JP7747282B2 - Coated seeds with controlled germination time - Google Patents

Description

The present invention relates to coated seeds that can ensure good growth by suppressing germination until the appropriate time while maintaining seed viability when seeds are sown earlier and left to overwinter in fields in order to spread out agricultural work periods, primarily in cold regions.

Sugar beets are a staple crop in Hokkaido's field farming. To ensure stable yields, transplanting cultivation is practiced, in which seeds are sown in paper tubes filled with soil, and the seedlings are then transplanted after a certain period of cultivation. However, in recent years, direct seeding of sugar beets has become more common in order to reduce costs and save on the labor required for the work that has increased as the area of land planted per farm expands. While direct seeding eliminates the need for seedling cultivation, there is the issue of labor shortages, as the sowing period overlaps with the work of other crops. Furthermore, if bad weather in early spring restricts the access of agricultural machinery to the fields, the sowing period may be delayed, which could result in the crop not having enough time to grow.

One method for ensuring a crop growth period is to advance the sowing period. However, direct sowing in cold regions can usually be started after snow melts and freeze-thaw cycles in the field, and the period when sowing can be advanced is limited, so this does not provide a fundamental solution. As a solution to this problem, a technique is known in which directly sown seeds are allowed to germinate at any time, for example, by sowing them in the autumn of the previous year before snow accumulation, so that the seeds overwinter in the field and germinate in early spring.
Patent Document 1 discloses a technique for delaying the germination of seeds for a certain period of time by sealing the outer periphery of the seeds with a biodegradable plastic and isolating the seeds from outside air and water for a certain period of time.
Patent Document 2 discloses rice seeds that are sown in autumn with the aim of germinating in early spring, which are coated with a pinhole-free coating to impart hydrophobicity to the rice seeds so that they do not wither and die due to water absorption in the field during the winter, which is unsuitable for growth, and which are coated with hydrophobic polybutadiene having a number-average molecular weight of 400 to 1,000 and a viscosity at 20°C of 100 to 500 centipoise in order to control the duration of this hydrophobicity.
Patent Document 3 discloses a technology for suppressing seed germination for a certain period of time by coating seeds with an organic synthetic resin containing a biodegradable resin, thereby blocking at least one of the factors that cause seed germination: oxygen, water, and temperature, in a greening method using seed sowing on slopes and the like, thereby enabling seed sowing even at times when seed sowing is inappropriate by freely controlling the germination or germination time of the seeds.
Patent Document 4 discloses a technique in which seeds having a moisture content in the range of 0 to 20% by weight are coated on the surface with a polyethylene polymer, which is a water-insoluble resin, in order to maintain seed viability and inhibit germination until an appropriate time when the sowing time is arbitrarily brought forward from the start of cultivation.
Patent Document 5 discloses a technique for greening herbaceous plants on newly formed ground surfaces due to civil engineering works, such as road slopes, lake and river slopes, in which seeds are coated with a coating agent containing a biodegradable resin that is degraded and broken down by microorganisms in the soil so that the coating breaks down at a predetermined time after sowing, allowing the seeds to germinate and grow.

Japanese Patent Application Publication No. 8-21 Special Publication No. 61-033523 Japanese Patent Application Publication No. 8-256590 Japanese Patent Application Laid-Open No. 2017-35043 Japanese Patent Application Publication No. 8-149907

Namikoshi, T. , Hashimoto, T. , Urushisaki,M. ,Synthesis of poly(vinylether) plastics for optical use by cationic copolymerization oftricyclodecyl vinyl ether with n-butyl vinyl ether, Journal of PolymerScience, Part a: Polymer Chemistry, 45(18), 4389-4393 (2007)

However, the technologies disclosed in Patent Documents 1 and 3 rely on the decomposition of the coating layer (biodegradable resin) by microorganisms for the start of seed germination. If soil conditions are not constant depending on the area of the field where the seeds are sown, and if there is a bias in the decomposition activity due to, for example, the microbial population density or temperature conditions, there will be differences in the start of germination depending on the area of the field, which could result in a greater difference in subsequent growth.
The technology disclosed in Patent Document 2 was originally developed to solve the problem that rice seeds die when they are left in a state where they absorb moisture from the field during the winter period when growth is unsuitable, resulting in a decrease in the overall germination rate. However, it is not a technology intended to adjust the coating so that the seeds will peel off and germinate when the soil environment becomes suitable for germination.
The technology disclosed in Patent Document 4 aims to inhibit germination while maintaining seed viability by coating the surface of seeds with a coating containing an olefin polymer, which is a water-insoluble resin. The period of germination inhibition depends on the composition of the coating and the coating content relative to the seed, and is not a technology intended to adjust the coating to peel off from the seeds at a time when the soil environment is suitable for germination. Therefore, there are areas for improvement in terms of ensuring good seed growth by germinating seeds at the appropriate growth period.
The technology disclosed in Patent Document 5 enables seeds to germinate only after the degradation and breakdown of the biodegradable resin, and germination is suppressed for a certain period (3 to 6 months) after sowing, even if germination conditions such as temperature are appropriate.
As described above, with the conventionally proposed techniques, it is difficult to ensure good growth by inhibiting germination until the appropriate growth period and then germinating under any temperature conditions.

The present invention was made to solve the above-mentioned problems, and aims to provide a technology that can inhibit seed germination until the soil environment is suitable for germination, and then allow seeds to germinate when the appropriate growth period, such as temperature, is reached.

