Note: Descriptions are shown in the official language in which they were submitted.
'~ }
5~ CR 7 6 0 7 -1
BACKGROUND OF THE INVENTION
(1) Field Or the Inventlon
Thls lnventlon ls concerned wlth nontacky shaped
ob~ects o~ norm~lly tacky elastomers~ and ~ process for pre-
parlng them.
(2) Descri~tion of the ~rior Art
It is a well known process to emulsify polymeriz-
able monomers in water and then convert them to polymers in
dispersed form. The resulting dispersions are called latices.
Natural rubber also occurs as a latex. Some latices are
highly useful as formed, for example, basic formulations for
latex paints. For other uses, it is necessary to coagulate
the polymer and separate it from the latex. The most
important commercial form for these polymers is as washed
and dried, nontacky shaped objects. These shaped objects
should be washed until they contain less than about 3% by
weight of water soluble material, and dried until they con-
tain less than about 1~ by weight of volatile material.
If the coagulated polymer is inherently nontacky,
the polymer is readily isolated from the aqueous phase,
washed and dried to form a free-flowing powder which is
readily handled in further processinq. If, however, the
polymer is inherently tacky, coagulating of the latex yields
the polymer in an agglomerated mass which is difficult to wash
free of impurities and also difficult to dissolve, to blend
with other materials, and to feed in compounding, curing
and molding operations.
In the field of natural and synthetic r~bber, much
attention has been given to the problem of agglomcration of
3~ normally tacky polymers before curing. Some opcrable solutions
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q~
57
have keen found.
In U.S. 2,879,173, Yacoe shows a process for
coagulating a polychloroprene latex by suspending drops in a
volatile, water-immiscible, orqanic liquid in which the poly-
chloroprene latex is insoluble while maintaining the liquid
below about -20C until the drops are completely frozen and
coagulated. The resulting frozen pellets are separated and
coated, while still frozen, with from 5% to 20% by weight of
an inert powder, such as talc, so that they will not stick
together when thawed and dried. However, the use of this
process has been limited by the cost of organic liquid
recovery, the energy cost of the refrigeration, and the un-
desirable high loading of inert material. The need for a
more practical and economical method of preparing nontacky,
washed and dried shaped objects of normally tacky elastomers
remains.
In U.S. 3,053,824, Heinz shows coagulation of a
phosphate or borate buffered elastomer latex by running it
into an aqueous aluminum or titanium salt solution contain-
ing also an alkali metal or alkaline earth metal salt. The
patent states that the resulting coagulated particles do not
stick together before being washed to remove the coagulating
salts. There is no statement as to the tack of the par-
ticles after washing.
In U.S. 3,846,365, Berg et al. show a powdery,
filled polymer prepared by emulsifying together a dilute
solution of an elastomer in a volatile organic solvent and
a solid, finely-divided filler for the elastomer, passing
the emulsion into an aqueous alkali silicate solution at a
pH preferably of 7 to 12, and evaporating the organic
,,~,.
..~
solvent. A finely-divided, tack-free coprecipitate of the
latex and silicic acid residue is formed. It is stated that
condensation of the silicate anions should be avoided.
SUM~P~Y OF THE INVENTION
This invention is based on the discovery that
nontacky, uncured, washed ~nd dried,elastomeric snape~ ob-
~ects can be produced from a normally tacky elastomer latex
- by a simple and inexpensive process. This invention provides
nontacky, elastomeric shaped objects which comprise a normally
tacky, uncured elastomer containing, based on the total
weight of the shaped object, less than about 3% by weight of
water soluble material, and less than about 1% by weight of
volatile material, and having about 0.05 to about 3% by
weight of an integral, porous coating of a water insoluble,
hydrous inorganic oxide selected from the group consisting
of ~ilicic and aluminic ~cid polymers, siliclc acid-aluminic
acid copolymers, and mixtures thereof, said shaped objects
having a minimum dimension of about O.Ol to about lO milli-
meters. By "integral" is meant a coating which has unity,
rather than being composed of discrete particles such as in
the case of a powder coating. By "minimum dimension" is
meant the diameter of the smallest round hole through which
the shaped object will pass lengthwise.
A unique feature of this invention is that,prior
to removing the water soluble and volatile materials, the
nontacky shaped objects are highly porous. This porosity
is evidenced by the objects being opaque in appearance whcn
dispersed in water, and by their cross section having a
vesicular structure in micrographs. Because of this ~orosity,
water soluble and volatile materials are easily removed by
washing and drying techniques. Some of the porosity is
retained even after washing and drying.
The nontacky,elastomeric shaped ~bjects of this
invention are prepared by a process which comprises bringing
shaped bodies of a normally tacky, uncured elastomer latex
having a solids content of 20% to 65% by weight into contact
with an aqueous bath contalning, based on the total weight
of the bath,
a) about 0.5% to ab~ut 25% by weight o~ a
soluble coa~ulating salt for the latex,
and
b) about 0.01% t~ about 5~ by wei~ht Or a
soluble or colloidally dispersed, hydrous inorganic
oxide selected from the group conslsting of silicic
and aluminic acid polymers, silicic acid-alum nic
acid copolymers, a~d mixtures thereof,
aid bath having a p~ of about 2 to about 7 such
that, when a drop of l.ON NaOH is added to the
bath, the drop is immediately surrounded by a
cloudy coating of gelled, hydrous inorganic oxlde,
thereby coa6ulating the latex and forming highly porous
~haped obJects of the coagulated elastomer coated wlth
water lnsoluble, hydrous, inorganic oxide. These shsped
ob~ects can then be washed with water until the water
soluble material content is less than about 3~ by weight,
and drled until the ~olatile material content ls less than
about 1% by weight, thereby providin~ free-flowinG, nontac~
elastomerlc ~haped ob~ects. This lnvention ls partlcularly
cuitable for producing nontacky pellets of uncured neoprene.
The term "shaped body'l is used herein to designate
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~a~s~s7
the lQtex before it contacts the aqueous bath. The term
"shaped obJect n i8 used herein to designate the l~tex ~nd
subsequent elastomer after the ~haped body enters the bath.
BRl~ DESC~IPTION OF THE DRA~INGS
Flgure 1 illustrate~ a ~le~ ln central vertical
section and partlally in slde ele~atlon of a preferred
apparatus for carrying out one embodiment Or the process o~
thls invention. Thi6 apparatus and the method of using lt
is claimed ln U.S. Patent 4,110,491 of R. M. Secor, whlch
~ssued 1978 August 2g.
~ igure 2 illustrates a top vlew o~ the same
apparatus as Figure 1 taken through cut 2-2.
Flgure 3 i~ a photomicrograph of a cross sect~on
Or a porous shaped ob~ect ln accordance wlth this in~entlon.
DESCRIPTION OF TRE PREFERR}D EMBODIMENTS
In accordance ~ith this invention, an inorganic
oxide polymer coatlng is chemically deposited on a shaped
obJect Or normally tacky elastomer from solutlon or disper-
sion in an aqueous bath. The coatlng, as formed, is there-
rOre a porous, nonpartlculate, unltary pelllcle entirelysurroundlng each shaped ob~ect. Because of the integral
nature Or the coating, nontacky ob~ects can be obtained
with very small loadings Or coating material. Thi8 18
particularly lmportant for elastomers that are ~ubsequently
dlssolved berore curlng, and i8 ln sharp contra6t to the
requisite heary loadlngs of partlculate materlals, such as
talc, ~hich have previ~usly been used to render uncured
ela~tomeric ob~ects nontacky.
m e products Or this in~ention are nontacky 6haped
ob~ects Or normally tacky, uncured elastomers. The term
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57
"ela~tomer" i~ well known to those ~kllled ln the art ~nd
has be~n derined ~n publications such as "ASTM Gloss~ry of
Terms Relatin~ to Rubber and Rub~er l.lk~ Materials", page
38. By "normally tacky elastomer" ls meant an elastomer, two
~ieces of h;h~ch, w~en uncured and ~n the most decrystallized
condition, will stick together at room te~perature.
