Abstrict A solid calcium oxide desiccant dispersion for use in rubber compounds.
The dispersion comprises 30-94 weight percent calcium oxide and
3-55 weight percent asphalt and optionally 0.5-12 weight percent
fatty acid agent and 0.5-14 weight percent plasticizer. The dispersion
is added to rubber compounds at the rate of 1-20 parts per hundred
parts rubber.
Claims What is claimed is:
1. A desiccant dispersion for use in rubber compounds, said desiccant
dispersion comprising 30-94 weight percent calcium oxide and 3-55
weight percent asphalt, said desiccant dispersion being in solid
form and having a softening point of 90-190.degree. F.
2. A dispersion according to claim 1 said dispersion comprising
70-88 weight percent calcium oxide and 8-30 weight percent asphalt.
3. A dispersion according to claim 1 said desiccant dispersion
further comprising 0.5-12 weight percent fatty acid agent, said
fatty acid agent being selected from the group consisting of fatty
acids, fatty acid esters, and mixtures thereof.
4. A dispersion according to claim 1 said desiccant dispersion
further comprising 0.5-14 weight percent plasticizer.
5. A dispersion according to claim 1 said dispersion further comprising
3-5 parts ethylene-vinyl acetate per 100 parts asphalt.
6. A dispersion according to claim 1 said asphalt component being
35-75 weight percent unoxidized asphalt and 25-70 weight percent
oxidized asphalt.
7. A dispersion according to claim 1 said dispersion further comprising
0.5-12 weight percent stearic acid.
8. A dispersion according to claim 4 wherein said plasticizer
is selected from the group consisting of paraffinic oil, naphthenic
oil, aromatic oil, pine tar, paraffin wax, polyethylene wax, liquid
polybutadiene rubber, and mixtures thereof.
9. A dispersion according to claim 1 said dispersion further comprising
0.5-12 weight percent fatty acid, and 0.5-14 weight percent plasticizer.
10. A dispersion according to claim 1 wherein said asphalt has
a ring and ball softening point of 65-130.degree. C.
11. A solid desiccant dispersion comprising 30-94 weight percent
calcium oxide, 3-55 weight percent light-colored hydrocarbon resin,
0.5-14 weight percent plasticizer, and 0.5-12 weight percent fatty
acid agent.
12. A method of making a vulcanized rubber product comprising the
steps of: a) incorporating a desiccant dispersion into a rubber
compound at a rate of 1-20 parts desiccant dispersion per hundred
parts of rubber, said desiccant dispersion comprising 30-94 weight
percent calcium oxide and 3-55 weight percent asphalt, said rubber
compound comprising rubber selected from the group consisting of
natural rubbers, synthetic rubbers, and mixtures thereof; and b)
vulcanizing said rubber compound to yield said vulcanized rubber
product.
13. A method according to claim 12 said dispersion comprising
70-88 weight percent calcium oxide and 8-30 weight percent asphalt.
14. A method according to claim 12 said dispersion further comprising
0.5-12 weight percent fatty acid agent, said fatty acid agent being
selected from the group consisting of fatty acids, fatty acid esters,
and mixtures thereof.
15. A method according to claim 12 said dispersion further comprising
0.5-14 weight percent plasticizer.
16. A method according to claim 12 said dispersion having a softening
point between 90 and 190.degree. F.
17. A rubber compound comprising (a) rubber selected from the group
consisting of natural rubbers, synthetic rubbers, and mixtures thereof,
and (b) a desiccant dispersion comprising 30-94 weight percent calcium
oxide and 3-55 weight percent asphalt, said desiccant dispersion
being present in said rubber compound at a rate of 1 to 20 parts
desiccant dispersion per hundred parts rubber.
18. A rubber compound according to claim 17 said desiccant dispersion
further comprising 0.5-12 weight percent fatty acid agent, said
fatty acid agent being selected from the group consisting of fatty
acids, fatty acid esters and mixtures thereof.
