin~ the
olefin copolymer powders and the ability to produce fractional
melt flow rate polymer powders, 25 parts of the ethylene-
vinyltriethoxysilane copolymer po~wder of ExampleIX was
suspended in 200 parts glacial acetic acid. The mixture wa~
stirred for 1-l/2 hours while maintaining the temperature at
70-B0C. The resulting crosslinked powder had no measurable
melt flow, i.e., melt flow rate of zero. Furthermore, this
siqnificant reduction in melt index was accomplished without
significantly alterin~ the powder characteristics. The averaqe
particle size of the crosslink powder was 153 microns and
particle size distribution ranged from 88 to 261 microns,
essentially comparable to the starting specifications of the
powder. The powder particles retained their spherical sha~e
after the melt flow reduction.
.,
.. . .
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- , , . : . ~
: , , . :
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-32-
2~2~
- E~HP~R XII
To demonstrate the ability to crosslink the polymer
powders using other catalysts, 50 parts of the olefin copolymer
powder of Example IX and 2.5 parts stearic acid were combined
with 300 part~ deionized water. The.mixture was stirred for
1-1/2 hours at a temperature o~ 70-80C. The resulting powder,
after washing with ethanol and drying, had an average particle
size of 148 microns and particle size distribution from 83 to
254 microns. Whereas the original powder had a melt 1OW rate
of 3.06, the powder after the above treatment had no measurable
flow.
'
..
~, .
..
-33-
2 ~ 3
1 E~AMP~E XII~
The versatility of the process is further
demonstrated by the following experiment wherein the conditions
were varied. For the reaction, 40 grams dry ethylene-
~inyltrlethoxysilane copolymer powder (melt index 1.7, 4.1%
VTEOS) was charged to an 800 ml resin fiask containing 50 grams
acetone and 150 grams deionized water. The resin flask was
equipped with a reflux condenser, thermometer and agitator
driven by an electric motor (Gerald ~eller GT-21 with
controller). The stirred suspension was heated to about 50C
and 0.8 gram dibutyltinlaurate dissolved in 100 grams acetone
added. After stirring the mixture at 50-521C ~or 1-1/2 hour~,
the suspension was cooled and the crosslinked powder was
recovered by filtration. The powder was washed three times by
resuspending in acetone, agitating and refiltering. The dried
powder had no measurable melt flow rate. Average particle ~ize
of the powder was 141 microns and particle size distrib-ltion
was 80-~40 microns.
.
.
- : . ~ ' :
... ..
--34--
2~,2~
E~H IJE XIY
In a manner similar to that of Examplex~ o grams of
EVTEOS copolymer was suspended in ~olution of 188 grams
ethylene glycol and 2 grams deionized water. The mixture was
heated to 80C wlth agitation and a solution of 2 grams
laurylamine in 10 grams ethylene glycol added. The mixture was
then stirred at 80-85C for 1-1/2 hours. Cold deionized water
was added and the mixture was filtered to recover the powder
The product was washed by resuspending in water (2x) and
acetone t2x). The dried powder had ~ melt index of 0.012, an
average particle size of 127 micron~ and part~cle size
distri~ution of 60-Z21 microns.
..
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.: :
