Note: Descriptions are shown in the official language in which they were submitted.
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TIT~E
A MANUFACTURED GRANULAR SUBSTRATE
AND METHOD FOR PRODUCING THE SAME
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a manufactured granular
substrate suitable for use as a carrier for chemical
agents, as well as a method for producing a granular
substrate. More particularly, this invention relates to
a water dispersable, light weight manufactured granular
substrate having a bulk density of about 40 pounds per
cubic foot to about 55 pounds per cubic foot at a size
guide number of about 100 to about 230 and a uniformity
index at a minimum of 40.
2. Summary of Related Art
Generally, manufactured granular substrates are
utilized as carriers for active chemical agents, such as
for example herbicides or other pesticides. The
carriers, with the active chemical agents, are utilized
to distribute the active agent over a broad area. The
carriers are generally inert compounds that, upon
application, break down over time. Existing water
dispersable carrier compositions have larger than
desired particles sizes accompanied by high bulk
densities of greater than 65 pounds per cubic foot. It
is preferable to utilize a carrier with smaller granules
and a lower bulk density in order to efficiently
transport and distribute the required amount of active
chemical agent without utilizing excessive amounts of
inert carrier compounds.
Conventional manufactured granular substrates often
have a tendency to break apart thus creating handling
and distribution problems. Granular substrates that
resist attrition are preferred because they will not
degrade and therefore maintain their particle size
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during handling. While resistance to attrition is
important, the carrier compound must however breakdown
or disintegrate upon exposure to water.
U.S. Patent No. 5,078,779 discloses a binder
composition for the granulation of dry, stable,
particulate fertilizers. The composition generally
includes a reactive carbonate and a reactive sulfate, in
combination with a silicate strengthening agent and a
water dispersing agent. Dolomite is disclosed as a
carbonate source for the binder composition. The binder
is used in conjunction with ammonium sulfate to provide
a granulated fertilizer. In order to form the
granulated fertilizer, the patent teaches the use of a
reactive acid to initiate a reaction between the sulfate
salt and the metal ion of the carbonate to form a
complex salt.
A manufactured granular substrate having 10% to
100% plant fiber and 0% to 90% of a mineral filler is
disclosed in U.S. Patent No. 5,019,564. The substrate
is formed by the agitated agglomeration of a fibrous
slurry without the use of a binder. The plant fibers
are generally lmm to lOmm in length. The resulting
substrate has a bulk density of about 20 to 42 pounds
per cubic foot. The substrate is utilized as a carrier
for active chemical agents. However, the substrate does
not readily breakdown upon exposure to water.
Additionally, the fibrous nature of the substrate can
reduce the ability of the substrate to flow in bulk
form.
U.S. Patent Nos. 4,015,973, 4,954,134, and
5,228,895 all generally disclose the use of either
limestone or dolomite in conjunction with a
lignosulfonate binder in the formation of manufactured
granular substrates. The agglomerated particles
produced in accordance with the patents are either
outside the preferred size and bulk density or are
susceptible to degradation during handling.
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Additionally, U.S. Patent No. 5,242,690 discloses
an inert manufactured granular substrate as a carrier
for chemical agents. The granular carrier composition
includes grain dust and a binder of either calcium or
sodium lignosulfonate. The finished granular carrier
exhibits a bulk density between 30 and 35 lbs per cubic
foot.
Thus, existing manufactured granular substrates
utilize either limestone or dolomite with other binding
or reactive components to produce granular substrates as
carriers for active chemical agents. The existing
manufactured granular substrates are not of the desired
size or bulk density. Also, some of the existing
manufactured granular substrates have a tendency to
breakdown during handling thereby changing the bulk
density or creating distribution problems during
application. Other granular substrates produced from
primarily plant fiber, have some desirable physical
properties but fail to readily disintegrate upon
exposure to water.
It would be an advantage to produce a manufactured
granular substrate for use as a carrier compound for
active chemical agents that has a bulk density of 40 to
55 pounds per cubic foot at a relatively small particle
size. A manufactured granular substrate having the
noted properties is capable of delivering an appropriate
amount of active chemical agent to a desired area while
utilizing less inert material. Furthermore, smaller
particle sizes provide a greater surface area for the
chemical agent and result in an improved distribution or
coverage of the desired area of application.
