U.S. patent application number 11/292048 was filed with the patent office on 2006-06-01 for process and apparatus for coating a controlled release product in a rotating drum.
Invention is credited to Nicolette Mary Babiak, J. David Eastham, Robert Glen Ford, Lawrence Arthur Wilms, Nick Peter Wynnyk, Baozhong Xing.
Application Number | 20060115586 11/292048 |
Document ID | / |
Family ID | 36564714 |
Filed Date | 2006-06-01 |
United States Patent
Application |
20060115586 |
Kind Code |
A1 |
Xing; Baozhong ; et
al. |
June 1, 2006 |
Process and apparatus for coating a controlled release product in a
rotating drum
Abstract
The present invention is directed to a process for coating a
substrate in a rotating drum, wherein a pocket is created in a
substrate bed into which pocket coating materials are delivered.
Also provided is a controlled release product produced according to
this process, and an apparatus for carrying out the process.
Inventors: |
Xing; Baozhong; (Calgary,
CA) ; Wilms; Lawrence Arthur; (Strathmore, CA)
; Wynnyk; Nick Peter; (Edmonton, CA) ; Ford;
Robert Glen; (Carseland, CA) ; Babiak; Nicolette
Mary; (Gibbons, CA) ; Eastham; J. David;
(Okotoks, CA) |
Correspondence
Address: |
KENYON & KENYON LLP
ONE BROADWAY
NEW YORK
NY
10004
US
|
Family ID: |
36564714 |
Appl. No.: |
11/292048 |
Filed: |
November 30, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60631409 |
Nov 30, 2004 |
|
|
|
Current U.S.
Class: |
427/212 ;
427/240 |
Current CPC
Class: |
B05B 13/0257 20130101;
B01J 2/12 20130101; C05C 9/005 20130101; C05G 5/37 20200201; B01J
2/006 20130101 |
Class at
Publication: |
427/212 ;
427/240 |
International
Class: |
B05D 7/00 20060101
B05D007/00; B05D 3/12 20060101 B05D003/12 |
Claims
1. A process for coating a substrate in a rotating drum, wherein a
pocket is created in a substrate bed into which pocket coating
materials are delivered.
2. The process according to claim 1, wherein the substrate is
fertilizer granules.
3. The process according to claim 1, wherein the pocket is created
by a mechanical device or high pressure air.
4. The process according to claim 1, wherein the pocket is created
by a plow means.
5. The process according to claim 4, wherein the coating materials
are delivered behind the plow means.
6. The process according to claim 1, wherein the coating materials
are delivered on the surface of the granule bed.
7. The process according to claim 1, wherein the coating materials
are delivered below the surface of the granule bed.
8. The process according to claim 1, wherein the coating materials
are substantially simultaneously delivered onto the surface of the
substrate bed by spraying or dribbling.
9. The process according to claim 1, wherein a device is used to
bury the coating materials in the pocket.
10. The process according to claim 9, wherein the burying device is
one or more blades.
11. The process according to claim 1, wherein the drum comprises
one or more baffles.
12. The process according to claim 11, in which the baffles are
oriented in a direction opposite to the drum's direction of
rotation.
13. A controlled release product produced according to the process
of claim 1.
14. A rotatable drum for coating a substrate comprising a mixing
zone and a drying zone, wherein the mixing zone comprises (a) one
or more means for creating a pocket in a substrate bed, and (b) one
or more means for delivering coating materials into the drum.
15. The drum of claim 14, wherein the means for creating the pocket
is a plow or high pressure air.
16. The drum of claim 14, wherein the means for delivering the
coating materials is a nozzle or pipe, or a combination
thereof.
17. The drum of claim 14, wherein means for creating the pocket is
a plow, and the means for delivering coating materials into the
drum are located behind the plow.
18. The drum of claim 14, further comprising baffles, oriented in a
direction opposite the direction of rotation of the drum.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/631,409, filed Nov. 30, 2004.
[0002] This invention relates to an improved process and apparatus
for coating a substrate in a rotating drum.