19. A rubber compound according to claim 17 said desiccant dispersion
further comprising 0.5-14 weight percent plasticizer.
20. A rubber compound according to claim 17 said desiccant dispersion
further comprising 3-5 parts ethylene-vinyl acetate per 100 parts
asphalt.
21. A rubber compound according to claim 17 said asphalt component
being 35-75 weight percent unoxidized asphalt and 25-70 weight percent
oxidized asphalt.
22. A rubber compound according to claim 17 said desiccant dispersion
further comprising 0.5-12 weight percent stearic acid.
23. A rubber compound according to claim 19 said plasticizer being
selected from the group consisting of paraffinic oil, naphthenic
oil, aromatic oil, pine tar, paraffin wax, polyethylene wax, liquid
polybutadiene rubber, and mixtures thereof.
24. A rubber compound according to claim 17 said desiccant dispersion
comprising 70-88 weight percent calcium oxide and 8-30 weight percent
asphalt.
Description FIELD OF THE INVENTION
The present invention relates to a desiccant dispersion, and more
particularly to a calcium oxide desiccant dispersion for removing
moisture from rubber compound formulations during processing.
BACKGROUND OF THE INVENTION
It is well known that the presence of moisture in a rubber compound
formulation during the vulcanization process can cause serious deleterious
effects in the finished rubber product. At normal vulcanizing temperatures,
excessive moisture will "gas-out," causing surface anomalies
such as blistering or voids on the cured rubber product. In addition
to being unaesthetic, such surface anomalies invariably reduce the
service life of functional rubber products, e.g. tires and extruded
rubber products.
Calcium oxide has long been employed in the art as a desiccant
to remove excessive moisture from rubber compounds. Though a very
effective desiccant for rubber formulations, the extreme hydrophilicity
of calcium oxide makes proper handling and storage prior to use
extremely difficult. If not properly stored, calcium oxide readily
absorbs ambient atmospheric moisture in a reaction yielding calcium
hydroxide, thus greatly depleting its effectiveness as a desiccant.
A second problem associated with calcium oxide is that it is typically
delivered to the rubber processing industry as a fine powder. Fine,
dry powders tend to increase mixing times and formulation viscosities,
and are easily airborne. Calcium oxide is extremely caustic to the
skin, eyes, and mucous membranes of humans, and therefore creates
a hazardous work environment when airborne.
A known calcium oxide dispersion for use in rubber compound processing
is Desical-P from Harwick, which is calcium oxide powder dispersed
in naphthenic oil. Such paste dispersion has been fairly successful
at improving rubber processing properties, such as homogeneity of
calcium oxide throughout the rubber formulation, as well as reducing
atmospheric moisture absorption during storage. However, a major
detriment to such existing paste formulations is that they tend
to sweat or exude oil to the surface when stored over time. Such
exuded oil makes handling and weighing of the paste quite difficult.
In addition, such pastes are provided in bulk form, and must be
cut to proper weight before they are added to a rubber compound
batch for processing. Such characteristics contribute additional
man-hours to rubber processing which translate directly into additional
expense. Lastly, though such calcium oxide paste absorbs moisture
at a lower rate than calcium oxide powder, such paste still absorbs
significant atmospheric moisture when stored.
Consequently, there is a need in the art for a calcium oxide dispersion
that is effective as a rubber compound desiccant, yet does not exude
oil when stored, has improved desiccant properties over existing
dispersions, is easy to handle and cut to weight, and further resists
atmospheric moisture absorption during storage.
SUMMARY OF THE INVENTION
A desiccant dispersion for use in rubber compounds comprising 30-94
wt. % calcium oxide and 3-55 wt. % asphalt. A solid desiccant dispersion
comprising 30-94 wt. % calcium oxide, 3-55 wt. % light-colored hydrocarbon
resin, 0.5-14 wt. % plasticizer, and 0.5-12 wt. % fatty acid agent.
