JPH1025336A - Levee sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a levee sheet which is made of poly(lactic acid) in no need of the sheet-recovering and removing operations after use without problem on waste disposal and can repel animals and plants giving damages to paddy field rice culture. SOLUTION: This sheet is composed of a biodegradable aliphatic polyester, particularly mainly composed of a poly(lactic acid) with an average-weight molecular weight of 50,000-500,000. In addition, a repellent against pest animals and plants which damages rice plant culture may be formulated in the above- described biodegradable aliphatic polyester to form sheets. The molar ratio (L/D) of L-lactic acid units to the D-lactic acid units in the above-described poly(lactic acid) is particularly 100/0-80/20. Thus, the polymer is excellent in biodegradability, high in safety to living body, the lactic acid as a hydrolyzate is absorbed in vivo, has a plant-growing activity and shows continuously animal and plant-repelling action.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ridge sheet used for paddy rice agriculture, and more particularly to a ridge sheet having biodegradability. The ridge sheet covers the surface of the ridge provided around the paddy field and is used for the purpose of preventing water leakage when the paddy field is flooded.

[0002]

2. Description of the Related Art Conventionally, various plastic films have been frequently used for agricultural purposes, and rigid polyvinyl chloride or polyethylene has been used as a material of the ridge sheet (Agricultural Materials Yearbook 1995-261, 1995).

[0003] However, these polymer materials remain semipermanently when left after use or buried in soil. Therefore, it is necessary to collect and remove the ridge sheet before or after harvesting paddy rice. However, in modern agriculture where mechanization is progressing, manual work is required as it is in the old state. The age of farmers is increasing, and manual work to remove and remove sheets is extremely hard work. Further, even if the levee sheet is collected, it is technically difficult to regenerate the collected sheet, and the collected sheet is treated as waste. Therefore, waste disposal of the sheet becomes a problem similarly to general plastics. That is, the current plastic waste treatment is incineration or burial treatment. However, burning incineration of polyethylene damages the incinerator and shortens its service life due to its high calorie burning.
In addition, when polyvinyl chloride is incinerated, harmful gases are generated. On the other hand, there are not enough disposal sites to bury plastic products. When plastics are disposed of in the natural environment, their chemical stability is extremely high.
Biologically, decomposition by microorganisms and the like hardly occurs, and it remains almost semi-permanently. For this reason, the landscape is damaged, and in addition, there is a problem that the living environment of marine life is polluted.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to eliminate the need for sheet collection and removal after use and to avoid waste disposal. Is to provide. It is another object of the present invention to provide the levee sheet further having an action of repelling animals and plants that damage rice cultivation.

[0005]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the above object can be achieved by using a biodegradable aliphatic polyester, particularly polylactic acid, as a material. It was completed.

That is, the ridge sheet of the present invention is composed mainly of polylactic acid.

In the present invention, polylactic acid includes lactic acid homopolymer and lactic acid copolymer.

[0008] Polylactic acid has excellent biodegradation properties and high biosafety. Furthermore, lactic acid as a decomposition product is absorbed in the living body, and dimer or oligomer of lactic acid as an intermediate decomposition product has a plant growth activity. (Plant Growth Regulation
9, 137-146, 1990), in that they are inexpensive, transparent, and have good colorability. For example, the biodegradability of poly-L-lactic acid is excellent, showing a biodegradability test in compost of 44 days, where cellulose is 73% degradable and 93% is degradable.

In the present invention, the polylactic acid has a weight average molecular weight of 50,000 to 500,000, preferably 100,000 to 300,000. When the weight average molecular weight is less than 100,000, the strength of the sheet tends to be insufficient. In addition, the decomposition rate of polylactic acid is increased. On the other hand, when the weight average molecular weight exceeds 300,000, the moldability tends to deteriorate. A more preferred weight average molecular weight is 15
10,000 to 250,000. The melting point of polylactic acid is 160-2.
It is about 00 ° C.

The molar ratio L / D of L-lactic acid unit and D-lactic acid unit in polylactic acid may be 100/0 to 0/100, but L / D is 100/0 to 60/40. Is preferred. More preferable L / D is 100/0.
８０80/20.

The lactic acid copolymer is obtained by copolymerizing another component copolymerizable with a lactic acid monomer or lactide. Examples of such other components include dicarboxylic acids, polyhydric alcohols, hydroxycarboxylic acids, and lactones having two or more ester bond-forming functional groups.