It would also be an advantage to produce a
manufactured granular substrate that does not degrade
during handling but breaks down when exposed to moisture
or water. The resistance to attrition ensures the
proper distribution of the active chemical agent upon
application. Furthermore, the ability to disintegrate
upon exposure to water is needed to provide the active
chemical agent to the soil.
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SU~MARY OF THE INVENTION
In accordance with the present invention, there is
provided a novel manufactured granular substrate
composition that is suitable for use as a carrier for
active chemical agents. The present invention also
includes a method for forming the manufactured granular
substrate.
The manufactured granular substrate composition of
the present invention includes one or more mineral
components, one or more light weight additives, and one
or more binders. The mineral component in the granular
substrate is 65 wt~ or more of at least one compound
selected from the group consisting of dolomite and
limestone. The light weight additive is included in the
substrate at about 5 wt~ to about 25 wt~ of one or more
compounds selected from the group consisting of expanded
silica, fly ash, hydrated lime, wheat flour, wood flour,
and soy flour. The binder is included in an amount up
to about 20 wt~ of one or more compounds selected from
the group consisting of brewers condensed solubles,
lignosulfonate, and sodium carbonate lignin.
Optionally, a coating, at about 1 wt~ or less, may be
added to the outer surface of the manufactured granular
substrate.
The granular substrate of the present invention has
a bulk density of about 40 pounds per cubic foot to
about 55 pounds per cubic foot at a particle size guide
number ranging from about 100 to about 230. The
preferred bulk density is greater than 42 pounds per
cubic foot to about 52 pounds per cubic foot.
Additionally, the substrates have a uniformity index at
a minimum of 40. The particle size and bulk density are
desirable properties for use of the granular substrate
as a carrier for active chemical agents, such as
herbicides or other pesticides. Additionally, the
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granular substrate resists attrition during handling but
is capable of breaking down once exposed to water.
The process of the invention involves the mixing
and pelletizing of the noted manufactured granular
substrate composition. The mixing of the present
inventive composition occurs at relatively low shear
forces to prevent the degradation of the mix components.
The pelletizing of the mixture composition may be
accomplished through conventional pelletizing equipment
such as pelletizing pans or drum granulators. The
manufactured granular substrate, in pellet form, is then
generally dried at a temperature of about 240~F to about
300~F to remove excess moisture and produce the
manufactured substrate of the present invention.
It is an object of the present invention to provide
a manufactured granular substrate, produced from at
least one mineral component and additional additives,
that has a bulk density of about 40 pounds per cubic
foot to about 55 pounds per cubic foot at a particle
size in accordance with particle size guide number
standards of about 100 to about 230. A manufactured
granular substrate having the noted characteristics is
desirable for use as a carrier for chemical agents
because the granular substrate, in bulk form, has a
greater surface area for receiving the chemical agent
while reducing the amount of inert material required for
application. Additionally, the smaller particle size
and lower bulk density of the present invention result
in an improved distribution of active chemical agents
over a specified area.
It is also an object of the present invention to
provide a manufactured granular substrate that does not
degrade during handling yet disintegrates upon
application and exposure to water.
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DETAIT,Fn DESCRIPTION OF T~ p~FFERRED EMRODIM~T
In accordance with the present invention, it has
been discovered that a combination of specific mineral
components, light weight additives, and binders results
5 in a preferred manufactured granular substrate which is
suitable for use as a carrier for active chemical
agents. Additionally, the present invention involves a
process for manufacturing the granular substrate.
The present invention provides a granular carrier
in pellet form that has a bulk density of about 40
pounds per cubic foot to about 55 pounds per cubic foot
at a nominal product sizing, in accordance with the size
guide numbering system, of about 100 to about 230. The
preferred bulk density is greater than 42 pounds per
15 cubic foot to about 52 pounds per cubic foot.
The manufactured substrate has an appropriate
crush strength and resistance to attrition to prevent
significant degradation of the substrate during
handling. Additionally, the manufactured granular
20 substrate quickly disperses when exposed to water. The
granular substrate also has the appropriate spherocity,
absorption, and solubility to enable the use of the
substrate as a carrier for active chemical agents such
as herbicides or other pesticides.
