Chemistry: fertilizers – Processes and products – Organic material-containing
Reexamination Certificate
1999-07-23
2002-01-15
Langel, Wayne (Department: 1754)
Chemistry: fertilizers
Processes and products
Organic material-containing
C071S064070
Reexamination Certificate
active
06338746
ABSTRACT:
FIELD OF INVENTION
This invention relates to controlled release fertilizers. More particularly, the invention relates to controlled release fertilizers comprising a nutrient, such as urea, coated with a polymer layer, sulfur layer and polymer layer in that order. The fertilizers have good impact and abrasion resistance, undergo controlled release and are manufactured at low cost.
BACKGROUND OF INVENTION
Slow release or controlled release fertilizers have received substantial attention in the marketplace, particularly for turfgrasses and ornamental plants grown in nurseries. The commercial controlled release fertilizers are of various types. Thus, sulfur-coated urea (SCU) as slow release fertilizers are well known. In the customary process for the production of sulfur-coated urea, granular .urea of nominal size range, 1.7-2.9 mm, which has been preheated to about 160° F. to about 180° F., is introduced into the front end of a rotating horizontal cylindrical drum, nominally 12 feet in length and 5½ feet in diameter. Lifting flights, or longitudinal ledges, which are fastened to the inside wall of the drum and evenly spaced around its circumference, lift and cascade the urea granules as the drum rotates. As the cascading granules pass through the drum, molten (290° F.) sulfur is sprayed onto the urea granules from a series of nozzles uniformly positioned within the length of the drum. When a droplet of molten sulfur contacts a granule, it quickly solidifies; and a continuous coating of sulfur is formed on a urea granule when a sufficient number of molten sulfur droplets have made contact with the granule. In this randomized coating process the granules are coated to an average target thickness of, for example, 40 microns (&mgr;) or about 13%-14% by weight sulfur-coating on the urea. However, because of the random distribution of sulfur droplets contacting the granules, the SCU granules which are discharging from the drum, have thin (<30&mgr;), medium (30&mgr;-50&mgr;) and thick (>50&mgr;) sulfur-coating thicknesses.
Because of the inherent brittleness of the crystalline solid sulfur-coating which forms on the granule, and the thin, or even noncontinuous coating on many of the granules, it is essential that some type of secondary outer coating or sealant be spray applied onto the sulfur-coated surface. Usually this is done in a second horizontal rotating drum in series with the sulfur-coating drum. This sealant conventionally is either a polymeric hydrocarbon, petroleum-based wax, or a combination of high viscosity polymeric paraffinic oil plus polyethylene, which is spray applied as a hot melt liquid onto the hot, but solidified sulfur-coating surface. Since the sealant melt will not solidify at the 160°-180° F. temperature of the sulfur-coated urea granules onto which it is applied, the liquid sealant distributes relatively uniformly onto all sulfur-coated granules, transferring by flowing from one granule to the next as they cascade through the rotating secondary sealant coating drum. These sealant coated sulfur-coated urea granules pass through a fluid bed cooler, after they are discharged from the sealant drum, wherein the sealant solidifies to a firm, but somewhat tacky coating. Although these sulfur coated fertilizers have received substantial uses, there are problems from the standpoint of obtaining uniform coating thicknesses, predictable release characteristics resulting from cracks in the sulfur coatings, essential abrasion and impact resistance, and the complexity of the processing steps necessary as above defined.
More recently, because of problems associated with sulfur coated fertilizers, such as above defined, polymer coated fertilizers have received substantial attention, particularly in view of the better controlled release properties obtained with certain polymer coated fertilizers. Thus, controlled release fertilizer particles which have remarkably high resistance to attrition, uniform release characteristics, and a method for their preparation are disclosed in Moore, U.S. Pat. Nos. 4,711,659 and 4,804,403. According to those patents, controlled release fertilizer particles are obtained by reacting a water-soluble central mass of plant food compound containing reactive functional groups, such as the NH
2
groups of urea, in particulate form, with a chemical coupling agent followed by reaction with a coating material, such as a polyol, to provide a water-insoluble polymer coating or sealing layer on the plant nutrient. The plant nutrient and sealing layer are chemically bonded to each other through the coupling agent. Specifically, the coupling agent reacts with and connects itself to functional group on a water-soluble central mass of plant nutrient to form generally a base coating having additional reactive groups. A water-insoluble coating or sealing layer then is bonded to the base coating through its reaction with the additional reactive groups on the base coat. Thereafter, multiple reacted layers of alternate applications of coupling agent and sealing layer are formed to provide a coating having a desired thickness. The coated fertilizer particles are highly resistant to attrition even under extreme vibration, impact and abrasion and have controlled release.
Although polymer coated fertilizers as above described have received substantial attention, and have been found to have many applications, they are expensive. Accordingly, in an effort to reduce the cost of controlled release fertilizers, fertilizers have been manufactured comprising a combination of sulfur and polymer coatings. Thus, U.S. Pat. No. 5,599,374 describes a fertilizer composition wherein a sulfur coating is applied to a nutrient, such as urea, and thereafter a polymer coating is applied over the sulfur. These compositions have good release characteristics and resistance to impact in comparison to sulfur coated fertilizers. However, such coatings are not completely acceptable for many applications and, additionally, are still substantially costly.
The present invention, therefore, is directed to controlled release fertilizers which have good release characteristics over prolonged periods of time but yet are cost effective, allowing their use in many applications including nursery ornamental and agricultural markets.
SUMMARY OF INVENTION
The present invention is directed to the discovery that it is possible to apply a uniform and continuous coating of sulfur over a polymer coated nutrient granule, such as urea, without detriment to the polymer coating and then applying a second polymer coating over the sulfur in a continuous application. Surprisingly, as will be developed hereinafter, the resultant granule is cost effective, in that the sulfur is relatively cheap compared to a polymer coating, permitting the build up of a coating thickness having the essential controlled release as well as good resistance to abrasion and impact.
Thus, as is recognized in the art, a controlled release, or timed release fertilizer as the terms are used herein, is effected by a coating such as sulfur or a polymer membrane encapsulating a fertilizer granule. The duration of release resulting from the encapsulated granule can be controlled by the thickness of the coating applied to the fertilizer granule, with thicker coatings providing longer duration of timed release. When a relatively thick polymer membrane coating is applied to the fertilizer particle, in order to achieve the desired controlled release duration, this results in a high weight percentage of coating relative to the weight percentage of encapsulated fertilizer. The result is a high cost coated product relative to the cost of the uncoated fertilizer product. Typically, polymers used in encapsulation are 20× to 30× the cost of the fertilizer which they encapsulate. Therefore, a fertilizer, with its cost indexed at 100, and a polymer, with a cost index of 2500, would result in a materials cost for the polymer-coated fertilizer (PCF) as shown below.
For example, if a 12% by weight, relatively thick polymer coating is used, t
Detrick John H.
Hargrove Garrard L.
Breiner & Breiner L.L.C.
Langel Wayne
RLC Technologies, L.L.C.
LandOfFree
Polymer-sulfur-polymer coated fertilizers does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polymer-sulfur-polymer coated fertilizers, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polymer-sulfur-polymer coated fertilizers will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2825924