The present invention covers the following [1] to [5].
[1]
A coated seed having a coating layer containing a vinyl ether copolymer on the surface of the seed,
The vinyl ether copolymer is characterized by having a softening temperature of 0.5°C or higher and a Tg of -35°C to 13°C, as defined by the following conditions:
Coated seeds.
<Softening temperature>
The vinyl ether copolymer was filled into an aluminum pan (φ5.8 mm × height 1.5 mm),
A roughly Y-shaped stainless steel rod (weight 0.21 g, total length of stainless steel rod 2.1 cm, length of handle 0.9 cm, bottom of handle: 1.0 mm x 0.7 mm (approximately rectangular), length from crotch of branch to top of branch 0.2 cm, thickness of branch 0.7 mm, distance between tops of branch 0.85 cm) having a cylindrical handle and a branch at its tip that spreads out in two directions and has a flat top surface was thrust into the center of the copolymer with the branch facing upward, and the stainless steel rod was placed in contact with the bottom of the aluminum pan. When the temperature was raised from -20°C,
The surface temperature of the copolymer measured with an infrared radiation thermometer at the moment when the stainless steel rod falls completely is taken as the softening temperature.
[2]
The vinyl ether copolymer has a viscosity of 30 to 300 Pa s at 25°C and a number average molecular weight of 800 to 15,000.
[1] The coated seed according to [1].
[3] The coated seed according to [2], wherein the vinyl ether copolymer has a molecular weight distribution (Mn/Mw) of 2.0 or less.
[4]
The coated seed according to any one of [1] to [3], wherein the vinyl ether copolymer comprises a repeating unit represented by the following formula (1):
(In formula (1),
_R1 represents an alkyl group having 3 to 10 carbon atoms;
_R2 represents a cyclic hydrocarbon group having an alicyclic group having 10 to 15 carbon atoms as a basic skeleton,
p represents an integer of 3 to 95, q represents an integer of 2 to 38, and p and q satisfy the relationship p:q=5.8:4.2-7.2:2.8;
m is the number of alkylene groups and represents an integer of 0 or 1.
[5]
_R1 is at least one group selected from the group consisting of an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an isopropyl group, an isobutyl group, a t-butyl group, an isopentyl group, a neopentyl group, an isohexyl group, an isoheptyl group, an isooctyl group, a 2-ethylhexyl group, an isononyl group, and an isodecyl group;
The _R2 is one or more groups selected from the group consisting of groups represented by the following formulas (2) to (6):
[4] The coated seed according to [4].
(In the formula, * represents a bond.)

The coated seeds of the present invention enable seeds to be sown in autumn or winter, instead of the traditional spring cultivation period, in order to spread out the work season. This allows seeds to be sown earlier, while maintaining their viability, and suppressing germination until the appropriate time. To achieve this, the seeds are coated with a hydrophobic polymer that inhibits water absorption by the seeds until temperatures suitable for germination are reached. Even when the seeds are wintered in the field, this prevents frost damage, which occurs when the seeds absorb moisture from the surrounding area and freeze, and prevents plant death due to germination during winter, which is a harsh winter season for survival. Furthermore, the coating layer peels off from the seeds at temperatures suitable for growth, allowing the seeds to germinate at the optimum time for growth and ensuring good subsequent plant growth.

FIG. 1 is a graph showing the theoretical values of Tg according to the Fox formula for copolymers containing n-butyl vinyl ether (NBVE) and tricyclodecane vinyl ether (TCDVE) at different composition ratios. FIG. 2 is a schematic diagram of the measurement of the softening temperature. FIG. 3 is a diagram showing the appearance of coated seeds (sugar beet seeds) before and after the peeling test. FIG. 4 shows the germination test schedules (1) to (3). FIG. 5 is a diagram showing the germination of coated seeds (sugar beet seeds) subjected to a germination test according to schedule (2). FIG. 6 shows the coating material found in the soil after the germination test.

(coating material)
The coating material used in the coated seeds of the present invention is made of a polymer that inhibits water absorption by the coated seeds until a predetermined temperature is reached. In other words, the coating material is a hydrophobic material (also called a hydrophobic polymer) that does not dissolve or disintegrate in the presence of moisture, and by remaining solidified until the predetermined temperature is reached, it prevents water from passing through the coating layer and penetrating into the seeds. In this specification, "hydrophobic polymer" means a polymer that has low affinity for water.