BACKGROUND
[0003] Typically fertilizer granules are coated in a rotating drum
by spraying and/or dribbling coating components onto the top
surface of the bed of fertilizer granules. In this method, the
coating materials, such as castor oil and isocyanate, do not easily
penetrate into the granule bed. One of the reasons for this is
their high viscosity and surface tension, which inhibits
penetration into the granule bed. Because these coating materials
do not readily penetrate into the bed, they first coat the drum
surface, and are subsequently transferred onto the surface of the
fertilizer granules. In this two stage process, the coating
materials cannot spread effectively on the surface of the
fertilizer granules within the time it takes for the castor oil and
isocyanate to react to form polyurethane (approximately four
minutes at 75.degree. C.). A similar problem exists when other
coating materials, such as other thermoplastic polymers or
thermoset polymers, are used. Accordingly, cured or dried coating
material builds up on the drum surface. This coating build up on
the drum surface is called "fouling".
[0004] In prior art processes, fouling is severe, especially on the
drum surface around the coating material nozzles. In many cases,
the coating drum must be cleaned every two weeks. Not only is the
cleaning process expensive, but the production interruptions and
higher raw material consumption negatively affects net profits.
Moreover, fouling adversely affects the quality of the controlled
release product.
[0005] Coating quality (and therefore product performance) is
reduced in prior art processes since there is limited opportunity
for coating materials to mix in the stoichiometric ratios necessary
to form the desired optimum coat on substrate granules. For
instance, isocyanate is typically dribbled onto the surface of the
granules in a narrow line, while castor oil is either dribbled or
sprayed. In either case, the opportunity for mixing of these two
components with each other and on the surface of the granules is
limited, even if the isocyanate and castor oil are delivered
substantially simultaneously. One reason for this is that granules
moving in a rotating drum exhibit a linear layer flow, with slow
lateral mixing between layers.
[0006] Attempts have been made to improve the coating process in a
rotating drum. One approach has been to dip injector nozzles into
the fertilizer bed so coating components are injected into the
fertilizer bed immediately below the surface of the bed. (See, for
example, U.S. Pat. No. 5,374,292; U.S. Pat. No. 5,547,486; U.S.
Pat. No. 5,858,094; and U.S. Pat. No. 6,537,611.) However, there
still remains a need in the art to further improve mixing and
reduce fouling to increase the efficiency of the coating
process.
SUMMARY
[0007] In one broad aspect of the invention, there is provided a
process for coating a substrate in a rotating drum, wherein a
pocket is created in a substrate bed into which pocket coating
materials are delivered.
[0008] The present invention is also directed to a controlled
release product produced according to the process of the
invention.
[0009] In a further broad aspect, there is provided a rotatable
drum for coating a substrate comprising a mixing zone and a drying
zone, wherein the mixing zone comprises (a) one or more means for
creating a pocket in a substrate bed, and (b) one or more means for
delivering coating materials into the drum.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 illustrates linear layer flow of substrate granules
in a rotating drum.
[0011] FIG. 2 shows the simultaneous delivery of polymer coating,
premix and/or monomers into a hole or pocket in a granule bed
created by a plow in a rotating drum according to an embodiment of
the invention.
[0012] FIG. 3 shows a number of possible shapes for a plow for use
in a process of the invention.
[0013] FIG. 4 shows the simultaneous dribbling of polymer coating,
premix and/or monomers along the back of a plow to multiple
locations onto and/or into a substrate granule bed according to an
embodiment of the invention.
[0014] FIG. 5 shows the use of the plow of FIG. 4 to simultaneously
delivery polymer coating, premix and/or monomers into a hole or
pocket in a granule bed created by the plow.
[0015] FIG. 6 shows the use of burying devices to bury coating
materials in a hole or pocket in a granule bed created by a plow
according to an embodiment of the invention.
[0016] FIG. 7 shows the placement of a plow in the wet zone of a
rotating drum and the effect on the dry zone when injection nozzles
are placed in front of and behind the plow according to different
embodiments of the invention.
[0017] FIG. 8 shows a baffle structure and orientation in the dry
zone of FIG. 7 according to an embodiment of the present
invention.