A method of making a vulcanized rubber product comprising the steps
of a) incorporating a desiccant dispersion into a rubber compound
at a rate of 1-20 parts desiccant dispersion per 100 parts of rubber,
said desiccant dispersion comprising 30-94 wt. % calcium oxide and
3-55 wt. % asphalt, said rubber compound comprising rubber selected
from the group consisting of natural rubbers, synthetic rubbers,
and mixtures thereof; and b) vulcanizing the rubber compound to
yield the vulcanized rubber product. A rubber compound comprising
rubber and the desiccant dispersion is also provided.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
In the description that follows, when a preferred range, such as
5 to 25 (or 5-25), is given, this means preferably at least 5 and,
separately and independently, preferably not more than 25. Unless
specifically otherwise indicated, all parts are parts by weight
and all percents are weight percents, both herein and in the appended
claims.
The invented desiccant dispersion has the preferred formulations
shown in Table 1. In this formulation or table of components, any
preferred or less preferred weight percent or weight percent range
of any component can be combined with any preferred or less preferred
weight percent or weight percent range of any of the other components;
it is not required or necessary that all or any of the weight percents
or weight percent ranges come from the same column. The invented
calcium oxide desiccant dispersion is in solid form and comprises
calcium oxide and asphalt according to a first preferred embodiment
of the invention. Preferably, the invented dispersion further comprises
fatty acid and plasticizer.
TABLE 1 Preferred composition of invented calcium oxide desiccant
dispersion (Listed in weight percents) Most Less Still Less Still
Less Component Preferred Preferred Preferred Preferred Asphalt 15
10-20 5-30 4-40 8-25 3-55 Fatty Acid 2 1.5-4 1-7 0.5-10 Agent 0-12
Plasticizer 3 2-5 1.5-7 0.5-12 0-14 Calcium 80 75-85 60-90 30-94
Oxide 70-88 45-92
Less preferably, the formulation contains 80 weight percent calcium
oxide and 20 weight percent asphalt. The asphalt component in the
invented dispersion is preferably a blend of 55 less preferably
50-60 less preferably 45-65 less preferably 40-70 less preferably
35-75 percent asphalt (unoxidized asphalt), and 45 less preferably
40-50 less preferably 35-55 less preferably 30-60 less preferably
25-70 percent oxidized (or blown) asphalt. Less preferably the
asphalt component can be 100% oxidized or 100% unoxidized asphalt.
The asphalt component preferably has a ring and ball softening point
of 65-130 more preferably 69-110 more preferably 72-100 more
preferably 75-90 more preferably 77-82 .degree.C. The unoxidized
asphalt is preferably a product sold by Sun Refining under the name
MONOR. Oxidized asphalt, also known as blown asphalt, is asphalt
and is produced by blowing air through asphalt at 400-600.degree.
F. followed by cooling. Raising the proportion of oxidized asphalt
will raise the softening point of the finished dispersion product.
The fatty acid agent, which is optional, is fatty acids, fatty
acid esters, or a mixture thereof. Most preferably, the fatty acid
agent is stearic acid because of its compatibility with the majority
of rubber compounding formulations, as well as its lubricity. The
stearic acid preferably has an acid value in the range of 193-212
and a maximum iodine value of 10. Less preferably, the fatty acid
agent is oleic, palmitic, linoleic, or linolenic acid, or a mixture
thereof. The fatty acid ester is preferably a triglyceride such
as a hydrogenated triglyceride, such as Neustrene 060 from Humko
Chemical Company. Other examples of suitable fatty acid esters include
Promix 200FE from Flow Polymers, and WB212 from Struktol Corporation.
The fatty acid agent is preferably uncrosslinked, and provides lubricity
to the dispersion which aids mixing and subsequent extrusion. The
fatty acid agent further aids wetting out of the calcium oxide powder,
which aids incorporation of calcium oxide powder into a rubber compound
by reducing the friction coefficient between the powder and the
rubber compound.
