JP2000333542A - Biodegradable cover material for agriculture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject cover material which has high light transmittance and high weather resistance, can easily perfectly be degraded by the actions of microorganisms after used, and can thereby easily be scrapped, by processing a polylactate-based filament non-woven fabric into the cover material having specific trarismittance, weatherability and strength retention rate. SOLUTION: This cover material comprises a polylactate-based filament non-woven fabric, and has a light transmittance of >=70%, a SE 300 of >=5 kg.%/5 cm wide determined by equation I SE 300 is a tensile product (kg.%/5 cm wide) after irradiated for 300 hr; S 300 is the tensile strength (kg/5 cm wide) of a sample after irradiated for 300 hr; E 300 is the tensile elongation (%) of the sample after irradiated for 300 hr; SE 0 is the tensile product (kg.%/5 cm wide) of the sample before irradiated) in a weather resistance test using a weather meter, and a strength retention rate of >=50% determined by equation II.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to agricultural coating materials which are almost completely decomposed by the action of microorganisms after use and are easy to dispose of. The present invention relates to a sheet suitable for an agricultural covering material (commonly referred to as a solid-coated sheet) for coating a sheet.

[0002]

2. Description of the Related Art Conventionally, various nonwoven fabrics have been widely used as agricultural materials such as grass-proof sheets, house lining curtains and sheets for raising rice seedlings. In addition to these uses,
The nonwoven fabric is used as a so-called solid sheet, making use of its air permeability, water permeability, and light weight. With this solid hanging, we cover crops directly and keep warm, water, frost, insect,
It produces effects such as bird protection and wind protection, thereby promoting the growth of crops, improving quality, and increasing sales. It is also used to control the growth rate of crops by selecting the presence or absence of nonwoven fabric coating to adjust the shipping time, to reduce insect damage by coating, to promote pesticide reduction, and to supply safe fresh vegetables.

[0003] In recent years, in the field of agriculture, how to treat various used materials without polluting the natural environment has become a major issue. By the way, the nonwoven fabric as an agricultural covering material as described above is conventionally composed of a thermoplastic polymer such as polyester or polypropylene, and does not decompose in a natural environment, so that a large amount of used material peeled off from a crop. Must be disposed of by a disposal method such as incineration, which is currently burdening the natural environment. In addition, such agricultural coating materials include:
Because it is used after being exposed directly or indirectly to sunlight for a long time, in addition to various performances such as light transmittance and heat retention, weather resistance is required, and a conventional long-fiber nonwoven fabric is used. In many cases, the thermoplastic polymer used for the long-fiber nonwoven fabric alone does not have sufficient weather resistance, and it was necessary to add some weathering agent. However, such materials are composed of a thermoplastic polymer such as polyester or polypropylene, and the added weathering agent is often thermally decomposed during melt spinning,
It is difficult to exhibit sufficient weather resistance. Although it is conceivable to employ a weathering agent having high thermal decomposition resistance, a weathering agent having a sufficient effect has not been found yet.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, and has high translucency and weather resistance. It is almost completely decomposed by the action of microorganisms after use and is easily biodegradable. Provide agricultural coating materials.

[0005]

The gist of the present invention is as follows. It is made of a polylactic acid-based long-fiber nonwoven fabric, has a light transmittance of 70% or more, and is obtained from the following formula (A) in a weather resistance test using a weather meter.
The tensile product SE300 after 5 hours irradiation is 5 kg ·% / 5 cm width or more, and the strength retention rate obtained from the following formula (b) is 50.
% Or more, a biodegradable agricultural coating material. SE300 (kg ·% / 5 cm width) = S300 × E300 (b) Strong retention (%) = (SE300 / SE0) × 100 (b) SE300: Tensile product of the sample after irradiation for 300 hours (kg ·%)
/ 5 cm width) S300: Tensile strength of sample after irradiation for 300 hours (kg
E300: Tensile elongation of sample after irradiation for 300 hours (%) SE0: Tensile product of sample before irradiation (kg ·% / 5cm)
width)