DETAILED DESCRIPTION
[0018] It has surprisingly been found that in a method for coating
fertilizer granules in a rotating drum, there is significant
reduction in fouling where a means is used to create a hole or
pocket in the fertilizer granule bed, with the coating materials
being delivered into the hole or pocket created. The means for
creating the hole or pocket is not particularly limited, and
includes a mechanical device, such as a plow, or high pressure air.
Where a mechanical device, such as a plow, is used to create the
hole or pocket in the fertilizer bed, it was further surprisingly
found that substantially improved results are obtained when the
coating materials are introduced behind the plow in the
applications of coating materials to fertilizer.
[0019] The improved method of the invention not only reduces
fouling, but there is also improved mixing of the fertilizer
granules with coating materials. An improved controlled release
profile is observed, suggesting that coating materials are more
uniformly distributed onto the granules because of improved mixing.
Improved mixing also reduces the time required to coat the
fertilizer granules, resulting in shorter residence drum times and
improved efficiency.
[0020] Although preferred substrates are fertilizer and plant
nutrients, the process of the invention could be applied to a
variety of other substrates. Other examples of substrates include
drugs, vitamins, etc.--any substrate for which controlled release
delivery would be beneficial, and which can be coated in a rotating
drum.
[0021] If a fertilizer or plant nutrient material is coated, the
fertilizer or plant nutrient material preferably comprises a water
soluble compound. Preferably, the plant nutrient comprises a
compound containing nitrogen, phosphorus, potassium, sulphur,
micronutrients, or a mixture thereof. A preferred plant nutrient
comprises urea. Other examples of useful plant nutrients are
ammonium sulphate, ammonium phosphate, diammonium phosphate and
mixtures thereof. Examples of useful micronutrients include copper,
zinc, boron, manganese, iron and mixtures thereof. Useful plant
nutrient materials are also described in U.S. Pat. No. 5,538,531
and U.S. Pat. No. 6,358,296.
[0022] A variety of coatings may be used on the substrate.
Preferably, a polymer coating is used, and more preferably a
thermoset polymer. Examples of thermoset polymers include those
derived from phenolic, aminoplastic or epoxy resins, some
polyesters, polysulphides, and polyurethanes. The thermoset polymer
is preferably derived from an epoxy resin. Yet more preferably, the
thermoset polymer is a polyurethane or a substituted
polyurethane.
[0023] In a preferred embodiment, the thermoset polymer is formed
by reacting a polyol or a mixture of polyols and an isocyanate or a
mixture of isocyanates. The polyol may be any hydroxy-terminated
polyol, such as a polyether, polyester, polycarbonate, polydiene,
polycaprolactone, or a mixture thereof. Preferred are polyols such
as hydroxy-terminated polyhydrocarbons, hydroxy-terminated
polyformals, fatty acid triglycerides, hydroxy-terminated
polyesters, hydroxymethyl-terminated polyesters,
hydroxymethyl-terminated perfluoromethylenes, polyalkylene-ether
glycols, polyalkylene-arylene-ether glycols and polyalkylene-ether
triols. Preferred polyols include polyethelene glycols, adipic
acid-ethylene glycol polyesters, poly(butylene glycol),
poly(propylene glycol) and hydroxy-terminated polybutadiene (see,
for example, British patent No. 1,482,213). More preferred are
polyether polyols and most preferred are polyether polyols having a
molecular weight in the range of from about 60 to about 20,000,
more preferably from about 60 to about 10,000 and most preferably
from about 60 to about 8,000.
[0024] Preferred polyols are also described in U.S. Pat. No.
5,538,531. In U.S. Pat. No. 5,538,531, polyols having from about 2
to about 6 hydroxy groups, and preferably having at least one
C.sub.10-C.sub.22 aliphatic moiety, are described.
[0025] Most preferably, the polyol is castor oil or a mixture of
castor oil with other polyols.
[0026] The polyol may also be derived from natural sources, such as
soybean, corn, canola, and the like. Polyols derived from natural
sources can be used as they are or can be used to derive a
synthetic polyol, such as a synthetic polyol based on soybean oil,
which is commercially available from Urethane Soy Systems Corp.
