THERMOPLASTIC CONTAINER FOR RUBBER CHEMICALS

PELLICULE THERMOPLASTIQUE POUR L'EMBALLAGE D'ELASTOMERES

English Abstract

Abstract of the Disclosure
A film comprising thermoplastic resinous
syndiotactic 1,2-polybutadiene is used to package
rubber chemicals (including polymers). The package
is added directly to a rubber batch being mixed, and
is easily dispersed in the stock even at conventional
final mixing temperatures.

Claims

What is claimed is;
1. A method of packaging an ingredient to be
added to a rubber stock during mixing of the said
rubber stock comprising enclosing the said ingredient
in a film of thermoplastic resinous syndiotactic 1,2-
polybutadiene as a packaging material to form a package
of said ingredient in the said film, whereby, when the
resulting package is added to a rubber stock and mixed
therewith at elevated rubber stock mixing temperature,
the film of thermoplastic resinous syndiotactic 1,2-
polybutadiene packaging material becomes incorporated
uniformly into the rubber stock within a short mixing
time, the said thermoplastic resinous syndiotactic 1,2-
polybutadiene having the following characteristics:
<IMG>
2. A method as in claim 1 in which the said
thermoplastic resinous syndiotactic 1,2-polybutadiene has
the following characteristics:
<IMG>
-9-

3. A packaged ingredient to be added to a
rubber stock during mixing of said stock comprising the
said ingredient enclosed in a film of thermoplastic
resinous syndiotactic 1,2-polybutadiene as a packaging
material to form a package of said ingredient in the said
film, the said package being characterized by the fact
that the film of thermoplastic resinous syndiotactic 1,2-
polybutadiene packaging material becomes incorporated
uniformly into the rubber stock within a short mixing
time when the package is added to a rubber stock and
mixed therewith at elevated rubber stock mixing tempera-
ture, the said thermoplastic resinous syndiotactic 1,2-
polybutadiene having the following characteristics:
<IMG>
4. A packaged ingredient as in claim 3 in which
the said thermoplastic resinous syndiotactic 1,2-poly-
butadiene has the following characteristics:
<IMG>
5. A method of incorporating an ingredient in
a rubber stock during mixing of the said rubber stock
comprising enclosing the said ingredient in a film of
-10-

thermoplastic resinous syndiotactic l,2-polybutadiene as
a packaging material to form a package of the said
ingredient in the said film, and thereafter adding
the resulting package to a rubber stock and mixing the
package and rubber stock together at elevated rubber
stock mixing temperature whereby the film of thermo-
plastic resinous syndiotactic 1,2-polybutadiene packaging
material becomes incorporated uniformly into the rubber
stock within a short mixing time, the said thermoplastic
resinous syndiotactic l,2-polybutadiene having the following
characteristics:
<IMG>
6. A method as in claim 5 in which the said
thermoplastic resinous syndiotactic l,2-polybutadiene has
the following characteristics:
<IMG>
7. A method as in claim 6 in which the said
mixing temperature is from 180 to 220°F.
8. A method as in claim 7 in which the said
rubber stock is a conjugated diene polymer rubber stock.
-11-

9. A method as in claim 8 in which the packaged
ingredient is sulfur.
10. A method as in claim 8 in which the packaged
ingredient is an accelerator of sulfur vulcanization.
-12-

Description

-` 108~3~33
--1--
This invention relates to a method of packaging
an ingredient to be mixed into a rubber stoc~, and to a
package containing such ingredient~ as well as to a
- method of incorporating an ingredient in a rubber stock.
It has previously been common practiceto wrap
or package rubber chemicals in a packaging material
comprising low density polyethylene resin, to form a
package which could be added directly to a rubber mi~,
packaging material and all. Such prior practice has
proven to be unfiatisfactory, in particular because of
difficulty of obtaining satisfactory dispersion of the
low density polyethylene packaging material in the
final stage mixing of rubber stocks.
In accordance with the present invention, it has
now been found that thermoplastic resinous syndiotactic
1,2-polybutadiene of controlled crystallinity having a
low melting point can be used to form a package for
rubber chemicals (including polymers) which can be
added to a rubber mix, package and all, and is easily
dispersed in the rubber stock at conventional final
mixing temperatures.
The thermoplastic resinous syndiotactic 1,2-
polybutadiene employed as a packaging material for
ingredients to be added to a rubber in accordance with
the invention usually has a crystallinity of from about
8 to about 35~, preferably about 22-28~, by weight,
as measured by X-ray diffraction and density of the
polymer. The polymer ordinarily has a crystalline
melting point of from about 70 to 77C., perferably
about 72 to 74C., and a glass transition point from
:
--1--

