Aqueous emulsions of crystalline polymers for coating seeds

Details Aqueous emulsions of crystalline polymers for coating seeds Aqueous emulsions of crystalline polymers for coating seeds

1997-09-15

2001-03-13

Lankford, Jr., Leon B. (Department: 1651)

Plant husbandry

Coated or impregnated seed, method or apparatus

C047S05810R, C524S156000

Reexamination Certificate

active

06199318

ABSTRACT:

BACKGROUND
This invention relates to protective coatings for controlling the germination of seeds.
One of the most critical periods for plant emergence is the period between seed planting and germination. After planting, seeds usually must take in water before germination can start. This process is called imbibition. Most seeds initiate imbibition irrespective of the temperature of the soil. Once imbibition starts, however, germination must occur within a short period of time.
In contrast, ideal germination occurs only after the soil temperature increases to reach a critical soil temperature. If imbibition occurs long before the critical soil temperature is achieved, the seed can become diseased or die from chilling injury and crop yields are correspondingly lower. For example, dry seeds such as dry soy bean seeds typically contain about 7% to 14% by weight of moisture in their dormant state. If the seed imbibes substantial amounts of water above 14% at temperatures below the critical soil temperature, the seed is likely to suffer injury.
Thus, it is advantageous to control seed water uptake so that imbibition occurs only when the soil temperature is in the temperature range that promotes ideal germination for the end result that crop yields will be enhanced.
One of the inventors for the present invention, Ray F. Stewart, previously invented temperature-sensitive seed germination control as described in U.S. Pat. No. 5,129,180, which is incorporated herein by reference. In this invention, various types of coated organisms, such as coated seeds, were provided with a coating comprised of a polymeric material which has a temperature-dependent permeability. Preferred polymeric materials were side-chain crystallizable polymers. The polymer coating, when applied to a seed, prevents germination of the seed due to lack of water. The coating is permeable to water at a temperature above a transition temperature of the polymers for allowing germination of the seed.
A difficulty with the coatings described in U.S. Pat. No. 5,129,180 is that the coating systems are organic solvent based. There is concern that organic solvents can adversely affect the seeds, and any residual solvent left in the coatings can adversely affect plant growth and be deleterious to soil. Moreover, difficulties in the seed shedding the coating when temperatures are sufficiently high for seeds to germinate and grow have been noted, whereby the non-shed coating inhibits seed germination and plant growth.
Another problem noted with preexisting coatings is cracking at low temperatures due to the brittleness of the coating. Under these circumstances, water can prematurely be imbibed by the coated seed, resulting in premature germination and resultant stunted growth or death of the plant.
Accordingly, there is a need for a coating system for seeds and other organisms that is substantially solvent-free, and the formed coating does not crack at low temperatures and the coating is easily shed by the seed at temperatures conducive to ideal germination and growth.
SUMMARY
The present invention satisfies these needs with (i) novel, aqueous, non-phytotoxic compositions suitable for use in coating seeds, the compositions comprising crystalline polymeric particles suspended in water; (ii) use of the compositions for coating organisms; and (iii) coated organisms. The particles comprise a crystalline polymer having a melting temperature greater than 0° C. and less than about 40° C. A particulate coating is formed on an organism by applying the composition to the organism and having the water evaporate from the composition, either at ambient conditions or by application of heat. The composition contains sufficient particles that the particulate coating is impermeable to water at a temperature below the melting temperature, T
m
, of the crystalline polymer for extending the dormancy of the organism due to lack of water at temperatures below T
m
. The water permeability of the coating is at least three times more above T
m
as compared to the water permeability below T
m
so that the organism can become non-dormant above the Tm.
Preferably the particles comprise the crosslinked polymeric reaction product of a monomer component comprising (i) a hydrophobic monomer component, (ii) a hydrophilic monomer component, and (iii) a sufficient amount of at least one crosslinking monomer having at least two polymerizable groups that the polymeric reaction product has a gel content of at least 50%.
The hydrophobic monomer component comprises a first hydrophobic monomer such that a homopolymer thereof is crystallizable. Preferably the hydrophobic monomer component includes a second hydrophobic monomer having a glass transition temperature T
g
, wherein a homopolymer of the second hydrophobic monomer is amorphous. Preferably the monomer component contains a sufficient amount of the second hydrophobic monomer that a coating formed has a tack at (T
m
+10° C.) less than 50% of the tack at (T
m
+10° C.) of a coating formed without the second hydrophobic monomer.
The hydrophilic monomer component comprises one or more hydrophilic monomers, and is present in an amount of at least 2% and up to about 10% by weight based on the weight of the monomer component. Typically the weight ratio of the hydrophobic monomer component to the hydrophilic monomer component is from about 10:1 to about 50:1. The weight ratio of the hydrophobic monomer component to the hydrophilic monomer component is sufficiently large that the polymeric reaction product is crystalline. The coating composition contains sufficient surfactant to suspend the particles in the water.
Preferably the monomer content of the coating composition is less than 1% by weight based on the weight of the particles, i.e., there is substantially no residual monomer.
When coating corn, preferably the composition contains a fluorosurfactant.
Preferably the coating contains at least one seed coating additive, such as a colorant, filler, soil pH adjustor, phytotoxicity inhibitor, fungicide, herbicide, and/or insecticide. Colorant can be included in the coating so that it is easy to distinguish coated seeds from non-coated seeds.
It has been determined that the combination of the internal crosslinking of the particles, and the inclusion of the second hydrophobic monomer, results in a coating that maintains its integrity at low temperatures, and is easily removed from the seed at temperatures greater than T
m
. It has been learned that without the crosslinking, there is great difficulty in removing the coating from the seeds at temperatures greater than T
m
. Furthermore, we learned that without the second hydrophobic monomer, it is difficult to apply the coating, in that the coating is tacky at temperatures greater than T
m
that are typically required for applying the seed coating, and tends to form poor quality films.
The composition is prepared by an aqueous polymerization process. An aqueous reaction medium is provided, the medium comprising water, the monomer, the surfactant component, and a cosolvent. At least 99% by weight of the monomer component is polymerized to form the crystalline copolymer as latex particles of a latex, the particles having an average particle size of less than 0.5 microns. Typically, the cosolvent is then removed from the latex. Preferably, the aqueous reaction medium contains sufficient monomer component that the latex has a solids content of at least 30%.
The aqueous medium contains sufficient surfactant and sufficient cosolvent that the second hydrophobic monomer component is substantially randomly dispersed in the crystalline polymer. The more cosolvent used in the aqueous reaction medium, the less surfactant required. Preferably the surfactant component comprises at least one ionic surfactant having a hydrophilic lipophilic balance of from about 20 to about 40, and at least one non-ionic surfactant having a hydrophilic lipophilic balance of from about 5 to about 30. Typically the aqueous reaction medium contains the surfactant in an amount of about 0.8 to about 10% b

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