The dicarboxylic acids include succinic acid, azelaic acid, sebacic acid, terephthalic acid, isophthalic acid and the like.

The polyhydric alcohols include aromatic polyhydric alcohols such as those obtained by addition reaction of bisphenol with ethylene oxide, ethylene glycol, propylene glycol, butanediol, hexanediol, octanediol, glycerin, sorbitan, trimethylolpropane, neomethylol Examples include aliphatic polyhydric alcohols such as pentyl glycol and ether glycols such as diethylene glycol, triethylene glycol, polyethylene glycol and polypropylene glycol.

Examples of the hydroxycarboxylic acid include glycolic acid, hydroxybutyl carboxylic acid, and the like.
And the like described in JP-A-184417.

Examples of the lactone include glycolide, ε-caprolactone glycolide, ε-caprolactone, β-propiolactone, δ-butyrolactone, β- or γ-butyrolactone, pivalolactone, δ-valerolactone and the like.

The hydrolyzability of a lactic acid copolymer is affected by the content of lactic acid units in the copolymer. For this reason, the content of lactic acid units in the lactic acid copolymer is generally 50 mol% or more, preferably 70 mol% or more, although it depends on the copolymerization component used. The mechanical properties and biodegradability of the obtained sheet can be adjusted by the content of lactic acid units and the copolymer component.

Further, for the purpose of obtaining the same effect as in the copolymerization, polylactic acid and another aliphatic polyester may be simply blended. In this case, the contents of the monomers and polylactic acid constituting the other aliphatic polyester are the same as in the case of the copolymerization.

The polylactic acid can be synthesized by a conventionally known method. That is, Japanese Unexamined Patent Publication No. 7-33861, Japanese Unexamined Patent Publication No. Sho 59-96123, and Preliminary Proceedings of Polymer Symposium 44
Vol. 3, pages 3198-3199, can be synthesized by direct dehydration condensation from lactic acid, or ring-opening polymerization of lactic acid cyclic dimer lactide.

When direct dehydration condensation is carried out, L-lactic acid, D
Lactic acid, DL-lactic acid, or a mixture of these may be used. Also, when performing ring-opening polymerization, L-lactide, D-lactide, DL-lactide,
Either meso-lactide or a mixture of these may be used.

The synthesis, purification and polymerization of lactide are described, for example, in US Pat. No. 4,057,537, published European Patent Application No. 261572, Polymer Bulletin, 14, 49.
1-495 (1985), and Makromol Chem., 187, 1611-1628
(1986).

The catalyst used in the polymerization reaction is not particularly limited, but a known lactic acid polymerization catalyst can be used. For example, organic tin compounds such as tin lactate, tin tartrate, tin dicaprylate, tin dilaurate, tin dipalmitate, tin distearate, tin dioleate, tin α-naphthoate, β-tin naphthoate, and tin octylate Zinc powder, zinc halide, zinc oxide, organic zinc compounds; titanium compounds such as tetrapropyl titanate; zirconium compounds such as zirconium isopropoxide; antimony compounds such as antimony trioxide; Bismuth compounds such as bismuth (III) oxide; aluminum compounds such as aluminum oxide and aluminum isopropoxide;

Of these, a catalyst comprising tin or a tin compound is particularly preferred from the viewpoint of activity. The use amount of these catalysts is generally about 0.001 to 5% by weight based on lactide.

The polymerization reaction can be usually carried out at a temperature of 100 ° C. to 200 ° C. in the presence of the above-mentioned catalyst, depending on the type of the catalyst. It is also preferable to carry out two-stage polymerization as described in JP-A-7-247345.

In the present invention, a sheet can be formed by blending a biodegradable aliphatic polyester with an animal and plant repellent which damages rice cultivation. When the repellent is blended in the sheet, the repellent is gradually released as the biodegradable aliphatic polyester is decomposed, so that the repellent action of animals and plants can be continuously obtained. Further, the sheet may have a multilayer structure, and a repellent may be blended in an arbitrary layer. When a repellent is blended in the outermost layer, the sustained release rate of the repellent can be increased to some extent. The animals and plants that damage rice cultivation include moles, crayfish, insects and the like. Examples of such animal and plant repellents include Moglat (trade name, manufactured by Mituto Bussan Co., Ltd.). Each repellent may be blended according to the type of animal or plant to be repelled. The compounding amount of the repellent can be appropriately determined. For example, in the case of Mograt, it is generally about 1 to ³ ml / m ² per unit area of the sheet. Further, such a repellent can be applied to the sheet surface.