[0006]

The coating material of the present invention is composed of a non-woven fabric made of biodegradable polylactic acid-based long fibers. After the elapse of the period, the covering material is almost completely decomposed by microorganisms, so that it is not necessary to collect and dispose of the laid covering material and dispose of it, and furthermore, it does not pollute the natural environment. The polylactic acid-based polymer constituting the long fiber in the present invention is a thermoplastic aliphatic polyester having biodegradability, for example, poly (α-hydroxy acid) or a copolymer containing the polymer element as a main repeating unit. Coalescence. Specifically, poly (D-lactic acid), poly (L-lactic acid), a copolymer of D-lactic acid and L-lactic acid, a copolymer of D-lactic acid and hydroxycarboxylic acid, -Among the copolymers of lactic acid and hydroxycarboxylic acid or the copolymers of D-lactic acid, L-lactic acid and hydroxycarboxylic acid, those having a melting point of 80 ° C or higher are preferred. Here, examples of the hydroxycarboxylic acid in the case of a copolymer of lactic acid and hydroxycarboxylic acid include glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, hydroxyheptanoic acid, and hydroxycaprylic acid. Such a polylactic acid-based polymer has a number average molecular weight of about 20,000 or more, preferably 40,0.
It is preferable from the viewpoint of the fiber properties to obtain those having a value of 00 or more, and from the viewpoint of the spinning property during production.

The long fibers constituting the nonwoven fabric of the present invention preferably have a birefringence of 10 × 10 ⁻³ or more. The birefringence indicates the degree of molecular orientation of the polylactic acid-based polymer, and by setting the length in such a range, a long fiber or a nonwoven fabric has mechanical properties such as tensile strength that are practically sufficient. It is provided in.

The long fibers constituting the nonwoven fabric of the present invention preferably have a crystallinity of 10 to 40%. The crystallinity in this range can be achieved by adding a crystal nucleating agent such as talc, boron nitride, calcium carbonate, magnesium carbonate, and titanium oxide to the polylactic acid-based polymer. Addition of a nucleating agent promotes fiber crystallization, improves the mechanical properties and heat resistance of the obtained coating material, and furthermore, between the spun yarns in the melt spinning / cooling process during production. It is more preferable that fusion (so-called blocking) can be prevented from occurring. The amount of such a crystal nucleating agent is desirably in the range of 0.1 to 3.0% by weight, preferably 0.5 to 2.0% by weight. Incidentally, the polylactic acid-based polymer of the present invention, if necessary, other additives, such as matting agents and pigments, coloring agents, flame retardants, various additives such as other crystal nucleating agents, the effect of the present invention. You may add in the range which does not impair.

The long fibers constituting the nonwoven fabric according to the present invention may be those having a fiber form of a polylactic acid-based polymer alone or a composite of two or more polylactic acid-based polymers having different melting points. In addition, the cross-sectional shape is a hollow cross-section, an irregular cross-section, a side-by-side composite cross-section,
Multi-layer composite cross section, core-sheath type composite cross section, split type composite cross section, etc.
An arbitrary fiber cross-sectional shape can be adopted depending on the purpose and application, but from the viewpoint of biodegradability, a hollow cross-section, a modified cross-section, a split composite cross-section, or the like is preferable. In particular, the melting point is 20
In the case of a fiber in which two kinds of polylactic acid-based polymers different from each other by at least ℃ are combined in a core-sheath type, a high-melting polymer is used as a core component, and a low-melting polymer having a melting point lower than the polymer by 20 ° C or more is used as a sheath component. By doing so, the mechanical properties of the nonwoven fabric are improved, and as a result, when used as an agricultural coating material, the mechanical properties of the coating material can be maintained even after a certain period of time, which is preferable.