(Softening temperature)
The water absorption that triggers germination occurs when the coating layer made of the coating material that covers the seed softens at a predetermined temperature and begins to peel off from the seed. In the present invention, the temperature at which the coating layer softens, that is, the temperature at which the solidified coating material becomes fluid and liquid, and peeling of the coating layer covering the seed begins and progresses, is defined as the "softening temperature." The softening temperature is the temperature that triggers peeling of the coating layer from the seed at a predetermined temperature, and can be used as an indicator of the temperature conditions that initiate germination, but in the present application it is used as a separate concept from the optimum temperature for seed germination.
The appropriate softening temperature according to the present invention is a temperature at which coated seeds will not germinate during the severe cold season but will germinate at a temperature suitable for germination in early spring, and must be at least 0.5° C. or higher. Although the temperature also depends on the cold tolerance of the germinating seedlings, in order to prevent growth stagnation and/or a decrease in survival rate due to exposure to cold air after germination, a temperature of 3° C. or higher is preferred, 4° C. or higher is more preferred, and 5° C. or higher is even more preferred.
The softening temperature can generally be measured by the method described in JIS K 7206 A50, but in the present invention, the temperature measured by the following method is treated as the softening temperature.
First, an aluminum pan (e.g., a crimp cell for DSC measurement) (φ5.8 mm x height 1.5 mm) is filled with a coating material (polymer). If necessary, the polymer is heated and filled into the aluminum pan in a molten state. The polymer is then leveled to the top edge of the aluminum pan. The aluminum pan is then placed on a temperature control unit set to -20°C, and a roughly Y-shaped stainless steel rod is inserted into the center of the polymer in the aluminum pan so that it is in contact with the bottom of the pan, leaving the stainless steel rod standing upright. The roughly Y-shaped stainless steel rod used here weighs 0.21 g, has an overall length of 2.1 cm, a handle length of 0.9 cm, a bottom surface of the handle: 1.0 mm x 0.7 mm (approximately rectangular), a length from the crotch of the branched portion to the top surface of the branched portion of 1.2 cm, a thickness of the branched portion of 0.7 mm, and a distance between the top surfaces of the branched portions of 0.85 cm. The branched portions are inserted into the polymer so that they face upward.
Next, the temperature is gradually increased from -20°C, and the surface temperature of the polymer in the aluminum pan at the moment when the stainless steel rod completely falls over (the entire stainless steel rod is in contact with the polymer) is measured with an infrared radiation thermometer, and this surface temperature is taken as the softening temperature.

(viscosity, number average molecular weight)
In the coated seeds of the present invention, setting the softening temperature is important as the main factor for controlling the peeling of the coating layer from the seeds, but setting the viscosity and number average molecular weight of the coating material can also be considered as secondary factors.
For example, in order for the coating layer to peel off from the seeds, it is desirable for the coating material to have an appropriate viscosity in a softened state. That is, even if the coating material (polymer) reaches the glass transition temperature (Tg) described below, if the viscosity is high, the fluidity will be low, which may hinder the coating material from peeling off from the seeds.
In the present invention, the viscosity at 25°C can be used as an index of the viscosity at which the softened coating layer can be peeled off from the seeds. Specifically, the viscosity of the coating material (polymer) may be 30 to 300 Pa·s (value measured with a vibration type viscometer at 25°C), preferably 35 to 250 Pa·s, and more preferably 38 to 200 Pa·s.
Generally, the viscosity of a polymer increases as the molecular weight of the polymer increases. Therefore, in order for the coating material to have the appropriate viscosity, the number-average molecular weight (Mn) of the polymer used as the coating material is preferably 800 to 15,000, more preferably 1,000 to 14,000, and even more preferably 1,200 to 13,000. Note that if the number-average molecular weight (Mn) is 18,000 or higher, the viscosity increases, which may make it difficult for the coating layer to peel from the seeds under temperature conditions that allow germination. In other words, the general trend is that if the viscosity is reduced by decreasing the molecular weight, it is possible to reduce the temperature difference between the Tg and the softening temperature, and if the viscosity is increased by increasing the molecular weight, it is possible to reduce the temperature difference between the Tg and the softening temperature.
Thus, one method for adjusting the viscosity of a coating material is to control the molecular weight of the polymer. For example, molecular weight control can be achieved by using living cationic polymerization, which allows molecular weight control during polymer preparation. That is, the polymer of the coating material according to the present invention can be a living cationic polymer. Of course, commonly used polymerization methods such as anionic polymerization, living anionic polymerization, cationic polymerization, free radical polymerization, and living radical polymerization can be used to prepare the polymer.
The coating material (polymer) according to the present invention preferably has a molecular weight distribution (Mw/Mn) of 2.0 or less, for example, 1.5 or less, or preferably 1.2 or less.
The number average molecular weight (Mn) and molecular weight distribution (Mw/Mn) may be values obtained by gel permeation chromatography (GPC) in terms of polystyrene.

(glass transition temperature)
The glass transition temperature (Tg) is the freezing temperature of the micro-Brownian motion of the polymer main chain, i.e., the temperature at which the coating material begins to change from a glassy state to a viscous state, and is a physical property that serves as an index of the ease with which the polymer softens. In the present invention, it is assumed that the coating material passes through a state in which it is released (viscous state) from a solidified (frozen state) as a preliminary stage before reaching a "softened" state (where peeling of the coating layer progresses). In other words, for the solidified coating material (polymer) to soften and peel off from the seed, it is necessary for at least the polymer of the coating material to reach the glass transition temperature and transition from a frozen state to a viscous state.
From this perspective, in the present invention, when the glass transition temperature (Tg) of the polymer used as the coating material is taken into consideration, the lower limit thereof should be at least −35° C. or higher, preferably −10° C. or higher, more preferably −3° C. or higher, and even more preferably 0° C. or higher. Furthermore, from the viewpoint of promoting peeling at a temperature suitable for germination in early spring when the air temperature has risen, the upper limit of Tg should be 10° C. or lower, preferably 7° C. or lower, and more preferably 5° C. or lower. Taking into consideration the risk of frost damage, the upper limit of Tg can be determined taking into account the temperature of the sowing environment, given that newly germinated sugar beet seedlings have low resistance to frost damage. For example, if the goal is to germinate the seeds in early May in the Tokachi region of Hokkaido, when the underground temperature reaches 10 to 15° C., the upper limit of Tg can be set to 13° C.