Examples of the biodegradable aliphatic polyester in the present invention include poly (α-hydroxy acid) such as polyglycolic acid and polylactic acid; poly (β-hydroxyalkanoate) such as poly-β-hydroxybutyric acid; Poly (ω-hydroxyalkanoate) such as poly-ε-caprolactone; and polyalkylene alkanoate such as polybutylene succinate and polyethylene succinate. These aliphatic polyesters generally have a melting point of 60 to 200 ° C. and a weight average molecular weight of 50,000 to 500,000, preferably about 100,000 to 300,000. With such a molecular weight range, the moldability is good, and
The strength of the sheet obtained is also good.

In the present invention, if necessary, a plasticizer (such as a phthalate ester) and a stabilizer (2-tert-butyl-6- (3-tert-butyl-) may be added to the biodegradable aliphatic polyester. 2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, etc.), coloring agent (red-mouthed graphite, titanium oxide, etc.), filler (calcium carbonate, clay, talc, etc.),
Antioxidants (alkylphenols, organic phosphites, etc.), UV absorbers (salicylates, benzotriazoles, etc.), flame retardants (phosphates, antimony oxide, etc.), antistatic agents, lubricants, foaming agents, antibacterial and antimicrobial agents Conventionally known various additives such as a mold agent and the like can be blended and formed into a sheet. These blending amounts can be appropriately determined according to the purpose of use.

In the present invention, the method of blending the above-mentioned various additives with the aliphatic polyester is not particularly limited, and can be carried out by a conventionally known method. For example, mixing and kneading may be performed using a mill roll, a Banbury mixer, a super mixer, a single screw or twin screw extruder, or the like.

The polymer composition thus kneaded can be formed into a film by a melt extrusion method, a calender method, a solution casting method, or the like. Melt extrusion is performed by the T-die method,
It can be performed at an extrusion temperature of about 100 to 250 ° C. by an inflation method or the like. The extrusion temperature is appropriately determined according to the properties of the aliphatic polyester. Further, a film may be formed into a multilayer sheet by co-extrusion. In this case, a repellent can be blended in any layer of the sheet. The calendering method can be performed using a calender of an inverted L-shape, L-shape, Z-shape, or the like, at a roll temperature substantially equal to the extrusion temperature. In the solution casting method, a polymer is dissolved in a solvent such as chloroform, acetonitrile, toluene, xylene, acetone, dimethylformamide, and dimethylsulfoxide, and then cast on a smooth surface to remove the solvent. The solution casting method is usually preferable to obtain a sheet having a small area.

In the present invention, it is preferable to uniaxially or biaxially stretch the sheet obtained as described above in order to increase the strength of the sheet. In the case of biaxial stretching, sequential biaxial stretching or simultaneous biaxial stretching may be used. The stretching ratio is
Generally, it is about 1.1 to 10 times in one axis direction.

The thickness of the ridge sheet of the present invention is not particularly limited, but is usually about 10 to 1000 μm, preferably 15 to 500 μm, more preferably 20 to 2 μm.
00 μm. Further, the strength and flexibility of the sheet are not particularly limited, but generally, the tensile strength is 5 to 30 k.
gf / mm ² , elongation at break 5 to 1000%, Young's modulus 20
About 500 kgf / mm ² . Preferably, the tensile strength is 5 to 20 kgf / mm ² , the breaking elongation is 50 to 150%,
The Young's modulus is about 200 to 400 kgf / mm ² . With such a range, a sheet having practical mechanical properties as a ridge sheet is obtained.

The ridge sheet of the present invention can be used as follows. A ridge sheet is installed on the ridge prior to paddy rice cultivation, as in the case of conventional rigid polyvinyl chloride or polyethylene sheets. Levee sheet prevents water leakage when paddy fields require flooding. When the flooding is no longer needed, the biodegradation of the aliphatic polyester proceeds to some extent, and the strength of the sheet starts to deteriorate, and it decomposes after a predetermined period of time depending on the thickness of the sheet and the like. As described above, the ridge sheet of the present invention is composed of a biodegradable aliphatic polyester as a main component and is decomposed in a natural environment, so that it is not necessary to collect and remove the sheet after use, and to treat waste. No problem. In addition, when a repellent for animals and plants that damage rice cultivation is incorporated in the sheet, the repellent is gradually released as the aliphatic polyester is decomposed, so that the repellent action of animals and plants is continuously obtained. be able to.