[0010] The filaments constituting the nonwoven fabric of the present invention preferably have a single-fiber fineness in the range of 2 to 15 denier. If the single-fiber fineness is less than 2 denier, the number of constituent fibers per unit area in the obtained nonwoven fabric increases, so that the inter-fiber voids become small and the light transmittance of the nonwoven fabric decreases. On the other hand, if the single yarn fineness exceeds 15 denier, not only the cooling property of the spun yarn in the melt spinning process is poor, but also the inter-fiber void is large because the number of constituent fibers per unit area in the obtained nonwoven fabric is reduced. Become
The mechanical properties, heat retention, and frost protection required for the coating material are inferior. For these reasons, the single yarn fineness is 2 to 15
Denier, preferably 5 to 12 denier, more preferably 6 to 10 denier. The coating material of the present invention preferably has a basis weight in the range of 10 to 30 g / m ² . When the basis weight is less than 10 g / m ² , the number of constituent fibers per unit area in the nonwoven fabric is reduced, so that the interfiber space is increased, the heat retention is inferior, and the mechanical properties are also reduced. On the other hand, if the basis weight exceeds 30 g / m ² , the number of constituent fibers per unit area in the nonwoven fabric increases, so that the inter-fiber voids become small, the light transmittance and the air permeability are poor, and when used as a coating material. , Hinders the growth of crops. Note that the basis weight and the above-described single-fiber fineness are particularly closely related. For example, when the single-fiber fineness is small, the same non-woven fabric becomes a dense nonwoven fabric, but it is necessary to consider that the light transmittance is reduced. When the mechanical properties of the fiber itself are low, it is necessary to increase the single-fiber fineness and the basis weight in order to obtain a practically constant strength as a nonwoven fabric. These basis weight nonwoven fabrics may be obtained in one step, or may be obtained by laminating two or more nonwoven fabrics.

[0011] The coating material of the present invention is composed of a nonwoven fabric having a basis weight in the above-mentioned range formed of polylactic acid-based long fibers of the above-mentioned single-filament fineness, and has a light transmittance of 70% or more. If the light transmittance is less than 70%, the covering material cannot sufficiently transmit the sunlight, which hinders the growth of the crop, which is not preferable.

The coating material of the present invention can be obtained from the above formula (A) in a weather resistance test using a weather meter.
Tensile product SE300 after irradiation for 00 hours is 5kg.% / 5cm
It has a width of not less than 50% and a strength retention of at least 50% determined from the above formula (b). The weathering resistance of a coated material is an index that indicates whether the strength and elongation of the coated material do not decrease due to climatic changes or the like before the material collapses due to biodegradation. If the elongation decreases, abnormalities such as breakage are likely to occur, which will adversely affect the translucency and heat retention of the covering material in the process of using it as an agricultural covering material, and hinder the growth of the crop. Become. Therefore, in the present invention, the tensile product SE300
Is 5 kg ·% / 5 cm width or more, and the strength retention rate is 5
When the tensile product SE300 is less than 5 kg ·% / 5 cm width and / or the strength retention rate is less than 50%, the strength decreases with time when used as an agricultural covering material,
This will adversely affect the growth of the crop and shorten the useful life of the covering material.

In the coating material of the present invention, the long fibers constituting the nonwoven fabric may be, for example, colored fibers containing a black pigment or a black dye typified by carbon black.
By using such colored fibers, the nonwoven fabric becomes black, and when used as an agricultural covering material, the covering material easily absorbs solar heat, so that a heat retaining effect is obtained, which is effective for growing crops. When the amount of such a pigment or dye is too large, the spinnability at the time of melt spinning is reduced. Therefore, the amount of the pigment or dye is 0.1 to 3.0% by weight, preferably 0.5 to 2. It is important that the content be in the range of 0% by weight. The colored fiber is preferably a spun fiber obtained by melt-spinning a polymer in which the black pigment has been previously kneaded. When such a soaked fiber is used, since the pigment is previously contained in the fiber, it is not necessary to perform post-processing such as dyeing, and problems such as heat deterioration during dyeing and an increase in the number of manufacturing steps may occur. Absent.