The manufactured granular substrate of the present
invention includes one or more mineral components
preferably selected from the group consisting of
dolomite and limestone. The mineral components make up
about 65 wt~ or more of the manufactured granular
30 substrate. In general, the mineral components have a
sizing of 100~ passing through a 30 mesh screen and 50~
or more passing through a 200 mesh screen. The mineral
components have a preferred sizing of about 100~ through
a 50 mesh screen and 80~ or more through a 200 mesh
35 screen. The noted mesh sizes and all those mentioned
hereafter conform with U.S. standard sieve sizes.
Additionally, the mineral components have a bulk density
of about 75 to about 90 pounds per cubic foot. The
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sizing of the mineral components may vary with respect
to other ingredients utilized in the agglomerated
substrate. In addition to the preferred mineral
components, other stone or mineral dust compounds
conforming with the size and bulk density parameters may
be suitable for use with the present invention.
One or more light weight additives are utilized
with the present inventive composition to obtain the
desired bulk density of the finished substrate. The
manufactured granular substrates include about 5 wt~ to
about 25 wt~ of the additives. The light weight
additives are generally inert compounds having a bulk
density of less than 35 pounds per cubic foot and a
sizing of at least 20% passing through a 40 mesh screen.
It is preferred that the additives have a sizing of 100
passing through a 40 mesh screen. Additionally, the
light weight material should be a non-fibrous material
as indicated by the sizing parameters. Fibrous material
can adversely impact the dispersability and the flow
characteristics of the finished granular substrate. The
light weight additives are preferably selected from the
group consisting of expanded silica, fly ash, hydrated
lime, wheat flour, wood flour, and soy flour. However,
other inert compounds meeting the bulk density and
sizing specifications may be suitable for use in the
present inventive composition.
A most preferred embodiment includes the use of
wood flour resulting from finely milled particle board.
The particle board contains approximately 10 wt~ of a
urea-formaldehyde resin. The additional resin assists
in producing a granular substrate that does not degrade
during handling but breaks down upon exposure to water.
A binder is utilized to agglomerate the ingredients
of the present invention. The binder is utilized at an
amount up to about 20 wt~ (dry basis) of the granular
composition. The preferred amount of binder is
generally 2 wt~ to 20 wt~. The binder is selected from
the group consisting of brewers condensed solubles,
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lignosulfonate, and sodium carbonate lignin. The binder
is generally added to the composition as a solution.
The solution is typically provided as a water based
slurry having about 40~ to 50~ solids by weight and
weighing about 10 pounds per gallon. In an alternative
embodiment, an amount of sodium silicate may be utilized
with one or more of the noted binders.
optionally, a coating may be included with the
manufactured granular substrate to provide a harder
outer shell. The coating is generally added to the
composition at 1 wt~ or less. The coating material is
added directly to the dried, finished pellets and
enhances the strength of the granular substrate to
prevent degradation. The preferred coating material is
polyvinyl alcohol. However, other coating compositions
capable of strengthening the substrate without adversely
affecting the desired properties are suitable for use
with the present invention.
The composition of the present invention is
generally produced by first creating an admixture of the
noted components within the specified ranges. The
mixing of the components may occur in either a batch or
continuous mixing process. Conventional mixing devices
are suitable for use with the present invention. The
components should be thoroughly mixed at conditions
which prevent degradation or compaction of the
materials. During the mixing step, the binder
composition is generally added to the mixture as a
solution. Optionally, at least part of the water
soluble binder may be added to the pelletizing apparatus
during pelletizing. Additional water, up to about 15
by weight, may be necessary for agglomeration of the
materials in the inventive composition.
The admixture is then fed into a pelletizing
apparatus to produce the manufactured granular substrate
of the present invention. Conventional pelletizing
equipment is suitable for use in producing the substrate
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in pellet form. The preferred pelletizing equipment is
a pelletizing pan. Additionally, drum granulators or
other types of granulation equipment may be used to
produce the granular substrate of the present invention.
Water may be added to the mixture during the
pelletizing step of the process to assist in granulation
of the material. The water is generally added at an
amount which results in no greater than 35~ by weight in
the substrate.
In accordance with the present invention, the
operation of a pelletizing pan may vary with the
specific formulation or ingredients in order to produce
a granular substrate with the preferred properties. For
example, feed rates and locations of the admixture or
the water, the angle of the pan, the speed of rotation
of the disc, or the depth of the pan may be varied to
produce the desired product. One skilled in the art of
pelletizing is capable of recognizing the variables and
making adjustments to obtain the granular substrate in
pellet form.
