Coated seeds with controlled germination time

Abstract

To provide a coated seed capable of contributing to dispersion of work periods by advancing a sowing period to autumn or winter from a conventional cultivation system of sowing in spring.SOLUTION: There is provided a coated seed that makes it possible to suppress germination until an appropriate time while maintaining seed viability by coating the seed with a coating material that can inhibit water absorption, which triggers seed germination, until a temperature is suitable for germination and can be peeled off from the seed at a temperature that allows for growth (for example, a hydrophobic coating material containing a vinyl ether copolymer consisting of repeating units of the following formula (1), where R1 represents an alkyl group having 3 to 10 carbon atoms, and R2 represents a cyclic hydrocarbon group whose basic skeleton is an alicyclic group having 10 to 15 carbon atoms).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to coated seeds that can ensure good growth by suppressing germination until an appropriate time while maintaining seed viability when the sowing time is brought forward and the seeds are allowed to overwinter in fields in order to spread out agricultural work periods, mainly in cold regions. [Background technology]

[0002] 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 then transplanted after a certain period of seedling raising. Meanwhile, in recent years, direct seeding of sugar beets has expanded to reduce costs and save on labor, which increases with the expansion of the cultivated area per farm. While direct seeding eliminates the need for seedling raising, it poses the challenge 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, potentially preventing the crop from having sufficient time to grow.

[0003] 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 blocking 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. To prevent the rice seeds from absorbing water in the field during the winter, which is unsuitable for growth, they are coated with a pinhole-free coating to impart hydrophobicity to the rice seeds, and to control the duration of this hydrophobicity, the rice seeds are coated with hydrophobic polybutadiene having a number-average molecular weight of 400 to 1000 and a viscosity at 20°C of 100 to 500 centipoise. 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, or temperature, in a greening method using seed sowing on slopes, etc., so that seed germination or the germination time can be freely controlled, making it possible to sow seeds even at times when sowing is inappropriate. Patent Document 4 discloses a technique in which seeds with a moisture content in the range of 0 to 20% by weight are coated with a polyethylene polymer, which is a water-insoluble resin, on the surface, in order to maintain seed viability and inhibit germination until the 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-21 [Patent Document 2] Special Publication No. 61-033523 [Patent Document 3] Japanese Patent Application Publication No. 8-256590 [Patent Document 4] Japanese Patent Application Laid-Open No. 2017-35043 [Patent Document 5] Japanese Patent Application Publication No. 8-149907 [Non-patent literature]

[0005] [Non-Patent Document 1] Namikoshi, T., Hashimoto, T., Urushisaki, M., Synthesis of poly(vinylether) plastics for optical use by Cationic copolymerization of tricyclodecyl vinyl ether with n-butyl vinyl ether, Journal of PolymerScience, Part a: Polymer Chemistry, 45(18), 4389-4393(2007) Summary of the Invention [Problem to be solved by the invention]

[0006] 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. 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 film containing an olefin polymer, which is a water-insoluble resin. The period of germination inhibition depends on the composition of the film and the content of the film relative to the seed, and the technology is not intended to adjust the film so that it peels 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 allows seeds to germinate only after the biodegradable resin has deteriorated and broken down, and germination is inhibited 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.

[0007] The present invention has been made to solve the above-mentioned problems, and aims to provide a technology that can inhibit seed germination until the soil environment becomes suitable for germination, and can cause seeds to germinate at the appropriate timing for growth, such as when the temperature is suitable. [Means for solving the problem]

[0008] 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, handle length 0.9 cm, bottom of handle: 1.0 mm x 0.7 mm (approximately rectangular), length from crotch of branch to top of branch 1.2 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 the present invention. [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): [ka] (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 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; wherein R2 is at least one group selected from the group consisting of groups represented by the following formulas (2) to (6): [4] The coated seed according to the present invention. [ka] (In the formula, * represents a bond.) [Effects of the Invention]

