JP3494404B2 - Biodegradable agricultural coating materials - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a covering material for agriculture, which is almost completely decomposed by the action of microorganisms after use and is easy to dispose of. In particular, in open field cultivation, tunnel cultivation or greenhouse cultivation, a crop is directly The present invention relates to a sheet suitable for an agricultural coating material (commonly referred to as a solid sheet) for coating a sheet.

[0002]

2. Description of the Related Art Conventionally, various non-woven fabrics have been widely used as agricultural materials such as weed-preventing sheets, lining curtains for greenhouses, and sheets for raising rice seedlings. Besides these uses,
The non-woven fabric is used as a so-called sticking sheet by taking advantage of its breathability, water permeability and lightness. This solid coating covers the crops directly and keeps them warm, water, frost, insects,
By producing effects such as bird protection and wind protection, it aims to promote the growth of crops, improve their quality, and increase their yield. It is also used to control the growth rate of crops by adjusting the presence or absence of non-woven fabric to adjust the shipping time, or to reduce insect damage by coating to promote pesticide reduction and to supply safe fresh vegetables.

In recent years, also in the agricultural field, how to treat various used materials without polluting the natural environment has become a major issue. By the way, the non-woven fabric as the agricultural coating 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 a large amount of used material peeled from the crop is used. However, the current situation is that this must be disposed of by a disposal method such as incineration, which is burdening the natural environment. Also, such agricultural coating materials,
Since it is used by being exposed directly or indirectly to sunlight for a long time, it is required to have weather resistance in addition to various performances such as translucency and heat retention. In such a sheet, the thermoplastic polymer used in the long-fiber nonwoven fabric often does not have sufficient weather resistance by itself, and it is necessary to add some weather resistance agent. However, such a material is composed of a thermoplastic polymer such as polyester or polypropylene, and the added weatherproofing agent is often thermally decomposed during melt spinning,
It is difficult to develop sufficient weather resistance. Although it may be possible to adopt a weathering agent having a high thermal decomposition resistance, the current situation is that no weathering agent having a sufficient effect has been found yet.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, has high translucency and weather resistance, and is biodegradable which is easily decomposed by the action of microorganisms after use and is easily disposed of. It is intended to provide a covering material for agriculture.

[0005]

The gist of the present invention is as follows. Birefringence of polylactic acid long fibers
The rate is 10 × 10 ⁻³ or more and the crystallinity is 10% or more.
Made of a polylactic acid-based long-fiber non-woven fabric with a light transmittance of 70%
As described above, in the weather resistance test using the weather meter, the tensile product SE after irradiation for 300 hours, which is obtained from the following formula (a)
300 is 5 kg /% / 5 cm width or more, and the following formula (b)
A biodegradable coating material for agriculture, which has a high retention rate of 50% or more. SE300 (kg ・% / 5cm width) = S300 × E30
0 (a) Strong retention rate (%) = (SE300 / SE0) x 100
(B) SE300: Tensile product of the sample after irradiation for 300 hours (kg
% / 5cm width) S300: Tensile strength of the sample after irradiation for 300 hours (kg
/ 5 cm width) E300: Tensile elongation of the sample after irradiation for 300 hours (%) SE0: Tensile product of the sample before irradiation (kg ·% / 5 cm width)

[0006]

DETAILED DESCRIPTION OF THE INVENTION The coating material of the present invention is composed of a non-woven fabric made of polylactic acid-based long fibers having biodegradability. After the lapse of the period, the covering material is almost completely decomposed by microorganisms, and it is possible to save the trouble of collecting and disposing of the laid covering material, and to avoid contaminating the natural environment. The polylactic acid-based polymer that constitutes the long fibers in the present invention is a thermoplastic aliphatic polyester having biodegradability, and for example, poly (α-hydroxy acid) or a copolymerized polymer having the polymer element as a main repeating unit. An example is 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, and L Of the copolymer of lactic acid and hydroxycarboxylic acid or the copolymer of D-lactic acid, L-lactic acid and hydroxycarboxylic acid, a polymer having a melting point of 80 ° C. or higher is preferable. 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 40,000.
It is preferable from the standpoint of fiber characteristics that a fiber number of 00 or more can be obtained, and from the standpoint of spinnability during production.