(Princeton, Ill.).
[0027] Another useful class of polyols are oleo polyols, such as
described in U.S. Pat. No. 6,358,296.
[0028] A mixture of polyols may also be used, for instance, castor
oil with ethylene glycol, castor oil with oleo polyol, castor oil
with polyethylene glycol, castor oil with polypropylene glycol, or
a polypropylene (or polyethylene) glycol mixture of different end
groups and molecular weight.
[0029] Any suitable isocyanate may also be used. Generally, the
isocyanate compound suitable for use may be represented by the
general formula: Q(NCO).sub.i wherein i is an integer of two or
more and Q is an organic radical having a valence of i. Q may be a
substituted or unsubstituted hydrocarbon group (e.g., an alkylene
or arylene group). Moreover Q may be represented by the formula:
Q.sup.1-Z-Q.sup.1 wherein Q.sup.1 is an alkylene or arylene group
and Z is chosen from the group comprising --O--, --O-Q.sup.1--,
CO--, --S--, --S-Q.sup.1-S-- and --SO.sub.2--. Examples of
isocyanate compounds which fall within the scope of this definition
include hexamethylene diisocyanate, 1,8-diisocyanato-p-naphthalene,
xylyl diisocyanate, (OCNCH.sub.2CH.sub.2CH.sub.2OCH.sub.2O)
2,1-methyl-2,4-diisocyanatocyclohexane, phenylene diisocyanates,
tolylene diisocyanates, chlorophenylene diisocyanates,
diphenylmethane-4,4'-diisocyanate, naphthalene-1,5-diisocyanate,
triphenylmethane-4,4'4''-triisocyanate and
isopropylbenzene-alpha-4-diisocyanate.
[0030] In another embodiment, Q may also represent a polyurethane
radical having a valence of i. In this case Q(NCO).sub.i is a
compound which is commonly referred to in the art as a prepolymer.
Generally, a prepolymer may be prepared by reacting a
stoichiometric excess of an isocyanate compound (as described
above) with an active hydrogen-containing compound, preferably the
polyols described above. In this embodiment, the polyisocyanate may
be, for example, used in proportions of from about 30 percent to
about 200 percent stoichiometric excess with respect to the
proportion of hydroxyl in the polyol.
[0031] In another embodiment, the isocyanate compound suitable for
use in the process of the present invention may be selected from
dimers and trimers of isocyanates and diisocyanates, and from
polymeric diisocyanates having the general formula:
[Q''(NCO).sub.i].sub.j wherein both i and j are integers having a
value of 2 or more, and Q'' is a polyfunctional organic radical.
Such isocyanates may be used together with compounds having the
general formula: L(NCO).sub.k wherein k is an integer having a
value of 1 or more and L is a monofunctional or polyfunctional atom
or radical. Examples of isocyanate compounds which fall within the
scope of this definition include ethylphosphonic diisocyanate,
phenylphosphonic diisocyanate, compounds which contain a
.dbd.Si--NCO group, isocyanate compounds derived from sulphonamides
(QSO.sub.2NCO), cyanic acid and thiocyanic acid.
[0032] See also, for example, British patent No. 1,453,258 for
other examples of useful isocyanate compounds.
[0033] Non-limiting examples of suitable isocyanates include:
1,6-hexamethylene diisocyanate, 1,4-butylene diisocyanate,
furfurylidene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene
diisocyanate, 2,4'-diphenylmethane diisocyanate,
4,4'-diphenylmethane diisocyanate, 4,4'-diphenylpropane
diisocyanate, 4,4'-diphenyl-3,3'-dimethyl methane diisocyanate,
1,5-naphthalene diisocyanate,
1-methyl-2,4-diisocyanate-5-chlorobenzene,
2,4-diisocyanato-s-triazine, 1-methyl-2,4-diisocyanato cyclohexane,
p-phenylene diisocyanate, m-phenylene diisocyanate, 1,4-naphthalene
diisocyanate, dianisidine diisocyanate, bitoluene diisocyanate,
1,4-xylylene diisocyanate, 1,3-xylylene diisocyanate,
bis-(4-isocyanatophenyl)methane,
bis-(3-methyl-4-isocyanatophenyl)methane, polymethylene polyphenyl
polisocyanates and mixtures thereof.