Suitable elastomers for use in accordance with
this invention include homopolymers and copolymers of
conjugated dienes such as neoprene and natural rubber;
copolymers of conjugated dienes with other polymerizable,
organic monomers, for example butadiene-acrylonitrile and
butadiene-styrene copolymers; elastomeric fluoropolymers
(fluorine-containing polymers), preferably copolymers of
vinylidene 1uroide and at least one other fluorine-
containing monomer, for example copolymers of vinylidene
fluoride and hexafluoropropene (U.S. 3,051,677), and ter-
polymers of tetrafluoroethylene, vinylidene fluoride and
hexafluoropropene (U.S. 2,96~,649); adhesive-type elastomers
such as polyvinyl acetate and ethylene-vinyl actate co-
polymers; acrylate rubbers such as the lower alkyl acrylate
ester polymers; hydrocarbon elastomers such as polyiso-
butylene, the terpolymers of ethylene, propylene and non-
conjugated dienes; and similar materials.
The preferred elastomer is neoprene. By "neoprene"
is meant an elastomer comprisins at least about 50g chloro-
prene (2-chloro-1,3-butadiene). Representative comonomers
. that can be used with chloroprene include vinyl aromat~c
compounds, such as styrene, the vinyl toluenes, and vinyl-
naphthalenes; aliphatic conjugated diolefin compounds such
a5 1,3-butadlene, isoprene, 2,3-dimethyl-1,3-butadiene J and
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1:~9~57
2,3-dichloro-1,3-butadiene; vinyl ethers, esters, and ketones,
such as methyl vinyl ether, vinyl acetate, and methyl vinyl
ketone; esters, amines, and nitriles of acrylic and meth-
acrylic acids, such as ethy] acrylate, methyl methacrylate,
methacrylamide, and acrylonitrile; and the like.
~ eoprene latices for use in this invention may be
prepared by the known aqueous emulsion polymerization of
chloroprene, using a sodium rosinate dispersant and a free-
radical type polymerization catalyst such as potassiul~
persulfate. The sodium rosinate dispersant may be prepared
n situ from rosin acids and sodium hydroxide.
Additives such as fillers, antioxidants and the like
may be present during the polymerization. The polymerization
is allowed to proceed to a predetermined degree of completion,
after which a catalyst shortstop can be added, and residual
chloroprene monomer is stripped off. Minor variations in the
procedure yield latices of polymers varying in molecular
weight, viscosity, crystallinity, and other properties. In
order to form pellets in the process of this invention,the
latex should have a solids content of at least about 20~
by weight. Suitable latices can have solids contents up to
about 65~. Latices generally coagulate when the solids
content goes above about 65go. Preferably the latex has a
solids content from about 35~ to about 50~.
This invention involves the process Or acld !'~
drops, a controlled stream~ or so~e other di5pensed form
of a latex of the normal]y tacky elastomer to an aquec)us
coagulating and coating bath thereby forming a coated
shaped object. The latex emulsion should be stable enough
to survive through the addition step until the shaped
~99~57
object ~ 5 fully penetrated by the coagulating salt and any
neutralizing agent present. Neoprene latices arc normally
stabilized against premature c~alescence by sodium rosinatc;
natural rubber by ammonia.
The aqueous coagulating and coating bath contains
a coagulating salt for the latex, that is, a salt which will
coagulate the elastomer latex. Suitable coagulating salts
are well known to those skilled in the art; for example, see
~Neoprene Latexr, by J. C. Carl, pages 19-21, published by
E. I. du Pont de Nemours and Company (Inc.), Wilmington,
Delaware. Operable salts which may be employed include the
water soluble sulfates, chlorides, bromides, nitrates,
citrates, acetates, formates and phosphates of ammonium,
sodium, potassium, calcium, magnesium, strontium, barium,
lithium, beryllium, aluminum, manganese, zinc, yttrium,
iron and cadmium. Mixtures of such salts may also be used.
Desirable, but nonlimiting, characteristics of the
coagulating salt include low cost, colorless solutions,
catlons and anions which are no~ readlly oxidizable or re-
ducible, noncopreclpitating wlth the alkali metal salt
accumulating in the bath, nontoxic, and nonpolluting. Pre-
ferably, the salt should be chemically inert to the elasto-
mer and insoluble therein. The preferred salts are soluble
chlorides, sulfates, acetates, nitrates and phosphates of
80dium, 2otassium, ammonium, calcium, magnesium and
aluminum. The most preferred salts are the soluble chlorides
and sulfates of the above cations. The coagulating salt
may constitute from about 0.5~ to about 25~ by weight of
the bath. The operable amount of coagulating salt within
this range in any given case will depend upon thc particular
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1099~S7
latex, the pH of the bath,and the particular inor~anic
oxide present. Generally, the optimum and preferred amol~nt
of salt is in the range of about 1% to about 10%.
The bath al80 contains a solu~le or colloldally
dispersed, hydrous lnoreanic oxide ~elected from the group
consistlng of sillclc and aluminlc acid polymers, sillcic
acid-aluminic acid copolymers, and mixtures thereof. These
oxides are those commonly considered as existing in poly-
meric form, the structure of which may be linear chains~
ribbonsJ or when highly cros6-linked, even globules, in
which atoms of the inorganic element alternate wlth oxygen
atom6. In such polymers, some Or the peripheral groups are
-OH groups.
The inorganic oxide may be used in water soluble
form, as in the case of polysilicic acid and polyaluminic
acid, or in more highly polymerized, particulate form as
in the case of colloidally dispersible silica sols as
described in ~.S. 2,574,902 and alumina sols as described
in U.S. 2,590,833. In practice, most aqueous systems
containing such compounds have at least part of the
polymeric oxide in the form of disperséd particles. The
terms, "silicic acid polymers" and "aluminic acid polymers"
are intended to include these polymers in both the soluble
and the colloidally dispersible form. The inorganic oxides
may be in crystalllne or amorphous form, and a mixture Or
two or more such oxides may be used. The most preferred
inorgan~c oxides are polysilicic acid, polyaluminic acid
and siliclc acld-aluminic acid copolymers.
If the coagulating salt employed is an alumlnum
salt and the inorganic oxide is polysillclc acld, some of
57
the alumlnlc hydroxylQ generated at the alkallne surface
of the latex may copolymerize by condensation with sllanol
groups to form an aluminic acid-sillcic ~cid copolymer. If
the coagul~tin~ salt employed ls not ~n aluminum salt,
partlcularly if the bath i~ utillzing polyslliclc acid as
the coatlng materlal, it i8 desirable, though not essential,
to add to the bath about 0.002~ to about 2~ by welght of
an lonlzable alumlnum salt. Although copolymerizatlon of
the aluminum has not been established, it is believed that
thls accounts for the inorganic oxide being rendered more
e~fective as a coatlng, posslbly by reduclng any subsequent
~olubility of the coating ln the wash water. ~or this pur-
pose, it has been found that yttrlum salts are equlvalent
to aluminum salts and may be substituted in whole or in
part therefor. Accordingly, the term "silicic acid-alumlnlc
acid copolymer" should be construed in the claims to cover
thls substltution of equlvalents.
It is generally recognized that, in freshly prepared
silicic acid solutions, the silicic acid is not monomeric,
but has a molecular weight of the order of about lO00. As
the silicic acid solution ages, the molecular weight
continues to rise until finally the solution gels (see
Bechtold, J. Phys. Chem., 59, 532-541 (1955)). The silicic
acid solution used in accordance with this invention should
not have aged for more than about 90Qo of its gel time prior
to being added to the bath. Preferably, the silicic acid
solution has aged for about 5~ to about 70% of its gel time
prior to being added to the bath. When operating in a
continuous manner, silicic acid is continuously added to
and removed from the bath, whereby the average age of the
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1~99~57
polysilicic acid reaches a const~nt value which i8 less than
its gel time.
The hydrous inorganic oxide may constitute from
about 0.01~ to about 5~ by weight of the coagulating bath.
~he presence of more than about 5% inorganic oxide does
not lead to any further improvement in the nontacky
properties of the product. Preferably the inorganic oxide
is present in the amount of about,0.03% to about 2~. The
oxide may be polymerized or crystallized during the coating
operation. One criterion for determining when a bath is
no longer suitable for the present process is coagulation
of the bath due to changed conditions such as pH or to
exhaustion of essential ingredients.
Optionally, the bath may also contain a minor
amount of surfactant to reduce the air-liquid interfacial
tension and assist penetration of the shaped latex body
into the bath. Suita~le surfactants are characterized by
being effective at low concentrations and being compatible,
that i~ not causing polymerization or cross-linking of the
hydrous oxide component, and being inert to the coag~lating
salt. A wide variety of nonionic, anionic, cationic and
amphoteric surfactants may be used. Examples of suitable
surfactants include lower alkyl alcohols such as ethanol,
the trimethylnonanol ether of ethylene oxide, sodium
heptadecyl sulfate, sodium lauryl sulfate, the condensation
product5 of tertiary amines wlth ethylene oxlde, fluori-
. nated ~mphoteric 8urractants, and the like. The ~urractantpreferably is added in an amount sufficient to reduce the
air-liquid interfacial tension to less than about 50
dynes/cm and particularly less than about 35 dynes/cm.