The nonwoven fabric constituting the coating material of the present invention is such that the web made of such long fibers is partially thermocompression-bonded and the form of the nonwoven fabric is maintained. That is, the nonwoven fabric is bonded by hot-pressure only in the point-formed fusion bonding area formed partially, and such a structure improves the shape retention of the nonwoven fabric. In such partial thermocompression bonding, a point-like fusion zone is formed on the nonwoven web by an embossing process or an ultrasonic fusion process. Specifically, the heated embossing roll and the surface A method of forming a point fusion area between fibers through a web between a smooth metal roll or a point fusion area between fibers corresponding to a pattern portion by applying high frequency by ultrasonic waves on a pattern roll. The method of forming is adopted.

Next, a method for producing the coating material of the present invention will be described. First, the long-fiber nonwoven fabric for constituting the coating material of the present invention can be efficiently produced by a so-called spunbond method. That is, the above-mentioned polylactic acid-based polymer is heated and melted, discharged from the spinneret, and the obtained spun yarn is cooled using a conventionally known cooling device such as a horizontal spraying or an annular spraying. Using a suction device such as an air sucker or other well-known traction means, the fiber is finely drawn, and then the yarn group discharged from the traction means is spread, and then spread on a moving stacking device such as a conveyor made of a mesh screen. The web is deposited. Next, the web formed on the moving deposition apparatus is partially heated using a partial thermocompression bonding device such as a heated embossing roll and a smooth surface metal roll or a partial thermocompression bonding device such as an ultrasonic fusion bonding device. A long-fiber nonwoven fabric is obtained by performing a thermocompression treatment.

In the present invention, when producing a long-fiber nonwoven fabric by a so-called spunbonding method, the drawing speed of the spun yarn is preferably set to 1000 to 6000 m / min.
When the drawing speed at the time of drawing and thinning the spun yarn is less than 1000 m / min, the molecular orientation and crystallization of the polymer do not proceed,
The mechanical properties of the resulting nonwoven fabric are not improved, and the decomposition rate is too high. When the drawing speed is 3000 m / min or more, the molecular orientation of the polymer proceeds more and the birefringence becomes 10 × 10 ⁻³ or more, and the mechanical properties of the obtained nonwoven fabric are further improved, which is more preferable. On the other hand, when the towing speed is 600
If it exceeds 0 m / min, the spinnability deteriorates sharply and yarn breakage occurs. In addition, it is more preferable to add the above-mentioned nucleating agent to the polymer because the cooling property of the spun yarn at the time of melt spinning is improved.

[0017]

The biodegradable agricultural coating material of the present invention is composed of a non-woven fabric made of polylactic acid long fibers, so that after a certain period of use, the coating material is almost completely decomposed by biodegradation. This eliminates the need to collect and dispose of the coating material and dispose of it, and does not pollute the natural environment. In addition, since the light transmittance is 70% or more, sunlight can be sufficiently transmitted, and insufficient growth of the crop can be prevented. Further, since the tensile product SE300 in the weather resistance test using a weather meter is 5 kg ·% / 5 cm width or more and the strength retention rate is 50% or more, the strength of the coating material is prevented from decreasing and the service life is extended. can do.