The theoretical value of the glass transition temperature (θ) of a copolymer constituted by two or more monomers can be calculated according to a calculation formula. For example, in the case of a copolymer constituted by two types of monomers, the glass transition temperature (θ) can be theoretically calculated using the following Fox formula based on the Tg (θ1, θ2) of the homopolymer (homopolymer) of each copolymerizable monomer A and B and the composition ratio (C1, C2) of each copolymerizable monomer.
1/θ=c1/θ1+c2/θ2
That is, the glass transition temperature of a copolymer of a vinyl ether having an alkyl group in its skeleton (monomer A) and a vinyl ether having a cyclic hydrocarbon (monomer B), which will be described later, can be calculated from Tg(A) of the homopolymer of monomer A, Tg(B) of the homopolymer of monomer B, and the composition ratio of monomer A to monomer B.

For example, as shown in FIG. 1, it has been reported that the Tg of a copolymer obtained by copolymerizing poly(n-butyl vinyl ether) (poly(NBVE); a raw material monomer having a Tg of −56° C.) with poly(tricyclodecane vinyl ether) (poly(TCDVE); a raw material monomer having a Tg of 105° C.) can be controlled by the TCDVE fraction (or the NBVE fraction) according to the Fox formula (Non-Patent Document 1). In FIG. 1, black circles (●) indicate theoretical values of Tg calculated using mole fraction, and white circles (○) indicate theoretical values of Tg calculated using mass fraction.
According to this formula, when the molar ratio of NDVE:TCDVE is 5.8:4.2 to 7.2:2.8, the theoretical Tg of the copolymer is in the range of -10.2°C to 12.5°C. Furthermore, in the case of a copolymer of poly(n-decyl vinyl ether) (NDVE), a raw material monomer with a Tg of -62°C, and poly(tricyclodecane vinyl ether) (poly(TCDVE), a raw material monomer with a Tg of 105°C), the theoretical Tg is -33.0°C to -15.1°C when the molar ratio of NDVE:TCDVE is 5.8:4.2 to 7.2:2.8.

On the other hand, while Tg is one indicator of when the coating layer has transitioned to a state where it can be peeled off from the seed, the softening temperature mentioned above is a more direct indicator of whether the coating layer will peel off from the seed at a given temperature, rather than a temperature that indicates the fluidity of the polymer. Furthermore, Tg and the softening temperature mentioned above do not necessarily correlate. Note that Tg can be measured using differential scanning calorimetry (DSC) or TMA.

(Type of polymer)
The polymer used as the coating material in the present invention is a so-called hydrophobic polymer. When coated on seeds and solidified (polymer layer), it prevents the seeds from absorbing water due to water penetration into the polymer layer, and when the polymer layer softens at a predetermined temperature, it has a certain viscosity (fluidity) that allows it to be peeled off from the coated seeds. As mentioned above, "hydrophobic polymer" refers to a polymer with low affinity for water, and includes polymers with a hydrophobic structure. Examples of the hydrophobic structure include nonpolar groups and nonpolar skeletons, particularly hydrocarbon groups, cyclic hydrocarbon groups, and hydrocarbon main chains. Furthermore, copolymers whose constituent units are monomers with hydrophobic structures (hydrophobic monomers) can also be included in the hydrophobic polymer.

(hydrophobic polymer)
A vinyl ether copolymer consisting of two types of repeating units represented by the following general formula (1) can be used as a hydrophobic polymer having the above properties. In this formula, p is 2 to 95, q is 2 to 38, and m is the number of alkylene groups and represents an integer of 0 to 1 (i.e., a single bond or a methylene group). Furthermore, p and q satisfy the relationship p:q=5.8:4.2-7.2:2.8, and preferably fall within the range of p:q=6:4-7:3.

R ₁ in general formula (1) is an alkyl group having 3 to 10 carbon atoms, and specifically can represent a linear alkyl group such as an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, or an n-decyl group, as well as a branched alkyl group such as an isopropyl group, an isobutyl group, a t-butyl group, an isopentyl group, a neopentyl group, an isohexyl group, an isoheptyl group, an isooctyl group, a 2-ethylhexyl group, an isononyl group, or an isodecyl group.

_R2 in general formula (1) is not particularly limited as long as it is a cyclic hydrocarbon group having an alicyclic group having 10 to 15 carbon atoms as a basic skeleton, and preferably includes a tricyclo[5.2.1.0 ^2,6 ]decyl group represented by the following formula (2), a tricyclodecenyl group represented by formula (3) or formula (4), and a pentacyclopentadecyl group represented by formula (5) or formula (6). In each formula, * represents a bond.

The vinyl ether copolymer can be produced by polymerizing a vinyl ether (monomer A) having the above-mentioned R ₁ (alkyl group) and a vinyl ether (monomer B) having R ₂ (alicyclic group) in a solvent.
One embodiment of the polymerization method is living cationic polymerization, in which polymerization is carried out in an aromatic hydrocarbon solvent such as toluene or xylene, or a halogenated hydrocarbon such as methylene chloride, which dissolves the monomers and polymers. Living cationic polymerization allows for easy control of the degree of polymerization and is useful as a method for obtaining polymers with narrow molecular weight distributions. This allows for control of the molecular weight of the copolymer, making it easy to adjust the viscosity of the coating material. Other commonly used polymerization methods that can be used include anionic polymerization, living anionic polymerization, cationic polymerization, free radical polymerization, and living radical polymerization.