The bath is operable in a pH range of about 2 to
about 7. If the pH is below about 2, the inorganic oxide
is difficult to gel on the surface of the shaped object.
If the pH is above about 7, the inorganic oxide may be
converted to a soluble salt. The operable pH within this
range for any given system will depend on the particular
latex, coagulating salt and inorganic oxide present.
Within this range, pH values from about 2.5 to about 5.5
are particularly preferred for optimum balance of bath
stability with coating effectiveness. If the pH of the
bath is maintained in the desired range by proportional
addition of a neutralizing agent as the alkaline latex
bodies enter the bath, the life of the bath can be
substantially prolonged. Organic and inorganic acids such
as acetic acid and aquenous hydrochloric acid, and hydro-
lyzable acidic salts such as AlC13 are particularly suitable
neutralizing agents.
Operability of the bath to provide a coating on
the shaped object is a function of the amount and type of
hydrous inorganic oxide present and the pH of the bath. It has
been found that not all combinations of the above variables
lead to operable baths. Although the requirements for a
functional bath are not fully understood, a simple test
has been found for determining whether the bath is functional.
In this test, a drop of l.ON sodium hydroxide is added to the
bath. If the drop is immediately surrounded by a cloudy
coating of gelled hydrous oxide, the bath is functional.
Although the pH of various latices vary over wide
limits, it is preferable that the pH of-the latex be equal
3~ to or greater than the pH of the bath. When the latex is
X - 12 -
neoprene containing sodium rosinate as the stabilizer, the
pH of the latex will be greater than about 7 unless it has
been acidified.
When the latex is added as drops, the precipitated
shaped objects obtained may be lumps, beads, pellets (with
or without a "tail"), discs or rings depending on the sur-
face tension and density of the precipitating bath and the
speed and direction of the latex as it enters the bath.
When the latex is added as a controlled stream, the stream
may be filamentous, yielding a precipitated fiber or bead-
ing, or the stream may be spread out in flat or curved form
yielding a precipitated ribbon, sheet or tube. Drops and
controlled streams may be added either above or below the
surface of the bath. Preferably the latex is added as drops
above the surface of the bath.
Entry of the latex into the bath and movement of
the precipitated, coated object through the bath impart to
the bath a degree of agitation. Additional agitation in
the form of stirring or shaking may be supplied, if desired,
to assist in maintaining the uniformity of the bath. Agi-
tation is particularly desirable when the pH of the bath
is being maintained by addition of acid as noted above.
The present process may be operated at temperatures
in the range from about 0C to about 100Cr Temperatures
in the range from about 5C to about 70C are preferred,
with the range from about 10C to about 40C being par-
ticularly preferred because of the improved stability of
the bath in this range.
Pressure is not a critical Yariable in the present
process and pressures both above and below atmospheric
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1~99~57
pre~8ure are oper~ble. ~tmospheric pressure i~ preferred
~or convenlence.
The time from entry of a particular elastomeric
latex body into the bath until removal of the nontacky
elastomeric shaped object therefrom may be varied widely,
depending somewhat on the minimum dimension of the object
being coated. The time may vary from about 0.5 second up
to about 6 hours or more. On contact with the bath, the
latex starts to coagulate and a nontacky coating is formed
immediately on the surface of the coagulated shaped object,
e.g., within about 0.5 to about 5 seconds. Longer retention
of the coated object in the bath is employed when it is
desired to complete coagulation and neutralization of the
latex in the center of the coated object before it is removed
from the bath. In preferred baths, this requires less than
about 6 minutes. Complete coagulation in the bath is not
essential since coagulant which has penetrated the shaped
object can continue to migrate toward the center of the
object after removal of the object from the bath. It is
preferable, however, to leave the ob~ect in the bath until $
sufficient coagulant has penetrated the object to complete
the coagulation.
Referring now to the drawings, Figure 1 shows a
preferred embodiment of suitable apparatus for carrying out
the process of this invention. This apparatus comprises a
cylindrical tank 11 (27.94 cm i.d.) and a cylindrical draft
tube 12 ~12.7 cm i.d.) which is concentric with tank 11.
The tube and tank may be c~nstructed of any ri~,id materlal
such as ~lass, metal, or plastic. Drart tube 12 ~s extende~
on lts upper end by a wlre mesh screenl~ havin~ a mesh size
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1~99~57
smaller than the size of the shaped objects being produced.
Bathl4 containlng the lnorganic oxide po~ymer and the coagu-
lating salt is maintained at a liquid level such that the bath
surface 15 is slightly below the upper edge of screen 13.
Drops or discrete masses of polymer latex are introduced into
the bath within the zone circumscribed by screen 13. In this
embodiment, stainless steel capillary tubes 16 (1.9 cm long,
O.86 mm i.d. and 1.3 mm o.d.) are used for forming the latex
drops. These tubes are mounted through polytetrafluoroethyl-
ene plugs in a stainless steel plate bolted to the lower endof pipe 17 (10.1 cm i.d.). The center-to-center distance
between the tubes mounted in the plate is 1.11 cm. Sixty-
one tubes are arranged in a hexagonal array with five tubes
on a side. The frequency of drop addition to the bath is
adjusted by varying the level of latex in pipe 17.
An agitator 18 is provided in the bottom of tank
11 to promote circulation of the bath in such a manner that
flow of the bath solution is generally down through the
draft tube, up through the space between the draft tube and
the tank wall, and through the screen to the confined bath
surface. For this purpose, a 3-lobed (15.24 cm diameter)
marine propeller is used.
The screen at the top of the draft tube provides
a means of passing a solution which is free of shaped
objects to the top of the draft tube. It also keeps out
foam produced by the agitation and helps keep the surface
free of disturbances which might affect the uniformity of
the sha~eA ob~ects drop?ed throuah the surface. T~
increase agltation and thereby aid ~uspension of the coated
latex particles ln the annular EpaCC outslde the draft tube,
- 15 -
baffles 19 (3.81 cm wide) are placed vertically along
the walls of tank 11 at 90 intervals. These baffles are
not always necessary depending on the type of agitation used.
Through the action of the draft tube, screen,
agitator and baffles, the shaped bodies contact a
fresh solution, free of coated particles and foam. The
shaped objects remain discrete as they pass down through the
draft tube. By the time they emerge from the draft tube
they are coated so that the tendency to agglomerate with
previously coated shaped objects is eliminated. The
coated shaped objects are then held in suspension outside
of the draft tube until they are removed from the bath.
A typical batch run can be made using this apparatus
as follows: First, bath 14 comprising an aqueous solution
of an inorganic salt, a small amount of surfactant, and the
coating material is prepared. The salt serves to coagulate
the latex during coating and after it is coated. The
surfactant facilitates passage of latex drops through the
surface of the bath.
Latex is added to standpipe 17 to produce a
given head pressure and then continuously added to maintain
this head pressure on the capillary tubes. Since no solution
is withdrawn from the bath during the run, the bath level
rises due to the addition of latex. Both standpipe 17 and
draft tube 12 are mounted so that they can be moved vertically.
They are moved during the course of each run to maintain the
capillary exits about 2.54 cm above bath surface`15, and the
upper edge of screen 13 about 0.835 cm above bath surface 15.
Although the apparatus illustrated in the drawings
allows only batch removal of coated shaped objects at the
- 16 -
~q9~s~
conclusion of each run, the process can be operated contin-
uously by providing an overflow tube in tank 11 for continuous
removal of coagulated, coated shaped objects from the bath, fil-
tering the suspension of shaped objects passing through the
overflow tube, recycling the filtrate to the bath, and re-
placement of the bath components as they become exhausted.
A major advantage of the invention is that, when
large numbers of uncured shaped objects are stored in contact
with each other under ordinary conditions, they do not
agglomerate, but remain readily separable and free flowing.
The shaped objects have a minimum dimension of about 0.01 to
about lO millimeters. The minimum dimension should be at least
about O.Ol mm to avoid dusting. Shaped objects with a
minimum dimension above about 10 mm require excessive power
to mix with other ingredients in use applications.
Preferably the shaped objects have minimum dimensions of
about 0.1 mm to about 5 mm.