[0018]

The present invention will be described below in detail with reference to examples. The present invention is not limited by these examples. In the examples, each property value was obtained as follows. (1) Melting point (° C.): The temperature giving the extreme value of the melting endothermic curve obtained by measuring the temperature at a heating rate of 20 ° C./min using a differential scanning calorimeter DSC-7 manufactured by Perkin Elmer Co., Ltd. ° C). (2) Melt flow rate of polylactic acid (hereinafter abbreviated as MFR) (g / 10 min): ASTM D1238
It was measured according to the method described in (L). The melting temperature was 210 ° C. (3) Intrinsic viscosity of polyethylene terephthalate: Measured at a sample concentration of 0.5 g / dl and a temperature of 20 ° C. using an equal weight mixed solution of phenol and ethane tetrachloride as a solvent. (4) Polyethylene melt index (hereinafter MI)
Abbreviated. ) (G / 10 min): ASTM D1238
The measurement was performed according to the method described in (E). (5) Single yarn fineness (denier): The diameter of 50 fibers in a web state was measured with a microscope, and the average value of the fineness obtained by density correction was defined as single yarn fineness (denier). (6) Birefringence: The birefringence of the long fiber was measured by a conventional method using a polarizing microscope equipped with a Belek compensator and using tricresyl phosphate as an immersion liquid. (7) Crystallinity (% by weight): The crystallinity (% by weight) of long fibers was measured by the following method. That is, the long fiber to be measured is powdered and the Al sample frame (20 mm × 18 mm ×
(0.5 mm), and the measurement sample held in the vertical direction was irradiated with Cu-Kα rays from a right angle direction by a RAD-rB type X-ray generator manufactured by Rigaku Corporation. On the light receiving side, a curved graphite monochromator was used. Then, scanning was performed in the range of 2θ = 5 to 125 °, and the crystallinity (% by weight) was determined by the Ruland method. (8) Weight per unit area (g / m ² ): 10 samples from the standard sample
After preparing 10 sample pieces of 10 cm × 10 cm and reaching equilibrium moisture, the weight (g) of each sample piece was weighed, and the average value of the obtained values was converted into a unit area to obtain a basis weight ( g /
m ² ). (9) Tensile strength (kg / 5cm width): JIS L19
The measurement was carried out according to the strip method described in No. 06. That is, a test piece having a sample length of 20 cm and a sample width of 5 cm was formed at 10 points in the longitudinal direction of the nonwoven fabric, and a constant-speed elongation type tensile tester (Tensilon UTM-4-1- manufactured by Toyo Baldwin Co., Ltd.) was used.
100), each sample piece is stretched in the longitudinal direction of the nonwoven fabric at a holding interval of 10 cm and a pulling speed of 20 cm / min.
The maximum tensile strength (kg / 5 cm width) was determined, and the average of the obtained maximum tensile strengths was used as the tensile strength (kg / 5 cm) of the nonwoven fabric.
cm width). (10) Tear strength (kg): Measured according to the Benziram method described in JIS L1096. That is, five test pieces each having a sample length of 6.5 cm and a sample width of 10 cm were prepared in the longitudinal direction of the nonwoven fabric, and the tear strength was determined for each sample piece in the longitudinal direction of the nonwoven fabric, and the average value obtained was obtained. Was defined as the tear strength (kg) of the nonwoven fabric. (11) Light transmittance (%): The illuminance (B) when the sample is placed between the light source (reflamp) and the illuminometer of the light receiving unit and the illuminance (A) when the sample is not placed are measured. , The following formula (c)
The light transmittance (%) was determined from. Light transmittance (%) = (B / A) × 100 (c) (12) Tensile product (kg ·% /
(5 cm width): Tensile product SE300 after irradiation for 300 hours, which is an index of weather resistance, was determined as follows. That is, in a weather resistance test using a weather meter, the tensile strength S300 (kg / 5 cm width) of the sample after irradiation for 300 hours and the tensile elongation E300 (%) of the sample after irradiation for 300 hours were measured at a constant-speed elongation. It was measured using a test machine (Tensilon UTM-4-1-100 manufactured by Toyo Baldwin Co., Ltd.) and the tensile product SE300 (kg ·
% / 5 cm width). (13) Strength retention (%): The strength retention, which is an index of weather resistance, was determined as follows. That is, in a weather resistance test using a weather meter, the tensile product (strength × elongation) SE0 (kg ·% / 5 cm width) of the sample before light irradiation was 3%.
Tensile product (Strength × Elongation) SE300 of sample after irradiation for 00 hours
(Kg.% / 5 cm width) and a constant-speed elongation type tensile tester (Tensilon UTM-4-1-10 manufactured by Toyo Baldwin Co., Ltd.)
0), and the strength retention (%) was determined from the above equation (b). (14) Cooling property: The spun yarn was visually observed, and the following 3
It was evaluated on a scale. ；: No cohesive yarn was observed. Δ: A slight amount of cohesive yarn was observed. X: Most parts adhered, and opening was impossible. (15) Spreadability: The nonwoven web formed by the spun yarn discharged from the spreader was visually observed and evaluated according to the following three grades. ；: Most of the constituent fibers were separated, and no cohesive yarn or convergent yarn was observed. Δ: Cohesive yarn or convergent yarn was slightly observed. ×: Most of the constituent fibers adhered and the spreadability was poor. (16) Biodegradability: The sample was buried in the soil,
After 3 years and 3 years, take out and observe the form of the specimen,
The following three stages were used for evaluation. ：: The shape of the nonwoven fabric was retained until two years after the embedding of the sample, and it was broken after three years. Δ: The shape of the nonwoven fabric was disintegrated by two years after the sample piece was embedded. X: The nonwoven fabric was retained even after 3 years from the embedding of the sample.