[0034] Particularly preferred isocyanates are those described in
U.S. Pat. No. 5,538,531 and U.S. Pat. No. 6,358,296.
[0035] An isocyanate mixture may be preferred for some
coatings.
[0036] Preferably, the polyol and isocyanate are used in amounts
such that the ratio of NCO groups in the isocyanate to hydroxy
groups in the polyol is in the range from about 0.5 to about 3.0,
more preferably from about 0.8 to about 2.0, and most preferably
from about 0.9 to about 1.1.
[0037] In addition, a thermoset polymer may be formed by using
amine group-terminated or mercaptan-terminated monomers. For
instance a urea-formaldehyde resin may be used.
[0038] Additives may be included in the coating materials. For
instance, if the coating materials are hydrophilic, then they will
be compatible with hydrophilic substrate surfaces and they will be
easy to spread on the surface. If the coating materials are
hydrophobic however, there will be difficulty in spreading the
coating materials on the substrate surface. Under these
circumstances, additives like wetting agents, flow agents,
levelling agents and coupling agents may be used to improve
spreadability. If the viscosity of the coating is high, an additive
may be also be used to improve spreadability.
[0039] Another function of additives is to increase the
hydrophobicity of the coating. Hydrophobic additives reduce the
release rate of coated substrate.
[0040] Preferred additives are organic additives, such as petroleum
products, coal products, natural products and synthetic products.
Lubricants derived from these may also be used. Exemplary organic
additives include commercially available coating additives and
paint additives (such as wetting agents, flow agents, levelling
agents and coupling agents), wax, paraffin oil, bitumen, asphalt,
oil derived from coal, canola oil, soybean oil, coconut oil,
linseed oil, tung oil, vegetable wax, animal fat, animal wax, and
forest products such as tall oil, modified tall oil, tall oil
pitch, and pine tar. Mixtures of these materials may also be used.
Particularly preferred organic additives are hydrophobic
materials.
[0041] If the organic additive is wax, preferred waxes are those
described in U.S. Pat. No. 5,538,531 or a silicone wax, such as is
available from Dow Corning. Preferred waxes have a drop melting
point of at least 10.degree. C., preferably between about
20.degree. C. to about 120.degree. C., and more preferably between
about 30.degree. C. to about 120.degree. C. Most preferably, the
wax is substantially non-tacky below about 40.degree. C. The
preferred wax is a C.sub.10+ alpha-olefin, and more preferably a
C.sub.20-100 alpha-olefin. Most preferably, the wax is a C.sub.30+
wax, such as is available commercially from Chevron Phillips
Chemical Company.
[0042] The amount of organic additive may vary, depending on its
purpose in the mixture, as would be apparent to a person of skill
in the art. For instance, for some commercially available
additives, an amount as low as 0.001% by weight of the coating
composition may be used.
[0043] Preferred organic additives and amounts are those that
improve the release profile and mechanical handling of the polymer
coated substrate.
[0044] In a drum, substrate granules exhibit a linear layer flow as
shown in FIG. 1. The granules in contact with the drum wall and
those proximate to the drum wall move in the direction of the drum
due to friction forces between the granules and (a) the drum wall
and (b) other proximate granules. However, due to these same
friction forces between granules, the granules on the surface of
the granule bed and distal to the drum wall move in an opposite
linear direction to the linear direction of rotation of the drum.
This effect results in a layered flow pattern, which inhibits
penetration of coating components through the granule bed. It was
found that by creating a hole or pocket in the granule bed, deeper
penetration and a wider range of distribution of coating materials
into the granule bed is achieved, and mixing is improved. Also it
changes the flow pattern of the granules--i.e. breaks up the linear
flow pattern.