Since the shaped bodies added to the bath are com-
posed of latex, the water soluble coagulating salt quickly
penetrates into the aqueous phase of the shaped objects,
thereby coagulating the latex with a minimum of internal
coalescence. As a result, the coagulated elastomer within the
nontacky coating remains sufficiently porous for a sufficient
period of time to permit the washing out of water soluble
components, including the coagulating salt. In the case of
relatively crystalline elastomers, this porosity is retained
indefinitely. In the case of relatively noncrystalline
elastomers such as neoprene, the porosity decreases on long
standing, but it does not completely disappear.
After the precipitated shaped objects have been
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10~9057
coagulate~ and coated they can be sel?arated frorn the bath
by any ~uitable means. It is deslrable to remove watel
soluble and volatile materials ~rom the shaped obJects aIter
they have been separated from the bath. Thls may be
accomplished by washing with water or a polar organic solvent,
followed by squeezing, centrifuging or drying, using con-
ventional techniques. The shaped objects should be washed
until they contain less than about 3~ by weight of water
soluble material, and preferably less than about 1%.
After the water soluble material has been removed
to the desired extent, the shaped objects are dried to remove
volatile material. Drying may be carried out at air temper-
atures of about 25C to about 250C. Preferably the drying
is carried out at air temperatures of about 100C to about
135C. During this drying operation the temperature of the
shaped objects is kept below the known thermal decomposition
temperature of the polymer. Drying is continued until
the shaped objects contain less than about 1% by weight of
volatile material, and preferably less than about 0.5~.
Vuring these finishing steps, polymers that are
relatively stiff (because of crystallinity, for example)
remain opaque and porous, while normally tacky polymers
coalesce further to translucence. Nevertheless, even these
retain vestiges of their formerly highly porous
structure, and the nontacky nature of the hydrous oxide
coating deposited on their exterior surrace is retained.
This nontacliy coating may be supplemente~ by minor additions
of talc, for example, in the latter st~es of high tempera-
ture drying, if deslred.
~he nontacky coating on the normally tacky
lOq90S7
elastomer is initially also porous so that moisture, solvents,
soluble reaction ingredients and by-products can be readily
removed from within the coated object. The coating may
represent from about 0.05 to about 3% by weight of the
coated shaped object. Less than about 0.05% generally does
not provide adequate nontacky properties, while more than
about 3% usually gives no added advantage to offset increased
cost. Preferably the coating is about 0.5 to about 2% by
weight of the coated object. Washing operations, such as
noted above, point up the necessity for both the nontacky
coating and the coagulated elastomer being porous for a
period of time after formation of the shaped objects.
Figure 3 is a photomicrograph of a cross section
of a typical,porous shaped object in accordance with this
invention. In this photograph, the porosity of the shaped
object is apparent; voids appear as dark areas as observed
at 20. The nontacky coating appears as light areas as
is readily observed at 21.
The noniac~;y coated objects of this invention can
also contain fillers, pi~ents, color~nts, softeners,
extenders, antioxidants, st2bilizers, curing agents, and
the like. Such m~terials ma~ be incorporated by ~dding
them to the starting polymer latex or to the coa~ulatin~
and coatin~ bath.
The followin~ examples illustrate the prep2ration
Or nontacky,elastomeric shaped objects of this invention.
. Each ~f the ~ashed and dried,nontacky,elastGmeric-
shaped objects prepared in these examples had a water soluble
material content of less than about 3~ by weight and a
volatile material content of less than about 1~. In each
-- 19 --
case the inorganic oxide pol~mer coating was about 0.05 to
about 3~ by weight of the shaped objects and the minimum
dimension of the shaped objects was about 0.01 to about 10
millimeters. All parts and percentages are by weight
throughout the examples.
The neoprene latices used in these examples were
prepared as follows:
Neoprene Latex #l
This latex was prepared from an aqueous, alkaline
10 emulsion containing 100 parts of chloroprene and 0.23 part
of dodecyl mercaptan as modifier and stabilized by 2.9 parts
of the sodium salt of disproportionated wood rosin. Chloro-
prene was polymerized by adjusting the emulsion tempera-
ture to 40C and adding continuously, at a rate allowing
control of the temperature at 40C by external cooling, an
aqueous solution containing 0.3% K2S2O8 and 0.015~ Na salt
of anthraquinone-~- sulfonic acid. The polymerization was
- terminated at about 67% conversion of the chloroprene mono-
mer by the addition of an aqueous emulsion of a toluene
20 solution containing 0.015 part of phenothiazine and 0.015
part of 4~tert.-butylcatechol.
After removal of residual monomer by distillation,
the latex contained about 37~ solids. The polymer had an
inherent viscosity of 1.20 ~0.1 g/100 ml benzene at 30C).
The pH of the latex was about 12.
Neoprene Latex #2
An a~ueous, alkaline emulsion was prepared con-
taining 100 parts of chloroprene, 0.15 part of dodecyl mer-
captan and 3.5 parts of the sodium salt of disproportionated
wood rosin. Chloroprene was polymerized by adjusting the
- 20 -
~0~ ;7
emulsion temperature to 10C and adding continuously an
aqueous dispersion containing 1.0% X2S2O8, 0.05% sodium
salt of anthraquinone-~-sulfonic acid, and 0.14% cumene
hydroperoxide at a rate allowing control of the temperature
between 10 and 20C. The polymerization was terminated
at about 85% conversion of the chloroprene monomer by
addition in the form of an aqueous emulsion of a toluene
solution of 0.03 part of phenothiazine and 0.03 part of
4-tert.-butylcatechol.
After removal of residual monomer the emulsion
contained 37% solids and had a pH of 12.5.
Neoprene Latex #3
The preparation of neoprene latex #l was repeated
except that the 100 parts of chloroprene was replaced by a
mixture of 92 parts of chloroprene and 8 parts of 2,3-
dichloro-1,3-butadiene. The polymerization was stopped at
65~ conversion, and the latex, after stripping, contained
about 33% solids and had a pH of 12.
Neoprene Latex #4
The procedure described for neoprene latex #2 was
repeated except that the amount of dodecyl mercaptan in
the monomer emulsion was 0.12 part instead of 0.15 part.
The resulting latex had a solids content of 37~ and a pH of
12.5.
Example 1
A bath containing approximately 0.7% SiO2 and 3.9%
Ca(NO3)2 was made by combining 90 ml of 0.25M aqueous silicic
acid (produced by the ion exchange of H+ for Na+ in 0.25M
sodium metasilicate solution), 10 ml of a 50% aqueous
Ca(NO3)2 solution, and 100 ml of absolute ethanol. About
- 21 -
20 ml of neoprene latex ~l (37~ so:Lids, pH 12) was added
dropwise to this bath from an oriflce about 2 cm above it.
The surface of the drops coagulated on contact to yield
globules which withln a few minutes were coagulated through-
out and covered with a nontacky coating. The resulting
opaque pellets were lifted from the bath and dried in a 60C
oven. At room temperature they remained dry to the touch and
free-flowing.
For comparison the following experiment, not
within the scope of the invention, was carried out. The
above example was repeated using 90 ml of water in place
of the silicic acid solution. The drops of emulsion coagulated
rapidly, but remained very tacky and were difficult to
separate after drying at 60C.
Exam~le 2
A bath containing approximately 3.6% SiO2 and -
2.6% CaC12 was made by mixing lO00 ml of lM silicic acid,
60 ml of 50% CaCl2 solution, 700 ml of absolute ethanolr and
240 ml of distilled water. About 200 ml of neoprene latex #l
(37% solids, pH 12) was introduced into the bath dropwise. The
resulting pellets were allowed to remain in the bath for 30
minutes. They were removed, washed with 70% ethanol and
dried for 48 hours in a vacuum drying pistol heated by re-
fluxing acetone. The resulting pellets had the following
analysis: Ca, 0.25;Na, 0.38; Si, Q~51r% ash, 2.8. Pellets
prepared in this way retained a small amount of alkali.
Such amounts of residual alkali stabilize neoprene against
HCl degradation. A 5% suspension of these pellets in wa~er
had a pH of 9Ø The pellets were more than 90% soluble in
toluene, indicating little or no crosslinking of the neoprene
-~ - 22 -
1~99~57
had occurred.
Example 3
An alcohol-free bath containing approximately
1.5~ SiO2 and 2.1% CaC12 was made, utilizing a dilute
aqueous nonionic surfactant solution to reduce interfacial
tension at the air-liquid interface. A mixture of 10 ml
of freshly prepared 0.5~5 silicic acid, 9.4 ml of 0.2~ aqueous
trimethylnonanol ether of ethylene oxide (Tergitol~ TM~-6,
Union Carbide), and 0.6 ml of 50~ CaC12 completed the bath.