Monomer A is not particularly limited as long as it is a vinyl ether having an alkyl group with 3 to 10 carbon atoms. Examples include vinyl ethers having a linear alkyl group such as n-propyl vinyl ether, n-butyl vinyl ether, n-pentyl vinyl ether, n-hexyl vinyl ether, n-heptyl vinyl ether, n-octyl vinyl ether, n-nonyl vinyl ether, and n-decyl vinyl ether, as well as vinyl ethers having a branched alkyl group such as isopropyl vinyl ether, isobutyl vinyl ether, t-butyl vinyl ether, isopentyl vinyl ether, neopentyl vinyl ether, isohexyl vinyl ether, isoheptyl vinyl ether, isooctyl vinyl ether, 2-ethylhexyl vinyl ether, isononyl vinyl ether, and isodecyl vinyl ether.

Monomer B is not particularly limited as long as it is a vinyl ether having a cyclic hydrocarbon group with an alicyclic group as a basic skeleton, and examples thereof include 8-tricyclo[5.2.1.0 ^2,6 ]decane vinyl ether (formula (2-1)), 8-tricyclo[5.2.1.0 ^2,6 ]decane monomethyl vinyl ether (formula (2-2)), 8-tricyclodecene vinyl ether (formula (3-1), formula (3-2)), 8-tricyclodecene monomethyl vinyl ether, 8-pentacyclopentadecane vinyl ether (formula (5-1), formula (6-1)), 8-pentacyclopentadecane monomethyl vinyl ether (formula (5-2), formula (6-2)), 8-pentacyclopentadecane vinyl ether, and 8-pentacyclopentadecane vinyl ether tricyclodecene monomethyl vinyl ether. These vinyl ethers can be synthesized based on the method described in Japanese Patent No. 4,136,886.

(coated seeds)
The seeds used in the present invention are not particularly limited, and examples thereof include seeds of vegetables, flowers, pasture plants, grains, industrial crops, trees, etc., and more specifically, the following seeds are included:
Examples of vegetable seeds include seeds of the Cucurbitaceae family, such as cucumber, melon, pumpkin, etc.; seeds of the Solanaceae family, such as eggplant and tomato, seeds of the Legume family, such as pea and kidney bean, seeds of the Liliaceae family, such as onion and leek, seeds of the Brassica family, such as turnip, Chinese cabbage, cabbage, broccoli, and cauliflower, and seeds of the Brassica family, such as radish, seeds of the Apiaceae family, such as carrot and celery, seeds of the Asteraceae family, such as burdock, lettuce, and garland chrysanthemum, seeds of the Lamiaceae family, such as perilla, and seeds of the Amaranthaceae family, such as spinach.
Examples of flowering plant seeds include seeds of the Brassicaceae family such as snapdragon, stock, and alyssum; seeds of the Campanulaceae family such as lobelia; seeds of the Asteraceae family such as aster, zinnia, and sunflower; seeds of the Ranunculaceae family such as delphinium; seeds of the Scrophulariaceae family such as snapdragon; seeds of the Primulaceae family such as primula; seeds of the Begoniaceae family such as begonia; seeds of the Lamiaceae family such as salvia; seeds of the Violaceae family such as pansy and viola; seeds of the Solanaceae family such as petunia; and seeds of the Gentianaceae family such as eustoma.
Examples of grass seeds include seeds of timothy (timothy grass), Italian ryegrass (ryegrass), bermudagrass (cynodont), oat hay (oats), sudangrass, kraine grass, fescue, and orchardgrass (dactylis glomerata).
Examples of cereal seeds include rice, barley, wheat, soybean, foxtail millet, buckwheat, barnyard millet, and millet.
Examples of seeds of industrial crops include seeds of Amaranthaceae such as sugar beet, seeds of Solanaceae such as tobacco, seeds of Brassicaceae such as rapeseed, and seeds of Gramineae such as rush.
Examples of tree seeds include seeds of azalea, oak, cedar, cypress, Japanese oak, beech, pine, and azalea.

The method for producing the coated seeds of the present invention is not particularly limited, and for example, a known device such as a granulator can be used.
Specifically, the seeds may be fluidized using a fluidizer or a jet device, or may be tumbled using a rolling device such as a rotating pan or a rotating drum, and a molten liquid or solution of the coating material (vinyl ether copolymer) according to the present invention may be added to the seeds by dropping, spraying, or other methods to coat the surfaces of the seeds.

The sowing method for the coated seeds of the present invention is not particularly limited, as long as the seeds are sown below the softening temperature of the coating material, preferably below its Tg, in order to obtain the effects of the present invention, i.e., to prevent the coating material from peeling off from the seeds during sowing. Examples include a method in which the seeds are simply sown on the soil surface, a method in which the seeds are sown on the soil surface and then covered with soil, a method in which the seeds are sown on the soil surface and then mixed with soil, and a method in which the seeds are sown in seedling pots such as paper tubes filled with soil and then covered with soil. The type of soil is also not particularly limited, as long as it is of a type that is generally applicable to the above-mentioned seeds.

The present invention will be further illustrated by the following examples. However, the present invention is not limited in any way by these examples and comparative examples.

[Production Example 1] Preparation of seed coating polymers In order to prepare polymers with different viscosities, four copolymers with different molecular weights, target molecular weights of 1,000, 5,000, 10,000, and 10,000 or more, were prepared by the following procedure.
Furthermore, based on the relationship between the TCDVE fraction and Tg shown in Figure 1, two copolymer compositions were determined, with molar ratios of NBVE (n-butyl vinyl ether):TCDVE (tricyclodecane vinyl ether) = 6:4 and 7:3, so that the Tg of the copolymer would be 5 to 10°C, and various copolymers shown in Table 1 were prepared according to the following procedure. A homopolymer of TCDVE was also prepared.