[0007] long fibers constituting the nonwoven fabric in the present invention, Ru der its birefringence 10 × 10 ^-3 or more. This birefringence indicates the degree of molecular orientation of the polylactic acid-based polymer, and by setting it in such a range, mechanical properties such as tensile strength are practically sufficient for long fibers, that is, nonwoven fabrics. Be equipped with.

The long fibers constituting the nonwoven fabric in the present invention have a crystallinity of 10% or more, preferably 10 to 40%. The crystallinity in this range is achieved by adding a crystal nucleating agent such as talc, boron nitride, calcium carbonate, magnesium carbonate, or titanium oxide to the polylactic acid polymer. Addition of a crystal nucleating agent can promote crystallization of the fiber, improve the mechanical properties and heat resistance of the obtained coating material, and further improve the inter-spinning yarn spacing in the melt-spinning / cooling process during production. It is more preferable because it is possible to prevent the occurrence of fusion (so-called blocking). The addition 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. In the polylactic acid-based polymer of the present invention, if necessary, other additives such as a matting agent, a pigment, a colorant, a flame retardant, and other additives such as a crystal nucleating agent may be added to the effect of the present invention. You may add in the range which does not spoil.

The long fibers constituting the non-woven fabric in the present invention may be composed of a polylactic acid type polymer alone in the fiber form, or may be a composite of two or more kinds of polylactic acid type polymers having different melting points. In addition, the cross-sectional shape, in addition to the usual round cross section, hollow cross section, irregular cross section, parallel type composite cross section,
Multi-layer composite cross section, core-sheath composite cross section, split composite cross section, etc.
Any fiber cross-sectional morphology may be adopted depending on the purpose and application, but from the viewpoint of biodegradability, hollow cross-sections, irregular cross-sections, split-type composite cross-sections and the like are preferable. In particular, the melting point is 20
In the case of a fiber in which two kinds of polylactic acid-based polymers differing by ℃ or more are core-sheath type, a high melting point polymer is used as a core component, and a low melting point polymer having a melting point lower than that of 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, the mechanical properties of the covering material can be maintained even after a certain period of time when used as an agricultural covering material, which is preferable.

The long fibers constituting the nonwoven fabric in the present invention preferably have a single yarn fineness in the range of 2 to 15 denier. If the single yarn 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 void becomes small and the light transmittance of the nonwoven fabric decreases. On the other hand, when the single yarn fineness exceeds 15 denier, not only is the cooling property of the spun yarn reduced in the melt spinning process, but also the number of constituent fibers per unit area in the obtained nonwoven fabric decreases, resulting in large interfiber voids. Becomes
The mechanical properties, heat retention and frost resistance required as a covering material will be poor. For these reasons, the single yarn fineness is 2 to 15
Denier, preferably 5 to 12 denier, and more preferably 6 to 10 denier. The coating material of the present invention preferably has a basis weight 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 non-woven fabric decreases, the inter-fiber voids increase, the heat retention becomes poor, and the mechanical properties also deteriorate. On the other hand, when the basis weight exceeds 30 g / m ² , the number of constituent fibers per unit area in the non-woven fabric increases and the inter-fiber void becomes small, resulting in poor light transmission and air permeability, and when used as a covering material. , Hinder the growth of crops. It should be noted that there is a particularly close relationship between the basis weight and the above-mentioned single yarn fineness. For example, when the single yarn fineness is small, a dense non-woven fabric will be obtained even with the same basis weight, but it is necessary to consider that the light transmittance decreases. Further, when the mechanical properties of the fiber itself are low, it is necessary to increase the single yarn fineness and the basis weight in order to obtain a practically constant strength as a nonwoven fabric. The non-woven fabric having these fabric weights may be obtained in one step, or may be obtained by laminating two or more non-woven fabrics.

The coating material of the present invention is composed of a non-woven fabric formed of polylactic acid-based long fibers having the above-mentioned single yarn fineness and having a basis weight in the above range, and further has a light transmittance of 70% or more. When the light transmittance is less than 70%, the covering material cannot sufficiently transmit the sun rays, which hinders the growth of crops, which is not preferable.