About 2 ml of neoprene latex ~1 (37% solids, pH 12) introduced
dropwise into the bath formed opaque nonsticking pellets.
These were isolated, washed with water, and air dried to pro-
duce free-flowing, nonsticking pellets 3-4 mm in diameter. The
moisture content of the pellets was 0.38%; the ash
residue was 3.05%; other analyses were: Ca, 0.44%;
Na, 0.26%; Si, 1.11%.
Exam~le 4
A bath containing approximately 1.5% SiO2 and 2.1~
CaC12 was prepared from 1000 ml of 0.5M silicic acid (pH 3.3),
940 ml of 0.2~ aqueous trimethylnonanol ether of ethylene
oxide (Tergitol~ TMN-6), and 60 ml of-50% aqueous CaC12
solution. The initial pH of the bath was 4.45. One hundred
milliliters of neoprene latex #l (37% solids, p~l 12) was added
dropwise over a period of 10 minutes during which the bath
was stirred and the pH was maintained at 4.0 by continuous
addition of 1.0N hydrochloric acid. The bath showed no
evidence of gelation. The neoprene pellets which formed
were filtered from the bath on a 100 mesh stainless steel
screen, washed with cold water and dried. They were non-
tacky and free-flowing.
- 23 -
57
Example 5
A silicic acid solution was prepared from a sodium
silicate solution having an SiO2/Na20 ratio of 1.95. The
sodium silicate solution utilized was Grade 6 (Du Pont Co.)
which had a viscosity of 60,000 centipoises (68C), a specific
gravity of 1.708, % ~a20 = 18.4, and % SiO2 = 36Ø This
solution (166.5 ml) was diulted to 2 liters with distilled
water. The resulting solution was passed through a cation
exchange column in acid form containing 1300 gms of cation
exchange resin (Rexyn lOlj H ). The first 500 ml of effluent,
e~uivalent to the retention volume of the column, was dis-
carded and the remainder collected.
A 1000 ml portion of this 0.85M silicic acid
solution was employed in the procedure of Example 4 to give
a bath containing approximately 2.5% SiO2. At the start
of the addition of neoprene latex the bath was at pH 3.1
and at the conclusion the pH was 4~1. The resulting
pellets were washed with distilled water and dried. They
showed little tendency to aggregate.
Example 6
A bath containing approximately 1.4% SiO2 and 7.6%
NaCl was prepared from 15 ml of 10% aqueous NaCl and 5 ml of
l.OM aqueous silicic acid. About 2 ml of a 55% solids latex
of a copolymer derived about 18% from vinyl acetate and about
82% from ethylene was added dropwise to the bath. The drops
coagulated into pellets which were filtered from the bath,
dried under vacuum at 80C, washed with water to remove all
traces of NaCl and again dried. They were nontacky and
free-flowing.
For comparison, the following experiments, not within
~ - 24 -
~, ~ . .,
~9~57
the scope of the invention, were carried out. The above
example was repeated twice, first with replacement of the
NaCl solution by water, and second by replacement of the
silicic acid solution by water. In both instances, the
treated drops were too fragile to be removed whole from
the bath.
Example 7
A solution containiny approximately 1.4% SiO2 and
6.1% NaCl was prepared by adding 262 ml of lN HCl, 14.7 gm
of NaCl, and 38 ml of H2O to 100 ml of rapidly stirred 1~
Na2SiO3 9H2O. To this solution at about 0C were added 20
drops of the vinyl acetate/ethylene copolymer latex described
in Example 6. After 10 minutes, the resulting pellets were
removed from the bath and dried in a vacuum oven at 80C
for 2 hours. The pellets were coated with a nontacky coating
and were free-flowing.
About 200 ml of a 62% solids natural rubber latex
(LATEX TSC*, General Latex Co.) was added dropwise to a bath
containing approximately 0.9% SiO2 and 2.5~ CaC12 which was
prepared from 250 ml of lM silicic acid, 1750 ml of absolute
EtOH, and 60 ml of 50% aqueous CaC12. The latex rapidly
coagulated and a nontacky coating formed on the surface of
the particles. When isolated and dried, the pellets were
nontacky and free-flowing.
Example 9
Into neoprene latex #1 (37% solids, pH 12~ was
mixed enough carbon black ISTERLING R*, Cabot) to yield a
uniform emulsion containing 4% of carbon black based on
the neoprene. About 20 ml of this modified latex was added
*denotes trade mark
- 25 -
-
l~g~
dropwise to a bath containing 1.5~ SiO2 and 2.1% CaC12
prepared from 100 ml of 0.5M aqueous silicic acid, 94 ml
of 0.2% aqueous trimethylnonanol ether of ethylene oxide
(Tergitol~ TMN-6), and 6 ml of 50% aqueous CaC12. The drops
were delivered from a Pasteur pipette near the surface of the
bath and the bath was stirred by a magnetic bar. After 30
minutes in the bath the pellets which formed were removed by
decantation, washed three times with 500 ml portions of water
and air dried. The carbon-containing pellets were nontacky
and free-flowing.
Example 10
The procedure of Example 9 was repeated with the
exception that the 4~ of carbon black in the latex was re-
placed by 10% of atomized aluminum powder. Nontacky,
free-flowing aluminum-containing pellets were obtained.
Example ll
~he procedure of Example 9 was repeated with the
exception that the 4% of carbon black in the latex was re-
placed by 10% of alumina trihydrate (powder, baked at 135-
195C). Nontacky, free-flowing alumina-containing pellets
were obtained.
Exampl-e 12
The procedure of Example 9 was repeated with the
exception that the 4& of carbon black in the latex was re-
placed by 10% of magnetic iron oxide (Fe304 r M0-423~*, Pfi~er
Minerals). Nontacky, free-flowing iron oxide-containing
pellets were obtained which were readily manipulated with
magnets.
EXample 13
About 100 ml of a 65% solids latex of fluoro-
*denotes-trade mark
- 26 -
lOq9~5~
elastomer terpolymer derived from 45% vinylidene fluoride,
30% hexafluoropropylene and 25% tetrafluoroethylene was
added dropwise to a bath prepared from S~0 ml of 0.5M aqueous
silicic acid saturated with BaC12, 500 ml of water
saturated with BaC12, and 2 ml of 2~ aqueous trimethyl-
nonanol ether of ethylene oxide (Tergitol~ TM~-6). The
drops flattened on contact with the bath, but coagulated
throughout and were coated with a nontacky coating. The
particles were decanted from the bath, washed repeatedly
with water and air dried to give white, free-flowing flakes
about 5 mm in diameter.
Example 14
A mixture was prepared from equal volumes of neo-
prene latex ~1 (37% solids, pH 12) and the aqueous fluoro-
elastomer latex described in Example 13. This mixture (20 ml)was introduced dropwise into a bath containing approximately
1.5% SiO2 and 2.1% CaC12 prepared from 100 ml of 0.5M aqueous
silicic acid, 94 ml of 0.2% aqueous trimethylnonanol ether of
ethylene oxide (Tergitol~ TMN-6), and 6 ml of 50~ aqueous
CaC12. ~he pellets which formed were washed with water and
then dried, first in air and then over,P2O5 under vacuum at
room temperature. The resulting mixed elastomer pellets
were nontacky and free-flowing.
Example 15
A portion (422 ml) of sodium silicate solution
(Grade F, Du Pont Co., SiO2/Na2O ratio = 3.25, Na2O = 8.7~,
SiO2 ~ 28.4%, viscosity (68C) = 160 cp, specific gravity
e 1.386) was diluted to 4 liters with distilled water. This
solution was put through the cation exchange column in acid
form described in Example 5. A bath containing approximately
~"9QS7
0.5~ SiO2 and 7.6~ NH4Cl was prepared using 250 ml of the
resulting approximately 0.69M silicic acid solution, 1000 ml
of 15~ NH4Cl, 250 ml of distilled water, and 500 ml of
0.05% aqueous trimethylnonanol ether of ethylene oxide
(Tergitol~ T~-6). Two hundred ml of neoprene latex ~2
- (37~ solids, pH 12.5) was added dropwise to the bath. The
pellets which formed were allowed to remain in the bath
for 30 minutes. The bath was decanted and the pellets were
washed three times with 2-liter portions of water. The
pellets were air dried at room temperature and atmospheric
pressure. The resulting pellets were nontacky and free-flowing.