Example 1 Polylactic acid having a melting point of 169 ° C., a number average molecular weight of 59,100 and an MFR of 37 g / 10 min (D-form / L-form = 1.3 / 9)
8.7) (hereinafter abbreviated as PLA) as a core component,
Polylactic acid having a melting point of 140 ° C., a number average molecular weight of 60,100 and an MFR of 51 g / 10 min (D-form / L-form = 7.7 / 9)
2.3) (hereinafter abbreviated as PLA), a core-sheath type composite continuous fiber having a sheath component was melt-spun. Specifically, using a master batch containing 20% by weight of titanium oxide kneaded, the content of titanium oxide to polylactic acid was 0.5% by weight.
The high-melting polylactic acid and the low-melting polylactic acid having a titanium oxide content of 0.5% by weight were melted using separate extruder-type melt extruders, respectively. ° C, single hole discharge amount 3.
Under a condition of 7 g / min, the high melting point polylactic acid was melt-spun from the core-sheath type composite spinneret such that the core was low and the low melting point polylactic acid was a sheath [composite ratio (weight ratio) = 1/1]. After the spun yarn is cooled by the cooling device, it is subsequently drawn and thinned at a drawing speed of 4800 m / min by an air sucker provided below the spinneret, and is spread using a known spreader and moved. It was collected and deposited as a web on a screen conveyor. Next, the web was passed through a partial thermocompression bonding device composed of an embossing roll heated to a temperature of 105 ° C. and a metal roll having a smooth surface, and subjected to a partial thermocompression bonding under a linear pressure of 60 kg / cm. A long-fiber nonwoven fabric having a fineness of 7.0 denier and a basis weight of 15 g / m ² was obtained. Table 1 shows various characteristics of the obtained long-fiber nonwoven fabric.

Example 2 Polylactic acid having a melting point of 168 ° C., a number average molecular weight of 60,800 and an MFR of 44 g / 10 min (D-form / L-form = 1.8 / 9)
8.2) is used as a core component polymer and has a melting point of 150
° C, number average molecular weight 60100, MFR 55g / 10
In the same manner as in Example 1 except that the polylactic acid (D-form / L-form = 4.5 / 95.5) was used as the sheath component polymer and the partial thermocompression treatment temperature was set to 120 ° C. Fineness is 7.
A long-fiber nonwoven fabric having a basis weight of 0 denier and 15 g / m ² was obtained. Table 1 shows various characteristics of the obtained long-fiber nonwoven fabric.