10~13~3
--2--
about -14.5 to -29C., preferably about -17 to -21C.,
as measured by differential thermal analysis. The flow
temperature of the polymer is typically about 90-110C.,
preferably 94-110C., measured in a capillary or on a
melting bar. The intrinsic viscosity of this syndiotactic
polymer is frequently about 0.9-2.5, preferably 1.0-1.8,
deciliters per gram, measured in toluene at 30~C. It
has a high permeability (to gases). Such a 1,2-poly-
butadiene resin may be prepared for example as described
in U.S. patents 3,498,963, Ichikawa et al., March 3, 1970,
3,522,332, Ichikawa et al., July 28, 1970 and 3,864,430,
Umeno et al., February 4, 1975.
To use the described syndiotactic 1,2-poly-
butadiene resin as a packaging material it is first
converted into a film (or sheet) by a conventional
technique for making thermoplastic films, such as by
calendering or extrusion with or without subsequent
orientation. Bags or similar containers or wrapping
for rubber compounding ingredients (including poly-
ZO mers) may be made from the film, for example by heat
sealing.
The ingredients which may be prepackaged in this
manner for addition to rubber stocks include the usual
rubber chemicals or compounding ingredients such as
accelerators, vulcanizing agents, activators, ~illers
(e.g. carbon black, silica), polymers, pigments3 whether
solids or liquids (provided of course that the physical
properties of such liquids are not such as to permit
them to swell~ dissolve or otherwise destroy the plastic
packaging material) as in the case of some plasticizers

- ~08
or extenders. The resulting package of pre-weighed com-
pounding chemicals is serviceable and affo~s a convenient,
clean and accurate way of preparing a rubber stock, by
direct addition of the package to the rubber durlng the
mixing operation, whether in an open mixer such as a roll
mill or in an internal mixer such as a Banbury (trademark).
The present resinous packaging material melts low enough
to be easily dispersed into rubber stock at conventional
final mix temperatures, e.g., 180 to 210 or 220F.
The rubber to which the compounding ingredient,
prepackaged in syndiotactic l,2-polybutadiene film in
accordance with the invention~ may be added, may be any
suitable conventional rubber, whether natural or synthetic,
as exemplified by such unsaturated vulcanizable rubbers
as the con~ugated diene polymers, whether homopolymers
as in cis-polybutadlene, cis-polyisoprene (natural or
synthetic), or copolymers as in butadlene-styrene,
butadiene-acrylonitrile, butadiene-vinyl-pryridine, and
l isobutylene-isoprene copolymer rubbers. Another example
- 20 of a suitable rubber stock is that of the monoolefin
copolymer rubber type, as represented by the ethylene-
propylene-noncon~ugated diene terpolymers known as EPDM.
The method of the invention is adaptable to use
with mechanized or automated pre-weighing systems and
insures accuracy and reproducibility with a minimum
occasion for direct contact between an operator and
the rubber chemical. Use of packaged chemicals ensures
cleanliness (no powders blowing around), accuracy (no
hold-up in a dumped container), and speed (the mixer
attendant does not have to weigh up chemicals for each
-3

108~3~3
--4--
batch).
The following example~ will serve to illustrate
the practice of the invention in more detail
Example 1
Thermoplastic syndiotactic 1,2-polybutadiene
resin ("1,2-PBD") manufactured by Japan Synthetic
Rubber Company~ grade RB 820, is used in this example.
This material has an intrinsic viscosity of 1.27
decil~ters per gram, measured in toluene at 30~C.,
a crystallinity of 24.5% by weight, and a melt index
of 1.98 measured at 150C. and 2,160 g.load.
The resin is converted into a film by extrusion
in a 1-1/2 inch Davis-Standard Thermatic (trademark)
extruder in which all heating zones were at 330F.;
the cooling and polishing rolls (three in number) were
at 75F ; the die dimensions were 12 inches by 0.012
inch. Draw ratio at the windup was about plus 50~.
The fi~ produced was about 10 mils thick and had the
following properties, compared to a low density poly-
ethylene (LDPE) film:
1~2-PBD LDPE
Softening point (Vicat) 60C. 850C.
Heat-seal temp 75-80C. ~100C.
"Heat-seal temp." is measured by applying a heated
metal bar briefly to two sheets of the thermoplastic
film on a thermally insulated surface. "Vicat so~en-
ing pt " is measured according to ASTM D1525.
To e~aluate the films, a 2.75-inch roll
laboratory mill may be loaded with approximately 100
grams of approximately 48 Mooney (ML-4-212F.) carcass
-4-