The manufactured granular substrate is then dried
to a temperature of about 240~F to about 300~F to
remove excess water utilized during the agglomeration of
the components. The pellet is dried to a total moisture
content of 8~ or less in accordance with ASTM standard D
5033 Volume 11.04. The substrates have a preferred
total moisture content of 2.0~ or less. The upper
temperature limitation during the drying step prevents
the degradation or burning of the organic binder in the
granular substrate. The substrates may be dried in
conventional drying units such as for example a fluid
bed dryer or a rotary dryer.
The resulting granular substrates are then screened
to remove oversized and undersized granular substrates.
The improperly sized material may be recycled to the
mixing stage or milled to the appropriate size and
rescreened. Optionally, the finished product may be
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sprayed with a light weight mineral oil to prevent
dusting of the product in bulk form.
The sizing and bulk density are important finished
product specification for the present invention. The
composition of the present invention results in a
relatively low bulk density while having a smaller
particle size distribution. This is contrary to
conventional granular substrates where typically larger
particles have bulk densities in excess of 55 pounds per
cubic foot. The resulting manufactured granular
substrates of the present invention have a bulk density,
as measured by ASTM E 727 Volume 11.04 standards, of
about 40 pounds per cubic foot to about 55 pounds per
cubic foot.
The size of particles is determined by the size
guide number/uniformity index system used in the
fertilizer industry. The substrates of the present
invention have a size guide number between 100 and 230
and a uniformity index of at least 40. The size guide
number describes the relative particle size and is
obtained by multiplying the average particle size, in
millimeters, by 100. The uniformity index is a
comparison of large particles to small particles. The
index is expressed as a whole number between 1 and 100
with higher numbers indicating better uniformity and
tighter size range. Additionally, the sizing may be
determined in accordance with ASTM E 728-91 Volume 11.04
wherein the sizing is preferably 20~ or more passing
through a 14 mesh screen and retained on a 40 mesh
screen.
The manufactured granular substrate must be strong
enough so that the particle does not degrade during
normal conveying and handling operations. The
degradation of granular substrates would result in an
increase in fine material which in turn would increase
the bulk density. Additionally, dust or powder material
absorbs more chemical agent and therefore would result
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in the improper distribution of the active chemical
agent upon application.
It is preferred that the granular substrate not
degrade until subject to water. However, it is also
equally important that the substrate not degrade with
high humidity. The ability for the granular substrate
of the present invention to degrade with water is
generally measured in a water dispersability test. The
test involves placing about 10 grams of the granular
substrate into 100 ml of water at room temperature in a
closed glass container. The container is then inverted
and the time is observed until the material completely
disperses. After every minute, the container is
inverted. The granular substrate of the present
invention has a dispersability time of generally less
than 3 minutes.
The strength of the granular substrate is
determined through the crush strength test, ASTM E 382
Volume 3.06, and resistance to attrition test (RTA),
ASTM E 728-91 Volume 11.04. The manufactured granular
substrate of the present invention has a crush strength
between 2 and 8 pounds on an 8 mesh pellet.
Additionally, the granular substrate has an RTA value of
at least 85~.
The resulting granular substrate of the present
invention generally has a smooth surface and is
spherical in shape. The spherocity lends to desired
flow characteristics of the substrates in bulk form.
The angle of repose is a test utilized to measure the
ability of a substrate to flow in bulk form. The test
is conducted on a 14 x 30 mesh sample. The granular
substrates of the present invention all have an angle of
repose of 35 degrees or less.
The granular substrate must have the capability of
absorbing the active chemical agent in order to function
as a carrier. The active agent is generally absorbed in
the carrier up to about five percent by weight. The
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substrate is also water soluble and therefore degrades
upon exposure to moisture or water.
The manufactured granular substrate of the present
invention is suitable for use as a carrier for active
chemical agents. For example, active chemical agents
could include herbicides or other pesticides that are
commonly distributed through the use of a carrier in
bulk form.
The following examples, which constitute the best
mode presently contemplated by the inventors for
practicing the present invention, are presented solely
for the purpose of further illustrating and disclosing
the present invention, and are not to be construed as a
limitation on the invention:
Examples 1-7
A series of examples were produced in the lab to
demonstrate the composition of the present invention.