The coating material of the present invention is 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
The width is not less than the width, and the strength retention obtained from the above formula (b) is not less than 50%. The weather resistance of the covering material is an index indicating whether the strength and elongation of the covering material are not deteriorated due to climate change, etc. before the covering material collapses due to biodegradation. And, if the elongation decreases, abnormalities such as damage are likely to occur, which adversely affects the translucency and heat retention of the covering material during the process of using it as an agricultural covering material, and interferes with the growth of crops. Become. Therefore, in the present invention, the above tensile product SE300 is used.
Is more than 5 kg /% / 5 cm width, and the above strength retention rate is 5
When it is 0% or more, the tensile product SE300 is less than 5 kg ·% / 5 cm width and / or the strength retention is less than 50%, the strength decreases with time when used as an agricultural coating material,
This will adversely affect the growth of the crop and shorten the useful life of the covering material.

In the covering material of the present invention, the long fibers constituting the non-woven fabric may be colored fibers containing a black pigment or a black dye typified by carbon black, for example.
By using such colored fibers, the non-woven fabric becomes black, and when used as an agricultural coating material, the coating material easily absorbs solar heat, so that a heat retaining effect is obtained and it is effective for growing crops. Addition of such pigments or dyes lowers the spinnability during melt spinning if the amount added is too large, so the amount added is 0.1-3.0% by weight, preferably 0.5-2. It is important to set it in the range of 0% by weight. It is preferable that the colored fiber is an original fiber obtained by melt spinning a polymer in which the black pigment is kneaded in advance. When such a dyed fiber is used, since the pigment is contained in advance in the fiber, there is no need to perform post-processing such as dyeing, and problems such as heat deterioration during dyeing and an increase in manufacturing processes may occur. Absent.

The non-woven fabric constituting the covering material of the present invention is one in which the web made of such long fibers is partially thermocompression-bonded to retain the form of the non-woven fabric. That is, this non-woven fabric is thermo-bonded only in the spot-shaped fused regions that are partially formed, and such a structure improves the shape retention of the non-woven fabric. Such partial thermocompression bonding is one in which a dot-shaped fused area is formed on the nonwoven web by an embossing treatment or an ultrasonic welding treatment, and specifically, the heated embossing roll and the surface are A method of forming a point fusion area between fibers through a web with a smooth metal roll, or applying a high frequency by ultrasonic waves on a pattern roll to form a point fusion area between fibers corresponding to a pattern part. The method of forming is adopted.

Next, a method of manufacturing the covering material of the present invention will be described. First, the long-fiber nonwoven fabric for forming the covering material of the present invention can be efficiently manufactured by the so-called spunbond method. That is, the above-mentioned polylactic acid-based polymer is heated and melted and discharged from the spinneret, and the obtained spun yarn is cooled using a conventionally known cooling device such as horizontal spraying or annular spraying, After pulling and thinning using a suction device such as an air sucker or other known pulling means, the yarn group discharged from the pulling means is opened, and then spread on a moving deposition device such as a conveyor consisting of mesh screens. The web is deposited. Then, the web formed on the moving deposition apparatus is partially heated by using a partial thermocompression bonding apparatus such as a heated embossing roll and a metal roller having a smooth surface or a partial thermocompression bonding apparatus such as an ultrasonic welding apparatus. A long fiber non-woven fabric is obtained by performing thermocompression bonding treatment.

In the present invention, when a long fiber non-woven fabric is produced by the so-called spun bond method, it is preferable that the traction speed of the spun yarn is 1000 to 6000 m / min.
If the pulling speed at the time of pulling and thinning the spun yarn is less than 1000 m / min, 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 pulling speed is 3000 m / min or more, the molecular orientation of the polymer further proceeds, the birefringence becomes 10 × 10 ⁻³ or more, and the mechanical properties of the resulting nonwoven fabric are further improved, which is more preferable. On the other hand, the towing speed is 600
If it exceeds 0 m / min, the yarn-forming property deteriorates sharply and yarn breakage occurs. It is more preferable to add the above-described crystal nucleating agent to the polymer because the cooling property of the spun yarn is improved during melt spinning.