The plasticizer component, which is optional, is any known rubber
processing oil, wax or softening agent compatible with hydrocarbon
dispersions. Preferred plasticizers are paraffinic oil (such as
Sunpar 2280 from Sun Refining or Stanlube from Harwick Chemical
Company), naphthenic oil (such as Calsol from Calumet Lubricants),
aromatic oil (such as Sundex from Sun Refining), pine tar (such
as Tartac from CP Hall), paraffin wax (such as 130WAX from Akrochem),
or polyethylene wax (such as PE 617A from Allied Signal). Less preferably,
the plasticizer component may be another softening agent such as
Ricon liquid polybutadiene rubber available from Ricon Grand Junction
Company, or a mixture of the above. The amount of plasticizer can
be increased or decreased to decrease or increase the softening
point (or paste point) of the dispersion. A lower softening or paste
point will be useful to accommodate rubber compounds having low
processing temperatures. Preferably the dispersion is compatible
with the processing temperatures of the vast majority of rubber
compounds (having discharge temperatures in the range of 180-210.degree.
F.). The plasticizer also aids wetting out the calcium oxide powder.
The calcium oxide component is calcium oxide powder as known in
the rubber compounding art, which typically has a nominal particle
size of about 325 mesh and a specific gravity of about 3.3. Preferably,
the calcium oxide powder is between 90-99% pure calcium oxide with
the remainder being trace elements or materials and inert matter.
The above formulation yields a dark colored finished product that
may discolor or stain white or other light-colored rubber compounds.
Where color retention of light-colored rubber compounds is important,
a light-colored hydrocarbon resin is substituted for the asphalt
in the above formulation according to a second preferred embodiment
of the invention. When substituted for asphalt, the light-colored
resin is present in the desiccant dispersion formulation in the
same preferred proportions as stated for the asphalt component in
table 1. The light-colored resin can be any solid, light-colored
resin based on hydrocarbon chemistry that has a softening point
in the range of 65-130.degree. C. (149-266.degree. F.), more preferably
95-100.degree. C. (203-212.degree. F.). Acceptable resins include,
for example, Nevtac from Neville Chemical Company, Petrorez from
Akrochem, and Norsolene from Sartomer Corporation. Preferably the
light-colored resin is at least as light as at least one of these
three resins. Less preferably, the light-colored resin may be terpene
tackifiers or a phenolic resin such as SP1068 available from Schenectady
International.
The components of the dispersion are preferably mixed as follows.
At the preferred parts by weight (80 parts calcium oxide, 15 parts
asphalt, 2 parts fatty acid agent, 3 parts plasticizer), all four
components are charged into a heated mixer and blended together
at 250.degree. F. until the mixture becomes a homogeneous malleable
paste. Once fully mixed, the hot paste is removed from the mixer
and undergoes a forming stage. Preferably, the paste is delivered
to an extruder where it is extruded into small pellets, preferably
having a mean diameter of at least 0.1 inch and less than 1 more
preferably 0.8 more preferably 0.5 more preferably 0.25 inches,
and an average length preferably at least 0.1 inch and preferably
less than 1 more preferably 0.8 more preferably 0.6 more preferably
0.5 more preferably 0.4 inches. Optionally, the hot paste can
be delivered to some other forming apparatus capable of forming
the hot paste into discrete particles such as pellets, rods, flakes,
or some other desired shape that will facilitate easy introduction
into a rubber compound formulation and uniform dispersion therethrough.
Regardless of the particular type of forming apparatus chosen, the
whole process (mixing, heating, forming) is preferably a continuous
system. One such system is a twin screw mixing extruder, though
other systems and configurations are possible, and are known in
the mixing art.