~xample 16
A bath was prepared with a buffer to resist the
pH elevation associa~ed wi~h the addition o~ alkaline
neoprene latex. The buffer was prepared by diluting a mix-
ture of 1.75 ml of 2M HCl, 0.1 g of trimethylnonanol ether
of ethylene oxide (Tergitol~ T~IN-6), and 12.60 ml of 2~S
glycine solution to 50 ml with distilled ~ater. The buffer
was then addcd to 100 ml of 0.69~l silicic acid (prepared
according to Example 15), and 50 ml of 30~ aqueous ~114Cl.
Twenty ml of neoprene latex #2 (37~ solids, pH 12.5) was
added to the bath dropwise. The pH of the bath changed from
3.35 to 3.55 as compared to a p~ change to approximately 6.0
for a similar unbuffered bath. Approximately 80 ml of the
latex could be added to the buffered bath before the pH rose
above 6.0, at which pH gelation of the bath occurred rapidly.
Example 17
A bath containing approximately 2.0% SiO2 and 7.9%
~H4Cl was prepared from 1000 ml of 0.69M silicic acid,
(prepared according to Example 15) 500 ml of 30% NH4Cl~ and
- 28 -
~o99~s~
500 ml of 0.2S aqueous trimethylnonanol ether of ethylene
oxide (Tergitol~ TMN-6). A 200-ml sample of neoprene latex
#3 (33~ solids, pH 12) was adjusted from pH 12.0 to pH 12.5
by addition ~r lN ~aOH. This latex was added dropwise to
the bath. The pellets which formed were washed wit~ water
and then rreeze-dried at about -178~C under high vacuum.
At room temperature the dried pellets were nontacky and
free-flowing.
Ex~m~le 18
h bath was prepared usin~ an ~lumina-modiried
silica sol (Ludox~ 130M, Du Pont Co.), This product is a
30% solids, acidic, aqueous dispersion of positively-char~eQ
colloidal particles consistin~ o~ a dense silica core coated
with positively-char~ed polymeric alumina, The approximate
chemical composition is SiO2 = 26%, A1203 = 4.0~, Cl = 1.4~o~
MgO = 0.2%, viscosity (25C) = 5-15 cp, pH (25C) = 4.3-4.5,
approximate particle diameter = 16 m~, and speci~ic gravity
(25~C) = 1.23.
The bath containing approximately 0.7% SiO2/A1203
snd 6.1% NH4Cl was composed of 116 ml of 0.2~ aqueous sodium
heptadecyl sulfate anionic surfactant (Tergitol~ Anionic 7, ~.
Union Carbide), 80 ml of 15% aqueous NH4Cl, and 4 ml of the
slumina-modlrled sillca sol descrlbed abo~e. To this bath
wa~ added dropwlse 20 ml o~ neoprene latex #2 (~7% solids,
pH 12.5). The drop~ coagulated and the re6ultlng coated
pellets were wa~hed and dried. Nontacky, free-flowing
pellets were obt~lned.
Example 19
A bath containing approximately 1.0% SiO2 and
8.0~ AlC13 was prepared ~rom 5 ml of 0.69M aqueous silicic
~0~9Q~;~
acid (prepared according to Example 15), 9 ml of 30% aqueous
AlC13-6H20, 5 ml of 0.2% aqueous trimethylnonanol ether of
ethylene oxide (Tergitol~ TMN-6), and 1 ml of distilled water.
To this bath was added dropwise 2 ml of neoprene latex ~2
(37% solids, pH 12.5). The drops coagulated and were
removed from the bath, washed and dried. Nontacky, fre~-
flowing pellets were obtained.
Exam~les 20-23
Four baths were prepared, each from 2.5 ml o~
0.6~M aqueous silicic acid (prepared according to Exam~le
15), 5 ml of 0.5% aqueous trimethylnonanol ether Or ethylene
oxide (Tergitol~ TMN-6~,and 12.5 ml of a 30% aqueous
solution of the indicated salts~
Example 20 NH4Br
Example 21 tNH4)2Hc6H5o7(citrate)
Example 22 INH4)2Cr2O7
Example 23 NH4SCN
To each bath was then added dropwise 2 ml of neoprene latex
#2 (37% solids, pH 12.5). The elastomer pellets which formed
were separately washcd with water and dried. All yielded
nontacky, free-flowing pellets.
Example 24
Ten ml of naphthenic extender oil (Sundex~ 790,
Sun Oil Co.) was added to 90 ml of neoprene latex ~2 (37~
solids, pH 12.5) and the mixture vigorously shaken to give
~n emulsion. A bath containing approximately 1.0~ SiO2 and
7.6% NH4Cl was prepared from 50 ml of 0.69M aqueous silicic
acid ~prep:-red according to Example 15), 100 ml of 15% aqueous
NH4Cl, and 50 ml of 0.05~ aqueous trlmethylnonanol ether
Or ethylene oxlde tTergltol~ TMN-6). The oil extended
- 30 -
1099~'7
polymer latex was added dropwise tc the bath. The pellets
which formed were separated from the bath, washed with
water and dried to yield nontacky, free-flowin6 pellets
of oil-extended elastomer.
Example 25
A bath containing approximately 0.9% SiO2 and
10.0~ NaCl was prepared by dissolving 100 g of NaCl in
900 g of 0.35~1 aqueous silicic acid, dissolving 100 9 of
NaCl in 900 g of 0.05~ aqueous trimethylnonanol ether of
eth~lene oxide (Tergitol@ T~-6), and combining the two
solutions. The bath was maintained at pH 4-4.5 by additions
of lN HCl during the dropwise addition of 200 ml of neoprene
latex ~2 (37~O solids, pH 12.5). The pellets which formed
were allowed to stand in the bath for 16 hours, then washed
with water and dried to yield nontacky, free-flowing pellets
of uncured elastomer.
~xample ?6
A bath containing approximately 1.3~ SiO2, 3.9~
NH4Cl and 11.1% NaCl was made ~y combinin~ 25 ml of 0.69~1
silicic acid (prepared in accordance with ~xample 15), 10 ml
of 30~ NH4Cl in 0.2% aqueous trimethylnonanol ether of
ethylene oxide (Tergitol~ TMN-6), 40 ml of 20% NaCl in 0.2%
aqueous trimethynonanol ether of ethylene oxide (Tergitol~
TMN-6), and 125 ml of distilled water. The bath was adjusted
to pH 5.0 with lN NaOH. Twenty milliliters of neoprene
latex #2 (37% solids, pH 12.5) was added to the bath
dropwise while the pH was maintained at 5.0 by dropwise
addition of lN HCl. The resultln~ pellets were re~o~ed
rrom the bath after one hour, washed three times with
500-ml portions of distilled water, and air dried to
~()g9~57
yield nontacky, free-flowing pellets.
Example 27
A bath containing approximately 0.5% chlorhydrol
(aluminum chlorohydroxide polymeric complex containing 47.0%
A12O3 and 16.3% chloride, Reheis Chemical Co.) and 2.3% CaC12
was prepared by combining 10 ml of 10% aqueous chlorhydrol,
175 ml of 0.05% aqueous trimethylnonanol ether of ethylene
oxide (Tergitol~ TMN-6), and 15 ml of 25% aqueous CaC12. The
solution was brought to pH 5.0 with lM NaOH. As 20 ml of
neoprene latex #2 (37% solids, pH 12.5) was added dropwise, the
bath was gently stirred and maintained at pH 5.0 by dropwise
addition of IN HCl. The pellets were allowed to remain in
the bath for 1 hour, after which they were washed with three
250~ml charges of distilled water. The pellets were then
air dried to form free-flowing nontacky elastomer particles.
Example 28
A surfactant-free bath containing 1.0% SiO2 and 7.6%
NH4Cl was prepared from 100 ml of 0.69M aqueous silicic acid
(prepared according to Example 15), 200 ml of 15% aqueous
NH4Cl, and 100 ml of distilled water. A 100 ml graduated
cylinder was filled with this bath. From a 10 ml syringe
fitted with a 20 gauge needle r neoprene latex #2 (37% solids,
pH 12.5) was extruded as a continuous stream onto the surface
of the bath at one side of the graduated cylinder,
forming a small puddle. By grasping the edge of the puddle
with tweezers at the other side of the graduated cylinder
a continuous fiber of coagulated, hydrous silica-coated
polychloroprene was drawn off. After being washed and air
dried, the fiber was nontacky,
Example 29
- 32 -
lO~9~S~
The procedure of Example 28 was repeated except
that more ~orce was used on the syringe, thus causing the
stream o~ latex to ~o through the sur~ace Or the bath. ~he
weight Or the coagulating stream pulled it to the bottom Or
the bath ~here a nontacky continuous riber Or the elasto~
about 1-2 mm ~n diameter collécted.