[0009] 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 period. This allows seeds to be sown earlier, maintaining their viability while suppressing germination until the appropriate time. To this end, by coating the seeds with a hydrophobic polymer that inhibits water absorption by the seeds until temperatures suitable for germination are reached, even when the seeds are overwintered in the field, this prevents frost damage caused by the seeds absorbing moisture from the surrounding area and freezing, and prevents plant death due to germination in winter, which is a harsh winter environment. Furthermore, the coating layer peels off from the seeds at temperatures suitable for growth, allowing the seeds to germinate at the optimal time for growth and ensuring good subsequent plant growth. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a graph showing the theoretical values ​​of Tg according to the Fox equation for copolymers in which the composition ratio of n-butyl vinyl ether (NBVE) and tricyclodecane vinyl ether (TCDVE) is changed. [Figure 2] FIG. 2 is a schematic diagram of the measurement of the softening temperature. [Figure 3] FIG. 3 shows the appearance of coated seeds (sugar beet seeds) before and after the peeling test. [Figure 4] FIG. 4 shows the schedules (1) to (3) of the germination test. [Figure 5] FIG. 5 shows the germination of coated seeds (sugar beet seeds) subjected to a germination test according to Schedule (2). [Figure 6] FIG. 6 shows the coating material found in the soil after the germination test. DETAILED DESCRIPTION OF THE INVENTION

[0011] (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 condition is reached. In other words, the coating material is a material that does not dissolve or disintegrate in the presence of moisture, i.e., a hydrophobic material (also called a hydrophobic polymer), and by remaining in a solidified state until the predetermined temperature is reached, it prevents water from passing through the coating layer and penetrating into the seeds. In this specification, the term "hydrophobic polymer" refers to a polymer that has low affinity for water. Taste.

[0012] (Softening temperature) The water absorption that triggers germination occurs when the coating layer made of the above-mentioned coating material that covers the seed softens at a certain temperature, causing it to peel off from the seed. In the present invention, the temperature at which the coating layer softens, i.e., the temperature at which the solidified coating material becomes fluid and liquid, causing the peeling of the coating layer covering the seed to begin and progress, is defined as the "softening temperature." The softening temperature is the temperature that triggers the coating layer to peel off from the seed at a certain 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 it 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, the temperature is preferably 3° C. or higher, more preferably 4° C. or higher, and even more preferably 5° C. or higher. 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. 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, and the stainless steel rod is left standing. 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 handle base of 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 branch thickness 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 falls completely (as if 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.

[0013] (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) should be 30 to 300 Pa·s (measured with a vibration 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 that is the coating material is, for example, 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 more, the viscosity increases, which may make it difficult for the coating layer to peel off from the seeds under temperature conditions that allow germination. In other words, Generally, if the viscosity is reduced by decreasing the molecular weight, it is possible to control the temperature difference between Tg and softening temperature to a small value, and if the viscosity is increased by increasing the molecular weight, it is possible to control the temperature difference between Tg and softening temperature to a large value. 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. Furthermore, 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.

[0014] (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 released state (viscous state) from a solidified state (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 coating polymer to reach its 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 considered, the lower limit 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 temperatures have risen, the upper limit of Tg should be 10°C or lower, preferably 7°C or lower, and more preferably 5°C or lower. Considering 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.

[0015] The theoretical value of the glass transition temperature (θ) of a copolymer composed of two or more monomers can be calculated using a calculation formula. For example, in the case of a copolymer composed of two types of monomers, the glass transition temperature (θ) can be theoretically calculated using the Fox formula below, based on the Tg (θ1, θ2) of the homopolymer (homopolymer) of each copolymerization monomer A and B and the composition ratio (C1, C2) of each copolymerization 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) can be calculated from the Tg(A) of the homopolymer of monomer A, the Tg(B) of the homopolymer of monomer B, and the composition ratio of monomer A to monomer B.

[0016] For example, as shown in Figure 1, the Tg of the copolymer obtained by copolymerizing poly(n-butyl vinyl ether) (poly(NBVE); Tg = -56°C) with poly(tricyclodecane vinyl ether) (poly(TCDVE); Tg = 105°C) can be controlled by the TCDVE fraction (or NBVE fraction) according to the Fox equation. It has been reported that this is possible (Non-Patent Document 1). In Figure 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. In addition, for 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.

[0017] On the other hand, although Tg is an indicator of the transition of the coating layer to a state where it can be peeled off from the seed, it is not a temperature that indicates the fluidity of the polymer. As an indicator of whether the coating layer will peel off from the seed at a certain temperature, the softening temperature is a more direct indicator. Furthermore, Tg and the softening temperature do not necessarily correlate. Differential scanning calorimetry (DSC) or TMA can be used to measure Tg.

[0018] (Type of polymer) The polymer used as the coating material in the present invention is a so-called hydrophobic polymer, and is not particularly limited as long as it prevents the seeds from absorbing water due to water penetration into the polymer layer when coated on the seeds and solidified (polymer layer), and has a certain viscosity (fluidity) when the polymer layer softens at a predetermined temperature, thereby allowing 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 having a hydrophobic structure. Examples of the hydrophobic structure include nonpolar groups, nonpolar skeletons, and particularly hydrocarbon groups, cyclic hydrocarbon groups, and hydrocarbon main chains. Furthermore, copolymers whose constituent units are monomers having a hydrophobic structure (hydrophobic monomers) can also be included in the hydrophobic polymer.