The specified dry based raw materials for each example
were weighed out and placed in a Forberg type mixer made
by Paul O. Abbe, Inc. Of Little Falls, New Jersey. The
mixer was run for about one minute in order to
thoroughly mix the materials before adding the binder
composition. The binder composition, in solution form,
was added to the materials over a one minute time period
and then mixed for another minute.
The resulting wet mixture was then fed into a 36"
rotating pelletizing pan through a Vibra Screw feeder.
The feed rates to the pelletizer for each example are
listed in Table I. The pan angle was 50~ (from
horizontal). The pan depth was maintained at 6 inches
while the pan speed was 26 rpm. Additional water was
sprayed into the pelletizer to assist in the
agglomeration process. The substrates, in pellet form,
were collected from the pelletizing pan and placed in a
conventional lab oven. The granular substrates were then
heated to a temperature of about 240~F to about 300~F
. . .
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to remove excess water.
The finished substrates where then tested to obtain
the bulk density, particle size, crush strength, RTA,
and total moisture content. The results of each sample
are listed in Table I.
Example 8
The example was produced to demonstrate the
manufactured granular substrate and process of the
present invention on large scale production equipment.
The noted amounts of dry ingredients were mixed in a two
cubic foot Forberg type mixer for about 1 minute. The
binder composition was then added to the mixing vessel
and thoroughly mixed with the materials for about
another minute.
The mixture was then transferred to an AccuRate
surge hopper having a 2" feeder screw. The feeder screw
was used to continuously feed the mixture to a three
foot diameter pelletizing disc at a rate of 608 pounds
per hour. The three foot diameter pelletizing disc
utilized a 5 inch deep pan and was operated at a 56
degree (from horizontal) pan angle and a speed of 26
RPM. Additional water was introduced near the feed
inlet through spray nozzles to assist in the
agglomeration. Then the resulting pellets were
collected from the disc outlet. The moisture content of
the pellets was about 21~.
The pellets produced from the pelletizing disc were
transferred to TecWeigh feeder surge hopper having a 3"
feeder screw. The pellets were then continuously fed
into a 24 inch diameter by 20 foot long rotary dryer.
The granular substrates were fed into the dryer at about
1000 pounds per hour. The dryer was a co-current gas
fired dryer with internal lifters and rotating at about
11 rpm. The combustion temperature in the dryer was
controlled at about 1400~F while the outlet temperature
was monitored at 220~F. The outlet product temperature
was controlled at about 175~F. The total moisture
content of the finished pellet was less than 0.5~.
13
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The finished product was collected and tested to
obtain bulk density, particle size, crush strength, RTA,
angle of repose, water dispersability, and total
moisture content. The results are listed in Table I.
Example 9-12
The specified amounts of dry ingredients were mixed
in a Forberg type mixer, having a four cubic foot
capacity, for about one minute. For diluted binders,
the binder solution was previously prepared in a 3.5
cubic foot rotary drum mixer. The binder solution was
then added to the Forberg type mixer and then allowed to
mix for another minute.
The mixture was transferred to a Vibra Screw live
bin feeder having three cubic foot hopper and three inch
diameter screw. The material was continuously fed into
a 36" diameter disc pelletizer at a rate as indicated
in Table I. For Examples 9-11, the pelletizer was
operated at a pan angle of 50 degrees from horizontal
and a pan speed of 26 rpm. For Example 12, the
pelletizer was operated at a pan angle of 59.5 degrees
(from horizontal) and a pan speed of 24 rpm.
The wet pellets were then fed into a continuous
vibrating fluidized bed dryer having a 9' x 1'
perforated tray. The fluidized bed utilized an
oscillating tray to convey the material. Hot air was
blown through the perforated tray at a rate of 1400 cfm
and a temperature of about 500~F to about 550~F. The
hot air was utilized to dry a 3"-4" deep bed (when
fluidized) of granular substrate. For Examples 9-11,
the granular substrate was fed to the fluidized bed at a
rate of about 1200 pounds per hour. For Example 12, the
granular substrate was fed at a rate of about 400 pounds
per hour. The granular substrates were heated to a
temperature of about 270~F to 300~F.
The finished product was collected and tested to
obtain bulk density, particle size, water
dispersability, RTA, and total moisture content.
Additionally, the angle of repose was measured for the
14
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CA 02255063 1998-12-04
resulting granular substrate of Example 10. The results
of each sample are listed in Table I.