Example 30
The procedure Or Example 29 was repeated excep~
that, a~ter the interface at the surface of the bath had
been penetrated by the latex stream, the force on the syr~nge
was reduced and adjusted so that free drops fell from the
needle into the bath. The pellets which formed were non-
tacky and free-flowing when washed and dried,
Example 31
Part A
To 200 ml of a 30% solids aqueous colloidal sol
of alumina-modi~ied silica Or pH 8~6-~3 (Ludox~ AM, Du Pont
Co.) under agitation in a blender was added 2.0 ml Or con-
centrated ~Cl (38%). The resulting colloidal solution con-
taining approximately 29~ solids had a pH of 3ØPart B
A modified neoprene latex was prepared by adding 10
~1 of a 1~ aqueous solution of hydroxyethyl cellulose (Cello-
size~ QP 30,000, Union Carbide Corp.) to 90 ml of neoprene
latex #2 ~37% solids, pH 12.5). The emulsion was kept
agitated to avoid creaming.
Part C
A bath containing approximately 4.3% SiO2/A12O3
and 7.5~ NH4Cl was prepared by mixing 2.5 ml of the col-
loidal silica aolution prepared in Part A above, 10.0 ml of
- 33 -
9()57
15~ aqueous N~4Cl, 1 ml Or a 0.2~ aqueous solution Or an
amphoteric fluorinated surfactant (Zonyl~ ~SB, Du Pont Co.),
and 6.5 ml of wa~er. To this bath was addcd dropwise about
5 ml of the modified neoprene latex prepared in Part ~ above.
The pellets which formed were separated from the bath,
washed with water, and dried to obtain nontacky, free-flowing,
substantially spherical pellets o~` modified neoprene.
Example 32
A bath containing approximately 0.5% SiO2, 7.6%
NH4Cl and 0.01~ AlC13 was prepared by mixing 250 ml of 0.69
aqueous silicic acid (prepared according to Example 15 and
aged for two days), 1000 ml of 15% aqueous NH4Cl, 200 ml of
water, 500 ml of 0.05% aqueous trimethylnonanol ether of eth~l-
ene oxide (Tergitol3 TMN-6), and 50 ml of 1% aqueous AlC13-6H20
which had been adjusted to pH 5.0 by addition of lN NaOH.
This bath was kept at pH 4.5-5.0 by addition of lN HCl
~during the dropwise addition o~ 200 ml o~ neoprene latex ~2
(37~ solids, pH 12.5) which took eight minutes, and for one
hour thereafter. The drops, which coagulated, were separated
from the bath, washed three times with wa-ter, soaked for
three hours in water, and then air dried. The resulting
pellets were nontacky and free-flowing.
xample 33
A silica sol containing approximately 4.6~ solids
with a pH of 5.0 was prepared by adding 265 ml of a 15%
solids aqueous silica sol (Nyacol~ 215, Nyacol, Inc.,
pH 10.5) dropwise with vigorous stirring to a solution cf
70 ml of lN HCl in 595 ml of water. A bath containing
approximately 0.6% SiO2, 7.6~ N~34Cl and 0.013~ AlC13 was
prepared by mixing 250 ml of the above sol, 1000 ml of 15
- 34 -
~"9~57
a~ueous NH4Cl, 700 ml of a 0.03~ aqueous solution of an
amphoteric fluorinated surfactant (Zonyl~ FSB, Du Pont Co.),
and 50 ml of 1~ aqueous AlC13 6H2~ which had been adjusted
to pH 5.0 with lN NaOH. The resulting bath had a pH of 4.3.
This bath was stirred and kept at pH 4~5-5.0 by addition of
HCl during the dropwise addition of 200 ml of neoprene latex
#2 (37% solids/ pH 12.5). The pellets which formed were
stirred in the bath for one hour, separated, washed three
times with water and soaked in 2 liters of water. After dry-
ing the pellets were nontacky and showed little tendency toagglomerate.
Example 34
In the manner of Example 33, 42 ml of a 49~ solids
aqueous colloidal silica sol (Ludox~ TM, Du Pont Co~, pH
8.9, particles 220-250A in diameter) was blended with 3.9
ml of lN HCl and 454 ml of water to give an aqueous sol con-
taining 5.6% SiO2. A bath containing approximately 0.7~ -
SiO2, 7.6~ NH4Cl and 0.013~ AlC13 was prepared by substituting
250 ml of the above sol for the sol employed in Example 33
and maintained at a pH of 5.0 by addition of lN HCl. The
remaining procedure of Example 33 was then repeated to yield
nontacky, free-flowing elastomer pellets.
EXample 35
In the manner of Example 33, 125 ml of a 30%
solids aqueous colloidal silica sol (Ludox~ SM, pH 9.9,
Du Pont Co.) in 125 ml of distilled water, was blended with
28 ml-of lN HCl and 637 ml of water. A bath was prepared
by substituting 250 ml of the above sol for the sol employed
in Example 33 and the remaining procedure of Example 33 was
repeated. Nontacky, free-flowing pellets were obtained.
~, - 35 -
l~9~S7
Example 36
To 400 ml of a 30% solids aqueous colloidal sol
of alumina-modified silica of pH about 8.9 (Ludox~ AM,
Du Pont Co.) was added 4.0 ml of concentrated (38%) hydro-
chloric acid with vigorous agitation. The resulting sol had
a pH of 3.0 and a solids content of about 29.7%. A bath con-
taining approximately 4.3% SiO2 and 7.5% NH4Cl was prepared
from 250 ml of this sol, 1000 ml of 15% aqueous NH4Cl, 650 ml
of water, and 100 ml of a 0.2% aqueous amphoteric fluorosur-
factant solution (Zonyl~ FSB, nu Pont Co.). The bath had apH of 3.7 and was kept below pH 4.5 by adding O.lN HCl during
the dropwise addition of 200 ml of neoprene latex #2 (39%
solids, pH 12.5). The drops coagulated and were stirred in
the bath for 30 minutes, separated, washed three times with
water and dried at 60 C to obtain nontacky pellets.
Example 37
A bath containing approximately 1.5% SiO2 and 7.6%
NH4Cl was prepared by mixing 100 ml of 0.69M aqueous silicic
acid (prepared according to Example 15), 94 ml of 0.2%
trimethylnonanol ether of ethylene oxide tTergitol~
TMN-6) in ethanolj and 6 ml of a 50% aqueous solution of
CaC12 2H2O. To this bath was added dropwise about 20 ml of
a 40% solids butadiene/acrylonitrile copolymer latex
~Chemigum Nitrile Latex 550, Goodyear) having a pH of 8Ø
The coagulated drops were stirred in the bath for one hour,
separated, and dried under vacuum at 60C to obtain per-
fectly spherical pellets which were nontacky and free-flowing.
Example 38
A mixed latex was prepared from 100 ml of neoprene
latex #2 t37% solids, pH 12.5) and 60 ml of natural rubber
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X
lQ99~
latex TSC (62~ solids, General Latex Co.). The resulting mix-
ture was brought to pH 12.2 by adding 1~ NaOH. A bath w~s plC-
pared like the one in E~ample 37, e~cept on a 10-fold
larger scale. During dropwise addition of the mix~d ]atex
to the bath, the bath was maintained at pH 5.0 by the
addition of lN HCl. The coagulated drops remained in the
bath for one hour. They were then separated, washed three
times with water, and dried, first for five hours in air
and then for three days under vacuum over P205 at room
temperature. The coated pellets of neoprene/rubber were
nontacky and free-flowing.
Example 39
A bath containing approximately 0.7% SiO2/A12O3 and
7.6~ NH4Cl was prepared by mixing 40 ml of a positive
alumina-modified silica sol (Ludox~ 130 M, Example 1~),
1000 ml of 15~ aqueous NH4Cl, and 960 ml of 0.05% aqueous
sodium lauryl sulfate (Duponol@ WAQE, Du Pont Co.). The
bath had a pH of 4.9 and was maintained at pH 5.0 by addi-
tion of lN HCl during dropwise addition of 200 ml of neoprene
latex ~ (37~ solids,pH 12.5). The coagulated drops were
stirred in the bath for one hour, washed with water, and air
dried to yield nontacky, free-flowing pellets.