[0017]

Since the biodegradable agricultural coating material of the present invention is composed of a non-woven fabric composed of polylactic acid-based long fibers, the coating material after being used for a certain period of time is almost completely decomposed by biodegradation, There is no need to collect the covering material and dispose of it, and it does not pollute the natural environment. In addition, since the light transmittance is 70% or more, it is possible to sufficiently transmit sunlight, and it is possible to prevent insufficient growth of crops. 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, it is possible to prevent the strength of the covering material from lowering and to prolong the service life. can do.

[0018]

EXAMPLES The present invention will be specifically described below with reference to examples. The present invention is not limited to these examples. In the examples, each physical property value was determined as follows. (1) Melting point (° C.): The temperature that gives the extreme value of the melting endothermic curve obtained by measuring the temperature rising rate at 20 ° C./min using a differential scanning calorimeter DSC-7 type manufactured by Perkin Elma Co., Ltd. is the melting point ( ℃). (2) Melt flow rate of polylactic acid (hereinafter abbreviated as MFR) (g / 10 minutes): ASTM D1238
It measured according to the method as 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 a mixed solution of equal weight of phenol and ethane tetrachloride as a solvent. (4) Polyethylene melt index (hereinafter MI
Is abbreviated. ) (G / 10 minutes): ASTM D1238
It measured according to the method as 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 taken as the single yarn fineness (denier). (6) Birefringence: The birefringence of long fibers was measured by a conventional method using a polarizing microscope equipped with a Belek compensator and tricresyl phosphate as an immersion liquid. (7) Crystallinity (% by weight): The crystallinity (% by weight) of the long fibers was measured by the following method. That is, the long fiber to be measured is pulverized and the Al sample frame (20 mm × 18 mm ×
The measurement sample filled with 0.5 mm) and held in the vertical direction was irradiated with Cu-Kα rays from the perpendicular direction by the RAD-rB type X-ray generator manufactured by Rigaku Denki Co., Ltd. A curved graphite monochromator was used on the light receiving side. Then, scanning was performed in the range of 2θ = 5 to 125 °, and the crystallinity (% by weight) was determined by the Ruland method. (8) Unit weight (g / m ² ): 10 from the standard state sample
After making 10 sample pieces of 10 cm x 10 cm and reaching the equilibrium water content, the weight (g) of each sample piece was weighed, and the average value of the obtained values was converted to per unit area, and the basis weight ( g /
m ² ). (9) Tensile strength (kg / 5cm width): JIS L19
It was measured according to the strip method described in No. 06. That is, a sample piece having a sample length of 20 cm and a sample width of 5 cm was prepared at 10 points in the longitudinal direction of the non-woven fabric, and a constant speed elongation type tensile tester (Tensilon UTM-4-1-by Toyo Baldwin Co., Ltd. was used.
100) is used to stretch each sample piece in the longitudinal direction of the nonwoven fabric at a gripping interval of 10 cm and a pulling speed of 20 cm / min.
The maximum tensile strength (kg / 5cm width) was calculated, and the average value of the obtained maximum tensile strengths was used to determine the tensile strength (kg / 5
cm width). (10) Tear strength (kg): Measured according to the Benzirum method described in JIS L1096. That is, five sample pieces each having a sample length of 6.5 cm and a sample width of 10 cm were created in the longitudinal direction of the nonwoven fabric, and the tear strength in the longitudinal direction of the nonwoven fabric was calculated for each sample piece, and the average value of the obtained values was calculated. 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 (ref lamp) and the illuminance meter of the light receiving part, and the illuminance (A) when the sample is not placed are measured. , The following formula (C)
The light transmittance (%) was calculated from Light transmittance (%) = (B / A) × 100 (C) (12) Tensile product (kg ·% /) of the sample after irradiation for 300 hours
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 by a constant-velocity elongation type tensile test. Measured using a testing machine (Tensilon UTM-4-1-100 manufactured by Toyo Baldwin Co., Ltd.), and the tensile product SE300 (kg ·
% / 5 cm width) was determined. (13) Strength retention (%): 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 and 3
Tensile product (strength x elongation) SE300 of sample after irradiation for 00 hours
(Kg ·% / 5 cm width) and constant speed extension type tensile tester (Tensilon UTM-4-1-10 manufactured by Toyo Baldwin Co., Ltd.)
0), and the tenacity retention rate (%) was calculated from the above formula (b). (14) Coolability: The spun yarn was visually observed and
The grade was evaluated. ◯: No adhesion thread is observed. Δ: A small amount of adhesive thread is observed. X: Most of them adhere to each other and cannot be opened. (15) Opening property: The nonwoven web formed by the spun yarn discharged from the opening device was visually observed and evaluated according to the following three grades. ◯: Most of the constituent fibers are separated, and no adherent yarn or convergent yarn is observed. Δ: A small amount of the close contact yarn or the convergent yarn is recognized. X: Most of the constituent fibers are in close contact with each other and the openability is poor. (16) Biodegradability: A sample piece is buried in soil for 1 year, 2
After 3 years and 3 years, take out and observe the morphology of the sample piece,
The following three grades were used for evaluation. ◯: The shape of the non-woven fabric was maintained until 2 years passed after the sample piece was buried, and the sample piece collapsed after 3 years passed. Δ: The morphology of the nonwoven fabric was destroyed by 2 years after the sample piece was buried. X: The shape of the non-woven fabric was retained even after the sample piece was buried for 3 years.