In the present invention, polylactic acid is preferable as the biodegradable aliphatic polyester, and poly-L-lactic acid resin is particularly preferable.

[0033]

The present invention will be described more specifically with reference to the following examples.

100 parts by weight of L-lactide (manufactured by Shimadzu Corporation), 0.05 parts by weight of lauryl alcohol, and 0.2 part by weight of tin octylate ("Cosmos 29" manufactured by Goldschmidt, a catalyst for ring-opening polymerization) Was supplied to a raw material supply section of a twin-screw kneading extruder. The cylinder temperature was 190 ° C., the rotation was 60 rpm in the same direction, and nitrogen gas was supplied from the supply port. The average residence time in the twin screw kneading extruder was 15 minutes. The obtained polymer was extruded from a nozzle having a diameter of 2 mm. After cooling and solidifying, this was cut to obtain a chip of poly-L-lactic acid resin (weight average molecular weight: 180,000, melting point: 178 ° C.).

A repellent Mograt (trade name, manufactured by Santo Bussan Co., Ltd.) was blended with the poly-L-lactic acid resin so that the content per unit area of the obtained ridge sheet was 2 ml / m ² .
It was supplied to an extruder equipped with a T-die, melted at 210 ° C., and extruded to obtain an unstretched sheet having a thickness of 160 μm. This sheet was stretched twice in the longitudinal direction and then twice in the transverse direction to obtain a levee sheet having a thickness of 40 μm and a width of 300 mm.

The obtained ridge sheet was placed on the ridge surface in late March according to a normal paddy rice cultivation calendar.
We planted paddy rice in the month. As with the conventional rigid polyvinyl chloride or polyethylene sheet, there was no water leakage from the paddy field. Investigating the crayfish and other damage on the soil in August revealed no damage, such as holes in the sheets and ridges. After harvesting the rice in September, the cabbage was cultivated with a tillage machine to produce it later. The levee sheet was easily broken because the strength was deteriorated, and most of it was buried in the soil. When a new ridge sheet was installed again in March of the following year, most of the sheets were disassembled.

[0037]

According to the ridge sheet of the present invention, as described above, since it is composed mainly of biodegradable aliphatic polyester, particularly polylactic acid, it can be made of conventional rigid polyvinyl chloride or polyethylene. In addition to having the same function as a ridge sheet similar to a sheet, the work of collecting and removing the sheet after use is not required, and the labor of farmers is greatly reduced. Also, there is no problem of waste disposal.

The ridge sheet using polylactic acid as the aliphatic polyester is excellent in biodegradability, high in biosafety, and lactic acid, which is a decomposition product, is absorbed in vivo, and lactic acid, which is an intermediate decomposition product, is obtained. It is very useful in that the dimer or oligomer of has a plant growth activity.

Further, since the ridge sheet containing the repellent for animals and plants that damages the cultivation of paddy rice is gradually released, the repellent for animals and plants can be continuously obtained.

The ridge sheet according to the present invention is also used for preventing soil collapse of flowerbeds, gutters of waterways, headraces, water on slopes and lands where there is a difference in elevation, and prevention of collapse of ridges on the side walls of riverbeds. Can be used.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location // E02B 13/00 304 E02B 13/00 304Z (71) Applicant 000006172 Mitsubishi Plastics Corporation Chiyoda, Tokyo (72) Inventor Yoshihiro Minami 1 Nishinokyo Kuwabaracho, Nakagyo-ku, Kyoto City, Kyoto Prefecture Inside the Sanjo Plant of Shimadzu Corporation (72) Inventor Toshio Annaka 259, Saito, Oaza, Buzen-shi, Fukuoka Prefecture 1 (72) Inventor Toshiya Ozeki 4-6-27 Toyosaki, Kita-ku, Osaka-shi Kyoritsu Chemical Industry Osaka Sales Office (72) Inventor Jun Takagi 5-8 Mitsuyacho, Nagahama-shi, Shiga Prefecture Mitsubishi Plastics Nagahama Plant Inside

Claims (3)

[Claims] 1. A ridge sheet composed mainly of polylactic acid having a weight average molecular weight of 50,000 to 500,000. 2. A ridge sheet composed mainly of a biodegradable aliphatic polyester and containing a repellent for animals and plants that damages rice cultivation. 3. The levee sheet according to claim 1, wherein a repellent for animals and plants that damages rice cultivation is applied to the surface.