Example 40
A bath containing approximately 0.1~ chlorhydrol
and 7.6~ N1~4Cl was prepared by mixing 1000 ml of 15~
aqueous NH Cl, 980 ml of 0.1~ aqueous sodium lauryl sulfate
(Duponol~ WAQE), and 20 ml of 10 aqueous chlorh~drol
(A1203 47.0~, chloride 16.3~, Reheis Chemical Co.). To
the bath was added dropwise 200 ml of neoprene latex ~4
while maintaining the bath at p~3 ~.5 by adding lN ~3Cl.
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10~9~57
After the addition,the pellets were stirred in the bath
for one hour, washed with water, and air dried. The un-
cured elastomer pellets were nontacky and free-flowing.
Example 41
Using the apparatus illustrated in Figures 1
and 2,the following aqueous solutions were mixed in tank 1.
10,000 ml of 15~ aqueous ammonium chloride
9,500 ml of 0.03/r aqueous sodium lauryl sulfate
surfactant (Duponol~ WAQE)
500 ml of 30% solids colloidal alumina-modified
silica sol (Ludox~ 130M, Example 18)
The bath thus prepared had a pH of 5.4 and contained appro~i-
mately 0.9~ SiO2 and 7.6~o NH4Cl. While providing agitation,
3~80 g of a 40% solids neoprene latex prepared in the manner
of neoprene latex #2 was added through the capillary tubes
over a period of 13 minutes. Simultaneously, the pH of the
bath was maintained at 5.4 by gradual addition of 51 ml of
lN hydrochloric acid. Immediately following the 13-minute
latex addition period, agitation was continued for 17 minutes
with no further addition of acid, during which time the pH of
the bath rose to 6.6. The particles were kept in suspension
by agitation during the 17-minute holding period. The
agitator was then turned off, the particles were allowed to
settle, and the supernatant liquid was separated from the
pcrticles by decantation.
The particles were washcd by addition of 8000 ml
of distilled water followed by a 5-minute agitation per~od.
The agitator was then turned off and the supernatant
liquid was separated from the particles by decantation.
This washing procedure was repeate~ twice. The particles
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1~"9057
were allowed to dry in the zir to a constant weight of
1315 g. They were free-flowing ancl nontacky.
ExamPle 42
~ Blng the apparPtus lllustrated ln Flgures 1 and
2, a bath wa6 prepared by mlxing the rollowlng aqueous
solution-~ ln tank 1.
10,000 ml of 1~% aqueou~ ammonlum chloride
9,950 ml of 0.03% aqueous sodium lauryl sulfate
surfactant (Duponol~ WAQE)
50 ml of a polyaluminlc acid-modified aqueous col-
loldal slllca ~ol
The modified silica sol was prepared ~y slowly adding 500 g
of 35~ aqueous boric acid-stabllized basic aluminum ~cetste
solution (N~aproof~, Union Carbide Corp.) to 400 g of agueous
colloidal silica sol [Ludox~ SM, Du Pont Co., 30% SiO2,
averaqe particle size 7 m~, weight ratio SiO2/Na20 50, pH -~
(25C) 9.9, freezing point 0C] in a blender and filtering
the mixture through coarse filter paper tp remove the small
amount of gel. The bath thus prepared had a pH of 5.3 and
contained approximately 0.1% colloidal silica sol coated with
polyaluminic acid and 7.6~ NH4Cl.
While providing agitation,3590 g of 40~ solids neo-
prene latex prepared like neoprene latex #l was added to the
bath through the capillary tubes over a period of 9 minutes,
during which time the pH of the bath rose to 6.7. Agitation
was continued, keeping the particles in suspension for an
additional 51 minutes, with no appreciable change in pH of
the bath. The agitator was turned off, the particles were
allowed to settle and the supernatant liquid was separated
from the partlcles by decantation.
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10~
The particles were washed by addition of 8000 ml
of distilled water followed by a 10-minute agitation
period. The agitator was then turned off and the super-
natant liguid was separated from the particles by decanta-
tion. This washing pr3cedure was repeated three times.
The particles were allowed to dry in the air to a constant
weight of 1446 g. They were free-flowing and nontacky.
Example 43
Ucing the apparatus illustrated in Figures 1 and
2, the following aqueous solutions were mixed in tank 1.
10,000 ml of 15~ aqueous ammonium chloride
9,950 ml of 0.03% aqueous sodium lauryl sulfate
surfactant (Duponol~ WAQE)
5O ml of the polyaluminic ac~d-modlfled aqueous
colloldal sllica sol described in ~xalple 42
The bath thus prepared had a pH of 5.2. While providing
agitation, 4578 g of 40~ solids neoprene latex prepared
like neoprene latex ~2 was added through the capillary tubes
over a period of 18 minutes, during which time the pH rose to
6.7. Agitation was continued, keeping the particles in
suspension for an additional 42 minutes, with no appreciable
change in pH of the bath. The agitator was turned off, the
particles were allowed to settle and the supernatant liquid
was separated from the particles by decantation.
The particles were washed by addition of 20,000 ml
of distilled water followed by a 10-minute agitation period.
The agitator was then turned off and thc supernatant liquid
was separated from the particles by decantation. This
washing procedure was repeated once. The particles were
allowed to dry in air to a constant wcight of 1767 g. They
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lO9S~
were free-flowing and nontacky.
Example 44
A bath containing approximately 0.6~ SiO2, 0.9~
CaC12, 0.3~ AlC13 and 0.6~ NaCl was prepared by mixing 1694 g
of H2O, 10.0 g of AlC13 6H2O, 24.2 g of CaC12 2H2O, 12.0 g of
~aCl, 1.2 g of an amphoteric fluorinated surfactant (Zonyl~
~SB, Du Pont Co.), and 250 ml of a colloidal silica sol havina
a pH of 2.0 and containing 4.8~ SiO2. This colloidal sol
was prepared by adding a mixture of 125 ml of a 30~ solids
aqueous silica sol (Ludox~ SM, Du Pont Co.) and 125 ml
of H20 to a running blender containing 637 ml of H20 and
- 40 ml of lN HCl.
To this bath was added dropwise 198 ml of 40~ solids
neoprene latex prepared like neoprene latex ~1. After 30
minutes, the bath was decanted from the pellets which had
formed. The pellets were soaked in 2 liters of H2O for 30
minutes and then filtered from the wash water and spun for
2 minutes in a basket centrifuge. The pellets were then
shaken with 1.5% of their weight of talcum powder and spread
in a tray to air dry overnight. They were further dried over
P2O5 under vacuum at room temperature. The resulting non-
tacky free-flowing pellets contained 1.56 milliequivalents
of residual alkalinity per 100 g of isolated polymer, as
shown by nonaqueous titration to a bromophenol end point.
Example 45
A bath containing approximately 0.5~ SiO2, 0.9~
CaC12 and 0.3% AlC13 was prepared by mixing 1714.6 ml of H2O,
10.0 9 of AlC13 6H2O, 24.4 9 of CaC12-2H2O, 1.2 9 of the tri-
methylnonanol ~ther of ethylene oxidc (Tergitol~' TM~-fi) and
250 ml of 0.69M silicic acid which had aged for five days.
lO~91QS7
To this bath was added dropwise 200 ml of 40~ solids neoprene
latex prepared likc neoprene latex #1. The pellcts which
formed were isolated, washed and dried as in the procedure
of Example 44. The resulting free-flowing, nontacky pellets
had a residual alkalinity of 2.43 meq/100 g.
Example 46
A latex mixture was prepared from 2 ml of the
sodium silicate solution described in Example 15, 15 ml of
lN NaOH, and 198 ml of 40~O solids neoprene latex prepared
like neoprene latex $2. This mixture was added dropwise to
a bath containing approximately 1.8~ CaC12, 1.7% NaCl, 0.6%
AlC13 and 0.6% modified sol prepared from 898.6 ml of H2O,
1000 ml of 2% AlC13 6H20 (adjusted to pH 3.5 with lN NaOH),
36.4 g of anhydrous CaC12, 34 g of NaCl, 1.0 g of 30
sodium lauryl sulfate (Duponol~ WAQE), and 30 ml of
the modified aqueous colloidal silica sol described
in Example 42. The pellets which formed were removed from
the bath after 15 minutes, washed with water, centrifuged,
treated with talc and dried as described in Example 44.
The resulting pellets were nontacky and free-flowing.
The applicatlon 18 a division Or copending
Appllcation Serlal No. 281 448, filed 1977 June 27.
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