[0019] (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 to 7.2:2.8, and preferably fall within the range of p:q=6:4 to 7:3. [ka]

[0020] R1 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.

[0021] R2 in the 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 is preferably a tricyclo[5.2.1.0] group represented by the following formula (2). 2,6 ]decyl group, tricyclodecenyl group represented by formula (3) or formula (4), and pentacyclopentadecyl group represented by formula (5) or formula (6) can be preferably used. In each formula, * represents a bond. [ka]

[0022] The vinyl ether copolymer can be produced by polymerizing a vinyl ether (monomer A) having the above-mentioned R1 (alkyl group) and a vinyl ether (monomer B) having R2 (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.

[0023] Monomer A is not particularly limited as long as it is a vinyl ether having an alkyl group having 3 to 10 carbon atoms. Examples thereof 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.

[0024] Monomer B is not particularly limited as long as it is a vinyl ether having a cyclic hydrocarbon group with an alicyclic group as the basic skeleton. For example, 8-tricyclo[5.2.1.0 2,6 ]decane vinyl ether (formula (2-1)), 8-tricyclo[5.2.1.0 2,6 ]Decanol monomethyl vinyl Examples of vinyl ethers include 8-tricyclodecene 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 according to the method described in Japanese Patent No. 4,136,886. [ka]

[0025] (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, sudan grass, krain grass, fescue, and orchard grass (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.

[0026] 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 are fluidized using a fluidizer or a jet device, or are 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 is added to the seeds by dropping, spraying, or other methods to coat the surfaces of the seeds.

[0027] The sowing method for the coated seeds of the present invention is not particularly limited, as long as the seeds are sown at a temperature 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 of simply sowing the seeds on the soil surface, a method of sowing the seeds on the soil surface and then covering them with soil, a method of sowing the seeds on the soil surface and then mixing them with soil, and a method of sowing the seeds in a seedling pot such as a paper tube filled with soil and then covering them 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. [Example]

[0028] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples and comparative examples.

[0029] [Production Example 1] Preparation of seed coating polymer In order to prepare polymers with different viscosities, copolymers with four different molecular weights, target molecular weights of 1,000, 5,000, 10,000, and over 10,000, were prepared according to the following procedure. Furthermore, based on the relationship between 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. Various copolymers shown in Table 1 were prepared using the following procedure. A homopolymer of TCDVE was also prepared.

[0030] <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 (BFOEt (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; Aldrich, 1.0 M diethyl ether solution), diethyl ether ((C2H5)2O, Fujifilm Wako Pure Chemical Industries, Ltd., ultra-dehydrated), and toluene (C6H5CH3, 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 use in the following production.

[0031] 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 the molar ratio shown in Table 1 was cooled to -30°C, and then an initiator (BF3OEt2 / 1.5 ml) was added to form 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 monomer (12.0 ml) at 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 terminated by adding 2 mL of water containing a small amount of aqueous ammonia. The resulting polymer was then purified by dissolving it in a small amount of THF and adding it to a large amount (approximately 800 ml) of methanol to cause reprecipitation, yielding the desired polymer (coating material). The molecular weight, glass transition temperature and softening temperature of the resulting polymer were measured according to the following procedures.

[0032] (Test Example 1) Measurement of polymer molecular weight 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, 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℃)

[0033] (Test Example 2) Measurement of the 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, and measurements were performed in a nitrogen atmosphere using an aluminum sample pan. 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 were used for analysis.

[0034] (Test Example 3) Measurement of polymer softening temperature The resulting polymer was filled into a crimp cell (aluminum pan φ5.8 mm × height 1.5 mm) for DSC measurement, until it reached the top edge of the cell. Polymers that were liquid at the time of filling were left as they were, while polymers that were solid or highly viscous at the time of filling were heated to approximately 60 °C and then filled into the crimp cell. The cell 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 inserted 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 roughly Y-shaped stainless steel rod had an overall length of 2.1 cm, a handle length of 0.9 cm, a handle base of 1.0 mm × 0.7 mm (approximately rectangular), a length from the crotch of the branched portion to the top surface of the branched portion ... The temperature of the temperature control unit was gradually increased from -20°C. At the moment when the stainless steel rod was completely tilted and in contact with the polymer, the surface temperature of the polymer in the aluminum pan was measured with an infrared radiation thermometer (SK-8900, Sato Keiryoki Seisakusho Co., Ltd.) and recorded as the softening temperature.