Example 1 Polylactic acid having a melting point of 169 ° C., a number average molecular weight of 59100 and an MFR of 37 g / 10 min (D / L = 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 60100, and an MFR of 51 g / 10 min (D isomer / L isomer = 7.7 / 9)
2.3) A core-sheath type composite filament having a sheath component of (hereinafter, abbreviated as PLA) was melt-spun. Specifically, using a master batch containing 20% by weight of titanium oxide, the content of titanium oxide to polylactic acid was 0.5% by weight.
After melting the high melting point polylactic acid and the low melting point polylactic acid having the same titanium oxide content of 0.5% by weight using individual extruder type extruders, the spinning temperature is 200 C, single hole discharge rate 3.
Under the condition of 7 g / min, the high melting point polylactic acid was melt-spun from the core-sheath type composite spinneret so that the high melting point polylactic acid became the core part and the low melting point polylactic acid became the sheath part [composite ratio (weight ratio) = 1/1]. After the spun yarn is cooled by a cooling device, it is subsequently pulled and thinned by an air sucker provided below the spinneret at a pulling speed of 4800 m / min, and opened and moved using a well-known opener. It was collected and deposited as a web on the screen conveyor. Then, this web is passed through a partial thermocompression bonding apparatus consisting 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 treatment under the condition of a linear pressure of 60 kg / cm to obtain a single yarn. A long-fiber nonwoven fabric having a fineness of 7.0 denier and having a basis weight of 15 g / m ² was obtained. Table 1 shows various properties of the obtained long-fiber nonwoven fabric.

Example 2 Polylactic acid having a melting point of 168 ° C., a number average molecular weight of 60800 and an MFR of 44 g / 10 min (D isomer / L isomer = 1.8 / 9)
8.2) is used as the core component polymer and has a melting point of 150.
℃, number average molecular weight 60100, MFR 55g / 10
A single yarn was prepared in the same manner as in Example 1 except that polylactic acid (D-form / L-form = 4.5 / 95.5) was used as the sheath component polymer and the partial thermocompression treatment temperature was 120 ° C. Fineness is 7.
A long-fiber nonwoven fabric having a basis weight of 0 g / m ^{2 and} a basis weight of 15 g / m ² was obtained. Table 1 shows various properties of the obtained long-fiber nonwoven fabric.

Example 3 Polylactic acid having a melting point of 169 ° C., a number average molecular weight of 59100 and an MFR of 37 g / 10 min (D / L = 1.3 / 9)
8.7), using a master batch containing 20% by weight of titanium oxide kneaded and mixed, it was weighed and blended so that the content of titanium oxide in polylactic acid would be 0.5%, and melted using an extruder type melt extruder. After that, melt spinning was performed from a spinneret under the conditions of a spinning temperature of 200 ° C. and a single hole discharge rate of 3.7 g / min. After the spun yarn is cooled by a cooling device, it is subsequently pulled and thinned by an air sucker provided below the spinneret at a pulling speed of 4800 m / min, and opened and moved using a well-known opener. It was collected and deposited as a web on the screen conveyor. Then, the web was passed through a partial thermocompression bonding apparatus 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
Partial thermocompression treatment was applied under the condition of 0 kg / cm, and the unit weight of the continuous fiber having a single yarn fineness of 7.0 denier was 15
A long fiber non-woven fabric having a g / m ² was obtained. Table 1 shows various properties of the obtained long-fiber nonwoven fabric.