[0045] A variety of means can be used to create the hole or pocket
in the granule bed. Preferably the hole or pocket is created by a
mechanical device, such as a plow, or high pressure air. An example
of a plow (10) creating a hole or pocket (20) in a substrate
granule bed (30) in a rotating drum (40) is shown in FIG. 2. Where
a plow is used, a variety of different shapes can be used, such as
shown in FIG. 3. Preferably the plow has a linear arm, curved to
create a scoop at the end (e.g., a bent angle iron), which will
create the hole or pocket in the fertilizer bed. A sharply angled
arm (e.g., a straight angle iron) is less preferred, although it
too may be used.
[0046] In order to achieve a significant reduction in fouling, the
plow must dig into the granule bed. The approach angle of the plow
with respect to the substrate bed surface may be 5-175.degree.,
preferably 30-150.degree., more preferably 40-140.degree., and more
preferably still 45-145.degree.. The optimum approach angle of the
plow with respect to the substrate granule bed surface is related
to the shape of the plow and can be determined by one of ordinary
skill in the art through routine experimentation.
[0047] The depth of the plow in the substrate bed may be 5-95% of
the substrate bed depth, preferably 10-90%, more preferably 20-80%,
and more preferably still 30-70%. The optimum depth is related to
the plow shape, approach angle, and loading rate of the drum, and
can be determined by one of ordinary skill in the art through
routine experimentation.
[0048] The coating materials may be delivered substantially
simultaneously, as single or divided injections by spraying or
dribbling, into the hole or pocket in the substrate granule bed.
For instance, for a polyurethane coated fertilizer, (a) premix
(comprising a polyol and other coating components) or a polyol, and
(b) isocyanate may be delivered into the hole or pocket through the
same or different injection nozzles. FIGS. 4 and 5 illustrate the
delivery of polymer coating, premix and/or monomers (50, 60) in two
injection streams behind the plow (10) into the hole or pocket (20)
in the granule bed (30) of the rotating drum (40).
[0049] Where castor oil/premix comprising castor oil is used, the
castor oil or premix may be delivered into the hole or pocket by
dribbling or spraying. Where isocyanate is used, the isocyanate is
typically dribbled into the hole or pocket, although it too may be
sprayed. Surprisingly good results have been obtained where the
castor oil or premix and the isocyanate are dribbled, preferably
substantially simultaneously behind the plow.
[0050] For significant reduction in fouling, and improved mixing,
the first application of coating materials are delivered
substantially simultaneously behind the plow. According to one
theory for coating fertilizer with polymer, when coating materials
are delivered behind the plow, the materials begin mixing in the
hole or pocket created such that the higher temperature premix or
polyol helps to reduce the viscosity and surface tension of the
isocyanate. This in turn increases the penetration speed of the
isocyanate into the granule bed. If the coating materials are
delivered in front of the plow, the materials are not delivered
directly into the hole or pocket and the opportunity for mixing the
reactive monomers is reduced. Improved mixing of the coating
materials allows for a more even coating to be produced. Improved
mixing is particularly important for the first application of
coating materials.
[0051] The injection nozzles and pipes used to deliver coating
materials may be inserted below the surface of the moving granule
bed. Where the injection nozzles are below the surface of the
granule bed, there is a greater opportunity for mixing of coating
components in the hole or pocket. Where the injection nozzles are
inserted below the surface of the granule bed, the coating
materials are typically dribbled into the hole or pocket.
[0052] Burying devices, such as shown in FIG. 6, can also be used
to cover the hole or pocket (20) produced by a device such as a
plow (10) or high pressure air. A preferred burying device is one
or more blades (70). By sealing the cut made by the plow or air
with one or more burying devices, mixing may be further
improved.
[0053] When the coating materials are delivered onto or into the
granule bed, the materials wet the granules. This wetting of
granules creates a "wet zone" (80) in the drum, which is
illustrated in FIG. 7. The granules stick together in this zone and
move almost as a solid. In the wet zone, it is preferable for the
granules to be subjected to a severe or rapid tumbling, mixing or
rotating as described in co-pending U.S. patent application Ser.
No. 10/868,646.
[0054] Coating components can also be delivered into the wet zone
at multiple delivery points. If there is multiple delivery of
coating components, multiple plows may also be used at each or
some, but at least one, of these delivery points.