The invented dispersion according to the first preferred embodiment
(utilizing asphalt) typically is discharged as a dark brown, hard
rod or pellet with a softening point of 90-190 more preferably
100-180 more preferably 110-170 more preferably 120-160 more
preferably 130-155 more preferably 135-150 more preferably about
145 .degree. F. The invented dispersion also has a specific gravity
of preferably 1.7-2.8 more preferably 1.9-2.4 more preferably
about 2.15 in its final solid (extruded) form. The invented dispersion
according to the second preferred embodiment (utilizing light-colored
hydrocarbon resin) is an off-white, hard rod or pellet with the
same preferred physical attributes as stated above.
The invented dispersion is superior to existing calcium oxide pastes
because it exists in solid form at ambient conditions, does not
exude oil or other slippery residue to its surface, and does not
need to be manually cut to weight as is required of existing paste
dispersions. Pellets of the invented dispersion are preferably measured
out by volume to obtain the desired weight via calculation using
its known bulk density.
Optionally, ethylene-vinyl acetate (EVA) or other similar thermoplastic
material can be added to the invented dispersion formulation prior
to mixing in order to enhance pelletizing or other shape forming
during, for example, extrusion. Preferably, such a thermoplastic
will have a melting point in the range of 350-400.degree. F., and
is added to the invented dispersion as follows:
1. For the asphalt-containing formulation, at 3-5 parts EVA (or
other thermoplastic) per 100 parts asphalt.
2. For the resin-containing formulation, at 10-15 parts EVA (or
other thermoplastic) per 75 parts resin.
The invented dispersion is added to rubber compounds (comprising
rubber selected from the group consisting of natural rubbers, synthetic
rubbers and mixtures thereof) prior to vulcanization in the same
manner as other known desiccant dispersions are added to rubber
compounds comprising natural rubbers, synthetic rubbers and mixtures
thereof. The invented dispersion is most preferably used with ethylene-propylene-diene
(EPDM), polychloroprene (CR), styrene-butadiene (SBR), ethylene
(EPR), nitrile (NBR), bromobutyl, and halobutyl (IIR) rubber compounds.
Less preferably, the invented dispersion is used with epichlorohydrin
(ECO), silicone, acrylic, isoprene-acrylonitrile, polynorborene,
polyisoprene, and styrene-isoprene rubber compounds.
Rubber compounds utilizing the invented dispersion, particularly
EPDM compounds, find particular utility for vulcanized rubber products
such as tires, tire treads, carcasses, sidewalls, coating stocks,
hoses, belting, inner tubes, innerliners, general purpose rubbers,
and other uses. Such rubber compounds also find particular utility
as extruded goods such as seals, foams, tubes, and a variety of
automotive components. A rubber compound utilizing the invented
dispersion may include accelerators, retarders, activators, vulcanizers,
antioxidants, antiozonants, protective materials, other plasticizers,
processing aids, stabilizers, tackifiers, extenders, fillers, reinforcing
materials, blowing agents, lubricants, and other rubber compounding
materials known in the art.
The invented dispersion is preferably added to a rubber compound
formulation during the final productive stage of the mixing cycle
at a rate of 1-20 preferably 2-18 preferably 4-15 preferably
6-12 preferably about 7-10 phr (parts per hundred parts of rubber).
The rubber compound is then vulcanized as known in the art to produce
a vulcanized rubber product.
The following Examples further illustrate various aspects of the
invention.
EXAMPLE 1
An invented formulation containing 9.75 weight percent unoxidized
asphalt, 4.8 weight percent oxidized asphalt, 2 weight percent stearic
acid, 3 weight percent Sunpar 2280 paraffinic oil, 80 weight percent
calcium oxide powder and 0.45 weight percent EVA was tested against
a common calcium oxide dispersion paste sold by Harwick as Desical-P
(Desical). It is a soft, malleable paste that must be cut to weight
prior to addition to a rubber compound formulation. Desical is 80
weight percent calcium oxide, with the balance being naphthenic
oil, and optionally a stiffening agent such as paraffin wax or some
other wax like material.