108~3~3
stock ~e.g., lOO parts of a blend of SBR, cis-1,4-
polybutadiene and natural rubber in approximately
equal proportions, ll parts naphthenic oil, 40 parts
carbon black, 4 parts zinc oxide, 3 parts stearic acid,
2 parts acetone-diphenylamine condensation product
[antioxidant], l part disproportionated rosin~ 4
parts sulfur, and 2. 5 parts N-cyclohexyl-2-benzothiazole
sulfenamide [accelerator]). The nip is set to establish
a 1/8 inch thick band and an active bank. 3/4 inch by
4 inch strips of 5-mil LM E film and 10-mil 1,2-PBD
were compared by observing their behavior when intro-
duced directly into the bite, m e observations made
in four different experiments are listed in Table I,
below. No cutting of the band was employed except as
noted in Experiment 4.

10~1383
u~
o a) ~ ~ o ,~ ~ w ~ ~::
h ~ h
~ P~ O O ~ ~:2,~ I ~ ~d
a)~ O~
h h ~ 3 h ~ h S~
v~ ~ ~ h u~ cn u~
~n ~ S
o
O ,~ O ~: O O~ ~ ~ O~
n~ ~ v~ h ~ h ~ O S: rl O
cd 52 ~ ~ :~ ~15 h ~Q ~q ~ h
tq ~ O
~i h h t~ .C tl5 S O O ~I S:: ~Q
P ~ ~ h a5 ~ ~ ~ ~ S
O ~1 ~ ~ ~1 0 ~1 0 ~ S
~3
O ~ S
a) q) ~ ~ ,~ o a~
~1 ~ ~ ~1 ~1 0 ~ O ~ I) h
~1 m ~ o m~ m~
~rt ~ S~ d h bD
) O I ~ d O
~1 ~ O ~ O ~ O
P~ ~ ~ ,D O ~ S
~ O
~o ~ ~
~ ~ ~ l ~ . .
cCn~ ~ c~ O
E~.C ~ O ~D ~ I ~1
w~ C~
., ~0
0~
O
~1 ~
h ¢
O .
. C~ ~ O~
.: o 0
~1 O O ~I r~
Lt~ ~~ O
~ N
1~ ~
~ Lr
E~ o~ .
~ : :
.
O ll~ O
r~ ~ C`J
: , . : . . ,
:

1081383
--7--
It is concluded from the tabulated experiments
that 1~2-PBD offers a 15 to 30F. safety factor compared
to LDPE. The new resin packaging material of the in-
vention not only melts lower but is more compatible with
rubber stocks than LDPE ~note that stock ~t 150F. does
not band coherently on a roll mill). In addition, it
has the added virtue of being easily co-vulcanized with
the polymers in a rubber stock once it has been dispersed
into the stock.
; 10 Example 2
mis example illustrates the preparation of
small bags from 1,2-PBD film and use of them for adding
final cure chemicals to a second stage rubber mix.
Sheets 10 inches square may be cut from a calen-
dered film of 1,2-polybutadiene resin described in Ex-
ample 1. To make a bag two sheets are superimposed one
upon the other and heat sealed along three sides by
contacting with a metal bar heated to 75-80C., thus
providing an open-ended pouch. 4.32 pounds of sul~ur
and 2.47 pounds of N-cyclohexyl-2-benzothiazole sulfen-
amide (accelerator) are weighed separately into two
such pouches and the open ends are heat sealed as
described above to close the bags. Into a No. 11 Banbury
are charged 400 pounds of a masterbach, mixed in the
proportions of 100 pounds of SBR, 50 pounds of high
abrasion furn~nce black, 4 pounds of zinc oxide, 3
pounds of stearic acid, 1 pound of N,N'-diphenyl-p-
phenylenediamine, 1 pound of disproportionated rosin and
~ 3 pounds of pine tar, followed by the two pouches of
- 30 sulfur and accelerator. Within two minutes the pouches
-7

iO81383
and their contained chemicals will have become incorporated
into the batch, and the batch can be discharg~d to the
drop mill ~or conventional blending. Additional process- ;
ing and eventual vulcanization can be carried out in normal
fashion.
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