[0055] Once the coating begins to cure (e.g., thermoset polymer) or
dry (e.g., thermoplastic polymer), the coated granules enter the
"dry zone", in which the granules flow freely in a different flow
pattern than when wet.
[0056] During the curing or drying phase, coated particles come
into contact resulting in granules caking together and defects
(such as an uneven coating thickness, craters, tears, pinholes,
etc.) forming on the coating surface. To prevent these defects it
is preferable to minimize contact between coated particles in the
dry zone. In order to do this, the average linear velocity of
coated particles in the drum should be reduced. This may be done by
reducing drum speed, decreasing drum size, introducing baffles,
etc., and as described in co-pending U.S. patent application Ser.
No. 10/868,646.
[0057] If the drum speed alone is reduced, it is preferably slowed
to about 10% to about 80% of the speed of the drum in the wet zone.
The same percent reduction also applies to the size of the drum, if
it is the size that is reduced.
[0058] Baffles can also be used to reduce the velocity of coated
particles, depending on their orientation, height, and number. A
preferred baffle orientation is shown in FIG. 8. Preferably the
baffles are oriented in a different direction to the avalanche flow
of the coated particles (i.e., a direction different than or
opposite to the rotational direction of the drum), resulting in a
substantial reduction in velocity.
[0059] A combination of baffles and reduced drum speed/size can
also be used.
[0060] It has been surprisingly observed, as illustrated in FIG. 7,
that where the coating components in a first coating application
are introduced behind the plow in the wet zone, the length of the
dry zone increases (90) over that where the components are
introduced in front of the plow (100). This translates to a shorter
mixing time, and a shorter overall coating process.
[0061] A coating unit may be used in which multiple coating layers
are applied to substrate granules. For instance, a coating unit
having multiple regions for sequential application of coating
materials could be used, each region having a wet and dry zone. In
the wet zone of the first region, a device to create a hole or
pocket, such as a plow, is used. If a plow is used, preferably the
coating nozzles and pipes are located behind the plow. In the
second and subsequent coating region wet zones a device may also be
used to make a hole or pocket, although it is less important than
in the first region wet zone. If a plow is used in the second and
subsequent wet zones, it has been discovered that it is less
important for the coating nozzles and pipes to be located behind
the plow in order for there to be a substantial reduction in
fouling, although it is preferred to have the nozzles and pipes
behind the plow. Preferably a coating unit is used which has three
or four coating regions.
[0062] The wet and dry zones may comprise the same physical region
of the coating drum. The distinction between "zones" in this
embodiment is simply a way to describe the stage of the coating
process between application of coating materials (wet zone) and
stabilization of coating, i.e., curing or drying (dry zone).
[0063] In another embodiment, the wet and dry zones comprise two
distinct physical regions of the drum. For instance, the drum may
be angled, such that substrate granules enter the drum at one end,
comprising the wet zone, and move into the dry zone by
gravitational force.
[0064] The wet and dry zones may also comprise two drums, connected
in series.
[0065] Where there are multiple coating applications, a single drum
may be used or multiple drums may be used. Where multiple drums are
used, a variety of drum combinations can be used, including using
one or more of the drums or drum combinations described above.
[0066] Using a device such as a plow to create a hole or pocket in
a granule bed in a first application of coating material to the
granules, especially where coating materials are delivered behind
the plow if used, results in an improved controlled release
product. It has been surprisingly discovered that the product so
produced exhibits an improved front-end (i.e., under ten days)
water release rate in controlled release profiling tests compared
to product produced where (a) no plow is used, and (b) coating
components are delivered in front of the plow, if a plow is
used.
[0067] The following examples are offered by way of illustration
and not by way of limitation.
EXAMPLE 1
[0068] A rotary coating unit was used, having three coating
regions, with three groups of nozzles and pipes, one group in each
coating region.
[0069] In the wet zone of the first coating region, a premix
(comprising castor oil) and isocyanate were simultaneously
delivered through a pipe (i.e., dribbling or spraying) behind a
bent angle iron plow that was welded into the coating unit. In the
second and third coating regions plows were also used.