The invented dispersion, and the Desical dispersion were added
respectively to separate batches of an EPDM rubber compound formulation
during the productive stage of the mixing cycle. Both formulations
were mixed using a laboratory Brabender mixer at 65.degree. C. (149.degree.
F.) and a rotor speed of 55 rpm. First, identical master batches
of EPDM rubber compound were prepared as shown in Table 2.
TABLE 2 Ingredient Function Parts by Weight EPDM 6505 Rubber 100
N550 Carbon Black Filler 155 A-1 Whiting (CaCO.sub.3) Filler 60
ZnO Activator 5 Stearic acid Activator 1 Sunpar 2280 (Paraffinic
oil) Plasticizer 75 Flectol ODP (Octylated Antioxidant 1 diphenylamine)
PEG3350 (Polyethylene-glycol Lubricant 3 wax) TOTAL: 400
The master batch described in table 2 was divided into equal halves
each having a total of 200 parts by weight. Each half was then combined
with a desiccant dispersion (either the invented dispersion or Desical)
and an identical cure package comprising accelerators and vulcanizers
to make two separate productive batches in the following manner.
First the master batch was added to a Brabender mixer at 45.degree.
C. (113.degree. F.) with a mixing speed of 55 rpm. Next the appropriate
calcium oxide dispersion was combined with the cure package and
added to the master batch in the mixer. The mixing speed was held
constant and the temperature ramped up to 90.degree. C. (194.degree.
F.). At the top of the temperature ramp, the rubber compound batch
was discharged and immediately milled on a two-roll laboratory mill.
The compositions of each productive batch are listed in table 3
below.
TABLE 3 Productive batch compositions for invented and Desical
productive batches (parts by weight) Invented Desical Ingredient
Function Batch Batch Master Batch -- 200 200 Sulfur Vulcanizer 0.35
0.35 2-mercaptobenzothiazole Accelerator 0.10 0.10 (MBT) Benzothiazyl
disulfide Accelerator 0.60 0.60 (MBTS) Tetramethylthiuram disulfide
Accelerator 0.38 0.38 (TMTD) Dipentamethylenethiuram Accelerator
0.50 0.50 hexasulfide (DPTT) Tellurium Accelerator 0.10 0.10 diethyldithiocarbamate
(TDEC) Zinc dibutyldithiocarbamate Accelerator 0.38 0.38 Invented
Calcium Oxide Desiccant 7.00 0.00 Dispersion Desical-P Desiccant
0.00 7.00 TOTAL 209.41 209.41
The invented dispersion was in the form of solid extruded pellets,
and the appropriate weight was obtained via measuring an appropriate
number of extruded pellets. It was observed that the Desical paste
exuded a slippery oil to its surface making it difficult to handle
and cut to proper weight.
It was observed that both calcium oxide dispersions were readily
incorporated into the rubber batch, though the Desical dispersion
periodically adhered to the interior wall of the Brabender mixer,
and had to be pushed back into the batch during mixing. No such
wall-adherence occurred with the invented dispersion pellets. Once
cured, the physical and state-of-cure properties of the two finished
rubber products were measured in accordance with ASTM methods. Specifically,
hardness was measured using ASTM Testing Method # D2240 cured physical
properties (tensile strength, %-elongation and %-modulus) using
ASTM Testing Method # D412 Die-C Tear using ASTM Testing Method
# D624 and Mooney Viscosity and Scorch using ASTM Testing Method
# D1646 ODR (Oscillating Disk Rheometer). The results are as shown
in Table 4.
TABLE 4 Cured Physical Properties (100) %- Percent Tensile Tear
Batch Hardness modulus Elongation (psi) (C) Invented 78 575 270%
1365 212 Desical-P 78 565 270% 1365 207 Mooney Mooney Viscosity
Scorch (cP) (min:sec) Invented 68.0 10:55 Desical-P 65.0 10:09 State
of Cure (ODR) Max. Torque Min. Torque Ts(1) Tc(90) (inch-lbs.) (inch-lbs.)