Example 3 Polylactic acid having a melting point of 169 ° C., a number average molecular weight of 59,100 and an MFR of 37 g / 10 min (D-form / L-form = 1.3 / 9)
8.7) was mixed and weighed using a master batch containing 20% by weight of titanium oxide so that the titanium oxide content with respect to polylactic acid was 0.5% by weight, and melted using an extruder-type melt extruder. Thereafter, under the conditions of a spinning temperature of 200 ° C. and a single-hole discharge rate of 3.7 g / min, melt spinning was performed from a spinneret. After the spun yarn is cooled by the cooling device, it is subsequently drawn and thinned at a drawing speed of 4800 m / min by an air sucker provided below the spinneret, and is spread using a known spreader and moved. It was collected and deposited as a web on a screen conveyor. Next, the web was passed through a partial thermocompression bonding device composed of an embossing roll heated to a temperature of 140 ° C. and a metal roll having a smooth surface, and a linear pressure of 6 mm.
A partial thermocompression treatment is performed under the condition of 0 kg / cm, and the single yarn fineness is 7.0 denier.
g / m ² long fiber nonwoven fabric was obtained. Table 1 shows various characteristics of the obtained long-fiber nonwoven fabric.

Example 4 Single hole discharge rate: 5.0 g / min, single fiber fineness: 9.3 denier
20g / m ^TwoExample 1 except that
Similarly, a long-fiber nonwoven fabric was obtained. Obtained long fiber non-woven
Table 1 shows various properties of the cloth.

Example 5 A long-fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the single hole discharge rate was 1.6 g / min and the single yarn fineness was 3.0 denier. Table 1 shows various characteristics of the obtained long-fiber nonwoven fabric.

Example 6 Polylactic acid having a melting point of 170 ° C., a number average molecular weight of 45,000 and an MFR of 60 g / 10 min (D-form / L-form = 1.0 / 9)
9.0), except that the spinning temperature was 210 ° C., the single hole discharge amount was 1.8 g / min, the drawing speed was 5500 m / min, and the single yarn fineness was 3.0 denier. Thus, a long-fiber nonwoven fabric was obtained. Table 1 shows various characteristics of the obtained long-fiber nonwoven fabric.

Comparative Example 1 Polyethylene terephthalate having a melting point of 258 ° C., an intrinsic viscosity of 0.7 and a titanium oxide content of 0.3% by weight (hereinafter referred to as “polyethylene terephthalate”)
Abbreviated as PET. ) Having a melting point of 128 ° C.
High-density polyethylene having an MI of 25 g / 10 min (hereinafter referred to as P
Abbreviated as E. ) Was melt-spun out. Specifically, after the above PET and the above PE were respectively melted using separate extruder type melt extruders, the spinning temperature was 290 ° C., and the single hole discharge amount was 3.5 g /
Under the conditions of minute, the PET is a core and the PE is a sheath (composite ratio (weight ratio) = 2/1) and melt spun from a core-sheath composite spinneret, and the spun yarn is cooled by a cooling device. After cooling, the traction speed was set to 3 with the air sack provided below the spinneret.
It was drawn and thinned at 500 m / min, opened using a known opening machine, and collected and deposited as a web on a moving mesh screen conveyor. The web is then heated to a temperature of 118
Pass through a partial thermocompression bonding device consisting of an embossing roll heated to ℃ and a metal roll having a smooth surface, and a linear pressure of 30 kg / cm.
7. Partial thermocompression treatment is performed under the conditions described above to obtain a single yarn fineness of 8.
A long-fiber nonwoven fabric having a basis weight of 9 denier long fibers and having a basis weight of 15 g / m ² was obtained. Table 1 shows various characteristics of the obtained long-fiber nonwoven fabric.