<Polymer Preparation Method>
n-Butyl vinyl ether (NBVE, liquid monomer, Fujifilm Wako Pure Chemical Industries, Ltd.), tricyclodecane vinyl ether (TCDVE, liquid monomer, Maruzen Petrochemical Co., Ltd.), boron trifluoride diethyl etherate (BF ₃ OEt ₂ (liquid)), and hydrogen chloride solution (HCl; Aldrich, 4.0 M 1,4-dioxane solution) were each dispensed into ampoules, stored in a refrigerator, and used in the following production.
Furthermore, zinc chloride solution (ZnCl ₂ ; Aldrich, 1.0 M diethyl ether solution), diethyl ether ((C ₂ H ₅ ) ₂ O, Fujifilm Wako Pure Chemical Industries, Ltd., ultra-dehydrated), and toluene (C ₆ H ₅ CH ₃ , Fujifilm Wako Pure Chemical Industries, Ltd., ultra-dehydrated) were each commercially available products, and water was removed and purified using an organic solvent purification apparatus before being used in the following production.

A three-way stopcock-equipped eggplant-shaped flask was baked with a heating gun while flowing nitrogen to prepare an anhydrous reaction system. The liquid monomer, initiator (solution), and activator solution (described below) were added to the flask to achieve the desired concentrations, and the reaction was carried out.
Specifically, a recovery flask containing liquid monomers (13.5 ml) in a predetermined molar ratio shown in Table 1 was cooled to −30° C., and then an initiator (BF ₃ OEt ₂ /1.5 ml) was added to prepare a polymerization solution (Production Method A).
Alternatively, an initiator solution (HCl solution/1.5 ml) and an activator solution (ZnCl2 solution/1.5 _ml ) were added in this order to liquid monomers (12.0 ml) in a predetermined molar ratio shown in Table 1 to prepare a polymerization solution (Production Method B).
After carrying out the polymerization in this manner on a scale of 15 ml of polymerization solution, the polymerization was stopped by adding 2 mL of water containing a small amount of aqueous ammonia.
The resulting polymer was then dissolved in a small amount of THF and added to a large amount (up to 800 ml) of methanol to cause reprecipitation, thereby purifying the polymer and obtaining the target polymer (coating material).
The molecular weight, glass transition temperature and softening temperature of the resulting polymer were measured according to the following procedures.

(Test Example 1) Measurement of Molecular Weight of Polymer The number average molecular weight (Mn) and molecular weight distribution (Mw/Mn) of the obtained polymer were calculated using gel permeation chromatography (GPC) using a calibration curve prepared from standard polystyrene (molecular weights: 96,400, 37,900, 18,100, 9,100, 5,870, 2,670, 1,050, and 500).
Gel permeation chromatography (GPC)
Pump: HITACHI l-7100
Differential refractometer: TOSOH RI-8020
UV-visible spectrometer: SHIMADZU SPD-10a
Columns: Shodex LF-802, Shodex LF-804 (3 columns)
Solvent: THF
Flow rate: 1.0ml/min (40.0°C)

(Test Example 2) Measurement of Glass Transition Temperature (Tg) of Polymer The glass transition temperature (Tg) of the obtained polymer was determined by differential scanning calorimetry (DSC). A Shimadzu DSC-60 was used as the apparatus, and an aluminum sample pan was used in the measurement under a nitrogen atmosphere. The first heating and cooling rate was 10°C/min, and the second heating and cooling rate was 5°C/min. Data from the midpoint of the second heating was used for analysis.

Test Example 3: Measurement of Softening Temperature of Polymer The obtained polymer was filled into a crimp cell for DSC measurement (aluminum pan φ5.8 mm × height 1.5 mm) until it was leveled to the upper edge of the cell. Polymers that were liquid when filled were left as they were, while polymers that were solid or had high viscosity when filled were heated to approximately 60°C and then filled into the crimp cell. This was placed on a temperature control unit (TOB-1000, Hayashi Repic Co., Ltd.) set at -20°C, and a roughly Y-shaped stainless steel rod weighing 0.21 g was thrust into the center of the polymer so that it was in contact with the bottom of the cell, with the Y pointing upward (see Figure 2). The approximately Y-shaped stainless steel rod had an overall length of 2.1 cm, a handle length of 0.9 cm, a bottom surface of the handle: 1.0 mm x 0.7 mm (approximately rectangular), a length from the crotch of the branched portion to the top surface of the branched portion of 1.2 cm, a thickness of the branched portion of 0.7 mm, and a distance between the top surfaces of the branched portions of 0.85 cm.
The temperature of the temperature control unit was gradually increased from −20° C., and the surface temperature of the polymer in the aluminum pan was measured with an infrared radiation thermometer (SK-8900, Sato Keiryoki Seisakusho Co., Ltd.) at the moment when the stainless steel rod completely fell over and came into contact with the polymer, and this was taken as the softening temperature.

The results of measuring the molecular weight (number average molecular weight, molecular weight distribution), glass transition temperature, and softening temperature of the obtained polymer are shown in Table 1. The target number average molecular weight (Calc(Mn)) and the theoretical glass transition temperature (Calc(Tg)) calculated using the Fox formula are also shown in Table 1.

As shown in Table 1, the number average molecular weights (Mn) of the prepared polymers were all higher than the calculated values, but the molecular weight distributions (Mw/Mn) of the prepared polymers were narrow, ranging from 1.08 to 1.22, confirming that living polymerization was proceeding.
As shown in Table 1, the measured Tg and softening temperature tended to decrease as the TCDVE fraction decreased, similar to the theoretical values. Furthermore, for copolymers, the measured Tg values were all lower than the theoretical Tg values calculated by Fox's formula. Furthermore, for copolymers with the same composition, the measured Tg and softening temperature varied depending on the molecular weight.