Example 4 Single hole discharge rate is 5.0 g / min, single yarn fineness is 9.3 deniers
20g / m ²Example 1 except that
In the same manner, a long fiber nonwoven fabric was obtained. Obtained long-fiber non-woven
The various properties of the fabric are shown in Table 1.

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 properties 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 / L = 1.0 / 9).
9.0), the spinning temperature was 210 ° C., the single hole discharge rate was 1.8 g / min, the pulling speed was 5500 m / min, and the single yarn fineness was 3.0 denier. As a result, a long-fiber nonwoven fabric was obtained. Table 1 shows various properties 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
Abbreviated as PET. ) As the core component, the melting point is 128 ° C,
High-density polyethylene with MI of 25 g / 10 min (hereinafter P
It is abbreviated as E. The core-sheath type composite long fiber having a sheath component of (4) was melt-spun. Specifically, the above PET and the above PE are melted using individual extruder type melt extruders, and then the spinning temperature is 290 ° C. and the single hole discharge amount is 3.5 g /
Under the condition of minutes, PET is core and PE is sheath [composite ratio (weight ratio) = 2/1] so that melt spinning is performed from the core-sheath type composite spinneret and the spun yarn is cooled in a cooling device. After cooling, pulling speed is 3 with an air blower installed below the spinneret.
It was pulled 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
Passing through a partial thermocompression bonding device consisting of an embossing roll heated to ℃ and a metal roll with a smooth surface, linear pressure 30 kg / cm
Partial thermocompression bonding is applied under the conditions of No. 1, and the single yarn fineness is 8.
A long-fiber nonwoven fabric having a basis weight of 9 g / m ^{2 and} a basis weight of 15 g / m ² was obtained. Table 1 shows various properties of the obtained long-fiber nonwoven fabric.

[0026]

[Table 1]

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

[0028]

Biodegradable agricultural covering material of the present invention exhibits, double
Refractive index is 10 × 10 ^-3 or more and crystallinity is 10% or more
Since it is composed of the non-woven fabric made of polylactic acid-based long fibers as described above, the sheet is biodegraded almost completely after a certain period of time in use, saving the trouble of collecting the covering material and disposing of it. Moreover, it does not pollute the natural environment. In addition, since the light transmittance is 70% or more, it is possible to sufficiently transmit sunlight, and it is possible to prevent insufficient growth of crops. Furthermore, the tensile product SE300 in the weather resistance test using a weather meter is 5 kg ·%.
Since the width is / 5 cm or more and the strength retention is 50% or more, it has excellent weather resistance, little deterioration, and can withstand long-term use.

Claims (4)

(57) [Claims] 1. The birefringence of polylactic acid-based filaments is 10 × 1.
It is composed of a polylactic acid-based long-fiber nonwoven fabric having a crystallinity of 0 ^-3 or more and a crystallinity of 10% or more, a light transmittance of 70% or more, and is obtained from the following formula (a) in a weather resistance test using a weather meter. Tensile product SE300 after irradiation for 300 hours is 5k
A biodegradable covering material for agriculture, characterized by having a width of g ·% / 5 cm or more and a high retention rate of 50% or more, which is obtained from the following formula (b). SE300 (kg ・% / 5cm width) = S300 × E30
0 (a) Strong retention rate (%) = (SE300 / SE0) x 100
(B) SE300: Tensile product of the sample after irradiation for 300 hours (kg
% / 5cm width) S300: Tensile strength of the sample after irradiation for 300 hours (kg
/ 5 cm width) E300: Tensile elongation of the sample after irradiation for 300 hours (%) SE0: Tensile product of the sample before irradiation (kg ·% / 5 cm width) 2. Polylactic acid is 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, L-
A polymer selected from the group consisting of 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 long fiber 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 of 20 ° C. or more lower than that of the polymer A as a sheath component. The biodegradable agricultural coating material according to claim 1, which is a fiber. 4. The single yarn fineness of the polylactic acid-based long fiber is 2 to 15
Denier and coating weight of coating material is 10-30g / m
² biodegradable agricultural covering material according to any of claims 1, 2, or 3.