[0035] 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 equation are also shown in Table 1.

[0036] [Table 1]

[0037] 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 distribution (Mw / Mn) of the prepared polymers was narrow, ranging from 1.08 to 1.22, confirming that living polymerization was proceeding. As shown in Table 1, both the measured Tg and softening temperature tended to decrease as the TCDVE fraction decreased, just as with the theoretical values. Furthermore, for copolymers, the measured Tg values ​​were all lower than the theoretical Tg values ​​calculated by Fox's equation. Furthermore, for copolymers with the same composition, the measured Tg and softening temperature values ​​varied depending on the molecular weight.

[0038] [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 spoon and then removed. The removed seeds were left at a low temperature (-20°C) to harden the polymer, yielding coated seeds. 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 (CH2Cl2) to adjust the viscosity before being used to coat the seeds. Using the obtained coated seeds, a coating peeling test and a germination test were carried out according to the following procedures.

[0039] (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, then the incubator was cooled to 10°C and left for 3 days. The temperature inside the incubator was then lowered to 20°C, and the peeling of the coating from the seeds was visually confirmed. Observation began at 5°C, and was continued for 9 days at 20°C. If any part of the coating had peeled off from the seeds during this period, the seed was rated as "○", and if the coating remained completely intact, the seed was rated as "×". The results are shown in Table 2. In addition, the peeling status 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 (composition ratio) NBVE:TCDVE=6:4, and in Figure 3(B) for the coated seeds (sugar beet seeds) using a copolymer with Mn=18,700.

[0040] [Table 2]

[0041] As shown in Figure 3, when comparing copolymers with a composition ratio of 6:4 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 did not peel off even after heating to 20°C. That is, peeling was not confirmed 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). 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 partly due to the high viscosity of high molecular weight polymers, which makes them less susceptible to peeling and therefore unsuitable for the seed coating material of the present invention. However, Tg is the temperature indicating the freezing / release of 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 of the fluidity. 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, 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, resulting in 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.

[0042] (Test Example 5) Germination test Germination tests were 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. <Non-coated seeds> (1) Seeds that were not polymer-coated were soaked in water and grown in the above 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 submerged in water and 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 allowing the seeds to constantly absorb 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 and the immersion state was eliminated. Seedlings were then grown at 20°C for another 4 to 8 days, and germination was confirmed (see Figure 4: schedule (3)).

[0043] In a germination test using uncoated seeds according to schedule (1), germination was confirmed six days after sowing at 3°C. When seeds were sown at room temperature, germination occurred in three days. The germination rate was 100% under all conditions. These results also confirmed that soaking seeds in water and exposing them to low temperatures did not result in a loss of seed germination function.

[0044] 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 heating 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)).

[0045] 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), 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.

[0046] In addition, since the final temperature (germination temperature) for Schedules (2) and (3) was set to 20°C, 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 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 made from sugar beet seeds). From this, it is thought that the cause of germination was that the dichloromethane (CH2Cl2) used to adjust the viscosity when coating the seeds volatilized as the coating solidified, causing voids in the coating, which allowed the seeds to absorb water through these voids, crack the coating, and germinate.

[0047] [Table 3]

[0048] (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 poly(TCDVE) coated seeds used in Test Example 5. Using these coated seeds (2), the temperature inside the incubator was set to 20°C from the first day, and peeling tests and germination tests were conducted. 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.

[0049] (Test Example 7) Test showing the correlation between polymer viscosity and peeling To demonstrate the correlation between the viscosity of the polymer and its peeling from seeds, seeds were coated with the polymer and examined for its peeling. Preparation of the seed coating polymer (Preparation A), measurement of the polymer's molecular weight and softening temperature, preparation of coated seeds, and coating peeling tests 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.

[0050] [Table 4]

[0051] 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. In addition, in a copolymer with NBVE:TCDVE (molar ratio) = 6:4, there is little difference in softening temperature between the polymer with target molecular weight: Mn = 1,000 and the polymer with Mn = 5,000. However, it was confirmed that the polymer with a lower molecular weight was easier to peel off than the polymer with a 6:4 or 7:3 composition when the softening temperatures were similar.

Claims

1. 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.

2. The vinyl ether copolymer has a viscosity of 30 to 300 Pa s at 25°C. The coated seed according to claim 1.

3. The coated seed according to claim 2 , wherein the vinyl ether copolymer has a molecular weight distribution (Mn / Mw) of 2.0 or less.

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