[Production Example 2] Preparation of coated seeds Each polymer obtained in [Production Example 1] was placed in a sample bottle at room temperature, and uncoated seeds (sugar beet seeds or onion seeds) were added thereto. The seeds were stirred with a medicine spoon and then removed. The removed seeds were left at a low temperature (-20°C) to harden the polymer, and coated seeds were obtained.
The polymer (NBVE and TCVE molar ratio 6:4, Mn = 18,700) that was too viscous for coating seeds due to its high molecular weight, and poly(TCDVE) with a high Tg, were first dissolved in dichloromethane (CH ₂ Cl ₂ ) to adjust the viscosity before being used for seed coating.
Using the obtained coated seeds, a coating peeling test and a germination test were carried out according to the following procedures.

(Test Example 4) Coating Peeling Test Seeds coated with each polymer were placed on a petri dish and left in an incubator (KMH-207, AS ONE Corporation) at 5°C for 10 days, and then the temperature inside the incubator was lowered to 10°C and the seeds were left for 3 days. Thereafter, the temperature inside the incubator was lowered to 20°C, and peeling of the coating from the seeds was visually confirmed.
Observation was started at 5°C, and after the temperature was raised to 20°C and observation continued for 9 days, seeds in which even a small amount of coating had peeled off were rated as ◯, whereas seeds in which the coating remained completely intact were rated as ×. The results are shown in Table 2.
Furthermore, the peeling state before and 16 days after the start of observation (four days after the temperature was raised to 20°C) is shown in Figure 3(A) for the coated seeds (sugar beet seeds) using a copolymer with Mn = 1,700 in a composition ratio of NBVE:TCDVE = 6:4, and in Figure 3(B) for the coated seeds (sugar beet seeds) using a copolymer with Mn = 18,700.

As shown in Figure 3, when copolymers with a composition ratio of 6:4 were compared by molecular weight, the copolymer with Mn = 1,700 was confirmed to have completely peeled off 16 days after the start of observation, i.e., 4 days after heating to 20°C (Figure 3(A)). However, the copolymer with Mn = 18,700 was not confirmed to have peeled off even after heating to 20°C, i.e., 16 days after the start of observation (4 days after heating to 20°C) (Figure 3(B)). Peeling of the copolymer was not confirmed even after 32 days (20 days after heating to 20°C) from the start of observation. Despite the difference in Tg between these two copolymers being approximately 3°C, and even at 20°C, which is significantly higher than the Tg of these copolymers, the copolymer with Mn = 18,700 did not peel off from the seeds. This is thought to be due in part to the fact that high-molecular-weight polymers are difficult to peel off due to their high viscosity, making them unsuitable as seed coating materials for the present invention.
However, Tg is the temperature indicating the freezing/release of the micro-Brownian motion of the polymer main chain, and Tg itself cannot be said to be the temperature that indicates the fluidity of the polymer or an indicator thereof. In the present invention, the softening temperature, which is defined as the temperature at which a solidified polymer retains fluidity and becomes liquid, can be used as an indicator of the fluidity of the polymer.
As shown in Table 2, the softening temperatures of the copolymer with Mn=1,700 and the copolymer with Mn=18,700, both with a composition ratio of 6:4, were 8.2°C and 21.0°C, respectively. The difference in Tg was 3.2°C, while the difference in softening temperature was 12.8°C, which was a large difference. Since this peeling test was carried out below the softening temperature (21°C) of the copolymer with Mn=18,700, it is believed that the copolymer did not peel from the seeds.
These results show that a required characteristic of the coating material is that the peeling temperature must be higher than the softening temperature due to the viscosity inherent in polymers. In other words, it appears desirable to set the softening temperature of the coating material lower than the expected optimum temperature for seed germination.

(Test Example 5) Germination test A germination test was carried out according to the schedule (1) to (3) shown in Figure 4. The soil used for raising seedlings was a general seedling raising soil containing no solidifying agent.
<Uncoated seeds>
(1) Seeds that were not polymer-coated were soaked in water and grown in the soil in an incubator set at 3°C or at room temperature, and germination was confirmed (see Figure 4: Schedule (1)).
<Coated seeds>
(2) The polymer-coated seeds were sown in the soil and then grown in an incubator while the temperature was raised according to a schedule of 8 days at 3°C, 4 days at 10°C, and 1 to 7 days at 20°C, and germination was confirmed (see Figure 4: Schedule (2)).
(3) The pots containing the polymer-coated seeds sown in the soil were immersed in water, and seedlings were grown under the same schedule as in (2) (8 days at 3°C, 4 days at 10°C, and 1 to 7 days at 20°C) while constantly absorbing water. For samples that did not germinate after the period during which germination was confirmed at 20°C in schedule (2), the pots were removed from the water to remove the immersion, and seedlings were grown for a further 4 to 8 days at 20°C, and germination was confirmed (see Figure 4: schedule (3)).

In a germination test conducted according to schedule (1) using uncoated seeds, germination was confirmed six days after sowing at 3°C. Furthermore, when seeds were sown at room temperature, germination occurred three days later. The germination rate was 100% under all conditions. These results also confirmed that soaking seeds in water and exposing them to low temperatures does not result in a loss of seed germination function.