[0026]

[Table 1]

Each of the coating materials obtained in Examples 1 to 6 had a light transmittance of 70% or more, and when used as a coating material for agriculture, had good heat retention and good growth of crops. Also, the tensile product SE300 after irradiation for 300 hours showing weather resistance was as high as 5 kg ·% / 5 cm width or more, the strength retention was as high as 50% or more, and the weather resistance was also good. And since it is formed of a non-woven fabric made of polylactic acid fiber having biodegradability, it is buried in the soil and completely decomposed after 3 years,
There was no need for waste disposal such as incineration. On the other hand, since the coating material obtained in Comparative Example 1 used polyethylene terephthalate and high-density polyethylene as the polymer of the nonwoven fabric constituent fibers, the coating material was excellent in mechanical properties such as tensile strength and tear strength, but was particularly strong. The rate was low and the weather resistance was poor. In addition, since non-biodegradable polyethylene terephthalate is used, it is buried in the soil and does not decompose in the soil even after a certain period of time, and it is necessary to collect and incinerate the covering material after use. It also pollutes the natural environment.

[0028]

Since the biodegradable agricultural covering material of the present invention is composed of a non-woven fabric made of polylactic acid long fibers, the sheet after a certain period of use is almost completely decomposed by biodegradation. In addition, it is possible to eliminate the trouble of collecting and covering the coating material and performing disposal treatment, and furthermore, does not pollute the natural environment.
In addition, since the light transmittance is 70% or more, sunlight can be sufficiently transmitted, and insufficient growth of the crop can be prevented. Further, as the tensile product SE300 in the weather resistance test using a weather meter is 5 kg ·% / 5 cm width or more and the strength retention rate is 50% or more, the weather resistance is excellent, the deterioration is small, and long-term use is possible. Can withstand.

Continued on front page F-term (reference) 2B024 DA03 DB01 DB03 2B029 EB01 EB08 EC06 EC12 LA01 RA03 RA07 4L041 AA08 AA09 AA15 BA02 BA05 BA21 BC06 BC20 BD03 BD11 BD20 CA05 CA10 CB05 CB28 DD01 DD05 DD21 4L047 AA21 AACB CB07

Claims (5)

[Claims] 1. A tensile product SE300 of 5 kg after irradiation for 300 hours in a weather resistance test using a weather meter, which is made of a polylactic acid-based long-fiber nonwoven fabric and has a light transmittance of 70% or more. A biodegradable agricultural covering material characterized by having a width of not less than% / 5 cm and a strength retention of at least 50% determined from the following formula (b). SE300 (kg ·% / 5 cm width) = S300 × E300 (b) Strong retention (%) = (SE300 / SE0) × 100 (b) SE300: Tensile product of the sample after irradiation for 300 hours (kg ·%)
/ 5 cm width) S300: Tensile strength of sample after irradiation for 300 hours (kg
E300: Tensile elongation of sample after irradiation for 300 hours (%) SE0: Tensile product of sample before irradiation (kg ·% / 5cm)
width) 2. The polylactic acid comprises poly (D-lactic acid), poly (L-lactic acid), a copolymer of D-lactic acid and L-lactic acid,
A copolymer of D-lactic acid and hydroxycarboxylic acid, and L-
A copolymer of lactic acid and hydroxycarboxylic acid, and a copolymer of D-lactic acid, L-lactic acid and hydroxycarboxylic acid, or a blend thereof. The biodegradable agricultural coating material according to claim 1. 3. A core-sheath composite length in which a polylactic acid-based long fiber has a polylactic acid-based polymer A as a core component and a polylactic acid-based polymer B having a melting point lower than that of the polymer A by 20 ° C. or more as a sheath component. The biodegradable agricultural covering material according to claim 1, which is a fiber. 4. The polylactic acid long fiber has a birefringence of 10 × 1.
0 ^-3, and biodegradable agricultural covering material according to claim 1, 2 or 3 crystallinity is 10% or more. 5. The single-filament fineness of the polylactic acid-based long fiber is 2 to 15.
Denier, and the basis weight of the coating material is 10 to 30 g / m
^The biodegradable agricultural covering material according to any one of claims 1, 2, 3 and 4, wherein the number is 2.