[0070] It was discovered that the plow helped to reduce the release
rate of the product. It was also discovered that by introducing the
premix and isocyanate behind the plow, the dry zone of the first
coating region increased from about 1 to 11/2 feet to approximately
5 feet. This increase in the dry zone is comparable to that of the
second and third coating regions, which was not achievable before
adding a plow and delivering coating materials behind the plow.
This indicates better spreading of the coating materials on the
substrate.
[0071] By using this method, it was discovered that over a four day
period in which the coating unit ran continuously, fouling
thickness on the drum wall was reduced by about two-thirds.
[0072] Moreover, the controlled release urea (CRU) produced had a
15-20% N release at day 7. This release rate is difficult to
achieve both in the absence of a plow and, if a plow is used, with
the coating components added in front of the plow in the first wet
zone. The improved release rate demonstrates an improved mixing in
the first application of coating to substrate.
[0073] The % N release of CRU produced according to the above
process are shown in Table 1. TABLE-US-00001 TABLE 1 Day 7 Day 14
Day 21 (a) 42* 55 63 (b) 30 45 55 (c) 20 28 38 (d) 15 22 30 *% N
release (a) No plow and spraying premix and dribbling isocyanate on
the top of the substrate bed surface in the drum. (Control); (b)
with plow and spraying premix and dribbling isocyanate in front of
the plow; (c) with plow and spraying premix and dribbling
isocyanate behind the plow; and (d) with plow and dribbling premix
and isocyanate behind the plow.
[0074] The data shown in Table 1 indicate that delivering the
coating materials into the pocket behind the plow can significantly
reduce the nitrogen release rate over that of the Control (a)
[0075] The water release data for the controlled release fertilizer
material was also determined in accordance with the following
procedure.
Water Release Profile Test
[0076] A water release rate profile analysis was performed using a
Technicon AutoAnalyzer.TM., calibrated and used pursuant to the
teachings of Automated Determination of Urea and Ammoniacal
Nitrogen (University of Missouri, 1980).
The following procedure was used:
[0077] 1. Accurately weigh 15 grams (.+-.0.1 mg) of the sample into
a weigh dish. Record the weight of sample. Transfer the sample to
125 mL Erlenmeyer flask. [0078] 2. Add 75 mL of demineralized water
and stopper the flask. [0079] 3. Gently swirl the sample and water
until all the particles are submersed. [0080] 4. Let the sample
stand for a specified time at a constant temperature (typically at
room temperature). [0081] 5. Gently swirl the flask to mix the
solution and decant only the solution to a 100 mL volumetric flask.
[0082] 6. Rinse the sample with demineralized water adding to the
volumetric flask. [0083] 7. Bulk to volume of volumetric flask and
mix thoroughly. [0084] 8. If the test is to be repeated for another
time period, repeat starting at Step 2. [0085] 9. Once the
Technicon AutoAnalyzer II is on line, transfer some of this
solution (or perform the required dilutions if necessary) to the
Technicon sample cups for analysis. [0086] 10. Record the results
as parts per million N--NH.sub.3 (read directly from a Shimadzu
Integrator).
[0087] Although the foregoing invention has been described in some
detail by way of illustration and example for purposes of clarity
of understanding, it is readily apparent to those of ordinary skill
in the art in light of the teachings of this invention that certain
changes and modifications may be made thereto without departing
from the spirit or scope of the appended claims.
[0088] All publications, patents and patent applications cited in
this specification are incorporated herein by reference as if each
individual publication, patent or patent application were
specifically and individually indicated to be incorporated by
reference. The citation of any publication, patent or patent
application is for its disclosure prior to the filing date and
should not be construed as an admission that the present invention
is not entitled to antedate such publication, patent or patent
application by virtue of prior invention.
[0089] It must be noted that as used in the specification and the
appended claims, the singular forms of "a", "and" "the" include
plural reference unless the context clearly indicates
otherwise.
[0090] Unless defined otherwise all technical and scientific terms
used herein have the same meaning as commonly understood to one of
ordinary skill and the art to which this invention belongs.
* * * * *