In a germination test using coated seeds conducted according to Schedule (2), germination was confirmed in seeds coated with a copolymer of NBVE and TCVE in a molar ratio of 6:4 and Mn = 1,700 within one day (13 days after sowing) after the temperature was raised to 20°C at the earliest. As shown in Table 3, the germination rate of seeds coated with the copolymer of Mn = 1,700 was 50%, which was lower than that of Schedule (1) (germination rate: 100%), but it was confirmed that polymer coating can cause seeds to germinate without killing them (see Figure 5 (sugar beet seeds)).

In addition, in a germination test conducted using a sample with the same molar composition and molecular weight according to schedule (3), germination did not occur even after the germination period for schedule (2) had elapsed, but germination was confirmed four days after the water was removed.
The temperature conditions for Schedule (3) (with water soaking) and Schedule (2) (without water soaking) were the same, and germination occurred after the soaking was removed and seedlings were grown in normal conditions. This suggests that even in an environment above the softening temperature of the coating material, the presence of water around the seeds prevented the hydrophobic coating material from peeling off from the seeds, completely inhibiting water absorption by the seeds, thereby suppressing germination.

In addition, since the final temperature (germination temperature) was set at 20°C in Schedules (2) and (3), it was expected that seeds coated with copolymers (NBVE:TCDVE (molar ratio) = 6:4, Mn = 18,700) and poly(TCDVE), which have softening temperatures above 20°C, would not germinate because the coating would not peel off. However, as shown in Table 3, germination was confirmed even with these coating materials.
Regarding this result, when the soil was checked after germination, it was confirmed that the poly(TCDVE) coating had cracked and remained in a shell-like state (see Figure 6; Figure 6 shows the results for coated seeds using sugar beet seeds). From this, it is _thought that the cause of germination was that dichloromethane ( _CH2Cl2 ), which was used to adjust the viscosity when coating the seeds, evaporated when the coating solidified, causing voids in the coating, which allowed the seeds to absorb water through these voids, crack the coating material, and germinate.

(Test Example 6) Peeling test and germination test using re-coated coated seeds Coated seeds (2) with a thicker coating layer were prepared by repeatedly applying and drying the polymer to the poly(TCDVE) coated seeds used in Test Example 5. The temperature inside the incubator was set to 20°C from the first day, and peeling test and germination test were carried out using these coated seeds (2).
Coated seeds (2), which were re-coated with poly(TCDVE) [molecular weight 41,200], did not germinate, and no peeling of the coating material was observed. This result supports the conclusion that the cause of germination, as described above in Table 3, is due to the generation of voids during drying. Furthermore, when the temperature inside the incubator was raised to 25°C, no germination was observed either.

(Test Example 7) Test demonstrating the correlation between polymer viscosity and peeling To demonstrate the correlation between the viscosity of the polymer and peeling from seeds, seeds were coated with the obtained polymer and examined for peeling from the seeds. Preparation of the seed coating polymer (Preparation A), measurement of the polymer's molecular weight, measurement of the softening temperature, preparation of coated seeds, and coating peeling test were carried out according to the procedures described above.
The viscosity of the polymer was measured at 25°C using a vibration viscometer (Seconic Corporation, VM-10A-H model). The results are shown in Table 4. Peeling of the coating layer was confirmed at least at viscosities of 52 to 184 Pa·S.

From the above results, it was confirmed that when designing coated seeds according to the present invention, it is desirable to design the coating material so that the temperature at which the coating material peels off from the seed exceeds the softening temperature of the coating material (the softening temperature of the coating material is set lower than the expected optimum temperature for seed germination), and that high molecular weight polymers are not suitable as coating materials because they tend to have high viscosity and high softening temperatures.
Furthermore, in a copolymer with a molar ratio of NBVE:TCDVE = 6:4, although there is not much difference in softening temperature between a polymer with a target molecular weight of Mn = 1,000 and a polymer with Mn = 5,000, it was confirmed that the polymer is easier to peel off quickly (see Table 2). Therefore, when the softening temperatures are similar between compositions of 6:4 and 7:3, it is preferable to use a polymer with a lower molecular weight.

Claims (3)

A coated seed having a coating layer made of a vinyl ether copolymer on the surface of the seed,
The vinyl ether copolymer is a copolymer of n-butyl vinyl ether:tricyclodecane vinyl ether=5.8:4.2-7.2:2.8 (composition ratio), characterized in that it has a softening temperature of 0.5°C or higher, a Tg of -35°C to 13°C , and a number average molecular weight of 800 to 15,000 , as defined by the following conditions:
Coated seeds.
<Softening temperature>
The vinyl ether copolymer was filled into an aluminum pan (φ5.8 mm × height 1.5 mm),
A roughly Y-shaped stainless steel rod (weight 0.21 g, total length of stainless steel rod 2.1 cm, length of handle 0.9 cm, bottom of handle: 1.0 mm x 0.7 mm (approximately rectangular), length from crotch of branch to top of branch 0.2 cm, thickness of branch 0.7 mm, distance between tops of branch 0.85 cm) having a cylindrical handle and a branch at its tip that spreads out in two directions and has a flat top surface was thrust into the center of the copolymer with the branch facing upward, and the stainless steel rod was placed in contact with the bottom of the aluminum pan. When the temperature was raised from -20°C,
The surface temperature of the copolymer measured with an infrared radiation thermometer at the moment when the stainless steel rod falls completely is taken as the softening temperature. The vinyl ether copolymer has a viscosity of 30 to 300 Pa s at 25°C.
The coated seed according to claim 1. The coated seed according to claim 2, wherein the vinyl ether copolymer has a molecular weight distribution (Mn/Mw) of 2.0 or less.