(min) (min) Invented 48.07 6.20 1.02 2.42 Desical-P 47.44 6.00 0.98
2.31
State-of-cure properties for the two rubber compounds were measured
using an oscillating disk rheometer (ODR) under the following test
conditions: 350.degree. F., 55 rpm, 15-minute motor, 3.degree. arc
and 100 range. "Max. Torque" refers to the highest torque
value measured by an oscillating disk rheometer during a 15 minute
test. "Min. Torque," conversely, was the lowest torque
value measured during the test. Ts(1) was the length of time in
minutes required for the rubber compound to begin to vulcanize,
measured when the torque value rose 2 inch-lbs. from the baseline.
Tc(90) was the length of time in minutes required for the rubber
compound to become 90% vulcanized.
A Mooney Viscometer was used to measure both compound viscosity
and scorch times under the following conditions: Viscosity at ML
1+4 at 212.degree. F.; Scorch at Ms delta 5 at 250.degree. F.
As can be seen from table 4 rubber compounds utilizing the invented
desiccant dispersion exhibit essentially identical physical and
state-of-cure properties compared with rubber compounds utilizing
the currently widely used Desical-P dispersion. The result is that
the invented solid dispersion yields a finished rubber part of comparable
quality, while being significantly less cumbersome to handle and
to weigh.
EXAMPLE 2
Moisture absorption rates, paste points and specific gravity were
also measured for the invented desiccant dispersion tested in Example
1 and the Desical dispersion alone. These experiments demonstrated
the invented dispersion's superior resistance to atmospheric moisture
absorption during storage, permitting it to retain a significantly
higher proportion of its water-absorbing capacity during storage
than existing paste dispersions.
Moisture absorption values were determined by weighing a specimen
of each dispersion on an analytical scale and calculating the percent
of weight gain after specified moisture exposure times. Each specimen
was exposed to ambient conditions, i.e. 21.degree. C. (69.8.degree.
F.) and 40% relative humidity. Percent moisture absorption for each
specimen was measured once after 24 hours and again after 48 hours.
Paste points were measured by placing a small piece of each calcium
oxide dispersion onto a PTC melt point meter and recording the temperature
when the specimen became a malleable paste. The resulting physical
data for the calcium oxide dispersions is summarized below in table
5.
TABLE 5 Physical Properties Moisture Absorption Paste Point Specific
@ 24 hours @ 46 hours (.degree. F.) Gravity Invented 0.1314% 1.0350%
145 2.15 Desical-P 0.3878% 2.2581% 110 2.20
The two dispersions exhibit nearly identical specific gravity,
while the invented dispersion experienced less than half the rate
of moisture absorption of the Desical dispersion. In addition, the
invented dispersion exhibited a paste point of 145.degree. F. compared
with 110.degree. F. for the Desical dispersion, meaning that the
invented dispersion remained solid up until it reached the rubber
processing temperature when it softened to enable homogeneous mixing
throughout a rubber compound. The invented dispersion was thus easier
to handle and store than the Desical dispersion.
During the experiment, it was noticed that the Desical had become
an off-white part-paste, part-powder material after 24 hours of
exposure to ambient moisture. The invented dispersion had begun
to turn to a lighter shade of brown, however still remained solid.
After 48 hours, the Desical had become a white powder throughout,
indicating that a significant amount of moisture had been absorbed.
The invented dispersion turned tan in color, and had begun to develop
a light powdery film on the surface, however still remained solid.
These results indicated that, properly stored, the invented calcium
oxide dispersion enjoys a far greater shelf-life than the calcium
oxide pastes of the prior art, and retains more than twice the water
absorbing capacity.
Although the hereinabove described embodiments of the invention
constitute the preferred embodiments, it should be understood that
modifications can be made thereto without departing from the scope
of the invention as set forth in the appended claims. |